Time-varying full-order state-space modeling of variable-switching-frequency control for single-phase single-stage dual-active-bridge based AC/DC converter
Full-bridge power-factor-correction (PFC) front-end + dual-active-bridge (DAB) AC/DC topology is widely used and its small-signal model has been studied in depth. Compared to the two-stage design, the single-stage design, unfolding bridge + DAB, is attracting more attention nowadays. By eliminating the bulky DC link bus capacitor and operating the front-end with only 60Hz switching frequency, the DAB based single-stage AC/DC converter has the potential to increase the system power density and efficiency. Different from the conventional constant-switching-frequency (CSF) DAB control, a novel variable-switching-frequency (VSF) DAB control is more suitable for the single-stage design due to the 0 to peak input voltage. A full-order state-space model is proposed in this paper to describing the VSF control. The influence of DC blocking capacitor is stressed because there is always a low frequency excitation of VSF control which is not existed with CSF control. The resonance of DC blocking capacitor and transformer leakage inductor is well described by the full-order state-space model. Simulation and experimental results verified the correctness of proposed DAB full-order state-space model.