This paper investigates the new Class EF ₂ inverter and the already known Class E and E/F ₃ inverters. The purpose of this paper is to find the answer to the question: what should be added to a classic Class E inverter to improve its performance with minimum expenditure? Class EF ₂ and E/F ₃ inverters meet this requirement through operating under zero-voltage switching and zero-voltage slope switching conditions (as in Class E) with improved transistor waveforms (as in Class F and 1/F). Selected results of a numerical analysis of Class E, EF ₂ and E/F ₃ inverters are shown and discussed. The analysis is aimed at maximizing the power output capabilities of these inverters for soft-switching conditions and fixed voltage and current stresses on their transistors as constraints. Measurement results of the Class EF ₂ and E inverters are given to verify the validity of the presented theory. The measured output power of the inverters was 526 and 366 W with the total efficiency of 97.1% and 96.6% at 1 MHz, respectively

This paper presents a concept for improving the efficiency of a push-pull Class-E inverter. The concept consists of lowering the root-mean-square transistor current (in reducing the transistor power losses) only by adding a differential capacitor to a push-pull Class-E topology. Theoretical explanations and confirming experimental results are given.

An inductive power transfer subsystem for an integrated motor drive is presented in this paper. First, the concept of an integrated motor drive system is overviewed, and its main components are described. Next, the paper is focused on its inductive power transfer subsystem, which includes a magnetically coupled resonant circuit and two-stage energy conversion with an appropriate control method. Simplified complex domain analysis of the magnetically coupled resonant circuit is provided and the applied procedure for its component selection is explained. Furthermore, the prototype of the integrated motor drive system with its control is described. Finally, the prototype based on the gallium nitride field effect transistors (GaN FET) inductive power transfer subsystem is experimentally tested, confirming the feasibility of the concept.

In this article, a structure-reconfigurable series resonant DC-DC converter is proposed for a wide gain on-board charger application. The proposed converter consists of a dual-bridge structure on the primary side which can realize 0.5 to 1 voltage gain by using a reconfigurable half/full bridge structure, and a hybrid rectifier on the secondary side which can realize 1 to infinite voltage gain by replacing two diodes with active switches. Moreover, the proposed converter employs a control scheme based on fixed frequency PWM, with the operating frequency being identical to the series resonant frequency. Accordingly, magnetizing inductance of the transformer is independent of the converter gain characteristics, which simplifies the consideration of the resonance parameters design. In addition, soft switching can be realized during the entire charging process, and high efficiency can be achieved. To avoid the voltage spike and current impact in the transition between two operation modes, a unified switching modulation strategy is applied to achieve a smooth transition and improve the control stability. Finally, a 2.5 kW prototype with an output voltage range of 200V -500 V is established and tested to verify the effectiveness and feasibility of the proposed converter.

A chart design method for multi-coil resonant wireless power transfer (MC-RWPT) systems is presented in the paper. MC-RWPT system is described by a matrix model, which in combination with the coupling calculation method and after applying the optimization procedure, is used to determine the design charts. First, the transfer efficiency is depicted as a function of the number of applied coils and the relative transfer length. Next, the relations between the rest of the system parameters are identified. The influence of the winding filling factor and the relative air gap between the adjacent coils on the kQ factor are also discussed. The proposed chart design method has been experimentally verified. Representative parameters, voltage / current waveforms and the distribution of RMS currents of the coils of the MC-RWPT system are presented.