Sensorless Drive for Unipolar Three Phase Brushless DC Motors
First Claim
1. A system for controlling a brushless DC motor, including:
- a unipolar motor commutation circuit adapted to be coupled between a DC power supply and a brushless DC motor that includes first, second, and third stator windings corresponding to first, second and third motor phases, the stator windings having respective first, second, and third proximal end terminals coupled to a common node and having respective first, second, and third remote end terminals remote from the common node, the commutation circuit further being adapted to maintain each of the stator windings in one of two alternative states including an active state applying a predetermined drive voltage across the stator winding to drive the stator winding, and an inactive state in which the stator winding is not driven;
a controller operatively coupled to the commutation circuit to selectively apply the alternative states individually to different ones of the stator windings to operate the DC motor according to a commutation cycle including a plurality of primary commutation cycle steps arranged in a sequence over a motor electrical rotation of 360 degrees, wherein during each one of the primary commutation steps, a selected one of the stator windings is driven while the remaining two stator windings are in the inactive state;
a voltage sensor electrically coupled to the stator windings and adapted to generate first, second, and third phase-specific voltage signals corresponding respectively to the first, second, and third stator windings; and
a timing signal generator coupled to receive the phase-specific voltage signals, adapted to select the phase-specific voltage signals of the two stator windings in the inactive state during a given one of the primary commutation steps and to generate a timing signal responsive to each coincidence in the voltage levels of the selected phase-specific voltage signals;
wherein the controller includes a commutation circuit control function coupled to receive the timing signals and adapted to use the timing signals to determine motor position and speed.
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Accused Products
Abstract
A system for controlling a trapezoidally (square wave) driven DC motor includes a unipolar commutation circuit coupled between a DC power supply and a brushless DC motor. The motor has three phases formed by respective stator windings coupled at respective proximal ends to a common node and having respective opposite ends remote from the common node. The commutation circuit drives the motor according to a commutation cycle including three primary steps. During each primary step, one of the phases is driven while the other two phases are not driven. Voltages at the remote ends of the undriven phases are sensed, and timing signals are generated at points where the voltages coincide. The timing signals are used to determine motor position and speed, and to synchronize the commutation cycle with motor position and speed. In one embodiment, the commutation cycle includes transitional steps between the primary steps for smoother operation. The system is compatible with high side and low side switching configurations.
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Citations
27 Claims
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1. A system for controlling a brushless DC motor, including:
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a unipolar motor commutation circuit adapted to be coupled between a DC power supply and a brushless DC motor that includes first, second, and third stator windings corresponding to first, second and third motor phases, the stator windings having respective first, second, and third proximal end terminals coupled to a common node and having respective first, second, and third remote end terminals remote from the common node, the commutation circuit further being adapted to maintain each of the stator windings in one of two alternative states including an active state applying a predetermined drive voltage across the stator winding to drive the stator winding, and an inactive state in which the stator winding is not driven; a controller operatively coupled to the commutation circuit to selectively apply the alternative states individually to different ones of the stator windings to operate the DC motor according to a commutation cycle including a plurality of primary commutation cycle steps arranged in a sequence over a motor electrical rotation of 360 degrees, wherein during each one of the primary commutation steps, a selected one of the stator windings is driven while the remaining two stator windings are in the inactive state; a voltage sensor electrically coupled to the stator windings and adapted to generate first, second, and third phase-specific voltage signals corresponding respectively to the first, second, and third stator windings; and a timing signal generator coupled to receive the phase-specific voltage signals, adapted to select the phase-specific voltage signals of the two stator windings in the inactive state during a given one of the primary commutation steps and to generate a timing signal responsive to each coincidence in the voltage levels of the selected phase-specific voltage signals; wherein the controller includes a commutation circuit control function coupled to receive the timing signals and adapted to use the timing signals to determine motor position and speed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A device for controlling an electrically commutated motor, including:
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a voltage level sensor including at least three voltage sensing terminals adapted to be coupled to different stator windings to receive voltage information corresponding to their associated stator windings wherein the stator windings are coupled to a common node and correspond to three different motor phases of an electrically commutated motor; a commutation circuit controller adapted to be coupled to a unipolar commutation circuit of an electrically commutated motor to provide control signals to the commutation circuit to operate the commutation circuit according to a commutation cycle having commutation cycle segments arranged in a sequence over a motor electrical rotation of 360 degrees including a plurality of primary commutation cycle segments during which a given one of the stator windings is driven while the remaining two stator windings are not driven; and
;a timing signal generating function operatively associated with the voltage level sensor to receive the voltage information, operative during a given primary commutation cycle segment to select voltage levels of the two stator windings that are not driven during the given primary commutation cycle segment, and further adapted to generate a timing signal responsive to each coincidence of the selected voltage levels; wherein the commutation circuit controller comprises a commutation circuit control function coupled to receive the timing signals and adapted to use the timing signals to govern provision of the control signals to the commutation circuit. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. In a brushless DC motor configuration having a unipolar driver, a process for maintaining a commutation cycle synchronized with motor position and speed, including:
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sensing voltages at a plurality of stator windings corresponding to three different phases of a DC motor operated according to a commutation cycle including a plurality of primary commutation cycle segments arranged in a sequence over 360 degrees of electrical rotation during which a given one of the phases is driven by applying a predetermined drive voltage across each stator winding corresponding to the given phase while the other two phases are undriven; during each of a plurality of the primary commutation cycle segments, comparing first and second voltages corresponding individually to the undriven phases and generating a timing signal responsive to detecting a coincidence of the first and second voltages; and using the timing signals to indicate current angular or temporal motor positions and project future angular or temporal motor positions, to govern operation of the commutation cycle in a manner tending to synchronize the commutation cycle with motor position and speed. - View Dependent Claims (19, 20, 21, 22, 23)
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24. In a unipolar electrically commutated DC motor and driver configuration, a process for synchronizing a commutation cycle with motor position and speed, including:
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operating a three phase brushless DC motor with a unipolar driver according to a commutation cycle comprising primary commutation cycle steps during which one of the phases is driven while the other two phases are not driven; and while so operating the motor; (i) monitoring voltages of the undriven phases during the primary commutation cycle steps to detect coincidence episodes in which voltages of the undriven phases coincide; (ii) using the coincidence episodes as timing signals to project future timing points at which the voltages of the undriven phases are expected to coincide; (iii) upon reaching a selected one of the projected future timing points, measuring the voltages of the undriven phases to determine whether a voltage difference between said voltages at the selected timing point has a non-zero value; and (iv) responsive to determining that the voltage difference has a non-zero value, generating an error signal based on the voltage difference and using the error signal to bring the commutation cycle into a more synchronous relation to motor position and speed. - View Dependent Claims (25, 26, 27)
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Specification