Starting of switched reluctance generators
A switched reluctance drive is operated as a generator on a high voltage supply which has no long-term energy storage capability. A low voltage supply is used to start the generator through the use of a dedicated priming winding, which provides sufficient energy to allow the generator to build up charge in DC link capacitor(s). Once sufficient charge has built up, the priming winding is de-energized and the generator continues in a steady-state operation.
1. A switched reluctance generator comprising a rotor having a plurality of rotor poles, a stator having a plurality of stator poles, at least one phase winding for exciting two or more of the poles, a priming winding to excite two or more of the poles, and a priming power source separate from that used to excite the phase windings, wherein the priming power source is operably connected to the priming winding.
2. A switched reluctance generator according to claim 1 wherein the priming winding is energized while the rotor is being driven.
3. A switched reluctance generator according to claim 1 wherein the priming power source excites the priming winding independently of rotor position.
4. A switched reluctance generator according to claim 1 wherein the at least one phase winding is provided on the stator poles.
5. A switched reluctance generator according to claim 1 wherein the priming winding is provided on the stator.
6. A switched reluctance generator according to claim 5 wherein the priming winding extends along a longitudinal axis of the stator.
7. A switched reluctance generator according to claim 5 wherein the priming winding is of a gramme-ring type, wound around a back iron part of the stator.
8. A switched reluctance generator according to claim 5 wherein the priming winding is provided around at least one of the stator poles.
9. A switched reluctance generator according to claim 1 wherein the at least one phase winding is excitable by a DC link, the ratio of the voltage of the DC link to the supply voltage for the priming winding being greater than 3.
10. A switched reluctance generator according to claim 1 further comprising means for connecting the priming winding to the priming power source, the means for connecting comprising a switch, a chopper unit or a current controller.
11. A switched reluctance generator according to claim 1 wherein the priming winding and/or its associated priming power source, and/or associated connecting components, are rated for short-term use.
12. A method of starting a switched reluctance generator comprising a rotor having a plurality of rotor poles and a stator having a plurality of stator poles, at least one phase winding defining one or more phases, and at least one priming winding, the method comprising;
driving the rotor relative to the stator;
while the rotor is being driven, energizing the priming winding by forming an electrical connection between the priming winding and a source of electrical energy to excite two or more of the poles and to cause time-varying flux linkage in at least one of the phase windings; and
subsequently de-energizing the priming winding and energizing the phase winding(s) of the generator.
13. A method according to claim 12 wherein the switched reluctance generator is connected to a DC link and further comprising de-energizing the priming winding once the voltage of the DC link has reached a pre-determined value and subsequently energizing the phase winding(s) of the generator from the DC link.
14. A method according to claim 13 in which the DC link has a DC capacitor connected across the phase winding(s), the method further comprising:
charging the DC link capacitor by supplying current from the or each phase winding to the DC link capacitor and disconnecting the priming winding from the source once the voltage of the DC link capacitor has reached a pre-determined value.
15. A switched reluctance generator comprising a rotor having a plurality of rotor poles and a stator having a plurality of stator poles, at least one phase winding defining one or more phases, and at least one priming winding, the generator comprising;
means for driving the rotor relative to the stator;
means for energizing the priming winding, while the rotor is being driven, by forming an electrical connection between the priming winding and a source of electrical energy to excite two or more of the poles and to cause time-varying flux linkage in at least one of the phase windings; and
means for subsequently de-energizing the priming winding and energizing the phase winding(s) of the generator.
16. A switched reluctance generator according to claim 15 wherein the switched reluctance generator is connected to a DC link and further comprising means for de-energizing the priming winding once the voltage of the DC link has reached a pre-determined value and for subsequently energizing the phase winding(s) of the generator from the DC link.
17. A switched reluctance generator according to claim 16 wherein the DC link has a DC capacitor connected across the phase winding(s), the generator further comprising: means for charging the DC link capacitor by supplying current from the or each phase winding to the DC link capacitor and for disconnecting the priming winding from the source once the voltage of the DC link capacitor has reached a pre-determined value.
18. A switched reluctance generator comprising a rotor having a plurality of rotor poles, a stator having a plurality of stator poles and at least one phase winding arranged to be supplied from a DC link of a generator controller for exciting two or more of the poles and a priming winding arranged to excite two or more of the stator poles during a start procedure, thereby to establish a voltage of pre-determined value on the DC link.