The aim of this lecture series is to allow Faculty and staff to present and share their knowledge and research. The lectures are informal so bring your lunch and get inspired.  If not otherwise stated the lectures take place in room C2-304 at 12h00. The scheduled time is 30 minutes.

11.05.12
Christoffer Sloth
Safety Verification using Barrier Certificates

In this talk I will present a method for verifying the safety of a continuous dynamical system. The safety verification is conducted by generating a barrier certificate, which is similar to a Lyapunov function. The barrier certificate is found by solving an optimization problem, expressed as a sum of squares programming problem. Therefore, I will briefly introduce sum of squares programming and show how such problems can be solved in MATLAB. Finally, I will show how a barrier certificate can be found in a compositional manner, by use of dual decomposition.

27.04.12
Anders Bech Borchersen
Programming Python: Why Bother

In this FFL, I will give an overview of the Python programming language and why it is interesting for you to known about it. The reason selecting Python is that it in many cases can replace Matlab®, and that it currently is the "best" free alternative to Matlab®. Besides this Python is a very flexible and modular language used for small scripts to high performance computing.

20.04.12
Mikael Svenstrup
Shutdown Detection for a Wind Turbine

Abstract:
In this FLL I will give an overview over our collaboration with Vestas regarding a detection system for initiating a shutdown procedure for a wind turbine. The goal is to design a safety-related protection system ensuring the structural integrity of the turbine at all times.
In other words, a protection system that overrides other systems and takes over to shut down the turbine. This is, for example,  when controllers, actuators or the wind make up their mind to behave in a way that can damage the turbine.

13.0412
Benjamin Biegel
Closed-Loop Predictive Control of Distributed Energy Resources 

In this FLL, I will illustrate how aggregated distributed energy resources can be used to provide ancillary services for energy balancing. By using a closed-loop model predictive controller, the distributed energy resources are able to take preemptive action and prepare for unknown future reference ensuring low operating cost and high performance.

30.03.12
Jesper A. Larsen
Introduction to FPGAs

With the new curriculums for the EIT4 semester, students are now being taught how to design digital hardware use FPGAs. Since this type of technology opens new possibilities for the type of embedded control problems which can be handled online, I´ll spend this FLL introducing the concepts and some examples of how to use FPGAs for control

23.03.12
John-Josef Leth
Stabilization with relaxed controls

In will present (part) of the paper "Stabilization with relaxed controls" by Zvi Artstein. It describes how one can use continuous closed loop relaxed control to stabilize control systems which can not be stabilized by continuous feedback. Moreover it is shown that the existence of such a controller is equivalent to the existence of a C^1 Lyapunov function.  
 

16.03.12
Rafal Wisniewski
Analysis of balanced truncation for linear switched systems

During the luncheon talk, I will present the recent work of Mihaly Petreczky, Rafael Wisniewski and John Leth in the field of model order reduction.
I will start the talk with recollection of the balanced truncation method. I will refer to the results presented by Hamid some time ago showing how to implement the algorithm for linear switched systems.
I will show how to define and approximate the L_2 norm of a switched system. Subsequently, I will provide the main result of our work: the error bound for the balanced truncation for linear switched systems.
 

09.03.12
Seyed Ehsan Shafiei
Decentralized Robust Adaptive Control of Large Scale Interconnected Systems

This presentation addresses af decentralized direct adaptive control using Neural Networks (NNs) for a class of uncertain large scale interconnected systems with unknown nonlinear interconnections. The NN used here is of type Cerebellar Model Arithmetic Computer (CMAC) which provides more computational efficiency than other fully connected NNs. Moreover, the weight drift problem involved in CMAC approximators is solved by employing an alternative weight method. A stability analysis is however carried out that ensures the Uniform Ultimate Boundedness (UUB) of all signals. A simulation study illustrates not only the effectiveness of the proposed method and its superior than other traditional in the field approaches, but also the necessity of using an alternative method for CMAC adaptation rules.

02.03.12
Fabiano Daher Agedas
LQG Control of Flexible Wind Turbines in Modal Coordinates

In this presentation the modal approach, preferred by structural engineers to aeroelastic analysis, is extended to the synthesis of wind turbine controllers. With the aeroelastic model in modal coordinates, weights involved on the design of model based linear quadratic (LQ) regulators have an explicit physical interpretation in terms of natural frequencies and damping coefficients of modes. A low authority assumption, i.e. structural properties are preserved under controller action, holds well for large, flexible wind turbines. This in turn makes closed-loop properties attributed to rotor speed regulation quasi-independent of the low authority part of the controller responsible for increase damping of ressonant modes. The modal approach is applied to linear time-invariant models generated by the recently developed aeroelastic code HAWCStab2.

