SYSTEMS AND METHODS FOR CONTROLLED BATTERY HEATING
Systems and methods for heating a battery, which may be performed alone or in combination with charging or discharging a battery. In some implementations, heating involves applying an alternating current waveform, which may be sinusoidal, to a battery. In some implementations, the heating signal is applied at a frequency and/or current with little or no net charge to the battery.
1 . A method of heating a battery comprising:
generating a repeating signal to apply to a battery, the repeating signal having first portion and a second portion over a period, the first portion defining a leading edge rising to a body portion terminating in a falling edge, the second portion comprising an alternating current following the falling edge of the first portion, and
wherein a frequency of the alternating current is selected to be between 2 kHz and 1 MHz.
2 . The method of claim 1 , wherein the alternating current is a sinusoidal shape.
3 . The method of claim 2 , wherein the alternating current comprises an approximation of the sinusoidal shape.
4 . The method of claim 3 , wherein the approximation is a linear piecewise approximation of the sinusoidal shape.
5 . The method of claim 4 , wherein each period of the linear piecewise approximation comprises at least three linear segments having different slopes.
6 . The method of claim 1 , wherein the alternating current comprises a first linear ramp with a positive slope and a second linear ramp with a negative slope.
7 . The method of claim 1 , further comprising selecting an offset for the alternating current based on a state of charge of the battery.
8 . The method of claim 7 , wherein the offset is selected to charge the battery when the battery state of charge is about zero.
9 . The method of claim 8 , wherein the offset is a current offset at or less than C/20.
10 . The method of claim 8 , wherein the offset is selected to discharge the battery when the battery state of charge is about full.
11 . The method of claim 10 , wherein the offset is at or less than C/10.
12 . The method of claim 1 , wherein the frequency is selected such that at least one full period of the alternating current fits between the falling edge of the first portion of a first repeating signal and the leading edge of the first portion of a second repeating signal.
13 . The method of claim 1 , wherein the frequency of the alternating current is selected such that a number of alternating current periods completed between sequential first portions of the signal is a whole number.
14 . The method of claim 1 , wherein the frequency of the alternating current is selected to target a net zero coulomb exchange.
15 . The method of claim 1 , further comprising probing the battery to dynamically determine an upper frequency bound and a lower frequency bound with the lower frequency bound at an inflection point in a conductance response and the upper frequency bound at an inflection point in a susceptance response.
16 . The method of claim 15 , wherein the frequency is selected between the upper frequency bound and the lower frequency bound.
17 . A method of heating a battery comprising:
generating a repeating signal to apply to a battery, the repeating signal having first portion and a second portion over a period, the first portion defining a charging portion terminating in a falling edge, the second portion comprising an alternating current following the falling edge of the first portion, and
wherein a frequency of the alternating current is based on at least one of a conductance response or a susceptance response.
18 . The method of claim 17 , wherein the frequency is between an upper frequency bound and a lower frequency bound with the lower frequency bound at an inflection point in the conductance response and the upper frequency bound at an inflection point in the susceptance response.
19 . The method of claim 18 , further comprising probing the battery to dynamically determine the upper frequency bound and the lower frequency bound with the lower frequency bound at an inflection point in a conductance response and the upper frequency bound at an inflection point in a susceptance response.
20 . The method of claim 17 wherein the frequency is further based on a temperature of the battery.