Feasibility Study of Thyristor Rectifier With Unity Power Factor for Superconducting Magnet in Tokamak

A series connected rectifier with unity power factor is proposed for superconducting magnet in tokamak. It is composed of a conventional thyristor rectifier and a modified rectifier having small commutation capacitors and dump resistors. The modified rectifier provides leading currents in AC side and it cancels lagging currents generated by the conventional rectifier without external reactive power compensator. The dump resistor is used to suppress overcharging of the commutation capacitor and overvoltage of the DC output voltage. A design method for the dump resistor based on forced commutation conditions is proposed. Numerical simulation is carried out to confirm the reduction of reactive power and overvoltage.