Speed control of 3-phase induction motor using rotor impedance

Abstract

This paper introduces a method of rotor impedance control by using controlled capacitor/inductor connected in series in the rotor circuit. The proposed system can be operate as a speed control system or a soft starting system to limit the starting current of the motor. An approach to a three MOSFETs-based a rotor circuit of induction motor is presented. The experimental realization of the drive posed some serious problems, notably with regard to the successful driving pulses of MOSFETs over a wide speed range. Analysis of the secondary MOSFETs-controlled motor raised many interesting challenges. It was decided to use an equivalent circuit approach to the analysis because the primary voltage and current were both largely sinusoidal. The equivalent circuit used is based on the single-phase equivalent of a balanced sinusoidal three-phase system. The effective value of the external rotor inductance or capacitance is calculated. Moreover, the motor performance specially speed, motor starting current, and torque during the control of duty cycle of MOSFETs are studied. Also, MOSFETs performance has been studied. Closed loop speed control of the motor speed have been investigated using hysteresis control based on controlling MOSFETs duty cycle. Experimental results have been carried out in the Laboratory to verifying the analysis. The simulation results are given and proved to yield good agreement when compared with the experimental results.