
Conventional d.c. Motors 95
The solution to the problem of overcurrents lies in pro-
viding closed-loop current-limiting as an integral feature of
the motor/drive package. The motor current is sensed, and
the voltage V is automatically adjusted so that rated current
is either never exceeded or is allowed to reach perhaps twice
rated value for a few seconds. We will discuss the current
control loop in Chapter 4.
SHUNT,
SERIES AND COMPOUND
MOTORS
Before variable-voltage supplies became readily available,
most d.c. motors were obliged to operate from a single d.c.
supply, usually of constant voltage. The armature and field
circuits were therefor ...