Advanced Control of DFIG to Enhance the Transient Voltage Support Capability

Abstract

This paper presents a novel method to enhance the low-voltage ride-through (LVRT) capability of a doubly fed induction generator (DFIG) equipped with an energy storage system (ESS) to provide voltage support during grid faults. Specifically, the transient DC-link voltage is regulated by controlling the ESS, which is connected to the DC-link capacitor of the DFIG. This is actually equivalent to absorbing the power imbalance between the captured wind power and the power delivered to the grid by the DFIG during the fault so that the DC-link voltage and the rotor current dynamics can be greatly improved. Moreover, both the rotor speed and the pitch angle are also controlled to initially react to the low-voltage transient, which includes increasing rotor speed to store the unbalanced energy as kinetic energy and augmenting the pitch angle to reduce the captured wind power. Thus, because of less unbalanced power flowing into the rotor, the DFIG dynamics can be further improved and the required ESS capacity can be saved. As the grid-side converter (GSC) is not necessarily required to manage the transient DC-link voltage, it is manipulated to devote its entire capacity to injecting reactive power into the grid for voltage support during a fault. Comparisons with the conventional control strategy are obtained by simulating a single machine-infinite bus power system. It is verified that the proposed method can not only ensure the LVRT capability of DFIG by saving the ESS capacity, but also significantly improve the terminal voltage dynamics during the grid fault.