Modeling, hardware-in-the-loop simulations and control design for a vertical axis wind turbine with high solidity

Vertical axis wind turbines (VAWTs) are advantageous in gusty, turbulent winds with rapidly changing direction such as surface winds by the virtue of their omnidirectional and simple design. Thus, a small-scale VAWT is favorable in urban areas, e.g., on top of a building, as well as in rural areas away from integrated grid systems where it can be used as a portable generator. In this thesis, a methodology is presented for the assessment of overall performance for a small-scale VAWT system that consists of a three-straight-bladed rotor with high solidity, electromechanical and power electronics components and controller. Salient features of this approach include a validated computational fluid dynamics (CFD) model and a hardware-inthe- loop (HIL) simulation. The time-dependent, two-dimensional CFD model is coupled with the dynamics of the rotor subject to inertia and generator load. The HIL test-bed consists of an electrical motor, a gearbox, a generator, a rectifier and a programmable electronic load. In this setup, the electrical motor emulates the VAWT rotor. The HIL simulation is used to study the impact of electromechanical energy conversion on the overall performance and to evaluate control algorithms in real-time. For variable-speed control of the turbine, maximum power point tracking (MPPT) and model predictive control (MPC) algorithms and a simple MPC-mimicking control are designed and tested. According to results, the coupled CFD model is an effective tool in evaluation of the realistic transient behavior of the VAWT including the inertial effects of the rotor and the feedback control; the electromechanical energy conversion has a profound effect on the power characteristics and the efficiency of the VAWT system; the MPC and MPC-mimicking control algorithms outperform the MPPT algorithms in terms of energy output by allowing deviations from the maximum power instantaneously for future gains in energy generation; and all of the controllers perform satisfactorily under step wind, wind gust and real wind conditions

Inverse Dynamics Trajectory Optimization for Contact-Implicit Model Predictive Control

Robots must make and break contact to interact with the world and perform useful tasks. However, planning and control through contact remains a formidable challenge. In this work, we achieve real-time contact-implicit model predictive control with a surprisingly simple method: inverse dynamics trajectory optimization. While trajectory optimization with inverse dynamics is not new, we introduce a series of incremental innovations that collectively enable fast model predictive control on a variety of challenging manipulation and locomotion tasks. We implement these innovations in an open-source solver, and present a variety of simulation examples to support the effectiveness of the proposed approach. Additionally, we demonstrate contact-implicit model predictive control on hardware at over 100 Hz for a 20 degree-of-freedom bi-manual manipulation task

Comparisons of controller performance for small-scale verti-cal axis wind turbines

Small-scale vertical axis wind turbines (VAWTs) are attractive for portable power generation. Controller performance is very important in rapidly varying gusty winds commonly observed in urban and rural areas. In this paper, a hill-climb searching (HSC) maximum power point tracking (MPPT), an energy-maximizing model predictive control (MPC) and a simple nonlinear control (SNC) as an MPC surrogate are presented. The control algorithms are tested through a software-only electromechanical model and with hardware-in-the loop test-bed that includes electromechanical and power electronics components. Effects of power coefficient oscillations on dynamic performance are investigated. Results show that proposed controllers perform satisfactorily for wind gust and real wind profiles; the SNC serves as a viable surrogate for the MPC; the model-free, wind speed sensorless MPPT is favorable for small-scale applications; and power coefficient oscillations do not have a significant impact on the dynamic performance of the controllers

Hardware-in-the-loop simulations and control design for a small vertical axis wind turbine

Control design plays an important role in wind energy conversion systems in achieving high efficiency and performance. In this study, hardware-in-the-loop (HIL) simulations are carried out to design a maximum power point tracking (MPPT) algorithm for small vertical axis wind turbines (VAWTs). Wind torque is calculated and applied to an electrical motor that drives the generator in the HIL simulator, which mimics the dynamics of the rotor. To deal with disturbance torques in the HIL system, a virtual plant is introduced to obtain an error between the speeds in the HIL system and virtual plant. This error is used by a proportional-integral (PI) controller to generate a disturbance torque compensation signal. The MPPT algorithm is tested in the HIL simulator under various wind conditions, and the results are compared with numerical simulations. The HIL simulator successfully mimics the dynamics of the VAWT under various wind conditions and provides a realistic framework for control designs

Transient performance of a vertical axis wind turbine

A coupled CFD/rotor dynamics modeling approach is presented for the analysis of realistic transient behavior of a height-normalized, three-straight-bladed VAWT subject to inertial effects of the rotor and generator load which is manipulated by a feedback control under standardized wind gusts. The model employs the k-ε turbulence model to approximate unsteady Reynolds-averaged Navier-Stokes equations and is validated with data from field measurements. As distinct from related studies, here, the angular velocity is calculated from the rotor's equation of motion; thus, the dynamic response of the rotor is taken into account. Results include the following: First, the rotor's inertia filters large amplitude oscillations in the wind torque owing to the first-order dynamics. Second, the generator and wind torques differ especially during wind transients subject to the conservation of angular momentum of the rotor. Third, oscillations of the power coefficient exceed the Betz limit temporarily due to the energy storage in the rotor, which acts as a temporary buffer that stores the kinetic energy like a flywheel in short durations. Last, average of transient power coefficients peaks at a smaller tip-speed ratio for wind gusts than steady winds

