U.S. patent application number 13/346634 was filed with the patent office on 2012-05-03 for controller for ac generator.
Invention is credited to Charles Y. Lafontaine, Harold C. Scott, Dave E. Williams.
Application Number | 20120105020 13/346634 |
Document ID | / |
Family ID | 39732585 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120105020 |
Kind Code |
A1 |
Scott; Harold C. ; et
al. |
May 3, 2012 |
CONTROLLER FOR AC GENERATOR
Abstract
A control system that can accommodate the wide variations in the
output of a generator, such as a permanent magnet alternator, while
providing an output with relatively uniform phase ripple. The
control system includes a zero crossing detector and variable ramp
generator for generating control signals to a switching rectifier
to generate a regulated DC signal.
Inventors: |
Scott; Harold C.;
(Lafayette, CO) ; Williams; Dave E.; (Loveland,
CO) ; Lafontaine; Charles Y.; (Berthoud, CO) |
Family ID: |
39732585 |
Appl. No.: |
13/346634 |
Filed: |
January 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12848980 |
Aug 2, 2010 |
8093772 |
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13346634 |
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12025645 |
Feb 4, 2008 |
7768165 |
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12848980 |
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11347777 |
Feb 2, 2006 |
7327123 |
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12025645 |
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Current U.S.
Class: |
322/28 ; 310/208;
361/20 |
Current CPC
Class: |
H02P 9/48 20130101; H02K
3/24 20130101; H02P 2101/45 20150115; H02K 3/12 20130101; H02K 3/50
20130101 |
Class at
Publication: |
322/28 ; 361/20;
310/208 |
International
Class: |
H02P 9/48 20060101
H02P009/48; H02K 3/04 20060101 H02K003/04; H02H 7/06 20060101
H02H007/06 |
Claims
1. A system comprising: a generator configured to generate an AC
signal; and a control system coupled to the generator, the control
system responsive to at least one phase of the AC signal from the
generator, the control system for generating control signals to a
switching rectifier to generate a regulated DC signal, the control
system comprising: a zero crossing detector, responsive to a first
signal representative of the AC phase, for generating indicia of
zero crossings in the AC phase; a variable ramp generator,
responsive to a second signal representative of the AC phase and
the indicia of zero crossings, for generating a ramp signal
indicative of the time integral of the voltage of the AC phase
accumulated from the occurrence of a zero crossing and reset upon
the occurrence of the next successive zero crossing; and a trigger
signal generator, responsive to the time integral ramp signal and a
reference signal indicative of a desired firing angle to maintain a
set DC output, for generating the control signals to the switching
rectifier in accordance with a comparison of the time integral ramp
signal to the reference signal.
2. The system of claim 1, wherein the first and second signals
representative of the AC phase are different isolated signals.
3. The system of claim 1, wherein the first and second signals are
representative of the AC phase are generated by respective
secondary windings of an isolation transformer having a primary
driven by the AC phase.
4. The system of claim 1, wherein the zero crossing detector
comprises: a comparator, responsive to the first signal
representative of the AC phase, for generating a signal indicative
of the polarity of the AC phase signal, and transitions in the
polarity signal indicating a zero-crossing; a variable blanker for
generating a blanking pulse initiated in response to transitions in
the polarity signal and having a duration equal to a predetermined
portion of the period between successive zero crossings; and a
reset pulse generator for generating, in response to transitions of
a predetermined polarity in the polarity signal, a pulse of
predetermined duration as said indicia of zero crossings in the AC
phase.
5. The system of claim 4, wherein the variable blanker comprises a
one-shot having an associated timing capacitor, the pulse generated
by the one-shot having a duration controlled by the time required
to charge the timing capacitor, a current source disposed to charge
the timing capacitor, the current source being driven by a signal
proportional to the duty cycle of the one shot output so that the
time required to charge the timing capacitor is inversely
proportional to the duty cycle of the one shot output.
6. The system of claim 1, wherein the control system is responsive
to multiple phases of an AC signal, the control system comprising
for each phase: a zero crossing detector, responsive to a first
signal representative of the AC phase, for generating indicia of
zero crossings in the AC phase; a variable ramp generator,
responsive to a second signal representative of the AC phase and
the indicia of zero crossings, for generating a ramp signal
indicative of the time integral of the voltage of the AC phase
accumulated from the occurrence of a zero crossing and reset upon
the occurrence of the next successive zero crossing; a trigger
signal generator, responsive to the time integral ramp signal and a
reference signal indicative of a desired firing angle to maintain a
set DC output, for generating the control signals to the switching
rectifier in accordance with a comparison of the time integral ramp
signal to the reference signal.
7. The system of claim 6, wherein the control system is responsive
to a first phase of the AC signal, and at least one other phase,
the control system further including for each other phase a
respective AGC Amp to compare the average voltage of the ramp from
the ramp generator associated with the first phase with the average
voltage of the ramp from the ramp generator associated with such
other phase and adjusts the gain of the ramp generator associated
with such other phase so that the time integral of the ramp from
the ramp generator associated with such other phase is equal to the
time integral of the ramp from the ramp generator associated with
the first phase.
8. The system of claim 1, wherein the generator comprises: a
stator, wherein an outer peripheral surface of the stator is
axially crenellated with a predetermined number of teeth and slots;
an output terminal electrically coupled to a fusible link; an
electrically conductive phase ring coupled to the fusible link; and
a pole phase coil conductor, electrically coupled to the phase ring
and to a winding of insulated wiring disposed around at least one
of the teeth of the stator.
9. The system of claim 8, wherein the generator further comprises:
a second and third output terminal respectively electrically
coupled to a second and third fusible link; a second and third
electrically conductive phase ring respectively coupled to the
second and third fusible links; and a second and third pole phase
coil conductor, respectively electrically coupled to the second and
third phase rings and to a second and third windings of insulated
wiring respectively disposed around teeth of the stator.
10. The system of claim 9, wherein the winding, the second winding,
and the third winding are electrically coupled in one of a wye
configuration and a delta configuration.
11. The system of claim 10, wherein the electrical wye coupling is
exposed to a cooling fluid.
12. The system of claim 10, wherein the electrical delta coupling
is exposed to a cooling fluid.
13. The system of claim 9, wherein the phase ring, the second phase
ring, and the third phase ring are exposed to a cooling fluid.
14. The system of claim 8, wherein a pole phase coil conductor is
disposed as to exit the stator in a direction substantially
orthogonal from a face surface of the stator.
15. The system of claim 8, wherein: the winding of insulated wiring
comprises at least two turns of windings disposed around the at
least one tooth of the stator; and the insulated wiring is selected
from a predetermined gauge, wherein an internal short circuit
within the winding between two or more turns in the winding
produces sufficient heat to melt the wiring and clear the internal
short.
16. The system of claim 1, wherein the generator comprises: a
plurality of output terminals respectively electrically coupled to
a plurality of fusible links; a plurality of electrically
conductive phase rings respectively coupled to the plurality of
fusible links; and a plurality of pole phase coil conductors,
respectively electrically coupled to the plurality of phase rings,
and respectively electrically coupled to a plurality of windings of
insulated wiring respectively disposed around a plurality of teeth
of the stator.
17. The system of claim 16, wherein a cooling fluid is exposed to
at least one of: the plurality of output terminals; the plurality
of fusible links; the plurality of electrically conductive phase
rings; the plurality of pole phase coil conductors, and the
plurality of windings of insulated wiring.
18. The system of claim 16, wherein the plurality of windings are
electrically coupled in one of a wye configuration and a delta
configuration.
19. The system of claim 18, wherein the electrical wye coupling is
exposed to a cooling fluid.
20. The system of claim 18, wherein the electrical delta coupling
is exposed to a cooling fluid.
21. The system of claim 16, wherein a pole phase coil conductors
are disposed to as to exit the stator in a direction substantially
orthogonal from a face surface of the stator.
22. The system of claim 16, wherein: the plurality of windings of
insulated wiring respectively comprise at least two turns of
windings disposed around at least one tooth of the plurality of
teeth of the stator; and the insulated wiring is selected from a
predetermined gauge, wherein an internal short circuit in one of
the plurality of windings produces sufficient heat to melt the
insulated wiring and clear the internal short circuit.
23. The system of claim 1, wherein the generator comprises: a
first, second and third phase ring, respectively coupled to first,
second, and third output terminals through respective fusible
links; a first, second, and third phase coil, each phase coil:
respectively electrically coupled to the first, second, and third
phase ring through respective first, second, and third phase coil
conductors; and comprising a plurality of windings of insulated
wiring respectively disposed around a plurality of teeth of a
stator; and wherein the first, second, and third phase coils are
disposed about the plurality of the teeth of the stator so as to
produce electrical current in three predetermined phases.
24. The system of claim 23, wherein a cooling fluid is exposed to
at least one of: the first, second and third phase rings; the
first, second, and third output terminals; the first, second, and
third phase coils; and the first, second, and third phase coil
conductors, and the plurality of windings of insulated wiring.
25. The system of claim 23, wherein the first, second, and third
phase coil conductors are disposed to as to exit the stator in a
direction substantially orthogonal from a face surface of the
stator.
26. The system of claim 23, wherein: the winding of insulated
wiring comprises at least two turns of windings disposed around the
at least one tooth of the stator; and the insulated wiring is
selected from a predetermined gauge, wherein an internal short
circuit within the winding between two or more turns in the winding
produces sufficient heat to melt the wiring and clear the internal
short.
27. The system of claim 23, wherein the plurality of windings are
electrically coupled in one of a wye configuration and a delta
configuration.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims full
benefit of and priority to U.S. patent application Ser. No.
12/848,980, filed Aug. 2, 2010, which is a continuation of and
claims priority to U.S. patent application Ser. No. 12/025,645,
filed Feb. 4, 2008, (Now U.S. Pat. No. 7,768,165), which is a
continuation of and claims full benefit and priority to U.S. patent
application Ser. No. 11/347,777, filed Feb. 2, 2006, (Now U.S. Pat.
No. 7,327,123), the disclosures of which are hereby fully
incorporated by reference for all purposes.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to voltage and current control
systems for machines for converting between mechanical and
electrical energy, such as brushless AC generators, and in
particular to a control system for a compact permanent magnet high
power alternator, such as a compact permanent magnet high power
alternator suitable for automotive use.
BACKGROUND OF THE INVENTION
[0003] An alternator typically comprises a rotor mounted on a
rotating shaft and disposed concentrically relative to a stationary
stator. The rotor is typically disposed within the stator. However,
the stator may be alternatively positioned concentrically within
the rotor. An external energy source, such as a motor or turbine,
commonly drives the rotating element, directly or through an
intermediate system such as a pulley belt. Both the stator and the
rotor have a series of poles. Either the rotor or the stator
generates a magnetic field, which interacts with windings on the
poles of the other structure. As the magnetic field intercepts the
windings, an electric field is generated, which is provided to a
suitable load. The induced electric field (which is commonly known
as a voltage source) is typically applied to a rectifier, sometimes
regulated, and provided as a DC output power source. The induced
current is typically applied to a rectifier, sometimes regulated,
and provided as a DC output power source. In some instances, a
regulated DC output signal is applied to a DC to AC inverter to
provide an AC output.
