The first generation of wireless power transfer (WPT) standard Qi, launched in 2010, contains a wide range of transmitter and receiver designs with the aim of maximizing compatibility to attract many manufacturers to share the same standard. Such compatibility feature (i.e., interoperability) has not only attracted over 400 company members in the Wireless Power Consortium (WPC), but also facilitated a fast-growing wireless power market for a decade. The WPC is now expanding the scope of WPT applications to mid-power and high-power applications up to several kilowatts while the Society for Automobile Engineers also set the SAE standard for wireless charging of electric vehicles (EVs) up to tens of kilowatts. Without compromising compatibility, the authors share in this paper their views on the need for a paradigm shift from compatibility to optimal performance in terms of maximum energy efficiency for the entire charging process and minimum charging time. This paradigm change is imminent and important in view of the increasing power of WPT applications. Several enabling technologies essential to the paradigm shift will be addressed.

Two-dimensional (2-D) wireless power transfer (WPT) systems can be controlled by either the directional method or the rotational method. The rotational method refers to the use of omnidirectional transmitter generating rotational flux regardless of the load positions, while the directional method refers to the use of omnidirectional transmitter generating magnetic flux directly toward the power-consuming load directions. This article compares the overall efficiency of the two methods for 2-D WPT systems. Theoretical analysis reveals that the directional WPT can be more efficient than the rotational WPT with either single or multiple loads when the magnetic field vector is controlled within the feasible zones; and the efficiency difference between the two methods are more significant when the dimensions of the receiver coils are smaller. Both simulation and experimental results are consistent in validating the two discoveries. They indicate that the averaged efficiency of the directional method is at least 5% higher than that of the rotational one.

This paper presents the design of a two-stage 50W portable charger architecture with universal ac input and 5V/25W, 9V/45W, 12V/50W output. A 98.5% efficient valley-switched boost converter operating at 0.5-2MHz enables a 59% reduction in buffer capacitor volume compared to an example electrolytic capacitor while a stacked-bridge LLC converter with a Variable-Inverter-Rectifier-Transformer (VIRT) offers greater than 96% efficiency across the wide output voltage range. The design demonstrates the potential and trade-offs of a two-stage architecture at this operating power and illustrates the benefits of the utilized power stage topologies in achieving both small size and high efficiency over wide input- and output voltage ranges.

This article investigates the challenges of designing 6.78 MHz multi-kilowatt H-bridge inverters with high-voltage silicon carbide (SiC) and gallium nitride (GaN) devices, while comparing their performance. First, a design methodology for MHz-switching H-bridge inverters is proposed, addressing critical aspects such as switch selection, gate driver supply design, parasitic inductance minimization, zero-voltage switching, and thermal management. Three 1st-generation inverters are then implemented using 650 V wide-bandgap devices: SiC MOSFET (C3M0060065K), GaN field-effect transistor (FET) (TP65H070G4PS), and GaN FET (GS66506T). In multi-MHz and multi-kW testing, the SiC-based inverter reaches a switching limit of 4 MHz at 3.874 kW but suffers from gate driver overpowering and thermal constraints. The TP65H070G4PS GaN inverter achieves the optimal frequency-power balance, delivering 2.026 kW at 6.78 MHz, though it exhibits significant oscillations at low dc voltages (<250 V). Meanwhile, the GS66506T GaN inverter demonstrates superior high-frequency performance but struggles with thermal dissipation, attaining 1.105 kW at 6.78 MHz. To enable reliable 6.78 MHz power conversion, a 2nd-generation design is developed using enhanced SiC (C3M0120100K) and GaN (GS66508T) switches and evaluated in a 6.78-MHz and 2.4-kW isolated dc–dc converter. These inverters achieve 2.448 kW with 93.63% dc–dc efficiency for the SiC inverter, while the GaN variant reaches 2.483 kW at 95.17% efficiency. This marks the first practical demonstration of a multi-kW SiC H-bridge inverter operating at 6.78 MHz and highlights the performance tradeoffs between SiC and GaN technologies.

Mid-ranged wireless power transfer by induction or inductive power transfer (IPT), including the strong magnetic resonance method, has been widely adopted, in numerous applications where wires are restricted. The energy flow in space, of course, is invisible to engineers. The windings are often required to be irregular shapes to accommodate the industrial designs of the products, thus, a visualisation method for energy transfer paths could greatly help the design and optimization of such systems. A time-efficient methodology, including the model, analysis and plot of the three-dimensional energy flow for IPT systems, is proposed in this paper. Algorithms of fast describing arbitrarily shaped windings are proposed and the time complexities are evaluated. A software tool, IPTVisual, is developed. It takes the inputs of key coordinates of the windings, the assignments of voltage and/or current sources, any compensation capacitors and auxiliary circuits, and the required observation points to generate the 3D models of the windings and the Poynting vectors, rendered in web browsers for the most extendable compatibility. Several example scenarios have been tested and the results match with the expected operations.