LAUSR

Motivated by emerging oscillation issues of high-voltage direct-current (HVDC) transmission system resulted from the interaction with AC grids, impedance-based stability analysis becomes an attractive approach in the de-risking studies due to the capability of black-box modelling and clear physical meaning. However, impedance-based stability assessment of HVDC is typically conducted either from the AC side or from the DC side, without fully considering both AC and DC grid dynamics, thus impairs evaluation accuracy. In this paper, the nodal admittance matrix based resonance mode analysis method is extended to include both AC and DC dynamics through formulating a hybrid AC-DC admittance matrix. To achieve this goal, HVDC interfacing-converters are modelled as three-port admittance networks with one DC port and two AC ports (in dq-frame) integrating both the AC side frequency coupling and the AC-DC dynamic coupling. In contrast to the widely adopted Nyquist-based methods, the proposed method does not requires knowing the number of right half-plane poles of system minor-loop gain, thus simplifies stability analysis, and moreover, the participation factors of both AC and DC grid nodes in critical resonance modes can be identified through eigenvalue-decomposition analysis, which is in favor of the design of mitigation measures. The effectiveness of the proposed method is validated by EMT-simulations in MATLAB/Simulink.