Introduction

Direct-current permanent magnet (PM) motors provide high performance while maintaining low cost and are produced by the millions in automotive equipment, consumer electronics, power tools, toys, and appliances. Electronic DC motor control designs described in this chapter are divided into two main groups. The first group consists of standard PM DC motors with brush/commutator assemblies that can operate from a direct current power supply and do not necessarily utilize control electronics. The second group consists of stepper motors, servo motors, brushless DC motors (BLM), and other motor types that are powered from a DC supply and require electronics to function.

The control circuitry for the first group of DC brushed motors can vary from simple electrical switches to electronic speed controls. Examples include an on/off switch (vacuum cleaner), a reversal switch for direction control (automobile power windows), and speed or torque control electronics (tool motors). The availability of low-cost power electronic devices and associated integrated circuits allows many types of motor control designs for DC brushed motors. Most DC motors (<1 kW) use a permanent magnet structure instead of a wound field for higher efficiency. PM motors exhibit high-starting torque, and the motor's speed yields an inverse relationship to the load's torque requirements; loading down the PM motor causes the speed to drop but the torque to increase. The speed of a PM motor is directly related to the applied voltage, and, even at zero load, the motor's speed is usually limited to...