Fault-tolerant Utility Interface power converter for low-voltage microgrids

The utility interface (UI) converter is a three-phase power conversion unit equipped with energy storage which governs the interaction between the utility grid and the microgrid. The non-interruptive operation of UI is desired due to its several functions: (1) in grid-connected operation it performs as a voltage-supporting unit regulating the power flow through the microgrid point of common coupling, and compensating reactive power, unbalance and distortions caused by loads. (2) Whereas in islanded operation it performs as a voltage-forming unit and sets voltage amplitude and frequency for the entire microgrid. (3) Moreover, the UI ensures seamless transitions from grid-connected to islanded operation, actively decoupling the microgrid and the mains. Therefore, the UI plays a crucial role in centralized microgrid structures, and being a single-point of failure its safe and reliable operation entails directly the overall microgrid reliability. Thus, fault tolerant operation of such converter is a very important issue. The three-phase active neutral point clamped based power converter topology is capable to survive to successive open-circuit faults. Besides, it takes into account the advantages of the multilevel topologies: improved waveform quality, reduced filter size and equal loss distribution in the semiconductors. Simulation results are shown to analysis the operation of the fault-tolerant UI under faults.