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Failure mode analysis for single-phase Multi-level qZSI interfacing PV system to utility grid

Cascaded Multi-level inverter for synchronization of power generated from PV system to utility grid is reported in this paper. Inverters are prone to several types of faults e.g. switch failure or dc link capacitor failure. Failure mode analysis of cascaded H-Bridge is widely discussed in the literature. Various methods for post-fault operation with reduced capacity (due to module failure) but with balanced three-phase grid current has been proposed. Quasi Z Source Inverter with its unique capability of boosting the input voltage has become quite popular in solar PV applications. Implementation of Multi-level qZSI for grid synchronization has also been proposed. In this paper, control algorithm for the operation of Multi-level qZSI with module failures (up to three modules out of total 16) is discussed. The power deficit due to a failure of the module is reflected as a decrease in the grid current reference. The grid current injected will meet the THD requirement (< 5% THD) in the post-fault condition. To verify the proposed control algorithm, simulation results are presented and discussed.