Operation of an electrical machine
An electrical machine is controlled without using a physical rotor position detector. Rotor position is estimated by an algorithm which receives feedback from a parameter which represents the behavior of a phase of the machine. Before the algorithm estimates position, it checks the value of the parameter to ensure that the phase is healthy. In the event of the parameter indicating that the phase is faulty, the algorithm does not attempt to estimate position from that phase, thereby avoiding the generation of faulty position data. Operation of the machine may be continued using only the healthy phases.
1. A method comprising operating a polyphase electric machine using a control algorithm which includes rotor position estimation using at least one parameter which is obtained from the phases of the machine, including:
monitoring the at least one parameter to obtain a parameter value for each phase;
determining whether the parameter value is within a set of values appropriate for operation of the machine; and
preventing any parameter value that is not within the set of values from being used to estimate rotor position.
2. A method as claimed in claim 1 in which the determining includes determining the magnitude of the parameter.
3. A method as claimed in claim 1 in which the parameter is phase current.
4. A method as claimed in claim 1 in which the determining includes timing a period for monitoring the parameter; and deriving the parameter value from monitoring the parameter within the period.
5. A method as claimed in claim 1 in which the machine is a switched reluctance machine.
6. A computer executable medium loaded with a program for executing the method of claim 1 when loaded on a computer.
7. A method as claimed in claim 1 , wherein the operating further includes overriding the operation of the machine according to said control algorithm for a phase for which the parameter value is not within the set of values.
8. A method as claimed in claim 7 , in which the overriding includes inhibiting energization of said phase.
9. A method as claimed in claim 8 , in which the overriding is executed for said phase for subsequent cycles of the machine.
10. A method as claimed in claim 7 , including terminating the overriding for the phase when the parameter value for that phase is determined in at least one subsequent machine cycle to be within the set of values.
11. A method as claimed in claim 1 , wherein the operating includes continuing to estimate rotor position based on phases other than the phase for which the parameter value is not within the set of values.
12. A method as claimed in claim 1 , wherein the operating includes carrying out the rotor position estimation using a running average of the parameter values that are obtained during the monitoring; and wherein the preventing includes ignoring each parameter value that is not within the set of values when calculating the running average.
13. An apparatus comprising a system for operating a polyphase electrical machine, said system including:
first means for executing a control algorithm which includes rotor position estimation using at least one parameter which is obtained from phases of the machine;
second means for monitoring the at least one parameter to obtain a parameter value for each phase; and
third means for determining whether the parameter value is within a set of values appropriate for operation of the machine; and
wherein said first means is responsive to a determination by said third means that a parameter value is not within the set of values for preventing that parameter value from being used by said first means for estimating rotor position.
14. An apparatus as claimed in claim 13 , in which the third means is operable to determine the magnitude of the parameter.
15. An apparatus as claimed in claim 13 in which the parameter is phase current.
16. An apparatus as claimed in claim 13 including timer means for setting a period for the second means to monitor the parameter.
17. An apparatus claimed in claim 13 further comprising a reluctance machine, said system being coupled to and arranged to operate the reluctance machine.
18. An apparatus as claimed in claim 13 wherein said system further includes fourth means responsive to a determination by said third means that a parameter value is not within said range of values for overriding the operation of the machine according to said control algorithm for the phase for which the parameter value is not within the set of values.
19. An apparatus as claimed claim 18 in which the fourth means is operable to inhibit energization of said phase.
20. An apparatus as claimed in claim 18 , wherein said fourth means is operable for terminating the overriding of the phase in response to a determination by said third means in at least one subsequent machine cycle that the parameter value for that phase is within the set of values.
21. An apparatus as claimed in claim 19 in which the fourth means is operable to inhibit energization of said phase for subsequent cycles of the machine.
22. An apparatus as claimed in claim 13 , wherein said first means is operable for continuing to estimate rotor position based on phases other than the phase for which the parameter value is not within the set of values.
23. An apparatus as claimed in claim 13 , wherein said first means is operable for carrying out the rotor position estimation using a running average of the parameter values that are obtained during monitoring by said second means, including calculating the running average in a manner that ignores each parameter value that is not within the set of values.