Lars Finn Sloth Larsen - Academia.edu (original) (raw)

Papers by Lars Finn Sloth Larsen

Computer Aided Chemical Engineering, 2019

In this work, we analyze a generic supercritical CO 2-refrigeration system with parallel compress... more In this work, we analyze a generic supercritical CO 2-refrigeration system with parallel compression, based on systems used for supermarket use. In order to maximize energy efficiency, this system has a "heat-recovery" function, in which part of the heat rejected at high pressure and temperature can be recovered to provide heating. Operating conditions and active constraints are strongly affected by seasonal requirements and ambient temperature. Thus, it is necessary to find a control structure that satisfies operational constraints and maintains (near-)optimal operation with different sets of active constraints. In this paper, we use a systematic procedure to define such control structure.

Sustainable Energy, Grids and Networks

L'invention concerne un procede de commande d'une liberation d'energie thermique dans... more L'invention concerne un procede de commande d'une liberation d'energie thermique dans un bâtiment. Le procede comprend les etapes consistant a definir un critere de commande pour le bâtiment, definir un ensemble de variables de climat qui influencent la liberation d'energie thermique dans le bâtiment, et definir, pour chaque variable de climat, un indice de signification de climat qui definit l'importance de cette variable de climat pour la liberation d'energie thermique dans le bâtiment. Le procede comprend une etape consistant a recevoir un ensemble de variables de climat futur predit, et, ulterieurement, une etape consistant a combiner les indices de signification de climat et les variables de climat futur predit pour fournir des instructions de commande pour la liberation d'une quantite d'energie thermique dans le bâtiment afin de satisfaire aux criteres de commande. L'invention concerne en outre un systeme de commande du confort.

A wind turbine (101) comprising: a foundation (103) wherein said foundation (103) is a fixed foun... more A wind turbine (101) comprising: a foundation (103) wherein said foundation (103) is a fixed foundation; and a tower (102) connected to said foundation (103) wherein said tower (102) is inclined to a vertical position to reduce the load on said tower (102); wherein said tower (102) is inclined at a predetermined inclination angle to a prevailing wind direction; and characterized in that said predetermined inclination angle is determined based on an analysis of wind conditions at a location of said wind turbine (101).

IFAC-PapersOnLine, 2015

Wind turbine yaw error information is of high importance in controlling wind turbine power and st... more Wind turbine yaw error information is of high importance in controlling wind turbine power and structural load. Normally used wind vanes are imprecise. In this work, the estimation of yaw error in wind turbines is studied using support vector machines for regression (SVR). As the methodology is data-based, simulated data from a high fidelity aero-elastic model is used for learning. The model simulates a variable speed horizontal-axis wind turbine composed of three blades and a full converter. Both partial load (blade angles fixed at 0 deg) and full load zones (active pitch actuators) are considered. The validation step is done under different conditions of wind shear, speed and direction, giving good estimation results.

Renewable Energy, 2016

Optimal operation of wind turbines is important in order to minimize cost of energy, which is one... more Optimal operation of wind turbines is important in order to minimize cost of energy, which is one of the major focus areas of the wind industry. Model predictive control (MPC) is a candidate for a control solution which effectively balances the different and potentially conflicting objectives, e.g. generated power and structural loads. This article presents a method on how to tune multi-objective MPC problems using Pareto curves. The approach is applied to a realistic wind turbine MPC problem, in which a joint power and tower fore-aft fatigue load optimization is performed. The controller is evaluated on a high fidelity model using a Vestas wind turbine simulator. In addition to the multiple control objectives, a number of constraints are considered as well. The evaluation shows a good potential of using model predictive control for this problem compared with an industrial baseline controller as, it approximately obtains the same mean generated power, while lowering the tower fore-aft fatigue loads. The computed Pareto curves of the trade-off between tower fore-aft fatigue load and mean generated power for a number of different weight matrices, demonstrate a potential tool for tuning MPC solutions for a wind turbine.

