Fast Coordinated Control of DFIG Wind Turbine Generators for Low and High Voltage Ride-Through

This paper presents a fast coordinated control scheme of the rotor side converter (RSC), the Direct Current (DC) chopper and the grid side converter (GSC) of doubly fed induction generator (DFIG) wind turbine generators (WTGs) to improve the low voltage ride through (LVRT) and high voltage ride through (HVRT) capability of the DFIG WTGs. The characteristics of DFIG WTGs under voltage sags and swells were studied focusing on the DFIG WTG stator flux and rotor voltages during the transient periods of grid voltage changes. The protection schemes of the rotor crowbar circuit and the DC chopper circuit were proposed considering the characteristics of the DFIG WTGs during voltage changes. The fast coordinated control of RSC and GSC were developed based on the characteristic analysis in order to realize efficient LVRT and HVRT of the DFIG WTGs. The proposed fast coordinated control schemes were verified by time domain simulations using Matlab-Simulink

Application of Unified Power Flow Controller to Improve the Performance of Wind Energy Conversion System

This research introduces the unified power flow controller (UPFC) as a means to improve the overall performance of wind energy conversion system (WECS) through the development of an appropriate control algorithm. Also, application of the proposed UPFC control algorithm has been extended in this research to overcome some problems associated with the internal faults associated with WECS- voltage source converter (VSC), such as miss-fire, fire-through and dc-link faults

Techniques for Ensuring Fault Ride-Through Capability of Grid Connected DFIG-Based Wind Turbine Systems: A Review

Renewable energy sources (RES) are being integrated to electrical grid to complement the conventional sources to meet up with global electrical energy demand. Among other RES, Wind Energy Conversion Systems (WECS) with Doubly Fed Induction Generator (DFIG) have gained global electricity market competitiveness because of the flexible regulation of active and reactive power, higher power quality, variable speed operation, four quadrant converter operation and better dynamic performance. Grid connected DFIG-based WECS are prone to disturbances in the network because of direct connection of stator windings to grid. The ability of the Wind Turbine (WT) to remain connected during grid faults is termed the Fault Ride-Through (FRT) capability. The grid code requirement for integrating the DFIG-based WTs to power networks specified that they must remain connected and support the grid stability during grid disturbances of up to 1500 ms. The use of compensation devices offers the best FRT compliance thereby protecting the DFIG and the converters from voltage fluctuations and over currents during the grid fault. The paper presents a review of techniques employed in ensuring FRT compliance. The article also proposes the state-of-the-art techniques for compensating voltage sag/swell and limiting the fault short-circuit current. Keywords: Renewable energy sources, DFIG, wind turbine system, fault ride-through, grid codes, dual-functional DV

Offshore Wind Farm-Grid Integration: A Review on Infrastructure, Challenges, and Grid Solutions

Recently, the penetration of renewable energy sources (RESs) into electrical power systems is witnessing a large attention due to their inexhaustibility, environmental benefits, storage capabilities, lower maintenance and stronger economy, etc. Among these RESs, offshore wind power plants (OWPP) are ones of the most widespread power plants that have emerged with regard to being competitive with other energy technologies. However, the application of power electronic converters (PECs), offshore transmission lines and large substation transformers result in considerable power quality (PQ) issues in grid connected OWPP. Moreover, due to the installation of filters for each OWPP, some other challenges such as voltage and frequency stability arise. In this regard, various customs power devices along with integration control methodologies have been implemented to deal with stated issues. Furthermore, for a smooth and reliable operation of the system, each country established various grid codes. Although various mitigation schemes and related standards for OWPP are documented separately, a comprehensive review covering these aspects has not yet addressed in the literature. The objective of this study is to compare and relate prior as well as latest developments on PQ and stability challenges and their solutions. Low voltage ride through (LVRT) schemes and associated grid codes prevalent for the interconnection of OWPP based power grid have been deliberated. In addition, various PQ issues and mitigation options such as FACTS based filters, DFIG based adaptive and conventional control algorithms, ESS based methods and LVRT requirements have been summarized and compared. Finally, recommendations and future trends for PQ improvement are highlighted at the end

