Controller for a permanent magnet generator and a generator in combination with such a controller
View Patent ↗A generator controller for controlling a permanent magnet generator where each phase of the generator is connectable to a DC link via electrically controllable switches, the controller characterized by a data processor adapted to receive a measurement of generator current output and a demand current, and to form a current error between the demanded value and the measured generator current; derive a target voltage as a function of the current error; and form control signals for the electrically controllable switches as a function of the target voltage.
1. A method of controlling a permanent magnet generator where each phase of the generator is connectable to a DC link via electrically controllable switches, the method comprising the steps of:
i) receiving a measurement of generator current output and a demand current, and forming a current error between the demand current and the measured generator current;
ii) forming a target voltage phase angle as a function of a demanded power factor angle and a calculated current phase shift relative to a frame of reference and
iii) forming control signals for controlling the electrically controllable switches as a function of the target voltage and the voltage phase angle.
2. A method as claimed in claim 1 , in which the generator is a three phase generator and that measurements of the current are converted into a current vector having a magnitude and a phase with respect to a frame reference.
3. A method as claimed in claim 2 , in which the frame of reference acts as a common frame of reference for the current vector and a voltage vector.
4. A method as claimed in claim 2 , in which the frame of reference is an arbitrary frame of reference.
5. A method as claimed in claim 1 , in which a Clark's transform is used to convert measured generator currents from a phase-time based space into a further measurement space.
6. A method as claimed in claim 5 , in which a further transform is used to convert the values in the further measurement space to polar values such that the generator output current is represented by a magnitude and a phase angle.
7. A method as claimed in claim 1 , in which the current error is multiplied by a coefficient to produce a target voltage magnitude.
8. A method as claimed in claim 1 , in which one of the demanded current and the current error is used in the calculation of the voltage phase angle.
9. A method as claimed in claim 8 , in which one of the demanded current and the current error is used to calculate a compensating phase angle, which is combined with a demanded power factor angle and a current phase angle to produce the voltage phase angle.
10. A method as claimed in claim 9 , in which the current error is multiplied by a co-efficient to produce a target voltage magnitude, and that the target voltage magnitude and the voltage phase angle are transformed into phase voltages.
11. A method as claimed in claim 10 , in which the target voltage magnitude and voltage phase angle are operated on using an inverse Clark's transform.
12. A method as claimed in claim 10 , in which the target voltage is proportional to or partially proportional to the generator output current less the demanded current.
13. A computer program for causing a programmable data processor to execute the method of claim 1 .