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Poloidal field (PF) power supplies provide 20-25 kA to PF superconducting magnets to generate, maintain, and control the Korea Superconducting Tokamak Advanced Research (KSTAR) plasma. A substantial amount of grid power for PF power supplies is required. Before 2014, available grid power for PF power supplies reached only 50 MVA, which is comparably small to support the rated operation of PF magnets. To achieve high-performance and long pulse operation of KSTAR plasma, the motor generator (MG) system, whose maximum power is 200 MVA, was designed and tested up to 150 MVA with PF magnets in 2014. Frequency fluctuation of line voltage, voltage distortion, and harmonic current increases are found during the operation. The power supply control can be seriously affected by these problems because every PF power supply uses a 12-pulse thyristor converter that is sensitive to the power quality. In this paper, key features of power supply control under grid and MG power system are described, and the test results are presented.

A compact flywheel with superconducting bearings was developed and manufactured at our department, which integrates driving magnets (PM part of the motor generator (M/G) unit) and a bearing magnet (PM part of the SC bearing). Main goal of this development was to verify achievable losses with the proposed permanent magnets disc-type M/G unit. An early stage approach for specific no-load eddy current loss calculation is introduced, and by the application of the formulae I theoretically proved that it is possible to build industrial size double-rotor disc-type permanent magnet machines with no-load losses at the same order with the SC bearing losses. Practical verification of the method is also shown, and though according to the measurement results the existing stators do not show the expected low losses, the contradictions are discussed.

This paper presents the design of an ultrahigh speed permanent magnet (PM) motor/generator driven at a rated output and speed of 10 kW and 70 000 r/min, respectively, for use in an electric-turbo compounding system. When designing the very-high speed motor/generator, the mechanical and structural safety of the rotor and losses that occur when the motor operates at high speed should be considered for safe operation. In this paper, the optimal design of the ultrahigh speed PM motor is performed with finite element analysis and structural analysis. Especially, the electromagnetic and structural characteristics based on the sleeve material are analyzed. The optimal design for PM motor, using carbon fiber is proposed not only to reduce the eddy-current loss, which prominently occurs at very-high speed, but also to ensure its structural safety. Finally, the validity of the design method and the effectiveness of the fabricated prototype of PM motor is verified through experimental tests.