Methods for power system frequency estimation

V prispevku jc prikazan pregled metod za določanje frekvence elektroenergetskega sistema. Podrobneje so prikazane najbolj perspektivne metode: iterativna metoda najmanjše vsote kvadratov odstopanj, izboljšana diskretna Fourierjeva transformacija in dekompozicija v ortogonalne komponente. Predstavljene so teoretične osnove posameznih metod ter njihove prednosti in slabosti. Lastnosti posameznih metod so numerično ovrednotene z vidika natančnosti določitve frekvence, dinamike odziva na spremembe parametrov vhodnega signala in vpliv nernodcliranih komponent vhodnega signala (višje harmonske komponente, subharmonske komponente, merilni šum) na določitev frekvence. Metode smo testirali s testnimi signali, ki ponazarjajo različna stanja elektroenergetskega sistema

Power-Based Concept for Current Injection by Inverter-Interfaced Distributed Generations during Transmission-Network Faults

This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) response during transmission network faults. The simplest and safest solution is to switch IIDGs off during network faults without impacting the network voltages. A more elaborate and efficient concept, required by national grid codes, is based on controlling the IIDGs’ currents, involving positive- and negative-sequence voltage measured at the connection point. In this way the magnitude and phase of the injected currents can be adjusted, although the generated power will depend on the actual line voltages at the connection point. Therefore, an improved concept is proposed to adjust IIDGs’ fault current injection through the required active and reactive power, employing the same voltage characteristics. The proposed, i.e., power-based concept, is more definite than the current-based one, since the required power will always be generated. The discussed concepts for the fault current injection by IIDGs were tested in different 110-kV networks with loop and radial topologies, and for different short-circuit capabilities of the aggregated network supply. Based on extensive numerical calculations, the power-based concept during transmission networks faults generates more reactive power compared to the current-based concept. However, the voltage support by IIDGs during transmission networks faults, regardless of the concept being used, is influenced mainly by the short-circuit capability of the aggregated network supply. As regards distance protection operation, it is influenced additionally by the network topology, i.e., in radial network topology, the remote relay’s operation can be delayed due to a largely seen impedance