145 MVA modular thyristor converter system with neutral control for ASDEX upgrade

The power supply of the ASDEX Upgrade (AUG) tokamak consists of 11 thyristor converter modules which feed the poloidal field coils. All converters installed are powered by 10.5 kV flywheel generators starting at a frequency of 110 Hz, running down to 85 Hz during a pulse. For quasi-stationary advanced tokamak experiments with enlarged flat-top phase, the power supply system must be extended. The variable frequency of the pulsed network, fast load changes, together with the different parameters of the load coils require a very sophisticated converter design with reduced reactive power consumption. The paper describes the design and testing of the modular Thyristor Converter Group 6 with neutral control and four quadrant possibilities. It presents the various configurations available for operation on AUG magnetic coils, analyses the results of measurements obtained during commissioning, compares them to the calculated (design) values and reports on the performance achieved in fast four quadrant operation, improving the possibilities of the AUG feedback control of plasma shape and position.