2013 American Control Conference, 2013

This paper presents a systematic approach to design gain-scheduled predictive controllers for win... more This paper presents a systematic approach to design gain-scheduled predictive controllers for wind turbines. The predictive control law is based on Laguerre functions to parameterize control signals and a parameter-dependent cost function that is analytically determined from turbine data. These properties facilitate the design of speed controllers by placement of the closed-loop poles (when constraints are not active) and systematic adaptation towards changes in the operating point. Vibration control of undamped modes is achieved by imposing a certain degree of stability to the closed-loop system. The approach can be utilized to the design of new controllers and to represent existing gain-scheduled controllers as predictive controllers. The numerical example and simulations illustrate the design of a speed controller augmented with active damping of the tower fore-aft displacement.

IFAC Proceedings Volumes, 2006

This paper proposes novel control of the superheat of the evaporator in a refrigeration system. A... more This paper proposes novel control of the superheat of the evaporator in a refrigeration system. A new model of the evaporator is developed and based on this model the superheat is transferred to a referred variable. It is shown that control of this variable leads to a linear system independent of the working point. The model also gives a method for control of the evaporation temperature. The proposed method is validated by experimental results.

2007 American Control Conference, 2007

Abstract—This paper presents a non-linear model predictive control (NMPC) of a supermarket refrig... more Abstract—This paper presents a non-linear model predictive control (NMPC) of a supermarket refrigeration system. This is a hybrid process involving switching nonlinear dynamics and discrete events, on/off manipulated variables, like valves and compressors, continuous controlled ...

Page 1. Model Based Control of Refrigeration Systems Ph.D. Thesis Lars Finn Sloth Larsen Central ... more Page 1. Model Based Control of Refrigeration Systems Ph.D. Thesis Lars Finn Sloth Larsen Central R & D Danfoss A/S DK-6430 Nordborg, Denmark. Page 2. ii ISBN 87-90664-29-9 November 2005 Copyright 2005 cс Lars Finn Sloth Larsen Printing: Budolfi tryk Aps Page 3. ...

The thesis deals with control methods for exible and ecient power consumption in commercial refri... more The thesis deals with control methods for exible and ecient power consumption in commercial refrigeration systems that possess thermal storage capabilities, and for facilitation of more environmental sustainable power production technologies such as wind power. We apply economic model predictive control as the overriding control strategy and present novel studies on suitable modeling and problem formulations for the industrial applications, means to handle uncertainty in the control problems, and dedicated optimization routines to solve the problems involved. Along the way, we present careful numerical simulations with simple case studies as well as validated models in realistic scenarios. The thesis consists of a summary report and a collection of 13 research papers written during the period Marts 2010 to February 2013. Four are published in international peer-reviewed scientic journals and 9 are published at international peer-reviewed scientic conferences.

Black-box Models, Simple Turbine Interactions, and Integer Variables DTU Orbit (21/03/2019) Seque... more Black-box Models, Simple Turbine Interactions, and Integer Variables DTU Orbit (21/03/2019) Sequential Convex Programming for Power Set-point Optimization in a Wind Farm using Black-box Models, Simple Turbine Interactions, and Integer Variables We consider the optimization of power set-points to a large number of wind turbines arranged within close vicinity of each other in a wind farm. The goal is to maximize the total electric power extracted from the wind, taking the wake effects that couple the individual turbines in the farm into account. For any mean wind speed, turbulence intensity, and direction we find the optimal static operating points for the wind farm. We propose an iterative optimization scheme to achieve this goal. When the complicated, nonlinear, dynamics of the aerodynamics in the turbines and of the fluid dynamics describing the turbulent wind fields’ propagation through the farm are included in a highly detailed black-box model, numerical results for any given values of the parameter sets can easily be evaluated. However, analytic expressions for model representation in the optimization algorithms might be hard to derive and their properties are often not suitable for computationally efficient optimization either. To handle this, we propose a sequential convex optimization method, perturbing the model in each iteration, and demonstrate a typical convergence in fewer than 10 iterations. We derive a coupling matrix from the wind farm model, enabling us to use a very simple linear relationship for describing the turbine interactions. In addition, we allow individual turbines to be turned on or off introducing integer variables into the optimization problem. We solve this within the same framework of iterative convex approximation and compare with mixed-integer optimization tools. We demonstrate the method on a verified model and for various sizes and configurations of the wind farm. For all tested scenarios we observe a distribution of the power set-points which is at least as good as, and in many cases is far superior to, a more naive distribution scheme. We employ a fast convex quadratic programming solver to carry out the iterations in the range of microseconds for even large wind farms.

