A STATCOM based on cascade multilevel inverter with phase-shift SPWM

Static synchronous compensation (STATCOM) is a flexible ac transmission system (FACTS) device, which can be used to generate reactive power in long distance ac power transmission. The conventional STATCOM consists of several voltage-source inverters connected together through zigzag arrangement transformers, which arouse some problems, such as expensive, producing much loss, difficult to control and unreliable. This paper proposes another STATCOM, named a cascade multilevel inverter with phase-shift sinusoidal pulse width modulation (PS-SPWM) technique, which eliminates the bulky transformer and can respond much faster. The PS-SPWM switching scheme is employed to operate the switches of this inverter, which can: 1) reduce power loss because of transformless design; 2) expand the power capacity easily; 3) generate almost sinusoidal waveform voltage with high equivalent carrier frequency; and 4) make possible direct connection to power distribution system without any transformer. This paper focuses on feasibility and control schemes of the cascade multilevel inverter. Simulation of a three-phase 5-level inverter with reactive power regulation using MATLAB-Simulink power system blockset is carried out. The analytical and simulated results show the feasibility and superiority of the proposed inverter for static synchronous compensation.