Study On Multi-objective Optimal Operation And Control Strategy Of Microgrid

With the gradual depletion of fossil fuels and growing environmental pollution, the clean and renewable energy should be made full use of, and distributed generation (DG) technology should be developed greatly and integrated into large power grid in forms of Microgrid to meet the increasing load demand. Considering the characteristics of DG such as intermittent, complexity, diversity and instability, how to optimal operation of various DG to ensure economic operation of Microgrid, how to restrain circulating current and distribute power when multiple DG units operate in parallel, and how to implement grid-connected operation have been the new research hotspots in modern power industry technology. This paper studies these issues in depth, and the main contents are as follows:(1)Considering the undispatchable characteristics of photovoltaic and wind turbine and different fuel consumption, efficiency, operation and maintenance costs, greenhouse gas emission level of DG with various types and capacity, a novel environmental and economical model of Microgrid which considered generation cost and emission cost all together was presented.(2)In order to meet the load demand and achieve low carbon operation of Microgrid, a novel model of multi-objective low carbon operation of Microgrid was presented, which took the line losses, voltage difference, generation cost and CO2 emission on a whole.(3)Circulating current will be generated in autonomous Microgrid when multiple DG units operate in parallel. The hazards and conventional restrain strategy of circulating current were introduced, and four master-slave control strategies, namely equal voltage control strategy, equal current control strategy, equal power control strategy and hybrid control strategy, were proposed. Simulation results showed that all theses four strategies could restrain circulating current effectively.(4)When multiple DGs operate in parallel, power should be distributed reasonably among all DGs to meet the load demands, respond to demands changes rapidly and achieve stable operation of the system. Based on the analysis of the conventional power sharing control strategies of Microgrid, such as PQ control and droop control, a novel power sharing control strategy based on inverse droop control was proposed, in which the special impedance characteristic of low voltage Microgrid has been taken into account. More precise power sharing among the DGs and rapider dynamic response could be achieved by the proposed strategy.(5)Limitation of the traditional direct output current control method of the inverter was analyzed, the model of the grid-connect inverter with LCL filter and the inverter input-output feedback linearization control method were proposed. Simulation results showed that the proposed control method could implement grid-connected operation of inverter with prompt dynamic respond and little steady state error, and achive stable operation of the system without damping resisters.