U.S. patent application number 11/469147 was filed with the patent office on 2008-03-06 for system and method for adjustable carrier waveform generator.
Invention is credited to Russel J. Kerkman, David Leggate, Richard H. Radosevich.
Application Number | 20080054841 11/469147 |
Document ID | / |
Family ID | 38846786 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080054841 |
Kind Code |
A1 |
Kerkman; Russel J. ; et
al. |
March 6, 2008 |
SYSTEM AND METHOD FOR ADJUSTABLE CARRIER WAVEFORM GENERATOR
Abstract
A system and method for controlling an inverter of a motor
control unit includes a controller having a user interface
configured to allow user selection of a waveform increment value or
a waveform amplitude threshold. The controller also includes an
integrator configured to receive the waveform increment value and
generate a signal at least based on the waveform increment value. A
logic circuit is configured to monitor the signal and reset the
integrator when the signal reaches the waveform amplitude threshold
to generate a waveform having a frequency-independent amplitude. A
comparator compares the waveform to a modulating signal to trigger
gating pulses delivered to an inverter to drive an associated
motor.
Inventors: |
Kerkman; Russel J.;
(Milwaukee, WI) ; Leggate; David; (New Berlin,
WI) ; Radosevich; Richard H.; (Waukesha, WI) |
Correspondence
Address: |
ROCKWELL AUTOMATION, INC./(QB)
ATTENTION: SUSAN M. DONAHUE, E-7F19, 1201 SOUTH SECOND STREET
MILWAUKEE
WI
53204
US
|
Family ID: |
38846786 |
Appl. No.: |
11/469147 |
Filed: |
August 31, 2006 |
Current U.S.
Class: |
318/807 |
Current CPC
Class: |
H02P 6/14 20130101 |
Class at
Publication: |
318/807 |
International
Class: |
H02P 27/04 20060101
H02P027/04 |
Claims
1. A controller for controlling an inverter of a motor control
unit, the controller comprising: a user interface configured to
allow user selection of at least one of a waveform increment value
and a waveform amplitude threshold; an integrator configured to
receive the waveform increment value and generate a signal at least
based on the waveform increment value; a logic circuit configured
to monitor the signal and reset the integrator when the signal
reaches the waveform amplitude threshold to generate a waveform
having a frequency-independent amplitude; and a comparator
configured to compare the waveform to a modulating signal to
trigger gating pulses delivered to an inverter to drive an
associated motor.
2. The controller of claim 1 wherein the logic circuit is further
configured to calculate the waveform amplitude threshold based on
the waveform increment value.
3. The controller of claim 1 wherein the logic circuit is further
configured to calculate the waveform increment value based on the
waveform amplitude threshold.
4. The controller of claim 1 wherein the user interface is further
configured to allow user adjustment of the frequency-independent
amplitude.
5. The controller of claim 1 wherein the user interface is
accessible through at least one of a display integrated into the
motor control unit, a computer interfaced with the motor control
unit, and a network accessible address.
6. The controller of claim 1 wherein the integrator includes at
least one of a backwards Euler integrating circuit, a forward Euler
integrating circuit, and a differentiating integrating circuit.
7. The controller of claim 1 wherein the user interface is further
configured to allow user adjustment of the frequency-independent
amplitude to match periodic trigger points between the waveform and
the modulating signal to trigger the gating pulses delivered to the
inverter at a common periodic interval.
8. The controller of claim 1 wherein the waveform is a triangle
wave.
9. A method of generating a waveform for controlling an inverter
driving a motor, the method comprising the steps of: (A) generating
a first signal based on a first of a positive increment value and a
negative increment value; (B) calculating an amplitude threshold
value based on one of the positive increment value and the negative
increment value; (C) comparing the signal to the amplitude
threshold value; (D) upon determining the first signal has reached
the amplitude threshold value, generating a second signal based on
a second of the positive increment value and a negative increment
value; and (E) delivering the first signal followed by the second
signal to a controller as a carrier waveform to trigger gating
pulses delivered to an inverter driving a motor.
10. The method of claim 9 further comprising the step of (F)
adjusting a frequency of the carrier waveform without affecting the
amplitude of the carrier waveform.
