Paralleling of two large flywheel generators for the optimisation of the ASDEX Upgrade power supply

The power supply of the ASDEX Upgrade (AUG) tokamak consists of three pulsed distribution systems (110–85 Hz), each supplied by a dedicated flywheel generator: EZ2 (1.45 GJ/167 MVA) which solely feeds the toroidal field coils, EZ3 (500 MJ/144 MVA) and EZ4 (650 MJ/220 MVA). For quasi-stationary advanced tokamak experiments with extended flat-top phase, the power systems of EZ3 and EZ4 must be connected in parallel, so that full advantage of the installed generator power and flywheel energy can be realised. The variable frequency of the pulsed network, fast load changes (up to 1000 MW/s), together with the different parameters of the generators and saturation effects during pulsed operation, require detailed numerical models for an investigation of the stability limits of a parallel operation of the two machines on one common 10.5 kV busbar. The paper describes the dynamic load requirements of a feedback controlled plasma experiment, the controller development for paralleling two large flywheel generators, the results of system studies with optimised power supply and implications of these results on the technical realisation.