Adaptive Filtering Based on Normalized Time Scale for the Measurement of Phasors in Short Intervals

Short-circuit events occur more or less regularly on high-voltage lines, some events are caused by lightning, others are caused by equipment faults. If the short-circuit does not disappear by itself, the short-circuit event is eliminated within 60–150 ms and a reconnection of the lines is automatically attempted after a few seconds. Such events, which are triggered on high-voltage lines, can cause considerable voltage dips and phase jumps of the positive sequence phasor at all voltage levels. An example of a real event is presented that far exceeds the tested values of PMUs. Magnitude and phase jumps disturb the control loops in inverters and phasor measurement units, but also offer the possibility of grid characterization through distributed measurements, if it's possible to identify a steady state within this very short interval. In this article, we present the normalized time base with a fixed ratio to the angle of the fundamental. In this time base, the signals are again strictly periodic with a constant period duration, even if the frequency of the fundamental varies. This enables the definition of short filters with notches on all harmonics. In a discrete-time implementation with interpolated sampling, this concept is applied to an in-quadrature PLL with adaptive filtering on the positive sequence phasor, but the filter can be optimally and robustly designed and rigidly implemented in the normalized time base. In an implementation, the phasors and the frequency are calculated 16 times per line cycle and are therefore available approx. 800 times per second. The measurement interval of two line cycle duration is very short and is suitable for the identification of a steady state during these short circuit events.