Transient Performance Of System Research Articles

Study on the exponential path tracking control of robot manipulators via direct adaptive methods

Exponential path tracking control represents an important issue pertaining to the transient performance of robot control systems. In this paper, the so-called Exp-transformation is applied to obtain transformed robot dynamics models which are used to derive several adaptive control algorithms that achieve exponential path tracking. In contrast to the existing composite adaptive control method; where both the tracking error and the prediction error are used and persistent excitation (p.e.) is required, the proposed strategy requires only the tracking error. This makes the control structure simpler and easier to implement. The main contribution of this paper is the development of practical control strategies for which the p.e. requirement is completely removed (as opposed to relaxing it to semi-p.e. as was done in a recent work). The fundamental idea introduced for exponential stability analysis is conceptually simple and global results are obtained.

Detailed modeling of an actual static VAr compensator for electromagnetic transient studies

The authors present a detailed model of a static VAr compensator (SVC) for digital simulation of electromagnetic transients. It is also demonstrated that this model can adequately reproduce SVC transient behavior as verified in transient network analyzer studies carried out with a replica of the SVC control system. The SVC control system is described, with emphasis on some special blocking schemes needed to meet particular requirements of the power system transient performance. The complete system and SVC data are also included. >

Extension of linear quadratic optimal control theory for mixed backgrounds

The problem of finding an optimal controller, while both deterministic and stochastic signals are present in the feedback system, is addressed. A general framework is developed to solve the above problem and to unify conventional frequency domain LQ and LQG optimal control theories. Both the system transient and steady-state behaviours are considered and the exact tracking of the arbitrary reference signal is guaranteed. The decomposition of a mixed signal into the deterministic and stochastic parts gives a chance to investigate the effect of the weighting factors, which were specified in the cost function, on the compromise between transient and steady-state system performance. The solution, which characterizes the structure of the optimal controller, results in a set of independent diophantine equations, instead of a set of coupled ones. Moreover, the number of equations can be reduced under weak conditions. Finally, both transient command tracking and steady-state noise rejection capabilities can be optimized simultaneously by using a two-parameter control scheme.

Design and performance of solar MSF desalination systems

Solar desalination systems using flat plate or concentrating collectors are still in the development stage. Two main stages in the advancement of any solar desalination systems, namely design and performance are analyzed in the present work. In the design stage, the solar system together with the MSF chamber parameters are selected and analyzed to attain at the proper system configurations and operating conditions. Solar systems including flat plate and concentrating collectors with different collector fluids are investigated. The solar data are calculated for clear sky and corrected according to measurements. As a result the interaction of the design configurations and the thermal operating conditions are analyzed. A stage - to- stage design of the MSF chamber and the system transient performance are carried out. According to the selected solar system and MSF parameters, the transient performance analysis is obtained by modelling the system thermal performance through a small interval of time. As a result, transient system useful heat gain,distillate productivity, temperature, and other pertaining paraemeters are obtained. Some comparative results are included from measurements obtained from solar desalination plants operated in U.A.E.

An electromagnetic model for transients in grounding systems

The development and application of a computer model for analyzing the transient performance of grounding systems based on electromagnetic field theory is described. The use of a combination of numerical integration techniques, method of moments, adaptive interpolation, and fast Fourier transform constitutes the basis for the computation of various physical quantities such as the electric fields in the ground, longitudinal and leakage currents in the ground conductors, and ground impedances. It is shown that the analysis of conductors energized by current waves can require computations at frequencies higher than the significant frequencies in the spectrum of the excitation signal, while simpler models may fail to predict accurately the transient performance. The main limitation of the computer model is the time required for the analysis of large or complex grounding systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transient stability hierarchical control in multimachine power systems

The authors present the optimal transient stability control problem in a hierarchical structure for multimachine power systems. The two-level structure retains the local closed-loop controls, thereby easing its implementation on existing systems. The formulation accounts for nonlinearities and interconnections, and the optimization of the system transient performance is obtained with less computational effort. Since the computations are distributed among the many local feedback subsystems, the storage and solution times are considerably less than those required by a single overall centralized controller. This advantage becomes much stronger as the system size increases. For illustration purposes, this technique was applied successfully to a four-machine system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nonlinear Robot ARM Control Through Third Order Motor Model

