<p>The growing energy demand has caused the interconnected power systems to operate close to their stability limit. As a consequence, poorly damped low-frequency oscillations are becoming a common phenomenon. Such oscillations weaken the system security and if not effectively damped can lead to widespread blackouts. A contemporary solution is the addition of Power System Stabilizers (PSSs) to generators. A relatively recent solution based on the advancements in high-power semiconductors is the Flexible AC Transmission System (FACTS) technology meant for transmission locations. FACTS technology comprises of a multitude of FACTS devices among which the <i>Unified Power Flow Controller (UPFC)</i> possesses a unique capability of providing both power flow and voltage control. Particularly, with a suitable transient control system the UPFC can satisfactorily mitigate power system oscillations.</p> <p>This thesis proposes an adaptive control scheme that supplements an existing Proportional-Integral (PI) UPFC control system in damping power system oscillations. PI control is a well-established theory and a commonly used industrial controller. However, its application in a power system that experiences continuously changing system conditions demands its frequent re-tuning. On the other hand, the proposed scheme is a Self Tuning (ST) controller that automatically adapts to the system changes and thereby provides an optimal control for a wide range of operating scenarios. The proposition of assisting the primary PI control action is unique in its approach since it retains the functionality of the existing PI controllers and also enhances the overall damping performance through an add-on ST control loop.</p> <p>The proposed novel ST scheme consists of a Constrained Recursive Least Squares (CRLS) identifier that tracks system parameters recursively and a self-tuning Pole Shift (PS) controller that works on the identified system model to generate a robust control output. Also, to effectively smoothen out the rapid variations of identified system parameters and consequent ringing of control output during large disturbances, the thesis specifies the replacement of the standard-RLS identifier with a "constrained" RLS (CRLS) identifier. The damping enhancement achieved by the proposed controller has been verified through time-domain simulations. The test results clearly depict that the proposed add-on scheme not only enhances the overall damping but is also robust with respect to power flow level, fault type and location. Its inherent flexibility and the positive test results suggest that with little modification, it can be easily applied to other FACTS devices currently incorporated in transmission networks.</p>

Thesis (M.S.)--Baylor University, 2005. / Includes bibliographical references (p. 120-121).

This research deals with the modeling and control of a plasticating twin screw extruder (TSE) that will be used to obtain consistent product quality. The TSE is a widely used process technology for compounding raw polymers. Compounding creates a polymer with improved properties that satisfy the demand of modern plastic applications. Modeling and control of a TSE is challenging because of its high nonlinearity, inherent time delay, and multiple interactive dynamic behavior. A complete methodology is proposed in this thesis to design an advanced control scheme for a TSE. This methodology was used to develop a model predictive control scheme for a laboratory scale plasticating TSE and to implement the control scheme in real-time. The TSE has a processing length of 925 mm and a length to screw diameter ratio (L/D) of 37. High density polyethylenes with different melt indices were used as processing materials. Manipulated variables and disturbance variables were selected based on knowledge of the process. Controlled variables were selected using a selection method that includes a steady state correlation between process output variables and product quality variables, and dynamic considerations. Two process output variables, melt temperature (Tm) at the die and melt pressure (Pm) at the die, were selected as controlled variables. A new modeling approach was proposed to develop grey box models based on excitation in the extruder screw speed (N), one of the manipulated variables. The extruder was excited using a predesigned random binary sequence (RBS) type excitation in N and nonlinear models relating Tm and Pm to N were developed using this approach. System identification techniques were used to obtain model parameters. The obtained models have an autoregressive moving average with exogenous (ARMAX) input structure and the models explain the physics of the extrusion process successfully. The TSE was also excited using a predesigned RBS in the feed rate (F) as a manipulated variable. Models relating Tm and Pm to F were developed using a classical system identification technique; both models have ARMAX structures. The model between Pm and F was found to give excellent prediction for data obtained from a stair type excitation, indicating that the obtained models provide a good representation of the dynamics of the twin screw extruder. Analysis of the TSE open loop process indicated two manipulated variables, N and F, and two controlled variables, Tm and Pm. Thus, a model predictive controller (MPC) was designed using the developed models for this 2X2 system and implemented in real-time. The performance of the MPC was studied by checking its set-point tracking ability. The robustness of the MPC was also examined by imposing external disturbances. Finally, a multimodel operating regime was used to model Tm and N. The operating regime was divided based on the screw speed, N. Local models were developed using system identification techniques. The global model was developed by combining local models using fuzzy logic methodology. Simulated results showed excellent response of Tm for a wide operating range. A similar approach was used to design a global nonlinear proportional-integral controller (n-PI) and a nonlinear MPC (n-MPC). Both the controllers showed good set-points tracking ability over the operating range. The multiple model-based MPC showed smooth transitions from one operating regime to another operating regime. / Process Control

