Introduction to Wind Energy Systems

This paper introduces the GWIT EHD VAWT and the logic and history behind its development. We develop a simplified model to compare the performance of EHD VAWTs with conventional propeller machines. GWIT is engaged on a path to optimize the performance of its wind turbines in a wind farm setting. The paper details the characteristics of its first two prototypes - JJ and JJ3. The turbines are designed to meet the atmospheric conditions prevailing in China. While the EHD VAWT concept can be implemented in many configurations, GWIT has developed its turbines to operate over the broadest possible atmospheric conditions with an absolute minimum of moving mechanical components. We focus on turbine designs that more than double energy capture from the wind site. More than 90% of the turbine's content is of local manufacture. I. HISTORY OF THE EHD VAWT Wind turbines can trace their origins thousands of years into the past. Modern wind turbines can trace their current mission - the conversion of wind energy into electricity-back to the closing days of World War II when some Northern Continental European nations first converted some of their water pumping and grain milling wind turbines into producers of electricity. Since that time European nations began to devote significant research efforts into developing efficient machines to produce grid usable electricity from their abundant wind resources. More recently these efforts have been joined by North American and Asian nations. While some effort was devoted to the development of vertical axis wind turbines (VAWTs) almost all European research efforts were devoted to horizontal axis wind turbines (HAWTs). In Canada and the United States significant efforts were made to develop VAWTs, but the vast majority of wind energy research was devoted to HAWTs. By 1980 European designed HAWTs were focusing on economic parameters while Canadian and American efforts were still attempting to demonstrate feasibility. Numerous HAWT powered wind farms emerged but only two VAWT powered wind farms were in development or operation. Rely- ing on a Sandia National Laboratories design, FloWind fielded 512 170 kW F-17 and 300 kW F-19 VAWTs on two wind farms in California. Both wind farms operated successfully until they were replaced with Micon HAWTs between 1998 and 2002.

This paper discusses the design of a low tip-speed ratio, drag type vertical axis wind turbine which is incorporated with permanent magnet synchronous generator with maximum power point tracking (MPPT) strategy of control system to acquire the optimal performance. By using two dimensional large eddy simulations (LES) method as fluid dynamic model, the calculated power coefficient for this multi-blade vertical axis wind turbine may reach 0.34 at tip speed ratio (TSR) ranging from 0.8 to 1.0. Also, with the aids of simulation results, a direct coupled permanent magnet synchronous generator with 64-poles is designed and fabricated to generate 1.5 kW rated power at 90 rpm in 12 m/s wind speed. By changing the shape of magnet and applying approximate-skew method as stepped magnet configuration, the cogging torque and noise level of generator can be minimized. Moreover, MPPT control system with low current harmonic distortion level is designed to transfer energy into power grid with estimated 92% of power efficiency. Consequently, by eliminating gearbox system, low start-up wind speed, low current harmonic distortion and low cogging torque, the proposed of low acoustic/noise level wind turbine generator system can be applied for urban-environmental usage.

During recent years, wind energy has moved from an emerging technology to a nearly competitive technology. This fact, coupled with an increasing global focus on environmental concern and a political desire of a certain level of diversification in the energy supply, ensures wind energy an important role in the future electricity market. For this challenge to be met in a cost-efficient way, a substantial part of new wind turbine installations is foreseen to be erected in big onshore or offshore wind farms. This fact makes the production, loading and reliability of turbines operating under such conditions of particular interest.

Owing to its being an important component of renewable energy, wind energy is a kind of power generation method with the most mature, highly developed technologies and broad commercial prospects. The stable and efficient conversion of wind energy by wind turbines depends not only on the reliability of the wind power generation equipment itself, but also on the wind turbine control system, which, in turn, contributes to long-term safe and reliable operation of the wind farm fleet. It is exactly the wind turbine control system that is the main subject of this study. The key to efficient and stable operation of the entire wind energy conversion system is the control technology, which includes yaw control, pitch angle control, and maximum power point tracking control. The active yaw control system is one of the important components of a horizontal axis wind turbine's control system. To eliminate the uncertainty of wind direction influence on the turbine power output, a composite yaw control system has been checked. By using an active yaw system and maximum power point tracking system, the turbine position and its rotation speed are adjusted to enable the wind turbine to accurately track the wind direction and capture the wind energy to the fullest extent.

Commonly used horizontal-axis wind turbines (HAWT) have the following structure: two or three blades, a nacelle which contains power converting equipments, generators, and a tower which supports the nacelle. The generated power is transmitted from the nacelle to the ground. Due to this structure, the power transmission lines are twisted when the nacelle is yawing. Thus, slip ring or additional yaw control mechanism is required. We propose a new structure of HAWT which is free of this transmission line problem. Moreover, the size of inverter can be reduced since two generators are connected in parallel in our mechanism so that power is distributed. A controller for yawing is developed so that it works in harmony with the controller for power generation. An MPPT (Maximum Power Point tracking) algorithm is implemented for the proposed system and is validated by simulation.

