Multivariable interaction indicators for VSC transmission controller design

This paper describes the multivariable study of a controller for a VSC (voltage source converter) transmission system, with fast operation and good stability. Multivariable analysis based on frequency dependent condition number is used rather than the traditional root locus and step response investigation. The controller´s fastest loop is required to provide good performance for the inverter side DC voltage. The condition number is found suitable to select the most beneficial input/output combination for the stabilising feedback loop, which is used to improve performance of the fast DC voltage controller. The two particular combinations of input and output signals are found to have potential to improve performance of the DC voltage controller. The results and conclusions are verified using PSCAD/EMTDC time-domain simulation