Delayed signal cancellation-based open-loop approach for single-phase p-class PMU algorithm

Abstract

Phasor measurement unit (PMU) is anticipated to be the cornerstone of the monitoring, operation and control schemes of the future electric power network which is becoming progressively complicated due to the high expansion of nonlinear loads, deployment of power electronic devices, penetration of renewable energy sources and ever-rising market demand. It has evolved to estimate the amplitude, phase, frequency and rate of change of frequency (ROCOF) of the power grid signal in a synchronized way under both the grid statics and dynamics. Due to this purpose, the development of algorithm that allows the rejection of the grid disturbances but preserves the information of the fundamental phasor is of paramount concern. The IEC/IEEE 60255-118-1:2018 standard defines the standard tests and challenging performance requirements for P-class PMUs used for power system protection to guarantee faster dynamic response with higher accuracy. In this research work, a fast, robust, accurate, unconditionally stable and computationally efficient single-phase P-class PMU algorithm has been developed whose underlying principle is based on the delayed signal cancellation (DSC) operator. Properly chosen fixed-tuned DSC operators are cascaded to form a CDSC operator which can remove harmonics as demanded by the above standard. To tackle the fundamental frequency variation, two similar CDSC schemes are cascaded. This algorithm avoids the use of integrators, large-size matrix inversion, feedback paths and computationally demanding trigonometric functions or their inverse operations in its structure. It can be used for PMU data rates up to 100 frames per second. Among all types of the standard tests, the maximum total vector error (TVE), frequency error (FE) and rate of change of frequency error (RFE) were calculated as 0.0740 %, 2 mHz and 0.0658 Hz/s respectively. The algorithm also meets the requirements of TVE, FE and RFE response times, measurement delay time and maximum percent overshoot/undershoot with a broad safety of margin. However, to improve the noise robustness, a slightly modified scheme is also proposed which can provide the results within the allowable error limits for a noise level of greater than about 51 dB for signal frequency test. Finally, the performance of the modified scheme is compared with a computationally expensive single-phase P-class PMU algorithm based on corrected interpolated discrete Fourier transform (IpDFTc).