Performance Comparison of LCC and VSC HVDC Systems in Minimizing Long-Term Voltage Collapse

High-voltage direct current (HVDC) transmission helps transmit large energy blocks over long distances. Line-Commutated Converters (LCC) and Voltage Source Converters (VSC) can be used for this purpose. LCC transmission is a mature technology with some drawbacks regarding reactive power consumption. At the same time, VSC transmission is increasing due to its advantages, such as flexible control and reactive power support. LCC and VSC have been compared, but their impact on the performance of large power systems has not been directly analyzed, especially to prevent long-term voltage instabilities. In this paper, a direct comparison of LCC and VSC during an AC fault that leads to voltage collapse will be evaluated in the Nordic32 power system, a case study used for voltage collapse analysis. LCC and VSC technologies will be applied to verify their capacity to prevent system collapse and assess their impact on bus voltages, generator current limiters, and transformer tap changing. A scenario with no active power transmitted by the HVDC will also be analyzed, highlighting the VSC’s capacity to function as a STATCOM. Steady-state and electromechanical analyses will be conducted using PV curves and time-domain simulations. A total of six scenarios were analyzed and results show that both the LCC and VSC technologies were able to prevent long-term voltage collapse when transferring active power through the DC link, although the VSC presented a better performance, being able to prevent voltage collapse even when the active power transferred was set to zero. The VSC was also able to reduce the transformer’s tap changing and prevent generators from reaching their overexcitation limiters.