• Purpose

Self-commuted Voltage Source Converter (VSC) can significantly extend the flexibility and operability of HVDC system and be used to implement the concept of Multi-Terminal HVDC (MTDC) grid. In order to take full advantage of MTDC systems, its overall behavior must be characterized in quasi static and dynamic states. Based on the numerous literatures, a dedicated 2-level VSC model and its local controllers as well as DC grid voltage regulators are developed for this purpose. Furthermore, the requirement of the system to guarantee all the physical constrains must be well-assessed and concrete demonstrations must be provided by numerical simulations.

• Design/methodology/approach

Firstly, a 2-level VSC model and its local controllers as well as DC grid voltage regulators are developed. Then, various DC cable models are investigated and their characteristics are assessed in the frequency domain. Those developed models are combined to form a 3-Terminal HVDC grid system on Matlab/Simulink platform. To analyse the stability of this electrical system, the dynamics of the system against variations of power dispatch are observed.

• Findings

To analyse the stability of this electrical system, the dynamics of the system against variations of power dispatch are observed. The differences in the DC grid voltage dynamics and the power flow of the converter stations coming from the embedded primary controls are analysed and the technical requirements for both cases are assessed.

• Originality/value

In this paper, the dynamic stability of a MTDC system has been analysed and assessed through an ade-quate simulation model including its control scheme and the cable models. The interest of the improved PI model for cables are highlighted.