U.S. patent application number 10/155316 was filed with the patent office on 2003-11-27 for system and method for regulating a power system with feedback using current sensing.
Invention is credited to Allison, Nigel, Lidak, Petr.
Application Number | 20030218448 10/155316 |
Document ID | / |
Family ID | 29419603 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030218448 |
Kind Code |
A1 |
Lidak, Petr ; et
al. |
November 27, 2003 |
SYSTEM AND METHOD FOR REGULATING A POWER SYSTEM WITH FEEDBACK USING
CURRENT SENSING
Abstract
A system (10) regulates current and voltage in a power system by
using a correction signal that is modified to compensate for errors
associated with manufacturing variations. The correction signal
controls a power switch (49) that selectively sources/shunts
current to/from the output load (26) and power source. The
compensation technique applies to systems conducting either an A.C.
or a D.C. voltage. A current controller (44) is placed in a control
loop. The current controller contains circuitry having an offset
voltage and loop gain errors as a result of manufacturing
variations. At least one of the offset voltage and loop gain are
dynamically calculated by a loop controller (38) and the result is
used to modify the correction signal to provide an accurate output
load voltage and power line current.
Inventors: |
Lidak, Petr; (Hladke
Zivotice, CZ) ; Allison, Nigel; (Austin, TX) |
Correspondence
Address: |
MOTOROLA INC
AUSTIN INTELLECTUAL PROPERTY
LAW SECTION
7700 WEST PARMER LANE MD: TX32/PL02
AUSTIN
TX
78729
|
Family ID: |
29419603 |
Appl. No.: |
10/155316 |
Filed: |
May 24, 2002 |
Current U.S.
Class: |
323/222 |
Current CPC
Class: |
H02M 1/4225 20130101;
Y02B 70/10 20130101; H02M 1/0025 20210501 |
Class at
Publication: |
323/222 |
International
Class: |
G05F 001/10 |
Claims
1. A power system having a corresponding closed loop gain,
comprising: a voltage converter coupled to receive an input
voltage, the voltage converter having a power switch and an output
node to provide a desired D.C. voltage to a load; a current
controller coupled to receive a correction signal and to provide an
output signal to the power switch in response to the correction
signal, the current-controller having a corresponding offset
voltage; and a voltage controller coupled to the output node of the
voltage converter and coupled to provide the correction signal,
wherein the voltage controller selectively determines at least one
of a closed loop gain error and the offset voltage and determines
the correction signal based on the desired D.C. voltage, an actual
D.C. voltage provided at the output node when the output node is
coupled to the load, and the at least one of the offset voltage and
the closed loop gain error.
2. The power system of claim 1, wherein the voltage converter
comprises: an A.C. voltage to D.C. voltage converter; and a D.C.
voltage to D.C. voltage converter comprising the power switch.
3. The power system of claim 1, wherein the voltage controller
receives a scaled down version of the actual D.C. voltage at the
output node.
4. The power system of claim 1, wherein the voltage controller
measures the actual D.C. voltage.
5. The power system of claim 4, wherein the voltage controller
comprises a microcontroller to determine the correction signal and
calculate the at least one of the offset voltage and the closed
loop gain error.
6. The power system of claim 1, further comprising a line current
sensor coupled to sense a line current of the power system and
provide the line current to the current controller.
7. The power system of claim 6, wherein the current controller
comprises a sense amplifier having an input to receive the
correction signal, an input coupled to the line current sensor, and
an output coupled to the power switch.
8. A method for regulating a power system, comprising: setting a
correction signal to a first predetermined value corresponding to a
desired output load voltage; determining a first actual output load
voltage value; selectively adjusting the correction signal based on
the first actual output load voltage value; and determining an
offset voltage corresponding to a current controller in the power
system using the adjusted correction signal.
9. The method of claim 8, wherein selectively adjusting comprises:
determining whether the first actual output load voltage value is
within a predetermined amount of the desired output load
voltage.
10. The method of claim 9, wherein selectively adjusting further
comprises: if the first actual output load voltage value is not
within the predetermined amount, adjusting the correction signal
and determining a second actual output load voltage value.
11. The method of claim 9, wherein selectively adjusting further
comprises: if the first actual output load voltage value is within
the predetermined amount, adjusting the correction signal and
determining a second actual output load voltage value.
