Dear Dennis...
EN-Genius Network's Dennis Feucht answers your design
queries in his new Circuit Design Clinic!
February, 2009
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EN-Genius Network presents a new, interactive
analog design service to readers! Send us your design questions (with
relevant data; schematics in JPEG or GIF, please) for some free
engineering advice from EN-Genius Network's circuit
consultant, Dennis Feucht, on how you might solve a design problem or
improve circuit performance. Submissions may be edited for clarity or
brevity, and submitters and their email addresses will remain anonymous
(unless otherwise indicated). Please send your questions to Dennis here.
Motor-Drive Power Drivers from Power Converters
by Dennis L Feucht
The Problem
Permanent-magnet synchronous motor and step-motor drives consist of a motor controller and motor driver or switching amplifier. As motor-drive technology advances, both subsystems improve. Motor control has reached a certain plateau of refinement with field-oriented or vector control. However, external sensors are still commonly used to sense motor phase for high-performance applications, though the motor induced voltage contains the phase information.
The next advance in control is “sensorless” or winding-sensed control. It requires no position sensors other than the motor itself. Winding-sensed control is not uncommon nowadays for variable-speed applications where the low end of the specified speed range is high enough for the motor to generate a sufficiently large induced voltage waveform. For the low-speed range where the induced voltage is too small to reliably provide motor phase, something else must be done. In variable-speed applications, what is often used is a start-up scheme to turn the motor in the correct direction without phase control until it is rotating fast enough to be out of the low-speed region. For some schemes, shaft vibration is sufficient rotor motion to start the motor.
...download complete article here (123 KB PDF)
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