Advanced Control Strategy of DFIG Wind Turbines for Power System Fault Ride Through

Abstract

Abstract-This paper presents an advanced control strategy for the rotor and grid side converters of the doubly fed induction generator (DFIG) based wind turbine (WT) to enhance the low-voltage ride-through (LVRT) capability according to the grid connection requirement. Within the new control strategy, the rotor side controller can convert the imbalanced power into the kinetic energy of the WT by increasing its rotor speed, when a low voltage due to a grid fault occurs at, e.g., the point of common coupling (PCC). The proposed grid side control scheme introduces a compensation term reflecting the instantaneous DC-link current of the rotor side converter in order to smooth the DC-link voltage fluctuations during the grid fault. A major difference from other methods is that the proposed control strategy can absorb the additional kinetic energy during the fault conditions, and significantly reduce the oscillations in the stator and rotor currents and the DC bus voltage. The effectiveness of the proposed control strategy has been demonstrated through various simulation cases. Compared with conventional crowbar protection, the proposed control method can not only improve the LVRT capability of the DFIG WT, but also help maintaining continuous active and reactive power control of the DFIG during the grid faults.Index Terms-Doubly fed induction generator (DFIG), low voltage ride through, power system fault, wind turbine.

Coordinated Control Schemes of Super-Capacitor and Kinetic Energy of DFIG for System Frequency Support

“…The detailed dynamic model of the complete DFIG system in this paper can be referred to [4,26,27], including the induction generator model, the drive train model, the back-to back converter model and the controller model. The controller of the complete DFIG system mainly contains the rotor-side converter (RSC) controller, the grid-side converter (GSC) controller and the pitch angle controller, which will be introduced in the following sections.…”

“…where P s and P r are the active power from stator and rotor side of DFIG, which are expressed as [4]:…”

“…Once detecting the over-speed of WT rotor, the pitch angle control of WT is activated accordingly to constrain the rotor speed within its limit. Normally, the stator reactive power from the DFIG is controlled as zero [4].…”

“…The main function of the GSC is to control the DC-link voltage [4], as shown in Figure 1. Since the DC-link voltage is kept as a constant value, the rotor active power P r equals to the power transmitted to the grid side through GSC P g , which results in,…”

“…With this control logic, WTs rotational speed and the system frequency are effectively decoupled. Correspondingly, the system disturbance that would result in the system frequency excursion can somewhat only be smoothed by the synchronous generator (SG) available in the power systems [4,5]. To improve the inertia level of high wind power penetration system, many countries have requested WTs to contribute to the system inertia or frequency response in the national grid codes [6,7].…”