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 successively running the machine with a series of assumed errors in the rpt signals and building up a set of test results. These results are subsequently compared with each other so as to determine the optimum value of corrections to the control system of the machine. The correction 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 of determining a compensation value for the output of a rotor position transducer (rpt) of an electric machine, the method comprising;
repeatedly operating the machine under predetermined conditions and with selected candidate values of compensation applied to the output of the rotor position transducer;
recording at least one parameter of the machine as a set of test results for the candidate values of rpt output compensation;
selecting from the test results a desired value of the rpt output compensation; and
subsequently using the desired value to compensate the output of the rotor position transducer.
2. A method as claimed in claim 1 in which the machine is operated, and the test results are recorded, in accordance with a stored program.
3. A method as claimed in claim 1 in which the machine is controlled by a controller, the desired value of rpt output compensation being stored in the controller.
4. A method as claimed in claim 1 in which the parameter is one or more selected from the group consisting of supply voltage, DC link current, torque, machine output ripple, machine rate of change of output, acceleration, efficiency, supply power factor, machine vibration, voltage and current harmonics, phase current, acoustic noise and temperature.
5. A method as claimed in claim 1 in which the candidate compensation values are automatically varied for each test.
6. A method as claimed in claim 1 in which the desired value of the rpt output compensation corresponds to that producing the maximum or minimum value of the at least one parameter recorded.
7. A method as claimed in claim 1 in which the machine is controlled by a controller, the program being stored in the controller.
8. Apparatus for determining a compensation value for the output of a rotor position transducer of an electric machine according to the method claim 1 , the apparatus comprising:
means for storing the test results; and
means for selecting from the test results the desired compensation value.
9. Apparatus as claimed in claim 8 in which the electrical machine is operably connected with a controller, the means for storing being integrated with the controller.
10. A method of determining a rotor position compensation value for a rotor position output of a rotor position transducer of an electric machine, the method comprising:
repeatedly operating the machine under predetermined conditions and with selected candidate values of rotor position compensation applied to the rotor position output of the rotor position transducer;
recording at least one parameter of the machine as a set of test results for the candidate values of rotor position compensation;
selecting from the teat results a desired value of the rotor position compensation: and
subsequently using the desired value to compensate the rotor position output of the rotor position transducer.