Small signal modelling and stability analysis of multiterminal VSC-HVDC

Two control strategies are implemented for multiterminal voltage sourced converter (VSC)-based HVDC (M-VSC-HVDC). A test system consisting of five terminals was developed in PSCAD. In-Strategy 1, the Predictive controller is implemented in the inner control loop whereas strategy 2 using proportional-integral-derivative controller (PID). Small signal analytical models for two terminal VSC-HVDC are developed within MATLAB. Simulation is performed using PSCAD to verify and validate the conclusions from the analytical models. A detailed comparison study between the two strategies is carried out. An eigenvalues stability study for very weak AC system is also presented. Strategy II is seen to be adequate for advanced control design for multiterminal M-VSC-HVDC system for higher power applications. The potential of the supplementary DC voltage feedback to enhance the dynamic stability is considered. It is shown that in order to enhance system robustness it is important to use additional DC voltage feedback with strategy II on all stations operating with DC current/power regulation. The simulation results show that the supplementary DC voltage feedback contribute significantly toward improving the dynamic behavior of the M-VSC-HVDC system under a wide range of operating conditions.