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Browsing by Author "Dang, Zhigang"

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    High-density high-efficiency power magnetics
    (University of Alabama Libraries, 2016) Dang, Zhigang; Abu Qahouq, Jaber A.; University of Alabama Tuscaloosa
    This dissertation presents several concepts and techniques in order to (1) increase the inductance density and power density of power inductors (PIs) with high power efficiency and (2) achieve magnetically coupled wireless power transfer (WPT) systems with higher efficiency and longer transmission distances under varying conditions. Chapter 1 provides an overview and introduction on applications of power magnetic devices and systems along with the challenges facing the state-of-the-art PIs and WPT systems. Chapter 2 develops a concept which results in doubling the saturation current of a high current PI with NdFeB permanent magnet (PMPI). By adding a well-designed small piece of fabricated NdFeB magnet in the air gap of the PI, the saturation current of the PMPI is doubled with the same size and inductance value. Chapter 3 presents a two-phase coupled power inductor (CPI) that utilizes a PM in order to achieve almost doubled saturation current with the same size compared to the CPI and more than 70% core size reduction compared to the single-phase non-coupled PIs. Both the PMPI and PMCI concepts are experimentally verified in DC-DC power converter prototypes. Chapter 4 and 5 present a two-coil and a four-coil reconfigurable WPT system topology, respectively, in order to optimize transmission efficiency under different distance and misalignment conditions. The two-coil reconfigurable WPT system achieves re-configurability by switching between different values of series and shunt capacitors at Tx side and/or Rx side. The four-coil reconfigurable WPT system achieves re-configurability by switching between different sizes of drive loops and load loops. Experimental results verified effectiveness of developed reconfiguration methods. Chapter 6 presents a method to achieve wired power conversion and WPT using a hybrid “Power Converter-WPT system”. By achieving WPT using AC switching ripple of power converter, the system eliminates the need for a transmitter stage of conventional WPT system, which could be beneficial for system size and cost reduction. The method is verified and demonstrated using Buck-WPT system as an example. The last chapter summarizes this work and provides conclusions before discussing some possible future research directions related to the dissertation work.
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    Magnetic resonance coupled wireless power transfer systems
    (University of Alabama Libraries, 2013) Dang, Zhigang; Abu Qahouq, Jaber A.; University of Alabama Tuscaloosa
    Wireless power transfer (WPT) technology has many potential applications such as consumer electronics and electric vehicles (EV). High transmission efficiency with long transmission distance and with large lateral misalignment is desired in WPT systems. Magnetic resonance coupled (MRC) WPT systems are suitable for midrange high efficiency wireless power transfer (WPT). In chapter 2, commonly used four-loop and two-loop MRC-WPT system configurations are analyzed and compared in terms of transmission efficiency and transmission distance first based on the simplified circuit model. An example symmetrical system simulation shows that with the same Tx, Rx, source and load, the four-loop system has longer transmission distance but with relatively lower transmission efficiency compare to the two-loop system. Then, A 3-D physical model of 5-turn, 400mm outer diameter spiral shape four-loop WPT system is developed and simulated by using ANSYS® HFSS® software package. Operation distance of 550mm with nearly constant maximum transmission efficiency of 92.3% is achieved. Laterally misaligned MRC-WPT system is investigated in chapter 3. The TEVD, a region on the transmission efficiency versus Rx lateral misalignment amount curve where the transmission efficiency first sharply drops from high efficiency down to zero and then recovers to a low efficiency value, is identified in this work. The identification of TEVD is verified by simulation results obtained from a developed ANSYS® HFSS® 3-D physical model. Simulation results of the ANSYS® HFSS® 3-D physical model with 5-turn, 60cm outer diameter spiral shape MRC-WPT system show that when the Rx is 30cm vertically away from the Tx, TEVD exists when the lateral misalignment value ranges from 50cm to 70cm. An elimination method for TEVD is proposed in chapter 4. The proposed method utilizes angular rotation of the Rx (or Tx) to eliminate the zero-coupling point which causes the TEVD and boosts the coupling coefficient such that the TEVD is eliminated and the high efficiency region is extended. ANSYS® HFSS® 3-D physical model simulation results show that the proposed method eliminates the TEVD and extends the high efficiency region from 50cm lateral misalignment (83.3% of the Rx diameter) to 70cm lateral misalignment (117% of the Rx diameter). Chapter 5 summarizes the thesis conclusions and sheds the light on future work.