<p>In the stability assessment of large-scale renewable energy plants, the collector cables between voltage source converter (VSC)-based generation units usually cannot be neglected. However, when constructing the state-space model of the entire multi-converter-based power system, the interconnection between the <i>L</i>-/<i>LCL</i>-filtered VSCs and collector cables cannot be achieved, since they both use the node voltage as input. Moreover, accounting for the distributed parameter and frequency-dependent characteristics of long transmission cable (LTC) complicates the state-space modelling process of the system. In the paper, an innovative idea is proposed to combine the models of the collector network and LTC, and a new composite model is derived which can be interconnected with <i>L</i>-/<i>LCL</i>-filtered VSCs. Specifically, the fitting rational transfer function is generated by applying the vector fitting method on the terminal impedance model of the LTC considering the frequency-dependent characteristics. Then, based on this rational transfer function, a dq-domain state-space model of LTC is established. In addition, a modular subsystems interconnection method is presented for constructing the overall state-space model of the power system. The proposed modelling method does not require the additional virtual resistor used in previous literatures. Finally, the effectiveness of the proposed state-space model is validated by experimental results.</p>