Perturbation observer based adaptive passive control for damping improvement of multi-terminal voltage source converter-based high voltage direct current systems

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Abstract
This paper proposes a Perturbation Observer-based adaptive passive control (POAPC) for damping improvement of multi-terminal voltage source converter-based high voltage direct current (VSC-MTDC) systems. The POAPC is designed for an N-terminal VSC-MTDC system, and the perturbation is defined as a lumped term including interactions between terminals, unmodelled dynamics and unknown external disturbances, which are estimated online via a perturbation observer. Then an extra system damping is injected for each terminal to improve the transient dynamics via passivation. The POAPC does not require an accurate system model and measurements of full states; only the DC voltage and active and reactive power need to be measured. Case studies are carried out on a four-terminal VSC-MTDC system under four scenarios such as active and reactive power reversal, faults at AC bus, offshore wind farm connection, and fast time-varying parameter uncertainties. Simulation results verify its effectiveness under various operating conditions, compared with that of conventional proportional-integral (PI) control and classical passive control (PC).

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