Electric motor fault detection
An electric motor controller having fault detection comprises: a driver circuit configured to drive an electric motor in response to a received speed demand signal; a measurement circuit configured to measure current through windings of the electric motor, the measurement circuit comprising a back emf, BEMF, observer configured to determine an estimated BEMF value, a BEMF error threshold and an estimated rotor angular speed value from the measured currents; a detector circuit configured to receive the rotor speed demand signal, the estimated BEMF value, the BEMF error threshold, the estimated rotor angular speed value and a measured rotor speed from a rotor speed sensor on the electric motor and to detect a fault in the electric motor controller if the estimated BEMF value lies outside the BEMF error threshold and the measured rotor speed is within a defined rotor speed error threshold.
1. An electric motor controller comprising:
a driver circuit configured to drive an electric motor in response to a received speed demand signal;
a measurement circuit configured to measure current through windings of the electric motor, the measurement circuit comprising a back emf (BEMF) observer configured to determine an estimated BEMF value, a BEMF error threshold and an estimated rotor angular speed value from the measured currents;
a detector circuit configured to receive the rotor speed demand signal, the estimated BEMF value, the BEMF error threshold, the estimated rotor angular speed value and a measured rotor speed from a rotor speed sensor on the electric motor and to detect a fault in the electric motor controller if the estimated BEMF value lies outside the BEMF error threshold and the measured rotor speed is within a defined rotor speed error threshold.
2. The electric motor controller of claim 1 , wherein the detector circuit is configured to cause the driver circuit to disable the motor if a fault is detected.
3. The electric motor controller of claim 1 , wherein the detector circuit is configured to output a fault indication if a fault is detected.
4. The electric motor controller of claim 1 , wherein the rotor speed error threshold is defined from the rotor speed demand signal.
5. The electric motor controller of claim 1 , wherein the rotor speed error threshold is a range within around +/−10% of the rotor speed demand signal.
6. The electric motor controller of claim 1 , wherein the rotor speed error threshold is a range within around +/−5% of the rotor speed demand signal.
7. An electric motor system comprising:
an electric motor having a stator, a rotor and a rotor speed sensor connected to the rotor; and
an electric motor controller comprising:
a driver circuit configured to drive an electric motor in response to a received speed demand signal;
a measurement circuit configured to measure current through windings of the electric motor, the measurement circuit comprising a back emf (BEMF) observer configured to determine an estimated BEMF value, a BEMF error threshold and an estimated rotor angular speed value from the measured currents;
a detector circuit configured to receive the rotor speed demand signal, the estimated BEMF value, the BEMF error threshold, the estimated rotor angular speed value and a measured rotor speed from a rotor speed sensor on the electric motor and to detect a fault in the electric motor controller if the estimated BEMF value lies outside the BEMF error threshold and the measured rotor speed is within a defined rotor speed error threshold.
8. The electric motor system of claim 7 , wherein the electric motor is a permanent magnet synchronous motor.
9. A method of detecting a fault in an electric motor controller, the electric motor controller comprising:
a driver circuit configured to drive an electric motor in response to a received speed demand signal;
a measurement circuit configured to measure current through windings of the electric motor, the measurement circuit comprising a back emf (BEMF) observer configured to determine an estimated BEMF value, a BEMF error threshold and an estimated rotor angular speed value from the measured currents; and
a detector circuit configured to receive the rotor speed demand signal, the estimated BEMF value, the BEMF error threshold, the estimated rotor angular speed value and a measured rotor speed from a rotor speed sensor on the electric motor,
the method comprising the detector circuit detecting a fault in the electric motor controller if the estimated BEMF value lies outside the BEMF error threshold and the measured rotor speed is within a defined rotor speed error threshold.
10. The method of claim 9 , wherein the detector circuit causes the driver circuit to disable the motor if a fault is detected.
11. The method of claim 9 , wherein the detector circuit outputs a fault indication if a fault is detected.
12. The method of claim 9 , wherein the rotor speed error threshold is defined from the rotor speed demand signal.
13. The method of claim 9 , wherein the rotor speed error threshold is a range within around +/−10% of the rotor speed demand signal.
14. The method of claim 9 , wherein the rotor speed error threshold is a range within around +/−5% of the rotor speed demand signal.