Induction motor control unit

• US 5,821,727 A
• Filed: 04/14/1997
• Issued: 10/13/1998
• Est. Priority Date: 04/16/1996
• Status: Expired due to Fees

• Current Assignee: Okuma Corporation
• Original Assignee: Okuma Corporation
• Inventors: Yura, Motozumi
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/843,169
• Time in Patent Office: 547 Days
• Field of Search: 318/798-802, 318/804, 318/807-814
• US Class Current: 318/809
• CPC Class Codes: H02P 21/18 Estimation of position or speed
• CPC Class Codes: H02P 21/26 Rotor flux based control

Abstract

An induction motor controlling device realizes precise and discretional revolutional speed vector control without requiring a speed detector using an algorithm which is suitable for a system including a microcomputer.

A three-phase-to-two-phase converter detects a torque current inside a motor as a DC quantity based on instantaneous values of motor currents. A slip frequency is estimated using the torque current, and the slip estimation is used to obtain a motor'"'"'s revolutional speed. An error in revolutional speed estimation is compensated by a compensation value which is obtained by amplifying an excitation current common phase voltage command.

Claims

1. An induction motor control unit comprising:

an input terminal of a revolutional speed command ω

m*;

an input terminal of a magnetic induction command φ

*;

a two-phase sinusoidal wave generator (22) wherein a motor current angular frequency ω

is input and signals of sin ω

t and cos ω

t are output therefrom;

a three-phase-to-two-phase converter (16) into which the signals of sin ω

t and cos ω

t, and instantaneous values of motor currents iu, iv, and iw are input and from which an excitation current value id and a torque current value iq are output;

a three-phase-to-two-phase converter (3) to which an excitation current common phase voltage command ed*, a torque current common phase voltage command eq*, and the signals of sin ω

t and cos ω

t are input and from which each phase voltage commands eu*, ev*, and ew* are output to the motor;

a first subtracter (8) which subtracts the excitation current value id from an excitation current command id* based on the magnetic induction command φ

*, and obtains an excitation current error;

a first error amplifier (9) wherein an excitation current error is input, and the excitation current common phase voltage command is supplied therefrom to the motor;

a second subtracter (1) which subtracts a revolutional speed estimation ω

from the revolutional speed command ω

m*, and outputs a revolutional speed error;

a second error amplifier (2) wherein the revolutional speed error is input and a torque current command iq* is output therefrom;

a third subtracter (5) which subtracts the torque current value iq from the torque current command iq* and supplies a torque current error;

a third error amplifier (12) wherein the torque current error is input and the torque current common phase voltage command eq* is output therefrom to the motor;

a fourth error amplifier (23) where the excitation current common phase voltage command ed* is input and a compensation value for revolutional speed estimation is output therefrom;

a slip frequency estimater (6,7) wherein the torque current value iq is divided by the magnetic induction command φ

*, and a slip frequency estimation ω

s is output as a product of the immediately preceding division result and a coefficient equivalent to a secondary motor resistance r2; and

a revolutional speed estimater (19,20) wherein the compensation value for the revolutional speed estimation is subtracted from the motor current angular frequency ω

, and the revolutional speed estimation ω

s is output by a subtraction of the slip frequency estimation ω

s from the result of the immediately preceding subtraction result.

2. The induction motor control unit as claimed in claim 1 wherein the fourth error amplifier (23) can output the compensation value for the revolutional speed estimation by adding a proportional component obtained by amplifying the excitation current common phase voltage command ed* and a differential component obtained by amplifying a differentiated value of the excitation current common phase voltage command ed*.