Three-phase inverter based on isolated SEPIC/CUK converters for large-scale PV applications

Abstract

Modular multilevel inverters (MMIs) for medium-voltage (MV) grid-connected systems are gaining attention in solar photovoltaic power (PV) applications. Existing MV power electronic converters require large passive components, huge line-frequency step-up transformers, and additional conversion power stages for maximum power extraction. This paper presents a new three-phase modular inverter (TPMI) based on a novel dual-isolated SEPIC/CUK (DISC) converter for large-scale PV (LSPV) plants. The proposed TPMI is synthesized from series DISC submodules (SMs) to reduce the size and improve the performance of the energy conversion system. Employing high-frequency transformers (HFTs) into the SMs can provide the required galvanic isolation and voltage boosting in addition to reducing the size compared with line-frequency step-up transformers. The chosen DISC converter reduces the required filtering capacitances thanks to its operation as a current-source converter, resulting in improved lifetime, scalability, and resilience of the inverter. The state-space model of the DISC is presented and its performance in PV grid-tied systems using simulations is evaluated. To validate the mathematical analyses and computer simulations, a small-scale experimental prototype is built and tested.