Impact of DC-link fault on the dynamic performance of DFIG

The number of doubly fed induction generators (DFIG) connected to the existing network has increased significantly worldwide during the last two decades. This triggers off manufactures to improve the performance of DFIG through robust and reliable design. The stator in DFIG is directly connected to the grid whereas the rotor is interfaced to the grid through two voltage source converters; rotor side converter (RSC) and grid side converter (GSC), which are considered as the crux of the DFIG system. The converter stations determine the ability of wind turbine to operate optimally during wind speed fluctuation and it can provide reactive power support to the grid during grid disturbance events. The DC capacitor link between the two converters allows optimum and smooth power exchange between DFIG and the grid. Therefore, any faults within the DC link will affect the overall performance of the DFIG. This paper investigates the impact of open circuit and short circuit faults in the DC link capacitor on the dynamic performance of the DFIG. The compliance of the wind energy conversion (WEC) system with different grid codes such as those of Denmark, Spain, Nordic and Sweden under such faults is also investigated

Effect of intermittent voltage source converter faults on the overall performance of wind energy conversion system

The doubly fed induction generator (DFIG) is interfaced to the AC network through voltage source converters (VSCs) which are considered to be the core of the DFIG system. This paper investigates the impact of different intermittent VSC faults on the overall performance of a DFIG-based wind energy conversion system (WECS). The fault ride through capability of the DFIG under various VSC faults is also investigated. Faults such as open circuit and short circuit across the switches, when they occur within the grid side converter (GSC) and rotor side converter (RSC), are considered and compared in this paper. Short circuit and open circuit across the DC-link capacitor are also considered in this study as common VSC problems. Simulation results indicate that the short circuit faults have a severe impact on the overall performance of the DFIG, especially when they occur within the GSC. This is attributed to the fact that the GSC directly regulates the point of common coupling voltage. The open circuit faults have less impact on the performance of the DFIG-based WECS. A proper controller along with flexible AC transmission device should be available to compensate the required active and reactive power during these faults. A protection technique is necessary to detect these faults in advance to protect the VSC switches and the machine winding from any catastrophic failure

Voltage Distortion Mitigation in a Distributed Generation-integrated Weak Utility Network Via a Self-tuning Filter-based Dynamic Voltage Restorer

The dynamic voltage restorer (DVR) is mainly used in a utility grid to protect sensitive loads from power quality problems, such as voltage sags and swells. However, the effectiveness of the DVR can wane under unbalanced grid voltage conditions. Recently, DVR control algorithms have been developed that enable the elimination of voltage harmonics in weak and distorted utility networks. This paper presents a modified control method for the DVR, which can (1) compensate the voltage swell and (2) eliminate the voltage harmonics in a combined utility condition consisting of voltage unbalance and harmonic distortion. A self-tuning filter (STF) is used along with the pq controlmethod to increase the control performance of the DVR. One of the advantages of STF is that it eliminates the need to have multiple filters as part of the control method, and thus reduces the controller complexity. Analysis of the fault ride-through capability of the new DVR revealed an improvement in the voltage stability offered to distributed generation-integrated weak utility networks. The proposed DVR control method is modeled in MATLAB/Simulink and tested in both off-line and real-time environments using theOPALRT real-time platform. Results are then presented as a verification of the proposed system

