Universal Modulation Scheme to Suppress Transient DC Bias Current in Dual Active Bridge Converters

This article presents a modulation scheme to suppress the transient dc bias current in dual active bridge (DAB) converters. The current in the transformer at the commutating time is associated with the initial current in a switching period, so there must be a dc bias current during the transient response. To investigate the modulation scheme for suppressing the transient dc bias current, the article reviews the optimal TPS control strategy, which is derived from the zero voltage switching with the minimum current stress in the transformer. By analyzing the dc bias current, the transient dc bias current can be evaluated by the current in the transformer at the symmetry line of the primary full-bridge voltage waveform instead of the current at the commutating time. It can be concluded that the expressions of the transient dc bias current for different working modes are unified. Therefore, the modulation schemes without transient dc bias current for different working modes can be also unified. On this basis, a universal strategy can meet all the transient cases. There is no need to identify or select the working modes and power conditions in the transient dc bias current control, which simplifies the implementation of the modulation scheme in the digital signal processor. Finally, an experimental prototype has been built to verify the effectiveness of the proposed modulation scheme.