Controllerrollen har sitt ursprung i USA där den verkade i de amerikanska järnvägsbolagen under 1800-talet . Termen kom sedan till Sverige runt 1970-talet då intresset för en controller ökade i Europa. Behovet av controllerfunktionen har ökat bland annat beroende på en ökad decentralisering, som medför ett behov av exempelvis information kring företagets ekonomi till flera nivåer. I och med att omvärlden förändras så måste även företagen förändras. För att kunna behålla sin konkurrenskraft har ekonomistyrningen samt controllerrollen hamnat mer i fokus. Controllerns arbetsuppgifter har gått från att enbart vara inriktad mot bokföring till att ha en mer verksam roll i ledningsgruppen. När det anses otydligt vad en controller egentligen ska arbeta med blir det svårare för företagen att själva förstår motivet till varför de tillsätter en controller. Detta är viktigt för att de ska få den controllerroll de söker. Många företag söker en strategisk kompetens när de ska tillsätta en controller men ibland visar det sig att arbetsgivaren egentligen vill ha en klassisk rapporteringsekonom. Företagen måste förstå vilket kompetens den controller de söker ska ha. Syftet med denna studie är att beskriva de motiv till varför företag väljer att tillsätta en controller samt hur motiven påverkar controllerns placering i organisationen. Vi kommer även att beskriva vilken kompetens och erfarenhet företagen eftersökte samt vilka arbetsuppgifter och ansvarsområden controllern ska ha enligt företagen. Dessa två underfrågor ska stärka våra huvudfrågor. Vi kommer att utgå denna studie från den kvalitativa metoden. Datainsamlingen kommer att ske med hjälp av intervjuer med personer som varit med om att besluta kring tillsättandet av controllern i ett fåtal företag. Några företag, vilka inte ännu valt att tillsätta en controller, ingår också i studien för att även belysa hur företaget tänker innan de väljer att tillsätta en controller. För att stärka resultatet från intervjuerna har vi har även valt att använda oss av platsannonser i vår empiri för att se vad företagen anser att controllerns arbetsuppgifter är samt vilka behov de vill få uppfyllda med hjälp av controllern. Den teoretiska referensramen i studien baseras främst på ett antal böcker samt vetenskapliga artiklar, som beskriver ekonomistyrning samt controllerns roll och utveckling genom tiderna.

This research presents an investigation to actively improve the rollover stability of articulated heavy vehicles (AHVs) during high speed manoeuvres using anti-roll control systems. A 3-dimensional (3-D) linear yaw/roll model with 5 degrees of freedom is developed. Based on this model a linear quadratic regulator (LQR) controller is designed to improve the rollover stability of a tractor/semi-trailer combination. A design optimization method for AHVs using genetic algorithms (GAs) and multibody vehicle system models is also presented. AHVs have poor manoeuvrability when travelling at low speeds on local roads and city streets. On the other hand, these vehicles exhibit unstable motion modes at high speeds, including jack-knifing, trailer sway and rollover. From the design point of view, the low-speed manoeuvrability and high-speed stability have conflicting requirements on some design variables. The design method based on a GA and a multibody vehicle dynamic package, TruckSim, is proposed to coordinate this trade-off relationship. To test the effectiveness of the design method, a tractor/semi-trailer combination is optimized using the proposed method. It is demonstrated that the proposed design method can be used for identifying desired design variables and predict performance envelopes in the early design stages of AHVs. / UOIT

