Feasibility Study on Current Source Power Conversion for Superconducting Magnets Using Series Compensated Thyristor Converters

Thyristor converters are used as power conditioning systems for superconducting coils. The objective of this work is to discuss the series compensation of thyristor converters using variable series capacitors. Traditional thyristor converters operate with lagging power factor requiring large reactive compensation efforts. Similarly, the series capacitor can control the coil voltage through a unity power factor thyristor converter with a resulting leading power factor seen from the grid. Therefore, by combining the two, both leading and lagging reactive power control, and also the active power control of the superconducting coils can be achieved. In order to demonstrate the feasibility of the series compensation of the thyristor converter, a prototype converter using a gate-commuted series capacitor (GCSC) is developed. From the experimental results using a superconducting coil, the authors demonstrated the leading current control capability of the series compensated thyristor converter, and verified the leading, lagging, and unity power factor control capability based on thyristor converter systems. This feature leads to a potential reduction in reactive power compensation need of 50 percent of the conventional thyristor converter system.