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DC-Voltage fluctuation elimination through a dc-capacitor current control for PMSG under unbalanced grid voltage conditions

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 life span and reliability of the capacitors in voltage source converters. This project 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 dc capacitor current control loop, where a negativesequence 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 capacitor will be more reliable under unbalanced grid voltage conditions. A modular implementation method of the proposed control strategy is developed for the PMSG. Index Terms—Current control method, dc link, PMSG

P Kamalchandran, A.L.Kumarappan

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