Refrigerant mal-distribution in fin-and-tube evaporators for residential air-conditioning (RAC) i... more Refrigerant mal-distribution in fin-and-tube evaporators for residential air-conditioning (RAC) is investigated numerically in this paper. A model of the syste m is developed in the object-oriented modeling language Modelica. The models of the compressor an d expansion valve are static, whereas the condenser is a dynamic moving boundary model. The evapor ator model is a dynamic distributed one-dimensional homogeneous equilibrium model, in order t o capture the distribution phenomena. Fin-and-tube heat exchangers usually have a complex circui try, however the evaporator will be simplified to be two straight tubes. The refrigerant mal-dis tribution is then induced to the evaporator by varying the vapor quality at the inlet to each feeder tube, th pressure drop through each feeder tube and the air-flow across each tube. Finally it is shown tha t air-flow mal-distribution can be compensated by an intelligent distributor, that ensures eq ual superheat in both tubes. The refrigerant is R4...

IECON 2007 - 33rd Annual Conference of the IEEE Industrial Electronics Society, 2007

Modeling and control of an indoor climate using a floor heating system based on a heat pump is di... more Modeling and control of an indoor climate using a floor heating system based on a heat pump is discussed. The thermodynamic models of the heat pump, room, floor and circulated water are theoretically developed and then identified through experimental data. Several control strategies, namely relay control, P control, PID control and PID control with prefiltering of reference input, are developed and simulated based on the developed system model. The simulation results turn out that the PID control with pre-filtering strategy generated the best system performance in terms of the smallest overshoot, fast response, highest COP in the transient period, and the smallest deviation and the least sensitivity to disturbance in the steady period. Meanwhile, this strategy also uses least power compared with other strategies. Instead of using the standard relay control, this study reveals a huge potential to use advanced control techniques to optimize operation of this kind of thermal system from thermal comfort and energy consumption perspectives.

Computer Aided Chemical Engineering, 2019

In this work, we analyze a generic supercritical CO 2-refrigeration system with parallel compress... more In this work, we analyze a generic supercritical CO 2-refrigeration system with parallel compression, based on systems used for supermarket use. In order to maximize energy efficiency, this system has a "heat-recovery" function, in which part of the heat rejected at high pressure and temperature can be recovered to provide heating. Operating conditions and active constraints are strongly affected by seasonal requirements and ambient temperature. Thus, it is necessary to find a control structure that satisfies operational constraints and maintains (near-)optimal operation with different sets of active constraints. In this paper, we use a systematic procedure to define such control structure.

Sustainable Energy, Grids and Networks

L'invention concerne un procede de commande d'une liberation d'energie thermique dans... more L'invention concerne un procede de commande d'une liberation d'energie thermique dans un bâtiment. Le procede comprend les etapes consistant a definir un critere de commande pour le bâtiment, definir un ensemble de variables de climat qui influencent la liberation d'energie thermique dans le bâtiment, et definir, pour chaque variable de climat, un indice de signification de climat qui definit l'importance de cette variable de climat pour la liberation d'energie thermique dans le bâtiment. Le procede comprend une etape consistant a recevoir un ensemble de variables de climat futur predit, et, ulterieurement, une etape consistant a combiner les indices de signification de climat et les variables de climat futur predit pour fournir des instructions de commande pour la liberation d'une quantite d'energie thermique dans le bâtiment afin de satisfaire aux criteres de commande. L'invention concerne en outre un systeme de commande du confort.

A wind turbine (101) comprising: a foundation (103) wherein said foundation (103) is a fixed foun... more A wind turbine (101) comprising: a foundation (103) wherein said foundation (103) is a fixed foundation; and a tower (102) connected to said foundation (103) wherein said tower (102) is inclined to a vertical position to reduce the load on said tower (102); wherein said tower (102) is inclined at a predetermined inclination angle to a prevailing wind direction; and characterized in that said predetermined inclination angle is determined based on an analysis of wind conditions at a location of said wind turbine (101).

