Control of a Low-Voltage Microinverter with Secondary Phase-Shift Modulation for Grid-Connected Application

This paper discusses the development of a single-stage, high-frequency isolated DC-AC converter prototype to be used in a series-connected, low-Voltage microinverter for rooftop solar applications. In series-connected architectures, each module contributes to a part of the grid voltage, thereby eliminating the need for a high boost stage as required for a conventional microinverter. This improves the efficiency of the converter. However, as the output of each module is connected in series, only one module in the string implements current control while others operate under voltage control. The primary objective of this paper is to develop and validate a suitable current and voltage control strategy to be implemented in the individual modules. The control strategy developed is tested in grid-connected and transient conditions. The module is operated with a PV emulator connected to the input to validate its MPPT logic. The paper also discusses a suitable topological modification and control strategy to eliminate voltage overshoot problems in secondary side devices for secondary phase-shift modulation topologies. These developed control schemes are verified on a developed hardware prototype using a switching frequency of 100kHz.