Study On The Design Method Of High Temperature Superconducting Energy Storage Magnet Considering Electromagnetic Dynamic Characteristics

The zero resistance and high current carrying capacity of superconductor are the key strengths that provide the superconducting technologies with a number of technical advantages. The emergence of high temperature superconducting material promotes the development of superconducting technologies. At present, the experimental prototype of superconducting wind turbines, superconducting cables, superconducting fault current limiters, superconducting transformers and superconducting magnetic energy storage systems have been successfully developed. Some even step into the stage of field test. As one of the many superconducting power devices, high temperature superconducting magnetic energy storage system (HTS SMES) can rapidly respond to exchange active and reactive power independently in four quadrants with ac power grid connected. SMES could make a great difference in aspects such as improving the stability and power quality of power system, providing the reserve capacity of system and assisting the grid-connection of renewable energy sources. Therefore, HTS SMES has received extensive attention of domestic and foreign research institutions.Due to the complex electromagnetic properties, mechanical properties and thermal properties of high temperature superconductors, the design of high temperature superconducting energy storage magnet is not easy. Current design methods are faced with problems such as single design target, simple design consideration, rough simulation model, and so on. These methods generally regard SMES magnets as DC magnets without considering the dynamic current when SMES exchanges power with the grid. It is found from the experimental results that the induced losses when SMES charges and discharges not only cause serious temperature rise but also reduce the power exchange efficiency and affect the requirements of the cooling power. This thesis proposes to consider the effect of dynamic current on the magnet when designing SMES magnets. The design of HTS SMES magnet considering electromagnetic dynamic characteristics is studied. This thesis mainly completes the following tasks:(1) Based on the extensive summaries on the electromagnetic properties and mechanical properties of HTS tapes, the development of SMES and the status of the design methods for HTS SMES magnets, the design key points of HTS SMES magnets are summarized. The design method of HTS SMES magnets considering electromagnetic dynamic characteristics is proposed. Combining the genetic algorithm and finite element method, a piece of software for designing SMES magnet with a visual GUI was written. The design of a 150kJ SMES magnet is completed with this software to show the design process of HTS SMES magnets considering electromagnetic dynamic characteristics.(2) After analyzing and comparing the existing AC loss calculation methods of HTS magnet, an improved method of calculating the AC loss is proposed. An equivalent relative permeability is used to simulate the diamagnetism of superconductors in this method. The AC loss of a HTS coil with different current amplitudes and frequencies is calculated with the improved method and the H formula method. The calculation results of the two methods are compared. The comparison between the results of the two methods indicates that the precision of the improved method is able to meet the necessity of practical engineering. Meanwhile, the improved method takes much less computation time, which means more finite element divisions are allowed in the modeling of the magnet. Therefore, this method makes it possible to consider the electromagnetic dynamic characteristics in the design of magnets.(3) The design method of SMES cryogenic system considering electromagnetic dynamic characteristics is proposed. The influences of operation conditions, geometric parameters of cooling plates on eddy current loss are analyzed. The geometric parameters of cooling plates are optimized based on the assumed three potential SMES applications. Meanwhile, a technical economic evaluation method for SMES cryogenic system is proposed. A new factor is defined to assess the technological and economical validity of the cryogenic system. As an example, a technological and economical evaluation is conducted with a 5MJ SMES cryogenic system. This method provides a quantitative evaluation standard for the design of SMES cryogenic system, showing great significance to the improvement of the cooling efficiency and economical efficiency of the SMES cryogenic system.(4) In order to verify the design method of HTS SMES magnet considering electromagnetic dynamic characteristics, a thermal model of a 150kJ/100kW SMES is built. The AC losses and the eddy current losses are calculated when SMES exchanges power with the grid. The temperature distribution of the magnet is calculated when cooling the magnet based on the thermal model. And the temperature variation of the magnet is analyzed when SMES exchanges power with the grid. The simulation results were identical with the experimental data. Thus, it is verified that the analysis method proposed here is useful for designing a conduction-cooled HTS SMES.