Modelling and control of wind turbines with aeroelastically tailoring blades

The increased size of wind turbines (WTs) improves power generation efficiency but also imposes larger loading effects on the turbine system. A wind turbine with an aeroelastic tailoring blade (ATB) is proposed to alleviate the loading effect in wind turbine blades. A turbine with ATB is designed to respond to the incoming wind forces by deforming the shape of the blade and then reforming to its initial formation. The blade is manufactured with composite materials, incorporated with pre-twist angle and bend twist coupling (BTC) characteristics. Wind turbines with ATB are a new development that needs a better understanding of their operational performance and their potential when properly controlled. This PhD project aims to investigate the modelling and control of industrial-scale ATB WTs and assess the control performance with systematic studies. The thesis work includes two connected parts, model development, and control system design. A set of models has been developed for system analysis and controller design. To start with, a baseline model is revisited that covers key modelling elements of a 5MW standard HAWT wind turbine. This model is indexed as Model 0 in this thesis, it is the basis for other ATB WTs. To characterise ATB features, firstly the static BTC distribution is added to the turbine aerodynamics to account for the blade’s pre-bend-twist design. This static ATB model is integrated to the baseline model giving the full nonlinear turbine model, called Model 1, which will be used for the gain-scheduling baseline controller. Next, the ATB dynamics is approximated by a spring damper model to describe the blade structural dynamic response to wind speed variations. The developed turbine model combining the static ATB and dynamic ATB is called Model 2, based on which a linearised and discretised state-space model is developed for adaptive model predictive control (MPC). Additionally, a composite ATB model is established, in which the power coefficient values are generated from physical laboratory experiments for a composite materials blade. This model is referred to as Model 3, will also be used for adaptive MPC. Two controllers are investigated for the above-rated ATB WT operational control. The first controller is the gain scheduling baseline controller developed by the Wind Energy and Control Centre, initially for full envelope WT control of a standard machine without ATB. This baseline controller is redeveloped for the ATB WT using Model 1. The second controller is the adaptive MPC proposed and developed in this thesis work, which includes a general predictive controller enhanced by the use of a Kalman filter and online model update. This adaptive MPC is applied to Model 2 and Model 3 to examine the control performance. Several tools are used to support model development and controller design. Model 0 (including the baseline controller) is a nonlinear full-envelope model developed in Simulink (Chapter 3). Model 1 is developed by introducing the pre-twist angle and BTC in GL Bladed software, the generated power coefficients are then imported to the Simulink model. The simulation of Model 1 and the adapted baseline controller is made in Simulink (Chapter 3). Model 2 is developed by combining the data generated for static ATB in Model 1 and the dynamic ATB model. The full model for baseline control (Chapter 4) and the simplified state-space model for adaptive MPC (Chapter 5) are implemented in Matlab and Simulink. Model 3 is used for adaptive MPC, also realised in Matlab and Simulink (Chapter 6). Based on the comprehensive investigation, it is concluded that the ATB WT models developed in this work are suitable for controller design. Both the adapted gain scheduling baseline controller and the proposed adaptive MPC can be applied to achieve satisfactory control performance, that is, to mitigate fatigue load without compromising the power generation of the turbine system. With adaptive MPC, the system demonstrates improvement in reducing pitch activity, tower acceleration and blade root bending moment.The increased size of wind turbines (WTs) improves power generation efficiency but also imposes larger loading effects on the turbine system. A wind turbine with an aeroelastic tailoring blade (ATB) is proposed to alleviate the loading effect in wind turbine blades. A turbine with ATB is designed to respond to the incoming wind forces by deforming the shape of the blade and then reforming to its initial formation. The blade is manufactured with composite materials, incorporated with pre-twist angle and bend twist coupling (BTC) characteristics. Wind turbines with ATB are a new development that needs a better understanding of their operational performance and their potential when properly controlled. This PhD project aims to investigate the modelling and control of industrial-scale ATB WTs and assess the control performance with systematic studies. The thesis work includes two connected parts, model development, and control system design. A set of models has been developed for system analysis and controller design. To start with, a baseline model is revisited that covers key modelling elements of a 5MW standard HAWT wind turbine. This model is indexed as Model 0 in this thesis, it is the basis for other ATB WTs. To characterise ATB features, firstly the static BTC distribution is added to the turbine aerodynamics to account for the blade’s pre-bend-twist design. This static ATB model is integrated to the baseline model giving the full nonlinear turbine model, called Model 1, which will be used for the gain-scheduling baseline controller. Next, the ATB dynamics is approximated by a spring damper model to describe the blade structural dynamic response to wind speed variations. The developed turbine model combining the static ATB and dynamic ATB is called Model 2, based on which a linearised and discretised state-space model is developed for adaptive model predictive control (MPC). Additionally, a composite ATB model is established, in which the power coefficient values are generated from physical laboratory experiments for a composite materials blade. This model is referred to as Model 3, will also be used for adaptive MPC. Two controllers are investigated for the above-rated ATB WT operational control. The first controller is the gain scheduling baseline controller developed by the Wind Energy and Control Centre, initially for full envelope WT control of a standard machine without ATB. This baseline controller is redeveloped for the ATB WT using Model 1. The second controller is the adaptive MPC proposed and developed in this thesis work, which includes a general predictive controller enhanced by the use of a Kalman filter and online model update. This adaptive MPC is applied to Model 2 and Model 3 to examine the control performance. Several tools are used to support model development and controller design. Model 0 (including the baseline controller) is a nonlinear full-envelope model developed in Simulink (Chapter 3). Model 1 is developed by introducing the pre-twist angle and BTC in GL Bladed software, the generated power coefficients are then imported to the Simulink model. The simulation of Model 1 and the adapted baseline controller is made in Simulink (Chapter 3). Model 2 is developed by combining the data generated for static ATB in Model 1 and the dynamic ATB model. The full model for baseline control (Chapter 4) and the simplified state-space model for adaptive MPC (Chapter 5) are implemented in Matlab and Simulink. Model 3 is used for adaptive MPC, also realised in Matlab and Simulink (Chapter 6). Based on the comprehensive investigation, it is concluded that the ATB WT models developed in this work are suitable for controller design. Both the adapted gain scheduling baseline controller and the proposed adaptive MPC can be applied to achieve satisfactory control performance, that is, to mitigate fatigue load without compromising the power generation of the turbine system. With adaptive MPC, the system demonstrates improvement in reducing pitch activity, tower acceleration and blade root bending moment

Modelling and analysis of aeroelastic tailoring blade wind turbine systems

Modelling and performance analysis of wind turbine control systems with aeroelastic tailoring blades (ATBs) are investigated. An industrial scale horizontal axis wind turbine (HAWT) model with rigid blades is firstly developed as the baseline model using the blade element momentum (BEM) theory. Designed twist angle variation distributions along blades are then introduced to the baseline model to characterise the ATB nature. The developed ATB wind turbine models are analysed by employing a baseline control system. The performances of the ATB wind turbine systems are compared with that of the baseline turbine using both nonlinear models and linearised models at selected wind speeds. The impacts of ATB design can be clearly observed from the simulation studies. Preliminary results suggest that with ATB design in wind turbines, the blade fatigue loads and the pitching activities can be reduced for large turbines without compromising the energy capture performance