Hydraulic circuits with fast dynamic response are often characterized by low power efficiency; on the other hand, energy-efficient circuits under certain circumstances, can demonstrate slow transient responses. Continuously rising energy costs combined with the demand on high performance has necessitated that hydraulic circuits become more efficient yet still demonstrate superior dynamic response. This thesis introduces a new hydraulic circuit configuration which demonstrates high dynamic performance and high efficiency. A pump-controlled hydraulic motor system was used as the basis of the study because of its high circuit efficiency. This is primarily because there is no power loss between the pump and motor. To improve the dynamic response of the pump, a DC motor was designed to control the pump swashplate (and hence flow rate) directly. The pump and DC motor were mathematically modeled and their parameters were experimentally identified. Based on the model and experimental results, a nonlinear PID controller was designed for the DC motor. By means of the DC motors quick dynamic response (in the order of 10 ms), the DC motor controlled pump demonstrated a fast dynamic response with a rise time of 15 to 35 ms depending on the pump pressure. As the dynamic response speed of the pump flow rate was increased, overshoot of the hydraulic motor output also increased. To reduce this overshoot, a bypass flow control circuit was designed to bypass part of the flow during the transient. Due to the unique operating requirements of the bypass flow control system, a PID controller with a resetable integral gain was designed for the valve to reduce the rise time of the bypass control valve. The feasibility ("proof of concept") of the bypass flow control concept was first established using simulation techniques. The simulation results showed that the bypass flow control system could significantly reduced the overshoot of the hydraulic motor rotational speed. The bypass controller was applied to the experimental test circuit. The transient results for the pump-controlled motor system with the bypass flow control are presented under a constant resistive and an inertial load. The test results showed that the bypass flow control could reduce the overshoot of the hydraulic motor rotational speed by about 50%. The relative efficiency of the circuit with the bypass flow control system was 1% to 5% lower for the particular pump-controlled system that was used in this study. For a pump/motor that does not demonstrate significant flow ripple of the magnitude experienced in this study, the relative efficiency would be the same as the pump/motor system without bypass. It was concluded that the proposed bypass control system, combined with the DC motor-swashplate driven pump, could be used to create an energy efficient circuit with excellent dynamic transient responses.

Hydraulic circuits with fast dynamic response are often characterized by low power efficiency; on the other hand, energy-efficient circuits under certain circumstances, can demonstrate slow transient responses. Continuously rising energy costs combined with the demand on high performance has necessitated that hydraulic circuits become more efficient yet still demonstrate superior dynamic response. This thesis introduces a new hydraulic circuit configuration which demonstrates high dynamic performance and high efficiency. A pump-controlled hydraulic motor system was used as the basis of the study because of its high circuit efficiency. This is primarily because there is no power loss between the pump and motor. To improve the dynamic response of the pump, a DC motor was designed to control the pump swashplate (and hence flow rate) directly. The pump and DC motor were mathematically modeled and their parameters were experimentally identified. Based on the model and experimental results, a nonlinear PID controller was designed for the DC motor. By means of the DC motors quick dynamic response (in the order of 10 ms), the DC motor controlled pump demonstrated a fast dynamic response with a rise time of 15 to 35 ms depending on the pump pressure. As the dynamic response speed of the pump flow rate was increased, overshoot of the hydraulic motor output also increased. To reduce this overshoot, a bypass flow control circuit was designed to bypass part of the flow during the transient. Due to the unique operating requirements of the bypass flow control system, a PID controller with a resetable integral gain was designed for the valve to reduce the rise time of the bypass control valve. The feasibility ("proof of concept") of the bypass flow control concept was first established using simulation techniques. The simulation results showed that the bypass flow control system could significantly reduced the overshoot of the hydraulic motor rotational speed. The bypass controller was applied to the experimental test circuit. The transient results for the pump-controlled motor system with the bypass flow control are presented under a constant resistive and an inertial load. The test results showed that the bypass flow control could reduce the overshoot of the hydraulic motor rotational speed by about 50%. The relative efficiency of the circuit with the bypass flow control system was 1% to 5% lower for the particular pump-controlled system that was used in this study. For a pump/motor that does not demonstrate significant flow ripple of the magnitude experienced in this study, the relative efficiency would be the same as the pump/motor system without bypass. It was concluded that the proposed bypass control system, combined with the DC motor-swashplate driven pump, could be used to create an energy efficient circuit with excellent dynamic transient responses.

