STATCOM with the structure of main-auxiliary inverter

Abstract

This paper aimed at reactive power compensation of three-phase balancing loads for 6kV medium-voltage source, and proposed a new type of main-auxiliary structure STATCOM (static synchronous compensator) that can be directly connected to power source. This structure combined the characteristics of both diode-clamped multilevel inverter and cascaded multilevel inverter: the main inverter took the form of three-level diode-clamped inverter, while the auxiliary inverter adopted H bridge (full bridge) inverter. The three auxiliary H-bridge inverters were connected to the corresponding phase of main inverter in series, so that both of them constituted a five-level hybrid inverter. In this paper, the auxiliary H-bridge inverter was designed to produce a square wave voltage whose frequency equaled that of AC power supply, and the square wave acted as basic part of expected output phase voltage. Main inverter had two functions: one was to generate the compensatory part of expected output phase voltage, the other was to compensate harmonic component of output voltage. In the end, the superiority of the proposed STATCOM structure was validated by simulation.