Baseline Control System Research Articles

Equipment response spectra for wind turbines considering the baseline control system

As more and more wind turbines are installed in areas with high seismic intensity, various published works have studied the seismic performance of wind turbines. However, these studies usually focus on the wind turbine, and less attention is paid to the electrical equipment mounted on the wind turbine. Electrical equipment is a non-structural component on wind turbine, which is prone to failure and damage, resulting in the loss of function of the wind turbine. Therefore, it is necessary to study the seismic performance of the electrical equipment installed on the wind turbine. This study focuses on evaluating and quantifying the dependence of equipment spectrum accelerations on the location of the electrical equipment in the structure, the damping ratio of the equipment, and the baseline control system. The baseline control system is used to control the output power by adjusting the rotor speed and the blade pitch angle, which affects the equipment spectrum of the wind turbines. There is a stronger relationship between the equipment response spectrum and the peak floor acceleration. Therefore, the equipment spectral amplification function is calculated as the ratio of the equipment spectral acceleration to the peak floor acceleration for different height. The equipment spectra amplification function is proposed and validated to estimate peak acceleration demands on the design of electrical equipment placed on wind turbines. The results indicate that current seismic code provisions will not always provide an adequate characterization of equipment accelerations. And the effect of wind turbine baseline control and equipment damping is more pronounced in the range of the structural tuning period than in the non-tuning range.

Investigation on the Effect of the Baseline Control System on Dynamic and Fatigue Characteristics of Modern Wind Turbines

In order to investigate the effect of a baseline control system (BCS) on dynamic and fatigue characteristics of modern wind turbines, the simulation results of a 5-MW wind turbine subjected to wind loading without and with considering BCS (No. 1 and No. 2, respectively) were compared. The displacement and moment of tower and blades were compared, and the rainflow counting algorithm was used to analyze the fatigue load expressed in damage equivalent load (DEL). The results indicate that the mean and maximum values of structural dynamic responses in No. 2 have a great reduction with wind speed exceeding the rated speed comparing to No. 1; the 3P (3-times the frequency of rotor speed) of the wind turbine rotor speed will be close to the tower fore-aft (FA) natural frequency with the wind velocity around the cut-in speed in No. 2, which caused larger dynamic responses, number of load cycles, and DELs for the tower compared with No. 1; when wind velocity exceeds the rated wind speed, the BCS caused higher fluctuation of loads, increasing the related DELs. It is concluded that when analyzing the dynamic responses and designing wind turbine tower and blades, taking the BCS into account during analysis is significant.

Real-Time Adaptation of an Artificial Neural Network for Transfemoral Amputees Using a Powered Prosthesis.

Objective:We evaluated a two-step method to improve control accuracy for a powered prosthetic leg using machine learning and adaptation, while reducing subject training time.Methods:First, information from three transfemoral amputees was grouped together, to create a baseline control system that was subsequently tested using data from a fourth subject (user-independent classification). Second, online adaptation was investigated, whereby the fourth subject’s data were used to improve the baseline control system in real-time. Results were compared for user-independent classification and for user-dependent classification (data collected from and tested in the same subject), with and without adaptation.Results:The combination of a user-independent classifier with real-time adaptation based on a unique individual’s data produced a classification error rate as low as 1.61% [0.15 standard error of the mean (SEM)] without requiring collection of initial training data from that individual. Training/testing using a subject’s own data (user-dependent classification), combined with adaptation, resulted in a classification error rate of 0.9% [0.12 SEM], which was not significantly different (P > 0.05) but required, on average, an additional 7.52 hours [0.92 SEM] of training sessions.Conclusion and Significance:We found that the combination of a user-independent dataset with adaptation resulted in error rates that were not significantly different from using a user-dependent dataset. Furthermore, this method eliminated the need for individual training sessions, saving many hours of data collection time.

Enhancing Resilience of Airborne Wind Energy Systems Through Upset Condition Avoidance

Airborne wind energy (AWE) systems are tethered flying devices that harvest wind resources at higher altitudes, which are not accessible to conventional wind turbines. To become a viable alternative to other renewable energy technologies, AWE systems are required to fly reliably and autonomously for long periods of time while being exposed to atmospheric turbulence and wind gusts. In this context, the present paper proposes a three-step methodology to improve the resilience of an existing baseline control system toward these environmental disturbances. In the first step, upset conditions are systematically generated that lead to a failure of the control system using the subset simulation method. In the second step, the generated conditions are used to synthesize a surrogate model that can be used to predict upsets beforehand. In the final step an avoidance maneuver is designed that keeps the AWE system operational while minimizing the impact of the maneuver on the average pumping cycle power. The feasibility of the methodology is demonstrated on the example of tether rupture during pumping cycle operation. As an additional contribution a novel transition strategy from retraction to traction phase is presented that can reduce the probability of tether rupture significantly.

