A stability criterion based on the common denominator of system-level transfer functions for the multiple multifunctional converters systems

This paper addresses the stability issue of a multiple multifunctional converter system. The proposed criterion is based on impedance numerators and denominators. Firstly, the unified equivalent impedance model of the multifunctional converter is derived. Secondly, a dc bus system, consisting of n multifunctional converters, is introduced to present a number of potential control modes. The stability related transfer functions from each converter's perturbations to bus voltage are deduced. Instead of checking all these transfer functions' stability, their identical denominator T-s, containing equivalent impedances' numerators and denominators, is proposed as the stability criterion. The proposed criterion checks the right-half-plane zeros number (RHPZ) of T-s, once RHPZ number of T-s equals zero, the system is stable. When the system control modes changes, the proposed criterion form is not affected. Experimental results verify the effectiveness of the proposed criterion.