Transmission Power Error Compensation Method of Dual Active Bridge Converters under DC-bus Voltage Fluctuation

This paper proposes a compensation method for addressing transmission power errors in dual active bridge (DAB) converters operating under fluctuating DC-bus voltages. Transmission power errors arise from dead time, whose effect varies nonlinearly with the relationship between the transformer turn ratio and the voltage ratio. The proposed method classifies nonlinear errors into five operating modes within a three-level framework. By combining phase-shift control with zero-voltage period adjustment on both the primary and secondary sides, the method effectively compensates power errors while reducing switching losses. Unlike conventional two-level operation, where two legs undergo hard switching under dead-time influence, the proposed method limits hard switching to at most one leg. Experimental results show the effectiveness of the proposed method, demonstrating a reduction in the maximum power error from 0.43 p.u. to 0.024 p.u. when the output voltage is increased by 25%. Furthermore, the method achieves a maximum efficiency of 93.9%, reducing losses by up to 25.2% compared to conventional two-level operation.