Bi-directional PSFB DC-DC converter with unique PWM control schemes and seamless mode transitions using enhanced digital control

Isolated Bi-Directional DC-DC converters are commonly used in automotive and data storage applications where energy is transferred between a high-voltage DC bus and a low-voltage DC bus/battery in a bi-directional fashion. A typical implementation includes a phase-shifted full-bridge (PSFB) with synchronous rectification that controls power flow from the high-voltage bus to the low-voltage battery in step-down (buck) mode, and a current-fed push-pull converter that controls the reverse power flow from the low-voltage battery to the high-voltage bus in step-up (boost) mode. The major challenges to implement this PSFB bi-directional operation are; (1) High voltage bridge-FET rectification during reverse power flow (boost mode) in current-fed push-pull converter, (2) Fast seamless transitions between buck and boost modes. This paper presents system performance improvements obtained using 50% duty with phase-shift PWM control scheme to control high voltage bridge-FET rectification in reverse power flow. A new method that provides fast seamless transitions between buck and boost modes of operations is also presented. Experimental results obtained using a wide input range 400V ←→ 12 V, 300W digitally controlled isolated bi-directional DC-DC converter are presented.