Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-04-21
2001-10-30
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S139000, C318S434000, C318S715000, C318S716000, C318S718000, C318S719000, C318S720000, C318S721000
Reexamination Certificate
active
06310450
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to field of electric motors, and, more particularly, to a drive system for an electronically switched multi-phase motor and associated methods.
BACKGROUND OF THE INVENTION
The techniques for driving electronically switched multi-phase brushless motors commonly include forcing currents through the phase windings of the motor according to a voltage or current mode control and using Hall effect sensors for synchronizing the switchings. Depending on the number of phases, windings, and poles of the rotor, the driving system must command the phase switchings according to a proper sequential scheme. This scheme must be closely synchronized with the rotor's position to maximize efficiency and minimize ripple.
Frequently, in a three-phase motor with a rotor having two pairs of poles, the switching sequence has six phases, each phase being 60 electrical degrees. One of the techniques used for determining the rotor's instantaneous position is that of installing three Hall effect sensors. These sensors are commercially available and provide for three logic signals (codes) whose logic combination permits establishing the rotor's position and the correct phase to be excited.
In general, the decoding conventions of the logic signals produced by such sensors consider different schemes. These schemes depend upon the electrical sensors' phasing in terms of electrical degrees of separation, which in turn depends on the sensors' physical positions and the number of poles on the rotor. Therefore, by changing the sensors' physical positions and the number of rotor poles, there will be different sensor phasing, for example, of 60, 120, 240 and 300 electrical degrees.
Normally, the integrated devices installed in brushless motors for decoding signals produced by the Hall effect sensors and for processing the rotor's angular position (which are commonly used to realize the electronic driving systems) contemplate the possibility of pre-establishing which sensor phasing scheme must be selected for correctly decoding and processing the sensor signals. In practice, known devices dedicate one or more pins for presetting the decoding and processing circuit. Through these selection pins (or circuit nodes), an integrated circuit can be configured to decode signals originating from Hall effect sensors positioned at intervals of 120 electrical degrees, 60 electrical degrees, or even 240 or 300 electrical degrees.
An example of a commercially available decoding device is the MC33033 by Motorola. In this device, the selection of the actual angular separation between sensors of 60 or 120 electrical degrees is made through the pins
3
and
18
.
There is a need for a method and corresponding decoding circuit for decoding the logic signals produced by three Hall effect sensors relating to the instantaneous position of a rotor of a three-phase brushless motor. Such a decoding method and detection circuit should be capable of self recognizing, depending on the direction of rotation, the actual sensor positions, at intervals of either 60, 120, 300 or 240 electrical degrees, without the need for supplying such phasing information to the decoding circuit. Such a decoding method and circuit will permit the use of common devices without dedicating pins to allow for pre-setting phasing information, thus simplifying the manufacture of control systems for one or more brushless motors.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide for an improved decoding method for decoding the logic signals produced by three Hall effect sensors installed in a three-phase brushless motor. It is a further object of the invention to detect the instantaneous position of the rotor of such motor and to discriminate the actual sensors' positions at intervals of 60, 120, 240 and 300 electrical degrees to correctly decode the signals and identify the phase.
The invention is based on the fact that the signals provided by the three sensors produce a total of eight possible combinations. Six of these combinations are valid, for example, for a positioning at intervals of 60 electrical degrees, while another six are valid for a positioning at intervals of 120 electrical degrees; however, in both cases only two of the six combinations are specific to a 60 or 120 degree positioning, whereas four of the six combinations are identical in both cases. The sample is valid for the other two possible phasings of the sensors, i.e., 240 and 300 electrical degrees.
By decoding a full set of eight possible combinations of the signals originating from the three sensors, it is possible to recognize, from the two dissimilar combinations of the six combinations detected in an electrical turn, the effective phasing (i.e., the separation intervals in electrical degrees) of the three sensors. Therefore, the decoder may resolve the motor's position within a window of 60 electrical degrees for phasing of the sensors at 60, 120, 240 or 300 electrical degrees, without first supplying this phasing information to the decoding circuitry.
One prior art decoding circuit is pre-conditioned to decode the six combinations relative to a phasing of the sensors at intervals of either 60 electrical degrees or 120 electrical degrees. In contrast, the present invention decodes all eight possible input combinations and recognizes from the two dissimilar combinations which phasing (i.e., angular separation) is actually implemented. As such, the system processes the input combinations and determines the position of the rotor or the current phase of the running motor to permit the generation of the correct driving signals.
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Motorola Analog IC Device entitled “Brushless DC Motor Controller”, No. MC33033, (1996), pp. 1-24.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Jorgenson Lisa K.
Nappi Robert E.
Smith Tyrone
STMicroelectronics S.r.l.
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