Although PSpice is designed as an electronic circuit simulator, you can also use it to simulate mechanical
or electromechanical systems. Analog Behavioral Modeling makes simulating mechanical systems much
simpler. An example of an electromechanical system which can benefit from PSpice simulation is a
Brushless DC motor.
Brushless DC motors are used in computer disk drives and other applications where precise control of
motor operation is required. A brushless DC motor is built like a stepping motor. It has a permanent
magnet rotor attached to the motor shaft, and several electromagnets arranged around the stator. Each of
these electromagnet windings must be driven in sequence to make the motor shaft turn, a process called
commutation. Commutation must be synchronized with the motor shaft angle to make the motor turn at
the desired speed and direction. Implementing a commutation strategy and motor control system usually
requires both analog and digital circuit elements.
Because the motor is part of this closed loop control system, it is important to have an accurate model of
its mechanical and electrical behavior.
Figure 1: Brushless DC Motor Model Circuit
Modeling the Mechanical Properties
Note: The equations used in this document to explain motor behavior are from the book Brushless
Motor System Design and Analysis (Dr. C.K. Taft, Dr. R.G. Gauthier, & Dr. T.J. Harned,
"Brushless Motor System Design and Analysis", University of New Hampshire Press 1988).
