Four quadrant motor controller minimizing distortion index

• US 5,585,708 A
• Filed: 02/06/1995
• Issued: 12/17/1996
• Est. Priority Date: 02/22/1991
• Status: Expired due to Fees

• Current Assignee: Kenetech Windpower, Incorporated
• Original Assignee: Kenetech Windpower, Incorporated
• Inventors: Erdman, William L., Richardson, Robert D.
• Primary Examiner(s): Cabeca, John W.
• Application Number:
  US08/384,628
• Time in Patent Office: 680 Days
• Field of Search: 318/772-774, 318/778, 318/780, 318/798-812, 318/823, 318/256, 318/254, 318/739, 318/727, 318/549, 318/722, 363/37, 363/49, 363/50, 363/51, 363/71-72, 363/136, 363/132-134, 363/17, 363/89, 363/98, 307/82, 307/85, 290/31, 322/32, 322/5, 322/42, 322/10, 322/7
• US Class Current: 318/800
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements
• CPC Class Codes: H02P 21/06 Rotor flux based control involving the use of rotor position or rotor speed sensors
• CPC Class Codes: H02P 21/20 Estimation of torque
• CPC Class Codes: H02P 2207/01 Asynchronous machines
• CPC Class Codes: H02P 23/06 Controlling the motor in four quadrants
• CPC Class Codes: H02P 23/14 Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
• CPC Class Codes: H02P 23/30 Direct torque control [DTC] or field acceleration method [FAM]
• CPC Class Codes: H02P 27/06 using dc to ac converters or inverters H02P27/05 takes precedence

Abstract

A motor control apparatus and method is disclosed for controlling a multiphase AC motor by controlling electrical quantities such as voltage or current applied to the stator of the motor. The apparatus includes a motor command unit for defining a reference signal indicative of a desired motor parameter such as torque, speed, or position, a DC voltage link, a controller, a line-side converter including active switches in a bridge configuration for controlling the bidirectional flow of electrical power between the DC voltage link and a source of AC power, and a motor-side converter including active switches in a bridge configuration for controlling stator electrical quantities by controlling the bidirectional flow of electrical power between the DC voltage link and the motor, where the motor-side converter includes control means responsive to the reference signal for controlling the active switches to produce stator electrical quantities that correspond to the reference signal.

Claims

1. A multiphase AC self-commutated bridge circuit comprising:

active switches coupled in a bridge configuration and defining a current path for each phase, wherein the state of each active switch determines the direction of current flowing therethrough;

current sensor means for sensing currents in each current path;

means responsive to a reference signal for determining desired currents;

means for periodically determining a distortion index indicative of errors between the desired and actual currents; and

means for controlling the active switches to produce currents that minimize the distortion index, wherein the means for controlling the active switches generates signals that are complimentary for each pair of active switches causing one active switch of each pair to switch on and the other active switch of the pair to switch off as appropriate to minimize the distortion index.

2. A bridge circuit as recited in claim 1 further comprising means for periodically computing a distortion index for each combination of switch states of the active switches and for periodically selecting a switch state that minimizes the distortion index.

3. A bridge circuit as recited in claim 1 further comprising means for converting the desired bridge circuit currents into desired bridge circuit voltages, means for comparing the desired bridge circuit voltages to the voltages that would result from each combination of switch states of the active switches, and means for choosing the switch state having associated voltages that are nearest to the desired bridge circuit voltages.

4. A bridge circuit as recited in claim 1 wherein the distortion index is proportional to the sum of the squares of the current errors.

5. A bridge circuit as recited in claim 1 wherein the distortion index is proportional to the sum of the absolute value of the current errors.

6. A motor control apparatus for controlling a multiphase AC motor having stator windings and a rotor and powered by a source of AC power, the apparatus comprising:

motor command means for defining a reference signal indicative of a desired motor parameter;

current sensor means for sensing stator currents of the motor;

a DC voltage link including means for storing energy;

a self-commutated line-side converter means coupled to the DC voltage link for controlling the bidirectional flow of electrical power between the DC voltage link and the source of AC power, wherein the line-side converter includes active switches coupled in a bridge configuration between the source of AC power and the DC voltage link, and includes line-side control means for controlling the active switches therein to regulate the flow of electrical power therethrough; and

motor-side converter means coupled to the DC voltage link for controlling stator currents of the motor by controlling the bidirectional currents between the DC voltage link and the motor, wherein the motor-side converter includes active switches coupled in a bridge configuration between the DC voltage link and the stator windings of the motor, includes motor-side control means responsive to the reference signal for determining desired stator currents, includes means for periodically determining a distortion index indicative of errors between the desired and actual stator currents, and includes means for controlling the active switches therein to produce stator currents that minimize the distortion index, wherein the means for controlling the active switches generates signals that are complimentary for each pair of active switches, causing one active switch of each pair to switch on and the other active switch of the pair to switch off as appropriate to minimize the distortion index.

7. A motor control apparatus as recited in claim 6 wherein the motor-side control means further includes means for periodically computing a distortion index for each combination of switches states and for periodically selecting a switch state that minimizes the distortion index.

8. A motor control apparatus as recited in claim 6 wherein the motor-side control means further includes means for converting the desired stator currents into desired stator voltages, means for comparing the desired stator voltages to the voltages that would result from each combination of switch states of the active switches, and means for choosing the switch state having associated voltages that are nearest to the desired stator voltages.

9. The motor control apparatus of claim 6 wherein the means for storing energy in the DC voltage link includes a battery.

