A unified smith predictor approach for power system damping control design using remote signals

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Asymptotic properties of the spectrum of neutral delay differential equations

Spectral properties and transition to instability in neutral delay differential equations are investigated in the limit of large delay. An approximation of the upper boundary of stability is found and compared to an analytically derived exact stability boundary. The approximate and exact stability borders agree quite well for the large time delay, and the inclusion of a time-delayed velocity feedback improves this agreement for small delays. Theoretical results are complemented by a numerically computed spectrum of the corresponding characteristic equations.Comment: 14 pages, 6 figure

The pitch-heave dynamics of transportation vehicles

The analysis and design of suspensions for vehicles of finite length using pitch-heave models is presented. Dynamic models for the finite length vehicle include the spatial distribution of the guideway input disturbance over the vehicle length, as well as both pitch and heave degrees-of-freedom. Analytical results relate the vehicle front and rear accelerations to the pitch and heave natural frequencies, which are functions of vehicle suspension geometry and mass distribution. The effects of vehicle asymmetry and suspension contact area are evaluated. Design guidelines are presented for the modification of vehicle and suspension parameters to meet alternative ride quality criteria

Towards an Enhanced Wide Area Control System for Damping Out Low Frequency Oscillations in Power Grid

This thesis presents enhanced methodologies in a wide area control system to damp out low frequency oscillations. The primary motivation behind this work is to design a wide area controller to avoid power system blackouts by damping out low frequency oscillations which are existing for longer time duration. The wide area controller can be designed in two ways: state feedback control and output feedback control. From the input point of view, the state feedback controller requires the information about all system states and are not possible to observe all system states in real-time. From the output point of view, the output signals of the controller can be given to the AVR/excitation system of all generators in both control techniques which will increase the cost of the communication network. Moreover, the time delay due to the communication network will affect the wide are controller performance. Therefore, to overcome these problems, in particular, this work addresses the design of a wide area controller with limited measurements to resolve the input side problems. The problems associated with the output side can be overcome by employing a reduced- scale wide area controller design. In addition, the time delay effects can be resolved by using bi-layer wide area control architecture with the incorporation of the practical supplementary controller. The important contributions of this work are as follows. 1. Designing a wide area controller to damp out inter-area oscillations by consid- ering limited measurements with unknown load composition. 2. Designing a reduced-scale architecture of the wide area control system by means of modal sensitivity analysis. 3. Designing a practical supplementary controller design for the bi-layer wide area control architecture through structurally constrained H2-norm optimization. The contribution of the first work is to design a wide area controller with limited measurements without knowing load composition. The primary objective of this work is to design a state feedback controller to damp out the inter-area oscillations in the power system network with limited wide area measurements. The conventional state feedback controller designed through LQR optimization requires all the state variables as input. However, the dynamics of a power system is governed by a large number of state variables. Therefore, it is, practically, not possible to place sensors everywhere for monitoring the complete system state in real-time. To address the particular issue, an optimized state feedback controller is proposed, which can be implemented with the limited number of state inputs. The structurally constrained H2-norm optimization technique is employed to perform the proposed state feedback controller design. The reference frame requirement for defining the rotor angles of generators under the scenario of limited state observability is also investigated. The performance of the wide area controller with limited state inputs is verified through a case study on the New England 39-bus system under different scenarios of state unobservability. Since the WAC design requires a full system description, appropriate load modeling may be critical in the WAC design. Therefore, a mathematical framework is developed to carry out WAC design in the presence of multiple types of load. Both static and dynamic loads are considered. In order to exempt the dynamic load states from the input of WAC, the structurally constrained H2-norm optimized WAC design is performed. By recognizing the practical difficulty of obtaining the precise information about actual load composition, this work further investigates the suitability of representing all the loads as constant power loads in the WAC design. Detailed case studies are performed on the IEEE 39-bus system. The contribution of the second work is to develop an efficient scheme for the proper selection of entities in the wide area control (WAC) loop so as to yield a cost-effective and simplified WAC architecture without compromising with its damping performance. The methodology proposed is based upon a concept of mode-path susceptibility matrix that is obtained by means of the modal sensitivity analysis. Inspecific, the significance of a feedback path to change mode shapes is determined by evaluating the sensitivities of different modes to the respective elements of the feedback gain matrix. This is unlike the traditional controllability and observability based approaches. A generalized utility ranking of potential source and sink points of the wide area damping controller is further carried out based upon the mode- path susceptibility matrix. Both the state feedback and the output feedback are taken into account in the methodology proposed for the scale reduction of a WAC architecture. Detailed case studies are performed to verify the effectiveness of the proposed reduced-scale WAC architecture through both off-line simulations and real- time experimentations. The contribution of the third work is to develop a suitable methodology for the practical realization of the bi-layer wide area control (WAC) architecture. The bi-layer WAC system retains the capability to overcome the communication related problems to a great extent through the deployment of a supplementary wide area damping controller (WADC) along with the conventional WADC. The supplementary WADC was envisaged as a controller that may not have any communication requirements to deliver control signals. It is, therefore, essential to design the supplementary WADC in a way so that the same can be practically implemented without the requirement of any communication network. The precise concern of the present work is to address the proper design of the aforementioned supplementary WADC. The design of the supplementary WADC is carried out through a structurally constrained H2-norm optimization calculation. The solution procedure of the particular H2-norm optimization problem is established. Detailed simulation studies are performed to evaluate the performance of the proposed supplementary WADC in the standalone mode. The usefulness of the bi-layer WAC architecture to improve the damping of inter-area oscillations under the proposed controller design is thoroughly validated through real-time experimentations

