Considerations for Testing Full-Scale Wind Turbine Nacelles with Hardware-in-the-Loop

Full-scale wind turbine nacelle testing with Hardware-In-the-Loop (HIL) configuration allows full operational certification testing with native nacelle controllers, as opposed to open-loop testing which requires significant modification of the controller to bypass missing subsystems when the nacelle is mounted on the test bench. Implementation of Hardware-In-the-Loop testing involves running a real-time simulation of a full turbine model in parallel with the test bench in order to account for the missing rotor, tower, platform, and actuators. For successful implementation of this method, first, the simulation model should be able to capture the dynamic characteristics of the turbine accurately while also meeting the real-time requirements. Second, the deviations resulting from the different boundary conditions between the drivetrain in a full turbine and the test bench environment should be mitigated. In the first part of the study, a sensitivity analysis is performed using a baseline wind turbine model to determine the minimum drivetrain fidelity level necessary to capture the dynamics with a focus on the torsional characteristics that are crucial for performing electro-mechanical certification tests. The results show that the torsional dynamics are dominated by the flexibility of the main shaft and the gearbox supports. The rest of the components can be significantly simplified thereby reducing the total number of modes and degrees of freedom for real-time execution. In the second part of the study, the reduced drivetrain model is utilized in a comparative analysis to quantify the deviations in torsional dynamics resulting from the rigid connections and test bench components (motor, reduction gearbox, and the load application unit) replacing the tower and rotor, respectively. It is found that the different mechanical interfaces can shift the first torsional mode of the drivetrain by as much as 19% which can significantly impact electro-mechanical responses. The feasibility of exploiting the test bench speed controller to introduce virtual inertia, damping, and stiffness and compensating for such differences is studied. It is demonstrated that the controller can be tuned to perform pole placement and match the torsional frequencies between the coupled test bench-nacelle and the full turbine. Finally, the performance of the tuned controller is verified using two case studies: a) free response to characterize the torsional responses in a low voltage ride through scenario, and b) forced response to evaluate its ability to track a highly dynamic speed profile resulting from a turbulent wind profile

Determining Wind Turbine Drivetrain Test Bench Capability to Replicate Dynamic Loads: Evaluation Methods and Their Validation

Wind turbine drivetrain test facilities are impressive laboratories that offer a controlled environment to test the response of drivetrains under design conditions. The stochastic nature of the wind results in highly dynamic loads and this is reflected in the design standards and certification process of wind turbines. A wide range of wind conditions and turbine operating states are prescribed as design load cases. The design process of a wind turbine yields thousands of time series of fluctuating forces, bending moments and speed to cover these design load cases. The capability of a test bench to replicate such dynamic loads has been the subject of this research at Clemson University in cooperation with GE Renewable Energy. This collaborative research project used the 7.5-MW test bench of Clemson University to test two multi-MW drivetrain designs used on GE onshore wind turbines. This testing provided the first demonstration that the design load cases that typically drive the design of wind turbine drivetrains can be replicated on a test bench with an acceptable accuracy. The acceptance threshold for the accuracy was found to vary depending on the specific loads. The yaw and nodding bending moments are most critical to replicate accurately due to being generally much large than the forces, and the measurement error of the load application unit of the test bench was demonstrated to be an appropriate threshold based on multibody simulations. The dynamic response of one of the drivetrains tested was simulated using inputs to the model with and without the measured tracking error. This is the error between the loads commanded to the test bench and the loads that are measured at the point of application. For the drivetrain displacements considered, the multibody simulations quantified the impact of the tracking error on the displacements to be within 11% of the peak displacement. Most displacements were within 2.6%-3.1% of the peak displacement on average. Multibody simulations were also used to quantify the impact of a cross-coupling effect between forces and bending moments that occurs when the load application unit of the test bench applies loads dynamically. The impact on the dynamic response of the drivetrain from the cross-coupling was found to be generally small and acceptable despite significant tracking error on the forces. The testing also served as experimental verification of a novel method for the early assessment of the capability of a test bench to replicate dynamic loads. The identification of load time series that should be replicated with an acceptable level of accuracy and those that are likely beyond the capability of the test bench was validated. A new avenue of research in the wind energy sector has been initiated, and several recommendations are proposed for growing the knowledge base and the role of test benches for design certification purposes

Hardware in the loop, all-electronic wind turbine emulator for grid compliance testing

During the last years the distribution of renewable energy sources is continuously increasing and their influence on the distribution grid is becoming every year more relevant. As the increasing integration of renewable resources is radically changing the grid scenario, grid code technical requirements as are needed to ensure the grid correct behavior. To be standard compliant wind turbines need to be submitted to certification tests which usually must be performed on the field. One of the most difficult tests to be performed on the field is the low voltage ride through (LVRT) certitication due to the following resons: • The standards specify it must be performed ad different power levels. For this reasons it is necessary to wait for the right atmospheric conditions. • It requires a voltage sag generator which is usually expensive and bulky. • The voltage sag generator needs to be cabled between the grid and the wind turbine. • The voltage sag generator causes disturbances and perturbation on the power grid, for this reasons agreements with the distributor operator are needed. For all these reasons a laboratory test bench to perform the LVRT certification tests on wind turbines would be a more controlled and inexpensive alternative to the classic testing methodology. The research presented in this thesis is focused on the design and the realization of a test bench to perform certification tests on energy converters for wind turbines in laboratory. More specifically, the possibility of performing LVRT certification tests directly in laboratory over controlled conditions would allow faster testing procedures and less certification overall costs. The solution presented in this thesis is based on a power hardware in the loop implementing a digitally-controlled, power electronics-based emulation of a wind turbine. This emulator is used to drive the electronic wind energy converter (WEC) under test. A grid emulator is used to apply voltage sags to the wind turbine converter and perform LVRT certification tests. In this solution AC power supplies are used to emulate both the wind turbine and the grid emulator. For this reason the test bench power rating is limited to the AC supplies one. Two working versions of the test bench has been realized and successfully tested. The work here presented has evolved through the following phases: • Study of the grid code requirements and the state of the art. • Modeling of the parts of a wind turbine and complete system simulations