11. The method of claim 10 further comprising the step of (F)
adjusting at least one of the positive increment value, the
negative increment value, and the amplitude threshold value.
12. The method of claim 9 further comprising the step of (F)
adjusting the amplitude threshold value to match periodic trigger
points between the carrier waveform and a modulating signal to
trigger the gating pulses delivered to the inverter at a common
periodic interval.
13. A waveform generator for driving a pulse-width modulation
process designed to control an inverter to generate voltage pulses
to power a motor, the waveform generator comprising: a user
interface configured to allow user selection of at least one of an
increment value and an amplitude threshold; a logic circuit
comprising a switch, a D-latch, and an integrator; wherein the
integrator is configured to generate a signal at least based on the
increment value; and wherein the logic circuit is configured to
monitor the signal and control the integrator to adjust the signal
to generate a waveform having a frequency-independent
amplitude.
14. The waveform generator of claim 13 wherein the logic circuit is
further configured to calculate the amplitude threshold value based
on the increment value and reset the integrator upon determining
that the signal has reached the amplitude threshold value.
15. The waveform generator of claim 14 wherein the amplitude
threshold value is user selectable.
16. The waveform generator of claim 13 wherein the user interface
is further configured to allow user adjustment of the
frequency-independent amplitude.
17. The waveform generator of claim 13 wherein the waveform is a
triangle carrier waveform configured to be compared to a modulating
signal and wherein, when the modulating signal exceeds the triangle
carrier waveform, a gating pulse is generated.
18. The waveform generator of claim 17 wherein the user interface
is further configured to allow user adjustment of the
frequency-independent amplitude to match periodic comparison points
between the triangle carrier waveform and the modulating
waveform.
19. The waveform generator of claim 17 wherein the gating pulse is
delivered to the inverter to generate a voltage pulse to power the
motor.
20. The waveform generator of claim 13 wherein the integrator
includes at least one of a backwards Euler integrating circuit, a
forward Euler integrating circuit, and a differentiating
integrating circuit.
21. A trigger system comprising: a user interface configured to
allow user selection of at least one of a waveform increment value
and a waveform amplitude threshold; an integrator configured to
receive the waveform increment value and generate a signal at least
based on the waveform increment value; a logic circuit configured
to monitor the signal and reset the integrator when the signal
reaches the waveform amplitude threshold to generate a waveform
having a frequency-independent amplitude; and a comparator
configured to compare the waveform to a modulating signal to
trigger gating pulses.
22. The system of claim 21 wherein the gating pulses are used to
pulse width modulate one of a coils, a magnet, an induction heater,
a welder, and a motor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to motor systems
and, more particularly, to a system and method for controlling a
waveform generator designed to control an inverter driving a motor.
The waveform generator includes a user-selectable increment and
amplitude threshold and generates a waveform that has a
frequency-independent amplitude.
[0004] Motors and linked loads are one type of common inductive
load employed at many facilities. To drive a motor, an inverter
formed from a plurality of switches is controlled to link and
unlink positive and negative DC buses to motor supply lines. The
linking-unlinking sequence causes voltage pulses on the motor
supply lines that define alternating voltage waveforms of
controlled magnitude and frequency. When controlled correctly, the
waveforms cooperate to generate a rotating magnetic field inside a
motor stator core. In an induction motor, the magnetic field
induces a field in the rotor windings of the motor. The rotor field
is attracted to the rotating stator field and; thus, the rotor
rotates within the stator core. In a permanent magnet motor, one or
more magnets on the rotor are attracted to the rotating magnetic
field.
[0005] Referring to FIG. 1, a motor system 10 generally includes a
power supply 12, a motor drive unit 14, and a motor 16. The power
supply 12 provides power to the motor drive unit 14 that, in turn,
converts the power to a more usable form for the motor 16 that
drives an associated load 18.
