Revisiting frequency coupling effects in grid-tied converter: A phase shifting transformer based circuit modeling framework

•The frequency coupling effect is revisited from the viewpoint of complex circuit analysis.•A grid-tied converter system can be categorized into strongly, weakly coupled, and decoupled specifically.•The frequency coupling effect is caused by the rotation of complex-valued vectors and admittance mismatching.•The phase-shifting transformer-based circuit modeling and analysis framework is proposed.