| Energy storage system is one of the effective means to solve the large-scale grid-connection of all kinds of renewable energy(especially wind power and photovoltaic power generation).It is a key technology to solve the current energy crisis,which can promote the effective access of renewable energy generation,improve the safety,stability,economy and flexibility of the power grid.At present,although the chain energy storage cascade converter can realize the effective grid-connection of the energy storage battery,there are so many IGBT switch tubes required,which lead to the decrease of system reliability and the increase of switch loss.At the same time,the existing storage converter designs for energy storage battery equalization mostly adopt the method of injection of extra zero sequence current,which need very complicated hardware circuit design to calculate the current size and phase angle.Complex part of the converter does not take into account the secondary ripple effects of the problem such as battery life when grid energy storage and energy storage battery energy exchange.Aiming at these problems,thisdissertationputs forward a new type of multilevel inverter structure,specific work is as follows:(1)the cascade scheme of equivalent half-bridge two-way BUCK/BOOST circuit and half-bridge inverter is adopted to reduce the number of switch tubes and switch loss.The input voltage is clamped through the equivalent two-way BUCK/BOOST circuit and capacitance on the DC bus to meet the requirements of energy storage battery pack grid-connected for energy exchange and can effectively suppress the secondary ripple.(2)Grid-connected power control scheme of converter is designed.By constructing the virtual synchronous motor model,SVPWM algorithm is used to realize the effective grid connection of the energy storage batteries.It is verified that the newly designed converter structure is actually applied to the energy storage power station or the new energy vehicles' batterise and the grid for energy interaction.(3)Inthis dissertation a new kind of closed loop tracking control strategy which based on State of Charge(SOC)is designed,through the fuzzy control of each battery SOC mean no difference tracking control.According to different SOC values of each energy storage unit,the duty ratio of charging and discharging time in the charging and discharging cycle is determined,so as to achieve the balance of eachbattery group in series in each phase.On the basis of this,the balance scheme of electric vehicle's power battery is further studied and a new unified balance strategy is designed.(4)This dissertation analyzes the equivalent circuit under different operating modes of the topology,analyzes the stability of the system,and verifies the effectiveness of the control strategy by building MATLAB/Simulink model.The feasibility of the system in multi-level cascade connection of energy storage battery is proved.A variety of battery balancing schemes are compared by simulation and experiment to verify the effectiveness of the new and unified balancing strategy.Simulation and experimental results show that the topology can effectively realize the grid-connection function and balance the battery groups in the system,so as to meet the practical application requirements. |
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