DC motor speed control
DC drives are widely used in the industry for their variable speed, good speed regulation, braking, and reversing ability.
In the past, DC motors were used in most of the VSD applications in spite of the complexity, high cost, and high maintenance requirements of the DC motors.
Even today, DC drives are still often used for the more demanding VSD applications. Examples of this are the sectional drives for paper machines, which require a fast dynamic response and a separate control of speed and torque.
Methods of speed control are given below
1. Armature voltage control
2. Field flux control.
Most of the DC drives employ armature voltage control method and field flux control, in order to achieve speed regulation, both below the rated speed and above the rated speed respectively. In both cases, the half- and fully controlled rectifier or converter is used to achieve a variable DC voltage, from AC voltage, to supply to the armature voltage.
Both the AC and DC drives use a converter or rectifier and inverter usually. The following section details such devices.