An Active Damping Technique for Small DC-Link Capacitor Based Drive System

A small dc-link capacitor based drive system shows instability when it is operated with large input line inductance at operating points with high power. This paper presents a simple, new active damping technique that can stabilize effectively the drive system at unstable operating points, offering greatly reduced input line current total harmonic distortion (THD). The proposed method requires only a first-order, high-pass filter with a gain. Active damping voltage terms, linked directly to the dc-link voltage ripple through gain units, are injected to the drive machine for stabilizing the operating points. The stabilizing effect of the active damping terms is demonstrated for an induction machine based drive system. The effects of the added damping terms on the machine current and dc-link voltage are analyzed in detail. A design recommendation for the proposed active damping terms is given. Experimental results verifying the effectiveness of the new active damping method are presented.