Stabilizing positive feed-forward control design for a DC power distribution system using a passivity-based stability criterion and system bus impedance identification

DC distribution systems consist of several feedback-controlled converters interconnected to form a complex power distribution system. While the analysis and design of a single power converter and its control is well understood, in a DC distribution system the situation is different. Analyzing and designing a complex multi-converter system in such a way as to guarantee both system stability and performance is a complex problem that was not fully solved in the past. Difficulties stem from a lack of adequate analysis and design tools, limited understanding of the problem, difficulties in applying the existing stability criteria, and the need for stabilizing converter controllers. To tackle all these difficulties, this paper presents how two recently proposed tools, i.e. the Passivity-Based Stability Criterion (PBSC) and the Positive Feed-Forward (PFF) control, can be used together with a System Identification technique to address system level stability issues in DC distribution systems. In particular, after the frequency-domain measurement of the system bus impedance is taken, a parametric model of the bus impedance can be obtained and used to design a stabilizing PFF control that imposes passivity of the overall bus impedance. If passivity of the overall DC bus impedance is ensured, stability is guaranteed as well. The method is experimentally validated on a system consisting of the cascade of two converters. Two series of results are presented: when we have knowledge of the system model, and when we treat the system as a “black-box”.