Accurate fault location in bipolar flexible HVDC transmission lines is crucial for fault isolation, system restoration, and maintenance efficiency. However, due to the strong nonstationary nature of fault transient signals, along with noise, transition resistance, high-frequency attenuation, and harmonic interference, the initial traveling-wave wavehead is often difficult to identify precisely. To address this, this paper proposes a double-ended fault location method based on variational mode decomposition (VMD), synchrosqueezing transform (SST), and the whale optimization algorithm (WOA). First, WOA adaptively optimizes VMD's key parameters (mode number and penalty factor) to improve decomposition quality. Then, SST is applied to the selected sensitive IMF to obtain a concentrated time-frequency representation, enabling precise identification of the wavehead arrival instant. Finally, the double-ended traveling-wave equation yields the fault position. A bipolar flexible HVDC simulation model is established, and the proposed method is evaluated under various fault locations, types, transition resistances, and noise levels. Results show that the proposed method effectively improves wavehead extraction accuracy and achieves higher fault-location precision and robustness compared to conventional double-ended traveling-wave methods and other benchmark schemes. This method offers an effective technical approach for precise fault location in bipolar flexible HVDC transmission lines.

variational mode decomposition, synchrosqueezing transform, whale optimization algorithm, fault location