Battery temperature detection

1. A method comprising:

driving an alternating input current with a first frequency into a battery, the first frequency having a first predetermined value, and detecting a first imaginary part of an impedance of the battery at the first frequency;

driving the alternating input current with a second frequency into the battery, the second frequency having a second predetermined value different from the first predetermined value of the first frequency, and detecting a second imaginary part of the impedance of the battery at the second frequency; and

calculating, by a control and calculation circuit, an intercept frequency at which a third imaginary part of the impedance of the battery at the intercept frequency equals a predefined value at least based on the first imaginary part of the impedance of the battery at the first frequency and the second imaginary part of the impedance of the battery at the second frequency.

2. The method of claim 1 , wherein the predefined value is zero.

3. The method of claim 1 , wherein the predefined value is different from zero.

4. The method of claim 1 , further comprising obtaining temperature information from a look-up table that includes a plurality of frequency-temperature information pairs.

5. The method of claim 1 , wherein calculating the intercept frequency comprises:

calculating a straight line based on the first imaginary part of the impedance of the battery at the first frequency and the second imaginary part of the impedance of the battery at the second frequency; and

calculating the intercept frequency at which the calculated straight line intercepts the predefined value.

6. The method of claim 1 , wherein detecting the first imaginary part of the impedance of the battery and the second imaginary part of the impedance of the battery at each of the first and second frequencies comprises:

measuring a voltage across the battery to obtain a measurement signal;

demodulating the measurement signal to obtain a demodulated measurement signal; and

low pass filtering the demodulated measurement signal.

7. The method of claim 6 , wherein detecting the first imaginary part of the impedance of the battery and the second imaginary part of the impedance of the battery at each of the first and second frequencies further comprises:

measuring the alternating input current to obtain a further measurement signal;

detecting a phase shift based on the further measurement signal; and

detecting the respective imaginary part of the impedance of the battery based on the measured voltage and the detected phase shift.

8. The method of claim 6 , further comprising performing a calibration routine before detecting the first imaginary part of the impedance of the battery and the second imaginary part of the impedance of the battery at each of the first and second frequencies,

wherein the calibration routine comprises detecting a phase shift, and

wherein detecting the respective imaginary part of the impedance of the battery comprises detecting the imaginary part of the impedance of the battery based on the measured voltage and the detected phase shift.

9. The method of claim 6 , wherein demodulating the measurement signal comprises multiplying the measurement signal with a sinusoidal signal.

10. The method of claim 9 , wherein a phase shift between the alternating input current and the sinusoidal signal is 90°.

11. The method of claim 6 , wherein demodulating the measurement signal comprises:

multiplying the measurement signal with a first sinusoidal signal; and

multiplying the measurement signal with a second sinusoidal signal,

wherein a phase shift between the first sinusoidal signal and the second sinusoidal signal is 90°.

12. The method of claim 1 , further comprising:

driving, at least once, the alternating input current with a further frequency into the battery, the further frequency having a further predetermined value different from the first predetermined value of the first frequency and the second predetermined value of the second frequency, and detecting a further imaginary part of the impedance of the battery at the further frequency; and

wherein the intercept frequency is further calculated based on the further imaginary part of the impedance of the battery at the further frequency.

13. The method of claim 12 , wherein calculating the intercept frequency comprises calculating a linear function based on a least square method.

14. The method of claim 12 , wherein calculating the intercept frequency comprises calculating a non-linear function.

15. The method of claim 1 , wherein the battery comprises at least one battery cell.

16. The method of claim 15 , wherein the battery comprises two or more battery cells connected in series.

17. The method of claim 15 , wherein the battery comprises two or more battery cells connected in parallel.

18. The method of claim 1 , wherein at least one additional battery is connected in series with the battery.

19. A temperature detection circuit comprising a control and calculation circuit, wherein the temperature detection circuit is configured to:

drive an alternating current with a first frequency into a battery, the first frequency having a first predetermined value, and detect a first imaginary part of an impedance of the battery at the first frequency; and

drive the alternating current with a second frequency into the battery, the second frequency having a second predetermined value different from the first predetermined value of the first frequency, and detect a second imaginary part of the impedance of the battery at the second frequency,

wherein the control and calculation circuit is configured to calculate an intercept frequency at which a third imaginary part of the impedance of the battery at the intercept frequency equals a predefined value at least based on the first imaginary part of the impedance of the battery at the first frequency and the second imaginary part of the impedance of the battery at the second frequency.

20. The temperature detection circuit of claim 19 , wherein the predefined value is zero.

21. The temperature detection circuit of claim 19 , wherein the predefined value is different from zero.

22. The temperature detection circuit of claim 19 , wherein the temperature detection circuit is further configured to obtain temperature information from a look-up table that includes a plurality of frequency-temperature information pairs.

23. The temperature detection circuit of claim 19 , wherein the temperature detection circuit is configured to calculate the intercept frequency using the steps of:

calculating a straight line based on the first imaginary part of the impedance of the battery at the first frequency and the second imaginary part of the impedance of the battery at the second frequency; and

calculating the intercept frequency at which the calculated straight line intercepts the predefined value.

24. The temperature detection circuit of claim 19 , wherein the temperature detection circuit is configured to detect the first imaginary part of the impedance of the battery and the second imaginary part of the impedance of the battery at each of the first and second frequencies using the steps of:

measuring a voltage across the battery to obtain a measurement signal;

demodulating the measurement signal to obtain a demodulated measurement signal; and

low pass filtering the demodulated measurement signal.

25. The temperature detection circuit of claim 24 , wherein the temperature detection circuit is configured to detect the first imaginary part of the impedance of the battery and the second imaginary part of the impedance of the battery at each of the first and second frequencies further using the steps of:

measuring the alternating current to obtain a further measurement signal;

detecting a phase based on the further measurement signal; and

detecting the respective imaginary part of the impedance of the battery based on the measured voltage and the detected phase shift.

26. The temperature detection circuit of claim 24 ,

wherein the temperature detection circuit is further configured to perform a calibration routine before detecting the first imaginary part of the impedance of the battery and the second imaginary part of the impedance of the battery at each of the first and second frequencies,

wherein the calibration routine comprises detecting a phase, and

wherein detecting a respective imaginary part of the impedance of the battery comprises detecting the respective imaginary part of the impedance of the battery based on the measured voltage and the detected phase shift.

27. The temperature detection circuit of claim 24 , wherein demodulating the measurement signal comprises multiplying the measurement signal with a sinusoidal signal.

28. The temperature detection circuit of claim 27 , wherein a phase shift between the alternating current and the sinusoidal signal is 90°.

29. The temperature detection circuit of claim 24 , wherein demodulating the measurement signal comprises:

multiplying the measurement signal with a first sinusoidal signal; and

multiplying the measurement signal with a second sinusoidal signal,

wherein a phase shift between the first sinusoidal signal and the second sinusoidal signal is 90°.

30. The temperature detection circuit of claim 19 ,

wherein the temperature detection circuit is further configured to drive, at least once, the alternating current with a further frequency into the battery, the further frequency having a further predetermined value different from the first predetermined value of the first frequency and the second predetermined value of the second frequency, and detect a further imaginary part of the impedance of the battery at the further frequency, and

wherein the control and calculation circuit is further configured to calculate the intercept frequency based on the imaginary part of the impedance of the battery at the further frequency.

31. The temperature detection circuit of claim 30 , wherein the control and calculation circuit is configured to calculate the intercept frequency by calculating a linear function based on a least square method.

32. The temperature detection circuit of claim 30 , wherein the control and calculation circuit is configured to calculate the intercept frequency by calculating a non-linear function.