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This paper presents a novel approach to voltage and current measurement in power electronics using a sigma-delta A/D converter. The system converts the analog input signal into a digital stream of data. By averaging the digital data stream over a switching period of the power converter, the required measurement is obtained. Harmonic distortion of the input waveform and noise caused by EMI is inherently filtered out. The analog part of the sigma-delta A/D converter is very simple and operates synchronously to a clock. This makes it possible to integrate the sigma-delta converter into a small ASIC. The stream of digital data at the output of the ASIC can be transmitted using a fibre optic link that also insulates the sensing point from control electronics, so that noninsulating sensors can be used.
Mertens et al. (2002) studied this question.