Rotor resistance based motor thermal protection

A device for protecting an induction motor from thermal overload conditions, comprising:

• a processor;
• a storage unit communicatively coupled to the processor, the storage unit storing computer-readable instructions thereon for causing the processor to:
• compute a temperature rise estimate from a rotor resistance estimate for the induction motor;
• compute a motor thermal state estimate for the induction motor;
• compute an expected rotor temperature rise for the induction motor;
• check whether the temperature rise estimate exceeds the expected rotor temperature rise by more than a predefined threshold rotor temperature rise for the induction motor;
• and
• perform a corrective action in response to the temperature rise estimate exceeding the expected rotor temperature rise by more than the predefined threshold rotor temperature rise.

A non-transitory computer-readable medium containing program logic that, when executed by operation of one or more computer processors, causes the one or more computer processors to:

• compute rotor temperature rise estimates from rotor resistance estimates for an induction motor;
• compute motor thermal state estimates for the induction motor;
• derive a correlation between the thermal state estimates and the rotor temperature rise estimates;
• compute a new motor thermal state estimate for the induction motor;
• compute an expected rotor temperature rise for the induction motor using the correlation and the new motor thermal state;
• check whether the new temperature rise estimate exceeds the expected rotor temperature rise by more than a predefined threshold rotor temperature rise for the induction motor;
• and
• perform a corrective action in response to the new temperature rise estimate exceeding the expected rotor temperature rise by more than the predefined threshold rotor temperature rise.