Research On Active Equalization And Grid-connected Converter Topology For Energy Storage System

Energy storage system plays an important role in stabilizing the fluctuation of new energy power and improving the stability of power system,which has attracted wide attention and research in academia and industry in recent years.When the energy storage system is connected to the grid,it is necessary to eliminate the voltage deviation caused by the inconsistency of the energy storage cells,so as to avoid the over-charge and over-discharge of energy storage cells and ensure the maximum utilization of their effective capacity and safety.DC-DC converter and DC-AC converter are needed to meet the requirements of boost and grid connection.However,the existing topologies have the disadvantages of large number of components,slow equalization speed,large current ripple of cells and weak boost capability.In order to solve the above problems,this dissertation aims to reduce the impact of cell inconsistency on the performance of energy storage system,and studies the active equalization,DC boost and AC grid-connected circuit topologies,and proposes a series of new circuit topologies.The main research contents of this dissertation are as follows:(1)An equalization circuit based on switched-capacitor and switched-inductor is proposed.The circuit uses the switched-inductor unit and the parallel switched-capacitor unit to realize the automatic equalization within and between groups,respectively.Only a pair of complementary signals are required to complete the control of the switches,without the need for complex voltage and current detection circuit and control algorithm.Compared with the existing topology,fewer components are used in proposed topology,thereby reducing the cost and volume.(2)A two-switch multistacked equalization circuit is proposed,which uses only two switches controlled by the same signal to realize the automatic equalization of any number of energy storage cells without complex voltage and current detection circuit and control algorithm.Compared with the existing topology,the equalization speed is faster and the current ripple of cells is smaller.(3)A two-switch DC-DC boost converter is proposed,which realizes the voltage pumping of output and the continuous current of input through the charging and discharging of multiple capacitors.Compared with the existing topologies,proposed topology achieves higher voltage gain with fewer components.(4)An extendible multilevel inverter based on switched-capacitor is proposed in this dissertation.The circuit changes the connection of input DC source,capacitors and load by controlling the orderly on and off of switches,and realizes the AC output of multi-levels.Compared with existing topologies,proposed topology reduces the number of components,especially the number of high-voltage switches,and has the advantages of strong boost capability and self-balance of capacitor voltages.In this dissertation,the topologies,operational principles,parameter design and characteristics of the above circuits are analyzed in detail,experimental prototypes are built to verify the effectiveness and feasibility of the proposed circuit topologies.