Wireless Power System Design for Maximum Efficiency

With the potential of cutting the last cord, wireless power transfer (WPT) using magnetic resonant coupling is gaining increasing popularity. Evolved from the inductive WPT techniques used in commercial products today, resonant WPT can transfer power over a longer distance with higher spatial freedom. Experimental prototypes have shown power transfer across a 2 m air gap [1], proving the viability of resonant WPT. Industrial consortia such as the AirFuel Alliance have standard specifications that enable wide application in consumer electronics.Despite the promises of high efficiency and long transfer distance, resonant WPT has significant challenges to overcome before the broad adoption will occur. One of the critical challenges is the how to design the complicated system. A WPT system consists of multiple parts: the transmitter coil and the compensation capacitor, the receiver coil and the compensation capacitor, and the power stages which consists of the inverter in the transmitter side and rectifier in the receiver side. This thesis investigates the WPT system design for maximum efficiency. It explores modeling and design of individual stages as well as the entire system design method. From the careful literature review, it is found that current design method of coils is insufficient for consumer electronics applications due to the strict sensitivity of size. The current power stage design method is insufficient or inaccurate for WPT applications where wide loading situations need to be considered. The system-level design method is based on assumptions that are not generally true due to the neglect of ZVS requirement and diode rectifier reactance. Instead, previously established techniques in coil design are applied to invent a new coil structure for reduced ESR while achieving a compact size. Previous ZVS inverter and diode rectifier topology are combined with waveform and circuit analysis to develop new accurate modeling and design method for a wide load range. From the resulting coil and converter models, an entire WPT system model and design methodology are proposed which highlights the design parameters selection and the design sequence. These techniques together contribute to a WPT system in terms of both high efficiency and compact size

Isolated Wired and Wireless Battery Charger with Integrated Boost Converter for PHEV and EV Applications

Vehicle charging and vehicle traction drive components can be integrated for multi-functional operations, as these functions are currently operating independently. While the vehicle is parked, the hardware that is available from the traction drive can be used for charging. The only exception to this would be the dynamic vehicle-charging concept on roadways. WPT can be viewed as a revolutionary step in PEV charging because it fits the paradigm of vehicle to infrastructure (V2I) wirelessly. WPT charging is convenient and flexible not only because it has no cables and connectors that are necessary, but due more to the fact that charging becomes fully independent. This is possibly the most convenient attribute of WPT as PEV charging can be fully autonomous and may eventually eclipse conductive charging. This technology also provides an opportunity to develop an integrated charger technology that will allow for both wired and wireless charging methods. Also the integrated approach allows for higher charging power while reducing the weight and volume of the charger components in the vehicle. The main objective of this work is to design, develop, and demonstrate integrated wired and wireless chargers with boost functionality for traction drive to provide flexibility to the EV customers

Capacitive power transfer for maritime electrical charging applications

Wireless power transfer can provide the convenience of automatic charging while the ships or maritime vehicles are docking, mooring, or in a sailing maneuver. It can address the challenges facing conventional wired charging technologies, including long charging and queuing time, wear and tear of the physical contacts, handling cables and wires, and electric shock hazards. Capacitive power transfer (CPT) is one of the wireless charging technologies that has received attention in on-road electric vehicle charging applications. By the main of electric fields, CPT offers an inexpensive and light charging solution with good misalignment performance. Thus, this study investigates the CPT system in which air and water are the separation medium for the electrical wireless charging of small ships and unmanned maritime vehicles. Unlike on-road charging applications, air or water can be utilized as charging mediums to charge small ships and unmanned maritime vehicles. Because of the low permittivity of the air, the air-gapped capacitive coupling in the Pico Farad range requires a mega-hertz operating frequency to transfer power over a few hundred millimeters. This study examines an air-gapped CPT system to transfer about 135 W at a separation distance of 50 mm, a total efficiency of approximately 83.9%, and a 1 MHz operating efficiency. At 13.56 MHz, the study tested a shielded air-gapped CPT system that transfers about 100 W at a separation distance of 30 mm and a total efficiency of about 87%. The study also examines the underwater CPT system by submerging the couplers in water to increase the capacitive coupling. The system can transfer about 129 W at a separation distance of 300 mm, a total efficiency of aboutapproximately%, and a 1.1 MHz operating efficiency. These CPT systems can upscale to provide a few kW for small ships and unmanned maritime vehicles. But they are still facing several challenges that need further investigations