24.02.12
Torben Knudsen
Detection of Excessive Wind Turbine Tower Oscillations Fore-Aft and Sideways.

Fatigue loads are important for the overall cost of energy from a wind turbine. Loading on the tower is one of the more important loads, as the tower is an expensive component. Consequently, it is important to detect tower loads, which are larger than necessary. This paper deals with both fore-aft and sideways tower oscillations. Methods for estimation of the amplitude and detection
of the cause for vibrations are developed. Good results are demonstrated for real data from modern multi mega watt turbines. It is shown that large oscillations can be detected and that the
method can discriminate between wind turbulence and unbalanced rotor.

17.02.12
Lei Zhang
Navigation for an autonomous underwater vehicle

This project is to design an autonomous underwater vehicle (AUV) which is able to glide to a predefined target position on the seabed for exploring the seabed and recording data. One of the main tasks is to design a navigation algorithm which could supply the navigation information of the device. This will be achieved by combining sensor readings and mathematical modeling of the vehicle. The accuracy of the navigation depends on the type and quality of the sensors as well as the accuracy of the model. In this FLL, I will present the simulation of the AUV and the simulated navigation results based on various sensors such as IMU, magnetometer and pressure sensor.

10.02.12
Jan Dimon Bendtsen
Multiple Model Adaptive Control Using Dual Youla-Kucera Factorisation

We propose a multi-model adaptive control scheme for uncertain linear plants based on the concept of model unfalsification. The approach relies on examining the ability of a pre-computed set of plant-controller candidates and choosing the one that is best able to reproduce observed in- and output signal samples. The ability to reproduce observations is measured as an easily computable signal norm. Compared to other related approaches, our procedure is designed to be able to handle significant measurement noise and closed-loop correlations between output measurements and control signals.
 

16.12.11
Henrik Rasmussen
Adaptive Control/Nonlinear Control

In this FLL I shall give some examples of how adaptive/nonlinear control is used for new solutions to control problems.

The examples are:
*   Adaptive Steam Superheat Control in a Power plant
At Skærbækværket Tom and I made the first adaptive Power Plant controller in Denmark
*   Adaptive Superheat Control in a Refrigeration plant
At Danfoss I made an entirely new concept for the regulation of the eco flow value
*   Nonlinear Superheat Control without pressure measurement
An ongoing project where Jakob, Kasper and I cooperate with Danfoss
*   Welding Machine Control
At Migatronic they had a control problem where I made a simple solution with great impact
 

09.12.11
Torben Knudsen
Detection of Wind Turbine Tower Oscillations Fore-Aft and Sideways

Fatigue loads are important for the overall cost of energy from a wind turbine. Loading on the tower is one of the more important loads, as the tower is an expensive component. Consequently, it is important to detect tower loads, which are larger than necessary. This work deals with both fore-aft and sideways tower oscillations. Methods for estimation of the amplitude and detection of the cause for vibrations are developed. Good results are demonstrated for real data from modern multi mega watt turbines. It is shown that large oscillations can be detected and that the method can discriminate between wind turbulence and unbalanced rotor. 
 

02.12.11
Control Seminar series
 

25.11.11
Benjamin Biegel
Introduction to CVC - a convex Optimization Tool
In this FLL, I will give a short introduction to CVX, a Matlab-based modeling system for convex optimization. CVX allows you to state objective and constraints to a convex optimization problems using the standard Matlab expression syntax. I will demonstrate CVX based on a case study from my current work concerning model predictive control for power flows in networks with limited capacity.

18.11.11
Luminita Totu
Steady state Kalman gain for an undetectable linear system

This topic is based on the master project and will show a state-space system with a particular structure for which the Riccati differential equation diverges, yet the Kalman gain matrix converges. The case is taken from a report and a patent by D. Bayard and S. Ploen under a NASA/JPL contract. The presentation will start with a simple example of multiple identical sensors measuring the same physical property and show how knowledge of noise correlations can improve the averaging strategy for signal fusion. Then it will move to a dynamic model and discuss the associated Kalman filter. 

