Open Access
Modeling of a droop-controlled grid-connected DFIG wind turbine
(IEEE, 2022) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Traditionally, to characterize the response of droop-controlled systems RMS models have been used. However, as it is demonstrated in this work, when droop control is applied to doubly-fed induction generators, RMS models do not allow to predict the system stability and dynamic response. Thus, in this article, a linearized small-signal model that overcomes the limitations of RMS models is presented. The proposed model is validated by simulation in MATLAB/Simulink demonstrating that it allows to accurately analyze the stability and dynamic response of the system under study. This model is an interesting tool that can be used in future works to design and adjust grid-forming controllers for doubly-fed induction generators.
Open Access
Influence of the grid-side converter synchronization loop on the small-signal stability of a grid-forming DFIG wind turbine
(IEEE, 2024-08-30) Samanes Pascual, Javier; Oraa Iribarren, Iker; Gubía Villabona, Eugenio; López Taberna, Jesús; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
In grid-forming mode (GFM) doubly-fed induction generator based wind turbines connected to the grid, the converter connected to the rotor side is normally responsible for providing the grid-forming characteristics, while the grid-side converter commonly controls the DC-bus voltage thanks to a current control loop implemented in a rotating reference frame. The angle for the rotating reference frame is obtained by means of a phase-locked loop, which synchronizes the converter with the grid. However, this synchronization loop can introduce stability problems in weak grids. This paper proposes to synchronize the grid-side converter by means of the power synchronization loop of the GFM control of the rotor-side converter. This eliminates the need to use of a specific phase-locked loop, improving small-signal stability as demonstrated in the small-signal stability analysis performed in this paper.
Open Access
Control strategy for a droop-controlled grid-connected DFIG wind turbine
(IEEE, 2022) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The application of droop control techniques without inner current control loops to doubly-fed induction generator (DFIG) based wind turbines does not allow to provide a stable response at all operating points in terms of rotational speed and active and reactive power. After modeling the system dynamics and analyzing the causes of instability, this paper proposes a control strategy that allows to stabilize the system response at all possible operating points. Simulation results performed in MATLAB/Simulink validate the proposed control strategy proving its effectiveness.
Open Access
Modeling a grid-forming DFIG wind turbine
(IEEE, 2023-08-31) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This paper presents a small-signal state-space model that allows analyzing the dynamics of doubly-fed induction generator (DFIG)-based wind turbines in which grid-forming control strategies are implemented. Specifically, in this paper, a droop-controlled DFIG wind turbine is modeled. The system is modeled in the dq-axis, synchronized with the grid voltage, which simplifies the modeling by not having to linearize the terms dependent on the rotational speed of the dq-axis. Independent models for each element of the system are obtained, which are then combined to model the complete system under study. This modeling methodology provides great flexibility, allowing for easy inclusion of the LC harmonic filter, and enabling future incorporation of the grid-side converter to analyze its interaction with the rotor-side converter. The developed model is validated through simulation, demonstrating that it accurately reproduces the dynamic response of the system under study.
Open Access
Single-loop droop control strategy for a grid-connected DFIG wind turbine
(IEEE, 2023) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
When grid-forming droop control strategies are implemented in grid-connected power converters, two control strategies are widely used: the single-loop and multiloop droop controls. However, only multiloop droop control strategies with inner control loops have been implemented in doubly fed induction generator (DFIG)-based wind turbines so far. This article proposes the application of a single-loop droop control strategy to a DFIG wind turbine, which has not been previously explored or implemented. As shown in the article, the application of the conventional droop control without inner control loops to DFIG-based wind power systems does not ensure a stable response. After modeling the system dynamics and evaluating its stability, two causes of instability have been identified: a resonance at the rotor electrical frequency relevant at high slips and a phase margin reduction at low slips. To solve these instability issues two control solutions are proposed: the emulation of a virtual resistor and a phase rotation. The proposed control strategy allows stabilizing the system and achieving a fast and damped dynamic response. The effectiveness of the proposed control strategy is validated by experimental results.