Effects of Component Model Fidelity Level on Dynamic Analysis Accuracy of a Multi-MW Wind Turbine Drivetrain

Wind farms can incur major expenses due to turbine gearbox component failure that often occurs within five years of deployment. Turbine testing facilities such as Energy Innovation Center (EIC) in Charleston, SC are a growing resource used by the wind energy industry to improve our understanding of turbines in the field and accelerate turbine development. In the meantime, a multibody dynamics model has been developed in EIC for a mutli-MW wind turbine to carry out performance and life assessments to understand the influence of high-frequency mass and misalignment imbalance forces and gear transmission forces. This thesis aims to investigate multibody dynamics modeling options and understand how modeling fidelity level of four components of interest influences the simulated response of the entire drivetrain under load. The components of interest were the main shaft, bed plate, first planetary carrier, and gearbox housing. The model fidelity levels of these bodies were varied from flexible body representations containing many component modes to rigid body representation with few degrees of freedom. The system was subjected to ramped unidirectional loading input at the nose of the rotor hub, which emulates testing conditions that are periodically run on drivetrains at EIC. Campbell analysis was then performed on a subsystem gearbox model to understand how component flexibility affects the speed-dependent vibration of gearbox components. Activating more component modes was found to improve the relative accuracy in the motion of the high-speed shaft. This benefit was judged against the relative computational cost for activating each of the components\u27 modes. The bedplate\u27s dynamic modes had the greatest influence on the motion of the high-speed shaft. Representing all drivetrain bodies as rigid bodies leads to a significant overprediction of the internal motion and forces of the drivetrain. Activating the four components\u27 first thirty dynamic modes caused a computational cost increase of 5 times. Carrier and gearbox housing flexibility softens the vibration frequencies of the gearbox subsystem across the turbine operating speed range. Strategic recommendations are contributed according to some differing purposes in design and testing of turbine drivetrains

A nonlinear concept of electromagnetic energy harvester for rotational applications

Many industrial applications incorporate rotating shafts with fluctuating speeds around a required mean value. This often harmonic component of the shaft speed is generally detrimental, since it can excite components of the system, leading to large oscillations (and potentially durability issues), as well as to excessive noise generation. On the other hand, the addition of sensors on rotating shafts for system monitoring or control poses challenges due to the need to constantly supply power to the sensor and extract data from the system. In order to tackle the requirement of powering sensors for structure health monitoring or control applications, this work proposes a nonlinear vibration energy harvester design intended for use on rotating shafts with harmonic speed fluctuations. The essential nonlinearity of the harvester allows for increased operating bandwidth, potentially across the whole range of the shaft’s operating conditions

Evaluation of Input-Shaping Control Robustness for the Reduction of Torsional Vibrations

Aircraft drivetrains connect the engine to the electrical power system. In most cases, the drivetrains are relatively flexible and have vibration modes with values below 100 Hz to reduce weight and size. Therefore, electrical loads’ connection and disconnection may excite torsional vibrations in the machine's shaft, reducing the drivetrains’ lifespan. This interaction is known as electromechanical interaction. This issue can be mitigated using an input-shaping strategy, which reduces the excitation of torsional vibrations by connecting the electrical loads following a pattern, dependent on the drivetrain's natural frequencies. However, since this method is based on the knowledge of the vibration modes attributes, it can be susceptible to parameter's uncertainty. In this article, a pulsating input shaping method's robustness is assessed, analyzing simulation and experimental results. The effect of the inductances is analyzed, and a strategy to reduce its effect is proposed. Furthermore, the effect of uncertainty in the mechanical parameters is evaluated, and theoretical analysis is carried out to establish safe operating limits. The theoretical analysis is experimentally validated

Investigation into the use of variable speed drives to damp mechanical oscillations

Research report to School of Electrical and Information EngineeringAn investigation was conducted into how a variable speed drive can provide a damping torque when mechanical oscillations are present. The modeling of mechanical oscillations via an analogous electrical circuit was performed. Simulation was used to demonstrate how a variable speed drive is able to damp speed oscillations using Direct Torque Control (DTC). Damping of mechanical oscillations is done by means of the variable speed drive providing a damping torque component that is in-phase with the speed deviation. The simulation showed that by applying a small torque component with the speed variation results in torque oscillations being damped by 60% after the initial disturbance. Damping is further improved by applying a torque component equal to the speed variation resulting in the oscillations being damped by 80% when compared to the initial disturbance.MT201

Analysis of Dynamic Interactions between Different Drivetrain Components with a Detailed Wind Turbine Model

The presented work describes a detailed analysis of the dynamic interactions among mechanical and electrical drivetrain components of a modern wind turbine under the influence of parameter variations, different control mechanisms and transient excitations. For this study, a detailed model of a 2MW wind turbine with a gearbox, a permanent magnet synchronous generator and a full power converter has been developed which considers all relevant characteristics of the mechanical and electrical subsystems. This model includes an accurate representation of the aerodynamics and the mechanical properties of the rotor and the complete mechanical drivetrain. Furthermore, a detailed electrical modelling of the generator, the full scale power converter with discrete switching devices, its filters, the transformer and the grid as well as the control structure is considered. The analysis shows that, considering control measures based on active torsional damping, interactions between mechanical and electrical subsystems can significantly affect the loads and thus the individual lifetime of the components

Modelling of reduced electromechanical interaction system for aircraft applications

© 2019 Institution of Engineering and Technology. All rights reserved. Rotational systems such as aircraft engine drivetrains are subject to vibrations that can damage shafts. Torsional vibrations in drivetrains can be excited by the connection of loads to the generator due to electromechanical interaction. This problem is particularly relevant in new aircraft because the drivetrain is flexible and the electrical power system (EPS) load is high. To extend the lifespan of the aircraft engine, the electromechanical interaction must be considered. Since real-time constants of the electrical and mechanical systems have very different magnitudes, the simulation time can be high. Furthermore, highly detailed models of the electrical system have unnecessary complexity for the study of electromechanical interactions. For these reasons, modelling using reduced order systems is fundamental. Past studies of electromechanical interaction in aircraft engines developed models that allow the analysis of the torsional vibration, but these are difficult to implement. In this study, a reduced order electromechanical interaction system for aircraft applications is proposed and validated using experimental results. The proposed system uses a reduced drivetrain, simplified EPS, and sensorless measurement of the vibrations. The excitation of torsional vibrations obtained is compared with past studies to prove that the reduced order system is valid for studying the electromechanical interactions