FIR filter with reduced group delay based a sampling frequency conversion algorithm for differential protection

In intelligent substations, current digital sampled data are presented by electronic current transducers(ECTs) to the differential protection device. When the ECTs' sampling rates are not all the same, it is compelled to convert different sampling rates to the same one. In this paper, the concept of low-delay finite impulse response filter is presented. Furthermore, a low-pass filter for signal decimation and interpolation link cascade is designed based on the constrained least squares method, which has realized the fast response of any rational multiple rate conversion. A model of 500kV transformer system model is built for simulation analysis. Compared with the traditional low-pass filter based on the Chebyshev approximation principle, output data response of the designed filter is faster by 37.5%. And peak instantaneous error is controlled within 3.683%, which can effectively reduce the output delay and improve the operating speed of the differential protection.