The presence of inter-area oscillations has long affected stability constraints, and therefore, limited the power transfer capacity of interconnected power systems. Adequate damping of these inter-area oscillations is, thus, necessary to secure system operation and ensure system reliability while increasing power transfers. Power system stabilizers (PSS) are the most common devices used to enhance the damping of such oscillations. Many studies have demonstrated that PSSs using remote signals may perform better than using local signals. The advent of phasor measurement units (PMU) makes remote or wide-area signals become available, which enables various important applications. Of particular interest is wide-area damping control (WADC), which aims to utilize remote or wide-area measurements to damp the inter-area oscillations. However, two main challenges in WADC design are (1) feedback controller input signal selection (which PMU signal is best to use?), and (2) latency (which is inherent in the transmission of the measurements) considerations. In response to the first challenge, this thesis proposes a concept called dominant inter-area oscillation path, which serves to pinpoint a set of candidate signals that can be used as the feedback controller inputs by locating the interconnected corridors where the inter-area modal contents are the most observable. Derivation, identification, and use of the dominant inter-area oscillation paths are demonstrated throughout the thesis. Extensive analysis on the relationships between the proposed set of signals and system properties regarding stability and robustness is presented. To tackle the second challenge, the impacts of time delays on the system performance when using the dominant path signals are investigated. To date, several studies have proposed different control design methods using various oscillation dampers to design WADC. Nevertheless, neither a systematic method nor a concept that encompasses fundamental knowledge on power system dynamics has yet been offered. The objective of this thesis is, thus, to propose an analytical framework based on the dominant path concept which is built upon fundamental principles for feedback controller input signal selection in WADC. With this framework, a proper and systematic approach is developed. The proposed method allows to select appropriate signals and use them to effectively mitigate the inter-area oscillations that constrain power transfer capacity and affect system stability. / <p>QC 20150414</p>

The author received the Ph.D. degree in Automatic Control from the Saint-Petersburg State Electrical Engineering University (Russia) in 2001, and the Dr.Sc. degree in Automatic control in 2006 from Institute for Problems of Mechanical Engineering RAS (Saint-Petersburg, Russia). From 2000 to 2009 he was research fellow of the Institute for Problems of Mechanical Engineering RAS, Control of Complex Systems Laboratory. From 2006 to 2011 he was working with the LSS (Supelec, France), the Montefiore Institute (University of Liege, Belgium) and the Automatic control group at IMS lab (University of Bordeaux I, France). Since 2011 he joined the Non-A team at INRIA-LNE centre in Lille, France. He is a member of the IFAC TCs on Adaptive and Learning Systems and Control for Society. He is Senior member of IEEE. His main research interests include nonlinear oscillation analysis, observation and control, switched and nonlinear system stability. During his scientific carrier he published over 140 papers, books and technical reports. The subject of the dissertation deals with the main research direction of the author: analysis, estimation and control in nonlinear oscillating systems. It is an emerging area of research touching many applicative domains. This field strives for new estimation and control algorithms since frequently, due to peculiarities of this type of systems, the conventional approaches do not provide solutions with a satisfactory performance. Some control and estimation solutions for oscillating systems proposed by the author are given in the thesis. The hybrid or/and supervisory systems method is selected as the basement of design of new tools for analysis, observation and control of nonlinear oscillations. The first chapter of the thesis deals with presentation of scientific background and experience of the author. In the second chapter an approach to analysis of existence of oscillations is presented, an adaptive control algorithm for bifurcation control is briefly described, and an approach for entrainment of periodical systems based on PRC is introduced. In the third chapter the main planned future directions of research of the author are given. Appendices contain the full list of publications and the texts of four selected papers.

