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As a unified framework to describe a converter system in the presence of both source and load system interactions under both feedforward and feedback control, a general minor loop gain stability criterion using the two extra element theorem is proposed. To derive the general minor loop gain and analytically interpret the source and load system interactions, small-signal models by using the g-parameter representation are used. As an illustrative example, a buck converter system with a source and a load system is considered. The stability improvement of the whole system by a positive feedforward control is demonstrated by simulation in frequency and time domain. The proposed design approach of a positive feedforward control acts as active filter improving input port stability at high frequencies. The stability improvement is obtained with limited sacrifice of system bandwidth and no hardware modification of the physical system.
Cho et al. (Wed,) studied this question.