Analysis and Design of High-Frequency Soft-Switching DC-DC Converter for Wireless Power Charging Applications

Wireless power transfer (WPT) technology is becoming attractive in a wide variety of applications such as electric-vehicle charging, induction heating, charging portable applications, industrial robots, and biomedical implants. Recent studies have shown various techniques to implement wireless power transfer and these techniques differ based on the type of applications. For example, for electric vehicle charging, the power levels are in the range 5 kW to 25 kW and the operating frequency is in the range 70 kHz to 110 kHz. On the other hand, for consumer applications, the power levels vary from a few watts to hundreds of watts and operates at frequencies of the order of 5 MHz to 10 MHz. This thesis addresses the analysis, design, implementation, and simulation of a wireless charging system targeted towards a high-frequency, low-power portable application with wide separation between transmitter and receiver. The WPT system is composed of three important blocks: inverter (or transmitter), transformer (or coil), and rectifier (or receiver). Hard-switching inverters and rectifiers have major drawbacks at high frequencies due to large switching power loss. Therefore, soft-switching Class-E topology is chosen. The Class-E dc-ac inverter with CLL resonant tank, also referred to as pi2a impedance matching network is analyzed, designed, and simulated to observe its superior performance over other topologies at varying coupling coefficients and loads. Four soft-switching rectifier topologies are analyzed, designed, and simulated to evaluate their behavior at high frequencies. Their compatibility with Class-E inverters in the presence of loosely-coupled transformers is discussed. The physical and commercial limitations of using transformers with magnetic core is presented. Therefore, the preferred solution, an air-core transformer is designed and integrated with the rectifier to evaluate their characteristics at selected coupling coefficient. The overall system including the inverter, loosely-coupled air-core transformer, and rectifier was designed for the following specifications: operating frequency 6.78 MHz, output power across a single-load 40 W, output voltage 25 V, and target coupling coefficient of 0.5. Simulation results have been provided to validate the theoretical predictions. The major challenges faced during the integration of these building blocks are addressed. Finally, conclusions, contributions, and scope for future work are provided

Analysis and Design of High-Frequency Soft-Switching DC-DC Converter for Wireless Power Charging Applications

Wireless power transfer (WPT) technology is becoming attractive in a wide variety of applications such as electric-vehicle charging, induction heating, charging portable applications, industrial robots, and biomedical implants. Recent studies have shown various techniques to implement wireless power transfer and these techniques differ based on the type of applications. For example, for electric vehicle charging, the power levels are in the range 5 kW to 25 kW and the operating frequency is in the range 70 kHz to 110 kHz. On the other hand, for consumer applications, the power levels vary from a few watts to hundreds of watts and operates at frequencies of the order of 5 MHz to 10 MHz. This thesis addresses the analysis, design, implementation, and simulation of a wireless charging system targeted towards a high-frequency, low-power portable application with wide separation between transmitter and receiver. The WPT system is composed of three important blocks: inverter (or transmitter), transformer (or coil), and rectifier (or receiver). Hard-switching inverters and rectifiers have major drawbacks at high frequencies due to large switching power loss. Therefore, soft-switching Class-E topology is chosen. The Class-E dc-ac inverter with CLL resonant tank, also referred to as pi2a impedance matching network is analyzed, designed, and simulated to observe its superior performance over other topologies at varying coupling coefficients and loads. Four soft-switching rectifier topologies are analyzed, designed, and simulated to evaluate their behavior at high frequencies. Their compatibility with Class-E inverters in the presence of loosely-coupled transformers is discussed. The physical and commercial limitations of using transformers with magnetic core is presented. Therefore, the preferred solution, an air-core transformer is designed and integrated with the rectifier to evaluate their characteristics at selected coupling coefficient. The overall system including the inverter, loosely-coupled air-core transformer, and rectifier was designed for the following specifications: operating frequency 6.78 MHz, output power across a single-load 40 W, output voltage 25 V, and target coupling coefficient of 0.5. Simulation results have been provided to validate the theoretical predictions. The major challenges faced during the integration of these building blocks are addressed. Finally, conclusions, contributions, and scope for future work are provided