Thermo-acoustic instabilities in combustion chambers are generated by the interactions between a flame and the combustor acoustics, leading to a resonant coupling. These self-sustained oscillations may be observed in many practical systems such as domestic boilers, industrial furnaces, gas turbines or rocket engines. Although this phenomenon has already been the topic of many investigations, there is yet no generalized robust framework to predict the onset of these self-sustained oscillations and to determine the evolution of the flow variables within the combustor during unstable operation. This work builds on previous models and experiments to improve the description of the response of laminar conical flames to flow perturbations and the prediction of thermoacoustic instability in burners operating with conical flames. In the first part of the manuscript, an extensive review of conical flame dynamics modeling is undertaken and a general framework for the modeling of their Flame Transfer Function (FTF) is presented. The experimental setup and the diagnostics used to characterize their response to flow disturbances are then described. They are used to measure the FTF when the flames are submitted to harmonic flow perturbations. A novel experimental technique is also proposed to control the flow perturbation level at the burner outlet. It enables to modulate the flow with random white noise perturbations and to measure the FTF with a better frequency resolution. Results with this alternative technique compare well with results from the classical method using harmonic signals for small disturbances. Limits of this technique are also highlighted when the perturbation level increases. Different analytical expressions for the FTF of conical flames are derived in the second part of the thesis by progressively introducing more physics into the models. Models based on convected flow disturbances are extended by taking into account the incompressible nature of the perturbed velocity field. It is shown that the prediction of the FTF phase lag of a conical flame is greatly improved and collapses well with measurements. Then, a thorough investigation of the flame base dynamics interacting with the anchoring device is conducted by considering unsteady heat loss from the flame to the burner. This mechanism is shown to drive the motion of the flame base and the flame dynamics at high frequencies. It is also shown that this contribution to the FTF rules the high frequency behavior of the FTF as well as the nonlinear evolution of the FTF when the perturbation level increases. Finally, an analysis is conducted on the dynamics of a single conical flame placed into cylindrical flame tubes featuring different diameters. It is shown that confinement effects need to be taken into account when the burnt gases cannot fully expand. Large differences are observed between FTF measured for different confinement tube diameters. A new dimensionless number is derived to take these effects into account and make all the FTF collapse on a single curve. These different models are then used to model the response of a collection of small conical flames stabilized on a perforated plate. It is shown that by sorting out the different contributing mechanisms to the FTF, the expressions proposed in this work may be combined to capture the main behavior and correct phase lag evolution of these flames in the frequency range of interest for thermo-acoustic instability prediction.

Cytoplasmic dynein is a ubiquitous minus-end directed motor protein that is essential for a variety of cellular processes ranging from cargo transport to spindle and chromosome positioning. Specifically, in fission yeast during meiotic prophase, the fused nucleus follows the spindle pole body in oscillatory movements from one cell pole to the other. The three molecular players that are essential to this process are: (i) the motor protein dynein, which powers the movement of the nucleus, (ii) microtubules, which provide the tracts for the movement and (iii) Num1, the anchor protein of dynein at the cortex. Dyneins that are localized to the anchor protein at the cortex and simultaneously bound to the microtubule emanating from the spindle pole body, pull on that microtubule leading to the movement of the nucleus. The spindle pole body, by virtue of its movement establishes a leading and a trailing side. Previous work by Vogel et al. has elucidated the mechanism of these oscillations as that of asymmetric distribution of dynein between the leading and trailing sides. This differential distribution is a result of the load-dependent detachment of dynein preferentially from the trailing microtubules. This self-organization model for dynein, however, requires a continuous redistribution of dynein from the trailing to the leading side. In addition, dyneins need to be bound to the anchor protein to be able to produce force on the microtubules. Anchored dyneins are responsible for many other important processes in the cell such as spindle alignment and orientation, spindle separation and rotation. So we set out to elucidate the mechanism of redistribution of dynein as well as the targeting mechanism of dynein from the cytoplasm to cortical anchoring sites where they can produce pulling force on microtubules. By employing single-molecule observation using highly inclined laminated optical sheet (HILO) microscopy and tracking of fluorescently-tagged dyneins using a custom software, we were able to show that dyneins redistributed in the cytoplasm of fission yeast by simple diffusion. We also observed that dynein bound first to the microtubule and not directly to the anchor protein Num1. In addition, we were able to capture unbinding events of single dyneins from the microtubule to the cytoplasm. Surprisingly, dynein bound to the microtubule exhibited diffusive behaviour. The switch from diffusive to directed movement required to power nuclear oscillations occurred when dynein bound to its cortical anchor Num1. In summary, dynein employs a two-step targeting mechanism from the cytoplasm to the cortical anchoring sites, with the attachment to the microtubule acting as the intermediate step.

