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Detailed Introduction of DC Motors

By aoba | Published on Sep 14,2015

DC motor is a motor which converts DC electric energy into mechanical energy. It is widely utilized in electric drives for its good speed regulating characteristics. This article aims to introduce the construction, performance and control structure of the DC motor in detail.

Basic Construction

There are two parts of a DC motor: the stator and the rotor. The stator consists of the main magnetic pole, yoke, commutating pole and brush. The rotor consists of the armature core, armature winding, commutator, axle and fan.

The following will give a detailed introduction to the parts of the rotor such as armature core, armature and commutator.

1. Armature core: It is designed to inset the armature winding and enable the flux to pass by.

2. Armature: It is designed to generate electromagnetic torque and induced electromotive force for energy conversion.

3. Commutator: The commutator converts the direct current in the brush into the current in the armature winding in order to maintain the stability of electromagnetic torque. In a DC motor, the commutator converts the electromotive force in the armature winding into DC electromotive force in the brush.


The performance of a DC motor is closely related to its exciting mode. Usually there are 4 types of exciting mode of DC motor: DC separately excited motor, DC shunt motor, DC series motor and DC compound motor.

1. DC separately excited motor: There is no electrical connection between the field winding and the armature. The field circuit is supplied by another DC power. Therefore, the field current is not affected by the voltage or current in the armature.

2. DC shunt motor: The circuits are connected in parallel to the armature winding.

3. DC series motor: The current is connected in series. The field winding and the armature are connected in series, so there is distinct change of the magnetic field of the motor with the change of armature current.

4. DC compound motor: The flux of the motor is produced by the field current in the two windings.

Control Structure

As for DC brushless motor, the rotational speed of the rotor is affected by the speed of the rotating magnetic field of the stator and the poles (P) of the rotor, N=120, f/P. Under the condition that the poles of the rotor are unchangeable, it is possible to change the rotational speed of the rotor as long as the frequency of the stator rotating magnetic field is changed.

When there is any change in the load, DC brushless motors can control the rotor to maintain the rotational speed within the range of rated load.

The DC brushless drive includes the power part and the control part, both of which provides three-phase power to the motor and converts voltage frequency according to demands respectively.


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