A spread frequency band control scheme for high power impedance measuring converter with chirp signal injection

The impedance measurement is an effective solution for evaluating the stability of the power system with high penetration of renewable sources. In this paper, the impedance measurement is achieved by a typical high-power impedance measuring converter (HPIM-converter) with chirp signal injection. The modulation saturation phenomenon of the HPIM-converter is revealed and the frequency sweep boundary is analyzed in detail. For expanding the rated frequency range of the HPIM-converter, a spread frequency band control scheme based on the over-modulation technique is proposed in this paper. The proposed control method enlarges the rated frequency band and can inject a disturbance voltage into the system under test with consistent amplitude in the rated frequency band. Also, a smooth transition strategy between linear modulation mode and over-modulation mode is proposed for suppressing signal fluctuation. Finally, the effectiveness of the proposed method is verified by simulation tests.