12. The method of claim 8, further comprising: setting the
correction signal to a second predetermined value corresponding to
a second desired output load voltage; determining a second actual
output load voltage value; selectively adjusting the correction
signal based on the second actual output load voltage value; and
determine a gain slope error corresponding to the power system
using the adjusted correction signal and the offset voltage.
13. The method of claim 12, wherein selectively adjusting
comprises: determining whether the second actual output load
voltage value is within a predetermined amount of the second
desired output load voltage.
14. The method of claim 13, wherein selectively adjusting further
comprises: if the second actual output load voltage value is not
within the predetermined amount, adjusting the correction signal
and determining a third actual output load voltage value.
15. The method of claim 13, wherein selectively adjusting further
comprises: if the first actual output load voltage value is within
the predetermined amount, adjusting the correction signal and
determining a third actual output load voltage value.
16. The method of claim 12, wherein after determining the offset
voltage and the gain slope error, the method further comprises:
determining a third actual output voltage value; determining a
third desired output voltage of the power system; using the
determined offset voltage and gain slope error to determine a
correction value; setting the correction signal to the correction
value; and applying the correction signal to obtain the third
desired output voltage.
17. The method of claim 8, wherein after determining the offset
voltage, the method further comprises: determining a second actual
output voltage value; determining a second desired output voltage
of the power system; using the determined offset voltage to
determine a correction value; setting the correction signal to the
correction value; and applying the correction signal to obtain the
second desired output voltage.
18. The method of claim 17, wherein the correction signal is
applied to a current controller portion of the power system.
19. The method of claim 18, further comprising using the determined
correction signal to control a power switch of the power
system.
20. The method of claim 17, wherein determining offset voltage is
performed by a voltage controller portion of the power system.
21. A method for regulating a power system having a current
controller coupled to a voltage controller, the method comprising:
determining at least one of an offset voltage associated with the
current controller and a closed loop gain error associated with the
power system; determining an actual output voltage provided by the
power system and a desired output voltage of the power system; and
determining a correction signal based on the determined at least
one of the offset voltage and the closed loop gain error, the
actual output voltage, and the desired output voltage.
22. The method of claim 21, further comprising: providing the
correction signal to the current controller; and adjusting a line
current of the power system.
23. The method of claim 22, wherein adjusting further comprises:
controlling a power switch coupled to the current controller, the
power switch regulating the actual output voltage provided to the
voltage controller.
24. The method of claim 21, wherein the offset voltage is
associated with a sense amplifier within the current
controller.
25. The method of claim 21, wherein determining the at least one of
the offset voltage and the closed loop gain error comprising the
voltage controller calculating the at least one of the offset
voltage and the closed loop gain error.
26. A method for regulating a power system, comprising: setting a
correction signal to a first predetermined value corresponding to a
desired output load voltage; determining a first actual output load
voltage value; selectively adjusting the correction signal based on
the first actual output load voltage value; and determining a gain
slope error corresponding to the power system using the adjusted
correction signal.
27. The method of claim 26, wherein after determining the gain
slope error, the method further comprises: determining a second
actual output voltage value; determining a second desired output
voltage of the power system; using the determined gain slope error
to determine a correction value; setting the correction signal to
the correction value; and applying the correction signal to obtain
the second desired output voltage.
28. The method of claim 27, wherein applying further comprises
providing the correction signal to a current controller portion of
the power system.
29. The method of claim 28, wherein applying further comprises
using the correction signal to control a power switch of the power
system.
30. The method of claim 27, wherein determining the gain slope
error is performed by a voltage controller portion of the power
system.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to power supply systems,
and more specifically, to electronic controlled regulation of the
power supply systems.
BACKGROUND OF THE INVENTION
[0002] Power systems are commonly used to convert alternating
current (AC) voltage provided by a power company to a desired
voltage for various loads, such as AC and direct current (DC)
motors. Many countries use AC voltages having differing magnitudes
and frequency. A full wave bridge rectifier is often used to
convert an alternating current voltage to a direct current voltage.
A disadvantage with known bridge rectifiers is that they produce a
current waveform that contains multiple short current pulses or
spikes synchronized to the power supplier's voltage signal. As the
proliferation of small appliances and other electronics has
occurred, power suppliers have experienced a detrimental effect on
their distribution systems caused by the widespread current pulses
being injected onto the distribution system. The problem is severe
enough that government regulations are becoming common to establish
regulations that would minimize the problem. The spikes generate
harmonic signals into the distribution system often known as
electromagnetic interference (EMI).
