Samer Aldhaher

Electronic Tuning of Misaligned Coils in Wireless Power Transfer Systems

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 nonoptimum 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.

Tuning Class E Inverters Applied in Inductive Links Using Saturable Reactors

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 under nonoptimal 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 under 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.

Wireless Power Transfer Using Class E Inverter With Saturable DC-Feed Inductor

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 nonoptimum 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 resonant inductive coupling. It is shown that by controlling the duty cycle of the inverters switch and the value of the DC-feed inductance, the Class E inverter can be tuned to operate at optimum switching conditions as the distance between the resonant coils of the WPT system changes. Mathematical analysis is presented based on a linear piecewise state-space representation of the inverter and the resonant inductive link. Extensive experimental results are presented to verify the performed analysis and validity of the proposed tuning procedure.

High-Input-Voltage High-Frequency Class E Rectifiers for Resonant Inductive Links

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 that 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 diodes 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.

State-Space Modeling of a Class

This paper presents a state-space-based analysis of a Class E2 converter for wireless power systems based on a two-coil 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 rectifier. 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.

{\bf E}^{\bf 2}

Class EF and Class E/F inverters are hybrid inverters that combine the improved switch voltage and current waveforms of Class F and Class F-1 inverters with the efficient switching of Class E inverters. As a result, their efficiency, output power and power output capability can be higher in some cases than the Class E inverter. Little is known about these inverters and no attempt has been made to provide an in depth analysis on their performance. The design equations that have been previously derived are limited and are only applicable under certain assumptions. This paper is the first to provide a comprehensive set of analytical analysis of Class EF and Class E/F inverters. The Class EF2 inverter is then studied in further detail and three special operation cases are defined that allow it to either operate at maximum power-output capability, maximum switching frequency, or maximum output power. Final design equations are provided to allow for rapid design and development. Experimental results are provided to confirm the accuracy of the performed analysis based on a 23-W Class EF2 inverter at 6.78-MHz and 8.60-MHz switching frequencies. The results also show that the Class EF2 inverter achieved an efficiency of 91% compared to a 88% efficiency when operated as a Class E inverter.

Converter for Inductive Links

This paper will present the modelling, analysis and design of a load-independent Class EF inverter. This inverter is able to maintain zero-voltage switching (ZVS) operation and produce a constant output current for any load value without the need for tuning or replacement of components. The load-independent feature of this inverter is beneficial when used as the primary coil driver in multi-megahertz high power inductive wireless power transfer (WPT) applications where the distance between the coils and the load are variable. The work here begins with the traditional load-dependent Class EF topology for inversion and then specifies the criteria that are required to be met in order achieve load-independence. The design and development of a 240W load-independent Class EF inverter to drive the primary coil of a 6.78MHz WPT system will be discussed and experimental results will be presented to show the load-independence feature when the distance between the coils of the WPT system changes.

Modeling and Analysis of Class EF and Class E/F Inverters With Series-Tuned Resonant Networks

This paper presents the design and implementation of a Class EF2 inverter and Class EF2 rectifier for two -W wireless power transfer (WPT) systems, one operating at 6.78 MHz and the other at 27.12 MHz. It will be shown that the Class EF2 circuits can be designed to have beneficial features for WPT applications such as reduced second-harmonic component and lower total harmonic distortion, higher power-output capability, reduction in magnetic core requirements and operation at higher frequencies in rectification compared to other circuit topologies. A model will first be presented to analyze the circuits and to derive values of its components to achieve optimum switching operation. Additional analysis regarding harmonic content, magnetic core requirements and open-circuit protection will also be performed. The design and implementation process of the two Class-EF2-based WPT systems will be discussed and compared to an equivalent Class-E-based WPT system. Experimental results will be provided to confirm validity of the analysis. A dc-dc efficiency of 75% was achieved with Class-EF2-based systems.

Load-independent Class EF inverters for inductive wireless power transfer

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 nonoptimum 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 inverters 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.

Design and Development of a Class EF

Traditional rectifiers such as the half-wave and full-wave rectifiers have been the only configuration used in resonant inductive links. Despite their popularity, their input current contains a large amount of harmonics which makes them incompatible with resonant inductive links especially those driven by a Class D or Class E resonant inverter. This paper presents a half-wave Class D voltage-switching rectifier to be used as an alternative to the traditional rectifier. A complete circuit model is presented and detailed analysis is performed based on an analytical approach. The compatibility of the rectifier with resonant inductive links is demonstrated by a design case for a resonant inductive link driven by a Class E inverter. Experimental results are presented to confirm the modelling and analysis of the rectifier.