Extremum seeking control based integration of MPPT and degradation detection for photovoltaic arrays

Regarding the reduction of the cost of energy (COE) for photovoltaic (PV) systems, two important issues are maximizing the efficiency of power generation and fault diagnosis. This study presents an integrated framework that achieves both maximum power point tracking (MPPT) control and diagnosis of change in internal resistance simultaneously. An extremum seeking control (ESC) strategy is developed to maximize the power output of the PV array by regulating the voltage input to the DC-DC converter. Simulation results show that the ESC can achieve MPPT with periodic dither signals such as sinusoidal or square-wave signals. The degraded PV cells often demonstrate certain change of internal resistance, i.e. increase in the series resistance and decrease in the shunt resistance. The change of these internal resistances can induce the change of transient behavior of the dithered output remarkably for square wave dithering, which is validated with simulation study. The ESC with square-wave dithering can thus provides the dual benefits of MPPT and degradation detection simultaneously. Furthermore, simulation study on the PV modules under partial shading, though the P-V characteristic has changed, the proposed option is to pick the optimal regions to narrow down the ESC searching intervals and thus can locate the global maximum power point faster.