The point of common coupling of a photovoltaic energy conversion system (PVES) to the utility grid is the most critical interface point where voltage sag issues arise. This paper involves a comparative evaluation of Dynamic Voltage Restorer (DVR) and Distribution Static Compensator (D-STATCOM) in mitigating the voltage sag at the point of common coupling of a photovoltaic energy conversion system integrated onto AC auxiliary distribution system in a 110 kV/13.8 kV transmission substation in the national power grid in Saudi Arabia. The voltage sag due to a three-phase short circuit at the point of common coupling of the photovoltaic system with the AC auxiliary distribution system is investigated. The results indicate that the DVR is better than the D-STATCOM in mitigating the voltage sag issue.
This paper involves the characterization and the performance evaluation of various types of synchronous generator excitation systems in the transient stability enhancement of power systems. The Investigations are carried out by modelling the typical DC, AC and static excitation systems represented by IEEE types DC1A, DC2A, AC4A, AC5A, ST1A and ST2A attached with a generator connected to the infinite bus. The performance evaluation of these excitation systems is performed in terms of their response ratio and ceiling voltage together with the system settling time and the critical clearing time following a sudden three-phase short-circuit in the system. Each excitation system together with its power system stabilizer is considered in the analysis. 4th order Runge Kutta method is utilized for transient stability analysis of the power system with the 3rd order model for synchronous generator representation. The investigations reveal that the IEEE ST2A Excitation System is better than the other types of excitation systems.
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