Maximum Power Point Tracking Combining Deferential Flatness Control And P&O

The maximum power point of a photovoltaic (PV) system shifts when the external condition changes. Aiming at improving the efficiency of solar system, this paper mainly researched on the maximum power point tracking (MPPT) under partially shadowed condition, and realized complex PV array modeling and the implementation of differential flatness control theory.Adopting 5-parameters method and Lambert-W function, this paper deduced the output property of the PV battery based on the parameters given by the PV battery factory. By forming the working matrix, the allocation of PV array output voltage to each panel is calculated, and then the corresponding PV array output current is deduced. Thus the modeling of PV array is realized.Next the common MPPT methods were researched. The Perturb & Observation (P&O) and Incremental Conductance were improved by variable stepping size. The reference voltage needed by Fuzzy Logic Control is acquired by curve fitting. Changing the steps of duty cycles into ramps, the oscillation brought by Particle Swarm Optimization was mitigated.The PV system was built based on boost converter. This system was proved to be a deferential flatness system by definition. We choosing input capacitor charge as flatness output, adopting a second-order filter to track reference trajectory, the direct control of PV array output voltage was realized by differential flatness control.Finally, a new approach was proposed combining simplified deferential flatness control and adaptive stepping size P&O based on the researches on deferential flatness control and common MPPT strategies. Only PV array output voltage and current were needed to realize MPPT in the approach. The simulation results verified that this approach can correctly sense the outside environment changes, can efficiently avoid being trapped into local maximum power point and can track the global maximum power point fast, accurately, stably.