Inductive power transfer (IPT) presents a promising solution for opportunity charging of electric buses. However, achieving an optimal balance between pad area, power transfer efficiency, and misalignment tolerance remains a significant challenge. This article explores the tradeoffs between power transfer efficiency and area-related power density and investigates the electric field distribution in the charging pads of wireless charging systems. The design requirements are first established. Based on these, a multiobjective optimization (MOO) framework is developed to address insulation constraints and current density limitations within the windings. The resulting Pareto front reveals that lower area-related power densities correspond to reduced efficiency, highlighting a fundamental design tradeoff. Furthermore, the study identifies critical regions within the charging pads that are the most susceptible to insulation failure. A 50-kW prototype was implemented and tested, with experimental results showing a dc-dc power efficiency ranging from 97.165% to 96.824% under 100-mm X and Y misalignment, and a stray field of 13.86μ T.

This article presents an extended hybrid modulation (EHM) technique to achieve multistage constant-current (MSCC) charging of electric vehicles using wireless power transfer (WPT) technology. Although most research focuses on constant-current constant-voltage charging, MSCC charging offers key advantages, such as lower temperature rise, decreased charging time, and prolonged battery lifespan. However, the existing phase-shift-modulation (PSM) method encounters substantial circulating reactive power and significant efficiency drops in MSCC charging. To overcome this, an EHM strategy is proposed to expand the modulation range of PSM. By applying EHM to both the inverter and active rectifier, the proposed method provides up to 16 operating modes to facilitate multiple CC outputs. Furthermore, an optimal mode trajectory, specifically designed for the MSCC charging, is developed. By implementing this trajectory across different charging stages, zero-voltage-switching is achieved for all power switches, and the overall power loss of the system is minimized. Finally, a WPT prototype was developed to validate the proposed approach. Experimental results demonstrate that the proposed approach effectively enables the MSCC charging while notably enhancing transmission efficiency, achieving dc-to-dc efficiencies between 92.45% and 95.67% across a power range of 231 to 3.015 kW.

This article presents a dual-side capacitor tuning and cooperative control strategy for wireless electric vehicle (EV) charging. To improve the efficiency of wireless EV charging across broad output voltages and wide-range load variations, this article introduces a reconfigurable WPT system by incorporating two switch-controlled-capacitors (SCCs) into the double-sided LCC (DLCC) compensation network. Based on the analytical model of the system, optimal capacitor tuning factors are derived to reduce the rms values of the inductor currents and to minimize the turn-off currents across the semiconductors. Furthermore, a dual-side cooperative control strategy is proposed. Through the collaborative control of the inverter, rectifier, and SCCs, the proposed method achieves dual-side optimal zero-voltage-switching (ZVS), wide power regulation, and maximum efficiency tracking simultaneously. Compared with the existing triple-phase-shift (TPS) method, the proposed approach improves the system efficiency across a wide range of dc output voltages and power levels. Experimental results demonstrate that the proposed method achieves a maximum efficiency improvement of up to 1.8% in the boost mode and 1.9% in the buck mode.

This article presents an optimal multivariable control (OMC) strategy for the LCC-LCC compensated wireless power transfer systems. To mitigate reactive power and achieve higher efficiency, the proposed OMC method incorporates dual-side hybrid modulation and primary-side switch-controlled-capacitor (SCC) tuning into the triple-phase-shift (TPS) control. First, the impact of hybrid modulation and SCC tuning on the system characteristics is investigated. The inverter and rectifier zero-voltage-switching (ZVS) conditions are then analyzed to achieve dual-side ZVS with minimal reactive power. Furthermore, a multivariable optimization problem is established based on the power loss analysis. The solution to this problem provides optimal control variables that minimize the overall system loss. Through collaborative modulation and control of the inverter, rectifier, and SCC, the proposed method reduces the rms values of the currents and lowers the turn-off currents for the converters. As a result, this approach improves efficiency in both light- and heavy-load conditions, enabling wide output regulation and full-range efficiency optimization simultaneously. Finally, the proposed method is benchmarked with the existing TPS method. Experimental results demonstrate that the proposed method achieves higher dc-to-dc efficiency in the power range of 0.2-2.2 kW, with a maximum efficiency improvement of up to 6.3%.

This paper studies the power density limits of propulsion motor for electric aircraft considering thermal aspects and breakdown voltage reduction of insulation. The study em-ploys multi-objective optimization (MOO) to explore various mo-tor cooling options and filter configurations. The results show that motors with direct winding heat exchanger (DWHE) can reach higher specific power, while those equipped with water jacket cooling (WJC) offer a moderate design with simpler structure. Furthermore, the impact of sine wave and dv/dt filters on electric motors design is studied. The findings demonstrate that dv/dt filters enable designs with higher overall specific power compared to sine wave filters. Through simulations, this study identify the challenge faced by aviation motor design in significantly increased insulation thickness, necessitating advanced insulation materials with a minimum thermal conductivity of 5 W/(m.K) to facilitate a high specific power design. Based on this assumption, a preliminary design of 9.6 kW/kg with an efficiency of 98% is presented.

This paper proposes a variable-capacitance-based control strategy to improve efficiency for asymmetric LCC-LCC compensated wireless power transfer (WPT) systems. While the existing triple-phase-shift (TPS) method can achieve power regulation and wide-range zero-voltage-switching (ZVS), it results in significantly increased reactive power under asymmetric LCC-LCC compensation topology. To this end, this paper incorporates a switch-controlled-capacitor (SCC) on the primary side. The impact of variable capacitance on the system characteristics is first investigated. Furthermore, the optimal capacitor tuning factor is derived to achieve the inverter ZVS with minimal reactive power. Through the implementation of variable capacitance, the primary inductor current is notably reduced within a wide range of power. Moreover, the turn-off currents of power switches are minimized. These factors contribute to a reduction in inductor and inverter losses, thus improving the overall efficiency. Experimental results confirm that the proposed method improves the efficiency of an asymmetric LCC-LCC compensated WPT prototype, with a maximum efficiency improvement of up to 1.8%.

