Research On Control Strategy Of Battery Grid-connected Inverter

As a kind of clean power generation,distributed generation has a broad prospect of development, but there are serious instability. The microgrid based on battery energy storage can restrain the influence of distributed power supply to the power grid. Therefore, the research on battery energy storage technology is of great significance. The battery grid-connected inverter is connected to the power grid,which determines the effect of grid connected discharge. However, there are few researches on battery grid-connected inverter. In this thesis, the battery grid-connected inverter is studied in order to reduce the harmonic content and improve the stability of grid-connection.This thesis firstly constructs the main circuit of battery grid-connected inverter.After comparison and analysis, the diode clamped three-level inverter circuit and LCL filter circuit are selected as the main circuit in order to reduce the harmonic content and the volume of system. According to the resonance of LCL filter circuit,passive method of series-connection resistor on capacitor branch is used to increase the system damping. Simulation results show the effectiveness of the proposed method. And the design method of each component in the filter circuit is given. In order to facilitate the design of the control system, the mathematical model of the main circuit in the d-q reference frame is established.Secondly, the control strategy of inverter is studied in this thesis. The algorithm of three-level SVPWM is designed in order to reduce the harmonic content by symmetrical seven section mode. In order to solve the unbalance problem of the neutral point potential on the DC side,the distribution coefficient method is used to distribute the time of positive and negative small vectors. In view of the effect of dead time,a simple and feasible compensation method is used to reduce the influence of dead time and switching time. After comparative analysis, this thesis adopts decoupled double synchronous reference frame PLL for the sake of achieving fast and accurate phase tracking in non ideal grid environment. In order to achieve better effect of grid-connected discharge of battery, this thesis adopts current vector control strategy based on grid voltage orientation. And based on feedforward decoupling control, the control parameters of the current inner loop and the voltage outer loop are designed.Finally,this thesis uses Matlab/Simulink simulation software to simulate the control strategy of battery grid-connected inverter. The simulation results show that three-level SVPWM control method, decoupled double synchronous reference frame PLL and current vector control strategy based on voltage orientation can reduce the harmonic content and improve the stability of grid-connection.