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Fuzzy logic has been gaining increasing acceptance in control applications during the past few years. Usually, the membership functions and control rules of fuzzy logic controller are determined by trial and error which is cumbersome and time consuming. Therefore, to surmount such a drawback, this paper makes use of the Genetic Algorithm (GA) technique for optimal tuning of the parameters of the Fuzzy Logic Controller (FLC) used for the switching of the thyristor controlled braking resistor to improve power system transient stability. The braking resistor is installed at each generator bus, where rotor speed of the generator is measured to determine the firing-angle of the thyristor switch. By controlling the firing-angle of the thyristor, braking resistor controls the accelerating power in generators and thus improves the transient stability. The effectiveness of the proposed method has been demonstrated by considering both balanced (3LG: Three-phase-to-ground) and unbalanced (1LG: Single-line-to ground, 2LG: Double-line-to ground and 2LS: Line-to-line) faults at different points in a multi-machine power system.

This paper presents the results of analyses about transient stability augmentation by the fuzzy logic controlled braking resistor in a Multi-Machine power system. Following a major disturbance in electric power system, variable rotor speed of the generator is measured, and then the current through the braking resistor is controlled by the firing-angle of the thyristor switch which is controlled by the fuzzy logic. Thus the braking resistor controls the accelerating power in generators and makes the system transiently stable. Simulations are performed by using EMTP (Electro-Magnetic Transients Program). Through the simulation results of both balanced (3LG: Three-phase-to-ground) and unbalanced (1LG: Single-line-to ground, 2LG: Double-line-to ground and 2LS: Line-to-line) faults at different points in the IEEJ West-10 machines system model, the effectiveness of the proposed fuzzy logic controlled braking resistor is demonstrated and the optimal conductance value of the braking resistor in enhancing the transient stability is investigated.

An improved power system with many potential good properties may be obtained with introduction of Superconducting Generator (SCG), which has a superconducting field winding that leads to many advantages such as small size, high generation efficiency, low impedance, and so on. Many researches have confirmed the improving-effect of SCG on power system stability. In this work, the influence of SCG on power transfer capability is studied by way of conducting real-time simulation using a digital type SCG model and an existing analog type power system simulator. In the real-time simulation with a 5-machine infinite bus power system model, ATC (Available Transfer Capability) from generator site to load site are examined and, comparison is done between the ATCs in cases of SCG and the conventional generator (CG). The real-time simulation results have verified the effect that SCG can improve the ATC of power system and illustrated the advantage of SCG over CG from the point view of ATC enhancement.

This paper presents the results of analyses of the effectiveness of a superconducting fault current limiter (SFCL) to stabilize the synchronous generators, suppress turbine shaft torque oscillations, and limit the fault current in a two-machine-infinite bus system. In this study, the system model with two SFCLs having shunt resistance installed at each generator terminal was used taking 3LG (three lines to ground) fault at 12 fault points into account. These analyses were performed using EMTP/ATP. It is concluded that the use of SFCL with shunt resistance value of 1.1 pu is most effective for all fault points for the stabilization of synchronous generators, the suppression of turbine shaft torque oscillations, and the limitation of fault current.

To improve electric power system transient stability, synchronous generators are generally equipped with controllers such as AVR, PSS, and GOV. Fixed parameter controllers degrade control performance, since various oscillation modes occur depending on system conditions. This paper presents an adaptive power system stabilizer (PSS) using frequency domain analysis for improving the transient stability of a multimachine system. In the proposed method, first, the frequency components of the generator swings are detected by the FFT. The conventional PSS parameters are tuned online by a fuzzy controller and frequency domain analysis. We verify the proposed adaptive PSS using frequency domain analysis, which can damp the generator swings effectively. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(2): 10–20, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10129

Accuracy of the calculation method of transient DC component of three phase short circuit current is carefully studied. Using a multi-machine model system 4 different methods are compared, which are catenacci method, AIEE method, 4 parameters method, and the proposed method. Among all these four methods the proposed method gives the most accurate result, which gives almost identical wave form of the averaged wave obtained by the post processing of ATP-EMTP results. Compared to ATP-EMTP the proposed method is more convenient because it automatically gives the severest fault case while ATP-EMTP needs several computations.Main reason of the discrepancies of the conventional methods is based on the insufficient order of the internal models. In contrast to the proposed method, they use only a second order model at most. The usefulness of the proposed method is demonstrated using a test analysis of the saturation of a current transformer. Computing time is also discussed by comparing the results applied to two 10-machines systems and one 30-machines system.In conclusion, the proposed method is accurate and is ready to apply to multi-machine systems within a realistic computing time. The usefulness of the proposed method is confirmed by this study.

