Efficient Operation of a Four-Switch Buck-Boost Converter

A method for operating a four-switch buck-boost converter configured to transfer energy from a source battery to a target battery in an electric vehicle (EV), the four-switch buck-boost converter including an inductor and switches S1, S2, S3, and S4, the method comprising:

• operating the four-switch buck-boost converter a buck mode when voltage Vg across the source battery is higher than voltage VEV across the target battery, including keeping the switch S3 ON, and operating the switches S1 and S2 to control charging and discharging of the inductor;
• operating the four-switch buck-boost converter a boost mode when the voltage Vg is lower than the voltage VEV, including keeping the switch S1 ON, and operating the switches S3 and S4 control the charging and the discharging of the inductor;
• and
• operating the four-switch buck-boost converter in a buck-boost mode when the voltages VEV and Vg differ less by a predetermined amount, including:
• turning the switch S1 ON at a beginning of a switching cycle, and
• turning the switch S4 ON at an end of the switching cycle.

A charging station comprising:

• a source battery;
• a four-switch buck-boost converter configured to couple to the source battery and a target battery in an electric vehicle (EV), the converter including:
• an inductor, and
• switches S1, S2, S3, and S4 connected so as to define (i) a buck mode in which the switch S3 is always ON, and the switches S1 and S2 control charging and discharging of the inductor, (ii) a boost mode in which the switch S1 is always ON, and the switches S3 and S4 control the charging and the discharging of the inductor, and (iii) a buck-boost mode in which all of the switches S1, S2, S3, and S4 control the charging and the discharging of the inductor;
• and
• a controller configured to operate the four-switch buck-boost converter in:
• (a) the buck mode when voltage Vg across the source battery is higher than voltage VEV across the target battery,
• (b) the boost mode when the voltage Vg is lower than the voltage VEV, and
• (c) the buck-boost mode when the voltages VEV and Vg differ less by a predetermined amount, wherein the controller turns the switch S1 ON at a beginning of a switching cycle, and turns the switch S4 ON at an end of the switching cycle.