Method and apparatus for motor lock or stall detection

1. A method for detecting a rotor lock condition in a sensorless permanent magnet synchronous motor, comprising:

determining a first estimated back electromotive force (BEMF) voltage value in an estimated rotor-related reference frame using a Luenberger-based BEMF observer;

calculating a second estimated BEMF voltage value in a rotor-related reference frame based on at least a first motor constant and an estimated rotor speed {circumflex over (ω)};

generating a BEMF error filter value from the first and second estimated BEMF voltage values;

generating a BEMF error threshold value by calculating a product of a BEMF threshold coefficient (C BEMFThresholdCoef ) and an absolute value of the estimated rotor speed {circumflex over (ω)}, subject to the minimum threshold BEMF value;

detecting a rotor lock condition in the sensorless permanent magnet synchronous motor based on at least the BEMF error filter value and the BEMF error threshold value; and

discontinuing application of power to the sensorless permanent magnet synchronous motor upon detecting the rotor lock condition.

2. The method of claim 1 , where determining the first estimated BEMF voltage value comprises computing a first estimated BEMF voltage value ê δ as a δ coordinate in virtual rotating reference frame (γ,δ).

3. The method of claim 1 , where calculating the second estimated BEMF voltage value comprises calculating a second estimated BEMF voltage value ê q =+c BemfCoef ·{circumflex over (ω)}+c BemfOffset ·sgn({circumflex over (ω)}) as a q coordinate in rotating reference frame (d,q), where c BemfCoef is a first BEMF coefficient term defined from a measurement on the motor, where C BemfOffset is a second BEMF offset coefficient defined from a measurement on the motor, and where the sgn({circumflex over (ω)}) term represents a sign function having a first output if {circumflex over (ω)}>0 and having a second output if {circumflex over (ω)}<0.

4. The method of claim 1 , where generating the BEMF error filter value comprises filtering an absolute value of a difference between the first and second estimated BEMF voltage values.

5. The method of claim 4 , where detecting the rotor lock condition comprises determining if an absolute value of the BEMF error filter value exceeds the BEMF error threshold value.

6. The method of claim 1 , where generating the BEMF error filter value comprises filtering a difference between the first and second estimated BEMF voltage values.

7. The method of claim 6 , where detecting the rotor lock condition comprises determining if an absolute value of the BEMF error filter value exceeds the BEMF error threshold value.

8. The method of claim 1 , where generating the BEMF error filter value comprises filtering a squared difference between the first and second estimated BEMF voltage values.

9. The method of claim 8 , where detecting the rotor lock condition comprises squaring the BEMF error threshold value to generate a squared BEMF error threshold value and determining if the BEMF error filter value exceeds the squared BEMF error threshold value.

10. The method of claim 1 , where generating the BEMF error filter value comprises filtering a difference between the first and second estimated BEMF voltage values which is normalized by multiplying by a nonlinear scaling function before filtering.

11. The method of claim 10 , where detecting the rotor lock condition comprises determining if an absolute value of the BEMF error filter value exceeds the BEMF error threshold value.

12. The method of claim 1 , where generating the BEMF error filter value comprises filtering a squared difference between the first and second estimated BEMF voltage values which is normalized by multiplying by a nonlinear scaling function before power by two calculation.

13. The method of claim 12 , where detecting the rotor lock condition comprises squaring the BEMF error threshold value to generate a squared BEMF error threshold value and determining if the BEMF error filter value exceeds the squared BEMF error threshold value.

14. The method of claim 1 , where detecting the rotor lock condition comprises detecting if an absolute value of the estimated rotor speed value {circumflex over (ω)} falls below a minimum stall speed (ω StallMin ).

