Power Sharing And Economic Dispatch In Microgrids

With the development of the economy,the demand for energy is increasing,and the environmental protection is more and more important.The renewable energy,such as photovoltaic and wind energy,enters the rapid development channel for its cleanness and great potential,and significant progress has been made in generation efficiency improvement and cost reduction.Different from the conventional grid where the generators are controllable and centralized,the renewable generator has the characteristics of volatility,intermittence and dispersion.Based on the technology of power electronics,the microgrid integrates the renewable energy resources,energy storage devices and load as a unit.Using the excellent controllability of power electronic equipment,it can realize the maximum utilization of the renewable energy resources.Due to the the capacity and the cost difference of each distributed generator,it is necessary to adjust the output power to share the load demand and optimize the states and generation cost of the system.This paper research the problem of power adjustment in different scenarios and different layers and the main contributions are as follows:Firstly,the issue of reactive power sharing in AC microgrid without communication is studied.At first,the problem faced by the reactive power sharing is analyzed.Then,a control method based on the adaptive virtual impedance to improve the reactive power sharing accuracy is designed.Compared with the traditional droop control,the method significantly improves the sharing accuracy without increasing the voltage amplitude drop.Secondly,the transient performance of the active power control in an AC microgrid is studied.The control strategy of virtual synchronous generator is studied.Then,the improvement effect of washout filter on active control is analyzed.A compromise control strategy combining droop controller and washout is designed.The complete state space model of the system is established and the impact of different parameters on the system is analyzed..Thirdly,the distributed control in DC microgrid is studied.The coupling between the current sharing and voltage recovery process of a DC microgrid is analyzed.Then,a distributed control strategy based on the finite time consensus is introduced,which realizes the arrangement of the virtual impedance.IIIAt last,the economic dispatch problem within and between the microgrids is studiedA hierarchy distributed economic dispatch strategy is adopted.The lower layer realizes the economic optimization with the method of alternating direction method of multipliers.The upper layer receives the marginal cost of the lower nodes,the lower layer receives the power correction from the upper layer,and the lower layer adopts the droop method to maintain the power balance.The convexity of the upper layer cost function is proved,and the convergence of the cost function in the non-smooth condition is analyzed.