Kohshi Okumura

The Contribution of T. Sunaga to Interval Analysis and Reliable Computing

The contribution of T. Sunaga to interval analysis and reliable computing is not well-known amongst specialists in the field. We present and comment Sunaga’s basic ideas and results related to the properties of intervals and their application.

Characterization of a simple communication network using Legendre transform

We describe an application of the Legendre transform to communication networks. The Legendre transform applied to max-plus algebra linear systems corresponds to the Fourier transform applied to conventional linear systems. Hence, it is a powerful tool that can be applied to max-plus linear systems and their identification. Linear max-plus algebra has been already used to describe simple data communication networks. We first extend the Legendre transform as the slope transform to non-concave/non-convex functions. We then use it to analyze a simple communication network. We also propose an identification method for its transfer characteristic, and we confirm the results using the ns-2 network simulator.

Logically reversible arithmetic circuit using pass-transistor

This paper proposes novel reversible logic circuits, i.e., a reversible ExOR gate and a two-way AND gate. The gates operate in both directions and the input and output are indistinguishable. We design the circuits using dual-line pass-transistor logic. Applying the method to arithmetic circuits, we realize logically reversible arithmetic circuits. Because proposed circuits have no garbage output, the adder and multiplier operate as the subtracter and divider respectively by replacing the input with the output. We confirm the behavior of the circuits by both real experiments and SPICE simulations.

Solution of ill-conditioned load flow equation by homotopy continuation method

A homotopy continuation method is used to solve ill-conditioned load flow equations. It presents the predictor step effective for following the path of homotopy functions formulated from the load flow equation. The aim is to solve the ill-conditioned load flow equation, the solution of which has long been discussed. Using the homotopy method described, it is concluded that the ill-conditioned load flow equation discussed has no solution.<<ETX>>

An improvement of convergence of FFT-based numerical inversion of Laplace transforms

This paper presents an improvement on the FFT-based numerical inversion of Laplace transforms. Since the inversion obtained by the FFT-based method contains large errors for the latter half of the result, only the former half is acceptable. We analyze the truncation error which is the largest part of the error, and propose the acceleration method, taking notice of the property of the complex frequency s as the differential operator in the time domain. The errors are markedly reduced by this method, and the entire result becomes acceptable.

Algebraic representation of error bounds for describing function using Groebner base [nonlinear circuit analysis example]

This paper presents an algebraic approach to find the region where the true periodic solution of a nonlinear system or circuit lies when a describing function solution is given. Because algebraic representations of the error bounds are obtained by the Groebner base, the dependence of the bounds on parameter values becomes clear. Further, we propose an efficient method to improve the estimation. The Groebner base is shown to be applicable to the describing function method. The estimation is modified considerably.

A computation of power system characteristic by general homotopy and investigation of its stability

Presents an application of a general homotopy method to the computation of the characteristics of a power system such as PV curves. The load flow equations are derived from a set of nonlinear differential and algebraic equations. A homotopy continuation method is used for following the characteristics of the power system. The stability of the load flow solutions is discussed by deriving the variational equation.<<ETX>>

Subharmonic oscillations in three-phase circuits

Abstract This paper analyzes the subharmonic oscillations generated in three-phase circuits by the asymptotic method. As the result of the analysis, we find that there are three kinds of the 1 3 -harmonic oscillations, 1 3 -harmonic oscillation with beats, 1 3 -harmonic oscillation without beats and 1 3 -harmonic oscillation occurring in a single phase of the three-phase circuit. By means of an experimental circuit we confirm these oscillations.

An implementation of numerical inversion of Laplace transforms on FPGA

This paper presents an implementation of numerical inversion of Laplace transforms on FPGAs. To make real-time transient analysis possible using Laplace transforms, it is desirable to implement the hardware of numerical inversion of Laplace transforms. However, the implementation of the FFT-based numerical inversion method with fixed-point numbers results in severely large errors due to the exponential function which appears in the inversion formula. In order to overcome this difficulty, we propose the use of a block floating-point FFT in the implementation. As a result, the errors are much reduced.

A method for solving complex linear equation of AC network by interval computation

This paper proposes a method for computing the range of the solution of the AC network equation of which parameters are given by complex interval numbers. The results by the proposed method are compared with Monte Carlo method.<<ETX>>