10. A motor control apparatus for controlling a multiphase AC motor having stator windings and a rotor and powered by a source of AC power, the apparatus comprising:

motor command means for defining a reference signal indicative of a desired motor parameter;

current sensor means for sensing stator currents of the motor;

a DC voltage link including means for storing energy;

a self-commutated line-side converter means coupled to the DC voltage link for controlling the bidirectional flow of electrical power between the DC voltage link and the source of AC power, wherein the line-side converter includes active switches coupled in a bridge configuration between the source of AC power and the DC voltage link, and includes line-side control means for controlling the active switches therein to regulate the flow of electrical power therethrough, wherein the line-side control means includes means for determining desired line currents, includes means for sensing the actual line currents, includes means for periodically determining a distortion index indicative of errors between the desired and actual line currents, and includes means for controlling the active switches therein to produce line currents that minimize the distortion index, wherein the means for controlling the active switches generates signal that are complimentary for each pair of active switches, causing one active switch of each pair to switch on and the other active switch of the pair to switch off as appropriate to minimize the distortion index; and

motor-side converter means coupled to the DC voltage link for controlling stator electrical quantities of the motor by controlling the bidirectional flow of electrical power between the DC voltage link and the motor, wherein the motor-side converter includes active switches coupled in a bridge configuration between the DC voltage link and the stator windings of the motor, and includes motor-side control means responsive to the reference signal for controlling the active switches therein to produce stator electrical quantities that correspond to the reference signal.

11. A motor control apparatus as recited in claim 10 wherein the line-side control means further includes means for periodically computing a distortion index for each combination of switch states and for periodically selecting a switch state that minimizes the distortion index.

12. A motor control apparatus as recited in claim 10 wherein the line-side control means further includes means for converting the desired line currents into desired line voltages, means for comparing the desired line voltages to the voltages that would result from each combination of switch states of the active switches, and means for choosing the switch state having associated voltages that are nearest to the desired line voltages.

13. A method for controlling currents switched by a self-commutated bridge circuit containing active switches, the method comprising the steps of:

determining desired bridge circuit currents;

sensing the actual bridge circuit currents; and

switching the active switches to produce bridge circuit currents that minimize a distortion index indicating the magnitude of current errors between the actual and desired bridge circuit currents, wherein the step of switching the active switches comprises the steps of generating signals that are complimentary for each pair of active switches, and causing one active switch of each pair to switch on and the other active switch of the pair to switch off as appropriate to minimize the distortion index.

14. A method for controlling currents as recited in claim 13 further comprising the step of periodically computing a distortion index for each combination of switch states and selecting a switch state that minimizes the distortion index.

15. A method for controlling currents as recited in claim 13 further comprising the steps of converting the desired bridge circuit currents into desired bridge circuit voltages, comparing the desired bridge circuit voltages to the voltages that would result from each combination of switch states of the active switches, and choosing the switch state having associated voltages that are nearest to the desired bridge circuit voltages.

16. A method for controlling currents as recited in claim 13 further comprising the step of computing a distortion index that is proportional to the sum of the squares of the current errors.

17. A method for controlling currents as recited in claim 13 further comprising the step of computing a distortion index that is proportional to the sum of the absolute value of the current errors.

18. A method for controlling stator currents in a multiphase AC motor rotating at variable speeds, wherein the stator currents are switched by a self-commutated bridge circuit that includes active switches, the method comprising the steps of:

defining a reference signal indicative of a desired motor torque, speed, or position;

converting the reference signal into desired stator currents;

sensing the actual stator currents;

determining a distortion index indicative of the magnitude of current errors between the actual and desired stator currents; and

supplying pulse width modulation signals to the active switches to produce stator currents that minimize the distortion index, wherein the step of supplying pulse width modulation signals comprises the steps of generating signals that are complimentary for each pair of active switches, and causing one active switch of each pair to switch on and the other active switch of the pair to switch off as appropriate to minimize the distortion index.

19. A method for controlling currents in a motor as recited in claim 18 wherein electrical power for powering the motor is supplied to the bridge circuit from a second bridge circuit that is coupled to a source of AC power, wherein the second bridge circuit includes active switches, wherein the method further comprises determining a signal indicative of desired line currents of the second bridge circuit, sensing the actual line currents of the second bridge circuit, determining a second distortion index indicative of the magnitude of current errors between the actual and desired line currents, and supplying pulse width modulation signals to the active switches of the second bridge circuit to produce line currents that minimize the second distortion index.

20. A method for controlling stator currents in a multiphase AC motor rotating at variable speeds to obtain torque, speed, or position control of the motor, wherein the stator currents are switched by an self-commutated active rectifier that establishes a rotating flux field in the rotor of the motor, the method comprising the steps of:

defining a reference signal indicative of a desired motor torque, speed, or position;

determining a desired direct axis current representing rotor flux in a direction aligned with the rotor flux field in a rotating field coordinate system;

converting the reference signal into a desired quadrature axis current representing rotor torque, wherein the quadrature axis current is normal to the rotor flux field in the field coordinate system;

sensing the rotational speed of the rotor;

sensing the actual stator currents;

determining a rotor flux angle indicative of the instantaneous position of the rotor flux field;

converting the desired quadrature and direct axis currents into desired stator currents in a stationary stator coordinate system using the rotor flux angle;

determining a distortion index indicative of the magnitude of current errors between the actual and desired stator currents; and

supplying pulse width modulation signals to the switches of the active rectifier to produce stator currents that minimize the distortion index, wherein the step of supplying pulse width modulation signals comprises the steps of generating signals that are complimentary for each pair of active switches, and causing one active switch of each pair to switch on and the other active switch of the pair to switch off as appropriate to minimize the distortion index.