Apparatus and method for eliminating variable offset values of current detecting signals

Abstract

An apparatus for eliminating variable offset values of current detecting signals and its method having a current detector for detecting feedback current from a three-phase AC motor and for converting the feedback current into voltage detecting signals containing offset elements, differential amplifiers for differentially operating a feedback analog offset signal and the voltage detecting signals, output amplifiers for amplifying the differentially operated voltage detecting signals to fit within the input range for controlling, an analog/digital converter for converting the amplified signals into digital signals, a control part for adding up the digital signals to a digital offset value and for comparing the digital offset value with a predetermined offset command and for applying a proportional plus integral function to the compared result and for outputting a digital offset signal of a pulse-width modulation waveform, and a digital/analog converter for converting the digital offset signal into the analog offset signal and for providing a feedback loop of the analog offset signal to the differential amplifiers. The disclosed invention can adjust a current detecting signal to a desired level of signal even though the offset element which is contained in the detecting signal of a motor such as a current detecting signal of the ASIPM is being variably changed.