11.11.11
Convex approach to boolean optimization
Morten Juelsgaard

This talk is based on a challenge posed by Kim G. Larsen, relating to how one would solve a mixed integer or boolean optimization problem, when using convex methods. The results should be compared to those optained with the software tool 'UPPAAL'.

During the talk, I will briefly recap the most basic concepts of convex sets, -functions and -problems. I will present a very simple boolean optimization problem, whereafter I will illustrate different approaches for optaining a solution, using convex optimization tools. I will present numerical examples on the implementation of my suggestions, and lastly I will discuss the topic of computation time.

04.11.11
Navigation for an autonomous underwater vehicle/Postponed
Lei Zhang

This project is to design an autonomous underwater vehicle (AUV) which is able to glide to a predefined target position on the seabed for exploring the seabed and recording data. One of the main tasks is to design a navigation algorithm which could supply the navigation information of the device. This will be achieved by combining sensor readings and mathematical modeling of the vehicle. The accuracy of the navigation depends on the type and quality of the sensors as well as the accuracy of the model. In this FLL, I will present the simulation of the AUV and the simulated navigation results based on various sensors such as IMU, magnetometer and pressure sensor.

28.10.11
Load Reduction af Wind Turbines Using Receding Horizon Control
Mohsen Soltanie

Large scale wind turbines are lightly damped mechanical structures driven by wind that is constantly fluctuating. In this lecture, we address the design of a model-based receding horizon control scheme to reduce the structural loads in the transmission system and the tower, as well as provide constant (or at least smooth) power generation. Our controller incorporates two optimization problems: one to predict or estimate mean wind speed, given LIDAR data, and the other to carry out receding horizon control to choose the control inputs. The method is verified against an existing wind turbine control system, and shows reductions in both extreme loads and power fluctuations when compared to a conventional controller. 

14.10.2011
Fault Detection and Isolation of LTV Systems Using Set-Valued Observers
Paula Rosa

The talk is based on a paper presented in the last CDC. Here is the abstract of the paper:
This paper introduces the novel concept of using Set-Valued Observers (SVOs) in Fault Detection and Isolation (FDI), for discrete-time linear time-varying systems. The proposed method relies on SVO-based model invalidation to discard models that are not compatible with the input/output data. We argue that there are mainly three significant advantages of using SVOs for FDI, when compared to the most common strategies available in the literature: i) under suitable conditions, we can guarantee that there will be no false alarms; ii) unlike residual- based architectures, the proposed technique does not require the computation of a threshold to declare faults; iii) the SVOs can be used with a wide class of time-varying linear uncertain discrete-time systems. We further show, in simulation, that the proposed FDI algorithm in general requires a very small number of iterations to detect and identify a faulty behavior.

07.10.2011
What do we mean by wind turbine control, and how do we study it in Colorado?
Kathryn Johnson

This FLL event will give an informal overview of wind turbine control in general, followed by an overview of the research underway in this research area in Colorado, U.S.A. The focus will be on the overall objectives and methodologies rather than the detailed control architectures, such that the talk will be appropriate for a broad audience.  Discussion on opportunities for collaboration will be welcome. 

This FLL event will give an informal overview of wind turbine control in general, followed by an overview of the research underway in this research area in Colorado, U.S.A.    The focus will be on the overall objectives and methodologies rather than the detailed control architectures, such that the talk will be appropriate for a broad audience.  Discussion on opportunities for collaboration will be welcome.

24.06.2011
Robustness in Dynamical and Control Systems
Rafael Wisniewski

I compile some results on robustness of dynamical and control systems. As control theory is preoccupied with stability problems, the robustness put forward in this talk is related to stability. We ask the question whether an asymptotically stable system remains asymptotically stable when perturbations are affecting it. We analyze robustness of control systems by examining vector fields in Cr topology, by studying associated Lyapunov functions, and by studying corresponding input-output maps. In the first case, we conclude that there is an open set of perturbations such that the system that is affected by them stays asymptotically stable. In the second case, we estimate the size of perturbations that do not destabilize the system. In the third and last case, we provide conditions on the gains of the interconnected systems such that the closed loop system has finite gain.

27.05.2011
Market Integration of Virtual Power Plants
Mette Højgaard Petersen

This Friday at FLL I will give a presentation of the subject of PhD project titled “Market Integration of Virtual Power Plants”. Firstly I present the Smart Grid Idea and how it is intended to help handle the energy challenges of the future. I then present the concept of a Virtual Power Plant and the particular focus of my project, which is aggregation choices and the cost of aggregation.