[0004] Conventionally, alternators employed in motor vehicle
applications typically comprise: a housing, mounted on the exterior
of an engine; a stator having 3-phase windings housed in the
housing, a belt-driven claw-pole type (e.g. Lundell) rotor
rotatably supported in the housing within the stator. However, to
increase power output the size of the conventional alternator must
be significantly increased. Accordingly, space constraints in
vehicles tend to make such alternators difficult to use in high
output, e.g. 5 KW, applications, such as for powering air
conditioning, refrigeration, or communications apparatus.
[0005] In addition, the claw-pole type rotors, carrying windings,
are relatively heavy (often comprising as much as three quarters of
the total weight of the alternator) and create substantial inertia.
Such inertia, in effect, presents a load on the engine each time
the engine is accelerated. This tends to decrease the efficiency of
the engine, causing additional fuel consumption. In addition, such
inertia can be problematical in applications such as electrical or
hybrid vehicles. Hybrid vehicles utilize a gasoline engine to
propel the vehicle at speeds above a predetermined threshold, e.g.
30 Kph (typically corresponding to a range of RPM where the
gasoline engine is most efficient). Similarly, in a so-called "mild
hybrid," a starter-generator is employed to provide an initial
burst of propulsion when the driver depresses the accelerator
pedal, facilitating shutting off the vehicle engine when the
vehicle is stopped in traffic to save fuel and cut down on
emissions. Such mild hybrid systems typically contemplate use of a
high-voltage (e.g. 42 volts) electrical system. The alternator in
such systems must be capable of recharging the battery to
sufficient levels to drive the starter-generator to provide the
initial burst of propulsion between successive stops, particularly
in stop and go traffic. Thus, a relatively high power, low inertia
alternator is needed.
[0006] In general, there is in need for additional electrical power
for powering control and drive systems, air conditioning and
appliances in vehicles. This is particularly true of vehicles for
recreational, industrial transport applications such as
refrigeration, construction applications, and military
applications.
[0007] For example, there is a trend in the motor vehicle industry
to employ intelligent electrical, rather than mechanical or
hydraulic control and drive systems to decrease the power load on
the vehicle engine and increased fuel economy. Such systems may be
employed, for example, in connection with steering servos (which
typically are active only a steering correction is required), shock
absorbers (using feedback to adjust the stiffness of the shock
absorbers to road and speed conditions), and air conditioning
(operating the compressor at the minimum speed required to maintain
constant temperature). The use of such electrical control and drive
systems tends to increase the demand on the electrical power system
of the vehicle.
[0008] Similarly, it is desirable that mobile refrigeration systems
be electrically driven. For example, driving the refrigeration
system at variable speeds (independently of the vehicle engine rpm)
can increase efficiency. In addition, with electrically driven
systems the hoses connecting the various components, e.g. the
compressor (on the engine), condenser (disposed to be exposed to
air), and evaporation unit (located in the cold compartment), can
be replaced by an electrically driven hermetically sealed system
analogous to a home refrigerator or air-conditioner. Accordingly,
it is desirable that a vehicle electrical power system in such
application be capable of providing the requisite power levels for
an electrically driven unit.
[0009] There is also a particular need for a "remove and replace"
high power alternator to retrofit existing vehicles. Typically only
a limited amount of space is provided within the engine compartment
of the vehicle to accommodate the alternator. Unless a replacement
alternator fits within that available space, installation is, if
possible, significantly complicated, typically requiring removal of
major components such as radiators, bumpers, etc. and installation
of extra brackets, belts and hardware. Accordingly, it is desirable
that a replacement alternator fit within the original space
provided, and interfaces with the original hardware.
[0010] In general, permanent magnet alternators are well known.
Such alternators use permanent magnets to generate the requisite
magnetic field. Permanent magnet generators tend to be much lighter
and smaller than traditional wound field generators. Examples of
permanent magnet alternators are described in U.S. Pat. No.
5,625,276 issued to Scott et al on Apr. 29, 1997; U.S. Pat. No.
5,705,917 issued to Scott et al on Jan. 6, 1998; U.S. Pat. No.
5,886,504 issued to Scott et al on Mar. 23, 1999; U.S. Pat. No.
5,92,611 issued to Scott et al on Jul. 27 1999; U.S. Pat. No.
6,034,511 issued to Scott et al on Mar. 7, 2000; and U.S. Pat. No.
6,441,522 issued to Scott on Aug. 27, 2002.
[0011] Particularly light and compact permanent magnet alternators
can be implemented by employing an "external" permanent magnet
rotor and an "internal" stator. The rotor comprises a hollow
cylindrical casing with high-energy permanent magnets disposed on
the interior surface of the cylinder. The stator is disposed
concentrically within the rotor casing, and suitably comprises a
soft magnetic core, and conductive windings. The core is generally
cylindrical width an axially crenellated outer peripheral surface
with a predetermined number of equally spaced teeth and slots. The
conductive windings (formed of a suitably insulated electrical
conductor, such as varnished copper motor wire), are wound through
a respective slot, outwardly along the side face of the core around
a predetermined number of teeth, then back through another slot.
The portion of the windings extending outside of the crenellation
slots along the side faces of the core are referred to herein as
end turns. Rotation of the rotor about the stator causes magnetic
flux from the rotor magnets to interact with and induce current in
the stator windings. An example of such an alternator is described
in, for example, the aforementioned U.S. Pat. No. 5,705,917 issued
to Scott et al on Jan. 6, 1998 and U.S. Pat. No. 5,92,611 issued to
Scott et al on Jul. 27 1999.
[0012] The power supplied by a permanent magnet generator varies
significantly according to the speed of the rotor. In many
applications, changes in the rotor speed are common due to, for
example, engine speed variations in an automobile, or changes in
load characteristics. Accordingly, an electronic control system is
typically employed. An example of a permanent magnet alternator and
control system therefore is described in the aforementioned U.S.
Pat. No. 5,625,276 issued to Scott et al on Apr. 29, 1997. Examples
of other control systems are described in U.S. Pat. No. 6,018,200
issued to Anderson, et al. on Jan. 25, 2000. Other examples of
control systems are described in commonly owned co-pending U.S.
patent application Ser. No. 10/860,393 by Quazi et al, entitled
"Controller For Permanent Magnet Alternator" and filed on Jun. 6,
2004. The aforementioned Quazi et al application is hereby
incorporated by reference as if set forth verbatim herein.
[0013] The need to accommodate a wide range of rotor speeds is
particularly acute in motor vehicle applications. For example,
large diesel truck engines typically operate from 600 RPM at idle,
to 2600 RPM at highway speeds, with occasional bursts to 3000 RPM,
when the engine is used to retard the speed of the truck. Thus the
alternator system is subject to a 5:1 variation in RPM. Light duty
diesels operate over a somewhat wider range, e.g. from 600 to 4,000
RPM. Alternators used with gasoline vehicle engines typically must
accommodate a still wider range of RPM, e.g. from 600 to 6500 RPM.
In addition, the alternator must accommodate variations in load,
i.e., no load to full load. Thus the output voltage of a permanent
magnet alternator used with gasoline vehicle engines can be subject
to a 12:1 variation. Accordingly, if a conventional permanent
magnet alternator is required to provide operating voltage (e.g. 12
volts) while at idle with a given load, it will provide multiples
of the operating voltage, e.g. ten (10) times that voltage, at full
engine RPM with that load, e.g. 120 volts. Where the voltage at
idle is 120 V, e.g. for electric drive air conditioning, or
communications apparatus, the voltage at full engine RPM would be,
e.g. 1200 volts. Such voltage levels are difficult and, indeed,
dangerous to handle. In addition, such extreme variations in the
voltage and current may require more expensive components;
components rated for the high voltages and currents produced at
high engine RPM (e.g. highway speeds) are considerably more
expensive, than components rated for more moderate voltages.
[0014] Various attempts to accommodate the wide range of output
voltages from permanent magnet alternators have been made. For
example, the aforementioned Scott et al U.S. Pat. No. 5,625,276,
describes a controller that selectively activates individual
windings to achieve a desired output. The windings may be connected
in a fully parallel configuration to provide high current at
relatively low voltage levels, or in series to provide high voltage
capacity. As drive RPM increases, individual windings are, in
effect, disconnected from the operative circuit to control output
voltage and/or current. However, particularly in compact high
power, high speed ratio applications such as motor vehicles, the
switching transitions between windings have deleterious effects,
especially at the high end of the RPM range.
[0015] Other attempts have involved controlling the RPM of the
alternator, and thus its voltage, independently of the engine RPM.
An example of such an attempt is described in U.S. Pat. No.
4,695,776, issued Sep. 22, 1987 to Dishner. These solutions tend to
involve mechanical components that are large, require maintenance
and are subject to wear.
[0016] Other attempts have involved diverting a portion of the
magnetic flux generated in the alternator to modulate output
voltage. An example of a system is described in U.S. Pat. No.
4,885,493 issued to Gokhale on Dec. 5, 1989. Flux diversion,
however, typically requires additional mechanical components and
can be slow to react.
[0017] Rectification and regulation can be effected as a single
process using a switching bridge (e.g. SCR bridge) with phase angle
control of duty cycle. The bridge includes respective control
switching devices (e.g. SCRs) that are selectively actuated to
provide conduction paths between the input and output of the
bridge. In essence, each half cycle (irrespective of polarity) of
the AC signal produces a pulse of a predetermined polarity
(typically positive) at the output of the bridge. The duration and
timing of the conduction perhaps controls the output of the bridge.
Such switching bridges may be "half controlled", comprising a
respective controlled switching device (e.g. SCR) and diode for
each phase, or "full controlled", comprising for each phase two
switching devices (e.g. SCRs), one for each polarity.
[0018] Conventionally, the switching devices in the bridge are
actuated in accordance with "phase angle control of duty cycle" to
provide a predetermined voltage output level. Trigger signals to
the switching devices are generated by a controller that detects
zero crossings in the respective phases of the AC signal and
generates the trigger signal accordingly (typically after a delay
nominally corresponding to a predetermined phase angle in the AC
signal, and, concomitantly with a desired DC output level). More
particularly, in a conventional system, when a zero crossing is
detected in a particular phase, the controller delays by a time
period corresponding to the desired duty cycle (which, in turn,
corresponds to the desired output voltage level). The delay is
typically engendered by a one-shot or conventional timing circuit.
For example, a capacitor is charged with current when the voltage
across the capacitor exceeds a reference voltage, a trigger to the
SCR associated with the phase is generated, and the capacitor
discharged. In response to the trigger signal, the SCR turns on (is
rendered conductive) and remains on until the current through it
goes to zero, at which point it is rendered nonconductive until the
next trigger signal. The cycle repeated in response to the next
zero crossing of the appropriate polarity.
[0019] In a half controlled system, phase angle control of the
output duty cycle is effected by selective actuation of the
controlled switching devices during their associated half cycle of
the AC signal; the diode segments of the legs are rendered
conductive during the entire associated (opposite polarity) half
cycle of the phase. The range of output signals that can be
generated from a given AC signal level (and thus range of input AC
signals) is thus limited, as compared to a full controlled
system.
[0020] When full control is provided, the SCRs are each associated
with a particular half cycle (polarity) of an associated phase. A
trigger signal is generated in response to (e.g. after the phase
delay) the zero crossing beginning the associated half cycle of the
phase. Accordingly, provisions must be made to differentiate
between positive going and negative going zero crossings.