In this thesis, a grid-connected wind-energy converter system including a matrix converter is proposed. The matrix converter, as a power electronic converter, is used to interface the induction generator with the grid and control the wind turbine shaft speed. At a given wind velocity, the mechanical power available from a wind turbine is a function of its shaft speed. Through the matrix converter, the terminal voltage and frequency of the induction generator is controlled, based on a constant V/f strategy, to adjust the turbine shaft speed and accordingly, control the active power injected into the grid to track maximum power for all wind velocities. The power factor at the interface with the grid is also controlled by the matrix converter to either ensure purely active power injection into the grid for optimal utilization of the installed wind turbine capacity or assist in regulation of voltage at the point of connection. Furthermore, the reactive power requirements of the induction generator are satisfied by the matrix converter to avoid use of self-excitation capacitors. The thesis addresses two dynamic models: a comprehensive dynamic model for a matrix converter and an overall dynamical model for the proposed wind turbine system. The developed matrix converter dynamic model is valid for both steady-state and transient analyses, and includes all required functions, i.e., control of the output voltage, output frequency, and input displacement power factor. The model is in the qdo reference frame for the matrix converter input and output voltage and current fundamental components. The validity of this model is confirmed by comparing the results obtained from the developed model and a simplified fundamental-frequency equivalent circuit-based model. In developing the overall dynamic model of the proposed wind turbine system, individual models of the mechanical aerodynamic conversion, drive train, matrix converter, and squirrel-cage induction generator are developed and combined to enable steady-state and transient simulations of the overall system. In addition, the constraint constant V/f strategy is included in the final dynamic model. The model is intended to be useful for controller design purposes. The dynamic behavior of the model is investigated by simulating the response of the overall model to step changes in selected input variables. Moreover, a linearized model of the system is developed at a typical operating point, and stability, controllability, and observability of the system are investigated. Two control design methods are adopted for the design of the closed-loop controller: a state-feedback controller and an output feedback controller. The state-feedback controller is designed based on the Linear Quadratic method. An observer block is used to estimate the states in the state-feedback controller. Two other controllers based on transfer-function techniques and output feedback are developed for the wind turbine system. Finally, a maximum power point tracking method, referred to as mechanical speed-sensorless power signal feedback, is developed for the wind turbine system under study to control the matrix converter control variables in order to capture the maximum wind energy without measuring the wind velocity or the turbine shaft speed.

When a helicopter is flying, the dynamics vary depending on, for example, speed and position. Hence, a time-invariant linear model cannot describe its properties under all flight conditions. It is therefore desirable to update the linear helicopter model continuously during the flight. In this thesis, two different recursive estimation methods are presented, LMS (Least Mean Square) and adaptation with a Kalman filter. The main purpose of the system estimation is to get a model which can be used for feedback control. In this report, the estimated model will be used to create a LQ controller with the task of keeping the output signal as close to the reference signal as possible.Simulations in this report show that adaptive feedback control can be used to control a helicopter's angular velocities and that the possibility to use an adaptive control algorithm in a real future helicopter is good.

This paper is the result of a master thesis project on helicopter rotor downwash effects using computational fluid dynamics (CFD). The work was performed at the department of Aerodynamics and Flight Mechanics at Saab AB, Linköping in 2008. It completes the author’s studies for a M.Sc degree in Applied Physics and Electrical Engineering at the Department of Electrical Engineering at the Linköping institute of technology (LiTH), Linköping, Sweden.   The aim of the project was to study the rotor downwash effects and its influence on the helicopter fuselage. To fulfil this purpose, several CFD calculations were carried out and the aerodynamic forces and moments resulting from the calculations were implemented in an existing simulation model, developed in-house at Saab. The original (existing) model was compared to the updated model by studying step responses in MATLAB, Simulink. For some step commands, the comparisions indicated that the updated model was more damped in yaw compared to the original model for the hovering helicopter. When the helicopter was trimmed for a steady turn, the states in the updated model diverged much faster than the states in the original model for any given step command.     In order to investigate the differences between the original helicopter model and the updated model from a controlling perspective, a linear quadratic (LQ) state feedback controller was synthesized to stabilize the vehicle in a steady turn. The LQ method was chosen as it is a modern design technique with good robustness and sensitivity properties and since it is easily implemented in MATLAB.  Before synthesising, a simplification of the helicopter model was made by reducing states and splitting them into lateral and longitudinal ones. Step responses from simulations with the original and the updated model were studied, showing an almost identical behavior.   It can be concluded that the aerodynamic coefficients obtained from the CFD calculations can be used for determining the aerodynamic characteristics of the helicopter. Some further validation is needed though, for example by comparing the results with flight test data. In order to build an aerodynamic data base that covers the whole flight envelop, additional CFD calculations are required.