Comparative Analysis of Inter-Inverter Interactions in Emerging Hierarchical-Infeed and Conventional Multi-infeed LCC-HVDC Systems

The emerging hierarchical-infeed LCC-HVDC (HIDC) system has been recently commissioned for the long distance bulk power transmission in China. Compared to the conventional multi-infeed LCC-HVDC (MIDC) system with inverters coupling only in the ac-side, different inter-inverter interactions exist in the HIDC system where inverters couple in both the ac- and dc- sides. It is beneficial to reveal the underlying difference of the inter-inverter interactions in the HIDC and MIDC systems for determining which system should be adopted in the planning study. However, this difference has not been clearly revealed yet in earlier works. Thus in this paper, the inter-inverter voltage interaction factor (IVIF) index is firstly introduced to quantitatively assess the inter-inverter interactions. The analytical calculation methods of the IVIF for the HIDC and MIDC systems are also presented for the satisfactory accuracy and efficiency. Moreover, these methods are further used for comparative analysis of parametric dependence of the IVIF in the HIDC and MIDC systems considering various system parameters, operation variables and dc control modes. The analysis results clearly reveal the underlying difference of the inter-inverter interactions in the HIDC and MIDC systems. Finally, the effectiveness of the theoretical assertions is verified by experiments based on the hardware-in-the-loop platform.