Finite-State-Machine Model of Boundary Control for Dual-Active-Bridge Converter

To obtain a clear digital implementation structure for boundary control of dual-active-bridge converter (DAB), this paper proposes a finite-state-machine (FSM) model with excellent dynamic performance. It is based on a generalized way to analyze the natural switching surface (NSS) of DAB with explanation of its physical meaning. NSS illustrates the effect of charging and discharging of main energy storage elements. Its geometrical features help reveal the optimal transient process between different steady states. During load transient, the FSM model uses NSS to select switching state of the converter. Under this mechanism, both amount and direction of transmission power can be changed swiftly by only a few asymmetrical switching actions, while voltage overshoot and settling time can almost be eliminated. The proposed FSM model is a unified description of common boundary control, which makes its digital implementation more systematic and flexible. Simulation results have verified its feasibility.