Indirect current control scheme for a single-phase voltage-source utility interface inverter

This paper presents an indirect current control scheme for utility interface applications. The scheme, which employs a single-phase half-bridge voltage-source inverter and a third order T-filter, is based on sensing the capacitor current of the load filter in an inner feedback control loop and the capacitor voltage in an outer voltage control loop to ensure that both the load voltage and current follow reference sinusoidal waveforms. The stability of the proposed scheme is investigated using the state-space averaging technique and the root locus method. The results of the stability analysis are used to select appropriate feedback control variables that produce stable feedback operation. Computer simulation results of the proposed utility interface system for operation of the power circuit from `cold´ start to full load is presented. It is shown that the proposed control scheme offers improved performance for utility interface applications. It is simple to implement, and is capable of producing nearly perfect sinusoidal line current and voltage waveforms at any desired power factor with moderate switching frequency and reasonable size of filter parameters