PurposeThe purpose of this paper is to propose a predictive maintenance (PdM) system for hybrid degradation processes with continuous degradation and sudden damage to improve maintenance effectiveness.Design/methodology/approachThe PdM system updates the degradation model using partial condition monitoring information based on degradation type judgment. In addition, an extended multi-step-ahead updating stopping condition is adopted for performance enhancement of the PdM system.FindingsAn extensive numerical investigation compares the performance of the PdM system with the corresponding preventive maintenance (PM) policy. By carefully choosing the updating stopping condition, the PdM policy performs better than the corresponding PM policy.Research limitations/implicationsThe proposed PdM system is applicable to single-unit systems. And the continuous degradation process should be well modeled by the stochastic linear degradation model (Gebraeel et al., 2009).Originality/valueIn literature, there are abundant studies on PdM policies for continuous degradation processes. However, research on hybrid degradation processes still focuses on condition-based maintenance policy and a PdM policy for a hybrid degradation process is still unreported. In this paper, a PdM system for hybrid degradation processes with continuous degradation and sudden damage is proposed. The PdM system decides PM schedules by fully utilizing the condition monitoring data of each specific product, and can hopefully improve maintenance effectiveness.

The need for energy and electricity has been increasing globally, and this means more power is required from the power plants. Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming. Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges. Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy. Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). This paper firstly presents a general comparison between the HAWTs and VAWTs. Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient. Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions. This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum. The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles. Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas. hybrid Savonius-Darrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds. At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.

Wind energy is currently the fastest-growing energy source in the world, with a concurrent growth in demand for the expertise of engineers and researchers in the wind energy field. There are still many unsolved challenges in expanding wind power, and there are numerous problems of interest to systems and control researchers. In this paper, we first review the basic structure of wind turbines and then describe wind turbine control systems and control loops. Of great interest are the generator torque and blade pitch control systems, where significant performance improvements are achievable with more advanced systems and control research. We describe recent developments in advanced controllers for wind turbines and wind farms, and we also outline many open problems in the areas of modeling and control of wind turbines.

Large fixed and floating wind farms are planned in the US, the first of which will come on stream along the East Coast, and then possibly followed by the West Coast in deepwater. However, there are other regions in North and South America, and even the Caribbean that are rapidly aiming for offshore wind farms. One of those locations, offshore Texas, may develop ahead of the West Coast by taking advantage of the unparalleled expertise in ocean engineering in Texas gained through over 40 years of offshore oil and gas developments. In addition, Texas has regional competitive advantages that could result in another offshore boom for the region. Texas is the leading state for onshore wind power and consequently has some highly innovative research institutions and initiatives that could further push Texas to the forefront of regional, if not global, offshore wind technology development and deployment. The additional advantages that Texas can provide to wind farm developers based on its proximity to the Caribbean and South American offshore wind markets are also presented. As an example of innovation in Texas, the University of Texas at Dallas, DOE ARPA-E (Department of Energy Advanced Research Projects Agency – Energy) funded vertical axis wind turbine (VAWT) development is summarized (ARPA-E, 2020). While elements of VAWT technology are transferable to horizontal axis wind turbine (HAWT) technology to improve HAWT performance, more generally, the deployment of VAWTs overcomes many logistical and performance problems inherent in deploying HAWTs offshore. Such VAWT advantages are discussed. Two cases are presented comparing HAWT versus VAWT floating wind farms. The technology and execution differences of the two cases are compared and the net present value and internal rate of return are calculated conserving the technology differences. Discussion of forthcoming additional financing opportunities is also presented to illustrate how even in low-cost electric rate markets, offshore wind can still be feasible.

In wind turbines the power generation (power capture) and output torque depends on wind speed. Due to the rapid variations in wind speed, wind and inflow angle evaluating the output power becomes a challenging problem. Many optimization control techniques seek to extract the output power continuously. This paper focusses on dynamic analysis and control of variable wind turbine's rotor yaw angle and angular deflection. Earlier work used wind direction and pitch angle to control the performance of wind turbine. Using rotor yaw and angular deflection control of horizontal and vertical axis wind turbines is relatively new. For dynamic analysis, rotor yaw and rotor angular deflection, model techniques and experimental setup mechanisms were done in detail. Simulations were carried out in C++ to program an Arduino microcontroller and motor driver. Matlab software was used to interface wind turbine experimental setup, Arduino microcontroller and show the functions and aerodynamic forces. The result shows that the performance of wind turbine with this technique gives better result by increasing the power capture by about 15% more.

