Quasi-Fixed Frequency Triangular Modulation for Matrix-Type AC-DC Dual Active Bridge Converter with Enhanced Battery Charging

In the conventional triangular modulation (TRM), the phase shift ratio acts as the control variable, showing a linear relationship with the output power, while the transformer RMS current follows a non-linear relationship. During the constant voltage (CV) charging process, the phase shift ratio is regulated to reduce the output current. At lower phase shift ratios, the contribution of transformer RMS current to device conduction loss becomes significant in comparison to the current being processed. It has been found that regulating the switching frequency in a piecewise manner throughout the charging process not only reduces transformer RMS current but also improves the overall converter performance. In this paper, a quasi-fixed frequency (QF²) TRM is proposed for a 600 W prototype which achieves a peak reduction of 65.5% in conduction loss at the minimum phase shift ratio and enhancing the battery charging process while maintaining a linear relationship with the control variable.