Design Of Energy Storage Device Based On Bidirectional Converter And Research On Energy Distribution Strategy

Distributed grid is a new modular form of power supply,with the exhaustion of energy,the distributed grid form with photovoltaic system as the main power supply and energy storage device as the main control unit has been paid much attention,and will be a main form of energy utilization in the future.Based on photovoltaic power generation system and bidirectional energy storage converter,this paper studies the power allocation control strategy based on PVbattery-load system.The main research work is as follows:The lead-acid battery is the main form of energy storage in distributed grid.Based on the working principle of lead-acid battery,the equivalent circuit model of battery is studied.The discharge experiments of PNGV(the Partnership for a New Generation of Vehicles)model and third-order dynamic model are carried out under 110 A constant current condition and 110 A pulse condition.The experimental results show that,the third-order dynamic model for increasing parasitic reaction circuits can solve the problem of voltage mutation in static time of PNGV model,and the discharge effect is better.In order to realize energy bidirectional flow of energy storage device,aiming at the topology structure of bidirectional energy storage converter composed of PWM converter and Buck / Boost circuit,the control strategy of constant voltage and constant current based on double closed loop PI control is studied,and the simulation experiment of constant voltage charging and mode switching is carried out.The experimental results show that the bidirectional converter can control the voltage value and current value of the energy storage device steadily during charging and discharging,and can realize seamless switching between modes.On the experimental platform,the correctness and practicability of the strategy are verified by the engineering experiments under the island state and grid-connected state.In order to study the influence of external environment on PV output power,the mathematical model of photovoltaic cell is established.The experimental results show that the change of temperature and illumination intensity will affect the output power of PV cells.The maximum power point tracking technology is introduced,the results of simulation and engineering experiments show that the MPPT(Maximum Power Point Tracing)technology based on variable step perturbation method can track the maximum power point of photovoltaic cells quickly when the external environment changes.Aiming at the imbalance of power distribution caused by the change of bus power,the energy allocation strategy based on PV-battery-load system is studied.The control target and constraint condition of the strategy are discussed,and the implementation methods of the coordinated control strategy are studied under four conditions: grid-connected state,island state,grid-connected to island state and island to grid-connected state.According to the real-time situation of the power of photovoltaic,energy storage,load and connection point on a typical day,the power coordination control experiments under the grid-connected state and island state are carried out on the experimental platform of microgrid.The experimental results show that the system can change the charge and discharge modes of energy storage device and the switching of photovoltaic and load according to the change of bus power.It shows that the control strategy can not only maintain the stability of the system,but also realize the power coordination and optimization operation.