Local Oscillation Modes Research Articles

Development of a new adaptive PSS system for automatic parametric modeling techniques for power system oscillation waveforms

AbstractIn Japan, since the development of large power systems, there have been spontaneous low‐frequency oscillation and local mode oscillation. The conventional PSS has been applied to generators in a trunk power system as a measure to improve the damping power oscillation. However, it is difficult for this PSS to improve the damping power system oscillation because of the hardware and the design of fixed PSS control constants. It has therefore become necessary to develop a new adaptive PSS system. This paper explains the development of a new adaptive PSS system and the simulation of low‐frequency and local mode oscillation for this new PSS system. © 2002 Scripta Technica, Electr Eng Jpn, 139(1): 24–34, 2002; DOI 10.1002/eej.1143

Femtosecond dynamics of self-trapped excitons in quasi-one-dimensional halogen-bridged Pt complexes

Dynamics of the self-trapped excitons (STE) in quasi-one-dimensional halogen-bridged mixed-valence platinum complexes [Pt(en) 2][Pt(en) 2X 2](ClO 4) 4 (en=ethylenediamine, X=Cl or Br) has been studied by luminescence up-conversion technique. Time evolution of the luminescence from STE has been studied from 0.79 to 2.1 eV in the X=Cl system with a time resolution of 180 fs. The cooling time of hot STEs was determined as 210 fs, and the formation time of STE was found to be shorter than 140 fs, which is limited by our time resolution. In the X=Br system, we achieved a time resolution of 90 fs and succeeded in observing the wave packet oscillation in the adiabatic potential well of STE by luminescence for the first time. The period of the local mode oscillation is 290 fs (97 cm −1) and the damping time constant is 430 fs. Usefulness of the up-conversion spectroscopy for wave packet observation is demonstrated.

Design of non-negatively interactive FACTS-based stabilizers in multi-machine power systems

In this paper, a method is proposed for the design of a non-negatively interactive FACTS-based stabilizer in a multi-machine power system. It is demonstrated in the paper that the FACTS-based stabilizer can be designed to impose positive interactions upon other stabilizers in the power system through the correct selection of non-negatively interactive installing locations and feedback signals of the FACTS-based stabilizer and the proper setting of the phase angle of the FACTS-based stabilizer. An example power system is presented in the paper, where a TCSC-based stabilizer is designed, which is not only able to damp the target inter-area oscillation mode effectively but also imposes a positive interaction with a PSS in the power system to damp a local oscillation mode.

Simultaneous stabilization of multimachine power systems via genetic algorithms

This paper demonstrates the use of genetic algorithms for the simultaneous stabilization of multimachine power systems over a wide range of operating conditions via single-setting power system stabilizers. The power system operating at various conditions is treated as a finite set of plants. The problem of selecting the parameters of power system stabilizers which simultaneously stabilize this set of plants is converted to a simple optimization problem which is solved by a genetic algorithm with an eigenvalue-based objective function. Two objective functions are presented, allowing the selection of the stabilizer parameters to shift some of the closed-loop eigenvalues to the left-hand side of a vertical line in the complex s-plane, or to a wedge-shape sector in the complex s-plane. The effectiveness of the suggested technique in damping local and inter-area modes of oscillations in multimachine power systems is verified through eigenvalue analysis and simulation results.

Application of neural adaptive power system stabilizer in a multi-machine power system

Application of a neural adaptive power system stabilizer (NAPSS) to a five-machine power system is described in this paper. The proposed NAPSS comprises two subnetworks. The adaptive neuro-identifier (ANI) to dynamically identify the nonlinear plant, and the adaptive neuro-controller (ANC) to damp output oscillations. The backpropagation training method is used online to train these subnetworks. The effectiveness of the proposed NAPSS in damping both local and inter-area modes of oscillations and its self-coordination ability are demonstrated.

