Application Of Hybrid Energy Storage In Photovoltaic Grid-connected System

With the transformation of the energy structure consumption patterns,human beings are increasingly demanding new energy sources.Photovoltaic energy,as a clean renewable energy source,is attracting more and more attention from governments all over the world and will be one of the main methods to solve energy problems and environmental pollution problems in the future.However,the power fluctuation and intermittency of the photovoltaic power generation system will occur along with the time variation of the radiance and weather temperature.It is unfavorable to connect to the power grid,and a certain capacity of energy storage equipment should be added to solve this problem.Based on this,this thesis applies battery and super capacitor Hybrid Energy Storage System(HESS)to the photovoltaic grid-connected system to stabilize the power fluctuations and improve the grid-connected power quality.Firstly,the equivalent circuit structure of photovoltaic cells is analyzed and established.A Simulink simulation model is built according to the practical engineering general correction model of photovoltaic cells.The influence of external environment such as light radiation and weather temperature on the output characteristics of photovoltaic cells is deeply studied through the simulation results.For the photovoltaic grid-connected inverter control system,the topology and mathematical model of the inverter are introduced.The method of Space Vector Pulse Width Modulation(SVPWM)is used to generate the trigger signal,and the grid-connected photovoltaic simulation model is built by the simulation platform to complete the grid-connected unit power factor and sinusoidal waveform.Secondly,the equivalent circuit model of battery and super capacitor is established.Combining the characteristics of battery and super capacitor,the active parallel topology is used to form the HESS for the two energy storage devices.The energy flow model and power flow mode of the optical storage grid-connected system structure are analyzed.For the specific application of power compensation,the power allocation of HESS is analyzed in detail.Considering Low Pass Filter(LPF)in the power allocation,the selection of filter time constant is difficult problem in engineering application.A power distribution strategy based on the state of charge of super capacitor is proposed for two energy storage media.This strategy will adjust the power output of battery according to the capacity range of the state of charge of super capacitor,so as to increase the service life of battery.Meanwhile,the HESS control strategy is designed.Finally,the simulation model of photovoltaic grid-connected system based on HESS is built by Simulink simulation software.The LPF and the power distribution method based on the state of charge of super capacitor are simulated and compared.The results show that underdifferent optical irradiance,the proposed power distribution method can effectively distribute the fluctuation power of the photovoltaic power generation of battery and super capacitor.At the same time,the capacity of the state of charge of super capacitor is prevented from exceeding the safe area,so that it remains in the normal charge and discharge interval.In addition,compared with the LPF,the proposed power distribution method reduces the number of charging and discharging times of battery and achieves the purpose of extending the service life.Moreover,the DC bus voltage is stabilized and the photovoltaic array is well connected.