Low-Cost Semi-Z-source Inverter for Single-Phase Photovoltaic Systems

This paper presents several nonisolated semi-Z-source inverters for a single-phase photovoltaic (PV) system with low cost and doubly grounded features. These semi-Z-source inverters employ the Z-source/quasi-Z-source network and only two active switches to achieve the same output voltage as the traditional voltage-fed full-bridge inverter does. The two active switches of the semi-Z-source inverter are controlled complementarily. Different from the traditional single-phase Z-source/quasi-Z-source inverter, shoot-through zero state is not applicable to the semi-Z-source inverter. The input dc source and the output ac voltage of the semi-Z-source inverter share the same ground, thus leading to less leakage ground current advantages over other nondoubly grounded inverters, such as voltage-fed full-bridge inverter. This is a preferred feature for nonisolated grid-connected inverters, especially in PV application. A revised nonlinear sinusoid pulse width modulation method for a semi-Z-source inverter is also proposed. By using this method, desired duty cycle can be generated to output the sinusoidal voltage. Other dc-dc converters with similar voltage gain curve, which can also be used as a single-phase inverter, are also discussed and summarized. A single-phase semi-Z-source inverter prototype is built; experimental results are provided to verify and demonstrate the special features of the proposed circuit.