Quasi-Z-source inverter in grid-connected photovoltaic system

This paper presents a three-phase grid-connected PV system based on quasi-Z-source inverter. With an unique impedance network, Z-source inverter can utilize the shoot-through state to boost/buck the output voltage; Quasi-Z-source inverter not only inherits all the advantages of the Z-source inverter, but also has continuous input current (the voltage-fed type), and reduced passive component (capacitor) rating so as to decrease switching loss obviously. Compared with the traditional boost device, quasi-Z-source topology with MPPT has low cost, high efficiency and reliability. It is suitable for grid-connected photovoltaic (PV) power generation systems, where the input voltage varies in a wide range. The low harmonic current poured into grid is realized by the method of constant capacitor´s voltage. And a reinitialized particle swarm optimization (PSO) algorithm is used to track maximum power point (MPP) accurately in varied environment. The simulated results verify that the PV system processes good steady and dynamic performance.