This paper proposes the dynamic voltage and current assignment (DVCA) strategies for doubly fed induction generator (DFIG) wind power system, which is fed by nine-switch converter (NSC). With the proposed DVCA strategies, the voltage and current capacities of switches in NSC are dynamically assigned to the rotor- and grid-side branches, depending on different grid conditions. With dynamic voltage assignment, the rotor-side gets more voltage to suppress the overcurrent when the symmetrical grid voltage dips, and with dynamic current assignment, the grid-side gets more current capacity for reactive current compensation. Based on the proposed DVCA strategies and configuration, NSC-based DFIG system can be globally optimized, so that the rating capacities designed in the normal condition can also be fully used during low-voltage ride-through (LVRT) period, and no extra capacity margins or auxiliary circuits are needed. The proposed DVCA strategies and global optimization are designed, and also compared with those typical B2B-based DFIG systems. The experimental results from a 1.5-kW NSC-based DFIG system verify the validity of the analysis.
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Wen et al. (2016) studied this question.
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