Sensorless commutation position detection for brushless motors
First Claim
1. A method for determining a commutation position of a polyphase brushless motor having a plurality of field coils disposed about a rotor, said plurality of field coils having at least one active field coil for receiving a driving signal to generate a magnetic field that exerts the maximum amount of torque on said rotor, comprising the steps of:
- (a) selectively energizing said at least one active field coil with said driving signal, said driving signal comprising a voltage pulse train of successive on and off pulses;
(b) continuously monitoring the current waveform of said at least one active field coil during said step of selectively energizing;
(c) continuously normalizing said current waveform to define a normalized current waveform;
(d) continuously differentiating said normalized current waveform to define a current rate of change waveform; and
(e) continuously comparing said current rate of change waveform to a predetermined voltage threshold value to determine the commutation point, said commutation point being the point in time at which said current rate of change waveform fails to intersect said predetermined voltage threshold.
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Accused Products
Abstract
A method and apparatus for the sensorless determination of commutation position in a brushless motor. The electric current flowing within the active, or energized, stator coil during energization is differentiated to produce a current rate of change waveform. The current rate of change waveform is compared to a predetermined voltage threshold which is set to approximate the point at which the rotor is in direct positional alignment with the active stator. From this comparison, it is determined when the current rate of change waveform fails to intersect the predetermined voltage threshold. This information may be used to commutate the application of a driving signal to the next stator coil in succession to maintain continuous torque on the rotor. This information may also be indicative of a stalled condition, in which case a stall indicator is triggered to alert the user of the stalled condition.
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Citations
15 Claims
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1. A method for determining a commutation position of a polyphase brushless motor having a plurality of field coils disposed about a rotor, said plurality of field coils having at least one active field coil for receiving a driving signal to generate a magnetic field that exerts the maximum amount of torque on said rotor, comprising the steps of:
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(a) selectively energizing said at least one active field coil with said driving signal, said driving signal comprising a voltage pulse train of successive on and off pulses; (b) continuously monitoring the current waveform of said at least one active field coil during said step of selectively energizing; (c) continuously normalizing said current waveform to define a normalized current waveform; (d) continuously differentiating said normalized current waveform to define a current rate of change waveform; and (e) continuously comparing said current rate of change waveform to a predetermined voltage threshold value to determine the commutation point, said commutation point being the point in time at which said current rate of change waveform fails to intersect said predetermined voltage threshold. - View Dependent Claims (2, 3, 4)
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5. A method for commutating a brushless polyphase motor having a rotor and at least one active stator coil, comprising the steps of:
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(a) applying a driving signal to said at least one active stator coil; (b) normalizing said amount of electric current flowing within said active stator coil during step (a); (c) continuously differentiating the normalized electric current from step (b); and (d) continuously monitoring the normalized electric current from step (c) to determine when said rotor has reached a commutation point. - View Dependent Claims (6, 7, 8, 9)
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10. An apparatus for detecting a position of a commutator of a motor during commutation, comprising:
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a brushless motor having a plurality of coils and a rotor; commutation means for generating a driving signal, said commutation signal defining at least one active stator coil from said plurality of stator coils to receive said driving signal, said driving signal being pulsed to successively energize said at least one active stator coil to exert rotational torque on the rotor; electric current sensing means for sensing the electric current waveform flowing within each of said plurality of coils in response to said stator coil driving signal; normalization means for normalizing the current flowing within said active stator coil during the application of said stator coil driving signal to said active stator coil; differentiating means for continuously differentiating the electric current normalized by said normalization means; comparator means for comparing the electric current differentiated by said differentiating means to a predetermined voltage threshold value; and detection means for detecting a commutation point on the output of said comparator. - View Dependent Claims (11)
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12. A method for determining a position of a rotor with respect to a stator coil within a commutation cycle of a polyphase brushless motor, comprising the steps of:
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(a) energizing said stator coil with a voltage pulse train of sequential on and off pulses; (b) continuously measuring the amount of electric current flowing within said stator coil during step (a); (c) continuously differentiating the amount of electric current determined in step (b); (d) continuously comparing the amount of electric current differentiated in step (c) with a predetermined voltage threshold to identify the rate at which the amount of current differentiated in step (b) intersects a predetermined voltage threshold level. - View Dependent Claims (13, 14, 15)
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Specification