Switched capacitor-based PWM converter integrating string converter and voltage equalizer for photovoltaic strings under partial shading

In photovoltaic (PV) systems consisting of multiple strings connected in parallel, partial shading even on a single PV panel would hinder a whole string from generating power, significantly deteriorating energy yield of systems. To maximize energy yield from strings, PV systems require not only voltage equalizers to preclude partial shading issues but also converters for string control (or MPPT operation), resulting in the increased converter count and system complexity. This paper proposes the switched-capacitor-based integrated PWM boost converter integrating voltage equalizer. The proposed integrated converter can control an operation voltage of a string while automatically preventing the partial shading issues, hence achieving two functional roles at the same time. The operation analysis was performed, followed by the derivation of a dc equivalent circuit that contributes to reducing simulation burden and time. The experimental equalization tests using a 500-W prototype for three panels connected in series was performed emulating a partial shading condition. String voltages could be boosted based on PWM control while the prototype achieved 21% improvement in extractable maximum power, thus demonstrating the efficacy or the proposed integrated converter.