Modeling, Analysis and Suppression of Wide band Instability in Large Scale Power Systems with Single Phase and Three Phase VSCs

Abstract:
This PhD project focuses on generic modelling, stability analysis and broadband oscillation suppression of unbalanced multi-converter systems with both single-phase and three-phase voltage-source converters (VSCs), aiming at forming a series of methodologies by seeking solutions to these issues and thereby to instruct the validations in a more scientific and coherent way. Specifically, a harmonic state space (HSS) model will be built based on the linear time-periodic (LTP) system theory, which is applicable for three-phase unbalanced systems. The frequency coupling dynamics of multiple time-periodic operating trajectories can be captured by HSS modelling, which provides accurate assessments on the harmonic stability, though their multiple-input, multiple-output (MIMO) nature tends to complicate the system stability analysis with the high computational power as a demand. Therefore, Model Reduction Methods will be developed for lightening the computational burden. Apart from stability assessments and exploration of dynamic interaction between different converters, oscillation propagation and oscillation source localization will also be analyzed, which should be addressed in these large-scale systems consisting of multiple different converters. Simultaneously, an additional active damper that is effective in a wide frequency range will be proposed as an oscillation suppression measure, which might be a better option than the controller improvement method for a single converter and a specific frequency band. The proposed active damper should be independent from other converters in the system and self-stabilizing to avoid introducing new instability risks, and it can provide reasonable dynamic compensation with low power loss. The outcomes might achieve a breakthrough in stability improvement for large-scale power electronic-based power systems.

Funding:
CSC Scholarship