Single-Switch Voltage Equalizer Using Multi-Stacked SEPICs for Partially-Shaded Series-Connected PV Modules

Abstract:
Partial shading in a photovoltaic (PV) string consisting of series-connected PV modules is well known to cause serious issues, e.g. significantly reducing power generation and causing multiple power point maxima. Differential power processing (DPP) converters, whereby non-shaded modules support those that are shaded, have been proposed. However, since conventional DPP converters basically comprise multiple individual bidirectional converters, the number of switches increases proportionally with the number of PV modules connected in series, increasing complexity. In this paper, a single-switch voltage equalizer using multi-stacked SEPICs (Single Ended Primary Inductor Converters) is proposed for partially-shaded series-connected PV modules. The single-switch topology dramatically simplifies the circuitry compared to conventional DPP converters. Fundamental operation analysis is performed, and an equalization strategy and control circuit are also proposed. An experimental equalization for four PV modules in series was carried out, emulating a partial-shading condition. With the proposed voltage equalizer, virtually all the series-connected modules exhibited near-identical characteristics, and the available maximum power was dramatically increased, demonstrating the effectiveness and performance of the proposed voltage equalizer.