Impedance Specification and Stability Analysis for the AC Grid-Converter System in Modified Sequence-Domain

Abstract In the ac grid-converter system, the mismatching between the load-impedance and source-impedance have caused many instability issues, such as low-frequency oscillation, harmonic instability and sub-synchronous oscillation. Therefore, the individual impedance specification of every subsystem is very important to avoid impedance mismatching. In this paper, a typical impedance model and of the single-phase ac grid-converter is built in modified sequence-domain. And then, based on the forbidden-region-based criterion (FRBC), a novel impedance specification of the ac grid-converter system is proposed, which provides a sufficient condition for system stability and guide the individual impedance design of the source and load. Compared with the existing impedance specification of the ac grid-converter system, the proposed impedance specification is simpler and has less conservatism. Simulation results verify the effectiveness and the correctness of proposed impedance specification for the ac grid-converter system.