Transient AC voltage related phenomena for HVDC schemes connected to weak AC systems

A didactic explanation of voltage-stability-associated phenomena at HVDC terminals is presented. Conditions leading to AC voltage collapse problems are identified. A mechanism that excites control-induced voltage oscillations is shown. The voltage stability factor is used to obtain the maximum power limits of AC/DC systems operating with different control strategies. Correlation to Pd*Id curves is given. Solutions for eliminating the risks of voltage collapse and for avoiding control-induced oscillations are discussed. The results are supported by detailed digital simulations of a weak AC/DC system using EMTP.<
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