Stability improvement through HVDC upgrade in the Australian equivalent system

A case study on the Australian equivalent system - recently adopted as an IEEE benchmark for stability studies - is presented here to illustrate power oscillation damping through HVDC links. Wide-area signals are used for supplementary modulation of the HVDC power order driven through a multi-variable controller. The test case is set up in DIgSILENT and benchmarked against the standard results. Linearized model around the nominal condition is obtained by using subspace identification on a set of measurements derived out of probing the system through the HVDC link. Modal analysis is carried out to identify a set of appropriate feedback signals for the controller. Pole-placement technique is used to design a multi-input, single-output (MISO) controller in two different frameworks - i) observer driven state feedback and ii) optimized lead-lag compensators. The effectiveness of HVDC modulation for power oscillation damping is validated through eigen-value analysis and non-linear simulation (in DIgSILENT) over a range of operating conditions.