Deep neural networks as add-on modules for enhancing robot performance in impromptu trajectory tracking

High-accuracy trajectory tracking is critical to many robotic applications, including search and rescue, advanced manufacturing, and industrial inspection, to name a few. Yet the unmodeled dynamics and parametric uncertainties of operating in such complex environments make it difficult to design controllers that are capable of accurately tracking arbitrary, feasible trajectories from the first attempt (i.e., impromptu trajectory tracking). This article proposes a platform-independent, learning-based “add-on” module to enhance the tracking performance of black-box control systems in impromptu tracking tasks. Our approach is to pre-cascade a deep neural network (DNN) to a stabilized baseline control system, in order to establish an identity mapping from the desired output to the actual output. Previous research involving quadrotors showed that, for 30 arbitrary hand-drawn trajectories, the DNN-enhancement control architecture reduces tracking errors by 43% on average, as compared with the baseline controller. In this article, we provide a platform-independent formulation and practical design guidelines for the DNN-enhancement approach. In particular, we: (1) characterize the underlying function of the DNN module; (2) identify necessary conditions for the approach to be effective; (3) provide theoretical insights into the stability of the overall DNN-enhancement control architecture; (4) derive a condition that supports data-efficient training of the DNN module; and (5) compare the novel theory-driven DNN design with the prior trial-and-error design using detailed quadrotor experiments. We show that, as compared with the prior trial-and-error design, the novel theory-driven design allows us to reduce the input dimension of the DNN by two thirds while achieving similar tracking performance.

Study on the Influence of Baseline Control System on the Fragility of Large‐Scale Wind Turbine considering Seismic‐Aerodynamic Combination

The purpose of this paper is to explore the effect of the baseline control system (BCS) on the fragility of large‐scale wind turbine when seismic and wind actions are considered simultaneously. The BCS is used to control the power output by regulating rotor speed and blade‐pitch angle in real time. In this study, the fragility analysis was performed and compared between two models using different peak ground acceleration, wind speeds, and specified critical levels. The fragility curves with different wind conditions are obtained using the multiple stripe analysis (MSA) method. The calculation results show that the probability of exceedance specified critical level increases as the wind speed increases in model 1 without considering BCS, while does not have an obvious change in the below‐rated wind speed range and has a significant decrease in the above‐rated wind speed range in model 2 with considering BCS. The comparison depicts that if the BCS is neglected, the fragility of large‐scale wind turbine will be underestimated in around the cut‐in wind speed range and overestimated in the over‐rated wind speed range. It is concluded that the BCS has a great effect on the fragility especially within the operating conditions when the rated wind speed is exceeded, and it should be considered when estimating the fragility of wind turbine subjected to the interaction of seismic and aerodynamic loads.

${\mathcal{L}}_{1}$ adaptive control augmentation for a six-degree-of-freedom hypersonic vehicle model

In this paper, we present the design of an ${\mathcal{L}}_{1}$ adaptive control augmentation system for a six-degree-of-freedom generic hypersonic vehicle model. We focus on addressing system uncertainties, which lead to undesired performance if not properly addressed in the control design. The design begins with the development of a nonlinear dynamic inversion system as the inner-loop controller, which achieves linearization between system inputs and outputs. Linear feedback controllers are then designed as a baseline control system. In addition, the ${\mathcal{L}}_{1}$ adaptive control architecture is used to develop augmentation setups to enhance the control performance of the baseline controllers in the presence of system uncertainties and disturbances. The simulation results demonstrate that the proposed augmentation scheme improves the overall control performance and enhances the robustness of the control system.

Structured Control Design for a Highly Flexible Flutter Demonstrator

The model-based flight control system design for a highly flexible flutter demonstrator, developed in the European FLEXOP project, is presented. The flight control system includes a baseline controller to operate the aircraft fully autonomously and a flutter suppression controller to stabilize the unstable aeroelastic modes and extend the aircraft’s operational range. The baseline control system features a classical cascade flight control structure with scheduled control loops to augment the lateral and longitudinal axis of the aircraft. The flutter suppression controller uses an advanced blending technique to blend the flutter relevant sensor and actuator signals. These blends decouple the unstable modes and individually control them by scheduled single loop controllers. For the tuning of the free parameters in the defined controller structures, a model-based approach solving multi-objective, non-linear optimization problems is used. The developed control system, including baseline and flutter control algorithms, is verified in an extensive simulation campaign using a high fidelity simulator. The simulator is embedded in MATLAB and a features non-linear model of the aircraft dynamics itself and detailed sensor and actuator descriptions.

