| To meet the world’s growing energy needs,there is an urgent need to increase the share of electricity generated from clean energy and make more renewable energy available.Among them,the renewable energy represented by wind and solar energy has been widely concerned.However,due to the volatility and uncertainty of wind and solar energy,Access to a high percentage of renewable energymay have a great impact on the operation safety and voltage stability of the distribution network.In the developed countries or regions,wind power and photovoltaic can often be utilized as much as possible under strong support of the transmission network,so as to achieve a goal on energy structure with high proportion of renewable energy.But in remote mountains and islands,where the reliable,high-capacity traditional power supplies are lacking,and abundant wind and solar energy resources are not used effectively.In order to solve this problem,islanded microgrid has attracted more and more attention because it is a small power system that can effectively integrate a variety of renewable energy and improve the efficiency of renewable energy.However,due to the small capacity of island microgrid,the operation characteristics of all kinds of power equipment are different.How to effectively evaluate the voltage/Var control capability of the microgrid and how to coordinate various devices in the microgrid to maintain the system’s economic operation and voltage stability is an interesting topic.At present,there are few researches touching the above two kinds of problems.According to the above problem,The article starts from two aspects: voltage index and reactive power index.Under the voltage index,the three indexes of voltage deviation,voltage fluctuation and voltage harmonics are investigated.Under the reactive power index,the two indexes of static reactive power support capacity and dynamic reactive power support capacity are investigated,and finally an index system for comprehensively evaluating the volt/var control capability of the islanded microgrid is formed.And by using the analytic hierarchy process,the volt/var control capabilities of the islanded microgrid under different control strategies and different operating scenarios are comprehensively evaluated.Secondly,this paper models a variety of devices involved in the three aspects of source grid load in the island microgrid.The mechanism of active and reactive output and the randomness of wind and light are studied.Considering the randomness of wind and light output,a model predictive control theory with good adaptability and robustness is introduced in this paper.Considering the problem of different time scales of source-grid-load action and different fluctuation characteristics of renewable energy in different time periods,the problem of coordinated optimal scheduling of source-grid-load in island microgrid is divided into 15-minute MPC optimization and 5min MPC optimization multi-time optimization problem.The source grid load coordination voltage optimization problem in the island microgrid is divided into 15-minute MPC optimization and 5min MPC optimization MPC multi-period optimization problems,of which the 15 min MPC optimization problem is a mixed integer programming problem,using yalmip and The GUROBI toolkit solves the problem;the 5min level MPC optimization problem is a quadratic programming problem that can be easily solved.Finally,considering the future development of isolated island microgrids for "plug and play" distributed control requirements and how to maintain stable operation under the requirements of limited communication.Try to explore the impact of incomplete distribution on the system based on the double-layer MPC optimization in Chapter 3.Without changing the 15 min centralized optimization,the 5min optimization sub-problem in Chapter 3 is divided into 5min time scale optimization The problem is solved by setting the source agent and the charge agent separately,and comparing with the centralized MPC optimization results in Chapter 3 on the optimization goal and calculation cost.The results show that although distributed cooperative MPC loses a part of its performance,the corresponding calculation speed is greatly improved,and it can meet the control requirements at a faster time scale.At the same time,under the condition that the communication is completely interrupted,the distributed cooperative MPC is improved,and it is combined with neural network training and search algorithms to train the action instructions of each agent.The obtained results are compared with the distributed MPC under limited communication to verify the feasibility of this emergency optimal scheduling. |
PDF Full Text Request