Electric motor fault detection

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.

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.