Abstract: In this article, Optimal Control for Coordinated Control (COC) of Series Vectorial Compensator (SVeC) and Power System Stabilizer (PSS) in order to damp Low Frequency Oscillations (LFO) is proposed. SVeC is a series Flexible Alternating Current Transmission System (FACTS) device. The Optimal Control strategy based on state feedback control for coordination of PSS and SVeC controllers under different loading conditions has not been developed. So, the Optimal State Feedback Controller (OSFC) for incorporating of PSS and SVeC controllers in COC manner has been developed in this paper. The performance of the proposed controller is checked through eigenvalue analysis and nonlinear time domain simulation results. The proposed Optimal Controller design for the COC of SVeC and PSS results will be analyzed without controller. The comparative results show that Optimal Controller for COC of SVeC and PSSs improve greatly the system damping LFO than without controller.
Abstract: A microgrid (MG) is a small power grid composed of localized medium or low level power generation, storage systems, and loads. In this paper, the effects of a MG on power systems voltage stability are shown. The MG model, designed to demonstrate the effects of the MG, was applied to the IEEE 14 bus power system which is widely used in power system stability studies. Eigenvalue and modal analysis methods were used in simulation studies. In the study results, it is seen that MGs affect system voltage stability positively by increasing system voltage instability limit value for buses of a power system in which MG are placed.
Abstract: In this paper, the concept of a non-dominated sorting multi-objective particle swarm optimization with local search (NSPSO-LS) is presented for the optimal design of multimachine power system stabilizers (PSSs). The controller design is formulated as an optimization problem in order to shift the system electromechanical modes in a pre-specified region in the s-plan. A composite set of objective functions comprising the damping factor and the damping ratio of the undamped and lightly damped electromechanical modes is considered. The performance of the proposed optimization algorithm is verified for the 3-machine 9-bus system. Simulation results based on eigenvalue analysis and nonlinear time-domain simulation show the potential and superiority of the NSPSO-LS algorithm in tuning PSSs over a wide range of loading conditions and large disturbance compared to the classic PSO technique and genetic algorithms.
Abstract: For the synchronous generator simulation and analysis and for the power system stabilizer design and synthesis a mathematical model of synchronous generator is needed. The model has to accurately describe dynamics of oscillations, while at the same time has to be transparent enough for an analysis and sufficiently simplified for design of control system. To study the oscillations of the synchronous generator against to the rest of the power system, the model of the synchronous machine connected to an infinite bus through a transmission line having resistance and inductance is needed. In this paper, the linearized reduced order dynamic model of the synchronous generator connected to the infinite bus is presented and analysed in details. This model accurately describes dynamics of the synchronous generator only in a small vicinity of an equilibrium state. With the digression from the selected equilibrium point the accuracy of this model is decreasing considerably. In this paper, the equations’ descriptions and the parameters’ determinations for the linearized reduced order mathematical model of the synchronous generator are explained and summarized and represent the useful origin for works in the areas of synchronous generators’ dynamic behaviour analysis and synchronous generator’s control systems design and synthesis. The main contribution of this paper represents the detailed analysis of the accuracy of the linearized reduced order dynamic model in the entire synchronous generator’s operating range. Borders of the areas where the linearized reduced order mathematical model represents accurate description of the synchronous generator’s dynamics are determined with the systemic numerical analysis. The thorough eigenvalue analysis of the linearized models in the entire operating range is performed. In the paper, the parameters of the linearized reduced order dynamic model of the laboratory salient poles synchronous generator were determined and used for the analysis. The theoretical conclusions were confirmed with the agreement of experimental and simulation results.
Abstract: This paper presents small signal stability study carried
over the 140-Bus, 31-Machine, 5-Area MEPE system and validated
on free and open source software: PSAT. Well-established linearalgebra
analysis, eigenvalue analysis, is employed to determine the
small signal dynamic behavior of test system. The aspects of local
and interarea oscillations which may affect the operation and
behavior of power system are analyzed. Eigenvalue analysis is carried
out to investigate the small signal behavior of test system and the
participation factors have been determined to identify the
participation of the states in the variation of different mode shapes.
