Modified Current Controllers for Closed-loop Control of Induction Motor with LC Filter

Low-pass filtering of pulse width modulated (PWM) output voltages of a voltage source inverter (VSI) by sinusoidal LC filters is an established solution for squirrel cage induction motor (SQIM) drive. It reduces high dv/dt, bearing current, leakage current through ground, and core losses in the motor. However, it also deteriorates the performance of the rotor-flux oriented control (RFOC) of SQIM because of sustained resonant frequency oscillations. Additional proportional-integral (PI) controllers or active damping (AD) techniques are generally used to refine the performance of the SQIM drive with filter. This paper proposes new q- and d-axis stator-current controllers, which are basically the PI controllers with time delay. It does not require any change in the controller parameters previously calculated for RFOC of SQIM when there was no output LC filter. It successfully damps out the high amplitude oscillations at resonant frequency without using any AD technique or additional PI controllers and thus assures the suitable performance of the drive. The proposed controller has been discussed with mathematical expressions and its effects have been shown through stability analysis. The stability of the drive in RFOC with the modified controllers (MC) has been analyzed in details about an operating point. Multiple simulation and experimental results have also been presented to exhibit its performance at various operating conditions.