Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
1999-07-29
2001-04-03
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000
Reexamination Certificate
active
06211634
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to field-commutated motors and machines incorporating such motors.
BACKGROUND OF THE INVENTION
FIG. 1
shows a simple schematic of a field-commutated motor
10
powered by a power supply
12
, and having a stator
16
and a rotor
20
. The stator mounts excitation coils
17
(A-A′, B-B′, C-C′ and D-D′), which are sequentially excited such that the coils act as magnets, having north and south poles, to generate forces on the permanent magnets
21
mounted on the rotor
20
, thereby rotating the rotor
20
. A knowledge of the position of the rotor magnets
21
relative to the coils
17
is necessary for the coils to be excited in the proper sequence and with the proper timing to provide the desired torque, speed or direction of rotation of the rotor
20
. Typically, a sensor
22
provides raw data representative of the rotor angular position in a “sensor”, or uncalibrated, coordinate system. However, this data must be used to determine the position of the magnets
21
relative to the coils
17
. Initialization of the motor, as used herein, refers to determining the relationship between the uncalibrated coordinate system and a coordinate system having a known relationship to the excitation coils
17
, such that the relationship of the magnets
21
to the coils can be determined from the raw, or uncalibrated, angular data. The raw data is initialized and the initialized data is used in sequencing and timing the excitation of the coils
17
.
Initialization of the motor
10
can be rather straightforward if the motor
10
is accessible and not under load. Excitation of the stator
16
with a test voltage of a known orientation produces a known angular position of the rotor
20
, because the load angle is zero. The raw data from the sensor
22
, giving an angle in the uncalibrated coordinate system, can be related to a q-d rotor coordinate system, where d is the axis of the magnets
21
and q is the quadrature axis, such that the “error angle” between the uncalibrated and rotor coordinate system is determined. As the relationship between the q-d rotor coordinate system and the excitation coils
17
is known, the error angle is then used during operation of the motor to properly excite the coils
17
to obtain the desired performance of the motor
10
. Accordingly, initialization is not necessarily a difficult problem at the motor factory.
However, initialization as above requires that motors shipped from the factory include the sensor
22
and be subsequently carefully handled such that the physical relationship between the sensor
22
and rotor
20
is not disturbed. Such motors are often installed in complex machinery, such as elevators, at the site where the machinery is to be installed. Installation provides yet another opportunity for the initialization to be disturbed. Initialization, or re initialization, of an installed motor is tedious. The motor
10
is typically under load, and the load (e.g., the elevator) must be manually manipulated, such as by adjusting cables, to remove the load to allow the initialization procedure outlined above to be followed. Such manipulation can be time consuming and require additional personnel. Replacement in the field of a failed sensor
22
similarly requires removal of the load or installation of a new initialized motor including a new sensor
22
. A simpler and more efficient initialization procedure would represent a useful advance in the art.
Accordingly, it is an object of the present invention to address one or more of the aforementioned deficiencies and disadvantages of the prior art.
Other objects will in part appear hereinafter and in part be apparent to one of ordinary skill in light of the disclosure herein.
SUMMARY OF THE INVENTION
The present invention addresses the above object by providing methods and apparatus for calibrating a field-commutated motor when the motor is under non-zero load. Accordingly, zeroing of the load on the motor can be avoided, saving time and effort otherwise expended in commissioning apparatus incorporating the motor therein, such as an elevator.
A method according to one aspect of the invention includes the steps of: applying a first voltage of a first orientation and of a first magnitude to one of the rotor and the stator; determining a first rotor angle corresponding to application of the first voltage; applying a second voltage to the one of the rotor and the stator, the second voltage having an orientation substantially equal to the first orientation and a second magnitude different from the first magnitude, the second voltage being applied when the motor is under a load substantially equal to the load applied during the application of the first voltage; determining a second rotor angle corresponding to the application of the second voltage; and determining an error angle, as a function of at least the first and second rotor angles, for allowing calibration of the motor. The first and second voltages, or one or both of the respective currents that respectively correspond thereto, are used in the determination of the error angle. As is understood by one of ordinary skill, in light of the disclosure herein, the stationary currents and voltages are related by the resistance of the stator.
In another aspect of the invention, apparatus is disclosed for initializing and operating a field-commutated motor in accordance with the methods disclosed herein. The apparatus can include a processor, a sensor for determining rotor angular position, and a power supply. The processor is in electrical communication with the sensor and power supply, and includes provision, such as a hardware configuration or appropriate programming with software, for performing the above initialization and operating the motor. Processor, as used herein, can refer to specialized processor for initializing motors to determine the error angle, or to a more general processor, that in addition to calibrating the motor, operates the motor for use of the apparatus in which the motor is installed.
These and other features of the invention are more fully set forth below.
REFERENCES:
patent: 4561093 (1985-12-01), Doane et al.
patent: 5008608 (1991-04-01), Unsworth et al.
patent: 5274317 (1993-12-01), Utley et al.
patent: 5635810 (1997-06-01), Goel
patent: 5838122 (1998-11-01), Vu
patent: 5883344 (1999-03-01), Colby et al.
patent: 6051946 (2000-04-01), Yamada et al.
patent: 6111385 (2000-08-01), Nozaki et al.
patent: 0 490 024 A1 (1991-06-01), None
M. Stiebler, Y. Li, ETEP, Vol.9.No., Jan./Feb. 1999, pp. 43 through 47, “Detection of the Rotor Position of a Permanent-Magnet Synchronous Motor at Standstill”.
Peter B. Schmidt, et al., IEEE Industry Applications Society, Rockwell Automation, Pub. Date May 10, 1997, pp. 459 thru 463 “Initial Rotor Angle Detection of a Non-Silent Pole Permanent Magnet Synchronous Machine”.
Ernecke Christoph
Heller Marcus C.
Mann Michael
Duda Rina I.
Nappi Robert E.
Otis Elevator Company
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