
8.2. Synchronous Machines 103
Drives for DC machines generally follow the simplified block dia-
gram shown in Fig. 8.2. An inner current regulator loop is surrounded
by a voltage or speed regulator loop. The inner loop is necessary
because the DC machine appears as a very low resistance to dynamic
voltage changes. The voltage feedback loop may be augmented by
feedback from a tachometer or shaft encoder for precise speed con-
trol. The current regulator may be embellished with current ramps,
current limits, and thermal limits for optimum motor performance and
protection. A variable field supply may be added for extended speed.
The author once extended ...