Underwater Inductive Power Transfer with Wireless Charging Applications

Underwater wireless power transfer (UWPT) has become an area of great interest due to the advancement of autonomous underwater vehicles (AUVs) and electic boats. This paper seeks to investigate the variation of the coupling coefficient and power transfer in air versus in seawater. The design is based on a class E converter as it can achieve soft-switching inherently. I made the transmitter and receiver coils then measured self-inductance and parasitic resistance in air and in water. I noted that self-inductance increases when they are placed in water but the mutual inductance is lower. I then calculated the component values for the class E converter based on inductor values (140 μH and 105 μH) and simulated the circuit on LTspice. The power at the output was 74W which is lower than the required value. However, I noted that reducing the coils inductance values while maintaining the value of the other passive components increased the efficiency and power at the output upto four times (311W). The final value chosen for making the inductors was 115 μH and 75 μH as these values gave the maximum power at the output while achieving ZVS. I then designed the transmitter and receiver circuits on Altium and printed the PCBs. All the components were then soldered onto the board and the tests done

GaN-Based High Efficiency Transmitter for Multiple-Receiver Wireless Power Transfer

Wireless power transfer (WPT) has attracted great attention from industry and academia due to high charging flexibility. However, the efficiency of WPT is lower and the cost is higher than the wired power transfer approaches. Efforts including converter optimization, power delivery architecture improvement, and coils have been made to increase system efficiency.In this thesis, new power delivery architectures in the WPT of consumer electronics have been proposed to improve the overall system efficiency and increase the power density.First, a two-stage transmitter architecture is designed for a 100 W WPT system. After comparing with other topologies, the front-end ac-dc power factor correction (PFC) rectifier employs a totem-pole rectifier. A full bridge 6.78 MHz resonant inverter is designed for the subsequent stage. An impedance matching network provides constant transmitter coil current. The experimental results verify the high efficiency, high PF, and low total harmonic distortion (THD).Then, a single-stage transmitter is derived based on the verified two-stage structure. By integration of the PFC rectifier and full bridge inverter, two GaN FETs are saved and high efficiency is maintained. The integrated DCM operated PFC rectifier provides high PF and low THD. By adopting a control scheme, the transmitter coil current and power are regulated. A simple auxiliary circuit is employed to improve the light load efficiency. The experimental results verify the achievement of high efficiency.A closed-loop control scheme is implemented in the single-stage transmitter to supply multiple receivers simultaneously. With a controlled constant transmitter current, the system provides a smooth transition during dynamically load change. ZVS detection circuit is proposed to protect the transmitter from continuous hard switching operation. The control scheme is verified in the experiments.The multiple-reciever WPT system with the single-stage transmitter is investigated. The system operating range is discussed. The method of tracking optimum system efficiency is studied. The system control scheme and control procedure, targeting at providing a wide system operating range, robust operation and capability of tracking the optimized system efficiency, are proposed. Experiment results demonstrate the WPT system operation

A GaN-Based Synchronous Rectifier with Reduced Voltage Distortion for 6.78 MHz Wireless Power Applications

The call for a larger degree of engineering innovation grows as wireless power transfer increases in popularity. In this thesis, 6.78 MHz resonant wireless power transfer is explained. Challenges in WPT such as dynamic load variation and electromagnetic interference due to harmonic distortion are discussed, and a literature review is conducted to convey how the current state of the art is addressing these challenges.A GaN-based synchronous rectifier is proposed as a viable solution, and a model of the circuit is constructed. The precisely derived model is compared to a linearized model to illustrate the importance of exactness within the model derivation. The model is then used to quantify the design space of circuit parameters Lr and Cr with regard to harmonic distortion, input phase control, and efficiency. Practical design decisions concerning the 6.78 MHz system are explained. These include gate driver choice and mitigation of PCB parasitics. The model is verified with open loop experimentation using a linear power amplifier, FPGA, electronic load, and two function generators. Current zero-crossing sensing is then introduced in order to achieve self-regulation of both the switching frequency and input phase. The details of the FPGA code and sensing scheme used to obtain this closed loop functionality are described in detail. Finally, conclusions are drawn, and future work is identified

Design and Implementation of a Fixed-frequency Inductive Power Transfer System

Inductive power transfer (IPT) technology has gained immense interest for battery charging applications. IPT proves to be particularly efficient and suitable for high-power applications (≈1-20kW). This makes IPT an effective alternative for charging large batteries of electric vehicles (EVs), especially large electric transit vehicles, such as trains, trams, and buses. Because of the trend that this technology is having, it is important to understand the general characteristics and its applications. Nowadays, it is not a secret that IPT technology is and will continue revolutionizing the industry and our society. The future vision is to change the way electricity has been observed since its discovery: through wires. The main objective of this thesis is to study in details the fundamentals of IPT technology and analyze two principal stages of the system: the power supply and the resonant circuit, in order to design an IPT system using effective techniques, which will improve its performance. Additionally, the thesis helps identify and suggest a design procedure that can benefit and motivate future work on this technology. Moreover, the thesis presents a prototype setup that was built in the laboratory, in order to validate the theoretical analysis and simulation results. The thesis is structured into four main parts; the first part reviews the concepts of IPT systems, the different topologies, the explanation of important design considerations, and finally, presents initial simulation results. The second part explains the characteristics of the power supply in IPT systems, the control techniques to regulate the power flow, the explanation of a proposed control strategy, and the simulation results. The third part presents the experimental test setup and related results. Finally, the fourth part presents the conclusions and suggested future work

