Study On Economic Power Sharing Scheme In A Microgrid Considering Stability

Recently, with the mass accessing of renewable energy, wind and photovoltaic curtailment have become a commen phenomenon. Microgrid dominated by distributed generations, as an important technique to solve this contradiction, has drawn increased attention in both academia and industry. A whole package of theory about Microgrid modeling, control and economic dispatch has preliminarily formed. However, since the randomness of renewable energy and the constantly inceasing penetration of distributed generations in Microgrid, a growing problem that carries serious stability problem of Microgird and it often can not guarantee the safty and stability of microgrid in a particular operation mode using a general economic dispatch method. Accordingly, it possesses quite significant sense in both theory and realism to consider the stability in the economic dispatch of Microgird.This dissertation reviewed a large number of domestic and foreign literatures, performed significant modeling, analysis and simulation, and focused on intense research for the quasi-steady modeling of Microgrid, the stability analysis of autonomous Microgird, the coordinated economic dispatch of Microgrid in grid-connected mode and the economic dispatch of Microgrid considering stability. The main work is as follows:(1)The relevant theoretical foundation of Microgrid is discussed and it makes generalizaiton and summary to the research situation at home and abroad of the development process, economic dispatch methods and stability analysis in Microgrid respectively. It focuses on the similarities and differences of stability problems between the Microgrid and large grid. The concepts of electromagnetic stability, transient stability and small signal stability in Microgrid are identified. Based on the analysis of the characteristics for both the economy and stability in Microgrid, the key issues to the economy dispatch in Microgrid considering stability that need to be addressed are proposed, the research content and the logical connections of the whole dis-seration are sorted out.(2)In order to complete the transient stability analysis and simulation of Microgrid, three common distributed generations, including wind turbine, photovaltic and fuel cells, are modeled. And on this basis, an integrated model of Microgrid for typical transient stability analysis is constructed by adding the existing diesel generators, tansformers, lines amd loads in the relevant softeware library.(3)A novel method for estimating the stability domain of Microgrid is proposed from the stability analysis of an autonomous Microgrid, which can be applied to qucikly judge whether the Microgrid remains stability or not when operation mode changes. Based on the traisent simulation model in the seconed chapter, the saturation small signal model of Microgrid is established considering the constraints of the inverter capability. And the solution of the system stability domain is transformed to a standard Linear Matrix Inequality constraints extremum problem by using Lyapunov stability theory. Finally, through analyzing whether the initial system state values are located in the stability domain or not after disturbed, the stability of the system is determined.(4)For reducing the frequent power exchange between Microgrid and large grid, a coordinated economic dispatch method for Microgrid in grid-connected mode is proposed. Several factors, for example, the technical performaces of each distributed generations, the volatility of wind and photovaltic power, the balance between electicity supply and demand, the influence of electricity price fluctuation, the system reserve capacity and so on, are inclued into this method. The power output of various distributed generations in Microgrid and the exchange power between Microgrid and large grid are coordinated optimized to minimize the operation cost of Microgrid.(5)The analysis of stability in Microgrid is introduced into the process of economic dispatch and based on the droop control theory, the relationship between small signal stability and the economy in Microgrid is demenstrated. A novel economic dispatch method considering small signal stability of Microgrid is proposed. Meanwhile, the process of transient stability analysis is approximatley equivalent to the optimizaiton on the Integrated of Time-weighted Absolute Error indicator and based on multi-objective optimization theory, a novel economic dispatch considering trasient stability in Microgrid is proposed. Finally, the simulation results proves the feasibility and correctness of the proposed method.