Alternating current zero torque resistance heating

1 . A method for heating a battery pack in an electrified vehicle, comprising:

providing a zero d-axis current command and a zero q-axis current command to a field-oriented controller for an alternating current (AC) motor coupled to the battery pack through a power inverter module controlled by the field-oriented controller; and

injecting an AC signal onto the d-axis of the field-oriented controller.

2 . The method of claim 1 , wherein injecting the AC signal onto the d-axis of the field-oriented controller comprises injecting the AC signal onto the zero d-axis current command.

3 . The method of claim 2 , further comprising deriving an estimated rotor angular position error from a q-axis voltage command from the field-oriented controller based upon the following relationship:

V

~

qh

e

^

=

I

~

dh

e

^

(

-

Z

diff

⁢

sin

⁢

2

⁢

θ

^

err

)

where

{circumflex over (θ)} err is the estimated rotor angular position error,

Z diff is the difference between a stator impedance on the d-axis and a stator impedance on the q-axis,

V

˜

q

⁢

h

e

^

a q-axis voltage command, and

I

~

dh

e

^

is a d-axis current command subsequent to the AC signal injection.

4 . The method of claim 1 , wherein injecting the AC signal onto the d-axis of the field-oriented controller comprises injecting the AC signal onto a d-axis voltage command.

5 . The method of claim 1 , further comprising deriving an estimated rotor angular position from a q-axis voltage command from the field-oriented controller that is demodulated based upon the AC signal.

6 . The method of claim 5 , wherein the AC signal comprises an amplitude of low torque convergence of the estimated rotor angular position to a static rotor position.

7 . The method of claim 1 , further comprising controlling a rotor toward a predetermined angular position of maximum battery pack heating efficiency.

8 . The method of claim 1 , wherein the field-oriented controller comprises a resonant controller module.

9 . The method of claim 1 , wherein injecting the AC signal onto the d-axis of the field-oriented controller comprises controlling an amplitude, a shape and a frequency of the AC signal.

10 . An apparatus for heating a battery pack in an electrified vehicle, comprising:

an alternating current (AC) motor coupled to the battery pack through a power inverter module; and

a field-oriented controller controlling the AC motor based upon a zero d-axis current command and a zero q-axis current command and an AC signal injected onto the d-axis of the field-oriented controller.

11 . The apparatus of claim 10 , wherein the AC signal injected onto the d-axis of the field-oriented controller comprises the AC signal injected onto the zero d-axis current command.

12 . The apparatus of claim 11 , further comprising an angular position estimation module deriving an estimated rotor angular position error from a q-axis voltage command from the field-oriented controller based upon the following relationship:

V

~

qh

e

^

=

I

~

dh

e

^

(

-

Z

diff

⁢

sin

⁢

2

⁢

θ

^

err

)

where

{circumflex over (θ)} err is the estimated rotor angular position error,

Z diff is the difference between a stator impedance on the d-axis and a stator impedance on the q-axis,

V

~

qh

e

^

is a q-axis voltage command, and

I

~

dh

e

^

is a d-axis current command subsequent to the AC signal injection.

13 . The apparatus of claim 10 , wherein the AC signal injected onto the d-axis of the field-oriented controller comprises the AC signal injected onto a d-axis voltage command.

14 . The apparatus of claim 10 , further comprising an angular position estimation module deriving an estimated rotor angular position from a q-axis voltage command from the field-oriented controller that is demodulated based upon the AC signal.

15 . The apparatus of claim 14 , wherein the AC signal comprises an amplitude of low torque convergence of the estimated rotor angular position to a static rotor position.

16 . The apparatus of claim 10 , wherein the field-oriented controller controls a rotor toward a predetermined angular position of maximum battery pack heating efficiency.

17 . The apparatus of claim 10 , wherein the field-oriented controller comprises a resonant controller module.

18 . The apparatus of claim 10 , wherein the AC signal injected onto the d-axis of the field-oriented controller comprises an amplitude, a shape and a frequency of the AC signal.

19 . An electrified vehicle, comprising:

a rechargeable energy storage system including a battery pack;

an electric drive unit including a three-phase alternating current motor having a stator including three phase windings and a rotor, a traction power inverter module coupling the battery pack via a direct current (DC) link to the three-phase alternating current motor, a motor controller, and a gearbox mechanically coupling a rotor shaft of the rotor to at least one mechanical output;

at least one wheel mechanically coupled to the at least one mechanical output of the gearbox; and

the motor controller including a field-oriented controller controlling the three-phase alternating current motor based upon a zero d-axis current command and a zero q-axis current command, the motor controller further including an alternating current signal injected onto the zero d-axis current command effective to produce an perturbation on the DC link effecting an alternating current through the battery pack.

20 . The electrified vehicle of claim 19 , wherein the field-oriented controller comprises an angular position estimation module deriving an estimated rotor angular position from a q-axis voltage command from the field-oriented controller that is demodulated based upon the alternating current signal, and a resonant controller module.