DC drives are DC motor speed control systems. Since the speed of a DC motor is directly proportional to armature voltage and inversely proportional to motor flux, either armature voltage or field current can be used to control speed. A DC drive supplies voltage to the motor to operate at a desired speed. The motor draws current from this power source in proportion to the torque (load) applied to the motor shaft.
It is important to note that the voltage applied to a DC motor be no greater than the rated nameplate.
Armature windings are commonly wound for 500 VDC. The control logic in the drive must be adjusted to limit available DC voltage to 0 – 500 VDC. Likewise, the shunt field must be limited to the motor’s nameplate value.