Alternative Pulse-Width Modulation of T-Type DAB Converter for Natural-Loss Balancing

Conventional hybrid-bridge-based dual-active-bridge (DAB) converter generates low root-mean-square (rms) current with a small number of active power components and simple control. However, it suffers from unbalanced heat distribution among the secondary-side T-type switches. To overcome this problem, we propose the use of alternative pulse-width modulation (PWM) for a T-type DAB converter. One of the secondary-side leg switches and one of the bidirectional switches are operated with the main duty and the complementary duty; the role of secondary-side switches is changed in alternating halves of switching periods in both power-flow directions. Asymmetric current flows through the secondary-side switches, so extra dead-time is required for the switches with weak zero-voltage switching current in both power-flow directions. The different minimum dead-times required for all the switches are analyzed in detail. Under the alternative PWM, the resulting switching losses between the secondary-side T-type cells are well balanced. Experimental validation on a 2-kW prototype with an 800 V input and a wide output range of 500-1000 V confirms the balanced heat distribution among the secondary-side T-type cells while preserving its inherent advantages such as low rms current and simple control structure.