Active Damping of Output $LC$ Filter Resonance for Vector-Controlled VSI-Fed AC Motor Drives

For longer life of alternating-current (ac) machines, it is desirable to feed them by sinusoidal voltages. This can be achieved by connecting an LC filter between the voltage source inverter and the motor. However, the LC filter creates unwanted oscillation at system resonant frequency. A resistance connected in series with the capacitor is a solution to damp out the resonant-frequency oscillation, but this damping technique increases loss in the system. In this paper, a simple active damping technique is proposed for lossless damping of vector-controlled ac motor drives with an LC filter. In the proposed technique, the resistance drop is emulated in the control using the terminal motor voltages. The proposed technique is carried out in the three-phase domain for better accuracy of the control. The proposed technique neither affects the dynamic response of the drive nor changes the design of the standard vector control loops. Results from experimental ac motor drives are presented.