Power Oscillation Damping using VSC-based Multi-terminal HVDC Grids

This paper presents a Power Oscillation Damping (POD) controller for use with Voltage Source Converter based Multi-terminal Direct Current (VSC-MTDC) grids. The controller has been tested on a large meshed AC network into which a five bus, six line VSC-MTDC network has been incorporated. The controller is designed using a Modal Linear Quadratic Gaussian (MLQG) approach allowing targeted control action on critical low-frequency oscillatory modes. By taking multiple delayed wide area signals and modulating active power injection by multiple VSC-MTDC converter stations, significant improvement in system stability is seen. The effect of blocking the POD controller's active power modulation signals to specific VSC-MTDC converter stations is assessed. Such a blocking feature may be desirable at points of connection with weak AC networks which might be temporarily unable to tolerate modulation in active power injection and instead require a fast return to steady state constant power injection. Even with modulation signals blocked, the post disturbance system performance is significantly enhanced, demonstrating the redundancy in using VSC-MTDC for oscillation damping. The controller performance has been assessed through both small and large disturbance analysis.