This paper presents a new approach to deal with the problem of robust tuning of power system stabilizer (PSS) and automatic voltage regulator (AVR) in multi-machine power systems. The proposed method is based on a model predic- tive control (MPC) technique, for improvement stability of the wide-area power system with multiple generators and distribution systems including dispersed generations. The proposed method provides better damping of power system oscillations under small and large disturbances even with the inclusion of local PSSs. The effectiveness of the proposed approach is demonstrated through a two areas, four machines power system. A performance comparison between the proposed controller and some of other controllers is carried out confirming the superiority of the proposed technique. It has also been observed that the proposed algorithm can be successfully applied to larger multiarea power systems and do not suffer with computational difficulties. The proposed algorithm carried out using MATLAB/SIMULINK software package.

This paper presents a robust control approach to enhance the participation of Variable Speed Wind Turbines (VSWTs) in the primary frequency regulation during network disturbances. The proposed control system utilizes an H∞ Linear Matrix Inequality (H∞ LMI) based scheme to improve the closed-loop performance. In order to demonstrate the effectiveness of the proposed control scheme, it is compared with two classical control systems: the Inertial Control (IC) and the Modified Inertial Control (MIC). Several simulations on a multi-machine test system were performed in Matlab/Simulink environment. The H∞ LMI controller optimizes the trade-off between frequency deviation smoothing and wind turbine (WT) speed deviation after the disturbance. Results show a considerable improvement in frequency deviation smoothing, optimal speed recovery and power injection, during a sudden variation in the system load, compared with the two traditional approaches. A desirable robust performance was also obtained with the proposed scheme after variations in the system parameters.

Focusing on control that can be used to efficiently regulate SMES, unique control logics for power system stabilization were devised by combining the popularly used power deviation (ΔP) of a generator with the angular velocity deviation (Δω) of a generator or the phase correction. In the previous paper, we analyzed the performance and characteristics of the new control logics (ΔP + Δω control logic, ΔP + Δω + phase correction control logic) on both one-and multi-machine infinite-bus systems using the Y-method power system dynamics analysis program, and suggested that the new logics could improve the stability of power systems in comparison to the conventional ΔP control logic.For the next phase of research, we have evaluated the performance and characteristics of the control logics mentioned above based on analogue simulation. As a result, the logics have showed the same tendency as the case of the digital simulation and it have been confirmed that the logics, especially ΔP + Δω+ phase correction control logic, have the superior effect on the improvement of the stability of power system.

Superconducting generator (SCG) with superconducting field winding has many advantages such as small size, light weight, high generation efficiency. In particular, the property of low synchronous reactances, which is not realized in conventional generators, is able to improve power system stability. Installation scheme of SCGs in multi-machine power system becomes one of the topics that should be considered. It concerns how and where SCGs should be installed and parameters setting of machines and controllers. New methods for determining the optimal locations and machine parameters such as synchronous reactance Xd of SCG and control parameters based on approximated eigenvalue sensitivity and genetic algorithms for improving dynamic stability are proposed in this paper. Effectiveness of those methods are verified in IEEJ East 10-machine and it is shown that the proposed methods are effective installation schemes for improving power system stability.

In this paper, we propose new nonlinear stability indices for multi-mode oscillations in power systems by using normal form analysis. One of the indices indicates the characteristics of damping factor with regard to its amplitude change, and the other indicates the stability region for each oscillation mode. We could obtain more detailed information on the stability of power systems by using the proposed indices together with eigenvalues in comparison with eigenvalue analysis. We show the validity of the proposed indices by numerical simulation in a multi-machine power system.

This paper presents a systematic procedure of constructing a Lyapunov function for power system considering with induction machine dynamics characteristics by the state function method. Constructing Lyapunov function for power systems with induction machines is very difficult problem and is hoped for being settled for a long time. In the composition process of the proposed Lyapunov function, the slipping dynamic characteristic of the induction machine is implicitly expressed in the swing equation of power systems. As a result, the dynamic characteristic of an induction machine becomes equivalent to a synchronous machine with a voltage adjustment mechanism to which a dissipation function is added. Using this proposed system description, the Lyapunov function is composed by the state function method, which is based on an expanded energy function, under the condition of some approximations. The effectiveness of the proposed Lyapunov function is verified numerically for multi-machine power systems with induction machine loads.

Superconducting Generator (SCG) has many advantages such as small size, high generation efficiency, low impedance, and so on. An improved power system with many potential good properties may be obtained by introduction of SCG. In order to study the behaviors of SCG in power systems, a digital type SCG model for an existing analog type real-time power system simulator is developed in this work, which is suitable for real-time simulations when the generator constants and control systems are changed frequently. By use of the above-mentioned equipments, real-time simulation in cases of SCG with different generator constants and in case of SCG in multi-machine power system has been conducted. The real-time simulation results verify the effects of SCG on power system stability enhancement and show the influence of generator constants on its stability-improving effects.