A Variable Step Size P&O MPPT Algorithm for Three-Phase Grid-Connected PV Systems

The main objective of this paper is to propose a variable step size Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm for two-stage three-phase grid-connected photovoltaic (PV) systems. The previous-stage Boost circuit achieves the maximum power point tracking control. The inverter side of the rear-stage realizes the stability of the DC bus voltage and the control of the grid-connected current. By adopting a novel variable-step size P&O algorithm, a fixed step size is adopted when the distance is far from the maximum power point, and the step size is reduced by half every time the working point crosses the peak point, until the final step is smaller than the set threshold and the operating point is stable at the maximum power point. The proposed method effectively solves the problem of slow tracking speed and voltage disturbance near the power point in the conventional fixed-step P&O. In the inverter side, the use of double closed-loop control can ensure the stability of the DC bus voltage and achieve unit power factor grid-connected control. Finally, the proposed algorithm is applied to the two-phase three-phase grid-connected simulation model established in MATLAB. The simulation results show that the proposed method shortens the tracking time by 0.08s and eliminates the power oscillation phenomenon near the maximum power point compared to the fixed step P&O.