Design and development of the star-point control high voltage power supply of the ECRH system on HL-2A tokamak

To supply the cathode high voltage for the four gyrotrons (68GHz/500kW/1s) of the ECRH system on HL-2A, the star-point control high voltage power supply (HVPS) with rated output of 60kV/120A has been built. The filtering inductors in the HVPS are on the primary side of the rectifier transformers, so the required insulation level of the inductors to local earth is much smaller than that they are on the secondary side of the rectifier transformers. The output voltage can be modulated by changing the excitation current of the rectifier transformers. The high voltage pulse modulators based on tetrode vacuum tube (TM-703FB) are also applied in the power supply to realize the fast rising and falling of the output voltage. The over-current protection and voltage overshoot are executed by the star-point controller and the high voltage pulse modulators. The pre-charging circuit is used to avoid large voltage drop or overshoot at the beginning and the end of the pulse. The control system is also presented. The feed forward and feedback control methods are adopted in the control system to ensure the stability of the HVPS. Good controlling properties and reliable protective properties of the control system are proven by the experimental results.