An approach to the damping of local modes of oscillations resulting from large hydraulic transients

A new method of damping of local modes of oscillations under large disturbance is presented in this paper. The digital governor controller is used. The controller operates in real time to improve the generating unit transients through the guide vane position and the runner blade position. The developed digital governor controller, whose control signals are adjusted using the on-line measurements, offers better damping effects for the generator oscillations under large disturbances than the conventional controller. Digital simulations of a hydroelectric power plant equipped with a low-head Kaplan turbine are performed and the comparisons between the digital governor control and the conventional governor control are presented. Simulation results show that the new controller offers better performances, than the conventional controller, when the system is subjected to large disturbances.

A hybrid neuro-fuzzy power system stabilizer for multimachine power systems

A fuzzy basis function network (FBFN) based power system stabilizer (PSS) is presented in this paper to improve power system dynamic stability. The proposed FBFN based PSS provides a natural framework for combining numerical and linguistic information in a uniform fashion. The proposed FBFN is trained over a wide range of operating conditions in order to re-tune the PSS parameters in real-time based on machine loading conditions. The orthogonal least squares (OLS) learning algorithm is developed for designing an adequate and parsimonious FBFN model. Time domain simulations of a single machine infinite bus system and a multimachine power system subject to major disturbances are investigated. The performance of the proposed FBFN PSS is compared with that of conventional (CPSS). The results show the capability of the proposed FBFN PSS to enhance the system damping of local modes of oscillations over a wide range of operating conditions. The decentralized nature of the proposed FBFN PSS makes it easy to install and tune.

Improving the robustness of H/sub ∞/-PSSs using the polynomial approach

This paper proposes a new design procedure of H/sub /spl infin//-PSS (H/sub /spl infin//-optimal PSS) by incorporating high-frequency roll-off into the design using improper weighting function. This design is based on the polynomial approach where the 'numerator-denominator' uncertainty representation is used for practical uncertainty representations. Furthermore, to improve the dynamic and transient stabilities of the control system, the partial pole placement technique is employed to reassign dominant poles at suitable locations in the left-half s-plane. The effectiveness of using /spl Delta//spl omega/ (shaft speed) input and /spl Delta/P/sub e/ (electrical power) input H/sub /spl infin//-PSSs to damp local oscillation modes is also investigated by comparing the performances of these H/sub /spl infin//-PSSs. Simulation results show that the proposed approach is effective in improving the performance and robustness of the system.

Transmission capacity of longitudinal power systems and SVC voltage control

Power transfer between systems is important due to uneven distribution of generating plants. This paper investigates the relation between the transfer capacity of a longitudinal power system and voltage control of static var compensators. The transfer capacity is basically limited by the thermal capacity of transmission lines. However, the practical systems, it is much restricted by stability and the power transfer level is considerably lower than the thermal capacity. In this paper, we consider a basic case in which SVCs are applied to all buses except generator terminals. In this case, it is possible to transfer power up to the reciprocal of the transmission reactance. Two modifications are then applied to the basic case. One is removal of SVCs on the high-voltage sides of the generator transformers. In this case, generator damping torques deteriorate, and the local oscillation mode becomes unstable. The other is removal of SVCs at intermediate buses on the trunk system. In this case, the shapes of the oscillation modes change greatly, and the global mode becomes unstable. The voltage control of SVCs maintains the generator damping torques and prevents deformation of mode shapes. By investigating different system sizes and transmission circuits, we show that the system transfer capacity is determined by the capacities of the individual transmission lines. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(3): 49–60, 1997

Development of a new two‐input PSS to control low‐frequency oscillation in interconnecting power systems and the study of a low‐frequency oscillation model

AbstractIn Japan, large and small power systems were interconnected over time and thus ultimately grew into a large‐scale national power system. A highly important stability problem arising from large‐scale power system interconnections is low‐frequency oscillation (about 0.3 Hz to 0.5 Hz) of interconnected systems. The ΔP‐type PSS has been applied to all generators in trunk power systems as a measure to improve the damping of local mode oscillation (about 1 Hz). However, it is difficult for this PSS to improve the damping of low‐frequency oscillation because of the hardware and the design of PSS control constants. Therefore it has become necessary to develop a new two‐input PSS.This paper explains the development of this two‐input PSS and the study of a low‐frequency oscillation model. This paper can be summarized as follows: (1) The effect of control over low‐frequency oscillation is affected by the kinds of PSS detecting signals. The Δω‐type or Δf‐type detecting signals used for lead‐phase compensation are suitable for this purpose. (2) It is possible to cause low‐frequency oscillation studies in a one‐machine infinite‐bus power system model with medium loads. (3) According to the simulation of a three‐machine and actual large‐power system models, dynamic stability was largely increased by this two‐input PSS used for generators.