15. An electric motor controller comprising:

a Luenberger-based back electromotive force (BEMF) observer for determining a first estimated BEMF voltage value in an estimated rotor-related reference frame and for determining an estimated rotor speed {circumflex over (ω)};

a processor coupled to the Luenberger-based BEMF EMF observer to calculate:

a second estimated BEMF voltage value in a rotor-related reference frame based on at least a first motor constant and the estimated rotor speed {circumflex over (ω)},

a BEMF error filter value based on a difference between the first and second estimated BEMF voltage values, and

a BEMF error threshold value {circumflex over (ω)} by calculating a product of a BEMF threshold coefficient (C BEMFThresholdCoef ) and an absolute value of the estimated rotor speed {circumflex over (ω)}, subject to the minimum threshold BEMF value; and

an electric motor driver circuit coupled to the processor for providing drive signals for controlling delivery of power to an electric motor;

where the processor is configured to detect if a rotor lock condition exists at the electric motor based on at least the BEMF error filter value and the BEMF error threshold value; and

wherein the processor is configured to cause the electric motor driver circuit to discontinue application of power to the electric motor upon detecting a rotor lock condition.

16. The electric motor controller of claim 15 , wherein the Luenberger-based BEMF observer is configured to generate the first estimated BEMF voltage value by computing a first estimated BEMF voltage value ê δ as a δ coordinate in virtual rotating reference frame (γ,δ).

17. The electric motor controller of claim 15 , wherein the processor is configured to calculate the second estimated BEMF voltage value by calculating a second estimated BEMF voltage value ê q =+c BemfCoef ·{circumflex over (ω)}+c BemfOffset ·sgn({circumflex over (ω)}) as a q coordinate in rotating reference frame (d, q), where c BemfCoef is a first BEMF coefficient term defined from a measurement on the motor, where C BemfOffset is a second BEMF offset coefficient defined from a measurement on the motor, and where the sgn({circumflex over (ω)}) term represents a sign function based on whether the {circumflex over (ω)} is positive or negative.

18. The electric motor controller of claim 15 , wherein the processor is configured to calculate the BEMF error filter value by filtering an absolute value of a difference between the first and second estimated BEMF voltage values.

19. The electric motor controller of claim 15 , wherein the processor is configured to calculate the BEMF error filter value by filtering a difference between the first and second estimated BEMF voltage values.

20. The electric motor controller of claim 15 , wherein the processor is configured to calculate the BEMF error filter value by filtering a squared difference between the first and second estimated BEMF voltage values.

21. A system for detecting locked rotor in a sensorless permanent magnet synchronous motor, comprising:

a Luenberger-based back electromotive force (BEMF) device for producing an estimated rotor speed {circumflex over (ω)} and a first estimated BEMF voltage value ê δ as a δ coordinate in virtual rotating reference frame (γ,δ);

an estimator block coupled to receive the estimated rotor speed {circumflex over (ω)} from the Luenberger-based BEMF device for computing a second estimated BEMF voltage value comprises calculating a second estimated BEMF voltage values ê q =+c BemfCoef ·{circumflex over (ω)}+c BemfOffset ·sgn({circumflex over (ω)}) as a q coordinate in rotating reference frame (d,q), where c BemfCoef is a first BEMF coefficient term defined from a measurement on the motor, where c BemfOffset is a second BEMF offset coefficient defined from a measurement on the motor, and where the sgn({circumflex over (ω)}) term represents a sign function having a first output if {circumflex over (ω)}>0 and having a second output if {circumflex over (ω)}<0;

a threshold block coupled to receive the estimated rotor speed {circumflex over (ω)} from the Luenberger-based BEMF device for computing a BEMF error threshold signal as a product of a BEMF threshold coefficient (C BEMFThresholdCoef ) and an absolute value of the estimated rotor speed {circumflex over (ω)}, subject to a minimum threshold BEMF value;

a filtered back-EMF error block coupled to the Luenberger-based BEMF device and the estimator block for receiving the first estimated BEMF voltage value ê δ and the second estimated BEMF voltage value ê q , whereby the filtered back-EMF error block outputs a BEMF error filter signal indicative of a filtered comparison between the first estimated BEMF voltage value ê δ and the second estimated BEMF voltage value ê q ; and

fault handler coupled to the estimator block and threshold block for detecting a rotor lock condition at the sensorless permanent magnet synchronous motor based on at least the BEMF error filter signal and the BEMF error threshold signal; and

discontinuing application of power to the sensorless permanent magnet synchronous motor upon detecting the rotor lock condition.