Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Electrical Engineering

Sub-Department

Electrical Engineering

First Advisor

Enrico Santi

Abstract

In modern times there has been an increased penetration of power electronic converters into Power Distribution Systems. In particular, there has been a strong interest in DC Power Distribution Systems as opposed to conventional AC Power distribution systems. These DC Power Distribution Systems are enabled by power electronics converters. The strong interest is motivated by improvements in power electronic converter technology, like advances in power semiconductor devices, magnetics, control, and converter topologies which have made possible to build high-performance converters at low cost. In many systems, such as cars, ships and airplanes, there has also been a trend towards the replacement of a number of older mechanical and hydraulic systems with electrical power-electronic-based systems, since these systems provide a number of advantages such as increased system flexibility, reliability, long life expectancy and decreased weight, size, and cost.

Together with these advantages, DC Power Distribution Systems offer system-level challenges related to system stability issues and design of individual converter controllers to guarantee proper operation of the interconnected system. System-level stability issues may arise due to interactions among feedback-controlled power converters, which are part of such a large interconnected system. These feedback-controlled power converters exhibit negative incremental input impedance within their control bandwidth. As a result, a power converter that was satisfactorily performing when tested as a standalone unit may experience degradation in performance when connected as part of a system.

While the analysis and design of a single power converter and its controls is well understood, in a DC Power 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, the present work proposes two tools to address system level stability issues in DC Power Distribution Systems: the Passivity-Based Stability Criterion (PBSC) and the Positive Feed-Forward (PFF) control.

The PBSC is proposed as a tool for stability analysis in a DC Power Distribution System. The criterion is based on imposing passivity of the overall DC bus impedance. If passivity of the bus impedance is ensured, stability is guaranteed as well. The PBSC, which imposes conditions on the overall bus impedance, offers several advantages with respect to existing stability criteria, such as the Middlebrook criterion and its extensions, which are based on the minor loop gain concept, i.e. an impedance ratio at a given interface: reduction of artificial design conservativeness, insensitivity to component grouping, applicability to multi-converter systems and to systems in which the power flow direction changes, for example as a result of system reconfiguration. Moreover, the criterion is very designed-oriented because it can be used in conjunction with the second tool proposed in this dissertation, the PFF control, for the design of stabilizing virtual damping networks. The PFF controller design formulation guarantees both stability and performance (a challenge not fully solved in the past, as previously stated). By designing the stabilizing virtual impedance so that the bus impedance passivity condition is met, the approach results in greatly improved stability and damping of transients on the DC bus voltage. Simulation validation is performed using a switching-level-model of the DC power distribution system. Experimental validation is carried out on a DC power distribution system built in the laboratory.

Rights

© 2013, Antonino Riccobono

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