Browsing by Author "Aldhaher, Samer"

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    Design and optimization of switched-mode circuits for inductive links
    (Cranfield University, 2014-01) Aldhaher, Samer; Luk, Patrick Chi-Kwong
    Wireless power transfer (WPT) via magnetic induction is an emerging technology that is a result of the significant advancements in power electronics. Mobiles phones can now be charged wirelessly by placing them on a charging surface. Electric vehicles can charge their batteries while being parked over a certain charging spot. The possible applications of this technology are vast and the potential it has to revolutionise and change the way that we use today’s application is huge. Wireless power transfer via magnetic induction, also referred to as inductive power transfer (IPT), does not necessarily aim to replace the cable. It is intended to coexist and operate in conjunction with the cable. Although significant progress has been achieved, it is still far from reaching this aim since many obstacles and design challenges still need to be addressed. Low power efficiencies and limited transfer range are the two main issues for IPT. A tradeoff is usually associated with these two issues. Higher efficiencies are only achieved at very short transmission distances, whereas transferring large amounts of power at large distances is possible but at reduced efficiencies. This thesis addressed the limitations and design challenges in IPT systems such as low efficiency and short transmission range, in addition to poor power regulation and coil displacement and misalignment sensitivity. Novel circuit topologies and design solutions have developed for DC/AC inverters and DC/AC rectifiers that will allow for increased performance, higher efficiencies and reduced sensitivity to coil misalignments and displacements. This thesis contributes in four key areas towards IPT. Firstly, a detailed mathematical analysis has been performed on the electric circuit model of inductively coupled coils. This allows for better understanding on how power is distributed amongst the circuit’s elements. Equivalent circuit representations were presented to simplify the design process of IPT systems. Secondly, a review of the different classes and configurations of DC/AC inverters that can be used as primary coil drivers in IPT systems were presented. Class E DC/AC inverters were mathematically analysed in great detail and their performance as primary coil drivers in IPT systems was investigated. Thirdly, novel electronic tuning methods were presented to allow Class E primary coil drivers to operate at optimum switching conditions regardless of the distance between the coils of an IPT system and the value of the load. The saturable reactor was used as the electronic tunable element. Lastly, Class D and Class E AC/DC rectifiers have been used for the first time in IPT systems. Detailed mathematical analysis and extensive experimental results show their superior performance over the conventional half-wave and full-wave AC/DC rectifiers.
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    Dynamic analysis model of a class E2 converter for low power wireless charging links
    (IET, 2019-01-07) Bati, Akram; Luk, Patrick Chi-Kwong; Aldhaher, Samer; See, Chan H.; Abd-Alhameed, Raed A.; Excell, Peter S.
    A dynamic response analysis model of a Class E2 converter for wireless power transfer applications is presented. The converter operates at 200 kHz and consists of an induction link with its primary coil driven by a class E inverter and the secondary coil with a voltage-driven class E synchronous rectifier. A seventh-order linear time invariant state-space model is used to obtain the eigenvalues of the system for the four modes resulting from the operation of the converter switches. A participation factor for the four modes is used to find the actual operating point dominant poles for the system response. A dynamic analysis is carried out to investigate the effect of changing the separation distance between the two coils, based on converter performance and the changes required of some circuit parameters to achieve optimum efficiency and stability. The results show good performance in terms of efficiency (90–98%) and maintenance of constant output voltage with dynamic change of capacitance in the inverter. An experiment with coils of the dimension of 53 × 43 × 6 mm3 operating at a resonance frequency of 200 kHz, was created to verify the proposed mathematical model and both were found to be in excellent agreement.
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    Electronic tuning of misaligned coils in wireless power transfer systems
    (IEEE Institute of Electrical and Electronics, 2014-11-01T00:00:00Z) Aldhaher, Samer; Luk, Patrick Chi-Kwong; Whidborne, James F.
    The misalignment and displacement of inductively coupled coils in a wireless power transfer system (WPT) can degrade the power efficiency and limit the amount of power that can be transferred. Coil misalignment leads the primary coil driver to operate in an untuned state which causes non-optimum switching operation and results in an increase in switching losses. This paper presents a novel method to electronically tune a Class E inverter used as a primary coil driver in an inductive WPT system to minimize the detrimental effects of misalignment between the inductively coupled coils which may occur during operation. The tuning method uses current controlled inductors (saturable reactors) and a variable switching frequency to achieve optimum switching conditions regardless of the misalignment. Mathematical analysis is performed on a Class E inverter based on an improved model of a resonant inductive link. Experimental results are presented to confirm the analysis approach and the suitability of the proposed tuning method.
