Fuzzy logic based stator resistance compensation technique for PWM-VSI drives

Voltage-drop due to stator-resistance and voltage distortion due to dead-time effect are two of the major problems associated with PWM inverters. It severely affects low-speed operation of induction motor-drives. In lower speed region the variation of stator-resistance creates a big problem due to poor effectiveness of the cooling fan. In this paper, the above two problems are discussed and solution is presented to improve the lower speed region by combining and adapting two published work. The control scheme adapted uses the constant volts per hertz (V/f) method with low cost current sensors. A quasi-fuzzy method has been adapted for stator resistance estimation of the motor, in which the stator resistance is derived from stator-winding temperature estimation as a function of stator current and frequency. Dynamic thermal model of a machine and associated data are adapted in the paper. In the proposed implementation, real time variation of stator resistance is considered for the voltage compensation. The effectiveness of the proposed method in low speed region is presented and compared with the conventional v/f method using matlab Simulink.