[0021] When a switching bridge (e.g. SCR bridge) and phase angle
control of duty cycle is used in conjunction with an AC power
source that varies in magnitude and changes alternating frequency
very rapidly (as in the case of an motor vehicle alternator) the
variations in voltage output and ripple contents can be
particularly significant. This is particularly true in full
controlled systems. The variations in ripple contents in the output
of the bridge can produce unacceptable output ripple harmonics and
require extensive filtering. For example, the outputs of many
alternators are not a uniform sine wave. Non-uniformities in
amplitude and duration often occur between half cycles, and between
phases of the AC input signal to the bridge, and are reflected in
the outputs of the portions (legs) of the bridge circuitry
associated with the respective phases. Such distortions and
non-uniformities in the alternator output can occur for any of a
number of reasons, such as, for example, variations in the
placement of the winding turns relative to each other and, in the
case of permanent magnet alternators, relative to the magnets.
Further variations in the outputs of the portions (legs) of the
bridge associated with the respective phases (due to, e.g.
tolerances, temperature, etc) in component values between the
circuitry associated with the various phases, cyclic change in
frequency due to engine cylinder firing, variations in the magnetic
air gap, variations of the saturation of the stator teeth as the
magnet progresses etc.
[0022] In addition, the output of the generator often includes
spurious components (e.g. spikes) that can be mistaken for zero
crossings by the detector circuitry.
[0023] Thus, there is a need for a relatively inexpensive and
efficient control system using relatively rugged semiconductors
(such as SCRs) that can accommodate wide variations in the
frequency and amplitude of an AC source (e.g. alternator), while
minimizing output ripple harmonics and filtering requirements.
[0024] In some applications there may be relatively long lengths of
electrical cable connecting the output of the converter to the
load. For example, the cabling between the converter and battery
(load) can be sufficient to cause a voltage drop between the
converter and battery
[0025] There are also a number of other factors that can affect the
operation of alternator systems in the. For example, the operation
of alternator systems can be significantly affected, and sometimes
disabled, by the temperature of the system components. There is a
need for an alternator control including mechanisms for detecting
temperatures harmful to the operation of the alternator system.
[0026] In alternator systems used to charge batteries, battery
temperature has a direct impact on the optimal battery charging
voltage and battery sulfation is a major contributor to shortened
battery life. There is a need for alternator charging systems
(particularly in motor vehicle applications) that can dynamically
adjust output for optimized charging voltage and dynamically handle
battery sulfation.
[0027] There is a need for an alternator charging system including
a mechanism for intelligent control, (e.g. microprocessor),
providing for example: monitoring electrical system performance;
providing electrical system protection; and field adjustment of
system operating parameters.
[0028] The stator of a conventional high current motor vehicle
alternator is constructed with conductors of large cross sectional
area effectively connected in series. Several problems can exist
with this winding method. For example: because of the low number of
turns (in some instances only a single turn) per pole phase coil,
it is difficult or impossible to make a small change in design
output voltage by changing the number of turns of the phase pole
coil; the large cross sectional area of the conductors make the
stator difficult to wind; and a short circuit between coils will
typically burn out the entire stator and may stall the alternator,
resulting in possible damage to the drive system or overloading the
vehicle engine.
[0029] In general, permanent magnet alternators incorporating a
predetermined number of independent groups of windings, wound
through slots about predetermined numbers of teeth where the power
provided by each group is relatively unaffected by the status of
the other groups are known. For example, such an alternator is
described, together with a controller therefor, in U.S. Pat. No.
5,900,722 issued to Scott et al. on May 4, 1999. In the alternator
described in U.S. Pat. No. 5,900,722, the number of groups of
windings was equal to an integer fraction of the number of poles,
and the controller circuit selectively completed current paths to
the individual groups of windings to achieve a desired output.
[0030] However, there remains a need for a compact high power
alternator wherein a desired output voltage can be achieved by
changing the number of terms of the phase pole coil, that is
relatively easy to wind, and minimizes the consequence of short
circuits, while at the same time facilitating cooling. There is
also a need for a converter that can accommodate such an
alternator.
SUMMARY OF THE INVENTION
[0031] In accordance with various aspects of the present invention,
a relatively inexpensive, control system is provided that can
accommodate the wide variations in the output of a generator, such
as a permanent magnet alternator, while providing an output with
relatively uniform phase ripple.
[0032] In accordance with one aspect of the present invention, the
trigger signal to a switching device (e.g. SCR) is initiated in
accordance with the time integral of the voltage (e.g.
volt-seconds) of the corresponding AC phase half cycle. For
example, the trigger signal is generated when a ramp signal
representative of the volt-seconds in the associated AC signal
phase reaches a predetermined level. In the preferred embodiment,
the ramp is generated by charging a capacitor with a signal
representative of the voltage from the alternator itself.
[0033] In accordance with another aspect of the present invention,
the trigger signal to a switching device (e.g. SCR) is initiated
only in response to zero crossings occurring within a predetermined
window of time related to (e.g. tracking) the frequency of the AC
signal.
[0034] In accordance with another aspect of the present invention,
an automatic gain system is employed to compensate for component
value differences between the respective channels.
[0035] In accordance with another aspect of the present invention
the control can compensate for losses present in long cable runs
between converter and battery or other similar loses. Compensation
can be effected either by sensing voltage remotely from the
converter, e.g. in the vicinity of the battery, or locally within
the converter.
[0036] In accordance with another aspect of the present invention a
battery charging voltage can be optimized with respect to battery
temperature.
[0037] In accordance with another aspect of the present invention a
mechanism is provided to reduce battery plate sulfation.
[0038] In accordance with other aspects of the present invention
mechanisms are provided to monitor various system parameters and to
optimize various system parameters in the field.
[0039] In accordance with another aspect of the present invention
various system protection methods have been implemented.
[0040] In accordance with another aspect of the present invention
the stator winding is wound with a predetermined number of pole
phase coils, preferably equal to the number of magnetic poles. Each
pole phase coil is wound with enough turns to generate the required
output voltage of the alternator and a fraction of the output
current equal to 1 divided by the number of magnetic poles. These
individual pole phase coils are then connected in parallel.
[0041] In accordance with another aspect of the present invention,
a respective conducting phase ring corresponding to each output
phase is installed within the alternator with each coil
corresponding to the associated phase electrically connected to the
conducting phase rings to facilitate cooling and grouping and
transmission of output phases to the control
[0042] In accordance with another aspect of the present invention
the conducting phase rings are held in place by a non-conducting
support structure.
[0043] In accordance with another aspect of the present invention
the conducting phase rings are disposed to provide an efficient
cooling by exposure to the cooling fluids e.g. air, passing over
the conducting phase rings.
BRIEF DESCRIPTION OF THE DRAWING
[0044] The present invention will hereinafter be described in
conjunction with the figures of the appended drawing, wherein like
designations denote like elements (unless otherwise specified).
[0045] FIG. 1 is a block schematic of a system for converting
between mechanical and electrical energy.
[0046] FIG. 2A is a block schematic of a controller in accordance
with various aspects of the present invention.
[0047] FIG. 2B (collectively, together with FIG. 2A, referred to as
FIG. 2) is a block schematic of a single channel within controller
2A in accordance with various aspects of the present invention.
[0048] FIG. 3 is a schematic of a zero crossing detector suitable
for use in the controller of FIG. 2.
[0049] FIG. 4A is a schematic of a variable ramp generator, trigger
generator, and buffer suitable for use in the controller of FIG.
2A.
[0050] FIG. 4B is a diagram of the relative timing of waveforms of
the various signals involved in generation of the SCR trigger
signals in the controller of FIG. 2A.
[0051] FIG. 5 is a schematic of a variable ramp generator, trigger
generator, and automatic gain control circuit suitable for use in
the controller of FIG. 2A.
[0052] FIG. 6 is a schematic of an error amp and variable reference
voltage source suitable for use in the controller of FIG. 2A.
[0053] FIG. 7 is a schematic of a system enable circuit and
buffered optocoupler suitable for use in the controller of FIG.
2A.
[0054] FIG. 8 is a schematic of a No-Fire detect circuit suitable
for use in the controller of FIG. 2A.
[0055] FIGS. 9A and 9B (collectively referred to as FIG. 9) are
schematics of exemplary condition sensing circuits suitable for use
in the controller of FIG. 2A.
[0056] FIGS. 10A and 10B (collectively referred to as FIG. 10) are
simplified schematics of a switching bridge suitable for use in
conjunction with the controller of FIG. 2A.
[0057] FIGS. 11A and 11B (collectively referred to as FIG. 11) are
simplified schematics of an alternative switching bridge suitable
for use in conjunction with the controller of FIG. 2A.
[0058] FIGS. 12A-12Z, and FIGS. 12AA-12AG (collectively referred to
as FIG. 12) are schematic flowcharts of a microcontroller program
for effecting operation of the controller of FIG. 2A.
[0059] FIG. 13 is a schematic of a crowbar circuit suitable for use
in the controller of FIG. 2A.
[0060] FIG. 14 is a schematic of a relay indicator circuit suitable
for use in the controller of FIG. 2A.
[0061] FIG. 15 is a schematic of an auxiliary 12V supply circuit
suitable for use by the controller of FIG. 2A.
[0062] FIG. 16 is a block schematic of a microcontroller suitable
for use in the controller of FIG. 2A.
[0063] FIGS. 17A-17e are collectively referred to as FIG. 17.
[0064] FIG. 17A is a side view of the exterior of an alternator in
accordance with various aspects of the present invention.
[0065] FIG. 17B is a sectional view along A-A of the alternator of
FIG. 17A.
[0066] FIG. 17C is sectional view of a terminal in the alternator
of FIG. 17A.
[0067] FIG. 17D is a simplified sectional view along B-B of the
alternator of FIG. 17A showing the relative placement of the
conducting phase rings within the alternator.
[0068] FIG. 17E is a diagram showing possible variations of a
conducting phase ring.
[0069] FIG. 18A is a diagram showing an individual pole phase
coil.
[0070] FIG. 18B is a simplified perspective view of the stator
core, and the conducting phase rings of the alternator of FIG. 17A,
illustrating the connections between the conducting phase rings and
respective groups of windings (winding end turns omitted).
[0071] FIG. 18C is a side view of a stator with respective pole
groups of windings wound thereon.
[0072] FIG. 18D perspective view of the stator core, and the
conducting phase rings of the alternator of FIG. 17A, illustrating
all the connections between the conducting phase rings and all the
respective groups of windings (winding end turns omitted).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0073] Referring now to FIG. 1, a system 100 for converting between
mechanical and electrical energy in accordance with various aspects
of the present invention comprises a controller 110 and a switching
bridge 112. System 100 suitably cooperates with a source of AC
power, such as an alternator 102 and a source of mechanical energy
(e.g. drive) 104, e.g. an engine or turbine, a load 106, such as a
motor and, if desired, in energy storage device 108, such as a
battery, capacitor, or flywheel. If desired, an inverter (sometimes
categorized as comprising part of load 106) can also be provided to
generate an AC signal at a constant predetermined frequency and
amplitude (e.g. 60 Hz, 120V).
[0074] In general, alternator 102 generates AC power in response to
mechanical input from energy source 104. Alternator 102 preferably
provides multi-phase (e.g. three-phase, six-phase, etc.) AC output
signals, e.g. phase A (118), phase B (120), and phase C (122).
Those output signals are typically unregulated and may vary
significantly in accordance with drive RPM (source 104).
