Position detection for a brushless DC motor without hall effect devices using a time differential method
First Claim
1. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet or a DC current excitation winding, apparatus for controlling ordered application of electrical current to the phase windings and measuring the response thereto comprising:
- circuit means coupled to the phase windings for selectively establishing current paths through selected windings in response to control signals,driver means for applying short duration current pulses of first and second opposite polarities to each said selected winding,monitoring means for detecting the voltage detected at a current voltage converter connected to the energized winding by each of said applied current pulses of opposite polarities, anddetection means for identifying a rotational position of said rotor relative to said windings based on the sign of the time difference between the rise time of the responses to said pulses applied to the same selected winding.
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Accused Products
Abstract
The present method and apparatus detects the rotor position of a brushless DC motor with an accuracy of π/m electrical radians (where m=the number of motor phases) within one electrical period, and provides enough information to enable starting the motor in the correct direction with certainty. After starting the motor in an open loop mode of one or two steps, a closed loop mode may be switched on, using a dynamic indirect position detection as is already well known in the technology. More specifically, the position at start is determined by the injection of short current pulses in different motor phases, each phase or pair of phases being energized first by a pulse of one polarity and of the opposite polarity. The sign of the time difference between the rise times of the induced voltages is detected. By performing a succession of these tests on different phases or pairs of phases of the standing motor, a table of results is established which clearly defines the position of the rotor relative to the motor phases. The same table then defines what polarity currents should be applied to each phase to reliably and certainly start the motor in the proper direction.
143 Citations
22 Claims
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1. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet or a DC current excitation winding, apparatus for controlling ordered application of electrical current to the phase windings and measuring the response thereto comprising:
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circuit means coupled to the phase windings for selectively establishing current paths through selected windings in response to control signals, driver means for applying short duration current pulses of first and second opposite polarities to each said selected winding, monitoring means for detecting the voltage detected at a current voltage converter connected to the energized winding by each of said applied current pulses of opposite polarities, and detection means for identifying a rotational position of said rotor relative to said windings based on the sign of the time difference between the rise time of the responses to said pulses applied to the same selected winding. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A commutator less direct current motor comprising
a plurality of windings connected to define m phases of said motor, a rotor having a permanent magnet or DC current excitation winding positioned relative to said plurality of windings and rotatable relative to said windings and comprising means for establishing first, fixed magnetic fields, driver means connected to said plurality of windings for applying short term current pulses of opposite polarity separately to at least two different phases thereof for inducing at least two second, controlled magnetic fields, monitoring means for detecting each current established by said applied current pulses, each said current representing the interaction of said first, fixed magnetic field and said second, current pulse induced magnetic field, and detection means for identifying a rotational position of said rotor relative to said windings based on the sign of the time difference between the rise time of the responses to said pulses.
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14. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet or a DC current excitation winding, a method for controlling ordered application of electrical current to the phase windings and measuring the response thereto to determine the initial position of said rotor comprising the steps of
coupling circuit means to the windings for selectively establishing current paths through a selected winding or windings in response to control signals, applying short duration current pulses of first and second opposite polarities to each said selected winding, detecting the voltage detected at a current voltage converter connected to the energized winding by each of said applied current pulses of opposite polarities, and identifying a rotational position of said rotor relative to said windings based on the sign of the time difference between the rise time of the responses to said pulses applied to the same selected winding.
Specification