A Comparative Study of Two Discrete-time HVDC Converter Models

The paper describes the development of discrete-time six pulse HVDC converter models for small signal stability analysis and controller design. Assuming that the converter firing and the end of commutation period as two discrete time instants, a suitable linearized converter model is then interfaced with a current controller and an R-L load to determine the overall system model. Two separate, but similar, methods are used to find the system model. They are state space model with cyclic rate sampling and transfer function model derived using the modified-z transform. The models are then studied through their the stability boundaries and root loci and are verified through digital computer simulation.