Abstract
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
Highlights
Photovoltaic modules are usually series connected for higher voltage and power level
A photovoltaic generation system based on resonant switched capacitor converters and dual phase-shift full bridge converter is proposed and researched
A resonant switched capacitor (ReSC) converter used as differential power processor for cascaded power balancing in photovoltaic generation system is analyzed
Summary
Photovoltaic modules are usually series connected for higher voltage and power level. Compared with the centralized PV system which is composed of series connected PV modules and a central converter, overall output power of the PV system based on DPP is increased. In [14] and [15], a dual-phase-shift controlled full-bridge (DPS-FBC) converter is proposed, which features the wide voltage gain and soft switching for wide input voltage and load range. DPS-FBC is applied in the PV generation system as the centralized DC-DC converter for series- connected PV modules, and the control algorithm is proposed. The relationship between controlled variables (for example the output voltage and input voltage) and the phase-shift angle is studied and the grid-connected mode control and the islanding mode control are achieved for DPS-FBC. DPS-FBC is responsible for constant output voltage control while ReSC converters operate in equalization mode.
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