Research On The Three-port Power Converter And Its Control Strategy For Photovoltatic And Storage

Due to the intermittent and unpredictable nature of renewable energy,traditional renewable energy generation systems need to be equipped with energy storage to regulate and stabilize the power fluctuations of the power generation system.The three-port converter requires only one combined converter to achieve connection and control of renewable energy generation equipment,energy storage equipment and loads,which can effectively improve system efficiency and power density.In this dissertation,a novel wide voltage range non-isolated three-port converter is studied for its control strategy and energy management when applied to photovoltaic energy storage systems.By summarizing the research status of three-port converters,a novel threeport converter with wide voltage range,high efficiency,high power density and easy port expansion is studied in this dissertation.According to the working state of the converter,the voltage gain relationship and the device selection principle are derived.The state space averaging method is used to model the small signal of the converter,and the compensation network is designed by numerical solution.By analyzing the power flow relationship of the converter in the photovoltaic energy storage system,the working area and voltage mode of the converter are divided.A multi-mode and multi-frequency modulation method based on four loop controllers is presented by digital control,which enables energy flow in any direction between ports and arbitrary rise/down conversion of port voltages to be realized.At the same time,the traditional three-terminal power system control strategy is improved,so that accurate pattern recognition and smooth mode switching are achieved.The fault elimination of the three-port converter is discussed.The fault mode of the converter is divided according to the location of the fault,and the working state of the topology after removing the fault port is analyzed.The relationship between the input and output voltage gain is given.Aiming at the two-port topology,the principle and condition of implementing soft-switching are studied,and a soft-switching control strategy with variable phase-shift angle is given.The hardware circuit of the three-port converter was designed and the experimental prototype was built.Through the three-port basic function verification experiment,troubleshooting experiment and photovoltaic energy storage experiment,the correctness and feasibility of the three-port converter topology and control strategy are verified.