Globally Unified ZVS and Quasi-Optimal Minimum Conduction Loss Modulation of DAB Converters

Due to the quick development of wide bandgap power devices, the power density of the converters is expected to be much higher. In order to increase the power density and efficiency of the dual-active-bridge (DAB) converter, especially the efficiency under light load, a quasi-optimal current root-mean-square (rms) control strategy to achieve All-zero-voltage switching (ZVS) is proposed by taking the inductor rms current optimization algorithm into account in this article. First, the constraint conditions for realizing ZVS of all switching devices under different operating modes are concluded by analyzing the switching mode and the working principle of the DAB converter under the triple-phase-shift (TPS) modulation. The ZVS domain for All-ZVS operation in each operating mode is further obtained. Then, the global optimal control (GOC) strategy is combined with the ZVS condition to derive the novel modulation for all operating modes. Based on this scheme, the switching conditions of all switches can be improved, and the efficiency of the DAB system under the light load is optimized. With the ZVS operation, the switching frequency can be raised. Finally, a GaN HEMT-based prototype of a DAB converter was built, the switching frequency is 200 kHz, and the effectiveness of the proposed modulation scheme was verified by the experimental results.