Hybrid electric vehicle (HEV) and electric vehicle (EV) power electronics are designed to provide power flow from high-voltage batteries (400V/600V) to low-voltage batteries (12V) in normal operating mode. In addition, these automotive power electronics must be capable of bi-directional DC/DC conversion to provide power flow from a low-voltage battery to a high-voltage battery during emergency situations, where the HEV/EV needs a boost at start-up. In other words, the bi-directional design will need a buck mode to step the voltage down and a boost mode to step the voltage back up.
The Bidirectional 400V-12V DC/DC Converter Reference Design is a microcontroller-based implementation of an isolated bi-directional DC-DC converter. A phase shifted full-bridge (PSFB) with synchronous rectification controls power flow from a 400V bus/battery to the 12V battery in step-down mode, while a push-pull stage controls the reverse power flow from the low voltage battery to the high voltage bus/battery in boost mode.
In this implementation closed loop control for both directions of power flow is implemented using Texas Instruments 32-bit microcontroller TMS320F28035, which is placed on the LV side. This digitally-controller system can implement advanced control strategies to optimally control the power stage under different conditions and also provide system level intelligence to make safe and seamless transitions between operation modes and PWM switching patterns.