Voltage Stability Improvement in Multi-Terminal HVDC grids: A Case Study of Cigré B4 HVDC Test Grid

High voltage direct current (HVDC) breaker is among the essential components of HVDC grids. Currently, DC circuit breakers (DCCBs) of HVDC grids require relatively large DC reactors to limit the rate of increase of fault current. However, DC reactors have destructive effects on the multi-terminal HVDC (MT-HVDC) grid dynamic stability, and in such a system, despite the variety of controllers, the system dynamics are highly sensitive to the operating point. This paper proposes a modification to be applied to the droop control of Multi-terminal HVDC (MT-HVDC) grids for stabilizing the DC voltage and power variations in case of transient events by the introduction of a Dead Band Direct Current Power System Stabilizer (DBDC-PSS). Also, this paper presents the classification of MT-HVDC grid dynamic behavior in different scenarios including without DC-PSS, conventional DC-PSS, and DBDC-PSS. All simulations and analytical studies are conducted on Cigré DCS3 test HVDC grid in MATLAB/Simulink.