DC Microgrid Hierarchical Coordination Control Based Energy Router

Energy routers(or solid-state transformers),as key equipment for the energy internet,can not only achieve the functions of voltage level conversion and isolation of traditional transformers,but also suppress the impact of grid fluctuations on the load side.Researching,analyzing and designing of high-performance DC microgrid control systems based on energy routers have practical significance and application value.However,DC microgrid control system based on the energy router has unfavorable factors such as complex topology,poor scalability,low control accuracy,and low energy utilization,which directly results in the degradation of the control system performance.This paper summarizes the research status of energy routers'analysis and control,and improves the topology structure of cascaded H-type energy routers.It further studies the analysis and design of hierarchical microgrid based on energy routers and hoped to reveal the essence of the hierarchical coordinated control in DC microgrid beside provided a new idea and approach for the analysis and design for DC microgrid coordination control based on energy routers.The main research work and innovations are as follows:(1)In order to solve the voltage imbalance problem of cascaded H-type energy routers,a DC side voltage balance control strategy was proposed.analyzing of the working mechanism of cascaded H-type energy routers in depth,establishing its mathematical model.Firstly,analyzing the working principle of single-phase SVPWM,and then proposing a strategy to control the voltage stability of one H-bridge capacitor and adjust the vector pulse width of other H-bridges in SVPWM to achieve the voltage balance of the cascaded H-bridge.Finally,the simulation is performed in MATLAB/Simulink.(2)For DC microgrid system based energy router,a hierarchical and coordinated control method based on DC microgrid with energy router is proposed.Analyzing the inherent shortcomings of centralized control of DC microgrid and the character of the DC microgrid bus voltage stability.On this basis,the system is divided into three layers.The first layer judges the system energy flow according to the DC bus voltage'value,determining the working mode of each port and implements the system layering to realize the autonomous control of each port.At the same time,in order to realize the priority of clean energy,improve the constant voltage control strategy of distributed photovoltaic ports,realize the free switch between constant voltage control strategy and MPPT,and improve the energy utilization and the stability of the system.The second and third layers are optimized for control.According to the different bus voltages and SOC values,switching load and charging and discharging autonomously of energy storage are performed to optimize the control.Finally,the studies are carried out in MATLAB/Simulink and the proposed control strategy are proved feasibility through the simulation waveforms and experimental waveforms.