Publication Date


Document Type


First Advisor

Blank, Gary L.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Industry and Technology


Electric motors; Direct current; Electric controllers


This thesis introduces the brushless dc motor as a motion control device and uses it to implement a variable speed velocity control system. The report discusses the structural arrangement of the machine itself, and the functional arrangement of a generalized system to control it. This is shown in contrast to the mechanical structure and control scheme for the brush dc motor. The attributes of the brushless dc motor are compared to those of the brush dc motor and other ac machines, in terms of industrial application. A qualitative description of the operation of the brushless motor is given. The equations of motion of the machine are expressed in terms of both dc and synchronous motor models. The method of velocity control for the three phase, four pole brushless dc motor allows precise operation over a range of speeds and loads. The controller provides proportional/integral feedback into a pulse-width modulated, six step inverter. The loop gives exact cycle-for-cycle correspondence between a variable reference clock and a shaft-mounted encoder signal using a digital integrator and no phase detection. The use of the digital integrator for providing zero overshoot response at variable speeds has advantages over phase-locked systems. Observations are made regarding the advantages of the brushless dc motor in future control applications, including the flexibility of electronic commutation, which suggests interesting possibilities for the control of motor performance characteristics.


Bibliography: pages 111-114.


viii, 114 pages




Northern Illinois University

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