Model-Based Switching Frequency and Secondary-Side Phase-Shift Angle Matching for Optimizing Efficiency of PV Microconverters

In order to fulfill the requirements of high step-up, wide gain, and high efficiency in photovoltaic (PV) microconverter, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> resonant converter using a hybrid modulation strategy that combines variable-frequency and secondary-side phase-shift (VF-SSPSM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i>) is proposed in this article. By proposing a precise theoretical model, the most appropriate switching frequency (SF) and secondary-side phase-shift angle (SSPSA) that match the steady-state gain under the maximum power point (MPP) of the PV panel are determined, thereby enhancing efficiency while keeping MPP. First, in order to achieve the optimal matching of SF and SSPSA, the working principle of VF-SSPSM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> with PV panel is analyzed, and three operating states are defined according to the difference of resonant tank state. Second, the time-domain state trajectory model is built for three operating states, and the boundary conditions of each state are calculated. Third, the proposed model is employed to conduct loss analysis and derive the theoretical optimal efficiency curve, from which the corresponding SF and SSPSA are determined. Then, a simple efficiency optimization strategy for an MPP steady state of a PV panel is designed. Finally, a prototype is built to verify the accuracy and validity of the proposed theoretical model and optimization strategy.