Rotary-type high-temperature superconducting (HTS) flux pumps using permanent magnets (PMs) are effective
contactless superconducting excitation devices used for generating excitation in the field winding of HTS rotating
machines. Although contactless superconducting excitation devices overcome the disadvantages of conventional
contact-type excitation systems, those based on PMs are not the ideal solution because current supply to the field
winding is allowed only when the HTS rotating machine is rotating in the same direction: a rapid discharge
occurs when the rotation direction is reversed. They do not meet the practical operational requirements of
rotating machines, viz., initial start, load fluctuation, and direction change, and alternatives to actively control
excitation of field winding are essential. In this study, novel functions to improve the application feasibility in
various HTS rotating machine operation modes have been proposed. Based on a numerical analysis, a prototype
contactless superconducting active excitation device (CSAED) comprising PMs, alternating current (AC) and
direct current (DC) electromagnets was developed using the hybrid magnet concept. The operational characteristics of active control functions in the CSAED were experimentally analysed for stationary, forward, reverse,
and compensation operations of the HTS rotating machine and the qualitative effectiveness for active control of
the charged current was verified. The first novel function CSAED using AC electromagnet was successfully
demonstrated in initial current excitation by generating the alternating magnetic field without physical rotation
for a small-scale HTS magnet. However, upgrading of the AC electromagnet is required to apply for large-scale
load magnet due to small value in saturation current of the CSAED. The second novel function of CSAED using DC
electromagnet worked well in current-adjustment and current-conservation modes by controlling the magnetic
field density using the hybrid magnet. By controlling the current of DC electromagnets without any change in the
rotation speed, the saturation current was adjusted within the ranges from 61.4 A to 1.7 A, which are 86.6 and
2.4 % of critical current for load HTS magnet, respectively. In the reverse rotation, the current discharging time
of CSAED using activation of DC electromagnet increased by 2474 % compared to without energizing the DC
electromagnet.