Rotor position detection in an electrical machine
An electrical machine has a rotor position transducer which provides output signals to a control system. The output signals contain errors due to component shortcomings and manufacturing imperfections. A method is disclosed which is able to determine the errors in the signals by the use of a position detection algorithm so as to provide compensations to the control system of the machine. The compensations may be stored in the control system and used to improve the accuracy of the transducer output signals, thus improving the output of the machine.
1. A method comprising:
determining error in the output of a rotor position transducer that directly detects a position of a rotor of an electrical machine and that outputs first signals, the determining including:
operating the electrical machine so as to produce the first signals and to produce, from a sensorless position detection algorithm, second signals representing an estimate of the position of the rotor, the sensorless position detection algorithm producing the second signals independently of and without reference to the first signals; and
comparing the first and second signals to produce an error value representing the error in the output of the rotor position transducer; and storing the error value;
wherein the rotor position transducer provides binary first signals and is arranged in relation to the rotor of the electrical machine to produce no more than two transitions in the binary first signals in a phase inductance cycle.
2. A method as claimed in claim 1 in which the electrical machine is controlled by a controller, and wherein the storing of the error value includes storing the error value in the controller.
3. A method as claimed in claim 1 in which the machine is operated as an electrical generator when determining the error.
4. A method as claimed in claim 1 in which the machine is operated as a motor when determining the error.
5. A method as claimed in claim 1 in which the sensorless position detection algorithm is selected from the group consisting of a predictor/corrector model, a diagnostic pulse scheme, a current wave shape detection algorithm, and an inductance profile interrogation algorithm.
6. A method as claimed in claim 1 , including using the stored error value to compensate the first signals for error therein.
7. A method as claimed in claim 1 , including selecting as the electrical machine a switched reluctance machine.
8. A method as claimed in claim 2 in which the sensorless position detection algorithm is stored in the controller.
9. Apparatus comprising:
a rotor position transducer that directly detects a position of a rotor of an electrical machine and that outputs first signals;
means for carrying out a sensorless position detection algorithm that produces second signals representing an estimate of the position of the rotor, the sensorless position detection algorithm producing the second signals independently of and without reference to the first signals;
control means for operating the electrical machine so as to produce the first and second signals; and
means for comparing the first and second signals to produce an error value representing error in the output of the rotor position transducer;
wherein the rotor position transducer provides binary first signals and is arranged in relation to the rotor of the electrical machine to produce no more than two transitions in the binary signals in a phase inductance cycle of the machine.
10. Apparatus as claimed in claim 9 in which the control means for operating the machine is operable to store the error value.
11. Apparatus as claimed in claim 9 in which the control means is operable to use the error value in relation to the first signals from the rotor position transducer as error compensation.
12. Apparatus as claimed in claim 9 in which the control means is operable to operate the machine as an electrical generator or a motor.
13. An electric machine drive comprising apparatus as claimed in claim 9 and an electric machine having a moving part in relation to which the rotor position transducer is arranged to produce the first signals.
14. Apparatus as claimed in claim 9 wherein the machine is a switched reluctance machine.
15. Apparatus as claimed in claim 10 in which the means for carrying out the sensorless position detection algorithm is part of the control means for operating the machine.