The first part of this work was dedicated to the experimental study of basic principles of oscillating plate propulsors undergoing a combination of heave translation and pitch rotation. The oscillation kinematics are inspired by swimming mechanisms employed by fish and some other marine animals. The primary attention was the propulsive characteristics of such oscillating plates, which was studied by means of direct force measurements in the thrust-producing regime. Experiments were performed at constant Reynolds number and heave amplitude. By varying the Strouhal number, experimental depth and chordwise exibility of the plate it was possible to investigate corresponding changes in thrust and hydromechanical efficiency. After numerous measurements it was possible to establish an optimal set of parameters, including the system's driving frequency, the ratio of rigid to flexible segment length of the plate and the range of Strouhal number, that led to a peak efficiency near 80%. The experiments for different values of chordwise flexibility showed that greater flexibility increases the propulsive effciency and thrust compared with similar motion of the purely rigid foil. By submerging the plate at different depths, it was observed that the proximity of the propulsor to the channel floor led to overall increase in the thrust coefficient. However the increase in thrust coefficient was pronounced in the range from middepth to the floor of the water tunnel. The special case when the upper plate's edge is tangential to the undisturbed free surface is discussed separately. The second part of this work introduces a semianalytic approach for calculating the influence of piezoelectric (PZT) actuators on the free vibration characteristics of an Euler-Bernoulli clamped free beam. The beam represents a simplifled version of the fish tail whose stiffness is proposed to be controlled by placing a pair of PZT actuators in strategic regions along the caudal area of the tail. This approach, according to earlier studies, improves efficiency if tail natural frequency matches tailbeat frequency. The approach used an existing form of a transfer matrix technique developed for the analysis of non-proportionally damped slender beams. The PZT dynamics were incorporated into this recursive procedure through a modification that accounted for the tendency of the PZT patches to couple the dynamics of the node points of the segmented Euler-Bernoulli beam. To ensure stability of the system, an angular ve- locity feedback law, originally motivated by vibration suppression applications, was chosen for the PZT actuators. The sensitivities of the tail modes of vibration to the location of the PZT elements and the control gain were determined. Mode shapes for the revised modes were determined and it was shown that the first, second and the third modes maintained similar norms as tail shapes observed in anguilliform, sub- carangiform, and thunniform regimes of swimming. Using a semianalytic approach, it was shown that PZT location heavily in uences the frequency distribution of the modes of vibration. The control gain, when chosen within the limit of saturation voltage, is shown to be an effective control lever for vibration suppression and at rising the tail stiffness during rapid acceleration when the fish accelerates. However, the single PZT patch does not provide significant frequency adjustments such that different swimming modes could be employed efficiently with a single mechanical tail system primary actuator. To pursue such versatility for the sh tail, the tail structure must be very flexible to accommodate the significant frequency increase caused by the addition of the PZT material. Also, the use of additional PZT patches and negative control gains must be considered in order to use the PZT's to drop the higher modes (second and third) down into the frequency range of the primary actuation system, presuming the tail and primary actuator are designed for a thunniform regime of swimming.

