Switching Criteria Research Articles

An adaptive fuzzy logic power system stabilizer

The paper presents an adaptive fuzzy logic power system stabilizer (PSS) design for damping oscillatory electromechanical modes of oscillations and enhancing the first-swing synchronous stability margins. The novel design utilizes a multivariable damping signal vector consisting of machine speed deviation, rate of speed deviation, and voltage deviation. The design is based on a multizonal PID structure and fuzzy logic variable-gain scheduling to optimize the damping action. The fuzzy logic PSS is proposed for use in parallel with the conventional analog type PSS with added simple switching criteria. The two PSS blocks can be allowed independent, sequential, and/or combined operation with different effective stabilizing weighting. The paper investigates an individual conventional PSS, a rule based fuzzy PSS, and hybrid operation. The parallel operation of a conventional PSS and a fuzzy logic one provides optimal sharing of the damping action under small- as well as large-scale generation-load mismatch or variations in external network topology due to fault or switching conditions.

Optimisation of switching levels for adaptive modulationin slow Rayleigh fading

Multi-dimensional minimisation techniques are used to optimise, for specific applications, the upper bound bit error rate (BER) and bits per symbol (BPS) performances of adaptive modulation schemes over Rayleigh channels. This is achieved by modifying the switching criteria for selecting the appropriate modulation scheme.

PYSHA: a shadow-testing acceleration scheme for ray tracing

The paper presents a new data structure called a shadow pyramid for storing 3D objects to reduce the shadow-testing time during ray tracing. For each primitive object that first intersects a ray, a shadow pyramid is constructed in which all the candidate objects that possibly block the path from the relevant light source to any point on the primitive object are registered. Shadow testing of the intersection point, i.e. of whether the intersection point is shadowed or not, is then performed only against the objects registered in the shadow pyramid formed with the polygon in which the intersection point lies as the base. The registered objects are sorted in the order of so-called shadow form factors to reduce the number of ray-object intersections. The span coherency and the so-called D-list are used in the successive shadow testing of neighboring rays to further reduce the shadow-testing time. An efficient shadow-testing scheme called pysha is then proposed. pysha is a hybrid shadow-testing procedure in which the shadow testing on the surface of each primitive object (polygon and sphere) is determined between the conventional cell-traversal scheme and the proposed shadow-pyramid scheme for each light source according to a switching criterion. From the cost comparison of the two shadow schemes, two parameters N sp max , the maximum number of registered objects within a shadow pyramid, and A s min , the minimum screen-projected area of an object, are derived and used as switching criteria. Owing to the fast access to the candidate objects for intersection and the reduced number of intersection calculations, pysha is significantly faster than the conventional cell-traversal scheme or the shadow-pyramid scheme alone for the experimental scenes used in this work.

Adaptive Implicit Criteria for Two-Phase Flow with Gravity and Capillary Pressure

Based on monotonicity conditions, the switching criteria for an adaptive implicit discretization for two-phase flow in a porous medium with gravity and capillary pressure are derived. These criteria can be applied to ultidimensional flows, provided an easily checked condition is satisfied. Use of the monotonicity conditions is demonstrated for some example problems in one and two dimensions.

Automated Repair Service Bureau: The Context-Sensitive Switch of the Loop Maintenance Operations System

In a distributed system where the data base is partitioned, e.g., on a geographical basis, incoming transactions must be routed to the correct computer based on information in the data. In some instances, this is performed manually by the attendant entering the data, but as the switching criteria becomes more complex and the transaction load increases, a mechanized system which could examine the data and route automatically would decrease the time required for an attendant to handle an individual input and, thereby, increase the productivity of the attendant. This paper describes the design and implementation of a “context-sensitive” switch that is used to route transactions in the Loop Maintenance Operations System.

The renovation and automation of a tandem cold rolling mill

The goals and scope of a renovation and automation project for a tandem cold rolling mill are discussed with the emphasis on the computer control system. More stringent requirements for the finished product and the necessary centralization of the operator's functions lead to the design of special control algorithms to cope with the particular characteristic of the mill. These algorithms, which include features as bang-bang control, self-adaptive filtering, optimal switching criteria and several adaptation techniques, are based on detailed analysis of measuring data from the mill. Several control algorithms are described in detail. Also the experience of two years of operation of the renovated mill is discussed; in particular the experiences with the new control system are given.

The Elimination of the Constraint Equation And Modelling of Problems With a Non-condensable Gas In Steam Simulation

Abstract The numerical formulation previously used in CMG's (Computer Modelling Group) steam simulator used an equation set consisting of flow equations and a constraint equation. The effect of analytically eliminating this constraint equation from the basic equation set, thereby reducing the number of primary variables by one, is investigated. It is found that an alternating use of the two equation sets according to certain switching criteria yields the best results. A problem of convergence to non-physical answers, which arises in the simulation of steam displacement with a non-condensable gas, is described, and a method for circumventing this problem is proposed. The results of various test runs are included. INTRODUCTION The equations used to describe the steam or in-situ combustion processes can be divided into two groups. The "flow" equations (energy and mass balance) contain inter-block flow terms; the "constraint" equations (saturations and mole fraction constraint) depend only on variables in a single block(1). It is possible to eliminate the constraint equations analytically from the equation set, and thereby reduce the number of equations per grid block. However, previous in-situ combustion and steam simulators have retained the constraint equations in the basic equation set(2–4). These authors have reported that the addition of constraint equations to the basic equation set results in better stability and convergence rate, and permits larger time steps. As the amount of computation per time step is increased for a larger equation set, it is not clear that the addition of constraint equations will result in a net saving in computing cost. This 4-equation formalism has been discussed because it is a natural subset of CMG"s in-situ combustion model ISCOM(5), which is a fully implicit simulator. When ISCOM is run on combustion problems, the constraint equations are eliminated analytically. No difficulties have been observed with this procedure(5–6). Consequently, it was decided to investigate the effect of eliminating the constraint equation (1) from the steam model. Description of the Model If equation (1) is eliminated from the set (1–4), there are only three "basic" equations left, which express the conservation of oil, water and energy. In order to reduce the equation set, it is necessary to perform variable substitution on the appearance or disappearance of steam, while the equation set remains the same. This is in constrast to the previous method(5), where the independent variables remain the same, but the equation set is switched. For the situation in which there is no steam in a given grid block, the primary variables associated with each equation are: (Equation in full paper) The disappearance of the water phase is avoided using the pseudo k value method(4). The only other fully implicit steam simulator reported in the literature is that developed by Coats(l) as a subset of an in-situ combustion simulator.

