Design robust cascade control structure for voltage source converters

This paper proposes a novel robust cascade structure which has better performance when the transmission line undergoes a perturbation. Cascade control structure is normally used when the control procedure can be split into two (or more) cascaded parts. Compared with the conventional cascade control structure which has a limited ability to handle the perturbation in the plant model, the novel structure has better robustness when the transmission line inductance varies. After introducing their structures, the poles and zeros of the closed-loop system related to the conventional and the robust cascade structures will be generated and used to analyze their stability. To verify the theoretical analysis, both cascade structures are applied to a voltage source converter (VSC) and are simulated in MATLAB/Simulink. The different step responses are plotted and analyzed with increasing the transmission line inductance.