This paper investigates the steady-state and transient performance of high-voltage DC (HVDC) transmission systems connected to passive network. The VSC HVDC tie employing PWM may well represent the ultimate FACTS device. In addition to the control of the active power flow, it can supply reactive power and provide independent dynamic control at its two terminals. The control systems for rectifier and inverter are discussed in DC (HVDC) transmission systems based on three-level voltage source converters.
The study involves analysis of active-reactive power capabilities (P-Q envelope) including active power flow and provision of voltage support to AC networks. The transient performance is explored by examining the VSC_HVDC response to external AC faults. Finally, the models and results are presented and tested by simulations using Matlab Simulink and its toolbox SimPowerSystems.