A photovoltaic generation system based on wide voltage-gain DC-DC converter and differential power processors for DC microgrids

In this paper, a photovoltaic(PV) generation system based on front-stage differential power processors(DPP) and BACK-stage centralized wide voltage-gain converter is proposed. The resonant switched capacitor(ReSC) converter, which features high power density and high efficiency, is employed as the differential power processor and aims at processing the differential power among series-connected PV modules, avoiding the great power loss caused by power mismatch of PV modules. The ReSC converter in PV system can operate in equalization mode or MPPT mode and both modes are researched. The BACK-stage DC-DC converter is implemented as the dual-phase-shift controlled full-bridge converter(DPS-FBC). It has high conversion efficiency and wide voltage gain, suitable for PV generation applications. The current source control for grid-connected mode and the voltage source control for islanding mode are developed for DPS-FBC. Therefore, for the whole system with front and BACK stage converters, the dual-mode control strategy is proposed. When the system is connected to the grid, DPS-FBC operates as the current source for global MPPT for PV modules while ReSC converters operate in maximum power point tracking(MPPT) mode for local MPPT. When the system operates in an island, DPS-FBC works as the voltage source for constant output voltage control and ReSC converters work in equalization mode. The mode switch is based on the voltage of output DC bus. Simulations and experiments verify the feasibility of the proposed PV generation system and the effectiveness of the proposed control algorithm