Method and apparatus for electronically commutating a direct current motor without position sensors

• US 4,162,435 A
• Filed: 10/05/1976
• Issued: 07/24/1979
• Est. Priority Date: 10/05/1976
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Wright, Floyd H.
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Indyk, Eugene S.
• Application Number:
  US05/729,804
• Time in Patent Office: 1,022 Days
• Field of Search: 318/138, 318/254, 318/439
• US Class Current: 318/400.04
• CPC Class Codes: H02K 29/10 using light effect devices
• CPC Class Codes: H02P 6/182 using back-emf in windings

Abstract

Method and apparatus for electronically commutating a direct current motor is disclosed not requiring position sensors but rather sampling induced voltage across an unenergized motor winding to derive control signals therefrom. One motor winding is energized while the voltage across another winding is sampled and integrated to provide a flux indication. The integrated voltage sample is compared to a reference and when that integrated value exceeds the reference, the next winding of the motor is enabled and the voltage integral returned to an initial value. A ring counter maintains an indication of the currently energized winding and may also be employed to cause the sampling circuit to sample the induced voltage on the winding next in the motor sequence to be energized.

Claims

1. The method of providing commutating signals for a brushless direct current motor having a stationary armature with a longitudinal axis, a plurality of stator windings disposed in the armature to produce magnetic fields in response to selective winding energization, and a permanent magnet rotor adapted to rotate about the longitudinal axis in response to magnetic fields established by the selective winding energization comprising sequentially repeating the steps of:

energizing at least one of the plurality of stator windings;

selecting an unenergized winding which is another one of the plurality of windings available for energization for causing rotational movement of the permanent magnet rotor;

sampling the induced voltage across the selected unenergized winding during a sampling interval;

integrating the induced voltage during the sampling interval for developing a voltage integral with the integrating being initiated from a preselected initial integral value;

comparing the voltage integral to a predetermined reference voltage level which is indicative of a predetermined relative angular position of the permanent magnet rotor; and

returning the voltage integral to the initial value whereby integration of induced voltage of another unenergized winding may be subsequently performed and energizing another winding when the voltage integral exceeds the reference voltage level thereby providing selective commutation of the motor windings independently of rotor speed and in accordance with the relative position of the permanent magnet rotor.

2. The method of claim 1 wherein the step of integrating is performed over a time interval shorter than the time during which the at least one winding is energized.

3. The method of claim 2 wherein the step of integrating is initiated a short time after the at least one winding is energized.

4. The method of claim 1 including the further steps of retaining a digital indication of the at least one winding being energized and changing that digital indication when the voltage integral exceeds the reference voltage.

5. A commutation circuit for a brushless direct current motor comprising a stationary armature having a longitudinal axis, a plurality of stator windings disposed on said armature to produce magnetic fields, a permanent magnet rotor adapted to rotate about said axis in response to magnetic field established by said armature, said commutation circuit comprising:

counter means identifying an energized winding;

means for sampling the induced voltage in a winding not currently energized;

said means for sampling responsive to the counter means for selecting a winding not currently energized and for establishing a sampling interval;

means for integrating having an integration mode and an initial state, and connected to the means for sampling for integrating the induced voltage during the sampling interval for developing a voltage integral;

a comparator for comparing the voltage integral to a predetermined reference voltage level and providing an output signal when the voltage integral exceeds the reference voltage level thereby indicating that the permanent magnet rotor has reached a predetermined relative angular position;

means responsive to the comparator output signal for returning the integrating means to its initial state thereby readying the integrating means for responding to induced voltage of another selected unenergized winging and for incrementing the counter means for identifying still another winding to be energized.

6. The commutation circuit of claim 5 wherein the counter means comprises a ring counter.

7. The commutation circuit of claim 5 wherein the means responsive to the comparator output signal includes a one-shot timer for resetting the means for integrating, and a differentiating circuit responsive to the one-shot timer for incrementing the counter means.

8. The commutation circuit of claim 5 wherein the means for sampling includes a plurality of electrically actuable switches each in series with a motor winding lead and responsive to the counter means to sample an induced voltage in a winding not then identified by the counter means as being energized.

9. The commutation circuit of claim 8 wherein the counter means enables the means for sampling the winding next to be energized.

10. A commutation circuit for a brushless direct current motor comprising a stationary armature having a longitudinal axis, a plurality of stator windings disposed on said armature to produce magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic field established by said armature, said commutation circuit comprising:

counter means identifying an energized winding;

means for sampling the induced voltage in a winding not currently energized;

said means for sampling responsive to the counter means for selecting a winding not currently energized and for establishing a sampling interval;

means for integrating having an integration mode and an initial state, and connected to the means for sampling for integrating the induced voltage during the sampling interval for developing a voltage integral;

a comparator for comparing the voltage integral to a predetermined reference voltage level and providing an output signal when the voltage integral exceeds the reference voltage level thereby indicating that the permanent magnet rotor has reached a predetermined relative angular position;

means responsive to the comparator output signal for returning the integrating means to it initial state thereby readying the integrating means for responding to induced voltage of another selected unenergized winding and for incrementing the counter means thereby identifying still another winding to be energized; and

power circuit means responsive to the counter means for deenergizing a winding and energizing another winding in response to the incrementing of the counter means and thereby commutating the windings at the predetermined relative angular position of the permanent magnet rotor regardless of the rotor speed in accordance with the value of the integral of the induced voltage in an unenergized winding which is indicative of the relative angular position of the permanent magnet rotor.

11. The commutation circuit of claim 10 wherein the means responsive to the comparator output signal includes a one-shot timer for resetting the means for integrating, and a differentiating circuit responsive to the one-shot timer for incrementing the counter means.

12. The commutation circuit of claim 10 wherein the means for sampling includes a plurality of electrically actuable switches each in series with a motor winding lead and responsive to the counter means to sample an induced voltage in a winding not then identified by the counter means as being energized.

13. The commutation circuit of claim 10 wherein said counter means is operably connected to cause operation of said power circuit means without being subjected to winding energization voltage.