The Irremovable Properties Proof of Decaying DC Component for Dynamic Phasor Measurement

Abstract

Dynamic voltage can be described by two parts in time domain, sinusoidal steady state component and dynamic state component. The latter reflects the effect of the system’s characteristic root, and is also called decaying DC component. Decaying exponential signal has continuous spectrum, and this characteristic has a bad effect on the accuracy of phase angle’s measurement, therefore the idea of filtering the decaying exponential signal was proposed. To verify the possibility of this proposal, this paper analyzes the frequency formation of dynamic voltage signal mathematically, and points out that at the frequency of the sinusoidal component, measured voltage signal’s time domain description is the superposition of two sinusoidal signals with the same frequency, different phase angles and different amplitudes. This is the reason for the deviation between the measured voltage angle and the theoretical phase angle. The deviation angle not only shows the combined action of steady component and dynamic component, but also illustrates that the decaying exponential signal cannot be filtered out.