Research On Energy Management Of Hybrid Energy Storage System In Distributed Generation

Nowadays,renewable energy power generation has been developed rapidly.As an important part of renewable energy power generation,energy storage system plays a role in stabilizing power fluctuation and maintaining bus voltage stability.Traditional battery energy storage has low power density and short cycle life and other shortcomings,so the cost of energy storage system is higher.The hybrid energy storage system has been developed rapidly because of its low cost and comprehensive performance.The control of the hybrid energy storage system and the allocation of energy are the key technical problems.They determine whether the hybrid energy storage system can give full play to its performance characteristics and service life.It is also the focus of this dissertation.In this dissertation,lithium battery and super capacitor composed of hybrid energy storage system for the study.Firstly,the DC-side access mode of the hybrid energy storage system is determined.Based on the characteristics of the load of the hybrid energy storage system,the active connection mode and the bidirectional buck / boost topology of the energy storage system are established.The equivalent model of lithium battery and super capacitor are established.This dissertation analyzes the influencing factors of circulating life of lithium batteries,which lays the foundation for the following control methods and energy management strategy.A small signal model of bidirectional buck/boost circuit is established by using the state space averaging method.The advantages and disadvantages of the two control methods in the hybrid energy storage system are analyzed.Finally,the converter of the lithium battery is controlled by single current closed loop and different controller is designed at different charge and discharge state,to accurately track the upper power command.super capacitor bi-directional converter using voltage and current double closed-loop control method to maintain the bus voltage stability and power balance.And a state of charge judgment module is added to the controller,which can ensure the lithium battery maintain bus voltage stability and power balance when the super capacity out of state.The parameters of the controllers are designed by frequency design method,and the effectiveness of the converter control method is verified by simulation in MATLAB.According to the performance characteristics of lithium batteries and super capacitors,an energy management program is designed.A power distribution method is designed,which combine low-pass filter method with multi-objective optimization method.On the one hand the lithium battery assume a smaller smooth power to extend its life,on the other hand make full use of the capacity of super capacitors to reduce the loss of transmission process.At the same time,state management is added to the energy storage system,including overcharge and over discharge protection and maximum power limit protection,which can ensure the safe operation of hybrid energy storage system.In MATLAB,the proposed scheme is compared with the traditional scheme.The simulation results show the effectiveness of the proposed scheme.A hybrid storage system experimental platform and the corresponding control program are designed with DSP28335 as the control chip,to verify the effectiveness of the control method and energy management scheme designed in this dissertation.The experimental results show the effectiveness of the designed energy management program.