Extension of the reactive power compensation for the pulsed power supply of ASDEX Upgrade

Highlights: • Reliable 90 Mvar static reactive power compensation. • Reduction of generator apparent and reactive power compared to load power. • Reduction of thermal load (I²t) of generator stator windings. • Efficient operation close to the system limits. • Prospective of longer AUG plasma pulses. -- Abstract: ASDEX Upgrade (AUG) is an essential element of the European Medium Sized Tokamak (MST) program towards a fusion power plant. It investigates plasma control and performance from plasma core (e.g. current drive and central heating) up to plasma-wall interaction (e.g. plasma confinement and heat exhaust). In order to improve the possibilities and flexibility of the experiment, the heating (ECRH, ICRF and NBI) and power supply systems will be extended and optimized (Käsemann et al., 2017). For plasma ignition and current ramp up of the poloidal field coils high DC voltage is required. During plasma flattop only the ohmic losses of the copper made coils have to be covered. This partial load operation of the high current converters results in high reactive power demand. The power supply of AUG is based on flywheel generators with limited power and energy. To reduce the current load to the generator, a 90 Mvar static reactive power compensation unit has been installed at flywheel generator EZ4 with 2 × 15 Mvar and 2 × 30 Mvar switched compensation modules.