Charging EV battery using parallel buck and boost converters

1. A method for controlling a charging current while transferring energy from a source battery to a target battery in an electric vehicle (EV), the method comprising:

operating, by control circuitry, a buck converter at a fixed switching frequency to transfer power from the source battery to the target battery, in a first operational mode, wherein a pulse width modulation (PWM) duty cycle increases during the first operation mode;

in response to detecting a first trigger event, transitioning from the first operational mode to a second operational mode to operate the buck converter at a variable switching frequency to increase a resolution of the PWM duty cycle relative to the first operational mode; and

in response to detecting a second trigger event, transitioning to a third operational mode to activate a boost converter coupled to the source battery and the target battery.

2. The method of claim 1 , further comprising:

after transitioning to the third operational mode, regulating a charging current through the boost converter so as to substantially compensate for a differential between a desired charging current and a decaying current through the buck converter.

3. The method of claim 1 , wherein detecting the first trigger event includes determining that a voltage differential between the source battery and the target battery is below a threshold voltage value.

4. The method of claim 3 , wherein:

the source battery is a stationary charging battery; and

the threshold voltage value is 10V.

5. The method of claim 1 , wherein detecting the first trigger event includes determining that the duty cycle of the buck converter exceeds a threshold duty cycle value.

6. The method of claim 5 , wherein the threshold duty cycle value is 98%.

7. The method of claim 1 , wherein detecting the second trigger event includes determining that a voltage differential between the source battery and the target battery is substantially zero.

8. The method of claim 1 , wherein detecting the second trigger event includes determining that the duty cycle of the buck converter is substantially 100%.

9. The method of claim 1 , further comprising:

upon transitioning to the third operational mode, operating the boost converter at a variable switching frequency; and

in response to detecting a third trigger event, transitioning from the third operational mode to a fourth operational mode to operate the boost converter at a fixed switching frequency.

10. The method of claim 9 , wherein detecting the third trigger event includes determining that a voltage differential between the source battery and the target battery is below a second threshold voltage value.

11. The method of claim 1 , further comprising:

subsequently to transitioning to the fourth operational mode and in response to determining that no current flows through the buck converter, deactivating the buck converter.

12. A non-transitory computer-readable medium storing thereon instructions which, when executed by one or more processors, cause a circuit to control a charging current while transferring energy from a source battery to a target battery in an electric vehicle (EV), in a system that includes a buck converter configured to couple to the source battery and the target battery, a boost converter configured to couple to the source battery and the target battery, and a boost switch that connects an output to the boost converter to the target battery in a closed state, and disconnects the boost converter from the target battery in an open state; the instructions configured to:

(i) operate the buck converter at a fixed switching frequency in a first operational mode, wherein a pulse width modulation (PWM) duty cycle increases during the first operation mode,

(ii) in response to detecting a first trigger event, transition from the first operational mode to a second operational mode to operate the buck converter at a variable switching frequency and increase a resolution of the PWM duty cycle relative to the first operational mode, and

(iii) in response to detecting a second trigger event, transition to a third operational mode to activate the boost converter.

13. The non-transitory computer-readable medium of claim 12 , wherein the instructions are further configured to:

after transitioning to the third operational mode, regulate a charging current through the boost converter so as to substantially compensate for a differential between a desired charging current and a decaying current through the buck converter.

14. The non-transitory computer-readable medium of claim 12 , wherein to detect the first trigger event, the instructions are configured to determine that a voltage differential between the source battery and the target battery is below a threshold voltage value.

15. The non-transitory computer-readable medium of claim 12 , wherein to detect the first trigger event, the instructions are configured to determine that the duty cycle of the buck converter exceeds a threshold duty cycle value.

16. The non-transitory computer-readable medium of claim 12 , wherein the instructions are further configured to:

upon transitioning to the third operational mode, operate the boost converter at a variable switching frequency; and

in response to detecting a third trigger event, transition from the third operational mode to a fourth operational mode to operate the boost converter at a fixed switching frequency.

17. The non-transitory computer-readable medium of claim 16 , wherein to determine the third trigger event, the instructions are configured to:

determine that a voltage differential between the source battery and the target battery is below a second threshold voltage value.

18. The non-transitory computer-readable medium of claim 12 , wherein the instructions are further configured to:

subsequently to transitioning to the fourth operational mode and in response to determining that no current flows through the buck converter, deactivate the buck converter.