[0003] Another common problem for power suppliers is known as the
power factor issue. Optimally, a load in a power system would be
purely resistive. A purely resistive load will result in maximum
power efficiency and thus a power factor of one. The power factor
is defined as the cosine of the phase angle between the voltage
applied to a load and the current passing through it. For example,
a purely resistive load has a power factor of one where the voltage
and current are always in phase. A power factor of one is optimal
for power delivery and this condition is shown in FIG. 1. However
in reality, loads typically possess a significant amount of
impedance (both inductive and capacitive components) that
significantly lowers the power factor causing the voltage and
current to be out of phase. An example is shown in FIG. 2.
[0004] Prior solutions to address the EMI problem have included
correction circuitry known as power factor correctors. Power factor
correctors improve power distribution efficiency and reduce AC line
EMI. Power correction circuitry is often used in industrial control
and is increasingly required in home appliance dues to increasing
governmental regulations. Such power correction circuits are
typically isolated and independent integrated circuits that are
separated from conventional voltage regulation control circuitry.
Such integrated circuits typically have no compensation for the
commonly known problem of component value variation caused by
temperature variation. Also, such circuits often require precision
external components that add significant cost in order to increase
efficiency. Additionally, advanced digital signal processors (DSPs)
having high data throughput are often used to control advanced
voltage regulators. Less expensive power correction circuits
typically must be factory adjusted to compensate for manufacturing
variations of the components. Another approach in improving power
correction circuit performance is to use a less expensive processor
such as an eight-bit microcontroller in conjunction with very high
precision components, such as a precision comparator. If a lower
precision comparator is used in such an application, offset and
gain errors commonly associated with analog comparators contribute
significantly to reduce the efficiency of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The present invention is illustrated by way of example and
is not limited by the accompanying figures, in which like
references indicate similar elements.
[0006] FIG. 1 illustrates in graphical form a power system having a
power factor of one;
[0007] FIG. 2 illustrates in graphical form a power system having a
power factor that is less than one;
[0008] FIG. 3 illustrates in partial schematic form a power system
in accordance with the present invention;
[0009] FIG. 4 illustrates in graphical form voltage and current
relationships when output load current increases;
[0010] FIG. 5 illustrates in graphical form voltage and current
relationships when output load current decreases;
[0011] FIG. 6 illustrates in graphical form the relationship
between input current and output voltage in the power system of
FIG. 3;
[0012] FIG. 7 illustrates in graphical form voltage and current
relationships when the gain of the system of FIG. 3 limits the
maximum input current;
[0013] FIG. 8 illustrates in graphical form voltage and current
relationships when an offset voltage exists in the power system of
FIG. 3; and
[0014] FIGS. 9 and 10 illustrate in flow chart form the operation
of the loop controller of FIG. 3.
[0015] Skilled artisans appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help improve the understanding of the embodiments of
the present invention.
DETAILED DESCRIPTION
[0016] Illustrated in FIG. 3 is an exemplary power system for use
with the present invention. A power system 10 has a full wave
bridge rectifier 12 formed of diodes 14, 15, 16 and 17. An anode of
diode 14 is connected to a cathode of diode 15 at a first terminal
of an A.C. Input for receiving an A.C. input line voltage. A
cathode of diode 14 is connected to a cathode of diode 17. An anode
of diode 17 is connected to a cathode of diode 16 at a second
terminal of the A.C. Input. An anode of diode 16 is connected to an
anode of diode 15. A resistor 18 has a first terminal connected to
the cathode of diode 14 and a second terminal connected to a first
terminal of a resistor 19. A second terminal of resistor 19 is
connected to a ground terminal. A first terminal of an inductor 20
is connected to the first terminal of resistor 18. A second
terminal of inductor 20 is connected to an anode of a diode 22 at a
node 21. A cathode of diode 22 is connected to a first electrode of
a capacitor 24 at a node 23. A second electrode of capacitor 24 is
connected to the ground terminal. A first terminal of an output
load 26 is connected to node 23, and a second terminal of output
load 26 is connected to the ground terminal. A first terminal of a
resistor 30 is connected to node 23, and a second terminal of
resistor 30 is connected to a first terminal of a resistor 32 at a
node 31 and to an input of an analog-to-digital (A/D) converter 36.
