Research On SOC Estimation And Power Control Method Of The Hybrid Energy Storage System In Micro-grid

Micro-grid is one of the most effective ways to make use of wind and light as a new energy generation technology,but in the distributed generation system,the intermittent and random characteristics of the output power will also affect the stable operation of the micro-grid.This paper focuses on the key problem of reducing the output power fluctuation of the distributed power supply,the battery and super-capacitor are composed of hybrid energy storage system(HESS),and the charge state estimation of the energy storage element and the internal power coordination allocation of the HESS system are emphatically studied.The main contents of this paper are as follows:First,according to the working principle of wind power generator and photovoltaic array,the stochastic and intermittent characteristics of distributed generation power output in micro-grid are expounded.Establish the wind speed model which can reflect the random and intermittent characteristics of wind energy,and the working characteristics of the wind power generator are described,the output power characteristics of the photovoltaic array are analyzed with the equivalent circuit of the photovoltaic cell.At the same time,combining the distribution density of wind and light energy,it is shown that they have a certain natural complementarity within a long period of time,but this complementarity is not obvious in a short time.Then,the structure and principle of the micro-grid HESS system are described.The equivalent circuit model and charge or discharge characteristics of the battery and super-capacitor are analyzed.The working principle of the bidirectional DC-DC power converter in two modes of BUCK and BOOST is introduced,and the advantages and disadvantages of the three parallel ways of the battery and the super-capacitor are expounded.By establishing the mathematical model of the micro-grid HESS system,clear the power constraint conditions of an energy element in charge and discharge.Again,the BP neural network is used to accurately estimate the SOC of the HESS system in the micro-grid,and train the network model with new adaptive algorithm to improve the traditional learning model.The test results of the new scheme show that the error convergence speed is obviously accelerated,and the test results have reached the requirement of presupposition accuracy.It is proved that the accurate estimation of the state of charge of the energy storage system by BP neuralnetwork is effective and feasible.Finally,according to the problem of how to distribute the overall power of HESS system between energy type and power type energy storage element,a power coordination control method for HESS system of micro-grid is proposed.based on the method of power fluctuation frequency filtering,the power correction value of the battery is obtained through the relationship between the normal capacity interval of the super-capacitor and the limit function of the corresponding battery power range,so as to adjust the output power of the battery so that the super-capacitor will give the charge and discharge response priority to the battery,so as to prolong the service life of the battery.built a simulation model of HESS system for micro-grid,and the rationality and effectiveness of the above methods are verified.