Small-Signal Modelling of Hybrid Bipolar HVDC Transmission Systems

Hybrid high-voltage direct current (HVDC) transmission system combines the advantages of line commutated converter based high voltage direct current (LCC-HVDC) featuring large transmission capacity and low cost, with voltage source converter based HVDC (VSC-HVDC) systems that eliminate commutation failure risks. However, there are fewer studies dedicated to analyzing the stability of hybrid bipolar based HVDC transmission systems. In order to address the concern, this paper formulates a small-signal model for an HB-HVDC configuration where both poles utilize LCC rectifiers and VSC inverters to provide a critical model foundation for subsequent stability analysis. Firstly, the state space equations are obtained based on the system configuration and control mechanism. Secondly, the system-wide small-signal model is obtained by linearization at the steady state point of operation. Finally, under small disturbances, the results from the PSCAD/EMTDC electromagnetic transient simulation model are compared with those from the MATLAB dynamic small-signal model response to confirm the correctness of the established small-signal model.