Optimal Sizing And Coordinated Control Of Distributed Generation Units In Islanded Microgrid

Islanded microgrid is an important approach to solve the grid-connected problem of distributed generation, and it has been a research hotspot and direction in the fields of distributed generation and microgrid technology, because it can effectively reduce the adverse and negative influence resulted from renewable energy distributed generation, improve the power supply reliability and enhance the economic and environmental benefits. Thus, recently islanded microgrid has become an important way and approach to use renewable energy sources as to solve the power supply problem in the remote areas. However, the higher cost, the lower reliability and the poorer power quality are still the outstanding problems of islanded microgrid. Therefore, the optimal sizing and coordination control of distributed generation units in islanded microgrid has been studied from the viewpoint of system theory, and the main contents of this paper are as follows:Firstly, the concept and typical characteristics of islanded microgrid are summarized, and the core studies and key technologies such as optimal sizing, operation control and economic operation of islanded microgrid are reviewed and presented from the viewpoint of technical connotation.Secondly, the modelings and control methods of common distributed generation units in islanded microgrid, such as wind tubine generation, solar PV generation, battery energy storage system and diesel generation, are introduced and presented in detailed, and their different power output characteristics are also simulated, which lay the solid basis for the following-up research.Thirdly, a dynamic energy management strategy of islanded microgrid is presented based on the two different operation control modes where battery energy storage system and diesel generator can work as the sole master power source independently, and the multi-objective configuration optimization models are presented as to minimize the loss of power supply probability(LPSP), the utilization rate of renewable energy generation(URREG) and the annualized system cost(ASC) consisting of investment cost, fuel cost, maintenance and operation cost, pollutant emission. Moreover, NSGA-II algorithm with higher calculation speed and strong robustness is adopted to get the Pareto optimum set. Finally, numerical simulations are given to investigate the effect of different unit commitments, different optimization goals and energy management strategies on the optimal sizing of islanded microgrid, and results show that the proposed method is scientific and effective.Fourthly, in order to effectively solve or improve the frequency control problem of islanded microgrid, a hierarchical frequency robus control approach based on the coordinated control between battery energy storage system and diesel generator is designed and established by adopting the hierarchical control method and H infinite control theory. The frequency hierarchical control structure including the primary control of battery energy storage and the secondary control of diesel generator is presented. Two different H infinite controllers are designed to modify the conventional droop control of battery energy storage system and the conventional PI controller of diesel generator governor. The coordinated control strategies between the primary control of battery energy storage and the secondary control of diesel generator are also given. Finally, numerical simulations are given to analyze the islanded microgrid system frequency dynamic performance by adopting the proposed hierarchical frequency robust control method with comparison to the conventional frequency control methods, and the results achieved demonstrate the effectiveness and feasibility of the proposed method.Finally, the economic operation optimization thinking of islanded microgrid is given clearly with two distinct levels of the stability control and the minimum cost economic operation. The dynamic economic dispatch strategy is presented based on the two different operation control modes where battery energy storage system and diesel generator can alternate to operate as the master power source. And on the basis to establish an economic operation optimization model as to minimize the total system generation cost including the depreciation cost, operation cost, pollutant emission cost and price subsidies available for renewable energy sources, while meeting lots of linear or nonlinear constraints such as power balance, spinning reserve capacity, power generation limits of distributed generation and others. Moreover, a dynamic economic operation optimization process, which combined the proposed dynamic dispatch strategy and modified partical swarm optimization algorithm(MPSO), is proposed for the joint-optimization of optimal control mode and minimum generation cost goal. Finally, the comparisons by adopting the proposed MPSO and PSO, as well as the proposed dynamic dispatch strategy and the static dispatch strategy are given to analyze the affect on the economic operation performance of islanded microgrid, and the simulation results show clearly that the proposed method is effective and scientific.This work is supported by the National High Technology Research and Development Program(863 Program) of China(No. 2014AA052001), the National Natural Science Foundation of China(No. 61273172) and the Key Technology Projects of Strategic Emerging Industries of Guangdong Province(No. 2012A032300001).