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

The control of power electronic converters for grid code compliance in wind energy generation systems

This research report reviews some of the latest control schemes for the power electronic converters found in modern variable speed wind turbines in order to comply with various grid codes. Various control schemes, in order to comply with low voltage ride-through requirements, active and reactive power control and frequency control, are presented. The report first investigates the South African grid code requirements for wind energy generation, and then makes a comparison to grid codes of countries with significant penetration levels and vast experience in wind energy generation. This is followed by a review of the state of the art in fixed and variable speed wind turbine technologies. The research revealed that Type 3 generators offer significant advantages over others but suffer due to grid faults. Various active control schemes for fault ride-through were researched and the method of increasing the rotor speed to accommodate the power imbalance was found to be the most popular. It was found that Type 4 generators offer the best fault ride-through capabilities due to their full scale converters. The research will assist power system operators to develop appropriate and effective grid codes to enable a stable and reliable power system. The research will also provide turbine manufacturers and independent power producers with a comprehensive view on grid codes and relate them to the associated turbine technologies

Large Grid-Connected Wind Turbines

This book covers the technological progress and developments of a large-scale wind energy conversion system along with its future trends, with each chapter constituting a contribution by a different leader in the wind energy arena. Recent developments in wind energy conversion systems, system optimization, stability augmentation, power smoothing, and many other fascinating topics are included in this book. Chapters are supported through modeling, control, and simulation analysis. This book contains both technical and review articles

Fault ride-through capability of multi-pole permanent magnet synchronous generator for wind energy conversion system

Thesis (MEng (Electrical Engineering))--Cape Peninsula University of Technology, 2019Wind has become one of the renewable energy technologies with the fastest rate of growth. Consequently, global wind power generating capacity is also experiencing a tremendous increase. This tendency is expected to carry on as time goes by, with the continuously growing energy demand, the rise of fossil fuels costs combined to their scarcity, and most importantly pollution and climate change concerns. However, as the penetration level increases, instabilities in the power system are also more likely to occur, especially in the event of grid faults. It is therefore necessary that wind farms comply with grid code requirements in order to prevent power system from collapsing. One of these requirements is that wind generators should have fault ride-through (FRT) capability, that is the ability to not disconnect from the grid during a voltage dip. In other words, wind turbines must withstand grid faults up to certain levels and durations without completely cutting off their production. Moreover, a controlled amount of reactive power should be supplied to the grid in order to support voltage recovery at the connection point. Variable speed wind turbines are more prone to achieve the FRT requirement because of the type of generators they use and their advanced power electronics controllers. In this category, the permanent magnet synchronous generator (PMSG) concept seems to be standing out because of its numerous advantages amongst which its capability to meet FRT requirements compared to other topologies. In this thesis, a 9 MW grid connected wind farm model is developed with the aim to achieve FRT according to the South African grid code specifications. The wind farm consists of six 1.5 MW direct-driven multi-pole PMSGs wind turbines connected to the grid through a fully rated, two-level back-to-back voltage source converter. The model is developed using the Simpowersystem component of MATLAB/Simulink. To reach the FRT objectives, the grid side controller is designed in such a way that the system can inject reactive current to the grid to support voltage recovery in the event of a grid low voltage. Additionally, a braking resistor circuit is designed as a protection measure for the power converter, ensuring by the way a safe continuous operation during grid disturbance

Analysis and Modeling of Advanced Power Control and Protection Requirements for Integrating Renewable Energy Sources in Smart Grid,

