Sensorless Open-Circuit-Fault Diagnosis Method for NPC-based DAB Converter

Open-circuit fault (OCF) on power switches can cause a severe threat to operation and safety of power electronic converters. In the neutral-point-clamped (NPC)-based dual-active-bridge (DAB) converters, the OCFs will result in an increase in the current stress, DC bias, and capacitor voltage imbalance. In order to address these issues, the faulty switch should be identified so that a fault-tolerant control can be employed to ensure the safe operation of the DAB converter. In existing fault diagnosis (FD) methods, extra voltage and/or current sensors are required, which will increase the hardware costs and volume. This letter proposes an FD method for the NPC-based DAB converters without additional sensors. In the proposed method, the faulty switch can be identified from the average bridge-leg-midpoint (BLM) voltages after blocking certain complementary inner switch (CIS). The average BLM voltage of each bridge leg is detected by an average-value-detecting (AVD) circuit, which is composed of an operational amplifier and passive components. Thus, the proposed FD approach will not increase the costs and volume of the DAB converter significantly. In addition, the proposed FD method also have the features of simple control structure, relatively fast diagnostic speed, and generic application to various modulation strategies. Finally, experimental tests are conducted to validate the effectiveness of the proposed FD method.