Performance comparison of a DFT-based Causal and Non-Causal PMU

Phasor Measurement Units (PMUs) have been on the rise since the inception of the smart grid. Being an integral part of the Wide Area Measurement System PMUs provide the required measurements for the wide area visualization of the inter connected grid. PMUs utilize different methods to compute phasors most of them involving signal processing concepts. Usually computing phasors using PMUs involves a group delay which is directly related to the length of the data window used for estimation. This group delay till recently was compensated using a non-causal approach in which the phasor computed at the end of the window is simply the Referred to the Center (RC) of the window. This approach involves a certain latency which can prove to be a hindrance in case the phasor estimates are to be used for Wide Area Measurement Protection and Control Applications (WAMPAC). To overcome this problem causal group delay compensation schemes are used which involve zero latency. Due to the recent nature of the method the performance of causal phasors has not been extensively covered in the literature so far. Hence, this paper introduces the concept of causal and non-causal phasors highlighting the key aspects of both the methodologies. A DFT-based PMU is designed involving both the causal and non-causal compensation schemes. The use of frequency and ROCOF estimates for angle compensation is also demonstrated. Several key differences between causal and non-causal phasor estimates are illustrated using PMU data available from a simulated 4-machine 10-bus power system.