Comprehensive review of stability criteria for DC distribution systems

Power-electronics-based DC power distribution systems, consisting of several interconnected feedback-controlled switching converters, suffer from potential degradation of stability induced by negative incremental impedances due to the presence of constant power loads. For this reason, the stability analysis of these systems is a significant design consideration. This paper reviews all the major stability criteria for DC distribution systems that have been developed so far: the Middlebrook Criterion, the Gain Margin and Phase Margin Criterion, the Opposing Argument Criterion, and the Energy Source Analysis Consortium Criterion. In particular, the paper discusses, for each criterion, the artificial conservativeness characteristics in the design of DC distribution systems, and the formulation of design specifications so that the system would be stable. Finally, the Passivity-Based Stability Criterion is discussed, which has been recently proposed to reduce design conservativeness and improve design-oriented characteristics. While all prior stability criteria are based on forbidden regions for the polar plot of the so-called minor loop gain which is an impedance ratio, the proposed criterion is based on imposing passivity of the overall bus impedance. However, stability is clearly an insufficient requirement for DC power distribution systems; performance is also a requirement. A simulation example is presented to illustrate that the Passivity-Based Stability Criterion guarantees both stability and performance.