A Switched-Photovoltaic Ladder DC-DC Converter for High Harvesting Efficiency under Nonuniform Illumination

This paper presents a switched-photovoltaic (SPV) ladder dc-dc converter that can extract nearly the maximum power available from a string of series-connected photovoltaic (PV) cells under nonuniform illumination and in environments of widely varying temperatures. The converter consists of two strings of PV cells. Instead of switching costly passive elements (i.e., inductors or capacitors) to perform input-to-output voltage conversion, one PV string is switched up and down periodically with respect to the other fixed string. In this way, the intrinsic capacitance in the flying PV string is used to shuttle any mismatch charge, induced by nonuniform illumination across a solar panel, sequentially between each two series-connected cells in a string to the output. Additionally, the implicit switched-capacitor ladder converter, established by the PV cells internal capacitance, allows reconfiguring the converter output terminal location within the fixed ladder, and hence the employed voltage conversion ratio, without degrading harvesting efficiency. Simulation results of a proof-of-concept design using radiation-hardened GaN devices demonstrate the efficiency advantage of the proposed SPV ladder over prior solutions, where up to 43% and 63% improvements in the efficiency are realized.