[0075] The AC phase signals from alternator 102 are applied to
system 100, preferably through input fuses 128. System 100
rectifies the AC signal from alternator 102, i.e. converts it into
a DC signal and regulates the voltage of that signal at a
predetermined level, e.g. 28V. Switching bridge 112 selectively, in
response to control signals from controller 110, provides
conduction paths between the various phases of the AC signal from
alternator 102 and a load 106. Exemplary switching bridges 112 are
shown in FIG. 10 (a classical fully controlled SCR bridge) and FIG.
11 (an array of independent bridges). Controller 110 selectively
generates control signals to switching bridge 112 to produce a
regulated output signal at a predetermined voltage. As will be more
fully explained later, controller 110 samples the regulated output
either locally at input 114, or remotely at input 140 and adjusts
the signals to bridge 112 to maintain the proper output.
Additionally, the output current is sensed at input 116 to further
modify the control signals to bridge 112.
[0076] The regulated DC signal Voltage Regulated Output (VRO) is
then applied, suitably through an output fuse 136, to load 106 and
energy storage device 108. Load 106 may be any device that uses
power, such as, e.g. lights, motors, heaters, electrical equipment,
power converters, e.g. inverters or DC-to-DC converters. Energy
storage device 108 filters or smoothes the output of control system
110 (although, in various embodiments, controller 110 may itself
incorporate or otherwise provide adequate filtering).
[0077] Additionally, as will be more fully explained later, other
outputs, 150, and 160, are also provided. Also crowbar circuit 142
is provided for system protection.
[0078] Alternator 102 may be any suitable device that generates AC
power in response to mechanical input, such as a brushless AC
generator or a permanent magnet alternator, and preferably an
alternator of the type described in commonly owned co-pending U.S.
patent application Ser. No. 10/889,980 by Charles Y. Lafontaine and
Harold C. Scott, entitled "Compact High Power Alternator" and filed
on Jul. 12, 2004. The aforementioned Lafontaine et al application
is hereby incorporated by reference as if set forth verbatim
herein. As will be further described, in the preferred embodiment,
alternator 102 is of the compact high power alternator type, but
includes for each pole, a respective group of windings (including
at least one winding corresponding to each phase) with all of the
windings corresponding to a given phase connected in parallel.
Preferably, the parallel connection between coils corresponding to
the same phase is effective through a corresponding conducting
phase ring 138, and includes fusible links 124, disposed between
the conducting phase rings 138, and the output terminals 126 of the
alternator. Conducting phase rings are a means to efficiently
collect the output of each individual coil to its respective
conducting phase ring, which is in turn attached to its respective
output terminal. As the total number of poles increases so too do
the number of individual coils. The conventional method of
gathering coils involves soldering the motor wire to conventionally
insulated motor lead wire. As the rated output of the alternator
increases, a corresponding increase in the load carrying capacity
of the motor lead wire is also required. The only means available
to meet the increasing load demand on the lead motor wire is to
increase the cumulative gauge of the wire by increasing the gauge
of a single wire or by using multiple wires in parallel. The net
effect is increasingly larger and larger cross sectional areas of
motor lead wire. When considering the total number of coils and
their respective end turns along with the lead wire and its
associated insulation, the resulting stator assembly with conductor
and motor lead wire tied together insulate the end turns,
detrimental to cooling. The resulting assembly also restricts the
only available airflow over the end turns further reducing cooling.
A preferred embodiment of alternator 102 will be described in
conjunction with FIG. 17.
[0079] Briefly, alternator 102 suitably comprises a rotor mounted
on a rotating shaft and disposed concentrically relative to a
stationary stator. The stator suitably includes respective phase
windings, A, B and C connected together at one end (neutral), in a
star configuration. In operation, the rotator is driven by external
energy source 104, either directly or through an intermediate
system such as a pulley belt. In motor vehicle applications,
alternator 102 is typically mounted under hood, and belt driven
from the vehicle engine. Relative motion between rotor and stator
causes voltage to be induced in the windings. Alternator 102 is
preferably designed such that it generates a predetermined minimum
voltage at idle or a minimum RPM under full load conditions. As
noted above, in motor vehicle applications, drive RPM can vary
widely, e.g. from 600 RPM at idle, to 3000 RPM for large diesel
trucks 600 to 4,000 RPM for light duty diesels, and from 600 to
6500 RPM gasoline vehicle engines. In addition, the alternator must
accommodate variations in load, i.e., no load to full load. Thus
the output voltage of a permanent magnet alternator 102 when used
with a gasoline vehicle engine can be subject to a 12:1 variation.
Accordingly, if a conventional permanent magnet alternator is
required to provide operating voltage (e.g. 18 volts) while at idle
speeds with a given load, it will provide multiples of the
operating voltage, e.g. twelve (12) times that voltage, at full
engine RPM with that load, e.g. 216 volts.
[0080] Referring now to FIGS. 2A, and 2B, controller 110 suitably
comprises a circuitry channel for each phase of the output signal
provided by alternator 102. Each circuitry channel comprises: a
respective phase isolation transformer 204 (e.g. transformers 204A,
204B, and 204C, respectively, for phases A (118), B (120) and C
(122) of a three-phase AC signal); a respective zero-crossing
detector 206 (e.g. 206A, 206B, and 206C, respectively, for phases A
(118), B (120) and C (122); a respective variable ramp generator
208 (e.g. 208A, 208B, and 208C, respectively, for phases A (118), B
(120) and C (122); and a respective trigger generator 210 (e.g.
210A, 210B, and 210C, respectively, for phases A (118), B (120),
and C (122)). Referring to FIG. 2B, zero-crossing detectors 206
suitably each comprise a filtered comparator 212, a variable
blanker 214, and a reset pulse generator 216. Trigger generators
210 suitably each comprise a comparator 218, and appropriate
digital routing logic 220.
[0081] Referring to FIG. 2, one of the phases (e.g. phase A (118),
see also FIG. 4) is designated as a reference phase and includes a
suitable buffer amplifier 224 receptive of the output of variable
ramp generator 208. In accordance with one aspect of the present
invention, the respective circuitry channels associated with other
phases (e.g. phases B (120) and C (122), see also FIG. 5) each
include an automatic gain control (AGC) amplifier 222 (e.g. 222B
for phase B (120); 222C for phase C (122)). AGC amplifiers 222
cooperate with the variable ramp generator 208 of the associated
circuitry channel, are referenced (through buffer 224) to the
output of the variable ramp generator 208 of the reference channel
(e.g. variable ramp generator 208A), the average voltage value of
the ramps generated by variable ramp generators 208 (e.g. 208A,
208B, and 208C) are made equal by AGC Amplifiers 222 (e.g. 222B,
and 222C).
[0082] Controller 110 suitably further comprises: circuitry, e.g.
error amplifier 226 and variable reference voltage generator 228,
for generating a reference signal indicative of the desired firing
angle to trigger generators 210 (e.g. 210A, 210B, 210C) against
which the output of the associated variable ramp generator 208
(e.g. 208A, 208B, 208C) is compared; a conventional microprocessor
or microcontroller 248 (e.g. a PIC18F242) for, in cooperation with
various other elements of system 100, generating signals indicative
of, or to react to, various operating conditions, (e.g. controlling
various fans in response to system temperatures, limiting current
or shutting the system down due to over-temperature conditions,
shutting the system down due to over or under voltage conditions,
etc.); an opto enable circuit 250, to selectively enable and
inhibit application of trigger signals to switching bridge 112; a
No-Fire circuit 252 for generating signals indicative of certain
designated conditions during which application of the trigger
signals to switching bridge 112 are inhibited; a system start
circuit 254 for inhibiting operation in the absence of signals from
all phases; a suitable logic power supply 256; and an over voltage
detect circuit 258.
[0083] Referring now to FIG. 2B, in general, each of isolation
transformers 204 has a primary winding driven by the associated
phase-to-phase voltage and, multiple, isolated secondaries (230A,
230B, and 230C). Zero crossing detectors 206 each examines one of
the secondaries (e.g. 230A) of the associated transformer 204 and
determines when the voltage waveform crosses zero.
[0084] As previously noted, zero-crossing detectors 206 suitably
each comprise a filtered comparator 212, a variable blanker 214,
and a reset pulse generator 216. Filtered comparator 212 determines
when the voltage is above or below a reference point, e.g. 0 volts
to 3.5 volts, preferably 2.5 volts. The changeover point is deemed
to be a potential zero crossing. Indicia of the polarity of the
signal are provided to the associated trigger generator 210.
Variable Blanker 214 provides a blanking pulse equal to a
predetermined portion, e.g. between 30% and 70% and preferably 50%,
of the zero crossing-to-zero crossing period so that spurious zero
cross signals that might be caused by noise following the actual
zero crossing, do not trigger the reset pulse generator 216.
Variable ramp generators 208 each generate a ramp with a shape
characteristic representing the volt-seconds appearing at the
secondaries (232A, 232B, 232C) of the associated transformer. The
ramp is compared to a ramp reference voltage (RAMP_REF), from error
amplifier 226. Coincidence at comparator 218 asserts a signal to
digital routing circuit 220 which generates a trigger signal that
turns on the appropriate switching device in bridge 112. The ramp
is reset by the associated reset pulse generator 216.
[0085] More specifically, each of phase isolation transformers 204
(e.g. transformers 204A, 204B, 204C) suitably include a primary
winding and multiple (e.g. 3) secondary windings, (230, 232 and
234) and generate several isolated, scaled, voltage waveforms which
embody the characteristics of the associated phase voltage at its
respective primary winding. The primary winding is driven by the
alternator phases A (118)-B (120), B (120)-C (122), or C (122)-A
(118). The secondary windings provide signals to the associated
zero crossing detector 206 and ramp generator 208 and to system
start circuit 254. Phase isolation transformers 204 are suitably
commercial transformers capable of providing sufficient isolation
for the particular application, such as, in the preferred
embodiment, Tamura 3FS-248 transformers.
[0086] A signal indicative of the waveform of the associated phase
from one of the secondary windings (e.g. A (230A), B (230B), or C
(230C)) of each transformer 204 is applied to the associated
zero-crossing detector 206 (e.g. 206A, 206B, and 206C). The
zero-crossing detector 206 detects the occurrence and polarity of
voltage zero crossings in the signal and generates waveform
polarity information and ramp reset signals. The output signals of
each zero-crossing detector 206 (e.g. 206A, 206B, and 206C) is
provided to the associated variable ramp generator 208 (e.g. 208A,
208B, and 208C) and trigger generator 210 (e.g. 210A, 210B, and
210C). The outputs of the trigger generators, if enabled by the
optocoupler enable circuit 250, are applied to fire the SCRs. The
optocoupler enable circuit will not enable the trigger generator if
the INHIBIT signal is asserted by either the microcontroller 248 or
No-Fire circuit 252.
[0087] As previously noted, zero-crossing detectors 206 suitably
each comprise a filtered comparator 212, a variable blanker 214,
and a reset pulse generator 216. Referring now to FIG. 3, filtered
comparator 212 suitably comprises a low pass pre-filter 308, and a
comparator 310 (preferably with a slight DC hysterisis between 0.1
and 0.3 volts preferably 0.28 volts). Filter 308 effectively
removes high-frequency spikes from the AC phase signal from
transformer 204. Comparator 310 generates a signal indicative of
the polarity of the AC phase signal; transitions in the output of
comparator 310 indicate a zero-crossing. The output of comparator
310 (indicative of the polarity of and zero crossings in the
associated AC phase) is applied to the associated variable blanker
214 and provided, at nominal connection point 304, for application
to the associated trigger generator 210.
