Brushed DC Motor
The Brushed DC Motor gets its name from the “brushes” for commutation. Typically the rotor, also known as an armature, has windings on them terminated on to a commutator. Brushes make and break contact with commutation segments, thus commutating power to the armature. We will discuss this in more detail later. The stator, or outer cylinder, of a permanent magnet DC motor will have two or more permanent magnet pole pieces. The opposite polarities of the energized winding and the stator magnet attract causing the rotor to rotate until it is aligned with the stator. Just as the rotor reaches alignment, the brushes move across the commutator contacts and energize the next winding.
Easy to control because speed and torque are proportional to applied voltage/current. Rotor is heavy due to windings on armature, more inertia more difficult to start / stop. Heat is generated in windings on rotor, more difficult to remove.
Key characteristics of the Brush DC Motor:
- Good controllability:On/Off, Proportional
- Linear torque/current curve
- Speed proportionate to voltage applied
- Requires maintenance
- Low overloading capability
- Low heat dissipation
The speed of the Brushed DC motor is controlled by controlling the armature voltage, and the torque by the armature current, that is, the flux and the torque can easily be controlled separately. This is the main principle on which all the modern AC control methods nowadays rely. The first DC motors were controlled with some chopper technology, such as the pulse width modulation (PWM). Network-connected thyristor bridges were mainly used in higher power range, typically in a variety of applications.