This thesis presents novel series compensation schemes and adaptive control techniques to enhance power system dynamics through damping Subsynchronous Resonance (SSR) and low-frequency power oscillations: local and inter-area oscillations. Series capacitive compensation of transmission lines is used to improve power transfer capability of the transmission line and is economical compared to the addition of new lines. However, one of the impeding factors for the increased utilization of series capacitive compensation is the potential risk of SSR, where electrical energy is exchanged with turbine-generator shaft systems in a growing manner which can result in shaft damage. Furthermore, the fixed capacitor does not provide controllable reactance and does not aid in the low-frequency oscillations damping. The Flexible AC Transmission System (FACTS) controllers have the flexibility of controlling both real and reactive power which could provide an excellent capability for improving power system dynamics. Several studies have investigated the potential of using this capability in mitigating the low-frequency (electromechanical) as well as the subsynchronous resonance (SSR) oscillations. However, the practical implementations of FACTS devices are very limited due to their high cost. To address this issue, this thesis proposes a new series capacitive compensation concept capable of enhancing power system dynamics. The idea behind the concept is a series capacitive compensation which provides balanced compensation at the power frequency while it provides phase unbalance at other frequencies of oscillations. The compensation scheme is a combination of a single-phase Thyristor Controlled Series Capacitor (TCSC) or Static Synchronous Series Compensator (SSSC) and a fixed series capacitors in series in one phase of the compensated transmission line and fixed capacitors on the other two phases. The proposed scheme is economical compared to a full three-phase FACTS counterpart and improves reliability of the device by reducing number of switching components. The phase unbalance during transients reduces the coupling strength between the mechanical and the electrical system at asynchronous oscillations, thus suppressing the build-up of torsional stresses on the generator shaft systems. The SSR oscillations damping capability of the schemes is validated through detailed time-domain electromagnetic transient simulation studies on the IEEE first and second benchmark models. Furthermore, as the proposed schemes provide controllable reactance through TCSC or SSSC, the supplementary controllers can be implemented to damp low-frequency power oscillations as well. The low-frequency damping capability of the schemes is validated through detail time-domain electromagnetic transient simulation studies on two machines systems connected to a very large system and a three-area, six-machine power system. The simulation studies are carried out using commercially available electromagnetic transient simulation tools (EMTP-RV and PSCAD/EMTDC). An adaptive controller consisting of a robust on-line identifier, namely a robust Recursive Least Square (RLS), and a Pole-Shift (PS) controller is also proposed to provide optimal damping over a wide range of power system operations. The proposed identifier penalizes large estimated errors and smooth-out the change in parameters during large power system disturbances. The PS control is ideal for its robustness and stability conditions. The combination results in a computationally efficient estimator and a controller suitable for optimal control over wider range of operations of a non-linear system such as power system. The most important aspect of the controller is that it can be designed with an approximate linearized model of the complete power system, and does not need to be re-tuned after it is commissioned. The damping capability of such controller is demonstrated through detail studies on a three-area test system and on an IEEE 12-bus test system. Finally, the adaptive control algorithm is developed on a Digital Signal Processing Board, and the performance is experimentally tested using hardware-in-the-loop studies. For this purpose, a Real Time Digital Simulator (RTDS) is used, which is capable of simulating power system in real-time at 50 µs simulation time step. The RTDS facilitates the performance evaluation of a controller just like testing on a real power system. The experimental results match closely with the simulation results; which demonstrated the practical applicability of the adaptive controller in power systems. The proposed controller is computationally efficient and simple to implement in DSP hardware.

Background: The visual system may process spatial frequency information in a low-to-high, coarse-to-fine sequence. In particular, low and high spatial frequency information may be processed via different pathways during object recognition, with LSF information projected rapidly to frontal areas and HSF processed later in visual ventral areas. In an electroencephalographic study, we examined the time course of information processing for images filtered to contain different ranges of spatial frequencies. Participants viewed either high spatial frequency (HSF), low spatial frequency (LSF), or unfiltered, broadband (BB) images of objects or nonobject textures, classifying them as showing either man-made or natural objects, or nonobjects. Event-related potentials (ERPs) and evoked and total gamma band activity (eGBA and tGBA) recorded using the electroencephalogram were compared for object and nonobject images across the different spatial frequency ranges. Results: The visual P1 showed independent modulations by object and spatial frequency, while for the N1 these factors interacted. The P1 showed more positive amplitudes for objects than nonobjects, and more positive amplitudes for BB than for HSF images, which in turn evoked more positive amplitudes than LSF images. The peak-to-peak N1 showed that the N1 was much reduced for BB non-objects relative to all other images, while HSF and LSF nonobjects still elicited as negative an N1 as objects. In contrast, eGBA was influenced by spatial frequency and not objecthood, while tGBA showed a stronger response to objects than nonobjects. Conclusions: Different pathways are involved in the processing of low and high spatial frequencies during object recognition, as reflected in interactions between objecthood and spatial frequency in the visual N1 component. Total gamma band seems to be related to a late, probably highlevel representational process.