[0006] The motor drive unit 14 includes a variety of components,
such as a rectifier 20, an inverter 22, and a controller 24. During
operation, the power supply 12 provides single or multi-phase AC
power, for example, as received from a utility grid over
transmission power lines 26. The rectifier 20 is designed to
receive the AC power from the power supply 12 and convert the AC
power to DC power that is delivered to positive and negative DC
buses 28, 30 of a DC link 31. However, in some cases, the power
supply 12 may deliver DC power. In that case, the rectifier 20
would not be used, and the power supply 12 would connect directly
to the DC link 31.
[0007] The inverter 22 is positioned between the positive and
negative DC buses 28, 30 to receive the DC power delivered by the
rectifier 20. The inverter 22 includes a plurality of switching
devices (e.g., IGBTs or other semiconductor switches) that are
positioned between the positive and negative buses 28, 30 and
controlled by the controller 24 to open and close specific
combinations of the switches to sequentially generate pulses on
each of the supply lines 32 to drive the motor 16 and, in turn, the
load 18 through a drive shaft 34. Accordingly, the inverter 22 and
additional control circuitry are collectively referred to as a
motor drive unit 14. By controlling operation of these components,
the motor drive unit 14 controls the overall operation of the
motor.
[0008] As described, the controller 24 causes the switches of the
inverter 22 to open and close in a specific sequence to generate
pulses that, in turn, drive the motor 16. Traditional controllers
24 generally include pulse width modulation (PWM) generators with a
defined carrier-frequency dependent amplitude. One common generator
is a triangle comparison PWM generator. In such a generator, gate
pulses are generated in response to a comparison of a modulating
signal with the triangle carrier waveform. When the modulating
signal exceeds the triangle carrier waveform, one switch in the
inverter 22, for example an upper IGBT, is switched on by the
controller 24 for that particular phase.
[0009] Accordingly, the characteristics of the triangle carrier
waveform must be well known and carefully controlled to achieve
optimal control of the inverter 22 and, in turn, the motor 16.
However, generally, the amplitude of the triangle carrier waveform
decreases as the frequency is increased. This inverse relationship
limits flexibility and affects output waveform distortion.
[0010] Referring to FIG. 2, one common triangle carrier waveform
generator 36 is an up/down counter. In accordance with this
traditional design, the desired triangle carrier waveform is
produced as an output 38 of a summer 39 that, in general, is a sum
of a preset increment 40 and a feedback 41 of the output 38 after
being subjected to a delay 41 of one clock cycle.
[0011] The sign on the value added to the output 38 is selected by
a D-latch 46 controlling a switch 47 that is driven by a set of
combinational logic 48, in particular, opposing comparators 49, 50
together with an exclusive OR gate 52. One or more additional
delays 54 are typically added to the system to prevent
instabilities in the combinatorial logic 47.
[0012] Referring to FIGS. 1 and 2, since the output voltage of the
inverter 22 is controlled based on the clock frequency of the
controller 24, all PWM generators face the same fundamental
limiting relationship given by:
A N = f clk 2 * f c 1 ; Eqn . 1 ##EQU00001##
where N is the carrier incremental voltage or count, A is the peak
of the triangle carrier waveform, f.sub.clk is the clock frequency,
and f.sub.c1 is the frequency of the carrier signal. Hence, in a
traditional up/down counter waveform generator 36, the triangle
carrier waveform is determined by setting the peak of the triangle
carrier waveform (A) with an increment (N) of unity. Within this
configuration, the peak of the triangle carrier waveform is
established by the frequency of the clock (f.sub.clk) of the motor
control chip and the lowest carrier frequency (fc.sub.min). This
maximum count (A.sub.max) is then given by:
A max = f clk 2 * fc min . Eqn . 2 ##EQU00002##
For a given A.sub.max, fc.sub.min, and reduction in the increment
(N), the carrier offset is given by:
.DELTA. fc = N ( A max - N ) * fc min . Eqn . 3 ##EQU00003##
Accordingly, the frequency of the triangle carrier waveform is
given by:
fc=fc.sub.min+.DELTA.fc Eqn. 4.
[0013] For example, referring again to FIG. 2, the frequency of the
triangle carrier waveform is set by adjusting a value of an upper
limit variable 44. For example, if the lowest desirable frequency
of the triangle carrier waveform carrier is 2 kHz and this
corresponds to a count value of 2.sup.16, then a waveform having a
frequency of 4 kHz will have a peak of 2.sup.15.
