Analysis and design of a DC voltage-controlled static VAr compensator using quad-series voltage-source inverters

This paper presents a DC voltage-controlled static VAr compensator (SVC) using quad-series voltage-source non-PWM inverters. The SVC consists of four three-phase voltage-source inverters having a common DC capacitor and four three-phase transformers, the primary windings of which are connected in series with each other. Although each inverter outputs a square wave voltage, the synthesized AC voltage of the SVC has a 24-step waveshape. This results not only in a great reduction of harmonic currents and DC voltage ripples but also in less switching and snubbing losses. This paper develops the analysis of the transient response and the resonance between the AC reactors and the DC capacitor, with the focus on practical use. Experimental results obtained from a 10-kVA laboratory system are shown to agree well with the analytical results, thus verifying the analysis and leading to the design of DC capacitance value.