Dynamic Analysis of VSC-HVDC System with Disturbances in the Adjacent AC Networks

VSC-HVDC systems are widely used to integrate wind farms, asynchronous generations and networks operating at different frequencies. The Multi-terminal (MT) and multi-fed (MF) HVDC’s are the system mainly constituted of VSC’s, to integrate renewable sources and transmitting bulk power to conventional AC grids. A sudden change in the steady state even in adjacent networks may create severe disturbances in the operation of such HVDC systems. The disturbances in AC or DC networks directly influence the performance of systems, particularly in MT-HVDC and MF-HVDC systems. However, the HVDC systems are known for their intelligent control in modulating operational states as and when required. This paper presents the dynamic analysis of MF-HVDC system due to load changes, faults and other disturbances in the adjacent AC networks. The result indicates that VSC-HVDC provides decoupled control of active and reactive power with capability in adjusting operational mode during various minor and major disturbances. Based on the results obtained, the paper proposed a novel sensitivity factor indicating percentage coupling among various line parameters during disturbances. Furthermore, the VSC’s injects harmonic signals on both AC and DC sides of HVDC system. These harmonics voltage or currents signals may get amplified to a dangerously high magnitude at resonance frequencies. Thus, the frequency characteristics of different subsystems are also analyzed using FFT. A ±100 kV, 200 MW bipolar MF VSC-HVDC test systems is used to simulated the results in MATLAB/Simulink software.