1. Choice of converter type

Speed variation is most often achieved by varying the armature voltage, possibly supplemented by varying the excitation voltage. Power supplies are amplifiers, controllable by low-level voltages and consisting of static converters whose components (thyristors, transistors) work in commutation. The resulting voltages exhibit discontinuities, and the currents must be filtered. This filtering is naturally created by the motor inductance, if sufficient, otherwise by an additional inductance. The choice of converter and its environment is based on considerations of reversibility, source, power to be supplied, electromagnetic disturbances, desired bandwidth and, of course, eco-nomic criteria.