A Novel Rapid Wideband Impedance Measurement Method for Three-Phase Power System

Precise wideband impedance measurement for a power grid is crucial for small-signal stability analysis of the grid-connected converter system. Various techniques have been investigated for grid impedance measurements. However, errors may arise due to the coupling of system impedance. For example, an injection intended to perturb phase A only may inadvertently affect phases B and C, distorting the grid impedance measurement results. Traditionally, different injections at the same frequency are performed into each phase sequentially to avoid frequency overlap, making the measurement time-consuming and susceptible to operating point variations. To address these issues, this paper proposes a novel rapid wideband impedance measurement approach for the three-phase power system using alternate harmonic disturbance injection. The disturbance signal is innovatively designed into three groups of complementary or interleaved wideband perturbations, which are alternately injected into phases A, B, and C. This approach not only mitigates the response overlapping effect, thereby improving the measurement accuracy, but also enhances the speed of the impedance measurement. Additionally, a multifrequency harmonic perturbation device (MHPD) based on cascaded H-bridges is designed to generate target wideband perturbations. Finally, the hardware-in-the-loop (HIL) experimental results demonstrate the effectiveness of the proposed approach and MHPD.