[0088] Variable blanker 214 (in cooperation with trigger generator
210) effectively prevents spurious transitions in the comparator
output that might otherwise cause an SCR trigger signal to be
generated from doing so. Transitions occurring within a
predetermined portion of the comparator half cycle (e.g. within a
predetermined number of phase degrees after a zero-crossing) are
prevented from generating an SCR trigger signal. Still referring to
FIG. 3, variable blanker 214 suitably comprises a monostable
multi-vibrator (one shot) 312, a filter 314 and a variable current
source 316. One shot 312 is triggered by both positive going and
negative going transitions in the output of comparator 310. The
duration of the pulse generated by one shot 312 is a predetermined
portion (e.g. suitably in the range of 30% to 70%, and preferably
50%) of the time between triggers (transitions in the comparator
output), i.e., the duration of the half cycle of the output of
comparator 310.
[0089] In the preferred embodiment, the duration of the one shot
output pulse is controlled by the time required to charge a timing
capacitor (e.g. 318). The timing capacitor is typically discharged
when one shot 312 is triggered, and the output of one shot 312 is
maintained at a predetermined level (e.g. the Q output of one shot
312 is held high) until capacitor 318 recharges to a predetermined
level (at which point the Q output goes low). In conventional
applications, a timing capacitor is typically charged through a
resistor, and the duration of the one shot output pulse is
constant. In the preferred embodiment of the present invention,
however, the timing capacitor is charged through current source 316
driven by a signal proportional to the duty cycle of the one shot
output (and hence the frequency of the comparator output) so that a
time required to charge the timing capacitor is inversely
proportional to the duty cycle of the one shot output. More
specifically, the inverted output (Q bar of one shot 312) is
applied to filter 314 which generates a DC signal proportional to
the duty cycle of the one shot output to current source 316. Thus
if the duty cycle (percentage of the comparator output half cycle)
of Q output pulse decreases, the current provided to the timing
capacitor will decrease. With decreased charging current, more time
is required to charge the capacitor to the predetermined level, and
thus increasing the duration of the one shot output pulse.
Conversely, if the duty cycle of the one shot output signal
increases, the current to the timing capacitor is increased,
hastening the charge of the timing capacitor. The values of the
components of filter 314 are chosen such that the duty cycle of the
one shot output is equal to the predetermined value at a given
comparator output frequency. The net result is that the duty cycle
of the one shot output signal will self adjust to the predetermined
value regardless of the rate of trigger inputs. The output of one
shot 312 is provided to reset pulse generator 216, and, at
connection point 302, for application to the associated trigger
generator 210.
[0090] Reset pulse generator 216, in response to transitions of a
predetermined polarity (e.g. rising edge), generates a short
uniform duration pulse suitable for application to a switching
element (e.g. a transistor 414, FIG. 4) in ramp generator 208 to
reset the ramp (e.g. discharge capacitor 412, FIG. 4). Pulse
generator 216 suitably comprises a one shot 320, as shown in FIG.
3, providing the pulse at nominal connection point 306 for
application to the associated ramp generator 208, and associated
trigger generator 210. Since one shot 320 is responsive only to the
rising edge of the variable blanker pulse from one shot 312, the
reset pulse can be generated only once within the period defined by
the variable blanker.
[0091] Variable ramp generators 208 (e.g. 208A, 208B, 208C)
generate a voltage ramp indicative of the time integral of the
associated phase voltage (volt-seconds). The ramp is reset at phase
zero crossings. More particularly, variable ramp generators 208
each generate a volt/second ramp in response to signal from a
second secondary winding (e.g. 232A) of the associated isolation
transformer 204. Ramp generators 208 are reset (and begin a new
ramp) upon zero crossings in the associated phase, as indicated by
a reset signal from the associated zero-crossing detector 206
(reset pulse generator 216). The instantaneous output voltage of
ramp generator 208 is thus indicative of the volt seconds of the
associated phase half cycle. Variable ramp generators 208 provide
the volt/second ramp to the associated trigger generator 210 (210A,
210B, 210C). As will be further discussed, the associated trigger
generator 210, compares the ramp voltage to a reference voltage,
and, unless disabled by optocoupler enable circuit 250, generates a
SCR trigger signal accordingly (e.g. when the ramp voltage is equal
to the reference voltage).
[0092] In the case of the channel associated with designated
reference phase (e.g. phase A), the ramp is also applied through
buffer amplifier 224 to the respective AGC Amps 222 (222B, 222C)
associated with the other channels. As will be more fully
discussed, to facilitate automatic gain control certain components
(e.g. resistors 410, FIG. 4) of the ramp generator 208 associated
with the designated reference phase (e.g. 208A) are preferably of
values relative to the values of analogous components associated
with the other phases such that the output ramp of the ramp
generator 208 associated with the reference phase is greater than
the ramps generated by the other channels. An exemplary ramp
generator 208 suitable for use in association with the designated
reference phase (e.g. ramp generator 208A) is shown in FIG. 4. An
exemplary ramp generator 208 suitable for use in association with
the other phases (e.g. ramp generators 208B, 208C) is shown in FIG.
5.
[0093] Referring to FIGS. 4 and 5, ramp generators 208 suitably
comprise a rectifier bridge 408, a resistance (e.g. resistor or
resistance network) 410 cooperating with a capacitor 412, and a
switching device 414 (e.g. a transistor). Rectifier bridge 408
generates a DC signal (indicative of the voltage magnitude of the
associated AC phase) which is applied through resistance 410 to
charge capacitor 412. Switching device 414 is disposed to provide a
controllable discharge path for capacitor 412 (e.g. shunted across
capacitor 412). Switching device 414 is rendered conductive in
response to the reset pulse (generated at zero crossings) from
reset pulse generator 216 applied to nominal connection point 306
to discharge capacitor 412. Capacitor 412 is thus charged by a
current indicative of the AC phase voltage beginning at the zero
crossing initiating the instantaneous half cycle, so that the
voltage across capacitor 412 is indicative of the cumulative
volt-seconds of the AC phase during the half cycle.
[0094] Generating the ramp as a function of the voltage of the
alternator itself (e.g. the volt seconds of the waveform)
accommodates a wide range of alternator RPM. The time integral of
the voltage (volt seconds) generated by a given winding of the
alternator during a half cycle is constant at any RPM. As
alternator RPM (and hence frequency of the signals provided by
transformer 204) increases, the period the half cycle decreases,
but the voltage of the signal increases such that volt-seconds of
the half cycle remain constant. Thus the ramp is the same peak
value (total volt seconds) for each half cycle at any rpm.
[0095] Ramp generators 208 preferably, also include a compensating
filter 416, corresponding to pre-filter 308 in filtered comparator
212. Pre-filter 308 is preferably, as previously mentioned,
employed in filtered comparator 212 to eliminate spurious high
frequency transients in the output of the associated phase
isolation transformer 204. Pre-filter 308 tends to interject a
phase shift into the signal from which the zero crossings, (and
reset pulse) are generated. It is desirable that reasonable
fidelity be maintained between the generation of the ramp (e.g.
ramp interval) and the reset pulses. Accordingly, filter 416 is
provided to generate an analogous phase shift in the signal from
which the ramp is derived.
[0096] Referring again to FIG. 2, trigger generators 210 (e.g.
210A, 210B, 210C) compare the ramp indicative of the volt-seconds
of the associated phase (from the associated ramp generator 208)
applied at nominal connection point 404 to a control voltage
indicative of the desired firing angle e.g. RAMP_REF, (i.e., a
phase angle in the AC signal corresponding to a desired duty cycle,
and, concomitantly, a desired DC output level). A SCR trigger
signal is generated at voltage coincidence, and, unless disabled by
the optocoupler enable circuit 250, routed to the appropriate SCR.
An exemplary trigger generator 210 is shown in FIG. 4. Trigger
generators 210 suitably comprise a comparator 218, and appropriate
digital routing logic 220. Comparator 218 generates a signal
indicative of when the volt-second ramp from ramp generator 208
(provided at nominal connection point 404) exceeds a reference
signal (RAMP_REF) (provided, in the preferred embodiment, by error
amp 226 in cooperation with reference voltage generator 228)
indicative of the desired firing angle. Digital routing logic 220,
suitably comprises an RC network 450, respective D-type (e.g.
74HC74) flip-flops, 456 and 458 forced clock circuitry 464, a nor
gate, 452 and exclusive or gate,454 and respective opto-couplers
460 and 462. Responsive to: [0097] the output of comparator 218
(indicative of when the volt-second ramp from ramp generator 208
exceeds the reference signal (RAMP_REF); [0098] the output of
filtered comparator 212 (indicative of the polarity of the
instantaneous half cycle) provided at nominal connection 304;
[0099] the output of variable blanker 214, (indicative of the
predetermined portion of the half cycle during which transitions in
the AC phase are deemed spurious and ignored) provided at nominal
connection point 302; and [0100] the reset pulse (indicative of
zero crossing transitions in the AC phase) provided at nominal
connection point 306; and [0101] the ENABLE signal from opto enable
circuit 250 digital routing circuitry 220, when activated,
generates a trigger signal to the positive or negative SCR
associated with the phase at voltage coincidence between the
volt-second ramp and the reference signal (RAMP_REF). During normal
operation the ramp signal (at nominal connection point 404) will
exceed reference signal RAMP_REF, such that comparator 218A
generates an output signal, which is passed through gates 452 and
454 to clock in data from flip flop 456 into flip flop 458. The Q
BAR output of flip flop 456 is provided to the microcontroller as
signal ZC_SIG. The output of flip flop 458 is applied to buffered
optocouplers 460 and 462 (shown in more detail in FIG. 7). When the
output of flip flop 458 changes state, the optocouplers are (if
enabled) activated, sending a signal to the associated SCRs to
fire. Optocouplers 460 and 462 are enabled by opto enable circuit
250 in the absence of an INHIBIT signal being asserted by either
the microcontroller or No-Fire circuit 252. Polarity information
held by flip flop 456 is derived from the output of comparator 310
(in zero cross detector 206) provided at nominal connection point
304 and is clocked by the variable blanker signal at point 302
(suitably delayed by RC network 450). In the event that signal 404
never exceeds RAMP_REF, no clock signal will be generated. In the
event no clocking signal is generated, at the time of zero cross
(signal 306 RAMP RESET) transistor pair 464 initiates a forced
clock to flip flop 458 The waveforms of the various signals
involved in generation of the SCR trigger signals are shown in the
timing diagram of FIG. 4A. [,
[0102] AGC Amps 222B, and 222C compare the average voltage from the
ramp generator 208 associated with the designated reference phase
(e.g. 208A) with the average voltage from the associated ramp
generator (e.g. 208B or 208C) and adjust the gain of the associated
ramp generator (208B or 208C) so that the output ramp amplitude
matches that of 208A. An exemplary AGC Amp 218 suitable for use in
association with the designated reference phase (e.g. ramp
generators 208B, 208C) is illustrated in FIG. 5.
[0103] As previously noted, variations in the outputs of the
portions (legs) of the bridge associated with the respective phases
tend to occur due to variations in component values between the
circuitry associated with the various phases, due to e.g.
tolerances, temperature differences, winding voltage variation etc.
