Direct torque control motor controller with torque ripple reduction

摘要

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.

主权项

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.