ADVANCED BATTERY MANAGEMENT SYSTEM (BMS) FOR CHARGE EQUALIZATION OF SERIALLY CONNECTED ELECTRICAL STORAGE CELLS

1 . A method for controlling charging levels of a bank of serially connected electrical battery cells and performing equalization of charges in the battery cells, comprising:

a) alternately connecting an equalizing capacitor to pairs of adjacent battery cells by controlling switches at a predetermined switching frequency; and

b) adjusting said switching frequency to control an impedance of an equivalent resistance of transfer (R e ), such that charging/discharging current is maintained within a range of desired values.

2 . A method according to claim 1 , wherein equalization begins when a voltage difference between any two battery cells is larger than a predefined value and ends when the voltage difference is smaller than a predefined value.

3 . A method according to claim 1 , wherein the switching frequency changes according to a predefined profile of the switching frequency, versus time.

4 . A method according to claim 1 , further comprising:

determining when to start changing the switching frequency by measuring a temperature of a heatsink/heatsinks, which dissipates power losses during equalization of all battery cells, such that the temperature of the heatsink/heatsinks will not increase above a predetermined value; and

reducing the equivalent resistance of transfer by increasing the switching frequency, when the temperature of the heatsink/heatsinks is below a predetermined level, thereby expediting the equalization process.

5 . A method according to claim 1 , wherein drive signals are provided to all of the switches, without using isolated drivers by providing switching signals to each switch via series DC decoupling capacitors, such that when a pulse is fed into a respective series DC decoupling capacitor, a positive portion of the pulse passes to the gate of a respective switch to pass energy from the equalizing capacitor to one of the battery cells while allowing the respective series DC decoupling capacitor to charge back to a former voltage during a negative portion of the pulse, to be ready for a next cycle.

6 . A method for controlling charging levels of a bank of serially connected n electrical battery cells (B 1 . . . B n ) and performing equalization of the charges in the battery cells, comprising:

a) alternately connecting an equalizing capacitor to pairs of adjacent battery cells by controlling switches at a predetermined switching frequency;

b) alternately connecting an external capacitor to battery cells B 1 . . . B n-1 and to battery cells B 2 . . . B n ;

c) measuring a current of said external capacitor; and

d) adjusting said switching frequency to control an impedance of an equivalent resistance of transfer (R e ), such that charging/discharging current is maintained within a range of desired values.

7 . A method according to claim 6 , wherein the current of the external capacitor is passed through a sense resistor, a voltage drop across which is fed into a controller, being capable of changing the switching frequency.

8 . A method according to claim 7 , wherein the sense resistor is connected between ground and a transistor that toggles the external capacitor.

9 . A method according to claim 7 , wherein the controller decides to start or stop the equalization process based on a magnitude of the current of the external capacitor.

10 . Apparatus for controlling charging levels of a bank of serially connected electrical battery cells and performing equalization of charges in the battery cells, comprising:

a) circuitry configured for alternately connecting an equalization capacitor to pairs of adjacent battery cells by controlling switches at a predetermined switching frequency; and

b) circuitry configured for adjusting said switching frequency to control an impedance of an equivalent resistance of transfer (R e ), such that charging/discharging current is maintained within a range of desired values.

11 . Apparatus according to claim 10 , in which equalization begins when a voltage difference between any two battery cells is larger than a predefined value and ends when the voltage difference is smaller than a predefined value.

12 . Apparatus according to claim 10 , in which the switching frequency changes according to a predefined profile of the switching frequency, versus time.

13 . Apparatus according to claim 10 , in which the control circuitry is adapted to:

determine when to start changing the switching frequency by measuring a temperature of a heatsink/heatsinks, which dissipates power losses during equalization of all battery cells, such that the temperature of the heatsink/heatsinks will not increase above a predetermined value; and

reduce the equivalent resistance of transfer by increasing the switching frequency, when the temperature of the heatsink/heatsinks is below a predetermined level, thereby expediting the equalization process.

14 . Apparatus according to claim 10 , in which drive signals are provided to all of the switches, without using isolated drivers by providing switching signals to each switch via series DC decoupling capacitors, such that when a pulse is fed into a respective series DC decoupling capacitor, a positive portion of the pulse passes to the gate of a respective switch to pass energy from the equalizing capacitor to one of the battery cells while allowing the respective series DC decoupling capacitor to charge back to a former voltage during a negative portion of the pulse, to be ready for a next cycle.

15 . Apparatus for controlling charging levels of a bank of serially connected n electrical battery cells (B 1 . . . B n ) and performing equalization of charges in the battery cells, comprising:

a) circuitry configured for:

a.1) alternately connecting an equalizing capacitor to pairs of adjacent battery cells by controlling switches at a predetermined switching frequency;

a.2) alternately connecting an external capacitor to battery cells B 1 . . . B n-1 and to battery cells B 2 . . . B n ;

b) circuitry configured for measuring a current of said external capacitor; and

c) control circuitry configured for adjusting said switching frequency to control an impedance of an equivalent resistance of transfer (R e ), such that the charging/discharging current is maintained within a range of desired values.

16 . Apparatus according to claim 15 , in which the current of the external capacitor is passed through a sense resistor, a voltage drop across which is fed into a controller, being capable of changing the switching frequency.

17 . Apparatus according to claim 16 , in which the sense resistor is connected between ground and a transistor that toggles the external capacitor.

18 . Apparatus according to claim 16 , in which the controller decides to start or stop the equalization process based on a magnitude of the current of the external capacitor.