Sequence Control Verification of a Central Solenoid Converter for Nuclear Fusion Reactors by Using a Hardware-in-the-Loop

In this paper, verification of a four-series connected central solenoid (CS) converter sequence control of a nuclear fusion reactor to reduce reactive power by using a real-time digital simulator is described. The unit CS converter supplies voltage (±975 V) and current (±45 kA) to the CS superconducting magnets to induce current in plasma. The output voltage of the unit CS converter is limited because of the rated voltage of thyristor switches. However, the CS superconducting coil needs more operating output voltage. Thus, the CS converter must be connected in four series to provide the required operating output voltage. Adequate reactive power support is important to improve the electrical grid stability, because four-series connected CS converter generate large amounts of reactive power. However, other reactive compensators require high costs and a large area. Hence, sequence control is applied to the voltage control of the four-series connected CS converter in order to reduce the reactive power. The sequence controller calculates and transmits the individual voltage command to each unit CS converter according to the total voltage command via safe ring-type communication channel. To verify the feasibility of the proposed sequence control of four-series connected CS converter, five real Zynq-based controllers are assembled and a power system, including the four unit CS converters, is implemented in a real-time digital simulator for hardware-in-the-loop verification. Maximum reactive power is reduced by 16%, from 225 to 190 Mvar.