Research On Multi Issues In Development Of Stability Simulation System For Microgrid

Under the dual pressure of ener gy demand and environmental protection, distributedgeneration technology has attracted more attentions in fields of international energy. Withthe increasing penetration of distributed ge neration, a series of impacts on lar ge powersystem are coming forth. An ef fective way to eliminate the impacts is th e formation of amicrogrid with distributed resources. While more and more distributed generations connectto lar ge power system in for m of m icrogrid, new m ethod is essential to analy se thecomplex interac tions be tween m icrogrid and lar ge power system. Focus on stabilitysimulation of microgrid, the work in this dissertation is summarized as follows:For modeling of microgrid, a universal control structure for power electronics devicesis proposed. The control system is composed of outer controller and inner controller. Bothof the controller m odules contain mode switche s. By changing the state of the switches,power control, voltage control, droop control and constant voltage/frequency control canbe realized in outer con troller, while current co ntrol can be achiev ed in inner controller.The universal model can represent dif ferent kinds of control structures and strategies forpower electronic device, which is suitable for sim ulation software developm ent ofdistributed generation system based on object-oriented modeling.For steady-state calculation of microgrid, an AC-DC hybrid power flow algrithom formicrogrid system with distributed generation is proposed. PWM converter model and newnode types of distributed generation are presented, and the algorithm procedure is designedwith various node types. Based on the power flow results, initialization algorithm fordistributed generation model is developed. Furthermore, user-defined simulation programis developed and initialization algorithm based on cross-linked list is proposed, which is aneffective solution to automatic calculation of initial equilibrium point.For stability simulation algrithom of microgrid, an explicit-implicit hybrid integrationalgorithm s uitable for distributed generation system is proposed. Power electroniccomponents in distributed generation system have fast dynam ics, while distributedresources such as fuel cell, wind turbine, micro gas turbine, batteries etc, possess relativelyslow dynamics. Based on this characteristic, th e division principle f or stif f system i sdesigned. F or power electronic components with fast dynam ics, implicit integrationalgorithm is used and f or distributed resources with slow d ynamics, explicit integrationalgorithm is adopted. T he advantages of fast calculation speed of explicit integrationalgorithm and high num erical stability of implicit in tegration a lgorithm are bothconsidered. Moreover the adaptability for va riable s tructure oper ation of m icrogrid isbetter.Finally, a typical medium voltage and low voltage microgrid is designed according to the actual distribution system in China, and the rationality of the microgrid case is verifiedon a commercial simulation software. Simulation results on the microgrid case verify thecorrectness and effectiveness of the proposed model and algorithm.