Stability enhancement of an interconnected AC/DC power system through VSC-MTDC operating point adjustment

- Operating point adjustment for stability enhancement in a two-area power system.
- Power system areas interconnected by both a weak AC tie line and a VSC-MTDC network.
- Operating point adjustment executed using active and reactive power setpoints of VSCs.
- Setpoint adjustment based on sensitivity to HB for dynamic stability enhancement.
- Setpoint adjustment based on optimized PTDFs for transient stability enhancement.

This paper investigates the improvement of dynamic and transient stability in interconnected AC/DC power systems through operating point adjustment in an embedded VSC-MTDC network. Hopf Bifurcation (HB) is known to result in oscillatory instability in the power system, therefore a sufficient margin to HB has to be maintained to enhance the dynamic stability and ensure a secure operation of the system. The enhancement of dynamic stability is based on the adjustment of the MTDC converters' controller setpoints to drive the system away from HB point and increase the damping of oscillatory modes. The variation of each setpoint is calculated in proportion to the eigenvalue sensitivity to the respective setpoint. On the other hand, transient stability enhancement is based on operating point adjustment according to Power Transfer Distribution Factors (PTDFs) with the aim to reduce inter-area power flow over AC lines. The proposed method is applied to a VSC-MTDC network interconnecting two IEEE 14-bus sections. The results show an improvement in the system's stability margin in case of various disturbances such as load increase and short circuit fault. Time-domain simulations in DIgSILENT are used to corroborate the results obtained through small signal stability analysis.