A Hybrid Modulation Approach for Step-Up/ Down Partial Power Converter with Improved MPPT Efficiency Around Zero Partiality

Step-up/down partial power converters (PPCs) offer lower partiality and increased efficiency, as evidenced by the literature. However, their operation near zero partiality, i.e., with the same source and load voltage, is challenging if the converter maintains the same modulation technique. This is because the capacitor does not have enough energy to provide the required voltage gain when a PPC operates at zero series port voltage. This renders a step-up/down PPC unsuitable for practical use in photovoltaic (PV) applications, resulting from using a conventional modulation. At near-zero partiality operation, the maximum power point tracking (MPPT) efficiency drops around zero voltage in the series port. The paper proposes a hybrid modulation MPPT method that allows PPC to operate smoothly near zero partiality coefficient, enhancing MPPT efficiency. The proposed hybrid modulation utilizes a reverse power flow, i.e., the circulating energy, to charge the inductor with energy, enabling current controllability near zero partiality. However, PPC employs PSM outside the low partiality region due to the higher efficiency provided. Experiment studies confirm the effectiveness of the proposed approach. A 2.5 kW PPC prototype connected to a 350 V dc bus demonstrates MPPT efficiency of 99.56% during transitions between operating quadrants. A comparative assessment of the proposed approach with some existing methods is also carried out to justify its superiority.