Design of robot controllers are typically based on the second order model of rigid robot arms. However, the robot joint motor dynamics constitutes an important part of the overall robot dynamics, and should be included in robot controller design. A third order robot dynamic model is obtained in this paper which includes the robot arm dynamics as well as the actuator dynamics. Differential geometric control theory is used to linearize and decouple the resultant nonlinear and coupled dynamic system, yielding linear subsystems for each degree of freedom in the robot task space. Linear system control theory and optimal control theory are then used to obtain desired system performance. Extensive computer simulations are carried out using the joint actuators. They demonstrate that the controller designed in this paper produces excellent steady state as well as transient system performance, and it is robust in the presence of robot model parameter inaccuracy. The importance of robot motor dynamics is further illustrated by computer simulations, where a controller based on the second order robot arm dynamical model is adopted to control the third order robot dynamics and produces unacceptable transient state response.

Optimal Decentralized Load Frequency Control

The paper presents a novel methodology for feasibility analysis and design of optimal decentralized load frequency control for multi-area interconnected electric power systems. Feasibility of the proposed decentralized control scheme is determined with a fixed mode evaluation algorithm based on eigenvalue dynamics. The eigenvalue sensitivity expressions are also used to determine decentralized feedback gains that will result in system transient performance similar to the one obtained with a centralized optimal control law. The methodology is illustrated with a two-area power system example.

Validation of a compressor model

A mathematical model capable of simulating transient performance of fan and compression systems is described. The model is based on the dynamic forms of the conservation equations and incorporates a polytropic analysis. The steps taken to validate the model and several applications of the model are described.

Evaluating The Probabilitv Indices Of Transient Stabilitv For The Hellenic Transmission Svstem

During the last decade, there has been a considerable activity in the development of probabilistic model1ing and eva1uating techniques for power system re1iabi1ity eva1uation.During the same period, a continuous deve10pment of better techniques for assessing transient stabi1ity in power systems has been reported but the bulk of this work is based on deterministic mode1s. Very litt1e has been pub1ished on the probabi1istic nature of the basic functions which affect the transient stabi1ity performance of power systems. Scope ofthis paper is to describe the developed computational methods for eva1uating the probabi1ity indices of transient stabi1ity for the Hel1enic Transmission Power System.

Transient performance of a thermosyphon water heating system with n-units connected in series

Transient performance of a thermosyphon water heating system with n-units connected in series

Application of Static Var Compensators in Longitudinal Power Systems

The application of a Static Var Compensator (SVC) in a longitudinal power system is presented and the technical studies performed to evaluate its effect on system operation are described. Steady state analysis is based on the combination of SVC and system characteristics. Using this approach changes in loading conditions and SVC adjustable parameters can be easily analysed. Results of simulations are presented that show the effect of SVC reactive power support on the system transient performance. Cases with supplementary controls to protect the system against SVC loss are also included.

Transient performance of inverter systems

This report describes an investigation into the feasibility of using computer-modelling techniques for evaluating the transient performance of inverters. A computer-analysis package has been developed which can be used to model and investigate various aspects of the design and performance of power-electronic equipment. The feasibility of using this computer package for evaluating the transient performance of inverters has been demonstrated using a commercial static frequency changer (SFC). It is concluded that the results of this study have confirmed the validity and accuracy of the computer-modelling techniques used, and that these techniques can now be used to predict the performance of future inverter designs.

A stability measure for use in power system transient stability studies

Large system transient stability calculations may be carried out using network equivalents, and generator grouping, and by reducing the order and complexity of the system representation. Engineering judgement and, in most cases, prior knowledge of transient system performance is required to implement the models. In this paper a new parameter called ‘stability measure’ is introduced. The stability measure can easily be calculated on the basis of load flow and short-circuit results. Upon calculation of the stability measure set for a given fault condition, an estimate of the likely response of the respective generators to the fault is obtained. The validity and generality of the stability measure has been demonstrated by simulated tests on a sample power system. Application of the method with respect to grouping of generators in transient stability studies is also discussed.