A second terminal of resistor 32 is connected to the ground
terminal. An output of A/D converter 36 is connected to an input of
a loop controller 38. An output of loop controller 38 is connected
to an input of a D/A converter 40. An output of D/A converter 40
provides a correction signal 41 and is connected to an inverting or
negative input of a comparator 42 of a current controller 44. A
line current sensor 45 has a first terminal connected to the ground
terminal and a second terminal connected to the anode of diode 15.
An output of line current sensor 45 is connected to a positive or
non-inverting input of comparator 42. An output of current
controller 44 is connected to a gate or control electrode of a
power switch 49. A first current electrode or drain of power switch
49 is connected to node 21. A second current electrode or source of
power switch 49 is connected to the ground terminal. Although power
switch 49 is illustrated as an N-channel power MOSFET device, it
should be appreciated that other types of switches may be used. The
second terminal of resistor 18 is connected to a control input of
the loop controller 38 for providing a synchronizing (SYNCH) signal
47.
[0017] In operation, power system 10 receives an A.C. voltage at
two inputs of full wave bridge rectifier 12. The two inputs will be
referred to herein as the power line. Bridge rectifier 12 converts
the A.C. voltage to an approximating D.C. voltage in a conventional
manner. A D.C. to D.C. conversion is provided by inductor 20, diode
22, capacitor 24 and power switch 49 in a conventional manner. As a
result, no detailed explanation will be given regarding the
specific waveforms that are generated as the varying voltage and
current waveforms are generated across inductor 20, diode 22,
capacitor 24 and power switch 49. It should be appreciated that
other voltage converter structures and circuitry than that shown
may be used in connection with the present invention. For example,
a multi-phase voltage rectifier may be used in lieu of bridge
rectifier 12 to provide an approximating D.C. voltage.
[0018] A varying output load current conducts through output load
26. It should be further appreciated that output load 26 may be
either an A.C. or a D.C. load. Output load 26 may consist of
further voltage conversion stages (not shown). Additionally, output
load 26 may be a single-phase load or a multi-phase load.
[0019] The output load voltage across output load 26 at node 23 is
scaled by a resistive network formed by resistors 30 and 32 to
provide a proportional voltage input to the A/D converter 36. In
the illustrated form, the output load voltage is a varying value
D.C. voltage having noise and error content. In combination, A/D
converter 36, loop controller 38 and D/A converter 40 function as a
voltage controller to regulate the output load voltage and remove
noise and error content. The output load voltage is an analog
quantity and is converted to an equivalent multiple-bit digital
value by A/D converter 36. Loop controller 38 and D/A converter 40
function in combination to provide a correction signal 41 to
current controller 44. The current controller 44 provides a switch
control signal 48 to control conduction of power switch 49. The
current controller 44 controls the current flowing in the power
line based upon current measurements taken by Line current sensor
45. Line current sensor 45 provides an analog signal to the
positive input of comparator 42 that is proportional to the current
flowing in the power line. In order to make sure that the loop
controller 38 is synchronized and in phase with the AC input
signal, a synchronizing signal (SYNCH) is connected to loop
controller 38. Resistors 18 and 19 form a resistive network and
divide the voltage across the line terminals to a smaller value for
use by loop controller 38. Control signal 48 functions to
selectively cause current to flow through inductor 20 into the
ground terminal and hence through the power line. Control signal 48
also functions to selectively disrupt the current flowing through
power switch 49, causing the voltage at node 21 to rise. Whenever
the voltage at node 21 exceeds the voltage at node 23, diode 22
conducts supplying current into capacitor 24 and output load 26.
The loop controller 38 together with the current controller 44
function to drive (i.e. switch) power switch 49 resulting in the
power line current regulation and output load voltage regulation
required for power factor correction. Variations in the output load
current can be compensated by the current steering action
implemented when power switch 49 is being switched, thereby
affecting the size of the power line current. It should be noted
that while the following explanation of power system 10 is made in
the context of a sinusoidal input current, other trigonometric
waveforms may be utilized in connection with power system 10. For
example, step-wise sine wave approximations may be used.