Integration improvement of DFIG-based wind turbine into the electrical grid

[ENG] This doctoral thesis in electrical engineering is presented as five research works linked together by the same theme. Five articles were published in indexed journals. In this sense, each of these works forms a piece of the puzzle constructed around the subject ”wind farms integration into the electricity grid.” To better understand the articulation between these works, this thesis is structured in three parts: The first part treats the Fault Ride Through (FRT) capability of the Grid-connected DFIG-based Wind Turbine. The first proposed approach is a hybrid method combining two methods (active and passive methods): The active method aims to develop the control of DFIG. In contrast, the passive method is applied for severe voltage faults using hardware protection circuits. Otherwise, the second proposed approach is a control design implemented to the power converters using Proportional-Resonant regulators in a stationary two-phase(α−β) reference frame. The control performance is significantly validated by applying the real-time simulation for the rotor side converter and the hardware in the loop simulation technic for the experiment part of the generator’s grid side converter control. This thesis’s second part presents a new fault diagnosis and fault-tolerant control strategy for doubly fed induction generator with DC output based on predictive torque control. Generally, the current sensor failures can deteriorate the reliability and the performance of the control system and can lead to the malfunction of the predictive control strategy since the rotor-and stator flux cannot be estimated correctly. The proposed fault diagnosis can deal with all types of sensor faults. A non-linear observer adapted to the studied system to achieve smooth operation continuity when two or all the current sensors are faulty. The proposed approach’s feasibility and robustness are achieved by testing different sensor faults on the stator-and rotor-current and under different operation mode cases. The third part focuses on calculating the wind capacity credit by integrating the Moroccan project on the wind energy of 1000 MW in 2020. After introducing the Moroccan Integrated Wind Energy Project, a wind capacity credit assessment program will be implemented on Matlab software, including the complete information about” installed capacity, number of plants, failure rate, types of installed units, peak demand, etc.” This program will be used to calculate the safety rate of an electrical system as well as the capacity credit of Morocco’s electricity production network. The research provides conclusions according to comments and assessment of the impact of this electric energy integration based on wind generation. [SPA] Esta tesis doctoral en ingeniería eléctrica se presenta como cinco trabajos de investigación vinculados entre sí por un mismo tema. Se publicaron cinco artículos en revistas indexadas. En este sentido, cada uno de estos trabajos forma una pieza del rompecabezas construido en torno al tema “Integración de parques eólicos en la red eléctrica”. Para comprender mejor la articulación entre estos trabajos, esta tesis se estructura en tres partes: La primera parte trata la capacidad Fault Ride Through (FRT) de la turbina eólica basada en DFIG conectada a la red. El primer enfoque propuesto es un método híbrido que combina dos métodos (métodos activo y pasivo): El método activo tiene como objetivo desarrollar el control de DFIG. En contraste, el método pasivo se aplica para fallos severos de voltaje usando circuitos de protección de hardware. De lo contrario, el segundo enfoque propuesto es un diseño de control implementado para los convertidores de potencia utilizando reguladores de resonancia proporcional en un marco de referencia estacionario de dos fases (α−β). El rendimiento del control se valida significativamente aplicando la simulación en tiempo real para el convertidor del lado del rotor y la técnica de simulación de hardware en el bucle para la parte experimental del control del convertidor del lado de la red del generador. La segunda parte de esta tesis presenta una nueva estrategia de diagnóstico de fallos y control tolerante de fallos para un generador de inducción doblemente alimentado con salida de CC basado en control predictivo de par. Generalmente, los fallos del sensor de corriente pueden deteriorar la confiabilidad y el rendimiento del sistema de control y pueden conducir al mal funcionamiento de la estrategia de control predictivo ya que el flujo del rotor y el estator no se puede estimar correctamente. El diagnóstico de fallos propuesto puede tratar todo tipo de fallos del sensor. Un observador no lineal adaptado al sistema estudiado para lograr una continuidad de operación suave cuando dos o todos los sensores de corriente están defectuosos. La viabilidad y solidez del enfoque propuesto se logran probando diferentes fallos de sensor en la corriente del estator y del rotor y en diferentes casos de modo de operación. La tercera parte se centra en el cálculo del crédito de capacidad eólica mediante la integración del proyecto marroquí sobre la energía eólica de 1000 MW en 2020. Después de presentar el Proyecto Integrado de Energía Eólica de Marruecos, se implementará un programa de evaluación del crédito de capacidad eólica en el software Matlab, incluido la información sobre “capacidad instalada, número de plantas, tasa de fallos, tipos de unidades instaladas, pico de demanda, etc.” Este programa se utilizará para calcular la tasa de seguridad de un sistema eléctrico, así como el crédito de capacidad de la red de producción de electricidad de Marruecos. La investigación brinda conclusiones según comentarios y evaluación del impacto de esta integración de energía eléctrica basada en la generación eólicaEscuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Energías Renovables y Eficiencia Energétic