Multi-loop control of Z-source inverter for single-phase power conditioning systems

This paper presents a Z-source inverter as a power conditioning system, which has bucking and boosting feature, for a single-phase stand-alone AC system. The bucking as well as boosting feature is possible because of additional shoot through state introduced in zero state of the conventional inverter pulse width modulation. A small DG system requires power conditioning units with low cost, high efficiency and tolerance to wide range of input voltage variations and has to perform dc-ac conversion, output power quality and system control. In order to realize some of these goals, a two-loop control strategy is developed in this paper. Here the PID control loop regulates Z-source capacitor voltage, while the inductor current feedback loop performs sinusoidal current injection into grid. On account of PID control for Z-source capacitor voltage and inductor current feedback with voltage feedforward for AC current control, the inverter system ensures good dynamic response and rejection of source and load disturbances effectively. Mathematical analysis is developed for the proposed concept and validated through simulation results.