OUTPUT ATTENUATION COMPENSATION CIRCUIT OF LOW-PASS FILTER

• Main Authors: OZEKI EMIKO, HOSHINO TOSHINORI, MURAKAMI OSAMU, NISHIO KIYOTAKA
• Format: Patent
• Language: English
• Published: 22.01.1999
• Edition: 6
• Subjects: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORSOR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER; ELECTRICITY; GENERATION

PROBLEM TO BE SOLVED: To compensate the output attenuation of the low-pass filter(LPF) of a generator voltage effective value calculation circuit in a frequency range which is lower than its cut-off frequency. SOLUTION: When a generator voltage detected by an instrument transformer is let through an LPF with a cut-off frequency of 120 Hz and subjected to an A/D conversion to calculate the effective value of the voltage, the output of the LPF is attenuated even in a frequency range between 70 Hz and 120 Hz, which is the cut-off frequency of the LPF owing to the characteristics of the LPF. Therefore, when a generator frequency is elevated, the calculated result of the effective value shows a low value. As the 70 Hz-120 Hz attenuation characteristic of the LPF is linear, when the frequency of the generator voltage is elevated, an approximately linearly attenuated attenuation factor in a frequency range of 70 Hz-120 Hz, which is a frequency range of approximately 1.4-2.4 times that of a reference frequency, is calculated by a linear approximation formula, and the calculated result is added to the calculated voltage effective value to compensate for the attenuation of the voltage effective value owing to the characteristics of the LPF.