Research on the Voltage Supporting Capability of Multi-VSC-HVDC Subsystems Operation Strategy to Receiving-end LCC-HVDC Network in Weak AC Grid

For the hybrid multi-infeed HVDC system in which the receiving-end grid is a strong AC grid including LCC-HVDC subsystems and multiple VSC-HVDC subsystems, it has higher voltage support capability. However, for weak AC grid, the voltage support capability of the multi-VSC-HVDC subsystems to the LCC-HVDC subsystem (voltage support capability-mVSCs-LCC) can resist the risk of commutation failure. Based on this consideration, this paper proposes an evaluation index called Dynamic Voltage Support Strength Factor (DVSF) for the hybrid multi-infeed system, and uses this index to qualitatively judge the voltage support capability-mVSCs-LCC in weak AC grid. In addition, the proposed evaluation index can also indirectly judge the ability of the LCC-HVDC subsystem to suppress commutation failure. Firstly, the mathematical model of the power flow of the LCC and VSC networks in the steady-state is analyzed, and the concept of DVSF applied to hybrid multi-infeed system is proposed. Furthermore, the DVSF index is also used to qualitatively judge the voltage support capability-mVSCs-LCC. Secondly, the influence of multiple VSC-HVDC subsystems with different operation strategies on the DVSF is analyzed with reference to the concept of DVSF. Finally, the indicators proposed in this paper are compared with other evaluation indicators through MATLAB simulation software to verify its effectiveness. More importantly, the effects of multi- VSC-HVDC subsystems using different coordinated control strategies on the voltage support capability of the receiving-end LCC-HVDC subsystem are also verified.