Research On Single-phase Non-isolated Z-source Photovoltaic Grid-connected Inverter

Grid-connected inverter is an important part of photovoltaic (PV)grid-connected power system. High efficiency, high reliability, high power density,modularity and intelligence are the directions of grid-connected inverter. Because ofits small size, high efficiency and low cost, non-isolated grid-connected inverter,which meets the requirements of grid-connected inverter, is becoming a hot spot ofpresent PV grid-connected inverter. In order to realize complementary advantagesof Z-source inverter and non-isolated grid-connected inverter, and improve thecomprehensive performance of the system, this paper has researched on a new typeof PV grid-connected inverter—non-isolated Z-source inverter.Combined with the key technology of inhibiting common mode current whichis produced in non-isolated full-bridge grid-connected inverter, this paper from twoaspects—topological structure and modulation strategy, puts forward a new type ofsingle-phase non-isolated Z-source PV grid-connected inverter. The operatingprinciple and characteristic are analyzed in detail, and the principle of inhibitingcommon mode current is emphatically introduced, meanwhile its effectiveness isverified by the simulation.This paper analyzes on the switch stress and loss model of non-isolatedZ-source inverter, and compares it with the traditional Z-source inverter in a way ofquantitative analysis. As a result, the advantage of the new topology’s efficiency isconfirmed. Three loops for the whole PV grid-connected system are designed,including the PV array output voltage control loop, the grid current control loop andZ-source capacitance voltage control loop. The rationality of the design is validatedby the step response and bode chart. In MATLAB/Simulink environment, thesystem simulation model is bulit, and the feasibility of the new topology and theeffectiveness of the control strategy are proved by the simulation results.Based on the hardware and software design of single-phase non-isolatedZ-source PV grid-connected inverter, a set of1kW prototype has been bulit. Theexperimental results show that the proposed design scheme of single-phasenon-isolated Z-source PV grid-connected inverter is a practical and feasible designscheme, which ensures the reliability and efficiency of the system.