Development Overview of Solid-State Multimegawatt Regulated High-Voltage Power Supplies Utilized by NBI and RF Heating Systems

Regulated high-voltage power supplies (RHVPSs) are important power sources in high-power heating and current drive systems for a tokamak. Along with high power at output, these power supplies meet the requirements of fast dynamics (on the order of few microseconds), low ripple factor, and good output regulation. A development overview is presented for RHVPS ranging from 14 to 80 kV at several-megawatt power with typical output results. Having extensive tests performed with an 80-kV 75-A RHVPS, it is being regularly used for a neutral beam injector (NBI) at the Institute for Plasma Research (IPR). A large number of identical and series-connected switched power modules (SPMs) are fed from multisecondary transformers. Pulse step modulation control applied to an insulated-gate bipolar transistor switch within SPMs regulates output. Different rise and fall times of voltage can be set from few microsecond to millisecond range. Fast detection of instantaneous overcurrent reduces turnoff time within 2 μs. Due to higher frequency of ripple at higher voltages, output filter component value is of smaller order, which, in turn, limits fault energy below 10 J. The development of RHVPS at IPR started by making a functional prototype at lower rating (14 kV; 35 A) to have an experience in testing design concepts. This was divided in various activities like selection of topology, selection and design of different subparts, e.g., control, switching power converters with protections, and multisecondary transformers. Having successful results and testing all functional parameters on prototype, a series of RHVPSs at higher ratings (up to 80 kV), are developed and installed for NBI and radio-frequency heating system. The design details for each subsystem along with results are discussed.