Control methods for the superconducting magnetic energy storage system and their experiments

Abstract

The storage of magnetic energy using a superconducting magnet, to be explained here, has many advantages, including high storage efficiency (over 90%), and possibility of installing an energy storage power station near the load. A fast and flexible control including possibility of power peak feed can be materialized if a thyristor power converter is used in the charge-discharge control of the superconducting magnet. The following are unique requirements of its operational characteristics: (1) The charge-discharge operation under a constant power control is essential from the system operation point of view. Therefore, a control system, design of the magnet, and evaluation criteria of the operational characteristics for this particular mode of operation are necessary. (2) Energy must be stored efficiently in a persistent current mode by shunting both ends of the magnet coil by means of a superconducting persistent current switch after the charging operation is complete. The control system necessary to satisfy requirement (1) is clarified. Further, experiments with a small energy storage system and a simple control circuit built to satisfy the above requirements were performed and the design criteria for a practical electric power storage system were derived. In the experimental system a low loss switching circuit consistingmore » of a mechanical and a thermal superconducting persistent current switches for the persistent current mode and current transfer purposes combined with a shunt circuit with a room temperature circuit breaker was built to satisfy (2). The operating characteristics of the switch circuit are also reported in this paper.« less