Impedance measurement is an effective solution for evaluating stability of a 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. To expand the rated frequency range of the HPIM-converter

a spread frequency band control scheme based on an 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.