VSC transmission model for analytical studies

This paper presents a model of Voltage Source Converter (VSC) based transmission that can be used for wide range of stability studies and controller design with MATLAB software. The model is intended for analytical studies in the frequency domain above 5Hz. The system model has modular structure and includes three separate units in state-space form: AC rectifier model, AC inverter and DC system model. The converters, controllers and Phase Locked Loop (PLL) units are included in the DC model and the model is linked with other units using input-output matrices in the state-space models. The converter non-linear model is linearised assuming small deviations around the steady-state. The model is tested against the PSCAD/EMTDC non-linear model and the results show satisfactory accuracy. The tests also confirm that the analytical model well represents multivariable system properties. An example of the model use is given showing the eigenavlue study of the influence of PLL gains on the system stability. It is concluded that increased PLL gains deteriorate system stability.