This paper presents a hybrid rectifier mode control for broad-range output power regulation in wireless power transfer (WPT) systems. The proposed control method employs a secondary-side active rectifier for output tuning, thereby eliminating the necessity for communication links. Furthermore, leveraging the pulse-skipping technique, two hybrid modes are introduced in the proposed approach. These hybrid modes reduce circulating reactive power within the resonant circuits, thereby optimizing the transmission efficiency of the WPT systems. To validate the effectiveness of the proposed method, experiments were conducted using a WPT prototype. Experimental results demonstrate that the proposed approach achieves higher efficiency than the conventional phase-shift control strategy, with a maximum efficiency improvement of up to 3.7%.

This paper presents a hybrid modulation (HM) scheme to facilitate secondary-side control in wireless power transfer (WPT) systems. To achieve broad power regulation in WPT systems, the conventional pulse width modulation (PWM) exhibits a significant efficiency drop under light loads, while the existing pulse density modulations (PDMs) lead to considerable current and voltage ripples. To address this issue, an optimal discrete PDM (D-PDM) is proposed for active rectifier modulation. By symmetrically and uniformly distributing pulses, the proposed optimal D-PDM eliminates even-subharmonics in rectifier input voltage, thereby reducing the current distortions and output voltage ripple while removing the capacitor DC blocking voltages. Moreover, the pulse width regulation is incorporated into the optimal D-PDM, enabling continuous output tuning and further minimizing subharmonics in the voltage. Based on a WPT prototype, the proposed HM is benchmarked with the existing PWM and PDMs. Experimental results show that the proposed HM significantly mitigates current and voltage ripples while facilitating continuous tuning when compared with the existing PDMs. Additionally, when compared to the PWM, the proposed HM demonstrates notable efficiency improvements within the 10%-60% power range, achieving a maximum efficiency enhancement of up to 5.5%.

This article presents a parameter recognition-based impedance tuning method for the impedance mismatch caused by capacitance drift and coil misalignment in series-series-compensated wireless power transfer (WPT) systems. First, a parameter recognition method is proposed to identify the unknown parameters of the resonant circuits by only measuring the rms values of the coil currents. No phase detection circuits and auxiliary measurement coils are required. Furthermore, according to the recognized parameters, the reactance on both sides are minimized simultaneously by regulating the system frequency and the phase shift angles of the active rectifier. Compared with the existing methods, the proposed parameter recognition method adopts a dynamic frequency approaching strategy to avoid severe system detuning due to the bifurcation phenomenon. Moreover, based on the recognized parameters, the proposed impedance tuning method can simultaneously cope with the parameter deviations caused by capacitance drift and coil misalignment on both sides without using extra circuits and switches. Experimental results show that the unknown parameters of the resonant circuits are recognized accurately, with the average relative errors all less than 3%. Additionally, by implementing the impedance tuning method, the dc to dc efficiency of the WPT prototype is improved by 4.3%-15% in the experiments.

This article proposes a mode-switching-based phase shift control (MS-PSC) for wireless power transfer (WPT) systems, which is able to achieve power regulation, load matching, and wide ZVS operations simultaneously without using additional dc-dc converters. Based on the mode transitions between the full-bridge, mixed-bridge, and half-bridge modes of both the inverter and the rectifier, the MS-PSC method guarantees a wide-range ZVS with minimized circulation of reactive power. Therefore, the system efficiency is improved over a wider power range compared to the conventional triple-phase-shift (TPS) control and the existing hybrid modulation control. The principles of different operating modes are analyzed. Then, the implementation of the proposed MS-PSC method and the mode selection strategy are presented. Finally, the effectiveness of the proposed MS-PSC method is validated in a WPT prototype. Experimental results show that the proposed MS-PSC method can achieve a high overall efficiency in a wide power range. Compared with the conventional TPS control, the MS-PSC method further optimizes the efficiency in 10%-63% of the rated power, with efficiency improvements ranging from 1.5% to 6%. As a result, the system efficiency remains at 93.5%-96.1% in the power range of 1-10 kW, with the transformer coupling coefficient k = 0.19.

This article introduces a three-mode variable-frequency zero-voltage switching (ZVS) modulation method for the four-switch buck+boost converter. This method makes this circuit concept well suited for applications, such as wireless power charging of electric vehicles, where this circuit operates as a power buffer between the resonant converter and the battery with the function to implement the required charging profile. Herein, the buck+boost converter operation is subdivided into three operating regions according to the converter static voltage gain, i.e., buck-, buck-boost- and boost-type modes. A ZVS turn-on triangular current mode (TCM) control is adopted for buck-type and boost-type modes. In the buck-boost-type mode when the input-to-output voltage gain is close to unit, all the possible modulation cases are studied thoroughly based on the phase shift of the two half bridges in a full switching period. The selection of the most suitable modulation scheme is performed to minimize the rms value of the inductor current while taking into account the simplification of the practical implementation. Closed-form equations are derived, which makes it easy to implement in practice. The proposed strategy is described, analyzed, and finally verified through a 3 kW surface mounted device (SMD) silicon carbide (SiC) mosfet-based laboratory prototype with designed input voltage of 300-600 V and the typical output voltage of 400 V class battery. The efficiency from the measured results is remarkably high, i.e., between 99.2% and 99.6% in a power range from 1 to 3 kW. Finally, tests for the operating mode transitions demonstrated the feasibility of the proposed modulation method. The power density of this converter is 4.86 kW/L.