US 5,469,215 AGranted

Method and apparatus for controlling an electric motor with compensation or torque ripple

AssigneeOkuma Corporation

InventorMasayuki Nashiki

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Abstract

An electric motor control system compensates torque ripples to control the rotation of an electric motor more accurately. Compensated current amplitudes corresponding to the torques, speeds and rotational positions in the electric motor are stored in a memory 61. Address setting unit 91 prepares a read address AD.sub.1 in the memory 61 from the torque command T, speed information VL and rotational motor position P. The prepared read address AD.sub.1 is then used to read a torque error compensation data MD.sub.1 from the memory 61. An adder 12 adds the torque error compensation data MD.sub.1 thus prepared to the torque command T to determine current amplitudes AM in the electric motor. Three-phase current setting unit 10 sets three-phase AC current commands CU, CV and CW based on the current amplitudes AM and rotational motor position P. Thus, the rotation of the electric motor can be accurately controlled.

Claims8

Dependent claims

An electric motor control system for compensating for rotational error caused by torque ripple in a torque controlled electric motor operated by a torque command signal, said control system comprising:

control information storage means for storing torque ripple error compensation control information as a function of torque command level and of both the rotational speed and rotational position of said electric motor;
a position sensor for sensing the rotational position of said electric motor and outputting a rotational position signal;
a speed sensor for sensing the rotational speed of said electric motor and outputting a rotational speed signal;
control information reading means connected to receive said torque command signal, said rotational position signal and said rotational speed signal and comprising means for reading from said control information storage means said stored torque ripple error compensation control information based on said torque command signal, said rotational position signal and said rotational speed signal;
motor current setting means connected to receive said torque ripple error compensation control information from said control information reading means for generating a motor current command for said motor in response to said torque ripple error compensation control information;
and
means for supplying current to said motor in response to said motor current command.

4 more elements

A method of compensating the rotation error of an electric motor operated by a given torque command, comprising the steps of:

previously storing torque ripple error compensation control information as a function of torque command level, rotational speeds and rotational positions of the electric motor,
sensing the rotational position of the electric motor,
sensing the rotational speed of the electric motor,
reading the torque ripple error compensation control information corresponding to the torque command, rotational speed and rotational position of the running motor,
generating a motor current command based on the read torque ripple error compensation control information, and
supplying current and voltage corresponding to the motor current command to the electric motor.

3 more elements

Dependencies are inferred from the claim text.