Brushless DC-a modern approach to variable speed drives

The theory of brushless DC motor operation is briefly outlined. Similarities and differences with other types of drives are discussed, and a justification given for the use of the term brushless DC, drive as a distinct type of drive as opposed to referring it to as simply a variant of the variable-frequency drive. A comparison is made of operating characteristics and parameters of the brushless DC and traditional DC drives in the small-to-medium-horsepower range (to 150 hp). Particular emphasis is placed on the advantages to the end-user of the drive and how these advantages affect production, service, and operating cost. Included is information on efficiency, power factor, motor heating, and breakaway torque. Application benefits are discussed demonstrating some of the advantages of using brushless DC drives