Increasing the efficiency of P&O MPPT by converter dynamic matching

This paper shows that the efficiency of the perturb and observe (P&O) maximum power point tracking (MPPT) control technique can be improved by optimizing its sampling interval T_a according to the converter´s dynamics. During sunny days, when the maximum power point of the photovoltaic (PV) array moves very slowly, the sampling interval T_a must be set as short as possible without causing instability. If the algorithm samples the array voltage and current too quickly, it is subjected to possible mistakes caused by the transient behavior of the PV array+converter system, thus missing temporarily the MPP. As a consequence, the algorithm can be confused, the energy efficiency decays, and the operating point can become unstable, entering disordered behaviors. The solution proposed in this paper lies in choosing T_a according to the converter´s dynamics. The choice of the value of T_a according to the proposed approach ensures a three-level steady-state duty-cycle swing around the MPP, whatever the duty-cycle step-size and the irradiance level are. As an example, a boost MPPT battery charger has been studied.