Increased operating flexibility for superconducting magnetic energy storage systems through the use of self-commutation

In a superconducting magnetic energy storage (SMES) system, it is convenient to use a twelve-pulse converter as the electrical interface between the high-voltage transmission systems and the superconducting coil. The authors present a technique for the construction of a circular PQ diagram to analyze power flow for a converter and SMES. The method indicates that, if self-commutation is used, any operating state in the PQ plane may be attained. This flexibility in operating state implies that all operating conditions, from unity power factor to zero power factor lagging, are attainable in the rectifier as well as the inverter modes. The implications of this flexibility, including harmonic impact, are discussed.>