Research On Control Strategy Of Energy Storage System Of The Virtual Synchronous Generator

With the development of economy, people depend more and more on electric energy. Meanwhile, due to the rapid growth of the numbers and types of electrical equipment, it results that the power supply quality can not be guaranteed. Especially in the power supply terminal of low voltage distribution network, frequency and voltage deviation caused by the loads mutation and the three phase current unbalance problem caused by the single phase loads exists widely, seriously threatening the safety of the grid and electrical equipment.In order to support the frequency and voltage of the user side, the battery energy storage system is added in the transformer side of the low voltage distribution network,which is used to input and output active and reactive power. By this way, the deviation of frequency is reduced, the deviation of voltage is also reduced too; On the other hand,the three phase current unbalance is reduced through outputting the negative sequence current by the energy storage system. The main work carried out in this thesis are as follows:1) The goals of the energy storage system are set, and its structure and working principle are analyzed, the operation principle of the energy storage inverter is analyzed,which is the power conversion equipment of energy storage system. In order to put forward the control method of this paper, typical frequency and voltage control methods are comparied.2) In order to solve the frequency and voltage deviation caused by the end of the power supply loads mutation, the power control strategy of virtual synchronous generator in the energy storage inverter is adopted. First, the frequency and voltage control mechanism of synchronous generator is analyzed, and the relationship of frequency, voltage and power in the low voltage distribution network is analyzed. Then the active and reactive power control strategy is designed, and the user terminal voltage and frequency deviation is reduced through energy storage system of active and reactive power regulation capability. At last, the simulation model of Matlab/Simulink is built,the effectiveness of the control strategy is simulated and verified.3) In order to solve the three phase current unbalance problem caused by singlephase loads, the current control strategy of virtual synchronous generator in the energy storage inverter is proposed. The unbalance current is decomposed firstly. Then the characteristics of the unbalance current in the positive and negative double synchronous reference coordinates are analyzed. On this basis, the negative sequence current control strategy of closed-loop control is designed, and the current unbalance is reduced. Finally,the simulation model of Matlab/Simulink is built, the effectiveness of the control strategy is simulated and verified.