Wind Turbine Fault Ride-through Capability Research Articles

Calculation of current limiting reactance of hybrid SFCL for low voltage ride-through capability enhancement in DFIG wind farms

This paper presents a new approach for the low voltage ride-through capability enhancement of doubly-fed induction generator (DFIG) wind farms using a hybrid superconducting fault current limiter (SFCL) of the first peak current limiting type, which has the advantage of a fast recovery time. A design for the hybrid SFCL, focusing on current limiting reactor (CLR) reactance calculation, is proposed in this paper to determine an appropriate value for the CLR reactance that satisfies the grid code requirements of the DFIG wind turbines. High-temperature superconductors (HTS) such as Bi-2212, YBCO, Bi-2223, Ti-2223, and Hg-1223 are investigated for use in the hybrid SFCL. The recovery time and first peak current reduction effectiveness are the criteria for selecting the HTS. In the proposed method, a during-fault voltage from the grid code requirement is used as an input parameter to compute the reactance of the CLR. Based on the results of the base-case simulations conducted on the DIgSILENT PowerFactory software, the Bi-2223 HTS with the first peak of fault current less than 4.5 kA and recovery time of 2.5 s is selected for adoption in the hybrid SFCL. The calculated results of the proposed method are compared with the simulation results of the hybrid SFCL, in terms of the DFIG wind turbine fault ride-through capability enhancement, to demonstrate that the performance of the proposed method satisfies the grid code requirements.

Detailed study of DFIG-based wind turbines to overcome the most severe grid faults

This paper studies the effects of voltage sags caused by faults on doubly-fed induction generators to overcome grid faults. A wide range of sag duration and depth values is considered. It is observed that sag duration influence is periodical. Sag effects depend on duration and depth and on the fault-clearing process as well. Two approaches of the model are compared: the most accurate approach, discrete sag, considers that the fault is cleared in the successive natural fault-current zeros of affected phases, leading to a voltage recovery in several steps; the least accurate approach, abrupt sag, considers that the fault is cleared instantaneously in all affected phases, leading to a one-step voltage recovery. Comparison between both sag models reveals that the fault-clearing process smoothes sag effects. The study assumes that the rotor-side converter can keep constant the transformed rotor current in the synchronous reference frame, thus providing insights into wind turbine fault ride-through capability. The voltage limit of the rotor-side converter is considered to show the situations where the rotor current can be controlled. Finally, a table and a 3D figure summarizing the effects of the most severe grid faults on the rotor-side converter to overcome the most severe faults are provided.

A Novel Wind Turbine Concept Based on an Electromagnetic Coupler and the Study of Its Fault Ride-through Capability

This paper presents a novel type of variable speed wind turbine with a new drive train different from the variable speed wind turbine commonly used nowadays. In this concept, a synchronous generator is directly coupled with the grid, therefore, the wind turbine transient overload capability and grid voltage support capability can be significantly improved. An electromagnetic coupling speed regulating device (EMCD) is used to connect the gearbox high speed shaft and synchronous generator rotor shaft, transmitting torque to the synchronous generator, while decoupling the gearbox side and the synchronous generator, so the synchronous generator torque oscillations during a grid fault are not transmitted to the gearbox. The EMCD is composed of an electromagnetic coupler and a one quadrant operation converter with reduced capability and low cost. A control strategy for the new wind turbine is proposed and a 2 MW wind turbine model is built to study the wind turbine fault ride-through capability. An integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to study its fault ride-through capability and the impact on the structural loads during grid three phase and two phase short circuit faults.

Behaviour of the doubly fed induction generator exposed to unsymmetrical voltage sags

This study analyses the dynamic behaviour of the doubly fed induction generator exposed to unsymmetrical voltage sags, providing insights into wind turbine fault ride-through capability. The sags are assumed to be caused by faults. An analytical approach assuming that the rotor-side converter can keep constant the rotor current in the synchronous reference frame during the event is used. The voltage limit of the rotor-side converter is also considered in order to determine the situations where the rotor current can be controlled. The effects of sags on grid-connected equipments depend on the sag characteristics (duration and depth), but also on the fault clearing process. In this process, the fault is not cleared instantaneously, as in the case of abrupt sags (which is the usual approach in the literature), but in the successive natural fault-current zeros, leading to a voltage recovery in several steps known as discrete sags. The effects of both abrupt and discrete sags on the doubly fed induction generator behaviour are compared. This comparison reveals that the discrete clearing process smoothes the sag effects on the generator.

Doubly Fed Induction Generator Subject to Symmetrical Voltage Sags

The aim of this paper is to analyze the dynamic behavior of the doubly fed induction generator (DFIG) subject to symmetrical voltage sags caused by three-phase faults. A simple control algorithm is considered and assumed ideal: the rotor current in the synchronous reference frame is kept constant. This hypothesis allows the electrical transient to be solved analytically, providing a comprehensive description of DFIG behavior under symmetrical sags. The fault-clearing physics of symmetrical sags is also analyzed. That is, the fault is cleared in the successive natural fault-current zeros, leading to a voltage recovery in one, two, or three steps. This clearing process, called discrete fault clearing in this paper, results in a more accurate sag modeling than the abrupt or instantaneous fault clearing (the usual modeling in the literature). The fault-clearing process has a strong influence on the rotor voltage required to control the rotor current after fault clearing. To compare the effects of both abrupt and discrete sags, different wind turbine (WT) operating points, which determine different generated powers, are considered. This study helps in the understanding of WT fault ride-through capability.

Factors Influencing Design of Dynamic Reactive Power Compensation for an Offshore Wind Farm

This paper investigates factors that influence the design of dynamic reactive power compensation (DRPC) for an offshore wind farm consisting of fixed-speed wind turbines. Several influencing factors are considered including DRPC device types and locations, network strength, and fault ride-through (FRT) capability of individual wind turbines in the wind farm. The DRPC alternatives discussed in this paper comprise of a STATCOM and an SVC. It is found that the exclusion of wind turbine FRT capability results in too large DRPC size estimation. In the case of wind turbines equipped with FRT capability, it was found that the investment cost for both STATCOM and SVC options are comparable. The study also emphasizes the necessity of performing dynamic analysis to correctly design the size and location of the DRPC device.