Dynamic thermal features of insulated blocks: Actual behavior and myths

The latest updates in the European directive on energy performance of buildings have introduced the fundamental “nearly zero-energy building (NZEB)” concept. Thus, a special focus needs to be addressed to the thermal performance of building envelopes, especially concerning the role played by thermal inertia in the energy requirements for cooling applications. In fact, a high thermal inertia of the outer walls results in a mitigation of the daily heat wave, which reduces the cooling peak load and the related energy demand. The common assumption that high mass means high thermal inertia typically leads to the use of high-mass blocks. Numerical and experimental studies on thermal inertia of hollow envelope components have not confirmed this general assumption, even though no systematic analysis is readily available in the open literature. Yet, the usually employed methods for the calculation of unsteady heat transfer through walls are based on the hypothesis that such walls are composed of homogeneous layers. In this framework, a study of the dynamic thermal performance of insulated blocks is brought forth in the present paper. A finite-volume method is used to solve the two-dimensional equation of conduction heat transfer, using a triangular-pulse temperature excitation to analyze the heat flux response. The effects of both the type of clay and the insulating filler are investigated and discussed at length. The results obtained show that the wall front mass is not the basic independent variable, since clay and insulating filler thermal diffusivities are more important controlling parameters

Flexible aircraft flying and ride qualities

A brief analytic exposition is presented to illustrate a central principle in flexible mode control, some of the pertinent pilot centered requirements are listed and discussed. The desired features of the control methodology are exposed and the methodology to be used is selected. The example Boeing supplied characteristics are discussed and approximated with a reduced order model and a simplified treatment of unsteady aerodynamics. The closed loop flight control system design follows, along with first level assessments of resulting handling and ride quality characteristics. Some of these do not meet the postulated requirements and remain problems to be solved possibly by further analysis or future simulation

Taming Instabilities in Power Grid Networks by Decentralized Control

Renewables will soon dominate energy production in our electric power system. And yet, how to integrate renewable energy into the grid and the market is still a subject of major debate. Decentral Smart Grid Control (DSGC) was recently proposed as a robust and decentralized approach to balance supply and demand and to guarantee a grid operation that is both economically and dynamically feasible. Here, we analyze the impact of network topology by assessing the stability of essential network motifs using both linear stability analysis and basin volume for delay systems. Our results indicate that if frequency measurements are averaged over sufficiently large time intervals, DSGC enhances the stability of extended power grid systems. We further investigate whether DSGC supports centralized and/or decentralized power production and find it to be applicable to both. However, our results on cycle-like systems suggest that DSGC favors systems with decentralized production. Here, lower line capacities and lower averaging times are required compared to those with centralized production.Comment: 21 pages, 6 figures This is a pre-print of a manuscript submitted to The European Physical Journal. The final publication is available at Springer via http://dx.doi.org/10.1140/epjst/e2015-50136-