Improvement of Transient Performance of Synchronous Generator via Excitation Control

This paper investigates the improvement of a transient performance of a synchronous generator in a one-machine system via the excitation control. First, in regard to the optimal control of the excitation, the effects of the weighting coefficients on the optimal response are examined. The optimal control is approximately realized by the feedback from the state variables, and the obtained responses are compared with the optimal responses. Furthermore, the system responses, in a case of being installed with a fast acting excitation control system with a stabilizer, are calculated and compared with those by the optimal control system

EXPERT SYSTEM FOR RESTORING TRUNK POWER SYSTEMS FROM COMPLETE SYSTEM COLLAPSE

In this paper, an expert system for restoring bulk power systems from complete collapse is proposed. The system secures an initial power source, integrates the trunk transmission system, and restarts all power stations. The rules were divided into several groups, and mainly used to control the flow of the restoration process. The detailed procedures were left to functions defined in Lisp. A partial knowledge, such as priorities in choosing an initial power source, in restoring power stations and substations, is read from data files. By adopting this method, system operators can adjust the restoration process so as to fit each individual power system without changing programs

Transient Stability Analysis of Multi-machine Power System with Automatic Voltage Regulators via Lyapunov's Direct Method

In this paper, Lyapunov's direct method is applied to a multi-machine power system where generators are installed with atuomatic voltage regulators. The automatic voltage regulator and the thyrister exciter are represented by a third order transfer function. The stability of the power system is checked according to a generalized Popov criterion. This criterion guarantees that the system is stable if the gains of the voltage regulators are lower than the limit values. A Lur'e type Lyapunov function is constructed by the systematic method established by J. L. Willems. The obtained Lyapunov function is used in a transient stability analysis of a 10-machine power system. The direct method yields results which are very close to those obtained by simulations. It is concluded that Lyapunov's direct method is applicable with sufficient accuracy to transient stability analyses of power systems, where automatic voltage regulators are installed in generators on the condition that the gains of the automatic voltage regulators must be enlarged to practically used values in the future

Development of Simulator with Artificial Intelligence on Secondary Power System Operation

Centralized control from a control center is popular in secondary power systems. However, as operating systems are modernized and automated, operators rarely have opportunities to experience various situations. On the other hand, operators are expected to quickly cope with any situation once an accident happens. In this paper, artificial intelligence has been applied to the training of a secondary power system operation. The developed system has simulation, training, and inquiry modes. In the training mode, it helps operators train in restoring power systems. If an operator succeeds in restoration, the system evaluates executed operations. If he fails, the system generates and presents an example of restoration operations. These functions have been realized by expert systems of a production rule type. Methods of automatically generating restoration process and of evaluating executed operations have been described in detail. Restoration operations are generated so as to restore blackout load buses one by one. The used rules are very simple, and are easy for operators to understand. On an operator's request, it explains how each operation is generated. Evaluation is made on items such as new blackouts and overloads caused by executed operations. If any operations come under these items, then the system gives some warnings and corrections about them. The system was applied to an example power system, and its effectiveness was verified

Construction of Lur'e Type Lyapunov Function with Effect of Magnetic Flux Decay

In this paper a generalized stability criterion for a system with multi-argument non-linearities is derived. The new criterion is based on M. A. Pai's work, and is proved along B. D. O. Anderson's criterion. The new criterion enables us to construct a Lur'e type Lyapunov function in a systematic way. The new criterion is applied to a multi-machine power system with magnetic flux decays of generators. A new Lyapunov function is constructed in a well known manner established by J. L. Willems and other researchers. The new Lyapunov function is similar to the one which has already been obtained for a system without the magnetic flux decays, except for a few points which will affect a transient stability of the system

Dynamic Stability Analysis of Large-scale Power System by the Frequency Response Method

A frequency response method has been proposed to analyze a dynamic stability on power oscillations of large interconnected power systems. However, its application to large-scale power systems is severely limited because of its long computation time. In this paper, several measures were proposed to remove this disadvantage. A method of directly calculating the determinant of an operational transfer matrix was first proposed in order to shorten the computation time at each frequency. The determinant is efficiently obtained by utilizing sparsity natures of three intermediate matrices. Multiple step sizes of frequency were next introduced instead of a fixed step size in order to reduce the number of frequency points to be scanned. These measures were applied to an example system with 107 generators. The computation time for each frequency response was reduced to 122 of the usual method. The number of frequency points was reduced to 28% of the usual method. The total computation time was reduced to 17.1 seconds, which corresponds to 175 of the usual method. These results verify the effectiveness of the proposed measures

Transient Stability Analysis of Electric Power Systems via Lur'e type Lyapunov Function : Part II

It was found in the previous paper that the time derivative of the Lyapunov function used for the transient stability analysis can take a positive value in the case of a system with large transfer conductances ; and it makes the estimation error of the critical fault clearing time large. In this paper, the Lyapunov function is modified in order to remove the defect and fit it to the analysis of the transient stability. Moreover, a new method of determining the critical value of the Lyapunov function is proposed, which is derived from the consideration of the modification. The method uses the value of the potential energy as the critical value when the system gets out of the stability domain. The modified Lyapunov function and the new critical value are applied to a 10-machine system as a numerical example

Transient Stability Analysis of Electric Power Systems via Lur'e type Lyapunov Function : Part I

In this paper, a Lur'e type Lyapunov function derived from the generalized Popov's theorem is applied to the transient stability problem of electric power systems. Also described is the method of evaluating the critical fault clearing time using the Lyapunov function V. On the occasion of the estimation of the critical fault clearing time or the assessment of the transient stability region via the Lyapunov direct method, the determination of the critical value of the Lyapunov function is as important as the construction of the function. In this paper, it is examined what the transient stability region of electric power systems is practically like. It is shown that the degree of the conservativeness of the estimation can be reduced, if Vᵘᶜ, the value of V at the unstable equilibrium point corresponding to the first swing, is used as the critical value instead of the minimum of the values of V at all of the unstable equilibrium points. Two methods of approximately calculating Vᵘᶜ are proposed, and applied to the model systems as numerical examples. Large estimation errors were seen in some cases due to the defect of the Lyapunov function used, which will be overcome in the companion paper