[0014] These constraints significantly limit the feasible
resolution of the triangle carrier waveform and affects ability to
control the system. First, a fixed carrier spacing restricts
carrier selection for synchronous PWM, which limits the benefits of
synchronized carrier operation. Second, disturbance-free transition
to over-modulation may be prevented because of a conflict between
dead-time compensation and allowable triangle carrier waveform
frequencies. Third, the fixed carrier resolution requires the
system to round to the same resolution as the prescribed carrier
increment. Therefore, even if a processor or controller having
increased word size and processing power is selected, the ability
to exploit this increased bandwidth is limited.
[0015] For example, by doubling the frequency, the quantization
interval for the available voltage is doubled. This increased
quantization interval is imparted to the carrier waveform and is
not adjustable. As a result, the controller 24 has difficulty
matching comparison boundaries between the modulating signal
waveform and the triangle carrier waveform. This causes a loss in
accuracy due to rounding errors and can lead to increased harmonic
distortion in the output voltage of the inverter 22. As such, any
potential advantage sought by increasing carrier frequency can be
offset.
[0016] Additionally, traditional PWM generators typically drive
each of the PWM channels based on one common triangle carrier
waveform. As such, the accuracy with which the output voltage of
the inverter 22 can be controlled is significantly limited. In
fact, such traditional PWM generators are particularly limited at
low speeds, where the line-to-line voltages are comparable to dead
time. Dead time is typically defined as the state of non-conduction
of upper and lower power device. In this case, a typical voltage
would be:
2 .mu. sec .times. V bus 256 .mu. sec = 5 volts , t d .times. V bus
f c ; Eqn . 5 ##EQU00004##
[0017] where V.sub.bus is the voltage along the DC bus and td is
the dead time in microseconds.
[0018] Therefore, it would be desirable to have a system and method
for providing increased flexibility in the converter/inverter
output voltage generation. Furthermore, it would be desirable to
have a system and method for yielding improved voltage generation
and greater flexibility in waveform generation to reduce common
mode voltage, allow pole independent carrier selection, and control
dead-time compensation.
BRIEF SUMMARY OF THE INVENTION
[0019] The present invention overcomes the aforementioned drawbacks
by providing a waveform generator capable of generating a waveform
having a frequency-independent amplitude to trigger control of an
inverter driving a motor. Additionally, the waveform generator
includes a user-selectable increment and amplitude threshold to
generate a highly customizable waveform.
[0020] In accordance with one aspect of the present invention, a
controller is disclosed for controlling an inverter of a motor
control unit. The controller includes a user interface configured
to allow user selection of a waveform increment value or a waveform
amplitude threshold. The controller also includes an integrator
configured to receive the waveform increment value and generate a
signal at least based on the waveform increment value. A logic
circuit is configured to monitor the signal and reset the
integrator when the signal reaches the waveform amplitude threshold
to generate a waveform having a frequency-independent amplitude. A
comparator compares the waveform to a modulating signal to trigger
gating pulses delivered to an inverter to drive an associated
motor.
[0021] In accordance with another aspect of the present invention,
a method of generating a waveform for controlling an inverter
driving a motor is disclosed. The method includes generating a
first signal based on a first of a positive increment value and a
negative increment value and calculating an amplitude threshold
value based on the positive increment value or the negative
increment value. The method also includes comparing the signal to
the amplitude threshold value and, upon determining the first
signal has reached the amplitude threshold value, generating a
second signal based on a second of the positive increment value and
a negative increment value. Additionally, the method includes
delivering the first signal followed by the second signal to a
controller as a carrier waveform to trigger gating pulses delivered
to an inverter to drive a motor.
[0022] In accordance with yet another aspect of the invention, a
waveform generator is disclosed for driving a pulse-width
modulation process designed to control an inverter to generate
voltage pulses to power a motor. The waveform generator includes a
user interface configured to allow user selection of at least one
operational parameter including an increment value. The waveform
generator also includes an integrator configured to generate a
signal at least based on the increment value and a logic circuit
configured to monitor the signal and control the integrator to
adjust the signal to generate a waveform having a
frequency-independent amplitude.
