Accurate Discrete-Time Modeling of an Interleaved Current-Fed Dual Active Bridge DC-DC Converter

Current-fed bidirectional isolated DC-DC converters are often used in the photovoltaics and energy storage applications to interface the low voltage energy storage devices with the high voltage DC bus. However, a suitable modeling framework is not readily available, considering different operating modes to study its high frequency large- and small-signal behaviour and to design the controller. This paper presents a discrete-time framework for accurate modeling of an interleaved current-fed dual active bridge DC-DC converter, particularly highlighting its large- and small-signal dynamics. The proposed framework considers the exact dynamics of individual modes, taking into account the possible power circuit parasitics, and attempts to derive a generic form of approximate second-order discrete-time models. Various discrete-time small-signal transfer functions are derived and verified with the SIMetrix/SIMPLIS simulation in the frequency domain. A pair of complex conjugate poles and zeros are found to exist in the control-to-output transfer functions near the converter natural frequency. A GaN-based 300 W hardware prototype is made to validate the proposed model experimentally, and the modulation technique is implemented using an FPGA device. Discrete-time large-signal models are validated through the experimental results. The proposed framework can be extended to other isolated and non-isolated DC-DC converters, particularly when at least one of the state variables has zero steady state average value.