Parameter Identification With PMUs for Instability Detection in Power Systems With HVDC Integrated Offshore Wind Energy

Large-scale offshore wind farms can be integrated with onshore ac grids by the voltage source converter based high voltage direct current (VSC-HVDC) technology. The resulting impact on the security of ac grids can be significant. Therefore, it is important to develop an HVDC model for online stability monitoring of the integrated ac/dc systems. This paper proposes a new HVDC model based on a circuit-theoretic foundation. With the available phasor measurement units (PMUs) at VSC stations, the parameters of the HVDC equivalent model can be identified in real-time by synchronized voltage and current phasor measurements at VSC ac terminals. The proposed HVDC model is applied to online voltage instability detection for integrated ac/dc systems by the Thevenin impedance matching. The HVDC equivalent circuit enables the Thevenin equivalent impedance of the HVDC-connected offshore wind farm to be determined directly from the PMU measurements. Numerical simulations are performed on the IEEE 39-bus system with an HVDC-connected offshore wind farm to validate the effectiveness of the proposed HVDC model.