[0023] Various other features of the present invention will be made
apparent from the following detailed description and the
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0024] The invention will hereafter be described with reference to
the accompanying drawings, wherein like reference numerals denote
like elements, and:
[0025] FIG. 1 is a schematic illustration of a motor system having
a motor drive unit configured to control operation of a motor in
accordance with the present invention;
[0026] FIG. 2 is a schematic illustration of a traditional up/down
counter-based triangle carrier waveform generator for driving a
controller of the motor control unit of FIG. 1;
[0027] FIG. 3 is a schematic illustration of an adjustable
amplitude/increment triangle generator for driving a controller of
the motor control unit of FIG. 1; and
[0028] FIG. 4 is a schematic illustration of another adjustable
amplitude/increment triangle generator for driving a controller of
the motor control unit of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Referring now to FIG. 3, the present invention provides an
adjustable amplitude/increment triangle generator 60 that includes
an integrator 62 having an output 64 connected to a comparator 65
that, as described above, compares the waveform generated by the
integrator 62 to a modulating signal. When the modulating signal
exceeds the triangle carrier waveform generated by the integrator
62, a controller, such as the controller 24 of FIG. 1, switches one
switch in the inverter to drive the associated motor. In this
regard, the triangle carrier waveform delivered by the generator 60
is used by the controller 24 of FIG. 1 to control the inverter
22.
[0030] To control the integrator 62, the output 64 is delivered to
a set of combinational logic circuits 66 that includes a
less-than-or-equal-to rational operator 68, a
greater-than-or-equal-to rational operator 70, and an exclusive OR
logical operator 72 that serve as inputs to a D-latch 74. As will
be described, a "Q" output 76 of the D-latch 74 is provided through
a feedback loop 78 to function as a control input 80 of a switch 82
designed to control operation of the integrator 62.
[0031] In particular, the switch 82 is controlled via the input 80
to select one of a positive increment (N) and a negative increment
(-N). Thus, the switch 82 provides one of N and -N to an input 84
of the integrator 62. The integrator 62 is a differentiating
integrator and; therefore, based on whether the input 84 is
connected to N or -N, generates a steadily increasing or decreasing
waveform that is delivered to the output 64.
[0032] The peak (whether positive or negative) of the waveform
delivered by the integrator 62 is defined by an amplitude or peak
threshold 86 that may be defined based on the increment value (N),
which is preferably user selectable. In particular, the peak
threshold or amplitude (A) 86 is equal to one half of the increment
value (N) divided by the product of a sampling period (T.sub.samp)
and a pulse width modulation period (T.sub.PWM). Hence, the
amplitude (A) of the triangle carrier waveform generated by the
integrator 62 is given by:
A = 1 2 N T SAMP * T PWM . Eqn . 6 ##EQU00005##
[0033] As will be described, a user interface 87 is included that
allows user selection or adjustment of the increment values (N and
-N) and/or the peak threshold 86. That is, since, as illustrated
above in Equation 4, the peak threshold 86 is a function of the
increment (N), the user interface 87 is designed to allow a user to
select an increment value (N). In this case, the combinational
logic circuit calculates the peak threshold 86 based on the user
selected increment value (N). Alternatively, the user interface 87
may allow a user to select a peak threshold 86, which is expressed
as the desired amplitude of the triangle carrier waveform.
Accordingly, the corresponding increment value (N) is calculated
based on the selected peak threshold 86.
[0034] To control the amplitude of the waveform delivered by the
integrator 62, the output 64 of the integrator 62 is delivered as
secondary inputs 88, 90 to the less-than-or-equal-to rational
operator 68 and the greater-than-or-equal-to rational operator 70,
respectively. The primary inputs 92, 94 of the
less-than-or-equal-to rational operator 68 and the
greater-than-or-equal-to rational operator 70 are the peak
threshold 86 and a static lower limit 96, respectively.
