Techniques for synchronous rectification control of DC-DC converters in electrified vehicles

1. A method, comprising:

determining, at a controller of an electrified vehicle (EV), the controller including one or more processors, a required output current for a DC-DC converter based on a secondary voltage of a secondary battery system of the EV, the DC-DC converter being configured to convert a primary voltage from a primary battery system of the EV to the secondary voltage;

determining, at the controller, a switching frequency for the DC-DC converter that causes the DC-DC converter to output the required output current;

determining, at the controller, turn-on and turn-off delays of the DC-DC converter based on the required output current and the switching frequency using one or more look-up tables; and

controlling, by the controller, the DC-DC converter based on the turn-on and turn-off delays.

2. The method of claim 1 , further comprising determining, at the controller, an input current, an output current, an input voltage, and an output voltage of the DC-DC converter in response to controlling the DC-DC converter based on the turn-on and turn-off delays.

3. The method of claim 2 , further comprising calculating, at the controller, an efficiency of the DC-DC converter based on the input current, the output current, the input voltage, and the output voltage of the DC-DC converter.

4. The method of claim 3 , wherein the efficiency of the DC-DC converter is calculated as:

η

=

V

out

×

I

out

V

in

×

I

in

,

where η represents the efficiency of the DC-DC converter, V out and I out represent the output voltage and the output current, respectively, and V in and I in represent the input voltage and the input current, respectively.

5. The method of claim 3 , further comprising comparing, at the controller, the efficiency to a maximum efficiency of the DC-DC converter.

6. The method of claim 5 , further comprising selectively adjusting, at the controller, at least one of the turn-on and turn-off delays based on the comparison to obtain at least one of a modified turn-on delay and a modified turn-off delay.

7. The method of claim 6 , wherein selectively adjusting at least one of the turn-on and turn-off delays based on the comparison includes:

adjusting, at the controller, at least one of the turn-on and turn-off delays when the efficiency is less than the maximum efficiency to obtain the at least one of the modified turn-on delay and the modified turn-off delay; and

adjusting, at the controller, neither of the turn-on and turn-off delays when the efficiency is at the maximum efficiency.

8. The method of claim 7 , further comprising controlling, by the controller, the DC-DC converter based on the at least one of the modified turn-on delay and the modified turn-off delay.

9. The method of claim 6 , further comprising storing, at the controller, the turn-on delay, wherein selectively adjusting at least one of the turn-on and turn-off delays based on the comparison includes selectively adjusting the turn-off delay based on the comparison to obtain the modified turn-off delay.

10. The method of claim 8 , wherein selectively adjusting the turn-off delay based on the comparison includes:

adjusting, at the controller, the turn-off delay when the efficiency is less than the maximum efficiency to obtain the modified turn-off delay; and

not adjusting, at the controller, the turn-off delay when the efficiency is at the maximum efficiency.

11. The method of claim 10 , further comprising controlling, by the controller, the DC-DC converter based on the turn on-delay and the modified turn-off delay.

12. The method of claim 1 , wherein the turn-on delay is determined using a first look-up table relating delay to current and frequency, and wherein the turn-off delay is determined using a second look-up table relating delay to current and frequency.

13. The method of claim 1 , wherein the DC-DC converter is a inductor-inductor-capacitor (LLC) half-bridge DC-DC converter including a plurality of transistors controlled by pulse-width modulated (PWM) control signals.

14. The method of claim 1 , wherein the primary battery system is a battery pack including a plurality of lithium-ion battery cells, and wherein the primary voltage is within a range from 220 volts to 400 volts.

15. The method of claim 1 , wherein the secondary battery system is a lead-acid battery, and wherein the secondary voltage is within a range from 6.5 volts to 16 volts.

16. A method, comprising:

determining, at a controller of an electrified vehicle (EV), the controller including one or more processors, a required output current for a DC-DC converter based on a secondary voltage of a secondary battery system of the EV, the DC-DC converter being configured to convert a primary voltage from a primary battery system of the EV to the secondary voltage for at least one of recharging the secondary battery system of the EV and powering low-voltage components of the EV;

determining, at the controller, a switching frequency for the DC-DC converter that causes the DC-DC converter to output the required output current;

determining, at the controller, turn-on and turn-off delays of the DC-DC converter based on the required output current and the switching frequency using one or more look-up tables;

controlling, by the controller, the DC-DC converter based on the turn-on and turn-off delays;

determining, at the controller, input current, output current, input voltage, and output voltage of the DC-DC converter;

determining, at the controller, an efficiency of the DC-DC converter based on the input current, the output current, the input voltage, and the output voltage of the DC-DC converter;

comparing, at the controller, the efficiency of the DC-DC converter to a maximum efficiency of the DC-DC converter; and

selectively adjusting, at the controller, at least one of the turn-on and turn-off delays of the DC-DC converter based on the comparison to obtain at least one of a modified turn-on delay and a modified turn-off delay.

17. The method of claim 16 , further comprising controlling, by the controller, the DC-DC converter based on the at least one of the modified turn-on delay and the modified turn-off delay.

18. The method of claim 16 , wherein the efficiency of the DC-DC converter is calculated as:

η

=

V

out

×

I

out

V

in

×

I

in

,

where η represents the efficiency of the DC-DC converter, V out and I out represent the output voltage and the output current, respectively, and V in and I in represent the input voltage and the input current, respectively.

19. The method of claim 16 , further comprising storing, at the controller, the turn-on delay,

wherein selectively adjusting at least one of the turn-on and turn-off delays based on the comparison includes selectively adjusting the turn-off delay based on the comparison to obtain the modified turn-off delay, and

wherein selectively adjusting the turn-off delay based on the comparison to obtain the modified turn-off delay includes:

adjusting, at the controller, the turn-off delay when the efficiency is less than the maximum efficiency to obtain the modified turn-off delay; and

not adjusting, at the controller, the turn-off delay when the efficiency is at the maximum efficiency.

20. The method of claim 16 , wherein the turn-on delay is determined using a first look-up table relating delay to current and frequency, and wherein the turn-off delay is determined using a second look-up table relating delay to current and frequency.