Author

Silvia Arrua

Date of Award

Summer 2019

Document Type

Open Access Dissertation

Department

Electrical Engineering

First Advisor

Enrico Santi

Abstract

Evolution of semiconductor devices is allowing to implement power electronics technology in a variety of applications, moving traditional AC systems to more efficient and reliable DC systems. Some examples are shipboard power distribution systems, DC microgrids, electric vehicles and more electric aircrafts. Even though these types of systems offer significant advantages that make them attractive in different areas, the interconnection of feedback-controlled power converters leads to emergent dynamic behavior that a system designer must take into account to ensure proper operation of the system. Additionally, system reconfiguration is very likely to happen in applications such as a shipboard power distribution, where the loads and sources may change depending on the current mission or in case of contingency. In these cases, system dynamics will change and the overall stability may be compromised.

Several criteria can be found in the literature to evaluate system stability. More recently, it was shown that the DC bus impedance can be used for this purpose, overcoming some limitations that other criteria had. Additionally, system identification can be used to monitor the bus impedance. However, there is still a need for a method to evaluate the dynamic performance to guarantee that sudden changes in the system will not affect the DC distribution bus significantly.

Active and passive stabilization methods can be implemented to allow for the plug-in capability of new converters to increase the size of the system without compromising the overall stability of the power distribution system. One approach is to implement Positive Feed-Forward control on a load side converter, which introduces a virtual damping impedance at the DC bus. A proper design approach for this damping impedance that will ensure a good stability margin is needed.

To address these challenges, firstly a modelling approach that facilitates obtaining the transfer functions of a multi-converter system is presented. Second, a simplified model of the bus impedance will be developed that will allow to evaluate the system when it undergoes reconfiguration and to take fast corrective actions when they are needed. Third, a design procedure for the required damping impedance based on the bus impedance dominant poles will be proposed. And last, an adaptive and distributed stabilizing controller will be presented to account for changes in the load demand.

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