Type of stepper motor
As mentioned earlier, various types of BDC motors are distinguished by the manner in which the fixed magnetic field is generated in the stator. This section will discuss the different types of BDC motors and the advantages and disadvantages of each type.
Permanent magnets
Permanent Magnet Brushed DC (PMDC) motors are the most common BDC motors in the world. Such motors use permanent magnets to generate the stator magnetic field. PMDC motors are commonly used in applications including fractional horsepower motors because permanent magnets are more cost effective than winding stators. A disadvantage of PMDC motors is that the magnetism of the permanent magnets gradually decays over time. Some PMDC motors are also wound with permanent windings on their permanent magnets to prevent magnetic losses. The linearity of the performance curve (voltage versus speed) of a PMDC motor is very good. Current is linear with torque. Since the stator magnetic field is constant, such motors respond very quickly to voltage changes.
And
The exciting coil of the Shunt-WoundBrushed DC (SHWDC) motor is connected in parallel with the armature. The current in the field coil is independent of the current in the armature. Therefore, this type of motor has excellent speed control capabilities. SHWDC motors are typically used in applications that require five or more horsepower. In SHWDC motors, there is no problem of magnetic loss, so they are generally more reliable than PMDC motors.
String
The excitation coil of the Series-WoundBrushed DC (SWDC) motor is connected in series with the armature. Since the current in both the stator and the armature increases with increasing load, this type of motor is ideal for high torque applications. The disadvantage of SWDC motors is that they do not have precise speed control like PMDC and SHWDC motors.
Compound
The CompoundWound (CWDC) motor is a combination of a parallel excitation and a series motor. As shown in Figure 5, the CWDC motor can generate both series and excited magnetic fields. The CWDC motor combines the performance of SWDC and SHWDC motors with greater torque than SHWDC motors and better speed control than SWDC motors.
