Control Strategy for the Charge Current in a Buck-Boost Converter
A system for controlling a charging current while transferring energy from a source battery to a target battery in an electric vehicle (EV) comprises a four-switch buck-boost converter configured to couple to the source battery and the target battery and configured to operate in (i) a buck mode, in which voltage V g across the source battery is higher than voltage V EV across the target battery, (ii) a boost mode, in which the voltage V g is lower than the voltage V EV , and (iii) a buck-boost mode, in which the buck-boost converter operates between the buck mode and the boost mode, and in which the voltages V EV and V g differ less by a predetermined amount, and a controller configured to, when transitioning to or from the buck-boost mode, instantaneously adjust at least one a buck duty cycle d buck or a boost duty cycle d boost according to a predefined value.
1 . A system for controlling a charging current while transferring energy from a source battery to a target battery in an electric vehicle (EV), the system comprising:
a four-switch buck-boost converter configured to couple to the source battery and the target battery and configured to operate in (i) a buck mode, in which voltage V g across the source battery is higher than voltage V EV across the target battery, (ii) a boost mode, in which the voltage V g is lower than the voltage V EV , and (iii) a buck-boost mode, in which the buck-boost converter operates between the buck mode and the boost mode, and in which the voltages V EV and V g differ less by a predetermined amount, and
a controller configured to, when transitioning to or from the buck-boost mode, instantaneously adjust at least one a buck duty cycle d buck or a boost duty cycle d boost according to a predefined value.
2 . The system of claim 1 , wherein the controller is configured to, when transitioning to or from the buck-boost mode:
instantaneously adjust both the buck duty cycle d buck and the duty cycle d boost , so that d buck +d boost ≈1.
3 . The system of claim 1 , wherein the controller is configured to:
when transitioning from the buck mode to the buck-boost mode, instantaneously decrease the buck duty cycle d buck using the predefined value.
4 . The system of claim 3 , wherein to instantaneously adjust the buck duty cycle d buck , the controller is configured to multiply the buck duty cycle d buck by a multiplier M, so that a value d buck1 prior to the instantaneously adjusting becomes M*d buck1 immediately after the instantaneously adjusting.
5 . The system of claim 4 , wherein M is greater than 0.95 and less than 1.0.
6 . The system of claim 4 , wherein M is 0.98.
7 . The system of claim 1 , wherein the controller is configured to:
when transitioning from the buck-boost mode to the boost mode, instantaneously decrease the boost duty cycle d boost using the predefined value.
8 . The system of claim 1 , wherein the predetermined amount by which the voltages V EV and V g differ is between 20V and 30V.
9 . The system of claim 1 , wherein the controller is configured to select between the buck mode, the boost mode, and the buck-boost mode in view of a charging current I EVref through the target battery.
10 . The system of claim 1 , wherein:
in the buck-boost mode, the four-switch buck-boost converter with non-zero values of d buck and d buck .
11 . 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 a four-switch buck-boost converter coupled to the source battery and the target battery in (i) a buck mode, in which voltage V g across the source battery is higher than voltage V EV across the target battery, (ii) a boost mode, in which the voltage V g is lower than the voltage V EV , and (iii) a buck-boost mode, in which the buck-boost converter operates between the buck mode and the boost mode, and in which the voltages V EV and V g differ less by a predetermined amount, and
when transitioning the four-switch buck-boost converter to or from the buck-boost mode, instantaneously adjusting at least one a buck duty cycle d buck or a boost duty cycle d boost according to a predefined value.
12 . The method of claim 11 , further comprising, when transitioning to or from the buck-boost mode:
instantaneously adjusting both the buck duty cycle d buck and the duty cycle d boost , so that d buck +d boost ≈1.
13 . The method of claim 11 , further comprising:
when transitioning from the buck mode to the buck-boost mode, instantaneously decrease the buck duty cycle d buck using the predefined value.
14 . The method of claim 13 , wherein to instantaneously adjust the buck duty cycle d buck , multiplying the buck duty cycle d buck by a multiplier M, so that a value d buck1 prior to the instantaneously adjusting becomes M*d buck1 immediately after the instantaneously adjusting.
15 . The method of claim 14 , wherein M is greater than 0.95 and less than 1.0.
16 . The method of claim 13 , wherein M is 0.98.
17 . The method of claim 11 , further comprising:
when transitioning from the buck-boost mode to the boost mode, instantaneously decrease the boost duty cycle d boost using the predefined value.
18 . The method of claim 11 , wherein the predetermined amount by which the voltages V EV and V g differ is between 20V and 30V.
19 . The method of claim 11 , further comprising:
selecting between the buck mode, the boost mode, and the buck-boost mode in view of a charging current I EVref through the target battery.
20 . The method of claim 11 , wherein:
in the buck-boost mode, the four-switch buck-boost converter with non-zero values of d buck and d buck .