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Motor-Drive Power Drivers from Power Converters
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.
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