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Interaction between multimachine ac systems and a multiterminal dc (MTDC) grid and the impact on the overall stability of the combined ac-MTDC system is studied in this paper. A generic modeling framework for voltage-source converter (VSC)-based MTDC grids, which is compatible with standard multimachine ac system models, is developed to carry out modal analysis and transient simulation. A general asymmetric bipole converter configuration comprising positive and negative pole converters and dc cable network with a positive, negative, and metallic return circuit is considered to enable different types of faults and dc-side unbalance studies. Detailed dynamic representation of the dc cables with distributed pi-section models is used along with the averaged model and decoupled control for the converter stations. An averaged model in Matlab/SIMULINK is validated against the detailed switched model in EMTDC/PSCAD by comparing the responses following small and large disturbances (e.g., faults on the dc side). Modal analysis is performed to identify the nature and root cause of the dynamic responses. Interaction between a multimachine ac system and an MTDC grid is examined following faults on the ac and dc sides and outage of converters. It is shown that the cause of instability in certain cases could only be attributed to the dc-side state variables. An averaged model of the converter along with the dc cable network is shown to be essential to analyze the stability and dynamics of combined ac-MTDC grids. [ABSTRACT FROM AUTHOR]

Recent technological advances in the area of wide- area measurement systems (WAMS) has enabled the use of a combination of measured signals from remote locations for centralized control purpose. The transmitted signals can be used for multiple swing mode damping using a single controller. However, there is an unavoidable delay involved before these signals are received at the controller site. To ensure satisfactory performance, this delay needs to be taken into account in the control design stage. This paper focuses on damping control design taking into account a delayed arrival of feedback signals. A predictor-based H∞, control design strategy is discussed for such time-delayed systems. The concept is utilized to design a WAMS-based damping controller for a prototype power system using a static var compensator. The controller performance is evaluated for a range Of operating conditions. [ABSTRACT FROM AUTHOR]