A Novel Current Limiting Control Strategy for Three-Phase Three-Wire Inverter with Transformer

To meet the high reliability and testability of some inverters, they are required to be able to diagnose short-circuit faults in AC side. The inverter is generally switched to current-controlled mode from voltage-controlled mode to limit fault currents under short-circuit faults. No matter which diagnosis algorithm is chosen, inverter should execute current limiting control first, then diagnosis algorithm has a possibility to be achieved. However, over voltage or voltage limiting may occur under asymmetrical fault with traditional current limiting control. The over voltage or voltage limiting would trigger over-voltage protection to shut down the inverter, and the diagnosis algorithm would be terminated in this situation. To avoid over voltage and to successfully complete diagnosis algorithm, this paper proposes a novel current limiting control: adaptive current limiting reference control, whose reference is adaptive based on the pre-fault inductor currents. With the proposed method, precise diagnosis algorithms can be achieved and it would definitely reduce maintenance time. The relation between output voltages and inductor currents, and the implementation of the proposed control are analyzed in detail in this paper. The theoretical results are validated by simulations and experiments.