For DCMs, very quick and accurate torque response can be accomplished by maintaining a constant flux and varying the armature current via closed-loop control of a thyristor or dc/dc converter. Similar performance of converter (inverter)- fed ac motors can be achieved by mimicking the DCM dynamics through field-oriented control (FOC) or direct torque control [32]. A torque response in the millisecond range can be achieved, which is generally several orders of magnitude faster than the closed-loop mechanical dynamics. As a consequence, the electrical dynamics can be neglected (i.e., considered in the steady state as seen from the mechanical dynamics), which allows us to express