Research On Photovoltaic System Based On Hybrid Energy Storage Of Super Capacitor And Battery

In the photovoltaic grid connected power generation system,the output of photovoltaic cells,the load in the system and the dispatching demand of the public grid have certain randomness,which has a great impact on the grid connected power quality and system stability.The key to solve this problem is to achieve better power balance among photovoltaic output,load and public grid.A large number of studies show that adding energy storage unit to photovoltaic power generation system can effectively balance the power supply and demand relationship in the system.The hybrid energy storage unit composed of super capacitor and battery combines the advantages of high power density of super capacitor and high energy density of battery,which is very suitable for photovoltaic power generation system.In this paper,the photovoltaic grid connected power generation system with super capacitor and battery hybrid energy storage is studied,including the control strategy of photovoltaic power generation unit,hybrid energy storage unit control strategy and system energy management strategy.Firstly,the principle of maximum power point tracking(MPPT)is analyzed when the output of photovoltaic power generation unit is connected to DC bus.Aiming at the problem of power oscillation when the conventional disturbance observation method tracks to the maximum power point,a disturbance observation method based on hysteresis comparison is designed to alleviate the power oscillation of disturbance observation method at the maximum power point.The effectiveness of the control strategy is verified by simulation.Secondly,based on the topology of cascaded hybrid energy storage unit,a control strategy of hybrid energy storage system with super capacitor and battery for photovoltaic power generation system is proposed.Using this control strategy,when the DC bus power is disturbed,the super capacitor uses the advantage of high power density to quickly suppress the instantaneous impulse power fluctuation of the DC bus,and then the battery uses the advantage of large capacity to slowly compensate the energy loss of the super capacitor and provide long-term stable power compensation for the system.The simulation results show that the control strategy gives full play to the advantage of super capacitor to quickly suppress the power fluctuation of DC bus,and effectively reduces the impact current flowing through the battery at the initial stage of charging and discharging,which will help to extend the service life of the battery.Then,the energy management strategy of photovoltaic power generation system under the two modes of maximum power grid connection and constant power grid connection is studied,and a hierarchical control energy management strategy is designed to control the energy flow between each unit in the photovoltaic power generation system.The simulation results show that the energy management strategy can reasonably control the working mode of each unit,ensure the power balance in the system,and realize the stable operation of photovoltaic grid connected power generation system under the two modes of maximum power grid connected and constant power grid connected.Finally,an experimental platform of photovoltaic power generation system based on the hybrid energy storage of super capacitor and battery is built.The maximum power tracking experiment of photovoltaic power generation unit and the stable DC bus voltage experiment of hybrid energy storage unit are carried out on the experimental platform.The experimental results prove the feasibility of the control strategy.