19.05.2011
Kasper Vinther
Plug and Play Control of Refrigeration Systems

In this FLL, I will briefly describe my phD project, where I am working on development of control algorithms that works with a wide variety of refrigeration systems in a plug-and-play fashion, without the need for manual tuning. I will in particular talk about two approaches for evaporator superheat control using qualitative knowledge about system nonlinearities. In the first approach, the variance of the temperature at the evaporator outlet is calculated and used to generate a suitable control reference signal. I have named the second approach "harmonic control", because the first and second harmonic of an excitation signal, applied in closed loop, is used to generate a feedback signal.

13.05.2011
Revisiting Gain-Scheduled PI Control of Wind Turbines: an LPV approach
Fabiano Daher Adegas

The proportional and integral (PI) controller is widely used throughout wind energy industry. At high wind speeds, the PI speed control using pitch angle as controlled input strongly couples with the tower dynamics, denoting a multivariable problem, and should be properly designed. Inappropriate gain selection can make rotational speed regulation "loose" around the set-point or make the system unstable, as well as excite poorly damped structural modes. Faults on the pitch system such as high air content in the oil changes wind turbine dynamics also degrades speed regulation and increases tower oscillations.

In this talk, PI control of wind turbines will be revisited under the linear parameter varying (LPV) framework. Using recent theoretical developments carried on in our Section, an optimal PI gain-scheduled controller is synthesized with stability guaranteed by a parameter-dependent Lyapunov function. Moreover, the controller is made fault-tolerant to anomalies on the pitch actuator by scheduling PI gains according to the severity of the fault. Simulation results show the effectiveness of both gain-scheduling to cope with intrinsic system nonlinearities and occurrence of faults.

06.05.2011
The Lyapunov Equation
Rafael Wisniewski 

This time, I will not talk about my research but about a pearl in control theory: the Lyapunov equation. You have surely met it in stability theory, robust control theory, controllability, observability, or model-order reduction. I will give its definition, and present results on the existence of a solution. For this, I will introduce a concept of tensor product or better known in the control field as the Kronecker product. I will show relation between Lyapunov equation and stability. For this, I will introduce the definition of inertia of a matrix. I will finish up with some results concerning Lyapunov equation for switched systems.

29.04.2011
My PhD
Mikael Svenstrup

During the work on my Ph.D. project, I have been working on various aspects of robot motion in human environments. One of the tasks has been to plan safe and natural trajectories through crowded and dynamic human environments. To solve this trajectory generation problem, we have used a so called Rapidly-exploring Random Tree (RRT) planning algorithm. The RRT is a sampling based planning algorithm, which has been designed for efficiently finding a path in a non-convex and high dimensional search space. RRT's have gained widespread use in robot motion planning during the last decade.  In this FLL, I will explain the basics of the RRT algorithm; how we have used and modified the basic algorithm for trajectory planning in human environments; and how it has been optimized to run faster in an on-line system.

15.04.2011
Project for students
Lars Peter Jensen

In this lecture I will talk about a project to help internationalization in the engineering educations and improve the students’ intercultural competencies. The project was initiated by the Danish center for engineering education (DACIN) that in 2009 decided to start a formal research project to investigate some experiments helping mixed teams to cope with project work in intercultural teams. Four Danish engineering educations were involved and I will present the setup and the first research data collected in the autumn 2010 and the first months of 2011.

08.04.2011
My PhD  
Maryamsadat Tahavori

In this talk, I will describe my PhD project. As I am in the early stage of my PhD this would be more problem statement. In this project the aim is to develop a control concept for water supply systems while minimizing the pressure in the water supply networks. Surveying previous works on water supply systems shows the water supplies and the distribution networks are still inefficient and the losses in the water distribution networks are still significant. Water leakage is an important component of water losses. Many methods have emerged from urban water supply systems for leakage control, but it remains a challenge in many countries. The outcome of this project will also include contamination control, leakage and energy consumption reduction.

01.04.2011
Henrik Schiøler

25.03.2011
Path planning for small-scale helicopter in 3D environments  
Flemming Schøler 

This will be a presentation on my work with different approaches to path planning for small-scale helicopter in 3D environments. Path planning deals with challenge of finding a path that takes the helicopter from some initial state to some desired final state, without colliding with obstacles. Using certain simplifications, a minimal length solution to the 2D analogue can be found with a visibility graph. However this approach cannot easily be extended to 3D. One solution proposed here is based on approximating the shortest path.  

