Abstract
Grid codes are continuously evolving to improve the ride-through services during voltage sags. The main reason for this evolution is the increasing flexible capabilities of distribution generation inveters. The problem of selecting an appropriate strategy during grid faults is an open research topic that depends on many aspects. Among the possible solutions, this paper solves an optimization problem based on the maximization of the voltage support during grid faults. The control strategy is based on raising as much as possible the positive sequence voltage. This strategy allows to reduce the risk of disconnection by under-voltage that can led to a blackout. The problem is related to two main issues: the amount of injected current and the grid impedance. Regarding the injected current, it should be desirable to develop the references so as to inject the rated current of the inverter. Therefore the voltage support could be improved while keeping the inverter within a safety operation mode. Regarding the impedance, the strategy for inductive or resistive grids should be different. For a combination of both impedances, an optimal solution should exist in order to maximize the voltage increment. This solution is related to the amount of active and reactive current injected by the inverter. The work proposes a voltage support control strategy intended to increase as much as possible the positive sequence voltage and to inject the maximum rated current of the grid-connected distributed generation inverter. The problem is mathematically solved for any type of grid impedance, even resistive, inductive or a combination of both. Simulation results are presented to corroborate the theoretical solution.
Published Version
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