Test of Charging and Grid Connected Process for SMES

Superconducting magnetic energy storage (SMES) has a broad prospect in improving power quality in grid due to its advantages of high power density, fast response and low energy losses. Considering the actual conduction and switching losses of power devices, the energy stored in SMES would occur a certain attenuation. To maintain the current stored in SMES in rated level before grid-connected operation, an efficient charging method is indispensable. This paper proposes a feasible energy supplement method controlled by constant duty cycle Pulse-Width-Modulation (PWM). Simulation and experimental results demonstrate that proposed charging method is capable of charging SMES to high current while requesting small current from the voltage source. The influence of relevant parameters on charging characteristics is discussed as well. The whole process of charging and grid connected and the effect of SMES in improving power quality have been verified under the case of sudden voltage drop fault in dc bus.