Model-based flexible power point tracking method for photovoltaic systems under partial shading conditions

The extensive grid-connected photovoltaic (PV) systems have given rise to numerous challenges to the stability of power systems. Flexible power point tracking (FPPT) strategy can bring flexibility and frequency support functionality to PV power generation, which is designed to control the output active power to a given active power command value. As many maximum power point tracking methods under partial shading conditions (PSC) are studied, specific technical methods are still needed to realize FPPT under PSC. This paper proposes a mathematical model for determining the power-voltage (P-V) characteristics of PV array under PSC and a novel model-based FPPT method under PSC. Firstly, an analytical model is established to ascertain the features of the multi-peaks P-V curve of PV array under PSC. Secondly, the mathematical model for accurately calculating the voltage value of each trough point on the multi-peaks P-V curve is proposed, without measuring irradiance and temperature. Comparison between actual voltage value and calculated voltage value and sensitivity analysis have validated the high accuracy of the proposed mathematical model. Finally, according to the above analytical model, a skip-compare-locate FPPT method is proposed, which can realize quick and accurate tracking of any active power command value. Simulation results verify the advanced performance of the proposed FPPT method compared with other existing methods in terms of tracking accuracy, tracking speed, and algorithm complexity, especially under complex PSC with multiple peaks. Experimental results further prove the effectiveness and practicality of the proposed FPPT method.