Open-Circuit Fault Analysis and Fault-Tolerant Control for 2/3-Level DAB Converters

Open-circuit faults (OCFs) on power switches are crucial issues for the two-three (2/3)-level dual-active-bridge (DAB) DC-DC converters, resulting in various performance degradation such as DC hias, overcurrent and capacitor voltage imbalance. There are two necessary steps for overcoming these problems, i.e., limit diagnosis and fault-tolerant control. In order to identity the faulty switch, the characteristics of the transient waveforms when the OCF occurs on each switch are analyzed in this paper. Based on the analysis, the midpoint voltage of each bridge arm is employed as the diagnosis signals. According to the mean values and duty cycles of the midpoint voltages, the faulty switch can be located accurately. Subsequently, a fault-tolerant control method called "complementary-switch-blocking" (CSB) is proposed through modulation reconfiguration. In the proposed CSB method, when one switch breaks down, the gate-driving signal of its complementary switch is blocked and the OCF effects can be offset. Finally, simulation results demonstrate that the OCF effects can be reduced significantly with the proposed fault-tolerant method, and the power transmission capacity can be improved compared with the traditional fault-tolerant method.