Design and stability analysis of a robust wide-area measurement based damping controller for multiple HVDC systems
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Date
2018
Authors
Vaid, Rajesh
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Abstract
The presence of low-frequency oscillations in the power system network is a cause of
concern. If such oscillations are not suitably damped then they can lead to catastrophic
events in the power system. The issue of providing adequate damping for such oscillations has been approached in ways ranging from the use of local signals e.g rotor angle, machine speed to tune power system stabiliser, to development of power oscillation damping controllers that utilise line current, line voltage signals from special equipment (e.g. Flexible AC Transmission). The power network has embedded High Voltage DC (HVDC) transmission system and some power oscillation damping controllers make use of this resource to address the issue. The advent of Wide-Area Measurement Systems (WAMS) has enabled the use of remote system-wide information to enhance controllability of critical parameters and improve the stability of the overall system. This thesis investigates the use of such system-wide information to synthesise a feedback signal to impart damping to critical swing-modes. This research demonstrates that the use of selected system-wide information along with local signals result in a robust controller, whose performance does not deteriorate when the communication channel fails. The proposed controller utilises the concept of increasing the separation between the closed-loop poles and open-loop zeros, which leads to an increased range of controller gains to improve damping. This controller can be an add-on control module in the existing control system of the High Voltage DC transmission (HVDC) links. The research also demonstrates that varying damping controller gains beyond a given value adversely impact system stability, which is due to an adverse interaction between the damping controller and the Voltage Source Converter (VSC) HVDC system. This instability can be accurately captured through
electromagnetic transient simulation, rather than the linearised model of the system
largely due to the simplification of HVDC system in transient stability simulation. The
justification for the proposed controller design is provided using eigenvalue sensitivity
analysis. The frequency scanning based Nyquist analysis corroborates the occurrence of damping controller gain related system instability.
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Keywords
Damping controller, System stability, VSC-HVDC, EMT simulation, Frequency scanning technique, Nyquist Analysis