Variable switching frequency modulation scheme for PWM converter integrating series‐resonant voltage multiplier‐based voltage equalizer for photovoltaic strings under partial shading

Abstract

Conventional photovoltaic (PV) systems require not only a converter for string control but also preferably a voltage equalizer to preclude partial shading issues, which increases the system complexity because two separate converters are necessary. A single‐switch, single‐magnetic pulse width modulation (PWM) converter integrating a series‐resonant voltage multiplier (SRVM) as a voltage equalizer has been proposed in previous work to simplify PV systems by reducing the converter count. The equalization performance of the integrated converter employing a traditional PWM control scheme, however, is unavoidably impaired because the effective operation period of the SRVM in a switching cycle is relatively short at a fixed switching frequency fS. This paper proposes a variable‐fS PWM control technique to improve the voltage equalization performance of the SRVM. The proposed modulation scheme adjusts fS according to the duty cycle variation so that the SRVM's effective operation period is extended. Detailed mathematical analysis revealed that the proposed modulation scheme could improve the equalization performance of the integrated converter. The experimental equalization tests for three PV modules connected in series were performed emulating a partial shading condition. With the proposed modulation scheme, the extractable maximum power from the partially shaded string increased by up to 7%, demonstrating the improved equalization performance of the SRVM. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.