Method and apparatus for control of switched reluctance motors

1. A short pitched switched reluctance motor control apparatus comprising:

a voltage provider comprising a first coupling and a second coupling configured to be coupled to a phase winding of the switched reluctance motor for applying a voltage to drive current in the winding between the first and second coupling; and

a controller configured to apply a first voltage pulse to the first coupling, and to apply a second voltage pulse to the second coupling, wherein the start of the second pulse is delayed with respect to the start of the first pulse, and the end of the first pulse is delayed with respect to the end of the second pulse in which the controller is configured to time the pulses so that the centre of the first pulse is aligned with the centre of the second pulse.

2. The control apparatus of claim 1 wherein the voltage provider is operable to selectively apply voltage to the winding to drive current in the phase winding in a first direction and in a second direction opposite to the first direction.

3. The apparatus of claim 2 in which the controller is configured to control the voltage provider so that the current in the phase winding flows in the first direction for at least one cycle of the switched reluctance motor and in the second direction for at least one cycle of the switched reluctance motor.

4. The apparatus of claim 3 wherein the controller is configured to control the voltage provider so that the direction of the current alternates in successive cycles of the switched reluctance motor.

5. A short pitched switched reluctance motor control apparatus comprising:

a voltage provider comprising a first coupling and a second coupling configured to be coupled to a phase winding of the switched reluctance motor for applying a voltage to drive current in the winding between the first and second coupling in which the first coupling is coupled to a first supply voltage and to a second supply voltage by controlled impedances; and

a controller configured to apply a first voltage pulse to the first coupling, and to apply a second voltage pulse to the second coupling, wherein the start of the second pulse is delayed with respect to the start of the first pulse, and the end of the first pulse is delayed with respect to the end of the second pulse wherein the controller is operable to control the controlled impedances to control the voltage at the first coupling.

6. A short pitched switched reluctance motor control apparatus comprising:

a voltage provider comprising a first coupling and a second coupling configured to be coupled to a phase winding of the switched reluctance motor for applying a voltage to drive current in the winding between the first and second coupling in which the second coupling is coupled to a first supply voltage and to a second supply voltage by controlled impedances; and

a controller configured to apply a first voltage pulse to the first coupling, and to apply a second voltage pulse to the second coupling, wherein the start of the second pulse is delayed with respect to the start of the first pulse, and the end of the first pulse is delayed with respect to the end of the second pulse, wherein the controller is operable to control the controlled impedances to control the voltage at the second coupling.

7. The apparatus of claim 6 wherein the controlled impedances are arranged to provide a symmetric bridge such as an H-bridge.

8. The apparatus of claim 6 wherein the controller is configured to control the voltage provider to select the direction of current in the phase winding in successive cycles of the switched reluctance motor so as to balance the thermal load placed on the controlled impedances.

9. A short pitched switched reluctance motor control apparatus comprising:

a voltage provider comprising a first coupling and a second coupling configured to be coupled to a phase winding of the switched reluctance motor for applying a voltage to drive current in the winding between the first and second coupling; and

a controller configured to apply a first voltage pulse to the first coupling, and to apply a second voltage pulse to the second coupling, wherein the start of the second pulse is delayed with respect to the start of the first pulse, and the end of the first pulse is delayed with respect to the end of the second pulse;

wherein the voltage provider comprises controlled impedances arranged to provide an H-bridge, for example wherein the H-bridge is arranged to be electrically symmetric about a phase winding coupled to the voltage provider.

10. A of controlling a short pitched switched reluctance motor, the method comprising:

providing a first voltage pulse to a first coupling of a phase winding of the switched reluctance motor,

providing, to a second coupling of the phase winding, a second voltage pulse, delayed with respect to the start of the first pulse and wherein the end of the first voltage pulse is delayed with respect to the end of the second voltage pulse; and

wherein the voltage pulses are timed so that the centre of the first pulse is aligned with the centre of the second pulse.

11. The method of claim 10 comprising selecting the voltages of the first voltage pulse and the second voltage pulse so that current through the phase winding flows in a first direction for at least one cycle of the switched reluctance motor before flowing in a second direction, opposite to the first direction, for at least one cycle of the switched reluctance motor.

12. The method of claim 11 comprising alternating the direction of the current in successive cycles of the switched reluctance motor.

13. A tangible non-transitory computer-readable media carrying program instructions configured to program a processor of an electric motor controller to perform a method according to claim 10 .

14. A method of controlling current in a phase winding of a short pitched switched reluctance motor so that the current through the phase winding flows in the first direction for at least one cycle of the switched reluctance motor before flowing in the second direction for at least one cycle of the switched reluctance motor, further comprising alternating the direction of the current between successive cycles of the motor, wherein controlling the current comprises controlling a plurality of controlled impedances arranged to provide a an H-bridge for controlling the phase winding, the method further comprising selecting the alternation of current so as to balance thermal load placed on the controlled impedances.

15. A tangible non-transitory computer-readable media carrying program instructions configured to program a processor of an electric motor controller to perform a method according to claim 14 .

16. A system comprising at least a first apparatus and a second apparatus, wherein the first and second apparatus each comprise a short pitched switched reluctance motor control apparatus comprising:

a voltage provider comprising a first coupling and a second coupling configured to be coupled to a phase winding of the switched reluctance motor for applying a voltage to drive current in the winding between the first and second coupling; and

a controller configured to apply a first voltage pulse to the first coupling, and to apply a second voltage pulse to the second coupling, wherein the start of the second pulse is delayed with respect to the start of the first pulse, and the end of the first pulse is delayed with respect to the end of the second pulse;

wherein the controllers of the first apparatus and the second apparatus are arranged to control the timing of the currents in respective first phase and second phase windings of a switched reluctance motor to drive the motor, for example wherein the controllers are provided by a common controller adapted to control the voltage provider of both the first apparatus and the second apparatus, and wherein the controllers are configured to adjust the torque output from a short pitched SR motor by selecting the timing of a reversal in the direction of current in at least one of the first and second phase windings, wherein the torque adjustment is selected to reduce torque ripple and wherein the frequency of current reversals is selected based on the frequency of the torque ripple, wherein the timing of the current reversals is selected so that the contribution of the mutual inductance between the first and second phase windings combine additively with the contribution of the self-inductance to one of:

(a) increase the torque output from the motor; and

(b) reduce torque ripple.