A single-phase voltage-source utility interface system for weak AC network applications

This paper presents a novel control strategy for single-phase voltage-source electric utility interface systems. The proposed scheme employs a single-phase voltage-source half-bridge inverter and a third-order T-filter. The stability of the proposed scheme is first investigated, using the state-space averaging technique and root-locus method, in order to select appropriate feedback control variables that produce stable feedback operation. Secondly, based on the results of the stability analysis, both the capacitor current and voltage are employed in inner and outer feedback control loops respectively, in order to achieve stable operation of the proposed technique and to ensure sinusoidal load voltage and current in the power circuit. Thirdly, 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 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. Furthermore, it is compatible with both weak and large AC networks. Finally, experimental verification of the operation of the proposed scheme at various load power factors is provided