Stabilization of Rotor Flux-Oriented Control of Induction Motor with Filter by Active Damping

Sinusoidal LC filters are generally placed between the voltage source inverter (VSI) and squirrel cage induction motor (SQIM) to reduce the distortion in the output voltage of the VSI, voltage surges at the motor-terminals, core losses in the SQIM, bearing-current, and electromagnetic interferences. Rotor-flux oriented control (RFOC) of the SQIM is widely used in adjustable speed drives. However, the introduction of filter network may make the operating point of RFOC of SQIM drive unstable and may create sustained resonance frequency oscillations in the stator-current, stator-voltage of SQIM. This paper proposes a simple inverter-current-based active damping (AD) technique, which damps out the resonance frequency oscillation by emulating the virtual resistance connected in series with the filter inductor in its control structure. It also effectively stabilizes the unstable operating point of the closed-loop system without changing the parameters of the controllers used in RFOC. The idea of the proposed AD technique has been illustrated with mathematical expressions and justified through stability analysis. The instability of operating point and the impact of the AD technique are experimentally demonstrated on RFOC of VSI-fed SQIM with filters at different test conditions.