Also, the variations in oscillatory modes are presented to observe the
damping performance of the test system.
Abstract: This paper presents the details of a numerical study of
buckling and post buckling behaviour of laminated carbon fiber
reinforced plastic (CFRP) thin-walled cylindrical shell under axial
compression using asymmetric meshing technique (AMT) by
ABAQUS. AMT is considered to be a new perturbation method to
introduce disturbance without changing geometry, boundary
conditions or loading conditions. Asymmetric meshing affects both
predicted buckling load and buckling mode shapes. Cylindrical shell
having lay-up orientation [0^o/+45^o/-45^o/0^o] with radius to thickness
ratio (R/t) equal to 265 and length to radius ratio (L/R) equal to 1.5 is
analysed numerically. A series of numerical simulations
(experiments) are carried out with symmetric and asymmetric
meshing to study the effect of asymmetric meshing on predicted
buckling behaviour. Asymmetric meshing technique is employed in
both axial direction and circumferential direction separately using
two different methods, first by changing the shell element size and
varying the total number elements, and second by varying the shell
element size and keeping total number of elements constant. The
results of linear analysis (Eigenvalue analysis) and non-linear
analysis (Riks analysis) using symmetric meshing agree well with
analytical results. The results of numerical analysis are presented in
form of non-dimensional load factor, which is the ratio of buckling
load using asymmetric meshing technique to buckling load using
symmetric meshing technique. Using AMT, load factor has about 2%
variation for linear eigenvalue analysis and about 2% variation for
non-linear Riks analysis. The behaviour of load end-shortening curve
for pre-buckling is same for both symmetric and asymmetric meshing
but for asymmetric meshing curve behaviour in post-buckling
becomes extraordinarily complex. The major conclusions are:
different methods of AMT have small influence on predicted
buckling load and significant influence on load displacement curve
behaviour in post buckling; AMT in axial direction and AMT in
circumferential direction have different influence on buckling load
and load displacement curve in post-buckling.
Abstract: This paper investigates the application of Particle Swarm Optimization (PSO) technique for coordinated design of a Power System Stabilizer (PSS) and a Thyristor Controlled Series Compensator (TCSC)-based controller to enhance the power system stability. The design problem of PSS and TCSC-based controllers is formulated as a time domain based optimization problem. PSO algorithm is employed to search for optimal controller parameters. By minimizing the time-domain based objective function, in which the deviation in the oscillatory rotor speed of the generator is involved; stability performance of the system is improved. To compare the capability of PSS and TCSC-based controller, both are designed independently first and then in a coordinated manner for individual and coordinated application. The proposed controllers are tested on a weakly connected power system. The eigenvalue analysis and non-linear simulation results are presented to show the effectiveness of the coordinated design approach over individual design. The simulation results show that the proposed controllers are effective in damping low frequency oscillations resulting from various small disturbances like change in mechanical power input and reference voltage setting.
Abstract: A numerical method is proposed to calculate damping
properties for sound-proof structures involving elastic body,
viscoelastic body, and porous media. For elastic and viscoelastic body
displacement is modeled using conventional finite elements including
complex modulus of elasticity. Both effective density and bulk
modulus have complex quantities to represent damped sound fields in
the porous media. Particle displacement in the porous media is
discretised using finite element method. Displacement vectors as
common unknown variables are solved under coupled condition
between elastic body, viscoelastic body and porous media. Further,
explicit expressions of modal loss factor for the mixed structures are
derived using asymptotic method. Eigenvalue analysis and frequency
responded were calculated for automotive test panel laminated
viscoelastic and porous structures using this technique, the results
almost agreed with the experimental results.