18.03.2011
Mohsen Soltanie

11.03.2011
Ballistic walking with pre-emptive impact control  
Mads Sølver Svendsen

I will present an online trajectory generation scheme that, based on the current state of a biped, predicts the impact point of the leading foot that minimizes impact effects. The prediction model is based on first integral system equations divided in three phases. Each phase model is propagated based on events as opposed to time. Doing so makes the model applicable in a model predictive scheme. The scheme is compared with passive dynamics that still has a lower specific cost of transport but the new scheme is able to vary walking speed mid-step, initiate and terminate walking, and predict corrective trajectories when disturbances occur.

04.03.2011
Days and nights with FTP  
Jakob Stoustrup 

For almost five years, I was a member of The Danish Council for Independent Research | Technology and Production Sciences (FTP). In this talk, I will tell about my experiences during that period, how the Council reaches its decisions, and how to write an application that qualifies for FTP funding. 

25.02.2011
ASETA project  
Karl Damkjær Hansen

Adaptive Surveying and Early treatment of crops with a Team of Autonomous Vehicles—in short ASETA—aims to use autonomous helicopters to photograph a sugar beet field in order to guide autonomous ground robots to weed infestations in the field, so that they may treat it. I will give a presentation of how we envision the system will work and what I am working on in this context. My work package is called task management, this is the system that breaks down high level tasks into tasks executable by the robots. 

18.02.2011
Short presentations of (interesting) papers presented at last years CDC  
Jan Dimon Bendtsen 

G. Russo, M. Bernardo, E. Sontag: "Stability of networked systems: a multi-scale approach using contraction"

This paper is concerned with the stability of networked control systems.
Using contraction theory, a result is established on the network structure and the properties of the individual component subsystems and their couplings to ensure the overall contractivity of the entire network. The paper also describes a relative contraction result of interest in synchronization problems.
S. Sajjadi-Kia, F. Jabbari: "Multiple Stage Anti-Windup Augmentation Synthesis for Open-loop Stable Plants"
In this note the authors enhance the concept of scheduled anti-windup gains by developing an approach that uses a combination of dynamic and static augmentation loops. Synthesis LMIs for two levels of saturation are developed: moderate (static loop active) and severe (both loops active).

11.02.2011
AAUSAT3 student satellite project  
Jesper Abildgaard Larsen

One of the largest student projects at our section at the moment is the AAUSAT3 student satellite project. The project was started in 2007, and is now nearing the end. We have a fully working prototype satellite, and the flight version is currently being produced. In todays FLL I'll give an introduction to the project, the satellite and its different subsystems. Along the way I'll try to extract some of the novelties, which we're testing with this satellite along with some of the scientific results.

04.02.2011
Short presentations of (interesting) papers presented at last years CDC  John Leth and Jan Dimon Bendtsen 

Abstract (John)

The first paper I will present is by Liberzon and Trenn entitled "The bang-bang funnel controller".
In this paper a bang-bang controller is devised for relative degree one and two systems, with the purpose of ensuring reference tracking within time-varying error bounds. The two valued controller do not depend on system parameters and is governed by a simple switching logic.
The second paper I will present is by Schattler entitled "On classical envelopes in optimal control theory".
In this paper the classical concept of envelopes from the calculus of variation is generalized to the optimal control problem.

Abstract (Jan)

G. Russo, M. Bernardo, E. Sontag: "Stability of networked systems: a multi-scale approach using contraction"
This paper is concerned with the stability of networked control systems.
Using contraction theory, a result is established on the network structure and the properties of the individual component subsystems and their couplings to ensure the overall contractivity of the entire network. The paper also describes a relative contraction result of interest in synchronization problems.
S. Sajjadi-Kia, F. Jabbari: "Multiple Stage Anti-Windup Augmentation Synthesis for Open-loop Stable Plants"
In this note the authors enhance the concept of scheduled anti-windup gains by developing an approach that uses a combination of dynamic and static augmentation loops. Synthesis LMIs for two levels of saturation are developed: moderate (static loop active) and severe (both loops active).

07.10.11What do we mean by wind turbine control, and how do we study it in Colorado?Kathryn Johnson

no news in this list.