20 MW DC thyristor converter system with extremely low ripple and drift for high magnetic field research

For research on the behaviour of matter inside high magnetic fields (33 T continuous to 80 T pulsed) dissipative magnets are used and high DC power (2 times 10 MW) is required. Because the behaviour of a material can change completely, even at one hundredth percent of field increase, the magnet power supply must have a very high short time current stability (2 ppm of nominal current) and extremely low current ripple (< 15 ppm). Two 10 MW water-cooled thyristor converters, with passive and active filtering, operating in single or parallel mode, are constructed and put in operation, fulfilling all demands. The two 10 MW thyristor converters can also be operated in series delivering 20 kA at 1000 V in pulsed mode (typically 1s), facilitating operation with a two-coils arrangement (coil-in/coil-ex). The power system is described and design choices are explained. The configuration of the control loops are discussed and some test results presented