Bunji Kondo

Power System Voltage Stability

Power system voltage stability is characterized as being capable of maintaining load voltage magnitudes within specified operating limits under steady state conditions. In this paper, the first order delay model of a load admittance change is introduced. Then, using this model, a set of linearized dynamic equations is derived and stability conditions are obtained. An earlier result in the literature is shown to agree with that in this paper. The stability conditions are tested and verified in a 2-load, 2- power source system and a 13-node, 4-power source system.

Stability of sampled-data composite systems with many nonlinearities

A sampled-data composite system given by a set of vector difference equations x_{i}(\tau + 1) - x_{i}(\tau) = \sum \min{j = 1} \max{n} A_{ij} f_{j}[x_{j}(\tau)], i = 1 ..., n is dealt with. The system given by x_{i}(\tau + 1) - x_{i}(\tau) = A_{ij} f_{i}[x_{i}(\tau)] is referred to as the i th isolated subsystem. It is shown that the composite system is asymptotically stable in the large if the f i satisfy certain conditions and the leading principal minors of the determinant |b_{ij}|, i,j = 1, ..., n, are all positive. Here, the diagonal element b ii is a positive number such that \|x_{i}(\tau + 1)\| - \|x_{i}(\tau) \| \leq - b_{ij}\| f_{i}[x_{i}(\tau)]\| holds with regard to the motion of the i th isolated subsystem, and the nondiagonal element b_{ij} , i \neq j , is the minus of \|A_{ij}\| , which is defined as the maximum of \|A_{ij}x_{j}\| , for \|x_{j}\| = 1 . Some extensions of this result are also given. Composite relay controlled systems are studied as examples.

Application of a new stability criterion of composite systems to multimachine power systems

A new stability criterion of composite systems is applied to multimachine power systems. This criterion has advantage in evaluating the influence of the interaction by bilinear forms. In the examples, it is shown that the range of the values of parameters for which the new method can assure stability is considerably wider than that obtained by the Jocic et al. method.

Local stability of composite systems--Frequency-domain condition and estimate of the domain of attraction

This paper is concerned with such composite systems whose subsystems contain one nonlinearity each and whose interconnections are functions of the scalar outputs of subsystems. A frequency-domain condition which assures local asymptotic stability is given under the assumptions that each nonlinearity satisfies a sector condition, that interconnections are linearly bounded, and that linear parts of subsystems may have unstable poles. In deriving the above result, such Lyapunov functions of subsystems are constructed so that their weighted sum is a Lyapunov function of the overall system. A method to estimate the domain Of attraction based on the above Lyapunov functions is also studied. When the bounds on nonlinearities hold true in the entire space and when the linear parts do not have unstable poles, the present condition turns out to be the same with the L 2 -stability condition which was obtained before by Araki.

GG-Pseudo-Band Method for the Design of Multivariable Control Systems

Abstract The design method proposed here is a frequency-domain method and uses acertain class of generalized Gershgor in bands mapped on the gain-phase plane, which are referred to as GG-pseudo-bands. Its main advantages are that the GG-pseudo-bands have a same width for all loops which is in variant under the changes of the diagonal compensator and the unit systems, that no diagonal dominance is required at high frequencies, and that a quantitative guide line for pseudo diagonalization is given based on the interaction index which is a satisfactory scalor measure of the cross intreaction

Application of Optimal Control Theory and Root Locus Method to the Design of Linear Feedback Controllers for Synchronous Machines

Abstract A method to design a state-feedback type controller which attains good performance in regard to the voltage regulation in the prefault state and also to the transient response in the postfault state is proposed. The method is suggested by the observation that we have one freedom in the implementation of the optimal feedback law for the prefault state and that this freedom can be used to improve the postfault behavior. The root locus method is employed to determine the free coefficient so that the maximum stability in the postfault state is attained.

Discrete-Time Optimal Control of Systems with Time-Delays Resulting from Unilateral Flows

Abstract Industrial plants which contain unilateral flow of material are considered. First, we show that such plants can be represented by finite-dimensional difference equations after sampling without any approximating assumptions. Based on those difference equations we can design discrete-time optimal control systems with respect to the quadratic performance index. In that case, the dimension of the discrete-time systems becomes very large if the delay times are large compared with the sampling period. This causes serious computational difficulties. In the second half of the paper, we present an efficient algorithm to solve such a problem; i.e. we show that the optimal control law can be obtained by solving a Riccati equation of much smaller size and by substituting the solution into certain formula.

Stability criteria for multivariable non-linear feedback systems consisting of low order subsystems

Abstract Popov-type stability criteria are given for two types of multivariable feedback systems. The systems are regarded as interconnections of several subsystems and the composite-system method is used to derive the criteria. The values of constants which are needed in the criteria are calculated and tabulated for first- and second-order subsystems. By using these values, we can immediately obtain a stability criterion for the system consisting of first- and/or second-order subsystems. Examples show that the criteria obtained are as sharp as or sharper than previously reported criteria.

Comments on "Stability and transient behavior of composite nonlinear systems

It is shown that the estimate of transient behavior of composite systems presented in the previous paper can be extended to the case where some of the subsystems are not stable.

Synthesis of Feedback-Feedforward Controller by LQ Regulator Theory and its Application to Boiler Control

Abstract Methods to synthesize a feedforward control and a reduced order feedback compensator which is expected to be low sensitive to parameter variations are presented under the condition that the optimal state feedback regulator is already synthesized. The feedforward is designed so as to minimize the value of the performance index to the step change of measurable disturbance. The compensator is the mode reduced one of the Kalman-Bucy filter type optimal observer. A method to let poles of the optimal observer are almost the same as those of the optimal regulator is presented. A method to choose the poles to be reduced to synthesize the reduced order compensator is also presented. The methods presented apply to the design of boiler controller and verify the effectiveness by simulation study.