This chapter presents a low-cost, flexible lab test-bench wind farm for advanced research and education on wind turbine and wind farm design and control. The mechanical, electrical, electronic and control system design of the wind turbines, along with the dynamic models, parameters and classical pitch and torque controllers are introduced in detail. Furthermore, the study presents a variety of experiments that (a) quantifies the effect of the number of blades in the aerodynamic efficiency, (b) estimates the generator efficiency, (c) validates the rotor-speed pitch control system, (d) proves the concept of maximum power point tracking for individual wind turbines, (e) estimates the aerodynamic C p /λ characteristics, (f) calculates the power curve, and (g) studies the effect of wind farm topology configurations on the individual and global power efficiency. The experimental results prove that the dynamics of the test-bench corresponds well with full-scale wind turbines. This fact makes the test-bench wind farm appropriate for advanced research and education in wind energy systems.

Wind turbines (WT) maintenance management is in continuous development to improve the reliability, availability, maintainability and safety (RAMS)Ruiz de la Hermosa González-Carrato, Raúl of WTs, and to achieve time and cost reductions. The optimisation of the operation reliability involves the supervisory control and dataGarcía Márquez, Fausto Pedro acquisition to guarantee correct levels of RAMS. A fault detection and diagnosis methodology Alexander, Karyotakis is proposed for large-scalePapaelias, Mayorkinos industrial WTs. The method applies the wavelet and Fourier analysis to vibration signals. A number of turbines (up to 3) of the same type will be instrumented in the same wind farm. The data collected from the individual turbines will be fused and analysed together in order to determine the overall reliability of this particular wind farm and wind turbine type. It is expected that data fusion will allow a significant improvement in overall reliability since the value of the information gained from the various condition monitoring systems will be enhanced. Effort will also focus on the successful application of dependable embedded computer systems for the reliable implementation of wind turbine condition monitoring and control technologies.

Within a wind farm, multiple turbine wakes can interact and have a substantial effect on the overall power production. This makes an understanding of the wake recovery process critically important to optimizing wind farm efficiency. Vertical-axis wind turbines (VAWTs) exhibit features that are amenable to dramatically improving this efficiency. However, the physics of the flow around VAWTs is not well understood, especially as it pertains to wake interactions, and it is the goal of this thesis to partially fill this void. This objective is approached from two broadly different perspectives: a low-order view of wind farm aerodynamics, and a detailed experimental analysis of the VAWT wake. One of the contributions of this thesis is the development of a semi-empirical model of wind farm aerodynamics, known as the LRB model, that is able to predict turbine array configurations to leading order accuracy. Another contribution is the characterization of the VAWT wake as a function of turbine solidity. It was found that three distinct regions of flow exist in the VAWT wake: (1) the near wake, where periodic blade shedding of vorticity dominates; (2) a transition region, where growth of a shear-layer instability occurs; (3) the far wake, where bluff-body oscillations dominate. The wake transition can be predicted using a new parameter, the dynamic solidity, which establishes a quantitative connection between the wake of a VAWT and that of a circular cylinder. The results provide insight into the mechanism of the VAWT wake recovery and the potential means to control it.

The vertical axis wind turbine (VAWT) is considered an important device to utilize the renewable and sustainable wind energy. However, the relatively lower power coefficient has hampered its development. Therefore, this paper attempts to investigate the effect of swept blade employed in a VAWT on the enhancement in aerodynamic performance. A series of swept blades were studied in a small VAWT rotor, and the RANS SST k-ω turbulence model was utilized to simulate the flow field. The numerical model was validated against experimental data, and the aerodynamic performance was investigated with respect to force coefficients, vorticity distribution, static pressure distribution, and wind turbine wake, respectively. The results indicated that the swept blade could effectively increase power outputs by about 20% for the wind turbine. By reducing the drag coefficient, a high lift-drag ratio was achieved. And this configuration prevented the blade from suffering severe dynamic stall. Besides, the swept blade changed the distribution of low wind speed area in the wind turbine wake, which should be considered in the wind farm. It was concluded that this work provided a new way for the practical design and optimization of wind turbine.

In this work, a torque controller for a variable rotational speed wind turbine has been modelled using Reinforcement Learning and considering the Optimal Torque - Maximum Power Point Tracking problem as one of optimization. The reward optimization function is designed as a non-linear function depending mainly on the rotor power variation. Based on this, an optimal action (electromagnetic torque variation) regulates the turbine rotational speed. A simulated 1.5 MW three bladed wind turbine operation is managed by the torque controller. It keeps the turbine working at optimal operational conditions after a successful training process, which is carried out using the Proximal Policy Optimization algorithm. For the controller training, the turbine confronts constant and then randomly staggered wind speed behaviour. Time series of rotor angular speed, torque and power are presented. Our results show that the modelled controller is able to reach and maintain the wind turbine operation at its optimal power generation conditions. This methodology avoids using some empirical parameter characteristic of the Optimal Torque - Maximum Power Point Tracking algorithm widely used in wind turbine control systems.