[0020] In power system 10, the output power will approximately
equal the input power to the system. As a result, if the output
load current increases then the output voltage, Vout, will decrease
causing the input current, Iin, to increase in response. This
relationship is illustrated in FIG. 4.
[0021] Similarly, if the output load current decreases, then the
output voltage, Vout, will increase causing the input current, Iin,
to decrease in response. This relationship is illustrated in FIG.
5. Power system 10 then controls the input current Iin by using
correction signal 41 in order to restore Vout to its nominal
value.
[0022] Referring to FIG. 6, voltage/current curves illustrate the
impact that manufacturing and other errors have on the power line
current, referred to as the Input Current, and on the correction
signal 41 voltage. In the illustrated form, three undesired curves,
curves 60, 61 and 62 are possible. Every power system has a
specified maximum input current and output load voltage. Curve 60
represents an operating condition when the closed loop gain exceeds
the designed, value resulting in the maximum input current being
reached or exceeded before the maximum correction signal 41 has
been reached resulting in an error designated as an error 64. This
condition is represented graphically in FIG. 7 wherein distorted
waveforms are illustrated for the input current. In particular, the
correction signal 41 is unable to reach the V.sub.max value. As a
result, the input current prematurely reaches the I.sub.max value
and is either clipped or overshoots the I.sub.max value resulting
in a flattened, distorted waveform that contains undesirable
harmonics. As a result, the desired power will not be realized.
When the I.sub.max value is exceeded, components have to be
overspecified to account for this potential condition or otherwise
damage to components in the system may result.
[0023] Curve 61 represents an operating condition in which a
threshold voltage (V.sub.TH) error associated with comparator 42
offsets the output voltage in a positive direction which creates no
output current while some current is expected. All operational
amplifiers have an offset voltage, V.sub.offset, due to variation
in the component values. As a result, the slope of curve 61, which
is designated by an angle .theta., differs from the slope of curve
68. The slope of each curve represents the closed loop gain of
power system 10. Therefore, due to the offset voltage of comparator
42, an incorrect current gain, I.sub.gain, will occur resulting in
current errors present in the A.C. input. The offset voltage error
varies during operation and between products may be either a
positive voltage or a negative voltage. As a result of this wide
variation in manufacturing predictability, static compensation
techniques to correct this source of error do not effectively
remove the errors in the A.C. input current.
[0024] Curve 62 represents an operating condition in which when the
closed loop gain again exceeds the designed value but results in
the maximum correction signal 41 being reached or exceeded before
the maximum input current has been reached resulting in an error
designated as error 66. This condition is represented graphically
in FIG. 8 wherein distorted waveforms are illustrated for the input
current. In particular, the current curve is unable to reach the
I.sub.max value and results in a waveform with crossover distortion
and reduced amplitude that contains undesirable harmonics. The
current differential between the I.sub.max value and the actually
obtained maximum current is a function of error (i.e. deviation
from the intended value) in the closed loop gain and the offset
voltage of power system 10. The desired power will not be realized.
In contrast, curve 68 of FIG. 2 represents the desired waveform
wherein a predetermined slope represents the desired gain of the
closed loop of power system 10. When there is no correction signal
41, it is desired that there be no A.C. line input current.
Similarly, when a desired maximum correction signal 41 is reached,
a desired maximum A.C. line input current, I.sub.max should
result.
[0025] Illustrated in FIGS. 9 and 10 is a control method 70
implemented by loop controller 38 to provide the desired
current/voltage curve 68 of FIG. 6 in spite of the presence of
offset voltage error and gain error associated with current
controller 44. The control method uses both dynamic and static
techniques to accomplish the error compensation in power system 10.
