Impedance Characteristic Analysis and Phase-Locked Angle Feedforward-Based Stability Improvement for LCC-HVDC in Sending AC Grid

With the increasing penetration of wind power, the line-commutated converter-based high-voltage direct-current (LCC-HVDC) system in sending AC grid faces a potential risk of sub/super-synchronous oscillations (SSSOs), which threatens the stability of the power system. The impedance-based method is an effective way to analyze and suppress the SSSOs. However, since the effects of each control part in LCC-HVDC on the stability of sending AC grid are not yet well-investigated, there is a lack of theoretical guidance for implementing the impedance reshaping strategy for LCC-HVDC. Therefore, this paper establishes and analyzes the modular impedance model of LCC-HVDC, to elucidate the contribution of each control part and the interaction between different control loops. On this basis, an impedance reshaping strategy based on phase-locked angle feedforward (PAF) is proposed to improve system stability by attenuating the interaction. Compared to the existing virtual impedance-based method, the proposed PAF-based method addresses its possible failure in suppressing the SSSOs of sending AC grid. The theoretical analysis and experimental results validate the aforementioned conclusions and the effectiveness of the proposed impedance reshaping strategy.