The structure of an electromechanical drive system is given in Fig. 2.1. It consists of energy/power source, reference values for the quantities to be controlled, electronic controller, gating circuit for converter, electronic converter (e.g., rectifier, inverter, power electronic controller), current sensors (e.g., shunts, current transformer, Hall sensor), voltage sensors, (e.g., voltage dividers, potential transformer), speed sensors (e.g., tachometers), and displacement sensors (e.g., encoders), rotating three-phase machines, mechanical gear box, and the application-specific load (e.g., pump, fan, automobile). The latter component is given and one has to select all remaining components so that desirable operational steady-state and dynamic performances can be obtained: that is, the engineer has to match these electronic components with the given mechanical (or electronic) load.