PWM converter integrating switched capacitor voltage equalizer for photovoltaic modules under partial shading

Abstract

Various kinds of voltage equalizers have been proposed in order to preclude negative impacts of partial shading issues in photovoltaic (PV) systems. However, in addition to a converter to control a PV string, a voltage equalizer needs to be installed in a PV system, increasing the system complexity and cost. In this paper, a PWM converter integrating a switched capacitor (SC) voltage equalizer for PV modules under partial shading is proposed. A PWM converter and SC voltage equalizer can be integrated into a single unit without increasing the component count, achieving the system- and circuit-level simplification. The proposed integrated converter is compared with a conventional system using a converter and equalizer separately, from various aspects, such as voltage step-down ratio, total device power rating (TDPR) and converter size metrics. Furthermore, a dc equivalent circuit of the integrated converter, which can dramatically reduce simulation burden and time, is derived. Experimental tests using a 100-W prototype were performed for three modules connected in series under an emulated shading condition. The extractable maximum power from the string was dramatically increased by preventing the partial shading issues while the generated power from the string was transferred to the load, demonstrating the efficacy of the proposed integrated converter.