Research on the improved FCS-MPC strategy for Photovoltaic grid connection Based on the O-Z source inverter

In this paper, a finite state control set model predictive control (FCS-MPC) strategy was proposed for photovoltaic grid-connected control system drive of O-Z-source inverter in the two-phase stationary coordinate system. Firstly, The variable step size observation method is used to realize the photovoltaic maximum power tracking control of the Boost circuit. Secondly, The topology of the O-Z source inverter is given, and the dynamic mathematical model of O-ZSI was established using the state-space averaging method. Then, the reference value of excitation inductance current of the transformer was obtained by controlling the capacitor voltage of the O-Z-source inverter, and combining with the output power compensation of the network side.The cost objective function was constructed with the excitation inductance predicted current value to determine whether the straight-through (ST) or non-straight-through (NST) working state mode, in order to realize the boost control of DC side of O-ZSI. Finally, when the O-ZSI was in non-through (NST) working state mode, the stator voltage reference value of O-ZSI AC side was obtained by the stator current prediction equation of the grid-connected system, and cost objective function was constructed with excitation inductance current term by the basic stator voltage in the 8 switching states. The best switching state was selected to control the grid-connected system, so as to improve the control performance of the three-phase photovoltaic grid-connected system and reduce the online operation amount. The simulation results show that that the proposed control strategy could ensure the reliable and smooth operation of the photovoltaic grid-connected system, and could realize boost control of the O-Z source inverter. It could not only quickly track the maximum power point of the PV array, but also had s good grid quality, small grid voltage waveform and three-phase current total harmonics.