Atsushi Ishigame

An approach to stability analysis of second order fuzzy systems

The stability of fuzzy systems can be discussed by the theorem of K. Tanaka and M. Sugeno (1990). However, it is difficult to find the common positive definite matrix P which is introduced in the theorem, and satisfies, for example, two Lyapunov inequalities A/sub 1//sup T/PA/sub 1/-P<0 and A/sub 2//sup T/PA/sub 2/-P<0. The authors present a new simple approach for finding the whole region where a 2*2 real matrix P exists. As an example, two spring-mass physical systems with damping are treated, and the region of P is obtained. Also, three examples considered by Tanaka and Sugeno are discussed. It is emphasized that illustrating the P-region calculated by the approach aids the design of a fuzzy controller.<<ETX>>

Particle swarm optimization based on the concept of tabu search

This paper presents a new Particle Swarm Optimization based on the concept of Tabu Search (TS-PSO). In PSO, when a particle finds a local optimal solution, all of the particles gather around the one, and cannot escape from it. On the other hand, TS can escape from the local optimal solution by moving away from the best solution at the present. The proposed TS-PSO is the method for combining the excellence of both PSO and TS. In this method, particles are divided into two categories called swarm1 and swarm2. And they play the key roles of intensification and diversification respectively. Swarm1 playing roles of intensification searches the area around the best solution at the present, and swarm2 playing roles of diversification intends to avoid local optimal solutions and to find global optimal one. Then, the proposed method is validated through numerical simulations with several functions which are well known as optimization benchmark problems comparing to the conventional PSO methods.

Structural control of electric power networks for transient stability

This paper presents a sensitivity-based approach for structural control of electric power networks using FACTS (flexible AC transmission system) devices in order to improve the transient stability margin for one controlling unstable equilibrium point (u.e.p). It is comprised of the sensitivity analysis of critical energy of the TEF (transient energy function), network control strategy and evaluation. A related practical application to a 39-bus test system follows and shows that the structural control of power networks is effective for the enhancement of power system transient stability. >

Design of electric power system stabilizer based on fuzzy control theory

The authors present a method of constructing simple fuzzy control rules for controllers of electric power systems, by simplifying variables of condition parts and rules and minimizing the number of membership functions. The simplification is caused by a coordinate transformation with the rotation angle theta on the phase plane. An electric power system with controllers is modeled as a fuzzy model which is composed of a weighted average of linear systems. Based on the fuzzy model, stability analysis of the fuzzy control system is discussed. For optimal parameters setting, a quadratic performance index is considered and the quasi-Newton method is applied. The control effect was demonstrated by an application to a one-machine infinite-bus power system with an automatic voltage regulator and a governor as controllers.<<ETX>>

Basic study of proximate optimality principle based combinatorial optimization method

This paper proposes a new method for solving combinatorial optimization problems on the basis of Proximate Optimality Principle (POP). The proposed method has higher optimality and lower computational complexity than conventional methods. The proposed method is applied to several typical combinatorial optimization problems in order to verify the performance of the proposed method.

Transient stability analysis for power system using Lyapunov function with load characteristics

This paper presents constructing Lyapunov function of power system for estimating transient stability considering with load dynamics characteristics. An induction machine is treated as a representation of dynamic load. 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. The effectiveness of the proposed Lyapunov function is verified numerically for multimachine power systems with induction machine load.

A state estimation method for photovoltaic power generation using independent component analysis

A large number of Photovoltaic Generations (PVs) are expected to be introduced in distribution systems (D/Ss). Therefore the state estimation is important problem for stable and reliable system operation. However, it is difficult to estimate the total power of PVs connected to a D/S because metering spots and metering items are limited in existing D/S. In this paper, we propose an estimation method for sum of PV-outputs connected to a D/S. This method enables to estimate PV-outputs by analyzing a power flow data which include PV-outputs and various distribution loads using independent component analysis (ICA). The estimation by ICA needs the same number of observation signals as estimation signals. So we propose the method which is able to estimate PV-outputs and load-changes from active and reactive power flow those are recognized as two observation signals measured at one observation point on distribution lines. And the information of insolation as a priori knowledge is added to the method improving the estimation accuracy.

Similarity measure of proximate optimality principle and Multi-Point Tabu Search

This paper proposes a new method, multi-point Tabu search, for solving combinatorial optimization problems on the basis of the concept of Proximate optimality principle (POP). While the similarity measure of POP is defined using the concept of metric space on combinatorial optimization problems, some numerical simulations using several types of combinatorial optimization benchmark problems investigate POP. The proposed algorithm is applied to some typical combinatorial optimization problems in order to verify the performance of the proposed algorithm.

Neural Stabilizing Controller Based on Co-evolutionary Predator-Prey Particle Swarm Optimization

In this paper, an approach based on particle swarm optimization (PSO) and Lyapunov method to construct neural stabilizing controller is presented. The procedure to learn the value of neural network is formulated as min-max problem. And the problem is solved by the co-evolutionary predator-prey PSO which we newly propose. The PSO is able to generate an optimal set of parameters for neural controller. And then, the proposed neural controller can be satisfied the Lyapunov stability condition. The proposed method is validated through numerical simulations with power system stabilizing control problem comparing to the conventional control method.

Structural control based on genetic algorithm and neural network for electric power systems

This paper presents a method of structural control of electric power networks for improving their stability. The method is based on the FACTS concept, a genetic algorithm and neural network. FACTS equipment will provide some new ways for improving stability by controlling the reactance of transmission lines in terms of structure control of the power network. A case study with a multimachine power system is presented and discussed.<<ETX>>