Accordingly, an output 98 of the less-than-or-equal-to rational
operator 68 is a true or "high" value until the triangle carrier
waveform generated by the integrator 62 and provided to the
secondary input 88 reaches the peak threshold 86, when it switches
to a false or "low" value. Likewise, an output 100 of the
greater-than-or-equal-to rational operator 70 is true or "high"
value until the triangle carrier waveform generated by the
integrator 62 and provided to the secondary input 90 reaches the
static lower limit 96, when it switches to a false or "low" value.
These transitions to the false or "low" value can be delivered to
outputs 102, 104 that are designed to record the peak and valley
values of the triangle carrier waveform, respectively, for
additional processing or system analysis.
[0035] By design, as long as the current value of the triangle
carrier waveform is between the peak 86 and the lower limit 96, the
outputs 98, 100 of the less-than-or-equal-to rational operator 68
and the greater-than-or-equal-to rational operator 70 are the same,
in this case, both high. However, it is noted that the
configurations of the combinational logic 66 could be inverted such
that the outputs 98, 100 of the less-than-or-equal-to rational
operator 68 and the greater-than-or-equal-to rational operator 70
would both remain low as long as the current value of the triangle
carrier waveform is between the peak 86 and the lower limit 96
without changing the overall functionality of the adjustable
amplitude/increment triangle generator 60. In either case, the
inputs 106, 108 of the exclusive OR logical operator 72 both
receive a high (or low) signal from the outputs 98, 100 of the
less-than-or-equal-to rational operator 68 and the
greater-than-or-equal-to rational operator 70. As such, an output
110 of the exclusive OR logical operator 72 is held as false or
"low" until one of the outputs 98, 100 of the less-than-or-equal-to
rational operator 68 and the greater-than-or-equal-to rational
operator 70 is caused to change because, as described above, the
triangle carrier waveform has reached a peak or valley.
[0036] The output 98 of the less-than-or-equal-to rational operator
68 is delivered to a "D" input 112 of the D-latch 74 and the output
110 of the exclusive OR logical operator 72 is delivered to a clock
(clk) input 114 of the D-latch 74. Accordingly, by definition, the
current value delivered to the "D" input 112 of the D-latch 74 will
be delivered to the "Q" output 76 of the D-latch 74 as long as the
value delivered to the clock input 114 remains high.
[0037] The value delivered by the Q output 76 of the D-latch 74 is
then used to control the switch 82. In particular, a change at the
Q output 76 of the D-latch 74 is delivered to the control input 80
of the switch 82 that, responsive thereto, connects the input 84 of
the integrator 62 to either N (the positive increment) or -N (the
negative increment) to thereby reset the direction of the carrier
waveform delivered at the output 64 of the integrator 62. It should
be noted that, as described above, the Q output 76 of the D-latch
74 is delivered a feedback loop to the control input 80 of the
switch 82; however, it is also contemplated that the "NOT Q" output
116, though shown as unused, could be used to control the switch
82.
[0038] Therefore, a triangle carrier waveform is created that has
characteristics, that are adjustable. However, while various
characteristics of the triangle carrier waveform are adjustable,
the waveform has a frequency-independent amplitude. In particular,
the characteristics of the triangle carrier waveform delivered at
the output 64 of the integrator 62 can be augmented by adjusting
the increment (N/-N) that, in turn, adjusts the amplitude or peak
value 86 because, as described above, the amplitude or peak value
is calculated, in part, based on the increment value (N). As will
be described below, the adjustable amplitude/increment triangle
generator 60 allows a user to adjust the amplitude and associated
characteristics of the triangle carrier waveform without incurring
the wide variety of drawbacks associated with such changes using
traditional triangle waveform generators.
[0039] In particular, in traditional motor control chips employing
an up/down counter to generate a triangle waveform, an increase in
the effective frequency resolution can be achieved by changing the
amplitude (A) half way through the period of the carrier waveform
(T.sub.PWM/2). For example, if the amplitude is decreased one count
at the peak and reset to 5000 at the valley, the effective PWM
period (T.sub.PWM) becomes 4.0004 kHz, an effective resolution of
0.4 Hz. When changing the triangle peak by one count, from 5000 to
4999, the frequency of the triangle carrier waveform is changed to
4.0008 kHz.