Rotor-State Feedback Control to Alleviate Pilot Workload for Helicopter Shipboard Operations

This paper presents an integrated flight control system with rotor-state feedback for helicopter approaching to the ship deck. First, a high-order nonlinear flight dynamics model coupled with the reconstructed ship airwake turbulence is developed. Then, a rotor-state feedback control law is developed and integrated into the baseline explicit model-following control system to form an integrated control system. The feedback gains of body and rotor states are designed together to improve the disturbance rejection over the ship airwake frequencies (1 to ). A feedforward compensator is introduced to improve aircraft response bandwidth. Furthermore, a method to adjust the command model is developed for further improvement of the response bandwidth. Finally, the effectiveness of the integrated control system is demonstrated with linear analysis, and pilot workload is evaluated with nonlinear simulation. In comparison to the baseline control system, the integrated control system improves both the disturbance rejection over the ship airwake frequencies and attitude response bandwidths of rolling and pitching motions. The pilot workload for the roll and pitch attitude regulation in ship airwake turbulence is reduced by 45 and 26%, respectively.

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.

Fragility analysis of large-scale wind turbines under the combination of seismic and aerodynamic loads

The objective of this paper is to research the fragility of large-scale wind turbines considering the combination of seismic and aerodynamic loads. According to the International Electrotechnical Commission (IEC) 61400-1 and pushover analysis, the critical moment and displacement for wind turbines were proposed. The moment based and displacement based fragility curves under different wind speeds were obtained by using multiple stripe analysis (MSA) approach and compared between the first scenario of normal operation condition with the baseline control system (BCS) working and the second scenario of parked condition. The simulation results indicate that the effect of aerodynamic damping on structural response of a wind turbine during normal operation results in a reduction in the maximum values of dynamic response compared to the parked condition, which causes that the probability of exceeding limit state in the first scenario is less than that in the second scenario. It illustrates that, a wind turbine subjected to the combination of seismic and aerodynamic loads in normal operation condition is safer than in parked condition. Finally, it can be concluded that the fragility of large scale wind turbines can be reduced by keeping the BCS working when earthquake happens.

Rotor-state feedback control design to improve helicopter turbulence alleviation in hover

A helicopter flight control system with rotor-state feedback to improve turbulence alleviation in hover is presented. First, a flight dynamic model coupled with turbulence model is developed and validated. Then, an integrated control strategy with a rotor-state feedback control law is proposed based on the baseline control system. The feedback gains of body and rotor states are designed in synergy to improve turbulence alleviation in the interested frequency range of handling qualities. Subsequently, the effects of the rotor-state feedback gains on both the stability of rotor dynamics and helicopter turbulence alleviation are analyzed in detail. Finally, the effectiveness of the integrated control system is evaluated with linear analysis in frequency domain and nonlinear simulation in time domain. The results indicate that with the rotor-state feedback control law integrated into the control system, the helicopter turbulence alleviation in the interested frequency range is improved with less degradation in helicopter stability margins, and the roll and pitch rate responses of helicopter to turbulence, measured with Root-Mean-Square (RMS) values, are reduced by more than 50% and 35% respectively.

Frequency-varying synchronous micro-vibration suppression for a MSFW with application of small-gain theorem

This paper presents a novel synchronous micro-vibration suppression method on the basis of the small gain theorem to reduce the frequency-varying synchronous micro-vibration forces for a magnetically suspended flywheel (MSFW). The proposed synchronous micro-vibration suppression method not only eliminates the synchronous current fluctuations to force the rotor spinning around the inertia axis, but also considers the compensation caused by the displacement stiffness in the permanent-magnet (PM)-biased magnetic bearings. Moreover, the stability of the proposed control system is exactly analyzed by using small gain theorem. The effectiveness of the proposed micro-vibration suppression method is demonstrated via the direct measurement of the disturbance forces for a MSFW. The main merit of the proposed method is that it provides a simple and practical method in suppressing the frequency varying micro-vibration forces and preserving the nominal performance of the baseline control system.

Human-computer Interface Studies for Semi-autonomous Unmanned Surface Vessels

A series of four experiments were performed during an iterative design evolution of the human-computer interface (HCI) to a small unmanned surface vehicle (USV). The baseline control system was compared to several alternate designs using a simulated naval mission. User tasks included the monitoring and control of one or two vessels simultaneously. Faults and hazards were included to stimulate emergency responses during vessel transit. Alternate HCI designs varied across these factors: visual integration, synthetic audio feedback, sizing and placement of alerts, and use of a hand-held game controller as a primary input device. Results for N=32 sailors across the four studies indicated that for single or dual USV control conditions, the interface features added to the baseline design significantly improved speed and accuracy across multiple mission tasks. However, all design configurations still yielded some collision errors indicating that operator visual monitoring and manual control may be inadequate in complex, cluttered transit environments. Therefore, on-board automatic obstacle avoidance systems may be needed to safely support multiple vessel operations in cluttered complex transit environments.

