Steady-state stability of an HVDC system using frequency-response methods

An HVDC scheme is an amalgamation of both AC and DC components, the behaviour of which is often difficult to describe because of the interdependence of many of the parameters. The response of the DC system is dependent on the AC system and vice versa. The basic scheme controls also include both rectifier and inverter controls, which are basically separate but interdependent. The complete scheme could be described as a nonlinear multivariable control system which is sensitive to external disturbances. The paper describes the analysis of such an HVDC scheme using a simulator model and frequency-response techniques. The results described constitute a sensitivity analysis of the system to the principal parameters which affect the steady-state stability, such as the inverter short-circuit ratio and AC-system damping, as well as the sensitivity to control parameter changes.