To suppress ripples on the output voltage from a DC filter through an active filter by providing a ripple detection circuit with a circuit for detecting the voltage and the phase for each frequency component of a DC voltage ripple and controlling the gain and the phase of a detected signal specifically for each frequency.
AC power, fed from an AC power supply 1 through a converter 2, is converted into DC power which contains ripples which depend on the conversion characteristics of the converter 2. The DC voltage and DC current contain pulsating components (ripple voltage and current) which are removed through a DC filter, but the output therefrom contains pulsating voltage components which cannot be attenuated. A voltage is outputted from a reactor transformer 6 with independent gain and phase for each frequency of the pulsating voltage components, in order to nullify the load side DC voltage pulsation for each frequency component, thus suppressing the ripples.
KUBO HIROSHI
YABUKI MASAAKI
HITACHI ENG CO LTD
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