IFAC-PapersOnLine, 2015

Wind turbine yaw error information is of high importance in controlling wind turbine power and st... more Wind turbine yaw error information is of high importance in controlling wind turbine power and structural load. Normally used wind vanes are imprecise. In this work, the estimation of yaw error in wind turbines is studied using support vector machines for regression (SVR). As the methodology is data-based, simulated data from a high fidelity aero-elastic model is used for learning. The model simulates a variable speed horizontal-axis wind turbine composed of three blades and a full converter. Both partial load (blade angles fixed at 0 deg) and full load zones (active pitch actuators) are considered. The validation step is done under different conditions of wind shear, speed and direction, giving good estimation results.

Renewable Energy, 2016

Optimal operation of wind turbines is important in order to minimize cost of energy, which is one... more Optimal operation of wind turbines is important in order to minimize cost of energy, which is one of the major focus areas of the wind industry. Model predictive control (MPC) is a candidate for a control solution which effectively balances the different and potentially conflicting objectives, e.g. generated power and structural loads. This article presents a method on how to tune multi-objective MPC problems using Pareto curves. The approach is applied to a realistic wind turbine MPC problem, in which a joint power and tower fore-aft fatigue load optimization is performed. The controller is evaluated on a high fidelity model using a Vestas wind turbine simulator. In addition to the multiple control objectives, a number of constraints are considered as well. The evaluation shows a good potential of using model predictive control for this problem compared with an industrial baseline controller as, it approximately obtains the same mean generated power, while lowering the tower fore-aft fatigue loads. The computed Pareto curves of the trade-off between tower fore-aft fatigue load and mean generated power for a number of different weight matrices, demonstrate a potential tool for tuning MPC solutions for a wind turbine.

2013 American Control Conference, 2013

This paper presents a systematic approach to design gain-scheduled predictive controllers for win... more This paper presents a systematic approach to design gain-scheduled predictive controllers for wind turbines. The predictive control law is based on Laguerre functions to parameterize control signals and a parameter-dependent cost function that is analytically determined from turbine data. These properties facilitate the design of speed controllers by placement of the closed-loop poles (when constraints are not active) and systematic adaptation towards changes in the operating point. Vibration control of undamped modes is achieved by imposing a certain degree of stability to the closed-loop system. The approach can be utilized to the design of new controllers and to represent existing gain-scheduled controllers as predictive controllers. The numerical example and simulations illustrate the design of a speed controller augmented with active damping of the tower fore-aft displacement.

IFAC Proceedings Volumes, 2006

This paper proposes novel control of the superheat of the evaporator in a refrigeration system. A... more This paper proposes novel control of the superheat of the evaporator in a refrigeration system. A new model of the evaporator is developed and based on this model the superheat is transferred to a referred variable. It is shown that control of this variable leads to a linear system independent of the working point. The model also gives a method for control of the evaporation temperature. The proposed method is validated by experimental results.

2007 American Control Conference, 2007

Abstract—This paper presents a non-linear model predictive control (NMPC) of a supermarket refrig... more Abstract—This paper presents a non-linear model predictive control (NMPC) of a supermarket refrigeration system. This is a hybrid process involving switching nonlinear dynamics and discrete events, on/off manipulated variables, like valves and compressors, continuous controlled ...

Page 1. Model Based Control of Refrigeration Systems Ph.D. Thesis Lars Finn Sloth Larsen Central ... more Page 1. Model Based Control of Refrigeration Systems Ph.D. Thesis Lars Finn Sloth Larsen Central R & D Danfoss A/S DK-6430 Nordborg, Denmark. Page 2. ii ISBN 87-90664-29-9 November 2005 Copyright 2005 cс Lars Finn Sloth Larsen Printing: Budolfi tryk Aps Page 3. ...

