Development of high efficiency and crowbar switchless dc power supply for 1MW CW CPD gyrotron

A high efficiency and high power dc main power supply for the collector potential depression (CPD) gyrotron was developed and operated successfully with a real CPD gyrotron. The capacity of the power supply is 5 MW, 100 kV output voltage and 50 A maximum current, adopting a dc 100 kV IGBT switch for fast switching and a pair of 3-phase ac thyristor switches for dc output voltage control. The IGBT switch consists of 100 insulated gate bipolar transistors (IGBTs) connected in series. The switch can protect the CPD gyrotron by fast switching which achieves input energy below 10 J and has first turn-on performance within 10 mus. The ac thyristor switch controls the output voltage of the power supply using feedback control and feedforward control, so as to regulate the voltage in the case of load transition from no load to rated load at the IGBT switch turn-on timing. The combination of feedback and feedforward controls enables us to maintain the voltage stability of the main power supply between −1.0% and +3%. As the power supply does not include any heavy dissipation element such as a series regulator, its efficiency achieves more than 95%.