Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
1998-06-15
2001-03-06
Donels, Jeffrey (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000
Reexamination Certificate
active
06198239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to switched reluctance motors, and, more particularly, to a method and a circuit for controlling the current in each motor phase of a switched reluctance motor between two predetermined current levels.
2. Disclosure of Related Art
A conventional switched reluctance motor (SRM) includes a stator having a plurality of pairs of diametrically opposed stator poles and a rotor having a plurality of pairs of diametrically opposed rotor poles. Windings or coils are typically disposed about the stator poles and the windings around any two diametrically opposed stator poles may be connected in series or in parallel to define one motor phase of the multiphase SRM. The windings associated with a motor phase may be referred to as a phase coil. By generating current through the phase coil, magnetic fields are established about the stator poles and a torque is produced that attracts a pair of rotor poles into alignment with the stator poles. The current in the phase coils is generated in a predetermined sequence in order to produce a constant torque on the rotor. The period during which current is provided to the phase coil—and the rotor poles are brought into alignment with the stator poles—is known as the “active stage” of the motor phase. At a certain point—either as the rotor poles become aligned with the stator poles or at some point prior thereto—it becomes desirable to commutate the current in the phase coil to prevent a negative or braking torque from acting on the rotor poles. Once this “commutation point” is reached, current is no longer generated in the phase coil and the current is allowed to dissipate from the phase coil. The period during which current is allowed to dissipate from the phase coil is known as the “inactive stage” of the motor phase.
SRMs typically employ pulse width modulation (PWM) or current chopping to control the current level in each phase coil during the active stage of the motor phase. Conventional circuits and methods for performing PWM or current chopping have often incorporated microprocessors. The use of microprocessors is disadvantageous, however, because it increases the cost of the motor and limits the bandwidth of electrical signals within the control system for the motor.
There is thus a need for an apparatus and method for controlling a switched reluctance motor that will minimize or eliminate one or more of the above-mentioned deficiencies.
SUMMARY OF THE INVENTION
The present invention provides a circuit and a method for controlling the level of a current in a phase coil of a switched reluctance motor phase.
An object of the present invention is to provide a circuit and a method for controlling the current in a phase coil that are less expensive than conventional circuits and methods.
Another object of the present invention is to provide a circuit and a method for controlling the current in a phase coil that allow for a greater bandwidth for electrical signals within the control system of the motor.
A circuit for controlling a level of current in a phase coil of a motor phase in accordance with the present invention includes a current sensor, such as a sensing resistor, that generates a current indicative signal indicative of the current level in the phase coil and first and second comparators that compare the current indicative signal to upper and lower hysteresis band limit signals, respectively. The circuit further includes a drive circuit, which may comprise a flip-flop circuit, that outputs a drive signal responsive to the first and second comparators. Finally, the circuit includes means, responsive to the drive signal generated by the drive circuit, for providing the current to the phase coil. In a preferred embodiment of the present invention, the providing means comprises first and second switches that are connected to first and second ends, respectively, of the phase coil. The first switch is responsive to the output of an AND gate that is in turn responsive to the drive signal and a phase control signal. The second switch is responsive to the phase control signal.
A method in accordance with the present invention includes the steps of generating a current indicative signal indicative of the current level in a phase coil, comparing the current indicative signal with an upper hysteresis band limit signal and generating a first comparison signal responsive thereto, and comparing the current indicative signal with a lower hysteresis band limit signal and generating a second comparison signal responsive thereto. The method further includes the steps of generating a drive signal responsive to the first and second comparison signals and providing the current to the phase coil responsive to the drive signal.
A circuit and method in accordance with the present invention represent an analog implementation of a conventional current control strategy for the active stage of an SRM motor phase. Because the circuit and method do not require the use of a microprocessor, the SRM and the control circuitry for the SRM are less expensive than conventional motors and motor controls. Moreover, because the inventive circuit and method do not require the use of a microprocessor, the electrical signals within the control system for the motor can operate within a greater bandwidth than is possible with conventional control circuits.
These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.
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Dana Corporation
Donels Jeffrey
Duda Rina
Dykema Gossett PLLC
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