A Three-Port Converter Based Distributed DC Grid Connected PV System With Autonomous Output Voltage Sharing Control

A distributed dc grid connected photovoltaic (PV) generation configuration based on hybrid-connected three-port converters (TPCs) and its control strategy are proposed in this paper. Distributed maximum power point tracking (MPPT) and autonomous voltage sharing control are achieved with the proposed configuration and control strategy. The proposed system consists of multiple modular pulsewidth modulation plus phase-shift (PPS) controlled TPCs, which feature soft switching and low voltage stress. The input port of each TPC is connected to an independent PV energy source to achieve individual MPPT, and the output ports of these TPCs are connected in series to interface with a high-voltage (HV) dc bus, while the bidirectional ports are in parallel to build a low-voltage (LV) dc bus. The mismatch power of input sources can be transferred through the LV dc bus among these TPCs, and the power and voltage balancing at the HV output side can be realized. By regulating the voltage reference of a bidirectional port in a linear relationship with the output voltage, output voltage sharing is realized with only the module's own voltage and current being sensed. Fully modular design is achieved. System stability with the proposed control strategy is revealed by using the Routh-Hurwitz criterion. Simulation and experimental results are provided to verify the effectiveness and advantages of the proposed configuration and control strategy.