A Novel Forbidden-Region-Based Stability Criterion in Modified Sequence-Domain for AC Grid-Converter System

A novel forbidden-region-based criterion (N-FRBC) is proposed in modified sequence-domain for an ac grid-converter system. Compared with the forbidden-region-based criterion (FRBC) in
dq
-domain, the number of constraint conditions is reduced due to the mirror frequency symmetry of the impedance ratio matrix in modified sequence-domain. In addition, the improved forbidden region decreases the conservatism of the FRBC. Simulation and experimental results verify the effectiveness and correctness of the proposed N-FRBC in studying the stability issues of the ac grid-converter system.