**2.1 General motor classification**

There are several ways of classifying electric motors by their electrical supply, by rotor structures and stator types. One of the common ways is to categorize them as AC and DC motors as shown in Fig. 2. AC motors use alternating current or voltage as source while DC motors use DC voltage source to supply the windings. DC motors are classified by their field connections such as series, parallel or compound field excitation. AC motors, on the other hand, has two major types: One type is induction motors where rotor magnetic field is generated by electromagnetic induction principles and the other is synchronous motors where the magnetic field is generated by either field winding excitation or permanent magnets. Induction motors could be single or poly-phase and have squirrel-cage or wound rotor. Synchronous motors could have numerous options depending on the rotor type and excitation (Hendershot & Miller, 1995).

Fig. 2. Fundamental motor classification

(a) (b) (c)

addition, PM servomotors have better torque-speed characteristics and high dynamic response than other motors. Their long operating lives, noise-free operations and high speed

There are several ways of classifying electric motors by their electrical supply, by rotor structures and stator types. One of the common ways is to categorize them as AC and DC motors as shown in Fig. 2. AC motors use alternating current or voltage as source while DC motors use DC voltage source to supply the windings. DC motors are classified by their field connections such as series, parallel or compound field excitation. AC motors, on the other hand, has two major types: One type is induction motors where rotor magnetic field is generated by electromagnetic induction principles and the other is synchronous motors where the magnetic field is generated by either field winding excitation or permanent magnets. Induction motors could be single or poly-phase and have squirrel-cage or wound rotor. Synchronous motors could have numerous options depending on the rotor type and

Fig. 1. Surface mounted PM (a), buried PM (b) and spoke type PM (c) motor types

ranges are some of the advantages of brushless servomotors.

**2. Classification of electric motors** 

excitation (Hendershot & Miller, 1995).

Fig. 2. Fundamental motor classification

**2.1 General motor classification** 

Electric motors are also classified by their slots. They are called slotted motors if they do have slots and called non-slotted or slotless motors if they do not have any slot structures. Furthermore, one major classification method is identified by the main flux direction. If the motor has a main flux component which is radial to the shaft, they are called radial flux motors and if the flux component is axial to the motor shaft, then the motors are called axial flux motors where they find various applications because of their structural flexibility.
