Bi-directional battery voltage converter

1. A method of balancing current in a vehicle electric system, the vehicle electrical system comprising a system bus, a first battery, a first bi-directional

battery voltage converter selectively transferring a first current between the first battery and the system bus, a second battery, a second bi-directional battery voltage

converter selectively transferring a second current between the second battery and the system bus, and a controller controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter, the method comprising:

sensing the first current;

providing a first signal related to the first current to the controller;

sensing the second current;

providing a second signal related to the second current to the controller; and

controlling the first bi-directional battery voltage converter and the second bidirectional battery voltage converter so that the first current and the second current are portions of a load current supplied to an electrical load connected to the system bus, wherein the first bi-directional battery voltage converter includes an inductor, a plurality of switches including a first switch coupling the inductor to the first battery and a second switch coupling the inductor to the system bus, and a routing circuit connected to each of the plurality of switches, and controlling the routing circuit by the controller to open and close each of the plurality of switches to charge the inductor from one of the vehicle electrical system and the first battery and to discharge the inductor to the other of the vehicle electrical system and the first battery.

2. The method of claim 1 , further comprising:

sensing a first voltage of the first battery; and

adjusting a duty cycle of the bi-directional battery voltage converter to adjust at least one of the first current and a voltage being delivered by the first battery, so as to provide optimal discharging of the first battery.

3. The method of claim 2 , further comprising adjusting a duty cycle of the first bi-directional battery voltage converter to reduce the first current when the first current is greater than the second current.

4. The method of claim 2 , further comprising:

disabling the first battery if a terminal voltage of the first battery traverses a threshold value;

adjusting the duty cycle of the second bi-directional battery voltage converter such that the load current continues to be supplied.

5. The method of claim 4 , wherein the threshold value is based upon a voltage difference from a starting value.

6. The method of claim 4 , wherein the threshold value is based upon a voltage difference from a nominal value.

7. The method of claim 4 , wherein the threshold value is based on a ratio of the voltage of the vehicle electrical system to a starting voltage.

8. The method of claim 4 , wherein the threshold value is based on a ratio of the voltage of the vehicle electrical system to a nominal voltage.

9. A vehicle electrical system for supplying electrical power to an electrical load, the system comprising:

a system bus,

a first battery;

a first bi-directional battery voltage converter controllably transferring a first current between the first battery and the system bus;

a second battery;

a second bi-directional battery voltage converter controllably transferring a second current between the second battery and the system bus; and

a controller for controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter such that the first current and the second current are portions of a load current supplied to an electrical load connected to the system bus,

wherein the first bi-directional battery voltage converter includes an inductor, a plurality of switches with a first switch connecting the inductor to the first battery and a second switch connecting the inductor to the system bus, and a routing circuit connected to each of the plurality of switches, and

wherein the controller controls the routing circuit to open and close each of the plurality of switches to charge the inductor from one of the vehicle electrical system and the first battery and to discharge the inductor to the other of the vehicle electrical system and the first battery.

10. The vehicle electrical system of claim 9 , wherein the first battery can charge the second battery by altering a duty cycle of at least one of the first battery voltage converter and the second battery voltage converter.

11. The method of claim 1 , wherein controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter so that the first current and the second current are portions of the load current supplied to an electrical load connected to the system bus includes controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter so that the first current and the second current are proportionate portions of the load current supplied to the electrical load connected to the system bus.

12. The method of claim 1 , wherein controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter so that the first current and the second current are portions of the load current supplied to an electrical load connected to the system bus includes controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter so that the first current and the second current are equal portions of the load current supplied to the electrical load connected to the system bus.

13. The vehicle electrical system of claim 9 , wherein the controller controls the first bi-directional battery voltage converter and the second bi-directional battery voltage converter such that the first current and the second current are proportionate portions of the load current supplied to the electrical load connected to the system bus.

14. The vehicle electrical system of claim 9 , wherein the controller controls the first bi-directional battery voltage converter and the second bi-directional battery voltage converter such that the first current and the second current are equal portions of the load current supplied to the electrical load connected to the system bus.