Brushless DC spindle motor startup control
First Claim
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1. A multi-mode control method for controlling startup of a polyphase brushless DC motor comprising the steps of:
- determining with a programmed digital microcontroller an angular position of a rotor of the DC motor having a first plurality of permanent magnets and magnetic poles, and a stator having a core defining a second plurality of pole segments generally facing the magnetic poles and phase windings formed around the pole segments during a first operational mode,generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with the programmed digital controller based upon determined angular position of the rotor,applying the initial commutation sequence to the phase windings to start rotation of the rotor in a forward direction, without reverse rotation, with rotor angular position leading electrical phase angle of the initial commutation sequence,monitoring back-EMF induced in the phase windings to determine rotor angular position relative to the initial commutation sequence to determine a cross-over between rotor angular position and electrical phase angle of the initial commutation sequence during a second operational mode, andgenerating a back-EMF commutation sequence with a motor controller from monitored back-EMF and commutating the motor with the back-EMF commutation sequence following the cross-over, during a third operational mode.
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Abstract
Angular position of a polyphase brushless DC motor rotor is determined by the steps of generating a sequence of pulses with a programmed digital microcontroller, sequentially applying the pulses to selected ones of the plural windings or winding pairs, and sequentially measuring differential inductive coupling between the selected ones of the windings and selected others of the windings without rotating the rotor. Once angular position is determined, a multi-mode startup sequence is carried out to spin up the motor to a desired rotational velocity without any counter-rotation at startup.
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Citations
9 Claims
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1. A multi-mode control method for controlling startup of a polyphase brushless DC motor comprising the steps of:
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determining with a programmed digital microcontroller an angular position of a rotor of the DC motor having a first plurality of permanent magnets and magnetic poles, and a stator having a core defining a second plurality of pole segments generally facing the magnetic poles and phase windings formed around the pole segments during a first operational mode, generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with the programmed digital controller based upon determined angular position of the rotor, applying the initial commutation sequence to the phase windings to start rotation of the rotor in a forward direction, without reverse rotation, with rotor angular position leading electrical phase angle of the initial commutation sequence, monitoring back-EMF induced in the phase windings to determine rotor angular position relative to the initial commutation sequence to determine a cross-over between rotor angular position and electrical phase angle of the initial commutation sequence during a second operational mode, and generating a back-EMF commutation sequence with a motor controller from monitored back-EMF and commutating the motor with the back-EMF commutation sequence following the cross-over, during a third operational mode. - View Dependent Claims (2, 3, 4)
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5. A multi-mode control method for controlling startup of a polyphase brushless DC motor comprising the steps of:
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determining with a programmed digital microcontroller the angular position of a rotor of the DC motor having a first plurality of permanent magnets and magnetic poles, and a stator having a core defining a second plurality of pole segments during a first operational mode by the steps of; sequentially applying with the programmed digital microcontroller a driving current pulse at a power level below a level overcoming starting friction of the rotor successively and bidirectionally to each of the windings as a driven winding during a driving interval, sequentially measuring with an anolog-to-digital conversion means and the programmed digital microcontroller during a measuring interval immediately following the driving interval a response induced at a selected undriven winding of the core via inductive coupling of the stator core between the driven winding and the undriven winding, and determining with the programmed digital microcontroller the position of the rotor relative to the stator by identifying a driven winding and a current direction manifesting a lowest amplitude response in the selected undriven winding, generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with the programmed digital controller based upon determined angular position of the rotor in order to start rotation of the rotor in a forward direction without reverse rotation, applying the initial commutation sequence to the phase windings, monitoring back-EMF induced in the phase windings to determine rotor angular position relative to the initial commutation sequence to determine a cross-over between rotor angular position and electrical phase angle of the initial commutation sequence, during a second operational mode, generating a back-EMF commutation sequence with a motor controller from monitored back-EMF following the cross-over, including qualifying the back-EMF commutation sequence with the programmed digital microcontroller during a third operational mode until a predetermined rotational velocity is reached, and generating a back-EMF commutation sequence with the motor controller from monitored back-EMF without qualification by the programmed digital microcontroller after the predetermined rotational velocity is reached, during a forth operational mode.
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6. A method for determining the angular position of a rotor of a polyphase brushless DC motor for enabling startup in a forward direction of rotation without any reverse rotation, the motor including a rotor having a plurality of permanent magnets and magnetic poles and a stator having a core defining a different plurality of pole segments generally facing the magnetic poles and phase windings around the pole segments, the core becoming nearly saturated by the presence of magnetic fields emanating from the magnetic poles in the absence of any driving currents in the windings, comprising the steps of:
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sequentially applying a driving current pulse at a power level below a level overcoming starting friction of the rotor successively and bidirectionally to each of the windings as a driven winding during a driving interval thereby selectively to increase or decrease the level of magnetic saturation in the core, sequentially measuring during a measuring interval immediately following the driving interval a response induced at a selected undriven winding of the core via inductive coupling of the stator core between the driven winding and the undriven winding, the response being an inverse function of saturation level of the core, and determining rotor position relative to the stator by identifying a driven winding and a current direction manifesting a lowest amplitude response in the selected undriven winding. - View Dependent Claims (7, 8)
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9. A control method for controlling startup of a polyphase brushless DC motor having a movable rotor and phase windings, the method comprising the steps of generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with a programmed digital controller and a motor controller in order to start rotation of the rotor in a forward direction with rotor angular position leading electrical phase angle of the initial commutation sequence, applying the initial commutation sequence to the phase windings, monitoring back-EMF induced in the phase windings to determine rotor phase lead to determine convergence of rotor phase with an electrical phase angle of the commutation sequence and thereupon generating a back-EMF commutation sequence with the motor controller from monitored back-EMF and commutating the motor with the back-EMF commutation sequence following convergence.
Specification