Abstract: Recently, genetic algorithms (GA) and particle swarm optimization (PSO) technique have attracted considerable attention among various modern heuristic optimization techniques. Since the two approaches are supposed to find a solution to a given objective function but employ different strategies and computational effort, it is appropriate to compare their performance. This paper presents the application and performance comparison of PSO and GA optimization techniques, for Thyristor Controlled Series Compensator (TCSC)-based controller design. The design objective is to enhance the power system stability. The design problem of the FACTS-based controller is formulated as an optimization problem and both the PSO and GA optimization techniques are employed to search for optimal controller parameters. The performance of both optimization techniques in terms of computational time and convergence rate is compared. Further, the optimized controllers are tested on a weakly connected power system subjected to different disturbances, and their performance is compared with the conventional power system stabilizer (CPSS). The eigenvalue analysis and non-linear simulation results are presented and compared to show the effectiveness of both the techniques in designing a TCSC-based controller, to enhance power system stability.
Abstract: In this paper, multiobjective design of multi-machine Power System Stabilizers (PSSs) using Particle Swarm Optimization (PSO) is presented. The stabilizers are tuned to simultaneously shift the lightly damped and undamped electro-mechanical modes of all machines to a prescribed zone in the s-plane. A multiobjective problem is formulated to optimize a composite set of objective functions comprising the damping factor, and the damping ratio of the lightly damped electromechanical modes. The PSSs parameters tuning problem is converted to an optimization problem which is solved by PSO with the eigenvalue-based multiobjective function. The proposed PSO based PSSs is tested on a multimachine power system under different operating conditions and disturbances through eigenvalue analysis and some performance indices to illustrate its robust performance.
Abstract: Among all mechanical joining processes, welding has
been employed for its advantage in design flexibility, cost saving,
reduced overall weight and enhanced structural performance.
However, for structures made of relatively thin components, welding
can introduce significant buckling distortion which causes loss of
dimensional control, structural integrity and increased fabrication
costs. Different parameters can affect buckling behavior of welded
thin structures such as, heat input, welding sequence, dimension of
structure. In this work, a 3-D thermo elastic-viscoplastic finite
element analysis technique is applied to evaluate the effect of shell
dimensions on buckling behavior and entropy generation of welded
thin shells. Also, in the present work, the approximated longitudinal
transient stresses which produced in each time step, is applied to the
3D-eigenvalue analysis to ratify predicted buckling time and
corresponding eigenmode. Besides, the possibility of buckling
prediction by entropy generation at each time is investigated and it is
found that one can predict time of buckling with drawing entropy
generation versus out of plane deformation. The results of finite
element analysis show that the length, span and thickness of welded
thin shells affect the number of local buckling, mode shape of global
buckling and post-buckling behavior of welded thin shells.
Abstract: This paper presents a systematic approach for the
design of power system stabilizer using genetic algorithm and
investigates the robustness of the GA based PSS. The proposed
approach employs GA search for optimal setting of PSS parameters.
The performance of the proposed GPSS under small and large
disturbances, loading conditions and system parameters is tested.
The eigenvalue analysis and nonlinear simulation results show the
effectiveness of the GPSS to damp out the system oscillations. It is
found tat the dynamic performance with the GPSS shows improved
results, over conventionally tuned PSS over a wide range of
operating conditions.
Abstract: This paper presents a novel approach for tuning unified power flow controller (UPFC) based damping controller in order to enhance the damping of power system low frequency oscillations. The design problem of damping controller is formulated as an optimization problem according to the eigenvalue-based objective function which is solved using iteration particle swarm optimization (IPSO). The effectiveness of the proposed controller is demonstrated through eigenvalue analysis and nonlinear time-domain simulation studies under a wide range of loading conditions. The simulation study shows that the designed controller by IPSO performs better than CPSO in finding the solution. Moreover, the system performance analysis under different operating conditions show that the δE based controller is superior to the mB based controller.
