Reduction of Motor Parameter Sensitivity in Vector-Controlled Induction Motor without Shaft Encoder

Abstract

Reduction of the motor parameter sensitivity in a vector-controlled induction motor without shaft encoder has been studied using a new method of rotor flux estimator. Usually this system depends on stator parameters, particularly on the stator resistance. In this case, low speed operation is hardly performed, since its method is based on the rotor flux derived from stator voltage and current.
The proposed rotor flux estimator is constructed with a lag-circuit, the time constant of which is assumed the same value as the rotor-circuit, where the rotor flux command is added to stator voltage and current in order to calculate the rotor flux at standstill. In result, the esimated rotor flux phase error includes no stator resistance component at standstill. Consequently, the proposed system can be performed precisely by the torque-producing current calculated from the estimated rotor flux.
These features have been verified according to series of experimental results in implementing 30kW-motor and PWM-inverter system. And salient items are summed as follows:
(1) The torque control was performed independently from the variation of both rotor and stator resistances values practically.
(2) In the proposed system, both speed and torque controls resulted in good accuracy in a wide speed range of 18 to 1, 800rpm. Also torque was controllable even at standstill.
It is convinced that the approach solves the problem of high quality torque and speed control using induction motors without shaft encoder.