Fuji Electric Co., Ltd.

Other

Yoshizo Obata

Tadashi Naito

Takao Okada

Shinichiro Inoue

Junya Matsuki

Naoki Kunihiro

Chikasa Uenosono

Masaki Takahashi

A method for improving accuracy of estimating natural frequency of a distribution system. The estimation is performed in order to identify a rectifier load that generates harmonics due to commutation oscillation. It includes the steps of measuring a charging current flowing into a power factor improving capacitor to obtain first data, removing fundamental frequency from the first data to obtain second data, determining, from the second data, a first time at which the amplitude of commutating oscillation components takes a maximum value, picking up third data in the interval beginning from the first time and ending at a second time later than the first time by T/N, where T is the period of the fundamental frequency, and N is the number of rectifier phases, performing frequency analysis on the third data to form fourth data by expanding the third data into a Fourier series, and determining a local peak frequency, that is, the natural frequency in the fourth data. This prevents frequency components of particular orders from being emphasized, and reduces interference between the commutation oscillations, thereby making it possible to obtain a local peak value, that is, the natural frequency with ease at high accuracy.

Method for estimating natural frequency of distribution system

Apparatus for estimating natural frequency of distribution system

There is disclosed a system for predicting desynchronization of a synchronous machine by detecting a phenomenon of radical variation of the magnetic flux in the gap of a synchronous machine immediately before falling in an asynchronous state. For example, a functional value of the fundamental harmonic component and that of the higher harmonic component of the flux in the gap are detected for comparing the variation of each functional value with a predetermined reference level to predict desynchronization of the synchronous machine.

System for predicting desynchronization of a synchronous machine

Desynchronization of a synchronous machine is predicted by detecting a phenomenon of radical variation of the magnetic flux in the gap of a synchronous machine immediately before falling into an asynchronous state. For example, each functional value of the direct axis flux and the quadrature axis flux in the gap is detected for comparing the variation of each functional value with a predetermined reference level to predict desynchronization of the synchronous machine.

Growing community of inventors

Kawasaki, Japan

Tadashi Naito