Research on the Operation Performance Enhancement of Hybrid AC/DC Power System With Multi-Type Embedded HVDC

The embedded high voltage direct current (HVDC) transmission is a key strategy for augmenting power transmission capacity within limited corridors, particularly for large-scale renewable energy integration. Multi-type embedded HVDC combines advantages of different HVDC technologies, serving as an important method to improve the operation performance of the hybrid AC/DC power system. This paper investigates the impacts of multi-type embedded HVDC on the operation performance of the system, indicating the enhancement from multiple steady-state and transient perspectives. The coupling effects of power transmission and bus voltages are incorporated in the analysis, and three types of embedded HVDC systems are involved, including line-commutated converter (LCC), static synchronous compensator supported line-commutated converter (SLCC) and voltage source converter (VSC). The apparent increase in short circuit ratio (AISCR) indices are evaluated to measure the enhancement in terms of maximum available power (MAP), commutation failure immunity index (CFII) and temporary overvoltage (TOV) quantitatively. The fault recovery process is also studied with comprehensive analysis of the dynamic characteristics. The embedded SLCC-HVDC and VSC-HVDC systems provide reactive power compensation through tie lines, significantly enhancing MAP and fault recovery performance of the system. Static var generator (SVG) capacity cannot be fully exploited under the independent and constant control modes of SVG and VSC in analysis of CFII and TOV performance. A shorter electrical distance between receiving-end subsystems will be more beneficial to the enhancement and should be considered in the system planning.