Abstract: The main objective of this paper is a comparative
investigate in enhancement of damping power system oscillation via
coordinated design of the power system stabilizer (PSS) and static
synchronous series compensator (SSSC) and static synchronous
compensator (STATCOM). The design problem of FACTS-based
stabilizers is formulated as a GA based optimization problem. In this
paper eigenvalue analysis method is used on small signal stability of
single machine infinite bus (SMIB) system installed with SSSC and
STATCOM. The generator is equipped with a PSS. The proposed
stabilizers are tested on a weakly connected power system with
different disturbances and loading conditions. This aim is to enhance
both rotor angle and power system stability. The eigenvalue analysis
and non-linear simulation results are presented to show the effects of
these FACTS-based stabilizers and reveal that SSSC exhibits the best
effectiveness on damping power system oscillation.
Abstract: Genetic algorithms (GAs) have been widely used for
global optimization problems. The GA performance depends highly
on the choice of the search space for each parameter to be optimized.
Often, this choice is a problem-based experience. The search space
being a set of potential solutions may contain the global optimum
and/or other local optimums. A bad choice of this search space
results in poor solutions. In this paper, our approach consists in
extending the search space boundaries during the GA optimization,
only when it is required. This leads to more diversification of GA
population by new solutions that were not available with fixed search
space boundaries. So, these dynamic search spaces can improve the
GA optimization performances. The proposed approach is applied to
power system stabilizer optimization for multimachine power system
(16-generator and 68-bus). The obtained results are evaluated and
compared with those obtained by ordinary GAs. Eigenvalue analysis
and nonlinear system simulation results show the effectiveness of the
proposed approach to damp out the electromechanical oscillation and
enhance the global system stability.
Abstract: The stability of Newtonian and Non-Newtonian extending films under local or global heating or cooling conditions are considered. The thickness-averaged mass, momentum and energy equations with convective and radiative heat transfer are derived, both for Newtonian and non-Newtonian fluids (Maxwell, PTT and Giesekus models considered). The stability of the system is explored using either eigenvalue analysis or transient simulations. The results showed that the influence of heating and cooling on stability strongly depends on the magnitude of the Peclet number. Examples of stabilization or destabilization of heating or cooling are shown for Pe
Abstract: A numerical study is presented on buckling and post
buckling behaviour of laminated carbon fiber reinforced plastic
(CFRP) thin-walled cylindrical shells under axial compression using
asymmetric meshing technique (AMT). Asymmetric meshing
technique is a perturbation technique to introduce disturbance without
changing geometry, boundary conditions or loading conditions.
Asymmetric meshing affects predicted buckling load, buckling mode
shape and post-buckling behaviour. Linear (eigenvalue) and nonlinear
(Riks) analyses have been performed to study the effect of
asymmetric meshing in the form of a patch on buckling behaviour.
The reduction in the buckling load using Asymmetric meshing
technique was observed to be about 15%. An isolated dimple formed
near the bifurcation point and the size of which increased to reach a
stable state in the post-buckling region. The load-displacement curve
behaviour applying asymmetric meshing is quite similar to the curve
obtained using initial geometric imperfection in the shell model.
Abstract: In this paper, investigation of subsynchronous
resonance (SSR) characteristics of a hybrid series compensated
system and the design of voltage controller for three level 24-pulse
Voltage Source Converter based Static Synchronous Series
Compensator (SSSC) is presented. Hybrid compensation consists of
series fixed capacitor and SSSC which is a active series FACTS
controller. The design of voltage controller for SSSC is based on
damping torque analysis, and Genetic Algorithm (GA) is adopted for
tuning the controller parameters. The SSR Characteristics of SSSC
with constant reactive voltage control modes has been investigated.
The results show that the constant reactive voltage control of SSSC
has the effect of reducing the electrical resonance frequency, which
detunes the SSR.The analysis of SSR with SSSC is carried out based
on frequency domain method, eigenvalue analysis and transient
simulation. While the eigenvalue and damping torque analysis are
based on D-Q model of SSSC, the transient simulation considers both
D-Q and detailed three phase nonlinear system model using
switching functions.