A Novel Current Modulation Method to Eliminate Low-Frequency Harmonics in Single-Stage Dual Active Bridge AC-DC Converter

The dual active bridge (DAB) topology is frequently preferred in industry as a dc-dc converter with various current modulation methods, such as phase shift modulation (PSM), trapezoidal modulation (TZM), triangular modulation (TRM), and hybrid methods. The TZM and TZM-TRM hybrid methods can solve the current circulation problem of PSM, extend the zero voltage switching region to the full operating range, and thereby improve the light load efficiency. However, all these methods have been developed for a dc-dc converter, and cannot be directly applied to a single-stage DAB-based ac-dc converter due to the low input voltage close to the zero crossing points of the grid, otherwise significant distortion is created. This paper analyzes the line current distortion related with the modulation for a single-stage DAB-based ac-dc converter, and a novel hybrid current modulation (HCM) method that solves the distortion problem is proposed. However, since the HCM method increases the rms current as side effect, the improved version of the iHCM method is developed and the distortion-free current without increasing the rms current is obtained. The results obtained from the theoretical analysis are verified by an experimental prototype of 250 W.