After a start step 72, a step 74 sets the correction signal 41 to a
predetermined value that is calculated to create a desired output
load voltage. In a step 112, a determination is made as to whether
the predetermined value has a value that represents an output load
voltage having either zero current flow or the maximum current
I.sub.max flow as represented in FIG. 6. For these two areas of
operation, offset voltage can result in constant current values for
differing output voltage values due to offset error. An example of
each area of operation is respectively illustrated in connection
with curve 60, curve 61 and curve 62. If the answer to the
determination in step 112 is "no", then a step 76 is executed
wherein the actual output load voltage across output load 26 is
determined. In a step 77, a determination is made as to whether the
actual output load voltage is within a predetermined amount of the
desired output load voltage. The output load voltage is determined
by converting a scaled version of the actual output load voltage to
a digital value with A/D converter 36 and using circuitry within
loop controller 38 to measure the resulting value. If the actual
output load voltage is outside (i.e. greater than or less than) the
desired output load voltage by more than the predetermined amount,
the correction signal 41 is adjusted in a step 78 by using A/D
converter, loop controller 38 and D/A converter 40. In a step 80,
the actual output load voltage is again determined in response to
using the adjusted correction signal from step 78. Steps 77, 78 and
80 are repeated until the actual output load voltage is brought
within the predetermined amount of the desired output load voltage
and a step 84 is entered. This adjusted correction signal
represents the correction required taking into account all error
sources such as offset voltage and gain error.
[0026] If the answer to the determination in step 112 is "yes",
then a step 114 is executed wherein the actual output load voltage
across output load 26 is determined. In a step 118, a determination
is made as to whether the actual output load voltage is within a
predetermined amount of the desired output load voltage. If the
actual output load voltage is within the desired output load
voltage by the predetermined amount, the correction signal 41 is
adjusted in a step 120 by using A/D converter, loop controller 38
and D/A converter 40 to determine a point at which the actual
output load voltages differs from an expected value by more than
the predetermined amount. The correction signal at that point has a
value that compensates for the offset voltage and gain error that
exist in connection with either a zero or a maximum current value.
In a step 122, the actual output load voltage is determined in
response to using the adjusted correction signal from step 120.
Steps 118, 120 and 122 are repeated until the actual output load
voltage is brought outside the predetermined amount of the desired
output load voltage and step 84 is entered.
[0027] In a step 84, the offset voltage is determined using the
present value of the correction signal. It should be noted that the
method taught herein functions to determine both positive valued
offset error and negative valued offset error as the offset voltage
can vary with temperature, age of product and production
variations. Since most error amplifiers have output voltage swings
only in the positive voltage region, such amplifiers are capable of
compensating only negative offset voltages. When an offset voltage
exists, the present invention functions to provide a correction
signal that will adjust the output load voltage by controlling
power switch 49 to conduct at the proper time. In a step 86, the
correction signal is set to a second predetermined value that
corresponds to a second desired output load voltage. Two distinct
desired output load voltages are used in the method taught herein
for the purpose of calculating a gain error of the system as
determined from the slope of the voltage/current graph of FIG. 6
that is formed from the two predetermined desired output load
voltages.
[0028] Referring to FIG. 10, a continuation of the process is
illustrated. In a step 124, a determination is made as to whether
the second predetermined value is a correction value for the
operating condition of either zero current or maximum current,
I.sub.max. If neither the zero nor maximum current condition is
present in connection with the second predetermined value, the
actual output load voltage is determined in connection with the
second predetermined value for correction signal 41 during a step
88. In a step 87, a determination is made as to whether the actual
output load voltage is within a predetermined amount of the second
desired output voltage. If the output load voltage is within the
predetermined amount, then the process proceeds to a step 96.
However, if the output load voltage is not within the predetermined
amount, the correction signal 41 is adjusted in a step 90. After
the adjustment of the correction signal 41, the actual output load
voltage is again determined and step 87 is again repeated. Steps
87, 90 and 92 are iterative and repeated until the load voltage is
corrected to be within the predetermined amount of the second
desired output load voltage. At such point, the proper adjustment
of correction signal 41 has occurred for correcting for offset
voltage in connection with the second desired output load
voltage.
[0029] If in step 124 the determination is made that the second
predetermined value represents either zero current or I.sub.max in
the graph of FIG. 6, the actual output load voltage is determined
in a step 126. With the actual output load voltage known, a
determination is made in a step 128 whether the actual output load
voltage is within a second predetermined amount of the desired
output load voltage. Since this path of the process represents the
presence of either zero current or I.sub.max, a value for
correction signal 41 must be found that places the actual output
load voltage outside of the predetermined amount within the desired
output load voltage. If that amount initially is present, step 128
is immediately followed by step 96. Otherwise, steps 130 and 132
are processed one or more times by varying the correction signal 41
until the actual output load voltage is determined to no longer
have a value that is within the second predetermined amount of the
desired output load voltage. At the transition point where the
actual output load voltage exceeds the predetermined amount from
the desired output load voltage, this value of the correction
signal 41 can be used to determine the error in power system
10.
