Battery charge balancing circuit for series connections
Systems and methods are described for managing charging and discharging of battery packs. In one or more aspects, a system and method are provided to minimize overcharging of battery cells of specific battery chemistries while still enabling fast charging cycles. In other aspects, a buck converter may be used to reduce a voltage of power used to charge the cells. In further aspects, a fast overcurrent protection circuit is described to address situations involving internal short circuits of a battery cell or battery pack. In yet further aspects, a bypass circuit is provided in series-connected battery packs to improve the charging of undercharged battery packs while also increasing the efficiency of the overall charging process. In other aspects, a circuit is provided that permits a controller to determine a configuration of battery packs. In yet further aspects, a system may determine a discharge current for a collection of battery packs based on each battery pack's state of health (SOH) and forward that determination to an external device.
1. A battery pack comprising:
one or more battery cells;
a controller;
a first external power terminal;
a second external power terminal;
one or more switches connected in series between the first external power terminal and the one or more battery cells;
a buck converter circuit;
a bypass circuit comprising a first bypass terminal connected to the first external power terminal, a second bypass terminal connected to the second external power terminal, and a gate bypass terminal connected to the controller;
a first power pathway between the first external power terminal and the second external power terminal in which a first voltage difference is provided across the one or more battery cells;
a second power pathway between the first external power terminal and the second external power terminal in which a second voltage difference is provided across the one or more battery cells, wherein the second voltage difference is less than the first voltage difference, and wherein the second power pathway includes the buck converter circuit that reduces the first voltage difference to the second voltage difference;
a third power pathway between the first external power terminal and the second external power terminal, wherein the third power pathway includes the bypass circuit,
wherein the controller is configured to selectively enable one of the first power pathway, the second power pathway, and the third power pathway.
2. The battery pack of claim 1 ,
wherein, based on the controller controlling the bypass circuit to electrically connect the first external power terminal and the second external power terminal, a voltage difference between the first external power terminal and the second external power terminal increases with an increase in a temperature of the battery pack.
3. The battery pack of claim 1 , wherein the bypass circuit further comprises:
a positive temperature control (PTC) thermistor with a first terminal and a second terminal; and
a switch,
wherein the switch is connected in series with the PTC thermistor between the first external power terminal and the second external power terminal.
4. The battery pack of claim 1 , wherein the bypass circuit further comprises:
a switch connected between a first node and the second external power terminal, wherein the switch comprises a control terminal;
a resistor connected between the controller and the control terminal.
5. The battery pack of claim 4 ,
wherein the switch further comprises a first conduction terminal and a second conduction terminal, and
wherein the bypass circuit further comprises:
a second switch comprising a second conduction terminal and a second switch control terminal, wherein the second switch control terminal is connected to the first node;
a third switch comprising a third conduction terminal and a third switch control terminal, wherein the third switch control terminal is connected to the first node; and
a diode comprising is connected in series between the second conduction terminal and the third conduction terminal.
6. The battery pack of claim 5 , wherein the bypass circuit further comprises:
a fourth switch comprising a fourth conduction path connected between the first external power terminal and the second external power terminal, wherein the fourth switch further comprises a fourth control terminal connected to a terminal of the diode and the second conduction terminal.
7. The battery pack of claim 6 , wherein the bypass circuit further comprises:
a fifth switch comprising a fifth conduction path connected in series with the fourth conduction path and one of the first external power terminal or the second external power terminal.
8. The battery pack of claim 5 , wherein the bypass circuit further comprises:
a second diode, wherein the second diode is connected in series between a voltage supply and a fourth conduction terminal of the second switch.
9. The battery pack of claim 1 , further comprising:
an external control terminal electrically coupled to the controller,
wherein the controller is further configured to selectively control the bypass circuit based on commands received via the external control terminal.
10. The battery pack of claim 1 , further comprising:
a first pathway/second pathway switch configured to switch between the first power pathway and the second power pathway,
wherein the controller is configured to:
determine a state of charge (SOC) of the one or more battery cells, and
control, based on a determination of the SOC, the first pathway/second pathway switch and the gate bypass terminal.
11. A method comprising;
connecting, in series, a first battery pack with a second battery pack, wherein the first battery pack has a first high voltage terminal and a first low voltage terminal, wherein the second battery pack has a second high voltage terminal and a second low voltage terminal, and wherein the connecting comprises connecting the first low voltage terminal to the second high voltage terminal;
determining a state of charge (SOC) of each of the first battery pack and the second battery pack;
based on the SOC of the first battery pack being higher than the SOC of the second battery pack, controlling a first bypass circuit of the first battery pack to electrically connect, via the first bypass circuit, the first high voltage terminal with the first low voltage terminal;
comparing the SOC of the second battery pack to a first threshold; and
based on the comparison of the SOC of the second battery pack to the first threshold, controlling the second battery pack to charge battery cells of the second battery pack at one of a first voltage level or a second voltage level, wherein the first voltage level is higher than the second voltage level.
12. The method of claim 11 , wherein, based on the connection, via the first bypass circuit, between the first high voltage terminal and the first low voltage terminal, a resistance between the first high voltage terminal and the first low voltage terminal changes based on a resistance of a positive temperature control (PTC) thermistor within the first bypass circuit.
13. The method of claim 11 , further comprising:
based on a determination that the SOC of the second battery pack is below the first threshold, charging the battery cells of the second battery pack at the first voltage level.
14. The method of claim 13 , wherein charging the battery cells of the second battery pack at the first voltage level comprises electrically connecting one or more switches to permit voltage at the second high voltage terminal to charge the battery cells.
15. The method of claim 11 , further comprising:
based on a determination that the SOC of the second battery pack is above the first threshold, charging the battery cells of the second battery pack at the second voltage level.
16. The method of claim 15 , wherein charging the battery cells of the second battery pack at the second voltage level comprises electrically connecting one or more switches to permit voltage from the second high voltage terminal to be reduced, via a buck converter, to charge the battery cells at the second voltage level.