Convergence analysis and tuning of ripple correlation based MPPT: A sliding mode approach

The development of fast MPPT (Maximum Power Point Tracking) algorithms for photovoltaic (PV) systems able to track variable irradiation conditions with high bandwidth is becoming attractive, especially for mobile applications. This paper focuses on the well known ripple correlation technique, proposing an analysis that provides an upper bound to the convergence time in response to solar irradiation steps. The availability of an upper bound enables the prediction of the dynamic behaviour of the MPPT, and gives a set of guidelines for a proper tuning of the controller to fit specific dynamic requirements. The analysis is based on a simple application of sliding control theory, and it also includes chattering phenomena and the effects of parasitic reactive elements of the PV module. Matlab simulation and experimental tests are provided on a 35W panel interfaced to a 24V battery through a boost converter. A controllable LED illuminator has been used as solar generator, able to provide irradiation step changes with a bandwidth of 1kHz. The results confirm the effectiveness of both the analysis and tuning.