A Virtual Excitation-Based Method for Self-Impedance Measurement of Three-Phase Converters

With the massive deployment of converter-based power generation, low-frequency oscillations (LFOs) such as subsynchronous oscillations (SSOs) caused by converter-grid interactions have garnered widespread attention. Accurate fieldmeasurement of low-frequency impedance for grid-connected converters is essential for the stability assessment. However, it is challenging for high-voltage and power converter systems, due to the high cost of impedance measurement equipment. To address the issue, a three-step equivalent transformation of the external voltage excitation source to a virtual excitation source is proposed, which facilitates imposing the excitation signals directly into the control system of the converter under test. Such equivalence is mathematically proven, demonstrating that the virtual excitation source can ensure an accurate self-measurement of the lowfrequency impedance of grid-connected converters. Finally, the effectiveness of the virtual excitation source injection method is validated through experimental tests.