| With the development of battery energy storage technology,distributed battery energy storage has a wide range of application scenarios because it can meet the diversified energy storage needs of the user side,and has a broad development prospect.The distributed energy storage also faces the problems of further improving the safety protection performance,flexibility of energy storage capacity configuration and simplifying the installation and operation.The key lies in the selection of the system topology.Compared with the traditional energy storage system composed of high-voltage battery strings,the energy storage system composed of low-voltage battery modules is more secure for human body.It can flexibly configure the energy storage capacity according to the needs,with lower operation and maintenance costs,and more suitable for the energy storage needs of the application side.In the energy storage system based on the low-voltage battery module,the voltage difference between the high and low voltage sides of the converter is large,and the battery voltage and bus voltage will fluctuate greatly,so the gain of the converter needs to be improved;the battery side has the characteristics of low-voltage and high current,so the loss needs to be reduced;in addition,the high-voltage side of the converter can be paralleled to realize the flexible configuration of the capacity of the energy storage system,and the paralleling is over In the process,the module current sharing and battery power distribution should be realized,and the battery charge and discharge power should be adjusted in time due to the uneven battery capacity or residual power.In view of the above problems,the following problems in the energy storage system based on low-voltage battery module are studied in this paper:In view of the large voltage difference between high and low voltage sides of a single converter and the fluctuation of battery voltage and DC bus voltage,a single-stage LLC resonant converter topology with simple control and low cost is selected.PWM control and optimization of modulation mode are adopted to reduce the efficiency of forward operation.In view of the problem of limited reverse gain of LLC resonant converter,improved modulation strategy is adopted to improve the increase of reverse operation On this basis,due to the complexity of the converter gain calculation,the forward gain is calculated by combining the time domain analysis method and the fundamental analysis method,and the reverse gain is calculated by using the state plane method.On this basis,the parameter design method of the bidirectional converter is proposed and verified by simulation and experiment.In order to simplify the control and avoid the mode switching between parallel and off grid,the bi-directional DC / AC is used to control the power,the LLC resonant converter is used to control the high voltage side voltage,and the voltage current droop algorithm is used to realize the parallel and stable operation of the multi converter.In view of the problem of uneven battery capacity,the droop coefficient is adjusted to realize the adjustment of battery power,and the droop coefficient is used to realize the adjustment of battery power The bus voltage deviation caused by the control results in the deviation of power regulation.The bus voltage compensation link is proposed to optimize the droop control strategy to achieve the accurate adjustment of battery power.In view of the problem of large ripple current on the high voltage side of the parallel system,the mechanism of the generation is analyzed and the ripple suppression measures are proposed to reduce its adverse effects.Finally,by building a simulation model and cooperating with the enterprise to complete the prototype production,the parameter design method and control strategy proposed in this paper are verified.The energy storage system based on low-voltage battery module studied in this paper can meet the design requirements. |
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