| In recent years,with the evolution of new energy,intelligentize grid and electric cars,People are calling for better energy storage technology.Energy storage technology can make up the randomness and volatility of new energy power generation and energy during the power grid peak "cut" the role of PCS,As the interface of energy conversion in the energy storage system,PCS is responsible for the charge/discharge control of the energy storage medium as well as the on-off/off-grid control of the whole equipment.Its performance directly determines whether the energy storage system can run stably and efficiently.At the same time,the continuous expansion and development of the industrial scale makes the application of precision instruments more and more widely,and any power quality problem of the power grid may make these instruments unable to work properly or even damage.How to effectively control the voltage sag is extremely important.In view of the above problems,the main research content of this paper is as follows:(1)Converter topology and control strategy for PCS are summarized and compared the difference between the different topologies and their respective characteristics,concentrate on the working principle of T-type three-level topology,and comparing with the two level topology,highlight the advantages of T three level,and then introduces the formation reasons and management method of voltage sag,The principle of several common voltage sag control devices is analyzed.(2)Mathematical modeling is carried out for the main circuit of PCS,including DC/DC modeling and DC/AC modeling.The DC/DC part starts from a single Buck/Boost converter,draws circuit diagrams of different states according to switching on and off,lists state equations of each state through state space method,and then calculates the average state equations within a period to get its mathematical model.On this basis,the principle analysis and modeling of the dual Buck/Boost converter are carried out.In the DC/AC part,a T-type three-level inverter is selected.After writing KCL and KVL equations for inductance and capacitance,the mathematical model of the DC/AC part is obtained.(3)On the basis of the modeling of DC/DC converter and DC/AC converter in grid and off-grid different mode to control the distribution of respectively in grid constant current,constant power,and from the off-line for DC/DC converter and DC/AC converter control diagram to carry on the design,according to the control block diagram for simulation to verify the feasibility of the designed control strategy.(4)According to the actual production condition of the equipment,a control scheme of voltage sag is designed.In normal operation,PCS is in the floating charging state,and switches to the off-grid state when the voltage sag is detected.PCS supplies power to the load equipment.Finally,the feasibility of the designed treatment scheme is verified through simulation study.(5)The communication system is designed for the PCS.Modbus protocol is selected as the communication protocol,and automatic charge-discharge function is added.The man-machine interaction interface is introduced in detail,and the functions of each interface are shown.(6)The hardware platform of 20 k W bipolar T-type three-level PCS is built.The designed energy storage converter is used to carry out grid-connection,off-grid and voltage sag control experiments,and the experimental results prove the feasibility of the designed voltage sag control strategy for the energy storage converter. |
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