Operation and Control Techniques of SMES Unit for Fault Ride through Improvement of a DFIG Based WECS

Abstract— The energy storage in an SMES is in the state of magnetic field within a superconductor coil. The magnetic field is formed by flowing DC current in the SMES. To ensure proper operation the temperature of SMES should be maintained below critical temperature. At this temperature the resistance of the coil is zero and hence there is no loss in stored energy. The ability of SMES to store energy is influenced by the current density. The energy is fed back to the grid by conversion of magnetic field into electrical energy. An SMES system has a superconductor, refrigerant, power conditioning unit and control unit. The storage of energy is achieved by continuous circulation of current inside the coil. Since the energy is not converted in any form other than electrical there are lesser losses in SMES configuration than any other storage mechanism. Thus the efficiency is very high. It inhibits very low cycling time and the number of charge discharge cycles is very high. The major drawbacks of this technology being very high initial cost as well as losses associated with auxiliaries. This paper covers various aspects of SMES configuration and its connection in power system.