Review on hardware-in-the-loop simulation of wave energy converters and power take-offs

This paper reviews the state-of-the-art on Hardware-In-The-Loop simulation methodologies and technologies applied in the research field of wave energy converters. It reveals important issues, such as an unclear taxonomy and representations of these methodologies, which are critical for the success of the approach, mostly during the design of experiments and presentation of results. Moreover, a classification approach to these methodologies is not found in the literature. Thus, a generic taxonomical and classification framework is developed to support the review process. This framework is built based on three taxonomic subsystems that the review shows to be effective in organizing the reviewed methodologies: simulated, real and interface subsystems. In particular, the definition of the interface subsystem is key to overcoming the limitations found in the methodological representations. Furthermore, this review borrows the term actionability to this approach to better describe the nuances and gaps between the reviewed case studies. It is found that the different technical implementations are easily organized with the proposed framework, and the results cover a wide range of wave energy converter development phases. Likewise, this review shows opportunities for improvements in the methodology and application to a wider number of new case studies.info:eu-repo/semantics/publishedVersio

Influence of computational fluid dynamics on experimental aerospace facilities: A fifteen year projection

An assessment was made of the impact of developments in computational fluid dynamics (CFD) on the traditional role of aerospace ground test facilities over the next fifteen years. With improvements in CFD and more powerful scientific computers projected over this period it is expected to have the capability to compute the flow over a complete aircraft at a unit cost three orders of magnitude lower than presently possible. Over the same period improvements in ground test facilities will progress by application of computational techniques including CFD to data acquisition, facility operational efficiency, and simulation of the light envelope; however, no dramatic change in unit cost is expected as greater efficiency will be countered by higher energy and labor costs

An Experimental Approach to a Rapid Propulsion and Aeronautics Concepts Testbed

Modern aircraft design tools have limitations for predicting complex propulsion-airframe interactions. The demand for new tools and methods addressing these limitations is high based on the many recent Distributed Electric Propulsion (DEP) Vertical Take-Off and Landing (VTOL) concepts being developed for Urban Air Mobility (UAM) markets. We propose that low cost electronics and additive manufacturing can support the conceptual design of advanced autonomy-enabled concepts, by facilitating rapid prototyping for experimentally driven design cycles. This approach has the potential to reduce complex aircraft concept development costs, minimize unique risks associated with the conceptual design, and shorten development schedule by enabling the determination of many "unknown unknowns" earlier in the design process and providing verification of the results from aircraft design tools. A modular testbed was designed and built to evaluate this rapid design-build-test approach and to support aeronautics and autonomy research targeting UAM applications utilizing a complex, transitioning-VTOL aircraft configuration. The testbed is a modular wind tunnel and flight model. The testbed airframe is approximately 80% printed, with labor required for assembly. This paper describes the design process, fabrication process, ground testing, and initial wind tunnel structural and thermal loading of a proof-of-concept aircraft, the Langley Aerodrome 8 (LA-8)

Aeronautical Engineering: A continuing bibliography (supplement 158)

This bibliography lists 499 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1983

Advanced Concept Modeling

Advanced Concepts Modeling software validation, analysis, and design. This was a National Institute of Aerospace contract with a lot of pieces. Efforts ranged from software development and validation for structures and aerodynamics, through flight control development, and aeropropulsive analysis, to UAV piloting services

Aeronautical engineering: A continuing bibliography with indexes (supplement 250)

This bibliography lists 420 reports, articles, and other documents introduced into the NASA scientific and technical information system in February, 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Modelling and control for the oscillating water column

xxii, 219 p.Renewable energies are definitely part of the equation to limit our dependence to fossil fuels. Within this sector, ocean energies, and especially wave energy, represent a huge potential but is still a growing area. And like any new field, it is synonym to a high cost of energy production. Increasing the energy production, while keeping the costs controlled, has the leverage to drop down the cost of energy produced by wave energy converters (WECs). The main objective of this thesis is to make progress on the understanding of the effect of advanced control algorithms in the improvement of the power produced by wave energy devices. For that purpose, several control strategies are designed, compared, and assessed. To support this analysis, numerical models representing the overall energy conversion chain of WECs are developed. The Basque Country in Spain is fortunate enough to host the development and operation of two devices based on the Oscillating Water Column (OWC) principle. One is the Mutriku OWC plant, and the second is the floating buoy Marmok-A from Oceantec/IDOM, both devices were made available for sea trials. Several control algorithms were then implemented to be tested in real environments. Among them was a non-linear predictive control algorithm. Its test in real conditions represent a world first in the area of control for OWC systems, and maybe for the whole WEC sector if comparing with publicly available information. An outstanding results of the thesis is undoubtedly to move forward the predictive control algorithm from TRL3 to TRL6 after successful implementation and operation in both devices under real environmental conditions