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Latency techniques in power system transients simulation Moreira, Fernando Augusto

Abstract

This thesis work presents a methodology for exploiting time domain latency in EMTP-type programs for the simulation of electromagnetic transients phenomena. Latency exploitation is related to the capability of numerically solving the differential equations governing the behaviour of electric networks with different integration steps. In many situations, the efficiency of numerical simulation is compromised by the requirements of the fastest network components that force the choice of a very small integration step to accurately track the highest frequency transients developing on the network. Through an efficient and accurate network partitioning technique, the electric network is divided into distinct subsystems that present different dominant eigenvalues. The subnetworks can then be simulated according to their own time step requirements. The effect of the subnetwork couplings are taken into account by resynchronizing the global solution at certain time instants. For this reason, the ratio between the large time step AT and the small time step At is always an integer number. The thesis includes a detailed description of how the interface between the fast and slow subnetworks is adjusted, in order to guarantee maximum accuracy and efficiency. The latency approach followed in this thesis work results in an expanded form of the trapezoidal and backward Euler integration rules, which are then tested for accuracy and stability. The analyses performed show that the expanded rules are as accurate and stable as the conventional rules for single time step simulation. Lumped networks and networks containing transmission lines, modelled with the travelling wave equations, are simulated with the proposed latency technique. Different line-models are implemented and the results compared to those obtained from conventional EMTP simulations, where a single integration step is used for the complete network solution.

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