Application Of SMES In Micro-grid And Research Of SMES Status Evaluation Method

In recent years, energy shortage and enviromental pollution have gained much more attention among contries in the world. The technology of distributed generation using clean and renewable energy provides a new way for reducing consumption and improving reliability of power supply. Technology of micro-grid is an effective mean to integrate clean and renewable energy into power grid. As an important part of micro-grid, energy storage device is of great significance for improving the operation charcteritics, stability and reliablity of micro-grid. With characteristic of fast response and high power dendity, superconducting magnetic energy storage (SMES) can quickly exchange large power with micro-grid or power system. The instantaneous power imbalance of micro-grid can be adjusted. Therefore, SMES can be applied into micro-grid to improve its characteristics. Sponsored by the National Basic Research Program of China (973 Program) and High Tech. Research & Development Program of China (863 Program), this dissertation studies the SMES applications in micro-grid systematically, including theoretical analysis, mathematical modeling, simulation analysis, control strategy and dynamic experiment of a 150 kJ SMES in a simulated power system. SMES status evaluation method is proposed to determine the impact of superconducting magnet thermal stability on the operation charcteristics of SMES. The main work and achievements are as follows:(1) Based on the distributed application form of SMES in micro-grid, the function of SMES in improving stability of micro-grid frequency is studied. SMES control strategy based on virtual inertia is proposed to improve the inertia and stability of micro-grid operation frequency. Considering the restriction of SMES output power, current adjustment strategy based on fuzzy control is designed for dynamic adjustment of superconducting magnet current. Simulation platform of micro-grid is established, effectiveness of the proposed control strategy of SMES and current adjustment strategy is verified through simulation and analysis.(2) The application of SMES in electric vehicle (EV) charging station of micro-grid is researched. A topology of electric vehicle charging station based on DC bus is proposed. SMES is utilized to improve the voltage stability of DC bus with the designed control strategy. On this basis, the application of SMES in an EV fast charging station of micro-grid is studied to slove the problem of large changing rate of fast charging power. An energy management strategy based on SMES control is proposed to reduce the changing rate of fast charging power, which can help to the frequency stability of micro-grid or distributed network. The effectiveness of the proposed control and energy management strategy is verified by simulations.(3) With comprehensive consideration of interaction and influence between SMES and micro-grid or power system, a SMES status evaluation method is proposed and constructed. Based on the quantitative analysis of SMES power output characteristics, the impact of SMES dynamic operation on the thermal stability of superconducting magnet is analyzed. The expression of SMES status evaluation method (SSEM) is obtained by integrating all the influential factors, including superconducting magnet current and temperature. The effectiveness of SSEM in power system is verified by power regulation experiment and dynamic simulation experiment of 150 kJ SMES.(4) In order to construct SMES status evaluation system more systematically and accrately, this dissertation proposes a new modeling method of SMES based on field-circuit coupling to expand the research of SSEM. The model of 150 kJ SMES is established by the proposed field-circuit coupling based modeling method. Simulation and calculation results have similar variation trend with the experimental results, which can reflect the actual operation characteristics of SMES more closely. The field-circuit coupling based modeling method of SMES can also be applied in other superconducting power devices.