Attempts to reduce greenhouse gas emissions are promising with the recent dramatic increase of installed renewable energy sources (RES) capacity. Integration of large intermittent renewable resources affects smart grid systems in several significant ways, such as transient and voltage stability, existing protection scheme, and power leveling and energy balancing. To protect the grid from threats related to these issues, utilities impose rigorous technical requirements, more importantly, focusing on fault ride through requirements and active/reactive power responses following disturbances. This dissertation is aimed at developing and verifying the advanced and algorithmic methods for specification of protection schemes, reactive power capability and power control requirements for interconnection of the RESs to the smart grid systems. The first findings of this dissertation verified that the integration of large RESs become more promising from the energy-saving, and downsizing perspective by introducing a resistive superconducting fault current limiter (SFCL) as a self-healing equipment. The proposed SFCL decreased the activation of the conventional control scheme for the wind power plant (WPP), such as dc braking chopper and fast pitch angle control systems, thereby increased the reliability of the system. A static synchronous compensator (STATCOM) has been proposed to assist with the uninterrupted operation of the doubly-fed induction generators (DFIGs)-based WTs during grid disturbances. The key motivation of this study was to design a new computational intelligence technique based on a multi-objective optimization problem (MOP), for the online coordinated reactive power control between the DFIG and the STATCOM in order to improve the low voltage ride-through (LVRT) capability of the WT during the fault, and to smooth low-frequency oscillations of the active power during the recovery. Furthermore, the application of a three-phase single-stage module-integrated converter (MIC) incorporated into a grid-tied photovoltaic (PV) system was investigated in this dissertation. A new current control scheme based on multivariable PI controller, with a faster dynamic and superior axis decoupling capability compared with the conventional PI control method, was developed and experimentally evaluated for three-phase PV MIC system. Finally, a study was conducted based on the framework of stochastic game theory to enable a power system to dynamically survive concurrent severe multi-failure events, before such failures turn into a full blown cascading failure. This effort provides reliable strategies in the form of insightful guidelines on how to deploy limited budgets for protecting critical components of the smart grid systems

A coordinated control of PMSG based wind turbine generator to improve fault-ride-through performance and transient stability

With the high penetration of wind power into the medium and low voltage power grid, ensuring power quality and transient stability following the utility grid codes become challenging nowadays. Wind power fluctuates with the variation of wind speed which leads to the voltage regulation and frequency control problems in the power grid. Among the issues wind power systems are facing, grid fault is a major one. According to the utility grid codes, wind turbine generators (WTGs) need to have enough fault ride through (FRT) capability. Different configurations of power converters and control techniques have been developed to address this issue. However, a coordinated controller which is capable of the grid voltage regulation, frequency control, and DC link overvoltage minimisation altogether at the time of grid faults is yet to be reported in any literature. This PhD research is focused on developing such a coordinated control method for a permanent magnet synchronous generator (PMSG) based WTG. This coordinated control combines a pitch angle control, a flux weakening control and a reactive power control to enhance the low voltage ride through (LVRT) capability of the PMSG based variable speed wind energy conversion system (WECS). The design process of the controller parameters and the stability of proposed control strategy have been analysed. Here, the pitch angle controller is modified to adjust the pitch for wind power smoothing as well as LVRT enhancement during variable wind speeds and grid fault respectively. The flux weakening controller is used to reduce the flux linkages of PMSG by supplying negative field regulating current to reduce the DC link overvoltage during grid voltage dips. Additionally, static compensator (STATCOM) or grid side converter (GSC) is used to provide reactive power support during the grid faults. Extensive simulations of the proposed method have been carried out under different cases. The proposed control method is compared with the braking chopper (BC) and the battery energy storage system (BESS) based conventional controls via simulations results and are verified to perform better in providing FRT. Frequency stability of the grid connected WECS after the fault recovery is also an important issue which needs to be solved. If the frequency fluctuation goes beyond the safe limit, the power system will collapse creating a cascaded failure that was seen in the South Australian Power System in 2016. Therefore, it is essential to provide primary frequency control support for a stable operation of the power system. Two control methods are considered in this PhD research to provide the grid frequency stability. A simultaneous controller is developed based on the inertia support from the wind turbine and the DC-link capacitor energy to provide the primary frequency control from a PMSG based variable speed WECS. Another approach is developed based on the PMSG flux linkage controller with a Superconducting Magnetic Energy Storage (SMES). The SMES is considered here due to its higher efficiency over other energy storage devices. In this approach, the PMSG flux increases or decreases according to the frequency variation. Similarly, SMES also absorbs or injects some amount of real power when the system frequency is increased or decreased. Both strategies are verified with the WTGS connected to the single and multi-machine power systems under different wind speeds, load demand variations, and grid faults. Time series simulation results illustrate that a significant enhancement of frequency regulation is achieved with both proposed controllers