Research On Several Key Engineering Technologies In Microgrid

With the rapid development of national economy, in order to deal with the contradictions of growing energy demand and fossil energy depletion, as well as the great pressure of environment protection, effective use of renewable energy sources has been the concern of all parties. The active development and utilization of renewable energy sources, such as wind and solar energy, as well as improving energy efficiency, have come into the forefront as a major problem. Micro-grid system as the key to coordinating power grid and distributed generation, can effectively coordinate and control simple interconnection of many scattered distributed generators (DG) with different characteristics (especially random and intermittent renewable energy, such as wind, solar energy). Micro-grid can also insure the stability of systems and prevent the adverse effects (power quality’s decline and protection failure) caused by mass accessing of DGThis dissertation chooses the practical implementation of micro-grid as research object based on domestic and overseas development situation of micro-grid, meanwhile analyzing and discussing the key technology such as collocation of micro-grid, DG’s control strategy, coordinated operation and energy management of micro-grid. The main contents are listed as follows:This dissertation introduces the key technology and engineering application of micro-grid based on the further research on present situation of micro-grid demonstration project both in China and abroad. Optimal allocation method of micro-grid, research situation of DG and energy storage’s grid control strategy, coordinated control method of micro-grid and energy optimization technology are emphatically analyzed, and the deficiency in actual operation is put forward.In view of wind-solar-storage microgrid system, considering the aspects of its economy, reliability and utilization of renewable energy for capacity allocation, a computing method combining operation model with scheduling strategy is proposed. From the perspective of engineering applications, a method for calculating the power constraints of tie line, which meets the power system operation specifications and friendly access conditions of microgrid, is elaborated in this dissertation. Besides, an improved genetic algorithm based on constrained searching area and increased random individuals is proposed to solve the model and the actual configuration problem. The optimization results show the feasibility and superiority of improved algorithm.In view of the structure characteristics of energy storage system, a DC Peer-To-Peer coordinated control strategy of hybrid energy storage based on lithium-ion batteries and ultra-capacitors is proposed, which can effectively restrain impact and fluctuations of DC voltage and improve the dynamic response of system. For the interaction between load and storage of operation control in microgrid, a Storage-Load Integrated Control Unit(SLU) is designed and a storage coordination control strategy based on integrated control is proposed, which increase the power regulation scope of energy storage system with large volume of controllable load and compensate discreteness due to removing power when control load.by using smooth output of storage, so the proposed strategy can improve the reliability and economy of microgrid.Considering the common coordination control model and traditional hierarchical distributed control strategy of microgrid, a microgrid hierarchical control strategy based on dual mode distributed control is proposed with the existing defects of three levels control strategy. This dissertation analyzes the structure characteristics of three levels and the innovation of the proposed control strategy compared with the existing conventional control strategy. Theoretical analysis and engineering application show that the proposed dual model control strategy can guarantee the safety and stability of microgrid operation in both island state and grid-connected state.By considering of the characteristic that the prediction accuracy of renewable energy increases with the decrease of the time scale and the strong coupling between energy managements of different time scales, an improved model and energy management strategy for microgrid based on multi-time scale is proposed. A series of measures, such as adding super ultra short-term scheduling between ultra short-term scheduling and real-time scheduling, increasing buffer boundary constraints between long-term scheduling and short-term scheduling, putting the SOC penalty factor of energy storage related to long-term characteristics in ultra short-term, have been taken to refine micro-grid energy management step by step, and coordinate the global and local optimality of the system.