Sreyam Sinha

Improved Design Optimization for High-Efficiency Matching Networks

Multistage matching networks are often utilized to provide voltage or current gains in resonant conversion applications, such as large conversion ratio power converters and wireless power transfer. In the conventional approach, each stage of a multistage matching network is designed to have a purely resistive input impedance and assumed to be loaded by a purely resistive load. This paper introduces an improved design optimization approach for multistage matching networks comprising L-section stages. The proposed design optimization approach explores the possibility of improvement in efficiency of the network by allowing the L-section stages to have complex input and load impedances. A new analytical framework is developed to determine the effective transformation ratio and efficiency of each stage for the case when input and load impedances may be complex. The method of Lagrange multipliers is used to determine the gain and impedance characteristics of each stage in the matching network that maximize overall efficiency. Compared with the conventional design approach for matching networks, the proposed approach achieves higher efficiency, resulting in loss reduction of up to 35% for a three-stage L-section matching network. The theoretical predictions are validated experimentally using a three-stage matching network designed for 1 MHz and 100 W operation.

Design of efficient matching networks for capacitive wireless power transfer systems

High-power large air-gap capacitive wireless power transfer (WPT) systems require matching networks that provide large voltage or current gain and reactive compensation. This paper introduces an analytical optimization approach for the design of L-section multistage matching networks for capacitive WPT systems. The proposed approach maximizes the matching network efficiency and identifies the optimal distribution of gains and compensations among the L-section stages. The results of the proposed approach are validated using an exhaustive-search based numerical optimization for a 12-cm air-gap, 6.78-MHz, 125-W capacitive WPT system. A 6.78-MHz, 15-W prototype comprising a two-stage matching network is also designed using the proposed analytical approach and the theoretical predictions are validated experimentally.

A high power density single-phase inverter using stacked switched capacitor energy buffer

This paper presents a high power density 2 kW single-phase inverter, with greater than 50 W/in3 power density and 90% line-cycle average efficiency. This performance is achieved through innovations in twice-line-frequency (120 Hz) energy buffering and high frequency dc-ac power conversion. The energy buffering function is performed using an advanced implementation of the recently proposed stacked switched capacitor (SSC) energy buffer architecture, and the dc-ac power conversion is performed using a soft-switching SiC-FET based converter, with a digital implementation of variable frequency constant peak current control.

High-performance large air-gap capacitive wireless power transfer system for electric vehicle charging

This paper introduces a high-performance large air-gap capacitive wireless power transfer (WPT) module as part of a multi-modular capacitive WPT system for electric vehicle charging. This WPT module utilizes two pairs of metal plates separated by an air-gap as the capacitive coupler, incorporates L-section matching networks to provide gain and reactive compensation, and is driven by a GaN-based inverter operating at 6.78 MHz. The system achieves high efficiency and simplicity by eliminating the need for high-voltage capacitors, and instead utilizes the parasitic capacitances formed between the coupling plates and the vehicle chassis and roadway as part of the matching networks. This paper also presents a comprehensive design methodology for the capacitive WPT system that guarantees high performance by ensuring zero-voltage switching of the inverter transistors, and by selecting matching network component values to maximize efficiency under practical constraints on inductor quality factor and self-resonant frequency. Two prototype 6.78-MHz 12-cm air-gap capacitive WPT systems have been designed, built and tested. The first prototype with 625 cm2 coupling plate area transfers up to 193 W of power and achieves an efficiency greater than 90%, with a power transfer density of 3 kW/m2. The second prototype with 300 cm2 coupling plate area transfers up to 557 W of power and achieves an efficiency of 82%, with a power transfer density of 18.5 kW/m2, which exceeds the state-of-the-art for capacitive WPT systems by more than a factor of four.

High-power-transfer-density capacitive wireless power transfer system for electric vehicle charging

This paper introduces a large air-gap capacitive wireless power transfer (WPT) system for electric vehicle charging that achieves a power transfer density exceeding the state-of-the-art by more than a factor of four. This high power transfer density is achieved by operating at a high switching frequency (6.78 MHz), combined with an innovative approach to designing matching networks that enable effective power transfer at this high frequency. In this approach, the matching networks are designed such that the parasitic capacitances present in a vehicle charging environment are absorbed and utilized as part of the wireless power transfer mechanism. A new modeling approach is developed to simplify the complex network of parasitic capacitances into equivalent capacitances that are directly utilized as the matching network capacitors. A systematic procedure to accurately measure these equivalent capacitances is also presented. A prototype capacitive WPT system with 150 cm2 coupling plates, operating at 6.78 MHz and incorporating matching networks designed using the proposed approach, is built and tested. The prototype system transfers 589 W of power across a 12-cm air gap, achieving a power transfer density of 19.6 kW/m2.

Improved design optimization approach for high efficiency matching networks

Multistage matching networks are often utilized to provide voltage or current gains in applications such as wireless power transfer. Usually, each stage of a multistage matching network is designed to have a purely resistive input impedance and assumed to be loaded by a purely resistive load. This paper introduces an improved design optimization approach for multistage matching networks comprising L-section stages. The proposed design optimization approach explores the possibility of improvement in efficiency of the network by allowing intermediate stages to have complex input and load impedances. A new analytical framework is developed to determine the effective transformation ratio and efficiency of each stage for the case when input and load impedances may be complex. The method of Lagrange multipliers is used to determine the gain and impedance characteristics of each stage in the matching network that maximize overall efficiency. Compared with the conventional design approach for matching networks, the proposed approach achieves higher efficiency, resulting in loss reduction of up to 35% for a three-stage L-section matching network. The theoretical predictions are validated experimentally using a three-stage matching network designed for 10 MHz and 10 W operation.

Multi-objective optimization of capacitive wireless power transfer systems for electric vehicle charging

This paper presents a methodology for multi-objective optimization of capacitive wireless power transfer (WPT) systems for electric vehicle charging that allows for a favorable tradeoff between power transfer density and efficiency. By quantifying the tradeoff between these two objectives, this multi-objective optimization approach can inform engineering decisions, given the requirements of a particular charging application. The capacitive WPT system considered in this paper utilizes L-section matching networks with air-core inductors and capacitors realized using the parasitic capacitances of the system. The proposed optimization methodology incorporates constraints on achievable matching network capacitances, realizable inductor designs, and fringing electric fields set by safety considerations. The models used in the optimization methodology are validated using a 12-cm air-gap 6.78-MHz prototype capacitive WPT system, which transfers 589 W, achieving a power transfer density of 19.6 kW/m2 and an efficiency of 88.2%.

Active variable reactance rectifier — A new approach to compensating for coupling variations in wireless power transfer systems

This paper introduces a new approach to compensating for coupling variations in wireless power transfer (WPT) systems using an active variable reactance (AVR) rectifier. The AVR rectifier incorporates a lossless resonant network and two actively-controlled bridge rectifiers, which are interfaced with the output of the WPT system using dc-dc converters. The input reactance of the AVR rectifier can be continuously varied by changing the relative voltages at its two outputs while maintaining soft-switching of the rectifier transistors, enabling the rectifier to compensate for coupler misalignments while achieving high efficiency at high switching frequencies. The AVR rectifier also ensures that the output power of the WPT system is maintained at a fixed level even during coupler misalignments. A prototype AVR rectifier is designed, built and tested with a 6.78-MHz 20-W capacitive WPT system for tablet charging applications. The system is able to fully compensate, i.e., maintain a fixed output power level, for up to 50% lateral misalignments in the capacitive coupler, while maintaining high efficiency.