PWM Switched Capacitor-Based Cell-Level Power Balancing Converter Utilizing Diffusion Capacitance of Photovoltaic Cells

Abstract

This paper proposes a novel pulsewidth modulation cell-level diffusion charge redistribution (DCR) converter based on a switched capacitor converter (SCC) utilizing diffusion capacitance of photovoltaic (PV) cells for PV modules under partial shading. Although a discrete inductor and capacitor are additionally necessary, Joule losses associated with switching operations can be reduced compared to the conventional capacitorless DCR converter. First, ac impedance measurement for a PV cell with 125 × 125 mm was performed, and the diffusion capacitance values were measured to be approximately 6.0 mF at its maximum power point voltage of 0.574 V. Second, the theoretical loss model was derived based on the detailed analysis, and it revealed that an optimal duty cycle achieving the lowest Joule loss was dependent on shading conditions. Third, a dual maximum power point tracking (MPPT) algorithm that controls duty cycles of not only the DCR converter, but a front-end boost converter is also proposed. With the dual MPPT control, the DPP converter operates at its optimal duty cycle to minimize the Joule loss while the boost converter seeks the MPP. The experimental results demonstrated that the maximum power significantly increased, thanks to the DCR converter, and that both the DCR and boost converters operated with respective optimal duty cycles.