Adaptive Exponential Convergence Law Based Sliding Mode Control for Photovoltaic Maximum Power Tracking Control

Maximum power point tracking (MPPT) is one of the key control techniques for photovoltaic (PV) systems. Based on the analysis of PV cell output characteristics, a novel voltage-oriented PV MPPT strategy is proposed in this paper for a stand-alone PV system. The strategy is based on traditional Perturb and Observe (P&O) cascade adaptive exponential reaching law based sliding mode control (SMC), which is divided into inner-loop and outer-loop control. The outer loop uses a voltage P&O to generate the reference voltage at the maximum power point, and the inner loop uses adaptive exponential convergence law based SMC to provide a duty cycle signal for the pulse width modulation (PWM) signal of the power switch, so that the PV voltage is enforced to track the reference voltage of outer loop output. Stability of SMC is proved by Lyapunov's law. The simulation results show that the proposed control strategy has outstanding steady-state and dynamic performance when the solar irradiation changes rapidly compared with the conventional P&O and P&O cascaded PI controller.