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Abstract
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Grid-connected inverter plays an essential role as an interface between energy resources and the power grid. The performance of the inverters is adversely affected by the grid disturbances such as imbalances and asymmetrical short circuit faults. Then, it is necessary to enhance the functionality of the inverter under such conditions. This paper proposes an unbalance current limiting strategy for grid-connected inverters under asymmetrical short circuit fault conditions. In the proposed current limiting strategy, two main features are included: (i) second-order harmonic elimination from instantaneous active power injected into the grid, and (ii) reactive current injection according to the grid code demand. In the proposed current limiting strategy, proper positive and negative sequence current components are calculated, by which the aforementioned goals are achieved. Furthermore, to be compatible with the well-known control structure of the power converters, the current references are obtained in the form that is applicable with the commonly-used double-synchronous-references-frame control structure. To verify the effectiveness of the proposed method, the behavior of the current limiting strategy is examined by simulation of an asymmetrical short circuit fault condition in a test system. In the simulation, both the transient response upon fault occurrence and steady-state of fault condition are considered and analyzed. Furthermore, the simulation results are supported by experimental test results, verifying the effectiveness of the proposed strategy.
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