[0030] In a step 96, the gain slope is determined using the current
value of the correction signal 41 and the offset voltage previously
calculated in step 84. At this point, loop controller 38 has
dynamically determined the correct correction signal 41 to use to
compensate for both the comparator 42 offset voltage and for
voltage gain error caused by component value variation due to
manufacturing variations.
[0031] In general, step 96 may be implemented with two data values,
such as two output voltage values or two other values associated
with the system 10. In other words, the looping function
implemented in each group of steps 118, 120 and 122, steps 77, 78,
and 80, steps 128, 130 and 132, and steps 87, 90 and 92 is not
essential to implement. For example, the output of step 126 may be
used directly in step 96. If that is the case, the offset voltage
previously calculated in step 84 and the actual output load voltage
measured in step 126 are used to determine the gain slope in step
96.
[0032] Steps 100, 102, 104, 106 and 108 represent circuit operation
when power system 10 is in a normal operation mode. In a step 100,
the actual output load voltage is again determined. In a step 102
the desired output load voltage is determined. In a step 104, the
full error compensating correction signal 41 is determined using
the previously determined offset voltage error and the gain slope
error. In a step 106, the correction signal 41 is applied to obtain
the desired output load voltage that compensates for offset error,
gain slope error and the actual load condition. In a step
illustrated as step 107, input line current control is performed.
Although the current control is illustrated as a discrete step, it
should be well understood that the current control may be performed
at any point in time in parallel with the voltage control of steps
100, 102, 104, 106 and 108. In a step 108, a determination is made
whether repetition of power factor correction in the normal system
control process is to be repeated or not. When power factor
correction is complete, an end step 110 is executed.
[0033] In some applications, an initial calibration is performed
and the calibration is only performed once. In other applications,
the calibration can be more dynamic and the process repeated more
often.
[0034] The control method 70 may be implemented with software, with
hardware or with a combination of both hardware and software. By
now it should be apparent that a D.C. offset error cancellation
method for a digitally controlled feedback loop of a D.C. to D.C.
or an A.C. to D.C. converter has been provided. The control method
reduces the passive component count and eliminates manual trimming
of components within such a system, thereby reducing the total
system cost. The D.C. offset error of the hysteretic circuit has
been estimated and the gain value can be further exploited to
substantially cancel error in the feedback loop of power system 10.
No adjustable components or precision components are required and
neither is a production line calibration procedure. The present
invention is capable of compensating for both positive and negative
offset voltages of the current controller 44.
[0035] Because the apparatus implementing the present invention is,
for the most part, composed of electronic components and circuits
known to those skilled in the art, circuit details will not be
explained in any greater extent than that considered necessary as
illustrated above, for the understanding and appreciation of the
underlying concepts of the present invention and in order not to
obfuscate or distract from the teachings of the present
invention.
[0036] In the foregoing specification, the invention has been
described with reference to specific embodiments. However, one of
ordinary skill in the art appreciates that various modifications
and changes can be made without departing from the scope of the
present invention as set forth in the claims below. For example,
various processors, such as an eight-bit microcontroller or more
advanced processors such as DSPs (digital signal processors), may
be implemented within loop controller 38 to measure the threshold
voltage error. In many instances, the processing required to
implement the present invention may be performed using spare
resources of such processors that are present for other
functionality. The present invention is illustrated in the context
of a power system that is performing both voltage regulation and
power factor correction. However, the present invention is useful
in those power systems in which only voltage regulation is being
performed and only half-wave voltage rectification may be
implemented rather than full-wave rectification. Accordingly, the
specification and figures are to be regarded in an illustrative
rather than a restrictive sense, and all such modifications are
intended to be included within the scope of the present
invention.
[0037] Benefits, other advantages, and solutions to problems have
been described above with regard to specific embodiments. However,
the benefits, advantages, solutions to problems, and any element(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature or element of any or all the claims.
As used herein, the terms "comprises," "comprising," or any other
variation thereof, are intended to cover a non-exclusive inclusion,
such that a process, method, article, or apparatus that comprises a
list of elements does not include only those elements but may
include other elements not expressly listed or inherent to such
process, method, article, or apparatus.
* * * * *