Voltage and current sensing in power electronic converters using sigma-delta A/D conversion

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 clocked stream of low-resolution digital data. By averaging this stream of data over a time interval that can be defined individually for each switching cycle, a high-resolution measurement of the input signal is obtained. Harmonic distortion of the waveform to be measured (caused by the switching of the power converter) is inherently filtered out due to proper choice of the averaging interval. The system is insensitive to noise and ringing caused by EMI or cable oscillations. The simplicity of the analog part of the sigma-delta A/D converter and its synchronous operation make it possible to integrate the whole sigma-delta converter into a small application specific integrated circuit (ASIC). The stream of low-resolution digital data at the output of the ASIC can be transmitted to the control electronics via a fiber-optic link that also insulates the sensing point from the control electronics, so that noninsulating sensors can be used.