The Renovation and Automation of a Tandem Cold Rolling Mill

The goals and scope of a renovation and automation project for a tandem cold rolling mill are discussed with the emphasis on the computer control system. More stringent requirements for the finished product and the necessary centralization of the operator's functions lead to the design of special control algorithms to cope with the particular characteristic of the mill.These algorithms, which include features as: bang-bang control, self-adaptive filtering, optimal switching criteria and several adaptation techniques, are based on detailed analysis of measuring data from the mill. Several control algorithms are described in detail. Also the experience of two year of operation of the renovated mill is discussed, in particular the experiences with the new control system are given.

Optimal switching criteria for two-position configuration controls

Optimal switching criteria for two-position configuration controls

電気油圧サーボ系のシミュレーションと最適化

In this paper we discuss the time optimal control problem of an electrohydraulic servo system. This system is described by the 16th order nonlinear ordinary differential equations with multi-discontinuities. The control variables are inputs to the two servovalves with different nonlinear flow gains and dynamics. The performance index to be minimized is made up of integrated square errors of allowable system pressures, load displacement and velocity around the origin, and response time.This problem is solved by applying a hillclimbing algorithm to the 4th order Runge-Kutta method simulation of the state equations. As the pattern of this control is bang-bang, it is important to find the switching criteria as well as stability conditions. In this numericall experiment, a square root function is taken as closing control to a valve, and the amplitude of a feedback variable is limited to ensure reasonable stability.In spite of the several assumptions made throughout with the system, such that the valve dynamics is simple and the liquid flow is steady, the computational results have shown fairly good coincidence with the experimental results.

Application Guide for Shunt Capacitors on Industrial Distribution Systems at Medium Voltage Levels

Increased emphasis on energy conservation and reduction of purchased electric power bills have resulted in an increased awareness of the importance of capacitors on industrial systems. Larger banks of capacitors are being considered for installation and many questions relating to the application must be answered. Most of the commonly encountered factors relating to equipment selection, location on the system, protection, and switching criteria are reviewed. Motor terminal capacitor applications are also discussed. Economic justification for the purchase of the capacitors and harmonic resonance, as it relates to capacitor selection and application, are not included.

Liapunov switching criteria for an nth order differential equation

Liapunov switching criteria for an nth order differential equation

Dynamic Synthesis of Higher-Order, Optimum Saturating Systems

A new technique for the synthesis of optimum switching criteria for higher-order saturating systems is investigated in this paper. Basically, the technique consists of generating a linear switching criterion that is equivalent to the optimum switching criterion for each state of the system. Thus as a trajectory of the system is traced out, the optimum forcing function is determined point by point, resulting in the optimum trajectory for the system. The synthesis procedure has been proved experimentally by simulation of a third-order system on an IBM 797 digital computer.

Optimum switching criteria for higher order contactor servo with interrupted circuits

IN A contactor servo, the controlling elements determine only the instants of time at which the contactor operates. In between these moments the controlled system is left alone to follow its own equations of motion and is not in any way affected by the error and the time derivatives of the error. This is also true for continuous control systems with saturable elements in response to a large reference input. For optimum operation of a second-order system of this nature, Hopkin1 and McDonald2 showed that the switching criterion can be expressed as a nonlinear relationship between the error and its first time derivative. Their analyses were in terms of the phaseplane technique and the optimum switching boundary was shown to be a trajectory on the phase plane. Bogner and Kazda3 generalized the phase-plane criteria for second-order contactor servos1,2 to a phase-space criteria for higher order contactor servos. An implicit but basic assumption of their analysis is that in an n-order contactor servo the error and its derivatives up to the n-1 order are continuous at the moment of switching. What does this assumption imply physically?

An investigation of the switching criteria for higher order contactor servomechanisms

The use of a linear anticipatory switching network in an on-off servomechanism, while improving system stability, does not result in optimum response. Mathematical analysis of second order systems indicates that the network should be a nonlinear function of error and error rate. This paper describes a method for deriving the switching criterion for a ?piecewise? linear on-off servo of order greater than two, when the input variable is limited to a step function of position and velocity. The switching criterion results in system error and in derivatives of error reducing to zero in a minimum time. System behavior is described in the principal co-ordinate phase space. Starting at a point in the phase space corresponding to the initial conditions, the representative point moves in a series of discontinuous trajectories determined by the sign of the controlled variable, eventually reaching the origin. The sequence of sign reversals represents the desired switching criterion.

The transient response of transistor switching circuits

A model is presented for the interpretation of point-contact transistor switching phenomena. The assumption is made that the frequency cut-off is high when the transistor is not saturated and low when saturated. The low-frequency response in saturation can explain qualitatively the anomalous pulse requirements for switching transistors from saturation to cutoff. Some switching criteria are derived and the one-shot multivibrator is discussed.