Abstract—Unbalanced
grid voltage causes a large second-order harmonic current in the dc-link
capacitors as well as dc-voltage fluctuation, which potentially will degrade
the lifespan and reliability of the capacitors in voltage source converters.
This paper proposes a novel dc-capacitor current control method for a grid-side
converter (GSC) to eliminate the negative impact of unbalanced grid voltage on
the dc-capacitors. In this method, a dccapacitor current control loop,where a
negative-sequence resonant controller is used to increase the loop gain, is
added to the conventional GSC current control loop. The rejection capability to
the unbalanced grid voltage and the stability of the proposed control system
are discussed. The second-order harmonic current in the dc capacitor as well as
dc-voltage fluctuation is very well eliminated. Hence, the dc capacitors will
be more reliable under unbalanced grid voltage conditions. A modular
implementation method of the proposed control strategy is developed for the
DFIG controller. Finally, experiments are presented to validate the theoretical
analysis.
(Index
Terms—Control analysis, dc-capacitor current, doubly fed induction generator
(DFIG), resonant controller, unbalanced grid voltage.)
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