[0040] However, as explained above, such user-selected control is
achieved at the expense of the carrier waveform having an isosceles
form. In particular, while an effective resolution of approximately
0.8 Hz is achieved, this presents a problem at a 50% duty cycle
because the 50% duty cycle now falls between quantisized levels. In
fact, any amplitude that is odd will present a similar problem. As
a result, a 50% duty cycle or zero voltage is not attainable when
using the traditional motor control chips employing an up/down
counter to generate a triangle waveform. This can lead to
objectionable dither in the output current when diagnosing current
sensor functionality.
[0041] On the other hand, using the above-described adjustable
amplitude/increment triangle generator 60, the amplitude of the
triangle carrier waveform can match the effective resolution of the
traditional up/down carrier waveform without being plagued by the
"50% duty cycle problem" by doubling the amplitude and the
increment at the peak. In general, when the peak threshold 86 is
odd, the peak and increment are doubled to ensure proper delivery
of a 50% duty cycle. Furthermore, by increasing the increment
toward the peak threshold 86, single edge modulation is
possible.
[0042] For example, if the peak threshold 86 of the triangle
carrier waveform is set to 5000, with an increment of unity and a
clock frequency of 40 MHz, f.sub.c is 4 kHz. By simply decreasing
the peak of the triangle waveform to 4999 and maintaining an
increment of unity, f.sub.c is equal to 5000/4999 multiplied by 4,
or 4.0008 kHz. Comparing signal spectrums of a traditional up/down
counter-based generator to the above-described adjustable
amplitude/increment triangle generator 60 shows that at a clock
frequency of 40 MHz, f.sub.c of 4 kHz, increment of unity, and a
value of amplitude-to-increment ratio of 5000, identical waveforms
are generated. Therefore, the amplitude of the triangle carrier
waveform is not frequency dependent. By allowing the amplitude
and/or increment to be adjusted independent of frequency, increased
flexibility is achieved.
[0043] While, in general, the creation of a waveform generator that
is capable of creating a triangle waveform having an adjustable
amplitude/increment would lend itself to a variety of designs, the
constraints placed on such a generator when used in a motor control
unit present significant technical design impediments. For example,
while a variety of different implementations of the integrator 62
are possible, the advantages and disadvantages of each
implementation must be weighted.
[0044] Beyond the above-described configuration, it is contemplated
that a Backward Euler integrator 118 design may be utilized.
However, as shown in FIG. 4, this configuration 120 includes an
algebraic loop 122 and can produce timing conflicts when
implemented. Accordingly, to address the potential for timing
conflicts, it is contemplated that an additional delay 124 may be
added to the feedback loop 78. This delay 124, in effect, creates a
Euler Forward integrator configuration.
[0045] In the implementations described above with respect to FIGS.
3 and 4, the peak threshold and increment are user selectable. The
adjustable amplitude/increment triangle generator 60 may be
interfaced with or accessed by a variety of systems and/or may be
integrated into complex Field-programmable gate array (FPGA)
designs. In accordance with one embodiment, it is contemplated that
the user interface 87 may be presented that allows user selection
of the triangle amplitude and/or increment. In this regard, this
user interface may be provided to a user through a variety of
mediums, such as a user interface integrated into the motor drive
unit, a traditional or handheld computer that can be interfaced
with the motor drive unit to access the adjustable
amplitude/increment triangle generator 60, or a remote or network
accessible (intranet or internet) user interface.
[0046] Additionally, the user interfaces may be designed to provide
additional information for diagnostics and tracking. For example,
as described above, it is contemplated that the adjustable
amplitude/increment triangle generator 60 may store operational
information, such as the peak 102 and valley 104 values.
Accordingly, the user interface may provide this and additional
information for tracking, analysis, and the like.
[0047] The present invention has been described in terms of the
various embodiments, and it should be appreciated that many
equivalents, alternatives, variations, and modifications, aside
from those expressly stated, are possible and within the scope of
the invention. Therefore, the invention should not be limited to a
particular described embodiment.
[0048] May not be limited to motor control only, non-standard loads
such as coils, magnets, induction heaters, welders can utilize this
also
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