Grid-connected Conditioner Based On Energy Storage Modular Multilevel Converter

The rapid development of renewable energy power generation technologies such as wind power and photovoltaic power generation has brought hope to solve the problem of energy exhaustion.However,the massive grid-connected of these fluctuating renewable energy sources also brings challenges to the stable operation of the power system.High-voltage and large-capacity energy storage technology is an effective way to solve the distribution generation power fluctuation and stable frequency.Therefore,it is of great significance to study the high-voltage large-capacity energy storage technology to stabilize the distribution power grid frequency and improve the power quality.In this paper,a grid-connected conditioner based on energy-saving MMC with no common DC bus is proposed and its core technology is studied.The main research contents include the following aspects:Firstly,the energy-storage MMC topology without common DC bus is proposed and its mathematical model is deduced.The principle and equivalent model of the supercapacitor energy storage system are analyzed.Based on this,the system architecture of the grid-connected conditioner is studied.Its four-quadrant operating capability and compensation principle is studied.Secondly,the modulation method and control strategy of energy storage MMC are studied.Based on the topology of MMC without DC bus,the different modulation schemes of MMC are analyzed and the MMC strategy of energy storage is designed.The active current and reactive current decoupling control method of grid-connected conditioner are studied.Combined with the MMC modulation method,a sub-module energy balance control strategy is designed.The MMC circulation without DC bus is analyzed,and the circulation suppression strategy is designed.Thirdly,the control method and fault-tolerant operation strategy based on energy change of energy storage MMC grid-connected conditioner are studied.The influence of the modulation wave on the output of grid-connected conditioner and the effect on the inner current control loop when the DC voltage changes are analyzed.The fault-tolerant control strategy of the system is proposed after the energy storage MMC is fault-by-passed in the sub-module.Finally,reactive power compensation and dynamic active power compensation based on energy storage MMC grid-connected conditioner are studied.The principle and strategy of grid-connected conditioner for reactive power compensation are analyzed.The dynamic active power compensation strategy of grid-connected conditioner for weakly connected distribution network is studied and the dynamic active current buffer compensation function is designed.The coordinated reactive and active power compensation strategy of grid-connected conditioner under energy constraints is studied.A grid-connected conditioner experimental platform based on energy storage MMC is established.