Transient DC Bias Suppression for Hybrid Three-level Dual Active Bridge Converters

When the diode-clamped hybrid three-level dual active bridge converter adopts extended phase-shifting control, if the phase-shifting ratio between bridges changes abruptly, the current in the converter will produce DC bias, which will increase the current stress of switching devices, and even lead to system overcurrent and transformer saturation. To solve this problem, an improved transient DC offset suppression method based on reconstructed inductor current slope is studied. Firstly, the causes of transient DC bias are analyzed, and the transient DC bias model is constructed. Secondly, select the best switch state according to different inductance current slope, and maximize the inductance current slope in the shortest time to suppress DC bias. Finally, the improved method is simulated and compared with the traditional DC bias suppression method under different operating modes. The results show that the proposed method can successfully suppress the DC bias and reduce the overcurrent, and the transient process only accounts for 10.2% of a switching period, which improves the dynamic response speed of the system.