Employing SVC at weak LCC HVDC terminals and comparison with VSC HVDC

This paper studies system-level impact of an SVC connected to a LCC HVDC terminal, in particular in the context of weak AC systems. The real power flow is varied from zero to full power at each of the HVDC terminals and the system variables are observed when fixed capacitive support is applied and comparatively when an SVC is connected. The SVC at the LCC HVDC terminal brings significant operating advantages, and in particular it can provide a cost effective means of assisting HVDC operation into a weak AC system. The SVC can be used in combination with the filter and reactive power banks associated with the LCC HVDC terminal to meet the total reactive power demand of the system. The peak AC voltage at HVDC terminals connected to a weak AC system (SCR=2.5) can reach over 1.47pu for load rejection, when fixed capacitors provide reactive power. The study shows that using SVC with a TCR dynamic rating of 0.335pu, the peak AC voltage is limited to 1.16pu. This also substantially improves stability margin and transient response. The LCC HVDC with SVC is further analysed on PQ diagrams from the grid connection point. Comparing with PQ diagrams for similarly rated VSC HVDC and LCC HVDC converters With the addition of an SVC to the LCC it has a wider operating area at high powers compared to VSC HVDC, which may be welcome by grid operators.