The thesis deals with control methods for exible and ecient power consumption in commercial refri... more The thesis deals with control methods for exible and ecient power consumption in commercial refrigeration systems that possess thermal storage capabilities, and for facilitation of more environmental sustainable power production technologies such as wind power. We apply economic model predictive control as the overriding control strategy and present novel studies on suitable modeling and problem formulations for the industrial applications, means to handle uncertainty in the control problems, and dedicated optimization routines to solve the problems involved. Along the way, we present careful numerical simulations with simple case studies as well as validated models in realistic scenarios. The thesis consists of a summary report and a collection of 13 research papers written during the period Marts 2010 to February 2013. Four are published in international peer-reviewed scientic journals and 9 are published at international peer-reviewed scientic conferences.

Black-box Models, Simple Turbine Interactions, and Integer Variables DTU Orbit (21/03/2019) Seque... more Black-box Models, Simple Turbine Interactions, and Integer Variables DTU Orbit (21/03/2019) Sequential Convex Programming for Power Set-point Optimization in a Wind Farm using Black-box Models, Simple Turbine Interactions, and Integer Variables We consider the optimization of power set-points to a large number of wind turbines arranged within close vicinity of each other in a wind farm. The goal is to maximize the total electric power extracted from the wind, taking the wake effects that couple the individual turbines in the farm into account. For any mean wind speed, turbulence intensity, and direction we find the optimal static operating points for the wind farm. We propose an iterative optimization scheme to achieve this goal. When the complicated, nonlinear, dynamics of the aerodynamics in the turbines and of the fluid dynamics describing the turbulent wind fields’ propagation through the farm are included in a highly detailed black-box model, numerical results for any given values of the parameter sets can easily be evaluated. However, analytic expressions for model representation in the optimization algorithms might be hard to derive and their properties are often not suitable for computationally efficient optimization either. To handle this, we propose a sequential convex optimization method, perturbing the model in each iteration, and demonstrate a typical convergence in fewer than 10 iterations. We derive a coupling matrix from the wind farm model, enabling us to use a very simple linear relationship for describing the turbine interactions. In addition, we allow individual turbines to be turned on or off introducing integer variables into the optimization problem. We solve this within the same framework of iterative convex approximation and compare with mixed-integer optimization tools. We demonstrate the method on a verified model and for various sizes and configurations of the wind farm. For all tested scenarios we observe a distribution of the power set-points which is at least as good as, and in many cases is far superior to, a more naive distribution scheme. We employ a fast convex quadratic programming solver to carry out the iterations in the range of microseconds for even large wind farms.

Refrigerant mal-distribution in fin-and-tube evaporators for residential air-conditioning (RAC) i... more Refrigerant mal-distribution in fin-and-tube evaporators for residential air-conditioning (RAC) is investigated numerically in this paper. A model of the syste m is developed in the object-oriented modeling language Modelica. The models of the compressor an d expansion valve are static, whereas the condenser is a dynamic moving boundary model. The evapor ator model is a dynamic distributed one-dimensional homogeneous equilibrium model, in order t o capture the distribution phenomena. Fin-and-tube heat exchangers usually have a complex circui try, however the evaporator will be simplified to be two straight tubes. The refrigerant mal-dis tribution is then induced to the evaporator by varying the vapor quality at the inlet to each feeder tube, th pressure drop through each feeder tube and the air-flow across each tube. Finally it is shown tha t air-flow mal-distribution can be compensated by an intelligent distributor, that ensures eq ual superheat in both tubes. The refrigerant is R4...

IECON 2007 - 33rd Annual Conference of the IEEE Industrial Electronics Society, 2007

Modeling and control of an indoor climate using a floor heating system based on a heat pump is di... more Modeling and control of an indoor climate using a floor heating system based on a heat pump is discussed. The thermodynamic models of the heat pump, room, floor and circulated water are theoretically developed and then identified through experimental data. Several control strategies, namely relay control, P control, PID control and PID control with prefiltering of reference input, are developed and simulated based on the developed system model. The simulation results turn out that the PID control with pre-filtering strategy generated the best system performance in terms of the smallest overshoot, fast response, highest COP in the transient period, and the smallest deviation and the least sensitivity to disturbance in the steady period. Meanwhile, this strategy also uses least power compared with other strategies. Instead of using the standard relay control, this study reveals a huge potential to use advanced control techniques to optimize operation of this kind of thermal system from thermal comfort and energy consumption perspectives.