Control System for Start-up and Shut-down of a Floating Vertical Axis Wind Turbine

A baseline control system for the Deepwind floating vertical axis wind turbine (VAWT) concept is analysed with em- phasis on start-up and shut-down schemes. The turbine concept includes a rotating spar with a 2-bladed rotor at the top and a submerged generator at the bottom, anchored to the seabed with mooring lines attached to the stator-side of the generator. The controller is a typical PI control system with a notch filter to damp 2p torque variations. Start-up and shut-down logic is presented in detail, with simulation results demonstrating smooth start-up and shut-down at high wind speeds without severe spikes in generator torque.

두루미-II 무인기 기반의 조종력 할당 기법 성능 평가

논문에서는 두루미-II 무인기 모델을 이용하여 다양한 조종력 할당 기법의 성능을 평가하였다. 조종력 할당 기법은 먼저 조종면 고장을 고려하지 않은 상태에서 대상 항공기의 기준 비행제어 시스템을 설계한 후, 조종력 할당 알고리즘을 결합하여 구현할 수 있다. 본 논문에서 대상 항공기 모델인 두루미-II 무인기의 기준 비행제어 시스템을 고전제어 기법에 근거하여 설계하였다. 그리고 Psuedo-inverse CA 기법과 Direct CA 기법 및 Optimization CA 기법을 구현하여 두루미-II 무인기의 기준 비행제어 시스템과 결합한 후, 조종면 고장 시나리오에 따른 비선형 시뮬레이션을 통해 각 조종력 할당 기법의 성능을 평가하고 비교하였다. This paper focuses on the performance evaluation of various control allocation methods applied on DURUMI-II UAV system. In order to implement control allocation scheme to aircraft control system, control system can be designed through two step design procedure. The first step is to design a baseline control system for an aircraft without consideration of control surface failure. The second step is to design a control allocator that maps the total control command on the individual control surfaces. In this paper, several control allocation methods such as Psuedo-Inverse CA method, Direct CA method, and Optimization CA method are implemented and integrated to the baseline flight control system of DURUMI-II UAV. The performance of these control allocation methods is evaluated by nonlinear simulation under the flight scenario of control surface failure.

Enhancing Situational Awareness and Team Performance Using Network Centric Technologies

A network-centric oriented technology that fused the User Defined Operational Picture (UDOP) and the Lightweight Collaborative Whiteboard (LCW) was compared to the baseline Global Command and Control System (GCCS). The UDOP environment allows the user to personally tailor the dynamic map and collaborate on the map via drawing, marking, and annotation that instantly appears on all other team member's maps. The GCCS map provides none of these capabilities. It was hypothesized that the UDOP environment will foster higher situational awareness and more adequate shared mental models than GCCS. Given that quality shared mental models and situational awareness have been associated with higher performance it was hypothesized that the UDOP environment would produce higher situational awareness and performance than the GCCS environment. Findings supported these hypotheses; higher situational awareness and performance were associated with the UDOP environment.

Nonlinear Antiwindup Applied to Euler–Lagrange Systems

In this paper, we propose a nonlinear antiwindup scheme to guarantee stability and local performance recovery on Euler-Lagrange systems subject to input magnitude saturation. The antiwindup scheme consists in a dynamic augmentation to the baseline control system which, based on nonlinear analysis, is shown to induce global asymptotic stability and local exponential stability on the overall control scheme. To induce desirable closed-loop performance on a specific system, two parameters of the antiwindup law can be tuned for each position variable of the Euler-Lagrange system, similar to the tuning procedure for proportional-derivative gains. Simulation results are reported showing the behavior of the proposed antiwindup law on the model of a popular industrial robot. The resulting responses confirm the effectiveness of the antiwindup scheme, both for set-point regulation tasks and for trajectory tracking tasks where the saturation nonlinearity is repeatedly activated.

Active vibration suppression for the mast flight system

Active vibration suppression of a large flexible space structure is addressed. The system (experimental test bed), performance requirements, and system simulations and models are described. The structures is a 60-m truss beam attached to the Shuttle orbiter. A baseline control system is required to provide 5% structural damping for the first ten structural (flexible) modes of the truss beam. The control design approach used to achieve the damping is a decentralized velocity feedback type. Collocated actuator and sensor locations are given, with details of the model for the proof-mass actuating device, the linear DC motor. >