A practical approach to switching-loss reduction in a large-capacity static VAr compensator based on voltage-source inverters

This paper presents a simple method for reduction of switching and snubbing losses in a large-capacity static VAr compensator (SVC) consisting of multiple three-phase voltage-source square-wave inverters. The proposed method is characterized by a "commutation capacitor" connected in parallel with each switching device. The commutation capacitor allows the SVC to perform zero-voltage switching, and to reduce switching losses. The electric charge stored in the commutation capacitor is not dissipated, but regenerated to the DC-link capacitor. Moreover, a soft-starting method for the SVC is also presented to avoid forming a short circuit across the commutation capacitor during startup. Experimental results obtained from a 10 kVAr laboratory setup are shown to verify the viability of the operating principle of the commutation capacitor.