The use of AGC amplifiers 222 provides compensation for such
differences. With reference to FIG. 5, AGC amplifiers 222
preferably comprise: a differential amplifier 502; a variable
resistance device 504, such as, for example, a 4N25 optically
coupled isolator; respective filters 501 and 508, and a buffer 506
(analogous to buffer 224 in FIG. 4). Differential amplifier 502 is
receptive of signals indicative of the time integral (average) of
the volt-second ramp from the channel associated with designated
reference phase (e.g. the output of ramp generator 208A) and of the
time integral (average) of the output ramp from the associated
channel (e.g. the output of ramp generator 208B or 208C). More
specifically, the signal indicative of the reference phase ramp
provided by buffer 224 (FIG. 4) at nominal connection point 402 is
applied to filter 501. Filter 501 generates a DC signal
representing the time integral (average) of the reference phase
volt-second ramp, which is applied to one (e.g. the positive) input
of differential amplifier 502. The volt-second ramp from the
associated channel (e.g. the output of ramp generator 208B or 208C)
at nominal connection point 404 is passed through a buffer 506 and
applied to filter 508. Filter 508 generates a DC signal
representing the time integral of the associated phase volt-second
ramp, which is applied to the other (e.g. the inverting) input of
differential amplifier 502. Use of the integral of the volt-second
ramps permits comparison notwithstanding the phase angle difference
between phases (e.g. 120.degree.). The difference between the
integrals of the respective volt-second ramps, generated by
amplifier 502 is employed to control the resistance of variable
resistance 504. Variable resistance 504 is connected such that this
adjustment changes the effective resistance of resistance 410
controlling the time constant of capacitor 412 in the associated
ramp generator 208 (208B or 208C) so that the time integral of the
associated phase volt-second ramp (e.g. from 208B or 208C) is
identical to the time integral (average) of the reference phase
volt-second ramp (e.g. from 208A). Thus the effects of variations
between analogous components associated with the respective phases
are minimized.
[0104] As previously noted, trigger generators 210 (e.g. 210A,
210B, 210C) generate a trigger signal to the appropriate SCR when
the volt-second ramp indicative of the associated phase coincides
with a control voltage indicative of the desired firing angle. The
control signal can be fixed (constant), or variable, as in, for
example, a feedback loop tending to maintain a predetermined
regulated output voltage. In the preferred embodiment, the
reference signal is established as part of a control loop. By
comparing a fraction of the output voltage with the reference
voltage from variable reference voltage 228, error amplifier 222
provides a control voltage which ultimately varies the SCR trigger
latency and thus adjusts the output voltage.
[0105] Referring to FIGS. 1, 2, and 6, the voltage across load 106
is fed back through suitable connections to the voltage feedback
input (local 114 or remote 140 which will be explained more fully
later) to error amp 226. Error amp 226 generates control signal
RAMP_REF in accordance with deviation of the feedback signal from a
reference voltage indicative of the desired output voltage. Error
amp 226 preferably comprises a suitable scaling amplifier 602, a
differential amplifier 604 and a suitable inverter/level shifter
606. The local feedback voltage (114) provided by internal
connections inside the controller, or remote feedback voltage (140)
is appropriately scaled by amplifier 602, and the scaled voltage
applied as one input to differential amplifier 604. Additionally,
this signal is provided to the microcontroller as V_SENSE.
Differential amplifier 604 generates a signal indicative of
deviations in the scaled feedback signal from a reference voltage
(provided in the preferred embodiment by a variable reference
voltage source 228) indicative of the desired output voltage. The
difference signal is inverted and level shifted as appropriate by
inverter/level shifter 606, and applied as the control signal
RAMP_REF to trigger generators 210. As will be more fully explained
later, the RAMP_REF signal is also modulated by an elevated charge
signal applied at 610, a battery temperature signal applied at 608,
and a current control summing amplifier 612 which is responsive to
current signal 116, and current foldback signals FOLD_30 and
FOLD_60.
[0106] Variable reference voltage source 228 provides the reference
voltage. The reference voltage can be fixed (constant) or, as in
the preferred embodiment, dynamically modulated in accordance with
an environmental parameter. For example, in applications where
relatively long lengths of electrical cable connecting the output
of the converter to the load can be sufficient to cause a
significant voltage drop, the reference voltage can be modulated to
account for such voltage drop. As current to the load increases
(and the cabling voltage drop increases), the voltage regulation
point is adjusted upward to maintain the desired regulated voltage
at the load.
[0107] In certain applications suitable cabling may be installed
between the desired regulation point, (e.g. battery terminals) and
the remote sense input (140). However, in other applications
(particularly retrofit applications) installation of suitable
voltage sense cabling may not be practical. To accommodate such
adjustments in applications were remote sense is impractical, a
current sensor (e.g. hall effect device, shunt or similar device)
116, and variable reference voltage source 228 comprising parallel
potentiometers VR1 and VR2 are employed. Potentiometers VR1 and VR2
are initially adjusted in a no load (zero current) condition to
provide a reference voltage indicative of the desired output
voltage (e.g. the wiper of potentiometer VR1 is set to produce the
desired reference voltage with potentiometer VR2 wiper set to
ground). The system load is then increased and VR2 is adjusted to
bring the voltage at the load (or battery) back to the desired
nominal voltage. Thereafter, in operation, the current feedback
signal from sensor 116 applied to potentiometer VR2 effectively
modulates the reference voltage to compensate for resistive drops
in the cable so that the voltage across load 106 is substantially
constant irrespective of current flow and voltage drop in the
cable. Alternatively, remote sense input 140 may be utilized to
ensure the voltage at a regulation sense point (e.g. battery or
sensitive load applications) is maintained, negating inherent
system loses e.g. long cable lengths. In order to utilize remote
sense, suitable cabling should be installed to make connections
between the regulation point (e.g. battery terminals) and the
remote sense input (140). Due to the resistance at the input of
local sense 114, the remote sense signal applied at input 140 will
automatically override the local sense input at 114. When using
remote sense, the wiper of potentiometer VR2 is set to ground.
Thereafter, the system will regulate the VRO to maintain the
desired voltage at the sense point (e.g. battery terminals)
regardless of any losses between the output and the sense
point.
[0108] It is desirable to adjust the voltage output setpoint (VRO),
to accommodate changes in battery temperature. As shown in FIG. 6,
the output of a temperature sensor nominally provided to input
connection point 608 for generating a signal indicative of battery
temperature may be included. The output of the battery temperature
sensor applied to nominal connection point 608 is summed with the
output of the input and scaling amplifier, 602. The battery
temperature therefore controls a feedback signal which adjusts the
amplitude of the RAMP_REF signal thereby modulating the output of
switching bridge 112 (VRO) in accordance with battery temperature
(e.g. approximately 10 mV reduction in charging voltage for every
degree C. rise for a lead-acid battery). This will cause the
battery charging voltage to be optimized according to the battery
temperature.
[0109] It is further desirable to periodically raise the system
charging voltage, VRO in order to desulfate the battery plates. To
accomplish this, microcontroller 248 periodically asserts a signal
(provided at nominal connection point 610) to reference amplifier
604, resulting in RAMP_REF being lowered, thereby raising the
desired output voltage (VRO).
[0110] It is desirable to protect the system circuitry from over
current conditions to prevent system component failure. Again
referring to FIG. 6, a conventional summing amplifier 612 is
provided to sum the output of the current sense monitor 116, with
current limit signals from microcontroller 248. Microcontroller 248
suitably generates signals indicative of a desired current limiting
function, i.e. to limit the output current by a selected a
percentage, e.g. either 30% or 60%, in response to over temperature
conditions. Microcontroller 248 will assert a logic level low
signal to the appropriately scaled input of summing amplifier 612
(e.g. either the 30%, FOLD_30, or 60%, FOLD_60, reduction input).
The output of summing amplifier 612 is in turn summed with the
input to inverter/level shift amplifier 606 thereby modulating the
RAMP_REF signal in order to reduce the VRO setpoint during
over-current or current fold-back conditions.
[0111] In non-12 volt systems, (e.g. a 24 volt system) it may be
desirable to provide a source of 12 volt power for auxiliary
systems. In some 24 volt automotive applications the alternator
provides a 12 volt signal which controls an alternator warning
indicator typically by powering a relay connected to a warning
lamp. Accordingly, referring briefly to FIGS. 1 and 14, a circuit
150 may be included in the system 100 to provide a 12 volt source
suitable for powering the relay or indicator to provide an
indication of system operation (e.g. system operating normally).
Circuit 150 is activated by RELAY_ENABLE from microcontroller
248.
[0112] In some applications, it may be desirable to provide 12 volt
power sufficient to operate 12 volt subsystems within system 100,
in lieu of or in addition to the circuit of FIG. 14. Referring now
to FIGS. 1 and 15, a circuit 160 may be included in system 100 to
provide a 12 volt source sufficient to derive up to 10 amperes of
current from the output (VRO) of switching bridge 112. Power supply
160 is enabled by the SYSTEM_START signal from system start circuit
254. Alternatively, in motor vehicle applications, a signal from
the vehicle ignition switch may be used to enable circuit 160.
[0113] Neither, either, or both of sources 150 and 160 may be
included in system 100 as application requirements dictate or may
be replaced by a source of a different voltage.
[0114] It is desirable to provide various failsafe systems to
prevent potential damage to components in anomalous operating
conditions. As shown in FIG. 2, controller 110 suitably includes
various subsystems (e.g. microcontroller 248, system start circuit
254, over voltage circuit 258, etc.) to effectively disable
controller 110 under certain conditions, such as when an input from
alternator is not detected, control voltage RAMP_REF from error amp
226 approaches or exceeds the volt-second ramp value of the
designated reference phase (from e.g. variable ramp generator 208A
and buffer 224 at nominal connection point 402), or temperature
limits are exceeded. Such conditions are indicated by generation of
an INHIBIT signal by either microcontroller 248 or No-Fire circuit
252. Referring to FIGS. 2A, 4, and 7, opto enable circuit 250
suitably comprises a conventional switch for applying enabling
voltage to optocouplers 460 and 462 in the absence of application
of an INHIBIT signal from microcontroller 248, or No-Fire circuit
252 which allows the controller to operate normally. At the onset
of an INHIBIT signal, circuitry 250 removes the optocoupler ENABLE
signal.
[0115] An exemplary No-Fire circuit 252 is shown in FIG. 8. No-Fire
circuit 252 compares reference signal RAMP_REF to the output of
buffer 224, indicative of the voltage-second ramp generated by the
designated reference phase channel (provided at nominal connection
point 402). A RAMP_REF signal exceeding the buffered ramp signal at
point 402 indicates that error amp 226 is responding to very light
or no load condition. When reference signal RAMP_REF exceeds the
output of buffer 224 (at point 402) then No-Fire circuit 252
asserts the INHIBIT signal. This prevents firing of the SCRs until
the RAMP_REF signal lowers to a point below the output of buffer
224 (at point 402) at which point the SCRs begin to fire again.
[0116] An exemplary over voltage detect circuit 258 is shown in
FIG. 9B. Over voltage detect circuit 258 monitors the output (VRO)
of switching bridge 112 and produces the OVER_VOLT signal when VRO
exceeds a predetermined voltage value (e.g. VRO+15%). The OVER_VOLT
signal is passed to microcontroller 248 which in turn responds by
asserting the INHIBIT signal.
