Study Of Microgrid Emergency Control

The emergence of microgrid is not only a useful complement to traditional power grid but also an important way to make full use of distributed energy generation. Thus the research of microgrid control problems, especially emergency control is very important. Microgrid is significantly different with traditional power grid in terms of physical characteristics, relay protection, control methods and so on. Microgrid emergency control is necessary to ensure an on-grid microgrid to switch to an islanded microgrid smoothly and guarantee the stable operation of an islanded microgird after disturbance.Firstly, this paper introduces the differences between microgrid and traditional power grid emergency control in terms of several aspects such as frequency control requirement, coordinated control between power resources and the magnitude of short-circuit current. Then considering the characteristics of microgrid and control requirements, this paper reviews the current microgrid emergency control research in terms of several aspects such as load, power supply, power grid and energy management.The second part of this paper applies the distribution network reconfiguration theory to microgrid emergency control:First the distribution network reconfiguration theory is reviewed. The significance of distribution network reconfiguration, objective functions’selection and the key methods of distribution network reconfiguration are mainly described; then the microgrid emergency control optimization model based on reconfiguration theory is proposed. Both the minimum of load shedding cost and the number of switches are taken into account in the model and how to consider distributed power constraints is also presented.The third part of this paper applies the principle of controllable load stratification to microgrid emergency control:First water heater (EWH) and battery (Battery) are taken as an example to introduce the principle of controllable load; second the thinking of controllable load stratification is elaborated. Then the stratified load shedding optimization model that takes load frequency regulation effect into account, whose target is to minimize the cost of load shedding and voltage fluctuation, is proposed.