Method and apparatus for monitoring rotational position of an electric machine

1. A method for monitoring an electric motor employing a pulse-type rotational position sensor, comprising:

monitoring a signal output from the pulse-type rotational position sensor and a reference signal associated with a control signal for the electric motor;

determining a position of a rotor of the electric motor coincident with the reference signal based upon a nominal rotor position, a nominal rotational speed of the rotor and a time between the reference signal and a falling edge of the signal output from the pulse-type rotational position sensor; and

controlling the electric motor based upon the position of the rotor.

2. The method of claim 1 , wherein determining the position of the rotor coincident with the PWM reference signal comprises determining the position of the rotor in accordance with the following relationship:

θ Final [k]=θ MT [k]+ω MT [k− 1 ]×ΔT[k]

wherein

θ Final [k] is the position of the rotor,

θ MT [k] is the nominal rotor position,

ω MT [k−1] is the nominal rotational speed of the rotor, and

ΔT[k] is the time between the reference signal to the falling edge of the signal output from the pulse-type rotational position sensor.

3. The method of claim 1 , wherein the nominal rotational speed of the rotor is determined in accordance with the following relationship:

ω

MT

=

m

⁢

⁢

1

*

α

Ppr

⁡

(

Tsp

+

Δ

⁢

⁢

T

)

wherein

ω MT is the nominal rotational speed

Tsp is a sampling period,

m1 is a discrete quantity of sensor pulses during the sampling period Tsp, said sensor pulses comprising the signal output from the pulse-type rotational position sensor,

α is a rotational angle of the rotor between two adjacent sensor pulses,

ΔT is an elapsed time that is a difference between a fixed time interval and the sampling period Tsp, and

Ppr is a resolution of an encoder of the pulse-type rotational position sensor.

4. The method of claim 1 , wherein monitoring the reference signal associated with the control signal for the electric motor comprises monitoring a PWM reference signal indicating completion of one cycle of signals for controlling power flow to the electric motor.

5. The method of claim 1 , wherein monitoring the signal output from the pulse-type rotational position sensor comprises monitoring signal output from an edge-sensing device comprising a magnetoresistive sensor including a stationary sensing element mounted on the stator of the electric motor, said magnetoresistive sensor monitoring an encoder mounted on a shaft of the rotor of the electric motor.

6. The method of claim 1 , wherein monitoring the signal output from the pulse-type rotational position sensor comprises monitoring signal output from an edge-sensing device comprising a digital Hall-effect sensor including a stationary sensing element mounted on the stator of the electric motor, said digital Hall-effect sensor monitoring an encoder mounted on a shaft of the rotor of the electric motor.

7. A method for monitoring a multi-phase electric machine including an inverter generating pulsewidth-modulation signals for controlling power flow to generate torque, the electric machine employing a low-resolution pulse-type rotational position sensor for positional feedback, comprising:

monitoring a signal output from the low-resolution pulse-type rotational position sensor and a reference signal associated with a control signal for the electric machine originating from the inverter;

determining a position of a rotor of the electric machine coincident with the reference signal based upon a nominal rotor position, a nominal rotational speed of the rotor and a time between the reference signal and a signal output from the low-resolution pulse-type rotational position sensor; and

controlling the electric machine based upon the position of the rotor.

8. The method of claim 7 , wherein determining a position of the rotor coincident with the PWM reference signal comprises determining the position of the rotor in accordance with the following relationship:

θ Final [k]=θ MT [k]+ω MT [k− 1 ]×ΔT[k]

wherein

θ Final [k] is the position of the rotor,

θ MT [k] is the nominal rotor position,

ω MT [k−1] is the nominal rotational speed of the rotor, and

ΔT[k] is the time from the reference signal to the signal output from the low-resolution pulse-type rotational position sensor.

9. The method of claim 7 , wherein the nominal rotational speed of the rotor is determined in accordance with the following relationship:

ω

MT

=

m

⁢

⁢

1

*

α

Ppr

⁡

(

Tsp

+

Δ

⁢

⁢

T

)

wherein

ω MT is the nominal rotational speed of the rotor

Tsp is a nominal sampling period,

m1 is a discrete quantity of sensor pulses during the sampling period Tsp, said sensor pulses comprising the signal output from the low-resolution pulse-type rotational position sensor,

α is a rotational angle of the rotor between two of adjacent sensor pulses,

ΔT is an elapsed time that is a difference between a fixed time interval and the nominal sampling period Tsp, and

Ppr is a resolution of an encoder of the low-resolution pulse-type rotational position sensor.

10. The method of claim 7 , wherein monitoring the reference signal associated with the control signal for the electric machine comprises monitoring a PWM reference signal indicating completion of one cycle of signals for controlling power flow to the electric machine.

11. The method of claim 7 , wherein monitoring the signal output from the low-resolution pulse-type rotational position sensor comprises monitoring signal output from a magnetoresistive sensor including a stationary sensing element mounted on the stator of the electric machine, said magnetoresistive sensor monitoring a low-resolution encoder mounted on a shaft of the rotor of the electric machine.

12. The method of claim 7 , wherein monitoring the signal output from the low-resolution pulse-type rotational position sensor comprises monitoring signal output from an edge-sensing device comprising a digital Hall-effect sensor including a stationary sensing element mounted on the stator of the electric machine, said digital Hall-effect sensor monitoring a low-resolution encoder mounted on a shaft of the rotor of the electric machine.