[0117] In the preferred embodiment, system start circuit 254
prevents system operation in situations where all phases of the AC
input from alternator 102 are not present. Referring to FIGS. 2A
and 9A, system start circuit 254 receives signals indicative of the
outputs of the respective phases from a third secondary winding
(e.g. 234A, 234B, 234C, respectively) from each of isolation
transformers 204A, 204B, and 204C and generates a control signal,
SYSTEM_START, only when all phases are present. Activation of the
5V logic power supply 256 (FIG. 15) is contingent on all 3
isolation transforms 204A 204B and 204C supplying their respective
nominal outputs indicating the presence of all three phases from
alternator 102. In the event that any phase should fail, the system
will shut down.
[0118] To protect against over current conditions (e.g. electrical
short) fusible links 124, are provided in the phase wiring of
alternator 102, input fuses 128 and output fuse 136 are provided in
control system 100. (e.g. 350 amp fusible links, 350 amp input
phase fuses and 400 amp output fuse for a 350 amp system). In
addition, to protect electrical system components from over voltage
conditions, a shorting crowbar circuit 142 (FIGS. 1 and 13) is
provided at the voltage regulated output (VRO) of switching bridge
112. Crowbar circuit 142 shorts the output of system 100 in the
event of catastrophic over voltage (e.g. 130% of VRO). In another
embodiment, the crowbar circuit may be used to turn on all
switching bridge 112 SCRs thereby shorting the output of the
alternator. An exemplary crowbar circuit 142 is shown in FIG.
13.
[0119] Other sensor circuitry providing signals indicative of other
operating parameters may also be provided to generate inputs to
microcontroller 248 as parameters relevant to generation of the
INHIBIT signal. For example, referring to FIG. 16, signals from
sensor circuitry (not shown) providing signals indicative of
various system parameters such as, for example, the temperature of
alternator 102, the temperature of a heatsink on which various
components are mounted, the temperature and current into, or out
of, the battery, the rail voltage (VRO, the DC voltage to load 106
by sampling the output of the input and scaling amplifier 602, e.g.
V_SENSE, FIG. 6), the output current signal 116 and a buffered
signal from a zero-cross detector (e.g. ZC_SIG, FIG. 4) indicative
of the alternator RPM, are applied as inputs to microcontroller
248. Responsive to those inputs, microcontroller 248 executes a
program to generate: [0120] indicia of various operational
parameters, and [0121] control signals for various fans (not shown)
(e.g. an alternator cooling fan, a control system cooling fan)
including variable speed fans which may be utilized for enhanced
longevity [0122] A signal to periodically elevate the output of
switching bridge 112 (VRO) to a level sufficient to reduce
sulfation in the battery by driving sulfur from the battery plates
back into solution in the electrolyte. This elevated charging
voltage may be asserted in accordance with calculations of battery
capacity based on battery temperature, voltage, and rate of
discharge while the system is quiescent (e.g. engine off). For
example, the battery voltage at any given temperature may be
compared with a look-up table of nominal voltages for the type
battery used (e.g. Pb--Pb or Pb--Ca). Additionally, the rate of
voltage drop for any given current drain on the battery may be
calculated to provide an indication of battery capacity. The
elevated charging voltage signal may then be asserted at nominal
connection point 610 the next time the system is started. [0123] In
addition, based on the above battery capacity calculations, a
warning indicator, (e.g. dashboard lamp) may be activated to
indicate to the operator that the battery is nearing end-of-life,
in order to prevent failure in the field. Another indicator may be
activated as a warning that the battery charge is nearing depletion
to the point of being unable to start the engine. [0124] Other
warning indicators may alert the operator of excessive system
temperatures, (e.g. alternator temperature, control system
temperature) in order that the operator may reduce system loads to
prevent system shutdown. [0125] Signals to reduce the current
output first by 30% (FOLD_30), then by 60% (FOLD_60), and finally
to shut the system down, (INHIBIT), are provided in response to
elevated system temperatures. [0126] The INHIBIT signal for
application to opto enable circuit 250 to remove the ENABLE signal
to opto-couplers 460 and 462 (FIGS. 4 and 7) in digital routing
circuits 220, such that SCR firing is disabled when the
microcontroller 248 detects a system fault.
[0127] A flowchart of the program executed by microcontroller 248
is provided in FIGS. 12A-12AG. In general, the program is composed
of interrupt initiated and time sequenced threads and routines, as
follows:
Interupts
[0128] ISR_ExtInt 1: OVER-VOLTAGE [0129] This interrupt is the
response to detection of an over-voltage condition by over voltage
detect circuit 258 (FIG. 9B) as indicated by signal OVER_VOLT. This
is an error condition and all inhibits are asserted e.g.
microcontroller 248 produces the INHIBIT signal.
[0130] ISR_ExtInt_0: ZERO-CROSS [0131] This interrupt is the
response to a zero-cross of the alternator phase input going
through zero volts. A signal indicative of the zero-cross is
suitably applied to the microcontroller, (ZC_SIG, FIG. 4). The
period of the zero-cross is monitored to indicate engine speed.
[0132] ISR_Timer_0: ZERO-CROSS TIMER ROLL-OVER [0133] This
interrupt is the response to an internal counter, Timer 0,
incremented in accordance with an internal clock and reset upon
zero crossings (the zero-cross counter) rolling over. This is an
error condition indicating that the speed of the engine is too
low.
[0134] ISR_Timer_2: TIME-BASE [0135] This interrupt is the response
to the general system delay. It is a repetitive event that
maintains delays within the firmware.
Threads and Routines
[0136] UpdatePeriodBuffer [0137] This thread is responsible for
buffering each zero-cross period. Each time a new period is read, a
flag indicating whether the new value is valid is tested, if set,
store a "full-count". The value is stored in the buffer and the
average is calculated. A flag is set for the other threads to
indicate that the average has been updated.
[0138] GetAnalogInputs [0139] This thread is responsible for
sampling all of the analog channels. Each channel is acquired
through the on-chip Analog-to-Digital converter. The readings are
stored in a buffer for each channel. The average of each buffer is
calculated for use by other threads. A flag is set for the other
threads to indicate that the averages have been updated.
[0140] TestAnalog [0141] This routine tests if the analog averages
have been updated. If so, a series of bounds checking is performed
for the output of switching bridge 112 (rail voltage, VRO), the
heatsink temperature and the alternator temperature.
[0142] TestVoltage [0143] This routine tests a signal
representative of the average rail voltage (VRO) (e.g. V_SENSE FIG.
6) of the system against a series of limits to declare one of the
following conditions: too low, normal and too high.
[0144] TestAlternatorTemp [0145] This routine tests the average
alternator temperature against a series of limits to declare one of
the following conditions: normal, current limit level 1 (e.g.
FOLD_30), current limit level 2 (e.g. FOLD_60), and system
inhibit.
[0146] TestHeatSinkTemp [0147] This routine tests the average
heatsink temperature against a series of limits to declare one of
the following conditions: normal, current limit level 1 (e.g.
FOLD_30), current limit level 2 (e.g. FOLD_60) and system
inhibit.
[0148] TestPeriod [0149] This routine tests the average period of
the alternator (as determined by the period between successive zero
crossings) against a series of limits to declare one of the
following conditions: too low, normal and too high.
[0150] BoostControl [0151] This routine tests the elapsed time
against the specified boost start and end times. The elevated
charging voltage signal applied to nominal connection point 610,
(for reducing sulfation in the battery) is controlled by this
routine
[0152] UpdateControls [0153] This routine is responsible for
controlling the output of the processor based on faults declared
from the various tests. This routine is also in control of the fans
for the heatsink and the alternator.
[0154] TestEndStartUp [0155] This routine is responsible for
holding the system from running until all faults are cleared from
the various tests.
[0156] Referring now to FIG. 10A As previously noted, switching
bridge 112, in response to control signals from controller 110,
selectively provides conduction paths between the various phases of
the AC signal from alternator 102 and a load 106. Controller 110
selectively generates control signals to switching bridge 112 to
produce a regulated output signal at a predetermined voltage. FIG.
10 depicts a conventional 3 phase, fully controlled SCR bridge. The
salient features of this circuit include:
[0157] A 3 wire connection to the (three-phase) alternator. Whether
the windings are joined as a "Delta" or "Wye" as shown here, only 3
output wires are required for operation. Alternatively, in the
"Wye" alternator configuration, neutral may be exported from the
alternator depending upon application requirements (e.g. split
supply operation).
[0158] Conduction to the output requires that 2 SCRs are in
conduction. There are therefore conduction losses due to the
voltage drop across 2 SCRs.
[0159] Because of the rolling nature (120 degrees apart) of the
phase voltages generated by the alternator, the correct SCR must be
fired in the correct order to control conduction properly. Thus,
there is only one solution for the order of the SCR triggers for a
given alternator phase order and alternator rotation direction. The
directionality is brought about by the fact that if the rotation of
the alternator is reversed, so too is the phase order of the
outputs, necessitating reversal of the SCR trigger timings.
[0160] Referring to FIG. 10B, an alternative bridge may be
comprised of single SCRs paired with diodes. This embodiment
results in more ripple in the output, but has the advantage of
having less heat loss due to the forward voltage of the diodes
typically being less than that of an SCR.
[0161] FIG. 11A depicts an alternative 3 phase fully controlled SCR
bridge. Significantly, all windings in the alternator are
completely separate, with no common connections. Further, 4 SCRs
are utilized to form an independent full wave bridge for each
individual winding. Six wires are required to connect the
alternator to the bridge. While seeming a disadvantage over 3 wires
in a conventional 3 phase bridge, higher power circuits may benefit
by the division of currents into multiple conductors. Such an
embodiment of a fully controlled SCR bridge has particular utility
in connection with embodiments of alternator 102 employing multiple
winding coils connected in parallel.
[0162] FIG. 11B depicts an alternative 3 phase partially controlled
SCR bridge. Like the embodiment shown in FIG. 11A, the SCR bridge
of FIG. 11B has particular utility in connection with alternators
having all windings in the alternator completely separate, with no
common connections. However, 6 diodes are used instead of SCRs such
that 2 SCRs and 2 diodes are utilized to form an independent full
wave bridge segment for each individual winding.
[0163] The features of this arrangement are:
[0164] As in the embodiment of FIG. 11A, six wires are required to
connect the alternator to the bridge. Again, while seeming a
disadvantage over 3 wires in a conventional 3 phase bridge, higher
power circuits may benefit by the division of currents into
multiple conductors.
[0165] Lower losses due to lower conduction drop. Typically a diode
has lower conduction drop than a SCR. Since only one SCR and one
diode are involved in the current path to the output, the
conduction losses will be lower than for 2 SCRs.
[0166] In both FIGS. 11A and 11B, each of the individual full wave
bridge segments function independently. While the trigger signals
for each bridge must be timed correctly to conduct the required
current, the need for timing coordination due to phase rotation is
eliminated. Thus there is no system-wide requirement to trigger the
SCRs in the correct order. Moreover, because of this timing
independence, the alternator windings may be connected to any of
the bridges arbitrarily. Further, the polarity of connection
between an individual winding and each bridge may be arbitrary as
well, since both SCRs within each bridge may be triggered
simultaneously and only the device with the proper polarity for
conduction will do so. This eases installation complexity and
avoids connection errors. Further, the alternator may rotate in
either direction without reassigning the SCR triggers.
[0167] It should be noted that the control circuitry previously
disclosed for conventional 3 phase controlled bridges, will control
the alternative configuration of FIG. 11B, without any
modification. Most of the differences is in lifting the
restrictions as to which winding is associated with which bridge
connection to assure proper operation, and the lifting of the
alternator rotation direction restrictions, etc.
