| With the continuous consumption of fossil fuels and intensifying global environmental issues, there is a growing demand for generating electricity by using clean energy instead of fossil fuels. Distributed generation technology in the form of micro-grid can significantly ensure the full utilization of renewable energy and shows great potential in its applications. Stand-alone PV generation system is one of the composition formations which isn’t connected to the AC grid. Aiming at such kind of renewable energy system structure, scholars proposed the topologies of three-port converters which can integrate multiple energy sources in the sys tem and have advantages like high conversion efficiency, high reliability and compact system structure compared with traditional generation structure.This paper takes stand-alone PV generation system as application background and conducts in-depth analysis and research on the operation principle and hardware-decoupling method of phase-shift controlled three-port converter. Firstly, the expressions of power transmission between ports are derived with the Y type and ? type equivalent models of converter, and small-signal model is established through Fundamental Harmonic Analysis(FHA). The ZVS conditions of switches in three active bridges are also derived.Secondly, the hardware-decoupling method of series resonant-based three-port converter is studied, and power transmission model of decoupled converter is deduced according to the equivalent models of topology and resonant working principle. The inhibitory effect of resonant network on the nonlinear property of control system is analyzed and operation modes in single cycle and soft switching characteristic are obtained, which provide bases for the design of independent control loops and selection of resonant parameters.Based on the modeling of three-port converter, the parallel comparative control strategy is designed for PV-storage generation system, which can achieve MPPT control of PV unit, limited voltage and current charging control of battery and constant voltage control of local load. Besides, the adopted INC-type MPPT control is analyzed and possible operation modes of system are illustrated. The configuration approach of system capacity is introduced. Meanwhile, simulation experiments are conducted to verify the effectiveness of control strategy.Finally, the hardware platform of three-port converter is set up and required control algorithms are designed. The operation modes of hardware-decoupled topology are verified based on the experimental platform, and feasibility and effectiveness of parallel comparative control strategy are proved through dynamic respond performance of system under various conditions. |
