Development Of The Bipolar Power Conversion System Device

As the proportion of new energy generation methods such as wind power generation and photovoltaic power generation in the traditional power grid continues to increase,due to their intermittent and uncertain output power,they have a significant impact on the stable operation of the traditional power grid.Therefore,it is necessary to introduce energy storage system to adjust the power fluctuations in the grid.As an important part of the energy storage system,the Power Conversion System(PCS)is responsible for peak and valley filling,peak and frequency modulation,power fluctuation suppression and power quality improvement in the power grid.Therefore,it is of great significance to study the control strategies of Power Conversion System in different working modes.In this paper,the bipolar T-type three-level Power Conversion System is taken as the research object,and its control strategies in on-grid mode,off-grid mode and switching mode are studied respectively.According to the design principles of industrial-grade devices,an experimental device was developed.The main research contents of this paper are as follows:(1)Starting from the topology of the Power Conversion System,it compares the differences between the single-stage topology and the bipolar topology,then it summarizes the advantages and disadvantages between the bipolar topology and the single-stage topology,and explains the differences and superiority between the three-level topology and the two-level topology.The topology structure of three three-level Power Conversion System is compared,and the current Power Conversion System topology and control strategies are summarized.(2)According to the main circuit topology,the working principles of the pre-stage DC/DC converter and the post-stage DC/AC converter are analyzed respectively,and then the overall mathematical model of the Power Conversion System is obtained.(3)The control strategies of the Power Conversion System are studied for its on-grid mode,off-grid mode and switching mode.In the on-grid mode,the P/Q decoupling method is used to control the on-grid current.In the off-grid mode,the constant voltage and constant frequency V/f control strategy is used to achieve the AC voltage amplitude and frequency on the inverter side.In the switching mode,this paper completes the on-grid charging/discharging switching control and the on-grid/off-grid switching control,achieving a smooth transition in the switching process.(4)The system simulation of on-grid/off-grid operation of Power Conversion System was realized through Matlab/Simulink,and the feasibility of the control strategy of the Power Conversion System studied in this subject was verified.According to the design principles of industrial-grade platforms,a PCS hardware experimental device,and the key design parameters of the device are given.The standardized experiments of the device further prove the correctness of the control strategy in this subject.