An Optimal Sequence-Based-Controller (OSBC) for a grid-connected three-phase photovoltaic HFL inverter

This paper presents discontinuous modeling and design of an Optimal Sequence-Based-Controller (OSBC) for a grid-connected isolated high-frequency-link (HFL) converter. The OSBC directly controls the switching sequences of the power devices without the need for an intermediate pulse-width modulator as in conventional power converter control schemes. OSBC is realized by solving an optimization problem, determining an optimal switching sequence (comprising a union of feasible sequences) and corresponding time horizon for each switching state of the sequence. Maximum Power Point Tracking (MPPT) is realized using the Perturb & Observe algorithm as embedded in a unified OSBC controller optimizing the overall efficiency of the PV + HFL inverter. The effect of optimizing various control parameters with slow and fast dynamics at different scales is demonstrated. The results are verified using Matlab simulation for a 3 kW, 40 V/208 V three-phase inverter.