Direct torque control motor controller with torque ripple reduction

Patent metadata

Field	Value
Publication number	US-9407189-B2
Application number	US-201414332433-A
Country	US
Kind code	B2
Filing date	Jul 16, 2014
Priority date	Jul 16, 2014
Publication date	Aug 2, 2016
Grant date	Aug 2, 2016

Abstract

An AC motor controller is provided that utilizes a direct torque controller and primary and secondary control loops. The primary control loop operates in a relatively conventional manner, determining a voltage vector that sets the inverter switching variables for the motor's power inverter, where the voltage vector is based on the motor's torque and flux as estimated from the measured voltage and current of the motor. The secondary loop, utilizing a faster sampling rate than the primary loop, estimates a more up-to-date torque error which is compared to a secondary torque error band, where the secondary torque error band is preferably narrower that the primary torque error band. If the secondary loop determines that the up-to-date torque error has exceeded the secondary torque error band, it sets a null voltage vector, thereby limiting torque ripples.

First claim

What is claimed is:

1. A method of controlling an AC motor, wherein said AC motor is coupled to a power inverter, the method comprising the steps of:
estimating an instantaneous output torque at a primary sampling frequency;
estimating an instantaneous stator flux at said primary sampling frequency;
comparing said instantaneous output torque and a reference torque to determine an estimated torque error;
providing said estimated torque error to a torque hysteresis comparator, wherein said torque hysteresis comparator outputs a torque error status based on whether the estimated torque error falls within a primary torque error band or exceeds either a primary upper torque error limit or a primary lower torque error limit, wherein said primary upper torque error limit and said primary lower torque error limit correspond to said primary torque error band;
comparing said instantaneous stator flux and a reference stator flux to determine an estimated flux error;
providing said estimated flux error to a flux hysteresis comparator, wherein said flux hysteresis comparator outputs a flux error status; and
selecting and applying a voltage vector based on said torque error status and said flux error status, wherein said voltage vector determines a set of inverter switching variables for said power inverter coupled to said AC motor; and
estimating an updated output torque at a secondary sampling frequency, wherein said secondary sampling frequency is at least two times faster than said primary sampling frequency;
comparing said updated output torque and said reference torque to determine an updated torque error;
providing said updated torque error to a pulse-width-modulation (PWM) controller, wherein said PWM controller compares said updated torque error to a secondary torque error band, wherein said secondary torque error band is narrower than said primary torque error band, and wherein a secondary upper torque error limit corresponding to said secondary torque error band is selected to be closer to said reference torque than said primary upper torque error limit corresponding to said primary torque error band;
leaving said voltage vector selected based on said torque error status and said flux error status unchanged when said updated torque error does not exceed said secondary torque error band; and
selecting a null voltage vector when said updated torque error exceeds said secondary torque error band.

2. The method of claim 1 , further comprising the step of selecting said secondary sampling frequency to be at least four times faster than said primary sampling frequency.

3. The method of claim 1 , further comprising the step of selecting a secondary lower torque error limit corresponding to said secondary torque error band to be closer to said reference motor torque than said primary lower torque error limit corresponding to said primary torque error band.

4. The method of claim 1 , wherein prior to said steps of estimating said instantaneous output torque and said instantaneous stator flux said method further comprises the steps of determining an applied stator voltage and measuring a stator current.

5. The method of claim 1 , wherein said step of selecting said null voltage vector further comprises the step of selecting between a first null voltage vector, V 0 , and a second null voltage vector, V 7 .

6. The method of claim 5 , wherein said step of selecting between said first null voltage vector, V 0 , and said second null voltage vector, V 7 , is based on minimizing changes in a set of switching state variables for said power inverter.

7. The method of claim 1 , further comprising the step of synchronizing a primary cycle counter corresponding to said primary sampling frequency with a secondary cycle counter corresponding to said secondary sampling frequency.

8. A control system coupled to an AC motor via a power inverter, comprising:
a primary A/D converter, wherein said primary A/D converter converts a measured analog stator current to a first digital stator current at a primary sampling frequency;
a flux and torque estimator coupled to a voltage sensor and to said primary A/D converter, wherein said flux and torque estimator outputs an estimated stator flux and an estimated output torque;
a flux error estimator, said flux error estimator comparing said estimated stator flux and a reference stator flux and outputting an estimated flux error;
a torque error estimator, said torque error estimator comparing said estimated output torque and a reference torque and outputting an estimated torque error;
a flux hysteresis comparator coupled to said flux error estimator, said flux hysteresis comparator outputting a flux error status;
a torque hysteresis comparator coupled to said torque error estimator, said torque hysteresis comparator outputting a torque error status based on said estimated torque error relative to a primary torque error band;
a sector evaluator outputting a spatial sector;
a first device containing a vector selection table, wherein said first device is coupled to said flux hysteresis comparator and to said torque hysteresis comparator and to said sector evaluator, wherein said first device outputs a voltage vector based on said torque error status and said flux error status, wherein said voltage vector determines a set of inverter switching variables;
a secondary A/D converter, wherein said secondary A/D converter converts said measured analog stator current to a second digital stator current at a secondary sampling frequency, wherein said secondary sampling frequency is at least two times faster than said primary sampling frequency;
a pulse-width-modulation (PWM) controller coupled to said first device and to said secondary A/D converter and to said voltage sensor and to said power inverter, wherein said PWM controller estimates an updated output torque at said secondary sampling frequency and determines an updated torque error based on said updated output torque and said reference torque, wherein said PWM controller compares said updated torque error to a secondary torque error band, wherein said secondary torque error band is narrower than said primary torque error band, and wherein a secondary upper torque error limit corresponding to said secondary torque error band is selected to be closer to said reference torque than a primary upper torque error limit corresponding to said primary torque error band, and wherein said PWM controller sets said voltage vector to a null voltage vector whenever said updated torque error exceeds said secondary torque error band.

9. The control system of claim 8 , wherein said control system is configured to synchronize a secondary cycle counter corresponding to said second sampling frequency with a primary cycle counter corresponding to said primary sampling frequency.

10. The control system of claim 8 , wherein said secondary sampling frequency is four times faster than said primary sampling frequency.

11. The control system of claim 8 , wherein a secondary lower torque error limit corresponding to said secondary torque error band is closer to said reference motor torque than a primary lower torque error limit corresponding to said primary torque error band.

12. The control system of claim 8 , wherein said PWM controller is comprised of a field-programmable gate array (FPGA).

13. The control system of claim 8 , wherein said PWM controller is comprised of a complex programmable logic device (CPLD).

Assignees

• Atieva Inc

Inventors

• Tang Yifan

Classifications

• H02P6/10

  Arrangements for controlling torque ripple, e.g. providing reduced torque ripple · CPC title

• H02P21/30 Primary

  Direct torque control [DTC] or field acceleration method [FAM] · CPC title

• H02P21/05

  specially adapted for damping motor oscillations, e.g. for reducing hunting · CPC title