Showing papers by "Srdjan Lukic published in 2015"

Receivers for Multifrequency Wireless Power Transfer: Design for Minimum Interference

Abstract: Inductive (or wireless) power transfer is proving to be an effective way to deliver power over short distances in a wide range of applications. Frequently, there is a need to deliver power from a single transmitter to multiple mutually coupled receivers. In this paper, we quantify how the power delivered to each receiver is affected due to the resonant frequency shift resulting from receiver mutual coupling. We show that the effect on power delivered is quite severe, especially in high-quality-factor systems. We develop the mathematical framework and demonstrate experimentally that the problem disappears if each receiver is tuned at one of the frequencies emitted by a single transmitter. We adopt the concept of frequency traps as a method to completely decouple the receivers.

A universal restart strategy for permanent magnet synchronous machines

Abstract: In many industrial settings, momentary power disruptions commonly occur, resulting in tripping of large electric machines, which then have to be brought to zero speed before the machine can be restarted. This approach can result in frequent interruptions in an industrial process, which can have negative effects on productivity. A more practical control implementation would restart the machine back to the original speed as soon as power is restored, not having to wait for the machine to be at a standstill. This concept is known as flying restart. In this paper we propose an approach to implement the universal restart for PMSM through a simple identification algorithm which determines the speed and position of the machine back-emf so that the correct voltage vector can be applied and thus minimize the inrush current during the restart. Beyond the development of the basic algorithm, implementation issues will be considered to provide general guideline for the application of the developed algorithm.

Multi-layer tubular conductor for high Q-factor wireless power transfer system resonators

Abstract: In this paper we investigate multi-layer tubular conductor for multi-MHz Wireless Power Transfer (WPT) systems high-Q (quality factor) resonators. The conductor layers thickness and current sharing between them are optimized at 13.56 MHz, showing significant reduction in conductor AC resistance (R AC ). Capacitive ballast is used as a practical method for current sharing between layers and operation of coil near resonance. A two-layer conductor is designed, fabricated and characterized showing 18.1% reduction in R AC at 27.93 MHz using capacitive ballast.

An improved distance relay model with directional element, and memory polarization for TCD based fault propagation studies

Abstract: Modern Power Systems have evolved into a very complex network of multiple sources, lines, breakers, loads and others. The performance of these interdependent components decide the reliability of the power systems. A tool called “Reasoner” is being developed to deduce fault propagations using a Temporal Causal Diagram (TCD) approach. It translates the physical system as a Cause-effect model. This work discusses the development of an advanced distance relay model, which monitors the system, and challenges the operation of reasoner for refinement. Process of generation of a Fault and Discrepancy Mapping file from the test system is presented. This file is used by the reasoner to scrutinize relays' responses for active system faults, and hypothesize potential mis-operations (or cyber faults) with a confidence metric. Analyzer (relay model) is integrated to OpenDSS for fault analysis. The understanding of the system interdependency (fault propagation behavior) using reasoner can make the grid more robust against cascaded failures.