Optimization of 8-Plate Multi-Resonant Coupling Structure Using Class-E\u3csup\u3e2\u3c/sup\u3e Based Capacitive-Wireless Power Transfer System

Capacitive-wireless power transfer (CPT) effectively charges battery-powered devices without a physical contact. It is an alternative to inductive-wireless power transfer (IPT) which is available in the present market. Compared with IPT, CPT offers flexibility in designing the coupling section. Because of its flexibility, CPT utilizes various coupling methods to enhance the coupling capacitance. Misalignment is a common issue in any WPT system. Among IPT and CPT, IPT has better performance for misalignments, but it requires bulk and expensive ferrite core to attain a high coupling coefficient. This work focuses on designing a CPT system to minimize the impact of misalignments. In this research, a novel 8-plate multi-resonant Class-E2 CPT system is developed to improve the performance of the CPT system for misalignments. The proposed CPT model expands the resonant frequency band, which results in better performance for misalignments compared with the regular 4-plate CPT system. The 8-plate coupling structure is designed to charge a 100 Ah drone battery. For this application, the coupling is formed when the drone lands on the capacitive- wireless charging pad. This work also presents the analysis of several dielectric materials with different dielectric constants. A well-designed capacitive coupler can effectively limit harmonics during the interaction between transmitter and receiver. Also, the effect of coupling plate shape is identified on the CPT system. The hardware tests indicate the round-shaped plates have better stability in coupling capacitance with the variation in frequency. The effect of misalignments is studied through the impedance tracking of the Class-E2 power converter. Impedance plots for 50 μH, and 100 μH resonant inductors are used to determine input current peak for each case. Additionally, hardware tests are performed to study the variation of input current and output voltage for a range of frequencies. The test results indicate the efficiency at optimal impedance point for a resonant inductor with 50 μH is 8% higher compared to the CPT with a 100 μH resonant inductor which highlights the effects of the resonant inductor on efficiency. The zero-voltage-switching (ZVS) limits are also identified for varying frequencies and duty cycles. Later in this research, the optimal design of the Class-E rectifier is identified to enhance the power transfer. Several cases were considered to investigate the impact of the secondary inductor on the output voltage and the ZVS property. Hardware tests validate that under optimal conditions the efficiency of the Class-E2 based CPT system improves by 18% compared with Ar \u3e\u3c 1. Further work presents the advantages of 8-plate multi-resonant coupling for misalignments. The proposed model has a simple design procedure which enhances the power flow from the inverter to the rectifier section. The hardware results of the proposed 8-plate multi-resonant coupling show an increase in efficiency to 88.5% for the 20.8 W test, which is 18% higher than regular 4-plate coupling. Because of the wider resonant frequency band [455- 485 kHz], compared with regular 4-plate coupling, the proposed design minimized the output voltage drop by 15% for 10% misalignment. Even for large misalignments, 8-plate improves the CPT performance by 40% compared with 4-plate coupling

A Design Method to Minimize Detuning for Double Sided LCC Compensated IPT System Improving Efficiency Versus Air Gap Variation

Inductive power transfer (IPT) technology has garnered considerable attention due to its widespread range of applications. The variation in the air gap can result in variations in the loosely coupled transformer (LCT) parameters, including self-inductance and mutual inductance, due to positional deviations with the ferrite cores on both sides. These variable LCT parameters can damage the resonant tank, ultimately resulting in reduced efficiency. To address this problem, a double-sided LCC-compensated IPT system with a compact decoupled coil is proposed in this paper to improve the system's efficiency with respect to the air gap variation. The key idea is to neutralize the variation in LCT parameters through the use of the self-inductance variation of the decoupled coil so that the detuning degree of the system can be suppressed. Subsequently, the analysis and parametric design process of the system are elaborated. Finally, a 1 kW experimental setup is built to verify the feasibility of the proposed method. Experimental results show that the efficiency of the system proposed in this work varies from 92.63% to 74.81%, as the air gap increases from 30mm to 90mm, wherein the primary and secondary self-inductance and mutual inductance increased by 19.3% and 135.3%, respectively. Compared with the traditional method, the maximum efficiency improvement is up to 8.16%

