A digital single-loop control of multi-phase dc-dc converter for fuel cell powered truck auxiliary power unit

Abstract-This paper proposes a digital single-loop control method which enables a seamless mode transition between voltage and current control mode and current slew rate control for a battery connected multi-phase dc-dc converter. The proposed algorithm consists of a current reference generator and a digital average current controller. The current reference generator changes the time constant of the digital integrator to implement ramp-up and ramp down of the current reference command. The digital average current controller is designed to track the current reference accurately. A small signal model of the current control loop is derived and the control parameters are determined by the small signal analysis. A startup method when the output of the dc-dc converter is connected to a battery is also proposed to prevent reverse current flowing back to the converter input which is connected to the fuel cell stack in the design. A prototype 5 kW four-phase dc-dc converter serving as an auxiliary power supply in heavy duty trucks has been built and tested to verify the effectiveness of the proposed method.