  Small-signal instability issues of interconnected converter systems can be
addressed by the impedance-based stability analysis method, where the impedance
ratio at the point of common connection of different subsystems can be regarded
as the open-loop gain, and thus the stability of the system can be predicted by
the Nyquist stability criterion. However, the right-half plan (RHP) poles may
be present in the impedance ratio, which then prevents the direct use of
Nyquist curves for defining stability margins or forbidden regions. To tackle
this challenge, this paper proposes a general rule of impedance-based stability
analysis with the aid of Bode plots. The method serves as a sufficient and
necessary stability condition, and it can be readily used to formulate the
impedance specifications graphically for various interconnected converter
systems. Experimental case studies validate the correctness of the proposed
method.
