Reconfiguration of NPC Multilevel Inverters to Mitigate Short Circuit Faults Using Back-to-Back Switches


The main focus of this paper is to propose a reconfiguration method to mitigate short circuit faults in a neutral point clamped multilevel inverter which is widely used as a power conversion system with distributed energy resources. Existing reconfiguration methods use either a redundant strategy or need a large number of additional devices pre-installed in the circuit; these will increase the bulk and complexity of the system. Most existing control-strategy-based methods distort the phase-to neutral voltage, which results in degradation of power quality. To maintain control-strategy-based reconfiguration, avoid significant change to the circuit topology, and avoid phase voltage distortion, a new and practical reconfiguration method is proposed in this paper. The proposed method is applicable to neural point clamped (NPC) multilevel inverters at any voltage level and can mitigate short circuit faults in any device. A technique of switching series connected switches is selected to combine with the proposed reconfiguration method since it’s a practical design consideration for realistic implementation. MATLAB/Simulink is used to simulate a five-level NPC inverter with non-idealities to verify the proposed reconfiguration method. A five-level NPC is also built and tested to experimentally verify the proposed method. Short circuit faults are injected to different devices and the proposed method is verified to quickly and effectively recover the NPC inverter from these faulty conditions.



  1. Fault tolerance
  2. Multilevel inverter
  3. Reconfiguration
  4. Short circuit fault





Fig. 1. Five-level NPC.


Fig. 2. Output waveform of healthy condition.

 Fig. 3. Output waveform of transmitting healthy condition to reconfigured condition.

Fig. 4. Output waveform of S1 short circuit fault.

Fig. 5. Output waveform of S3 short circuit fault.

Fig. 6. Output waveform of transmitting S1 short circuit condition to reconfigured condition.

Fig. 7. Output waveform of transmitting S3 short circuit condition to reconfigured condition.



A practical reconfiguration method for short circuit faults in NPC MLIs is proposed in this paper, which overcomes several weaknesses of existing reconfiguration methods. The proposed reconfiguration method is applicable to any NPC MLI with any number of voltage levels and can mitigate short circuit faults on any device. Simulations are shown to verify the effectiveness of the proposed reconfiguration method. A hybrid voltage balancing technique is selected and implemented to enhance the performance of the proposed reconfiguration method. A single- phase hardware platform is built and tested in healthy condition and reconfigured condition to demonstrate the effectiveness of the proposed method in mitigating short circuit faults. Future work focuses on achieving the proposed reconfiguration method at higher power and augmenting a fault diagnosis method to engage the proposed method.



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