Regular-sampled current measurement in AC drives using delta-sigma modulators

A delta-sigma modulator converts an analog input signal into a high-frequency stream of single bits with out-off band noise. A high-resolution signal is extracted from the bit-stream with an appropriate low pass filter. The paper emphasizes on the utilization of SincK-filters as low pass filter and proposes a sampling method that is synchronized with the controller to incorporate a regular sampling. The paper also covers the detailed analysis of SincK-filters (known as decimation filter) with different decimation ratios and filter orders, and a detailed analysis of the impulse response for the synchronization of the filter with the controller. The SincK-filter is integrated into a field-oriented control for permanent magnet synchronous motors. The whole system is realized on a FPGA-based control platform. The performance is validated by experimental results.