Artificial neural network power system stabilizers in multi-machine power system environment

The effectiveness of an artificial neural network (ANN), functioning as a power system stabilizer (PSS), in damping multi-mode oscillations in a five-machine power system environment is investigated in this paper. Accelerating power of the generating unit is used as the input to the ANN PSS. The proposed ANN PSS using a multilayer neural network with error-backpropagation training method was trained over the full working range of the generating unit with a large variety of disturbances. The ANN was trained to memorize the reverse input/output mapping of the synchronous machine. Results show that the proposed ANN PSS can provide good damping for both local and inter-area modes of oscillations. >

Damping of inter-area and local modes by use of controllable components

This paper deals with damping of inter-area and local electromechanical oscillation modes using controllable series capacitor (CSC) and controllable shunt capacitor (SVC). The impacts of SVC and CSC on the structure of the system closed loop matrix are investigated. By analyzing the sensitivities of the system inter-area and local modes to the control action of the controllable devices, some general conclusions concerning the damping of inter-area and local modes are made. A numerical example is provided to support the analytical findings. This paper provides an insight and understanding in the basic characteristics of damping effects of the studied devices. The insight is obtained by the study of a simple power system which exhibits both inter-area and local power swings. The understandings and findings could form the basis in analysis of realistic and more complex systems. >

Synchronizing and damping torque coefficients and power system steady-state stability as affected by static VAr compensators

The utilization of static VAr compensators (SVC) for supplying reactive power at certain points of an electric power system is an efficient way for fast control of transient and steady-state voltage changes following short-circuits, load rejection, opening of severely loaded transmission circuits, etc. Other SVC applications include the increase of power transmission capacity through interconnections between areas of a power system and the damping enhancement of local or inter-area electromechanical oscillation modes. This paper fundamentally deals with these last two issues by analyzing the results of synchronizing and damping torque coefficient calculations for a generation station connected radially to a much larger power system. The results presented pertain to a double-circuit, 800 km, 500 kV transmission system during a one-circuit out contingency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparison of power system stabilizers for damping local mode oscillations

The Bureau of Reclamation has examined the damping of local mode oscillations using three types of power system stabilizers (PSS): internal frequency; electrical power; and accelerating power. Comparisons of operating characteristics such as PSS output noise and sensitivity to load changes are also included. Results are based on the analysis of field test data and analog computer simulation, Methods that can be used at remote sites during PSS alignment tests have been employed. >

New polarisation-insensitive detection technique for coherent optical fibre heterodyne communications

A new technique for overcoming polarisation-induced fading in coherent optical fibre communications is described. The technique generates two IFs, which fade in antiphase, by mixing the signal light with orthogonally polarised local oscillator modes which have been separated in the frequency domain.

A Systematic Design of Excitation and Governor Control of Multi-Machine Power System

A systematic computer-aided procedure for the design of the power system excitation and governor controller, considering the parameter uncertainties, rapid and large load variations the network contingencies and the nonlinearities of the synchronous machine model is presented The design procedure consists in using three layer controllers with the first layer controller guaranteeing the maintenance of the nominal voltage, the nominal frequency and the scheduled powers even in the face of the disturbances, the second layer controller ensuring the desirable damping of the local and inter-tie mode oscillations and the third layer controller improving further the dynamic performance. The controller structure consists in the inclusion of an error driven filter to reject the said disturbances followed by the regulation of the augmented system consisting of the process and the filter using stabilizing compensators. The theoritical justification of the proposed multi-layer control strategy is given using input-output stability and Lyapunov reasoning.

