Fault diagnosis in multilevel converters is of great importance since they are comprised of more solid-state switches, compared to the conventional two-level converters. This paper proposes a fast and efficient real time open-switch fault diagnosis, based on failure mode algorithm for a single-phase five-level neutral-point-clamped inverter. Component modeling and complicated calculations are avoided and load parameters are not required for realizing the proposed approach. Furthermore, the proposed strategy does not require any extra sensor. The signals already available in the control system such as the applied switching pattern and terminal voltage fulfill the fault diagnosis. Thanks to the proposed fault detection strategy, any misdiagnosis arising from noise existence, response time of the sensors, turn on and turn off delay times of the power switches and measurement errors is avoided. The simulations and experiments are carried out to confirm the performance and effectiveness of the presented strategy.

In this paper, a fast and efficient open-circuit switch and clamping diode fault diagnosis for Neutral-Point-Clamped inverters is proposed. Multilevel converters employed in safety-critical applications should include fault tolerant capability, where fault diagnosis plays a vital role. The proposed fault diagnosis algorithm is based on failure mode analysis, which is a logic based approach. The required signals and measurements are available in the healthy control system. Furthermore, component modeling, load parameters and complicated calculations are not required. The fault detection and identification of the faulty switch or clamping diode are carried out based on the available data such as switching pattern and terminal voltage. Although switches are more fragile than clamping diodes, clamping diodes are also subjected to breakdown. Hence, it is also crucial to achieve a clamping diode fault diagnosis strategy. Moreover, for fault detection procedure, a voltage quantifier is proposed to avoid any misdiagnosis arising from measurement errors and voltage drop in the circuit. The simulation and experimental results are presented to validate the effectiveness of the proposed approach.

Ensuring service continuity in safety critical applications is crucial. In some of these applications, multilevel converters play a vital role. In this regard, this research work presents a self-healing fault-tolerant control approach to ensure the resiliency of a neutral-point clamped converter when a semiconductor component encounters an open circuit fault. The defective semiconductor can be a power switch or a clamping diode. By applying the proposed real-time fault-tolerance control, the rated output voltage and output current are restored during post-fault operation. Furthermore, the total harmonic distortion value of the output voltage during application of the real time self-healing control does not increase when compared with that during healthy operation. Since the realization of the proposed control strategy does not require any bidirectional switch, a fast transition between the healthy and fault-tolerant operation is accomplished. Moreover, the proposed structure can ensure service continuity in case of a fault event in the anti-parallel diodes, something which has been overlooked in previously conducted research works.

Multilevel inverters are increasingly used in industrial applications in which service continuity is crucial. This paper presents an original approach to ensure the fault-tolerant operation of neutral-point-clamped (NPC) inverters in the case of an open-circuit fault event in a clamping diode, which is rarely investigated in the conducted research work. The proposed fault-tolerant strategy meets the following criteria: restoring rated output voltage and current during post-fault operation, realizing fault-tolerant operation without additional components, maintaining rated total harmonic distortion (THD) during fault-tolerant operation, and fast transition between faulty operation and remedial operation. In the proposed approach, prior to applying the appropriate remedial action, identification of the defective clamping diode is required. In this respect, a very fast and simple logic-based fault diagnosis is presented whose implementation does not need any additional components and external circuit. Moreover, it does not require any component modeling and complicated calculations. The proposed strategy is validated by simulation and experimentation.

In this paper, a five-level neutral-point-clamped (NPC) inverter with short-circuit fault-tolerant capability is presented. Based on the proposed approach, in order to ensure service continuity subsequent to a short-circuit fault event in a switch, two steps are carried out. First of all, destructive consequences arising from short-circuit fault in a power switch is prevented. Afterwards, according to the defected component, remedial actions are taken. The proposed strategy does not require any redundant component. The service continuity is acquired by applying a remedial control and modifying switching commands applied to the power switches. Using the proposed approach helps to restore the rated voltage and rated current at the terminal, and there is no limit for modulation index during fault-tolerant operation under remedial control. Furthermore, compared to healthy operation, harmonic content of the terminal voltage and current is not deteriorated during fault-tolerant operation. Moreover, additional components, such as bidirectional switches and contactors, are not employed in this strategy. Only some fast fuses are placed in the converter circuit for protection purposes which do not impose a noticeable cost compared to the bidirectional switches and contactors.