Coordination Control And Black Start Strategy Of WTG-PV-DIESEL-BESS AC MicroGrid

Distributed energy resources are sometimes restricted and isolated to be connected to the power grid, due to detectable pulses and harmonics produced by large scale renewable energy power generation. Microgrid, a relatively new networking technology, provides better efficiency of the renewable energy and improves reliability of power supply. However maintaining the system operation stable and safe become the most difficulty that to be solved, because of the diversity of the distributed energy resources, the variety of its port's types and the complexity of the operating conditions.Due to the advantages like easy to realize “plug-and-play”, constant control strategy between on/off grid modes switching and high redundancy, the droop control method gets worldwide attentions and researches. In this paper, droop power control method, on-and-off grid switching technology and black start of the microgrid are fully analyzed and researched base on the droop controlled wind-solar-diesel-battery AC microgrid.Base on the research object just mentioned, the simulation models of grid connected PV system, wind power system, energy storage system and diesel system are built, working principles, system structures and control strategies are comprehensively introduced. All these made a valid foundation for the following researches.Traditional P-f/Q-V droop control can not always guarantee good power control results when applied to low voltage microgrid. In this paper, an improved droop control method with virtual impedance is designed based on detailed analysis of how the transmission line impendence effects the power decoupling control. Better control result is achieved by making the total connection impedance of the transmission line and the inverter output impedance inductive. A synchronous compensator control method is introduced to solve the on/off grid mode switching problem. By sampling frequency and voltage errors on both sides of the STS and going through PI controller to compensate for the reference frequency and voltage of the droop curve, the control method will adjust the output voltage of the inverter to realize the voltage synchronization of the microgrid and the main grid, and finally achieve a smooth switching from standalone mode to network mode.Black start function, whose basic concept, implementation process and recovery strategy are fully introduced in this paper, should be achieved to improve reliability of the power supply. An AC microgrid black start strategy is proposed based on power characteristics, network structure and transmission line of the mircogrid. An unique recovery process is specially designed for this system, whose feasibility is verified by simulation in Matlab/simulink.