Dynamic mechanical and dielectric relaxations of polystyrene below the glass temperature

AbstractDynamic mechanical and dielectric properties of various kinds of polystyrene, including bulk‐polymerized, monodisperse, isotactic, and thermally degraded samples, have been measured below the glass temperature to 4°K. Five relaxation processes are found, designated β, γ, γ′, δ, and ε in order of descending temperature. The β peak (350°K at 10 kHz) is attributed to the local oscillation mode of backbone chains and the γ′ peak (180°K at 10 kHz) to rotation of phenyl groups. The δ peak (100°K at 10 kHz) is observed only in dielectric properties of the bulk‐polymerized sample and is assigned to weak polar bonds, such as oxygen bonds in the chain. The δ peak (55°K at 10 kHz) which is prominent in dynamic mechanical properties is interpreted in terms of lattice defects due to a syndiotactic diad inserted between isotactic sequences in a chain or vice versa. The ε peak (ca. 25°K at 10 kHz) is first reported in the present work, but the mechanism involved is not yet clear.

The Dielectric Property of Polystyrene and Some Ring-substituted Polystyrenes in Glassy State

Measurements of dielectric properties of polystyrene and some substituted polystyrenes containing different substituents (methyl group and halogen atoms) in the phenyl ring are carried out over a temperature range from 93 to 343°K in vacuo (10-3 mmHg) at 1 and 10 kHz. The temperature dependence of dielectric loss ε'' is mardedly different according to the location of the substituent in the ring. The dielectric behavior of these polymers at temperatures around 150°K at 10 kHz is explained in terms of two modes of phenyl group motions: the hindered rotation of phenyl group around the bond to the main chain and the oscillation or wagging of phenyl rings. The relaxation observed as a shoulder at the foot of the α-loss peak in the ε''-temperature curve is attributed to the local-mode oscillation of the main chain.

Electronic Structure of theUCenter. II. Force-Constant Changes and Local Modes

The force constants and local-mode frequencies of the $U$ center in KCl, KBr, and KI have been obtained from a detailed quantum-mechanical calculation. The model which has been used corresponds to the static-well approximation. It takes into account both the electronic structure of the first-nearest-neighbor ions and the polarization of the ${\mathrm{H}}^{\ensuremath{-}}$ ion during the local-mode oscillations. The agreement of the calculated local-mode frequencies with the experimental values is greatly enhanced when the polarization of the ${\mathrm{H}}^{\ensuremath{-}}$ ion is included.

Microwave Background in a Steady-state Universe

IT has been widely claimed that the background microwave radiation observed by Penzias and Wilson1 and Roll and Wilkinson2 must originate from a radiation dominant, early phase of the Universe. Hoyle and Wickramasinghe3 have, however, discussed the possibility of a more local origin for this radiation. They point out that the energy density arising from the conversion of hydrogen to helium in all galaxies is about 10−13 erg/cm3, close to the energy density of the 3° K blackbody field. If an appreciable fraction of this energy could be thermalized by dust grains the observed “black body” microwave spectrum might be explained. The requirement is that quantum oscillators covering much of the frequency range 0.01 cm−1 to 10 cm−1 are present in the grains. While arguments may be given for the presence of localized oscillation modes within this frequency range, the strongest evidence at the present time would seem to be for the existence of oscillators close to about 10 cm−1 (Sievers4, Sievers and Takeno5). Such frequencies may be appropriate for the oscillation of weakly bound substitutional impurities in crystals. In a typical case the oscillator strength could be about 0.1 and the line width about 1/10 of the central frequency4. We shall consider here the effect of a few strong emission bands at about 1 to 10 cm−1 which may be present in grains. From a total of about 1055 grains in the Galaxy each containing approximately 105 impurity oscillators we could obtain an infra-red emission at about 10 cm−1 equal to approximately 1/3 of the entire luminosity of the Galaxy. This flux of Galactic radiation at ν ∼ 10 cm−1 (1 mm wavelength) could produce the observed excitation of the J = 1 rotational levels of cyanogen (CN) (Field and Hitchcock6), but it would not account for the microwave observations1,2.