Optimal Non-Linear Control of a Power System

A new approach to optimization of a closed loop excitation controller in a non-linear power system is presented. The controller is nonlinear, responding selectively to higher order deviations in the chosen state variables of the power system. Calculation of the respective feedback gains is described in the paper, which also gives examples illustrating system transient performance with this type of controller. The gains are not affected by fault type, but depend to some extent on system operating condition.The proposed method readily accomodates sub-optimal controller design, which involves fewer signals. An example of a simplified or sub-optimal controller is given, along with results showing system transient response patterns when the sub-optimal controller is utilized.

A computer modeling approach for LSI digital structures

The paper presents a novel modeling approach to LSI MOST circuits performed at the gate level. A macromodel is analytically derived and provides a direct relationship between the input function and output response of the gate. This approach or macromodeling has been implemented for over 10 000 devices in LSI with only 32K of computer core and very fast computing time. The method employed relates directly the performance parameters (e.g., turn-on voltage, rise, and fall times, etc.) to the device parameters. An insight into the propagation delay of LSI structures is gained by statistically studying the transient performance of the system using Monte-Carlo techniques. Experimental results give ample evidence of good agreement with the computed results, for which various values of x 0 , oxide thickness, are used.

The Transient Response of Orifices and Very Short Lines

It is generally assumed that orifices and valves follow closely their steady-state characteristics during transient operation. However, this assumption of quasisteady behavior may lead to errors in predicting transient flow conditions under certain circumstances. In order to evaluate the transient behavior of an orifice, a differential equation relating the flow through and the pressure drop across an orifice was derived. An extension was made to include an axial dimension for the orifice. The solution of this equation for transient flow through an orifice subjected to a step change in pressure drop across the orifice is significantly different than that obtained using the steady state relationship. An experiment was designed to evaluate the theoretical results in which an orifice on the end of a line was subjected to a sudden pressure change and the resulting transient pressures were observed. It was found that a significant short term transient occurs before the orifice flow reaches the new steady state condition. The observed short term transient agrees well with that predicted by the theory. It is concluded that the behavior of an orifice can deviate considerably from that predicted by steady-state equations during periods of rapid pressure or flow changes. The dynamic description of orifice flow may be combined with a larger system analysis (e.g., using the method of characteristics) to more accurately predict the overall transient performance of flow systems.

Transient stability of power systems containing both synchronous and induction machines

A method is described of calculating the effect of large induction motors on the transient performance of a multimachine power system under fault conditions. The representation of an induction motor is similar to that used for synchronous machines, and is therefore suitable for describing composite systems. The method is based on Park's equations and, unlike earlier methods, allows for the ‘deep-bar effect’ usually present in large cage induction motors. The most accurate result is obtained by using the full set of equations, but more approximate methods using simplified equations are considered. The method is verified by tests on model machines connected by impedances representing transmission lines. Preliminary tests were made on a simple system comprising an induction motor connected to an infinite busbar through an impedance, and were followed by tests on a composite system containing a synchronous machine and an induction motor connected in parallel parts of the system. The results slow that good results are obtained with the accurate calculation which, however, requires a large amount of computer time, but that any approximation introduces considerable error.

The Direct Adaptive Trajectory Control OfRobot Manipulators Via Fuzzy LogicAlgorithm

The paper is addressed to study the trajectory control of robotic mechanisms, particularly, to the transient performance of path tracking control systems. The coefficients and terms of the robot dynamic equations may be partly unknown and some dynamic effects may be unmodeled. One general scheme, which is a combination of the generalization of the computed torque method and the velocity gradient technique, provides a simple way to obtain some known and unknown parameter adaptive control laws, in particular, the exponential path tracking adaptive control algorithms with the important properties of robustness to bounded disturbances and unmodeled dynamics. The algorithms require the on-line measurements of the tracking error and its first derivative. The persistent excitation assumptions for desired paths are not required. The fuzzy logic control strategy is applied to obtain implement able algorithms on the base of the developed adaptive laws. The approach includes the attractive features of both strategies: robustness from direct adaptive control, and simple implementability from fuzzy logic control.

Detailed Hydrogovernor Representation for System Stability Studies

In studying transient performance of power systems, large computer programs are now used with representation of individual unit governing systems included. Detailed representation of hydrogovernors is not usually available, but, rather, an equivalent transfer function is employed.