Low-Complexity P Class to M Class PMU Model for Distribution Systems

Abstract

The paper presents a new PMU (Phasor Measurement Unit) signal processing model compliant with the IEC/IEEE 60255-118-1 standard. The disturbances are rejected by a cascade digital prefilter made of sections, each with one nominal cycle long rectangular impulse response. The frequency is next estimated by the discrete-time frequency-gain transducer (DTFGT). A single section prefilter with the DTFGT is a 1.5 nominal cycle long P class compliant PMU. M class compliance requires 13 sections prefilter what, along with the DTFGT, gives a 13.4 cycle long PMU. By the elongation of the prefilter cascade, with one cycle increment, the transition from the 1.5 cycle P class to the 13.4 cycle M class PMU is obtained. Each cascade section filter is implemented recursively with only two additions and one multiplication independently of the assumed sampling frequency. The phasor is precisely estimated thanks to the proposed correction of amplitude attenuation and phase shift caused by the prefilter. The main advantages of the proposed PMU model are: full compliance with the standard, low computational complexity, superior rejection of harmonics, and possibility of phasor quality assessment based on different length PMU estimations. The proposed PMU model is primary meant for the distribution systems because of high immunity to disturbances and low computational complexity that makes it suitable for implementation in a low-cost hardware platform or as a software module in a virtual instrumentation and large-scale deployment.