Events at Department of Energy Technology

PhD defence by Omid Lorzadeh

Time

14.10.2021 kl. 16.00 - 19.00

Description

Omid Lorzadeh, AAU Energy, will defend the thesis "Active Stabilization Techniques for Cascaded Systems in DC Microgrids"

TITLE

Active Stabilization Techniques for Cascaded Systems in DC Microgrids

PHD DEFENDANT

Omid Lorzadeh

SUPERVISOR

Associate Professor Mohsen Soltani

CO-SUPERVISOR

Associate Professor Amin Hajizadeh

MODERATOR

Associate Professor Matthias Mandø

OPPONENTS

Associate Professor Sanjay Kumar Chaudhary, Aalborg University (Chairman)
Professor Martin Ordonez, Electrical and Computer Engineering, The University of British Columbia, Canada
Associate Professor Maryam Saeedifard, School of Electrical and Computer Engineering, Georgia Institute of Technology, USA

ABSTRACT

In recent years, multi-converter DC power distribution networks or DC Microgrids (MGs) have been extensively used in applications such as more electric aircraft, more electric ships, hybrid vehicles, and data centers. This is owing to high power transfer capacity, no frequency and reactive power control requirements, and avoidance of numerous power conversions provided by these systems. Hence, this has led to the superiority of these types of systems over their AC MGs counterparts in terms of achieving simple control structures and higher productivity. DC/DC conversion cascaded systems (shortened cascaded systems) are known as the prevailing subsystems in DC MG relying on their modularity and high efficiency. Despite the potential instability resulting from interactions between the individually designed feedback-controlled converters in these predominant interconnections, supplying loads in a tightly-controlled form (active loads) such as constant power loads (CPLs) inject a destabilizing effect into the network. CPLs tend to destabilize the system owing to their negative resistance characteristics that cause reduced system damping, limited cycle oscillation and voltage collapse on the DC bus, degraded stability margins, and in the worst case, the shutdown of the whole system. 
Consequently, addressing active load's instability effect is one of the most vital issues in obtaining a stable cascaded system, which has lately become an attractive and challenging topic. Although several stabilization techniques have been proposed in this area, most of them suffer from shortcomings and limitations that include the use of complex corrective control structures with various levels of conservatism in the design and satisfaction of stability criteria. Besides, their effectiveness and applicability against unforeseen changes in the network, such as changes in input voltage level and load set, as well as step changes in the output voltage reference, have not been comprehensively evaluated.
Prompted by the mentioned challenges, this work proposes novel active damping (AD)-based stabilization techniques for suppressing CPL instability of cascaded systems in DC MGs without affecting the dynamic performance of the load-side converter. These proposed design-oriented active stabilization approaches take advantage of simple control structures with straightforward adjustment of a control parameter. The presented AD stabilization methods are tested by Matlab/Simulink in the discrete-time domain and also experimental implementation by dSPACE for three cascaded systems comprising basic DC/DC converters, i.e. Buck, Boost, and Buck-Boost converters loaded with CPLs and resistive load. The results are provided as proof of concept, thus validating the theoretical findings and demonstrating the advantages of the proposed approaches during different operational cases such as input voltage changes, plug and play (PnP) operational of CPLs, and step changes in output voltage references. The outcome of this work proves the effectiveness and operational feasibility of the AD-based stabilization techniques on the cascaded systems feeding multiple CPLs in DC MGs.

 

 

THE DEFENCE will be IN ENGLISH - all are welcome.

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Host

AAU Energy - Esbjerg