Extremum Seeking-Based Model Predictive MPPT for Grid-Tied Z-Source Inverter for Photovoltaic Systems

This paper proposes a maximum power point tracking (MPPT) method for a grid-tied Z-source inverter (ZSI) that interfaces photovoltaic (PV) sources to the grid. The proposed MPPT method maximizes the energy harvest by guaranteed convergence to maximum power point (MPP) under dynamic weather condition from the PV panels by the ZSI as a power electronics interface. The proposed method uses the concept of model predictive control (MPC) in conjunction with extremum seeking optimization to track the true MPP and can operate without a priori knowledge of the PV panel parameters or ambient condition. At the grid side, the system injects to the grid maximum harvested energy from the PV panel obtained using the proposed MPPT algorithm. In addition, the ratio of active/reactive power injected to grid is controlled (power factor control). The optimal switching signal is determined and applied to the ZSI by minimizing the developed MPC cost function, thus eliminating the need for a modulator that simplifies the controller schematic for ZSI and can be implemented with reasonable processing effort on an inexpensive digital controller. The proposed method in this paper features: fast dynamic response to change in ambient PV panel condition, true and guaranteed convergence to MPP, negligible oscillation around MPP, and simple control structure without requirement of many cascaded control loops.