The method of baryon acoustic oscillation (BAO) is among the best probes of the dark energy equation of state, and worldwide efforts are being invested in order to perform measurements that are accurate at the percent level. In current data analyses, however, estimates of the error about the BAO are based on the assumption that the density field can be treated as Gaussian, an assumption that becomes less accurate as smaller scales are included in the measurement. It was recently shown from large samples of N-body simulations that the error bars about the BAO obtained this way are in fact up to 15-20 per cent too small. This important bias has shaken the confidence in the way error bars are calculated, and is motivating developments of analyses pipelines that include non-Gaussian features in the matter density fields. In this thesis, we propose general strategies to incorporate non-Gaussian effects in the context of a survey. After describing the high performance N-body code that we used, we present novel properties of the non-Gaussian uncertainty about the matter power spectrum, and explain how these combine with a general survey selection function. Assuming that the non-Gaussian features that are observed in the simulations correspond to those of Nature, this approach is the first unbiased measurement of the error bar about the power spectrum, which simultaneously removes the undesired bias on the BAO error. We then relax this assumption about the similitude of the non-Gaussian natures in simulations and data, and develop tools that aim at measuring the non-Gaussian error bars exclusively from the data. It is possible to improve the constraining power of non-Gaussian analyses with `Gaussianizations' techniques, which map the observed fields into something more Gaussian. We show that two of such techniques maximally recover degrees of freedom that were lost in the gravitational collapse. Finally, from a large sample of high resolution N-body realizations, we construct a series of weak gravitational lensing distortion maps and provide high resolution halo catalogues that are used by the CFTHLenS community to calibrate their estimators and study many secondary effects with unprecedented accuracy.

The method of baryon acoustic oscillation (BAO) is among the best probes of the dark energy equation of state, and worldwide efforts are being invested in order to perform measurements that are accurate at the percent level. In current data analyses, however, estimates of the error about the BAO are based on the assumption that the density field can be treated as Gaussian, an assumption that becomes less accurate as smaller scales are included in the measurement. It was recently shown from large samples of N-body simulations that the error bars about the BAO obtained this way are in fact up to 15-20 per cent too small. This important bias has shaken the confidence in the way error bars are calculated, and is motivating developments of analyses pipelines that include non-Gaussian features in the matter density fields. In this thesis, we propose general strategies to incorporate non-Gaussian effects in the context of a survey. After describing the high performance N-body code that we used, we present novel properties of the non-Gaussian uncertainty about the matter power spectrum, and explain how these combine with a general survey selection function. Assuming that the non-Gaussian features that are observed in the simulations correspond to those of Nature, this approach is the first unbiased measurement of the error bar about the power spectrum, which simultaneously removes the undesired bias on the BAO error. We then relax this assumption about the similitude of the non-Gaussian natures in simulations and data, and develop tools that aim at measuring the non-Gaussian error bars exclusively from the data. It is possible to improve the constraining power of non-Gaussian analyses with `Gaussianizations' techniques, which map the observed fields into something more Gaussian. We show that two of such techniques maximally recover degrees of freedom that were lost in the gravitational collapse. Finally, from a large sample of high resolution N-body realizations, we construct a series of weak gravitational lensing distortion maps and provide high resolution halo catalogues that are used by the CFTHLenS community to calibrate their estimators and study many secondary effects with unprecedented accuracy.

Many problems in fluid mechanics and material sciences deal with liquid-vapour flows. In these flows, the ideal gas assumption is not accurate and the van der Waals equation of state is usually used. This equation of state is non-convex and causes the solution domain to have two hyperbolic regions separated by an elliptic region. Therefore, the governing equations of these flows have a mixed elliptic-hyperbolic nature. Numerical oscillations usually appear with standard finite-difference space discretization schemes, and they persist when the order of accuracy of the semi-discrete scheme is increased. In this study, we propose to use a Chebyshev pseudospectral method for solving the governing equations. A comparison of the results of this method with very high-order (up to tenth-order accurate) finite difference schemes is presented, which shows that the proposed method leads to a lower level of numerical oscillations than other high-order finite difference schemes, and also does not exhibit fast-traveling packages of short waves which are usually observed in high-order finite difference methods. The proposed method can thus successfully capture various complex regimes of waves and phase transitions in both elliptic and hyperbolic regimes