Simulation Studies For Mmc–Hvdc Grid Using Ieee-39-Bus System By Enhanced Dc Voltage Droop-Control With Active Filters

N Gangadhar


In this paper, the dc network dynamics of VSC-HVDC systems is investigated through enhanced dc voltage droop-control with active filters . The Filter analysis has been used to identify the factors that have an impact on the system stability. It has been determined that instability in the form of sustained oscillations can take place, and that the operating point, the dc side electrical characteristics, the strength of the ac system and the controller structure, are the major factors that impact the stability of the system. A frequency domain approach is proposed in this paper in order to explain the instability that occurs in the system. A two-terminal VSC-HVDC system is modelled as a SingleInput-Single-Output feedback system, and the VSC-system and the dc grid transfer functions are defined and derived. The proposed droopcontrol structure also autonomously imposes energy balance between the HVDC grid and its host ac system. Feasibility and performance of the proposed control method are evaluated based on time-domain simulation studies in the MATLAB platform, using the IEEE-39-Bus system that imbeds a five-terminal VSC– HVDC grid with filters. Each VSC station is a monopolar modular multilevel converter (MMC). The study results show that the proposed droopcontrol method enables the HVDC-AC system to reach a new steady state after transient events.

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