Digital Control of a Bi-Directional DC-DC Converter for Automotive Applications

This paper presents a microcontroller based implementation of an isolated bi-directional DC-DC converter for automotive applications. A phase shifted full bridge (PSFB) with synchronous rectification controls power flow from a high voltage bus/battery to the low voltage 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. Peak current mode control (PCMC) of the PSFB stage is implemented along with adaptive zero voltage switching (ZVS) and various synchronous rectification schemes in buck mode. An active clamp circuit is used to limit transient voltage overshoot on the push-pull switches in boost mode. Voltage mode control and average current mode control can be implemented for boost mode operation. Digital control allows implementation of different power converter control schemes on the same hardware with seamless transitions between different operating modes. Experimental results for system operation have been verified on a 600W system. In the buck mode constant high system efficiency for all loads above 10% rated load, ZVS across a wide load range and smooth synchronous rectifier mode transitions are achieved. Waveform generations for all operating modes along with functional details have been presented.