The Study Of Suppressing Low-frequency Oscillation Of Power System Based On Additional Damping Controller Of VSC-HVDC

By installing a gate controlled power electronic devices and pulse widthmodulation（PWM）in voltage source converter based high voltage DC (VSC-HVDC),a higher level of active power and reactive power controllability has been achieved.VSC-HVDC with auxiliary damping controllers successfully suppresses low-frequencypower oscillations for a better DC power modulation. This project, based on researchinga number of literature reviews of basic VSC-HVDC control theory and thecorresponding system modelling. Besides, auxiliary power oscillation damping (POD)controller for low frequency damping improvement in the real power system isconcerned in this project as well. The aim of this research is to analysis the potentialnegative impacts by utilizing auxiliary controller magnitude limiter.In this study, a basic theory of VDC-HVDC hierarchical control will be initiallystudied, then based on these literature reviews, the control of inner power and outercurrent were mainly concerned and will be assessed in detail. A classic VSC-HVDCmodelling was simulated first of all, by applying this system model, the control ofreactive power independent decoupling and the impact on DC voltage has beensuccessfully carried out. After that, by considering the principle of enhancing systempower damping by utilizing auxiliary power oscillation damping (POD) controller andits design strategies, a small four machine power system with DC transmission lineinstalled was utilized. In order to assess the damping improvement difference betweenthe system with POD controller and the one without controller and proved that powersystem with auxiliary controllers provides an acceptable level of power system stabilityimprovement and the suppression of unexpected low frequency oscillations. This paperdiscusses how the magnitude limiter in the damping controller influences control effect,then proposes a new method of using fault recovery signal for damping controller. Thefault recovery signal is a kind of exponentially decay power. By adding it to output ofthe damping controller as the dc power reference can reduce the magnitude of dc powerat early stage of dc power modulation. Within range of allowed dc voltage ripple, the dcpower modulation tends to be in an ideal free damping state, damping more rapidly in comparison with additional damping controller without fault recovery signal. Thus theinfluence of limiter is significantly reduced. This paper also gives the relationship curveof dc power ripple and dc voltage ripple. The simulation results validates theeffectiveness of the proposed damping controller.