Oscillating driving circuit for a wireless power transfer system

Thesis presented for the Master’s Degree in Electrical EngineeringIn this thesis a power converter is designed to power a wireless power transfer system. The Converter is composed by a DC-AC Class-E inverter, a matching circuit and a spiral antenna. The system is designed to provide 200W and has a working frequency of 13.57 MHz, to comply with the restriction of the radio regulations. Other solutions and the reason for the choice are presented. the theory of modes is briefly introduced characterize a wireless power transfer system. The components of the Class-E inverter were calculated to guarantee the Zero Voltage Switching (ZVS) operation, resulting in the only losses in the system been the conducting ones. When operating in optimal conditions, the converter has an efficiency higher than 90%. A spiral Antenna is designed and its self-inductance is calculated utilizing potential vectors. The antenna has the purpose of exciting the wireless power transfer system. To attach the antenna to the inverter a matching circuit is designed to make sure that the inverter operates with high efficiency, regardless of the antenna’s impedance. The results were provide by simulations using Orcad’s PSpice software and the components calculations were made using MATLAB. The simulation results show the behavior of the system working in non-optimum conditions and they are used to tune the components of the inverter and the matching circuit to achieve ZVS on the MOSFET and reach the highest efficiency.Nesta tese um um conversor de potência é desenvolvido com o objetivo de alimentar um sistema de transferência de energia sem fios. O conversor é composto por um inversor Class-E, um circuito adaptativo e uma antena espiral. O sistem é dimensionado para fornecer 200W e opera a uma frequência de 13,57 MHz, obedecendo os regulamento da leis internacionais de transmissão de radio. A teoria dos modos é brevemente introduzida para caracterizar um sistema de transferência de energia sem fios. Os componentes do inversor Class-E foram calculados para garantir o funcionamento em ZVS (Zero voltage Switching), portanto a unicas perdas são as perdas de condução. Quando operando nas condições ótimas de funcionamento, o inversor tem uma eficiência acima dos 90%. A antena espiral é dimensionada e sua auto-indutancia é calculada com vetores potênciais. O propósito da antena é excitar o sistema de transferência de energia sem fios. Para juntar a antena e o inversor, um sistema adaptativo é desenvolvido para compensar a mudança de impedancia causada pela antena. Dessa forma, o circuito pode operar na sua eficiência máxima. Os resultados foram obtidos por simulações utilizando PSpice, da Orcad, e os componentes foram calculados com MATLAB. As simulações mostram o funcionamento quando o sistema não opera no modo ótimo e como é possivel afinar os componentes do inversor e o cirucito adaptativo para atingir o ZVS no MOSFET e manter a eficiência alta.N/

Contactless Energy Transfer Techniques for Industrial Applications. Power and Data Transfer to Moving Parts

Contactless energy transfer (CET) systems are gaining increasing interest in the automatic machinery industries. For this reason, circuit equivalent networks of CET systems considered in the literature are introduced with emphasis on their industrial applicability. The main operating principles and the required compensating networks, along with different topologies of power supplies optimised for wireless powering, are discussed. The analysis of the wireless transfer, at the maximum efficiency, of high power levels shows that, in the kHz range, highly coupled inductive links are needed and soft-switching power sources required. The employment of CET units in controlled systems requires combining a link for data communication with the wireless power channel. At low frequencies, capacitive and inductive couplings are integrated in a unique platform to implement the wireless data and power links, respectively. Differently, at UHF, an increased data channel transfer efficiency is made possible by exploiting auto-resonant structures, such as split-ring resonators instead of capacitances, one at each far-end side of the link. The design procedure of a power CET system, including the dc/ac converter, a rotary transformer and its windings, is discussed and the results presented. A different version of a WPT system, which involves multiple transmitting coils and a sliding receiver, is also presented. A low frequency RFID capacitive data link is then combined with the rotary CET unit to provide the temperature feedback of a controlled system, wherein the rectifying part of a passive tag is exploited to simultaneously power and read a temperature probe. Subsequently, a split-ring based near-field UHF data link is designed to ensure an improved temperature detection in terms of accuracy and resolution. The sensor readout is performed at the transmitter side by measuring the reflected power by the load rectifier