Research And Optimization Of The Control Strategy Of Grid-connected Photovoltaic System Based On Z-source Inverter

In recent years, the solar power industry developing rapidly, and grid power gradually become the main trend of solar photovoltaic utilization. In the grid-connected photovoltaic(PV) system, as the connecting device, inverter plays a vital role. The research and improvement of the grid inverter control strategy can improve the efficiency of the system, prolonging the life of the system and reduce the cost. The Z-source inverter used in this paper has the functions of boost and buck at the same time. This topology applies to the occasions of large rang input voltage such as PV power generation, etc. In this topic, the control strategy of the Z-source grid-connected PV system based on Z-source inverter was analyzed in detailed.Firstly, the topology structure, working principle, pulse width modulation(PWM) technology of Z-source inverter and the theoretical wave of main parameters are studied and analyzed. For Z-source inverter, the state space average is used to modeling which lay the foundation for the next study.Secondly, the control strategy of grid-connected photovoltaic system based on Z-source inverter contains the control of grid current, the control of Z-source capacitance voltage and the maximum power point tracking(MPPT) of PV array. Grid current control and Z-source capacitance voltage control adopts the PI regulator and then design parameters of the regulator that satisfy the requirement of system based on step response of the control loop and the bode plot. A variable step disturbance observation method is used in this paper to achieve maximum power point tracking that reduce the oscillation near the maximum power point when the system is stable operation. According to international standard IEEE Std. 929-2000 and UL1741, the gird system needsto have non-islanding protection, so the active frequency drift method is used in this paper to detect islanding effectively and timely.Finally, the MATLAB simulation is carried out on the grid system and through the analysis of simulation results, verify the feasibility of the designed control strategy.