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    High input voltage high frequency class E rectifiers for resonant inductive links
    (IEEE, 2014-04-08) Aldhaher, Samer; Luk, Patrick Chi-Kwong; El Khamlichi Drissi, Khalil; Whidborne, James F.
    The operation of traditional rectifiers such as half-wave and bridge rectifiers in wireless power transfer applications may be inefficient and can reduce the amount of power that is delivered to a load. An alternative is to use Class E resonant rectifiers which are known to operate efficiently at high resonant frequencies and at large input voltages. Class E rectifiers have a near sinusoidal input current which leads to an improved overall system performance and increased efficiency, especially that of the transmitting coil driver. This paper is the first to investigate the use of Class E resonant rectifiers in wireless power transfer systems based on resonant inductive coupling. A piecewise linear state-space representation is used to model the Class E rectifier including the rectifying diode’s forward voltage drop, its ON resistance and the equivalent series resistance of the resonant inductor. Power quality parameters, such as power factor and total harmonic distortion, are calculated for different loading conditions. Extensive experimental results based on a 10 W prototype are presented to confirm the performed analysis and the efficient operation of the rectifier. An impressive operating efficiency of 94.43 % has been achieved at a resonant frequency of 800 kHz.
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    State-Space Modeling of a Class E2 Converter for Inductive Links
    (IEEE, 2015-01-06) Luk, Patrick Chi-Kwong; Aldhaher, Samer; Fei, Wei-Zhong; Whidborne, James F.
    This paper presents a state-space-based analysis of a Class E2 converter for wireless power systems based on a twocoil inductive link. The Class E2 converter consists of a 200-kHz Class E inverter as the primary coil driver and a voltage-driven Class E synchronous rectifier at the secondary coil of the inductive link. A piecewise linear seventh-order state-space model is used to calculate several parameters and values to achieve optimum switching operation of the Class E inverter and the Class E recti- fier. Simulation results are presented to compare the accuracy of the state-space modeling approach with the established analytical approach. For validation of the state-space analysis, an investigation of the influence of variation of coil alignment and load for a 20-W Class E2 converter prototype system is performed by means of a novel compensation method that maintains optimum switching conditions irrespective of variations. Experimental results are presented to confirm the accuracy of the state-space modeling approach over a wide range of operational conditions and the utility of the compensation method.
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    Tuning Class E Inverters Applied In Inductive Links Using Saturable Reactors
    (IEEE Institute of Electrical and Electronics, 2014-06-01T00:00:00Z) Aldhaher, Samer; Luk, Patrick Chi-Kwong; Whidborne, James F.
    This paper investigates the performance of Class E inverters used in wireless power transfer applications based on resonant inductive coupling. The variations in the load and the distance between the coils cause Class E inverters to operate in non-optimal switching conditions, which result in inefficient operation and can lead to permanent damage to its switching transistor. Therefore, a novel approach to tune Class E inverters electronically is proposed. The tuning method relies on saturable reactors to ensure that the inverter operates at optimal switching conditions regardless of variations in the load and the distance between the coils. In addition, a more accurate model of inductive links is presented in order to provide a better understanding of the major power losses in resonant inductive links. Experimental results are presented to confirm the improved accuracy of the inductive link model and the validity of the tuning method.
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    Wireless Power Transfer Using Class E Inverter With Saturable DC-Feed Inductor
    (IEEE Institute of Electrical and Electronics, 2014-07-31T00:00:00Z) Aldhaher, Samer; Luk, Patrick Chi-Kwong; Bati, Akram F.
    Resonant converters used as coil drivers in inductive links generally operate efficiently at optimum switching conditions for constant load values and ranges. Changes in load and range can shift the operation of the coil driver to a non-optimum switching state which results in higher switching losses and reduced output power levels. This paper presents a method to adapt to variations in range for a Class E inverter used as a coil driver in a wireless power transfer (WPT) system based on inductive coupling. It is shown that by controlling the duty cycle of the inverter’s switch and the value of its DC-feed inductance, the Class E inverter can be tuned to operate at optimum switching conditions as the distance between the coils of the WPT system changes. Mathematical analysis is presented based on a linear piecewise state-space representation of the inverter and the inductive link. Extensive experimental results are presented to verify the performed analysis and validity of the proposed tuning procedure.