Research On Distributed Energy Storage System Supporting Open DC Bus

Open DC bus can realize the free access of distributed generation,energy storage device,charging pile,air conditioning and other DC equipment,which is of great significance to improve the acceptance capacity of large-scale distributed generation and build a clean,low-carbon,safe and efficient modern energy system.In the environment of national policy support and industry demand,user side energy storage has great development potential.However,security protection and flexible capacity configuration restrict the rapid development of user side energy storage,and the key lies in the selection of energy storage system topology.This dissertation focuses on the distributed energy storage system which is suitable for user side and supports open DC bus.Firstly,in the selection of system topology,aiming at the key problems of user side energy storage development,such as security protection and flexible configuration of energy storage,the common energy storage system topology is compared,and the distributed energy storage system based on low-voltage battery module is selected;In the selection of system control strategy,the energy storage device is used to control the DC bus voltage.In the process of parallel off grid switching and black start,the control program is simplified,and the power quality of DC bus is improved,so as to build a distributed energy storage system which is convenient for a variety of DC equipment access and supports open DC bus.Secondly,for the large voltage difference and voltage fluctuation on both sides of the converter,a single-stage LLC resonant converter topology with wide voltage gain range,high efficiency and low cost is selected.The PWM modulation mode is improved to achieve zero voltage on and zero current off,and the reverse voltage gain of LLC resonant converter is improved.Because there are many working modes in the bidirectional operation under this modulation mode,the bidirectional voltage gain is calculated by combining the fundamental analysis method and simulation analysis method.On this basis,according to the design requirements,the parameters of LLC resonant converter are designed.Then,according to the control requirements of the battery management controller,compared with the common parallel control method,the P/U droop control method with high control stability and good system redundancy is selected.According to the calculation results of LLC resonant converter parameters in Chapter 3,a simulation model is built to verify the regulation effect of P/U droop control.In addition,the design results of converter control strategy are introduced.Finally,experiments are designed for verification,including converter black start,P/U droop control,power limiting mode switching and typical operation conditions of high-power load.The experimental results verify the correctness of the parameter calculation method and control strategy.