[0168] Referring now to FIG. 16, the general form of
microcontroller 248 has many inputs and outputs. Inputs and outputs
can be analog or digital, and reflect communications to external
stand-alone computing apparatus, interface to off-chip support
devices, or interface to off-board hardware. Examples of analog
inputs include, for example signals indicative of temperatures,
voltages, and current. Examples of temperatures measured are
alternator, heat sink, battery and ambient. Examples of voltage
sense are VRO and the voltage at energy storage device (e.g.
battery) 108. Examples of current are controller output current
(CUR_SIG) and battery current. Analog output examples include
variable current limit and variable voltage boost level. Example
digital inputs include over-voltage (OVER_VOLT) from 258,
zero-cross (ZC_SIG) from 214, alternator fan tachometer, heat sink
fan tachometer to ensure that the fans are not stalled (e.g. water
fording operations). Example digital outputs include fixed current
limit (e.g. FOLD_60), fixed voltage boost, heat sink fan control,
inhibit of SCR firing, relay output circuit enable, control of
several on-board indicators such as: speed error, voltage error,
alternator temperature conditions, heat sink temperature
conditions, alternator fan control, heat sink fan control. Examples
of alternator speed errors are low speed (e.g. engine cranking but
not yet started), and high speed (e.g. engine over-speed). Example
VRO voltage errors are low voltage and high voltage determined by
comparing V_SENSE with preprogrammed set points. Examples of
alternator temperatures include current limit reduction of 30%
(FOLD_30) due to elevated temperature, current limit reduction of
60% (FOLD_60) due to further elevated temperature, and system
inhibit due to damaging (destructive) temperature of the
alternator. Examples of heat sink temperatures include current
limit reduction of 30% (FOLD_30) due to elevated temperature,
current limit reduction of 60% (FOLD_60) due to further elevated
temperature, and system inhibit due to damaging (destructive)
temperature of the heat sink. Examples of communications to
external stand-alone computing apparatus could include RS232,
Universal Serial Bus, Fire-Wire. Examples of off-chip support
devices include non-volatile memory, additional input-output
capabilities, additional analog-to-digital converters, additional
digital-to-analog converters, standalone real-time-clock. Examples
of off-board hardware include display module, key-pad and status
indicators.
[0169] As previously noted there is a need for a compact high power
alternator wherein a desired output voltage can be achieved by
changing the number of turns of the phase pole coil, that is
relatively easy to wind, and minimizes the consequence of short
circuits, while at the same time facilitating cooling. In
accordance with various aspects of the present invention this is
achieved by employing a predetermined number of pole phase coils,
preferably equal to the number of magnetic poles, with pole phase
coil wound with enough turns [of a relatively small diameter wire]
to generate the required output voltage of the alternator and a
fraction of the output current equal to 1 divided by the number of
magnetic poles and connecting the individual pole phase coils in
parallel, preferably employing conducting phase rings 138. Use of
conducting phase rings 138 not only greatly simplifies assembly of
alternator 102, but also facilitates cooling of the windings.
[0170] Referring now to FIGS. 17A, B and C alternator 102
preferably comprises: a front endplate 1702, an outer cylinder
1704, a rear endplate 1706, output terminals 126 (one for each
phase), to which respective individual conducting cables can then
be attached to transmit phase output to the control 100. As best
seen in FIG. 17B (detailing the view along a section A-A in FIG.
17A), alternator 102 includes a cylindrical rotor (not shown, for
ease of illustration) with permanent magnets disposed on its
interior surface, a stator 1708 and a respective conducting phase
ring 138 for each phase. Stator is disposed concentrically within
the rotor casing, and suitably comprises a soft magnetic core, and
conductive windings. The core is generally cylindrical width an
axially crenellated outer peripheral surface with a predetermined
number of equally spaced teeth and slots. The conductive windings
(formed of a suitably insulated electrical conductor, such as
varnished copper motor wire), are wound through a respective slot,
outwardly along the side face of the core around a predetermined
number of teeth, then back through another slot. The portion of the
windings extending outside of the crenellation slots along the side
faces of the core are referred to herein as end turns. Rotation of
the rotor about the stator causes magnetic flux from the rotor
magnets to interact with and induce current in the stator
windings.
[0171] Output terminals 126 and fusible links 124 are positioned
radially about conducting phase rings 138. Conducting phase rings
138 are made of a suitable conductive material e.g. brass or plated
copper. The conducting phase rings may be formed of rod stock or
punched from a sheet of appropriate material. In the preferred
embodiment the conducting phase ring is continuous e.g. a single
piece which would necessitate soldering or brazing together the
ends of a formed conducting phase ring. Conducting phase rings 138
are fastened to non-conducting conducting phase ring mounting
structure 1712 preferably made of a high impact resistant and
chemically stable material e.g. polyamide-imide, so that each
conducting phase ring, one for each phase output, are isolated
electrically from each other and rear endplate 1706. Conducting
phase rings 138 are positioned in air passage 1710 to maximize
exposure to air flow produced by alternator 102 and directly over
stator 1708.
[0172] FIG. 17C detailing the view along section B-B shows output
terminal assembly 126 which is comprised of a threaded conducting
stud 1716, preferably a highly conductive corrosion resistant
material (e.g. brass or plated copper) along with an electrically
non-conductive bushing 1714, preferably a high impact resistant and
chemically stable material (e.g. polyamide-imide), to electrically
isolate the output terminal from alternator rear endplate 1706. The
threaded conducting stud 1716 in the preferred embodiment has an
incorporated shoulder 1720, to act as a seat from inside alternator
rear endplate 1706 to which nut 1718 can be tightened, capturing
the assembly in rear endplate 1706.
[0173] Fusible link 124 is made of a suitable material e.g. a
calculated diameter and length of wire (preferably plated copper)
that will melt when subjected to loads calculated to be destructive
to alternator 102, control 100 or electrical systems being powered
by said equipment. In the preferred embodiment fusible link 124 is
soldered or brazed to both the threaded conducting stud 1716 and
conducting phase ring 138. An alternate method to secure the
fusible link is to attach a suitable lug to the end of fusible link
124 which is then fastened to stud 1716 mechanically by means of a
threaded nut.
[0174] Referring now to FIG. 17D detailing partial section view C-C
(FIG. 17A). Conducting phase rings 138 are fastened to structure
1712. The conducting phase rings are exposed to airflow 1722,
cooling conducting phase rings 138. Stator 1708 is housed within
outer cylinder 1704 and fastened to rear endplate 1706. Conductors
1724 exit stator 1708 and are soldered or brazed to their
respective conducting phase rings. Conductors 1724 in the preferred
embodiment are exposed to airflow 1722. In certain cases it may be
desirable to sheath conductors 1724 with a thin walled electrically
isolating material 1726 e.g. Nomex to protect against
grounding.
[0175] Referring now to FIG. 17E. An alternate method of producing
conducting phase ring 138 is accomplished by forming it of
rectangular stock such that suitable surfaces are presented for
drilling and tapping holes 1728. The end of fusible link 124, can
in this embodiment, be attached with a suitable lug 1730 for
fastening by, e.g. a threaded fastener 1732 to conducting phase
ring 138. Equally, conductor 1724 can also be equipped with a
similar lug and fastened to conducting phase ring 138 using
fastener 1734. Conducting phase ring 138 is in turn secured in a
similar manner to rear endplate 1706 using an appropriate structure
similar to 1712.
[0176] Referring now to FIG. 18A. An individual pole phase coil
1802 is wound in slots 1804 of stator 1708. The number of turns of
conductor 1724 comprising coil 1802 is equal to the number of turns
required to generate the rated output voltage of one phase of the
alternator. The output current of the individual phase coil is
equal to 1 divided by the number of magnetic poles of the
alternator. Thus, the individual pole phase coil is made up of a
relatively large number of turns of relatively small wire.
[0177] This construction results in a number of advantages, both
during construction of the alternator and during operation of the
alternator. [0178] 1. Because the individual pole phase coil is
made up of a relatively large number of turns, small changes in
design voltage can be accomplished by changing the number of turns.
For example, a particular 12 pole alternator wound in a
conventional manner with all of the pole phase coils connected in
series may require 1.0417 turns of conductor equal to wire gage
6.285 to produce 14 VDC (after proper rectification), 300 amperes
at 1940 rpm. Neither the number of turns nor the equivalent wire
gage is practical numbers for production. By constructing the
example alternator with the pole phase coils connected in parallel,
each individual pole phase coil would be 12.5 turns of 17 gage
wire. (As a note, half turns can be constructed by terminate one
end of the individual pole phase coil, say the start, on one side
of the stator lamination stack, and the other end, say the finish,
at the other side of the stator lamination stack. This construction
is illustrated in FIG. 18A) Further to this example, increasing the
original design to 1.0833 turns (again, an impractical number)
would reduce the rpm to 1894. This could be accomplished in the
alternate construction by increasing each parallel pole phase coil
to 13 turns. The relatively small cross sectional area of the
conductors provides for easier winding of the coils. [0179] 2. A
short circuit between turns of an individual pole phase coil
results in most of the power being generated in the alternator
flowing in the shorted coils. Because the coils are constructed of
a relatively large number of turns of relatively small cross
sectional area conductors, the shorted turns will very quickly melt
and clear the short circuit. The decrease in output power resulting
from one pole phase coil opening up is approximately 1/(number of
magnetic poles+number of phases). For example the power output
reduction of a 12 pole, three-phase alternator with one pole phase
coil shorted and then self cleared is approximately 3%. [0180] 3.
Referring to example 3 above, a short circuit between turns of an
individual pole phase coil will typically clear in less than two
seconds. Damage to the alternator drive system is eliminated, the
engine continues operation with no additional load and the
alternator continues to produce power to the connected load.
[0181] Referring now to FIG. 18B conducting phase rings 138 are
individually identified as A ring 1806, B ring 1808 and the C ring
1810. Three individual pole phase coil conductors, A phase 1812, B
phase 1814 and C phase 1816 are illustrated without their
respective coils for clarity. Each of the three pole phase coils
that make up a pole phase coil group is, in this illustration
connected in a "Wye" connection 1824. As noted earlier, the use of
a "Delta" connection can also be implemented using phase collector
rings.
[0182] Referring now to FIG. 18C three individual pole phase coils
of a three phase alternator comprise an A pole phase coil 1818, B
pole phase coil 1820 and C pole phase coil 1822 which collectively
make up a pole phase coil group 1826. There is one pole phase coil
group for each pole of an alternator (e.g. 12 pole phase coil
groups in a 12-pole alternator). [0183] 4. Referring now to FIG.
18D, all the pole phase coil conductors 1724 of a 12 pole
alternator are illustrated attached to their respective conducting
phase ring 1806, 1808 and 1810. The "Wye" connection 1824 of each
pole group is also shown. For clarity the coils themselves are not
shown. FIG. 18D in part illustrates the challenge presented in
gathering the individual phase coil conductors in an efficient
manner that does not impede cooling. With phase coil conductors
leaving the phase coil end turn at 90 degrees to the face of stator
1708, the end turns are exposed to the greatest air flow possible
which in turn offers the best possible cooling of said end
turns.
[0184] Although the present invention has been described in
conjunction with various exemplary embodiments, the invention is
not limited to the specific forms shown, and it is contemplated
that other embodiments of the present invention may be created
without departing from the spirit of the invention. Variations in
components, materials, values, structure and other aspects of the
design and arrangement may be made in accordance with the present
invention as expressed in the following claims.
* * * * *