Küçük dikey eksenli rüzgâr türbini için basit kontrol tasarımı (Simple control design for a small vertical axis wind turbine)

Bu makalede, küçük dikey eksenli rüzgâr türbinin elde ettiği enerjiyi maksimize edecek basit bir kontrolör tasarlanmıştır. Bu önerilen kontrol algoritmasının amacı mevcut sistemlere kıyasla daha basit bir yapıda olmasıdır. Algoritma kontrol işlemini sisteme uygulanan yük katsayısını önceden belirlenen değer aralıklarında müdahalede bulunarak yapabilmektedir. Bunu yapmak için önceden enerjiyi maksimize eden bir optimizasyon yöntemiyle belirlenmiş olan sınır değerlerinden faydalanmaktadır. Bu makalede, değişik simülasyonlar sonucu elde edilen enerjiyi maksimize ederken, basitleştirilmiş bir dikey eksenli rüzgâr türbini modeli kullanılmıştır

A Holistic Approach to Human-Supervised Humanoid Robot Operations in Extreme Environments

Nuclear energy will play a critical role in meeting clean energy targets worldwide. However, nuclear environments are dangerous for humans to operate in due to the presence of highly radioactive materials. Robots can help address this issue by allowing remote access to nuclear and other highly hazardous facilities under human supervision to perform inspection and maintenance tasks during normal operations, help with clean-up missions, and aid in decommissioning. This paper presents our research to help realize humanoid robots in supervisory roles in nuclear environments. Our research focuses on National Aeronautics and Space Administration (NASA’s) humanoid robot, Valkyrie, in the areas of constrained manipulation and motion planning, increasing stability using support contact, dynamic non-prehensile manipulation, locomotion on deformable terrains, and human-in-the-loop control interfaces

Effects of wind gusts on a vertical axis wind turbine with high solidity

We present a time-dependent, two-dimensional computational fluid dynamics (CFD) model coupled with the dynamics of the rotor for a height-normalized, small-scale high-solidity vertical axis wind turbine (VAWT) that consists of three straight blades, which are cambered to fit the circular path. The model employs the k-ε turbulence model to approximate unsteady Reynolds-averaged Navier-Stokes equations. The CFD model is validated with data from field measurements. The angular velocity, wind torque, power output and the power coefficient of the rotor are obtained for different wind velocities and gusts from the CFD simulations. A simple rotor velocity feedback control is designed to maximize the power output of the VAWT and implemented in simulations for wind transients. Furthermore, local angle of attack and net incident velocity on the blades are calculated from the local velocity field. Oscillatory transient power coefficient has a very large amplitude owing to the oscillations in the wind torque, but the fluctuations in the generator torque are much smaller despite the large solidity of the VAWT. Overall results show that the proposed coupled modeling approach is an effective tool in evaluation of the transient performance of VAWT systems including the inertial effects of the rotor and the feedback control

Modeling, hardware-in-the-loop simulations and control design for small-scale vertical axis wind turbines

In this study, we present a methodology for the assessment of overall performance for vertical axis wind turbines (VAWT) with straight blades. Salient features of our approach include a validated computational fluid dynamics (CFD) model and a hardware-in-the loop (HIL) test-bed. The two-dimensional, time-dependent CFD model uses the k-ε turbulence model and is coupled with the dynamics of the rotor involving friction and generator torques. The power coefficient curve for the rotor is obtained from the CFD simulations by varying the generator torque over time, and then used in the HIL test-bed that consists of an electrical motor, a gearbox, a permanent magnet synchronous generator, and an electronic load. In this setup, the VAWT rotor is mimicked by the electrical motor based on a power coefficient curve obtained from CFD simula-tions. Effects of the electrical conversion and control design on the overall performance of the VAWT are studied in the HIL setup. Additionally, a simple nonlinear control (SNC) algorithm that mimics a model predictive controller and two different adaptations of the maximum power point tracking (MPPT) algorithm with fixed and variable step-sizes are designed and implemented in HIL simulations. According to results, the generator has a profound effect on the overall power output and the efficiency of the turbine; and the SNC and MPPT algorithms perform satisfactorily under step wind conditions

Modeling, hardware-in-the-loop simulations and control design for small-scale vertical axis wind turbines

In this study, we present a methodology for the assessment of overall performance for vertical axis wind turbines (VAWT) with straight blades. Salient features of our approach include a validated computational fluid dynamics (CFD) model and a hardware-in-the loop (HIL) test-bed. The two-dimensional, time-dependent CFD model uses the k-ε turbulence model and is coupled with the dynamics of the rotor involving friction and generator torques. The power coefficient curve for the rotor is obtained from the CFD simulations by varying the generator torque over time, and then used in the HIL test-bed that consists of an electrical motor, a gearbox, a permanent magnet synchronous generator, and an electronic load. In this setup, the VAWT rotor is mimicked by the electrical motor based on a power coefficient curve obtained from CFD simula-tions. Effects of the electrical conversion and control design on the overall performance of the VAWT are studied in the HIL setup. Additionally, a simple nonlinear control (SNC) algorithm that mimics a model predictive controller and two different adaptations of the maximum power point tracking (MPPT) algorithm with fixed and variable step-sizes are designed and implemented in HIL simulations. According to results, the generator has a profound effect on the overall power output and the efficiency of the turbine; and the SNC and MPPT algorithms perform satisfactorily under step wind conditions