Inverse Nyquist Stability Criterion for Grid-Tied Inverters.

A new impedance-based stability criterion was proposed for a grid-tied inverter system based on a Norton equivalent circuit of the inverter <xref ref-type="bibr" rid="ref18">[18]</xref>. As an extension of the work in <xref ref-type="bibr" rid="ref18">[18]</xref>, this paper shows that using a Thévenin representation of the inverter can lead to the same criterion in <xref ref-type="bibr" rid="ref18">[18]</xref>. Further, this paper shows that the criterion proposed by Middlebrook can still be used for the inverter systems. The link between the criterion in <xref ref-type="bibr" rid="ref18">[18]</xref> and the original criterion is the inverse Nyquist stability criterion. The criterion in <xref ref-type="bibr" rid="ref18">[18]</xref> is easier to be used. Because the current feedback controller and the phase-locked loop of the inverter introduce poles at the origin and right-half plane to the output impedance of the inverter. These poles do not appear in the minor loop gain defined in <xref ref-type="bibr" rid="ref18">[18]</xref> but in the minor loop gain defined by Middlebrook. Experimental systems are used to verify the proposed analysis. [ABSTRACT FROM AUTHOR]