Generalized modeling of DC grid for stability studies

This paper presents a mathematical model that can be used to analyze and study transient and small signal stability of large multi-terminal HVDC networks. The model describes converter ac side and dc grid electromagnetic transients in detail, and can also incorporate basic HVDC controllers, such as current, dc voltage, and active and reactive power controllers, including dc voltage-active power droop-control. Also, it shows the necessary interfacing procedures to link converter ac side and dc grid dynamic equations to that of the control systems using power balance equations, where the converter semiconductor losses are incorporated. The validity of the presented model is confirmed against a detail model where the converters are modeled by their switch models on a six-terminal dc grid. Additionally, results illustrate the model´s ability to predict dc grid transient response and small signal stability, which are presented and discussed.