Design of a Micro PM BLDC Motor

Build a Model of Micro Motor Structure, Dimensions, and Magnetic Field Analysis

A micro brushless PM motor is typically built in an external rotor structure. Its armature is built on the stator and the internal permanent magnet is installed to the inner side of the rotor. The following procedures are required when constructing a motor structure.

 1) Determine the dimensions of the motor’s structural design and these include stator inner diameter, stator core length,
 magnet volume, rated power of the motor’s load characteristics, rated voltage, and the rotation speed.

 2) Select the type of permanent magnet structure, PM material, approach of the magnet, and the stator core material. 3) Select the teeth/slots structure for the motor stator. Prior to designing the micro motor, it is required to determine the preliminary specifications and parameters based on practical motor usage requirements. These design parameters include: the motor’s main dimensions, stator structure, the rotor’s magnetic steel dimensions, magnetic energy, and electric circuit. 

When determining the number of motor phases and configuring teeth/slots layouts, it is also required to pay special attention to several design essentials: 

1) Phase count: The
phase count is related to the cogging torque. The more the phase count is, the smaller the cogging torque.

 2) Pole count: The increase in the pole count leads to the increase in iron loss. When the loss in the electronic commutator is increased, the motor efficiency decreases.

 3) Slot count: if the slot count is an integer, the stator’s copper rotor magnetic poles attract each other and this generates the orientation torque phenomenon, which leads to the deteriorating quality of motor operations.

 4) The motor poles and slots must match. 

5) The way of connecting the motor winding needs to be
considered.