Communication‐less Synchronous Rectification for In Motion Wireless Charging

This thesis puts forward a control scheme to allow for synchronous rectification for dynamic wireless power transfer. The automotive industry is transitioning away from internal combustion engines (ICEs) and towards electric vehicles (EVs). This transition is spurred by the environmental and economic benefits EVs offer over ICEs. However, further improvements can still be made to how electric vehicles operate. One of these improvements is the technology of in motion wireless charging or dynamic wireless power transfer. In motion wireless charging offers the ability to remove existing range anxiety concerns for EVs. It also offers the potential for a reduction in battery sizes for EVs, which are the primary cost of EVs, this in turn decreases the total costs of mass EV adoption. Traditional implementations of in motion wireless charging utilize passive rectification to simplify controls between embedded primary pads and the vehicle. However, this solution while effective, limits the potential benefits of wireless charging. The use of synchronous or active rectification techniques, offer improved performance, control techniques, and bidirectional capabilities. However, the reason synchronous rectification is not already used in in motion charging is the complexity of synchronization over wireless communication. To move past this challenge, this thesis investigates a synchronization scheme that can be achieved without communication by taking advantage of induced free resonant currents in the vehicle’s tuning network to synchronize the switching transitions to receive power. In this thesis a traditional in motion wireless charging system utilizing passive rectification is designed and built as a benchmark for dynamic charging. Simulations of this control scheme are presented. Practical considerations are addressed for hardware realization. Finally, the control approach is validated through hardware in static and dynamic applications

A Critical Analysis of a Wireless Power Transmission (WPT) with an Improvement Method for a Non-Radiative WPT

This paper describes the analysis of the wireless power transmission including recent progresses in non-radiative wireless power transmission (WPT) and the improvement methods. Generally, WPT transmitter side consists of a DC supply voltage source, inverter/power amplifier, transmitter impedance matching device (IMD), source resonator and primary coil. The WPT receiver meanwhile consists of the secondary coil, device resonator, receiver IMD, rectifier and load. In order to achieve an efficient WPT, the WPT transmitter must transmit energy with minimum loss at the receiver side.  This setup can be achieved by employing the power amplifier (PA). In this paper, the power amplifier in wireless power transmission for portable devices was designed. A Class E power amplifier was proposed and designed to improve the WPT transmitter side. The effects of zero voltage and zero derivative voltage switching on PA with optimization method was also discussed

Class-E rectifiers and power converters: the operation of the class-E topology as a power amplifier and a rectifier with very high conversion efficiencies

In the late 70’s, the interest in reducing the value and size of reactive components moved power supply specialists to operate dc-to-dc converters at hundreds of kHz or even MHz frequencies. Passive energy storage (mainly magnetics) dominates the size of power electronics, limiting also its cost, reliability and dynamic response. Motivated by miniaturization and improved control bandwidth, they had to face the frequency-dependent turn-on and turn-off losses associated with the use of rectangular waveforms in the hard-switched topologies of that time. Similar to approaches for RF/microwave power amplifiers (PAs), the introduction of resonant circuits allowed shaping either a sinusoidal voltage or current, with parasitic reactive elements absorbed by the topology in the neighborhood of the switching frequency. The resulting resonant power converters, obtained by cascading a dc-to-ac resonant inverter with a high-frequency ac-to-dc rectifier, first transform the dc input power into controlled ac power, and then convert it back into the desired dc output [1]. This paper provides some historic notes on the operation of the class-E topology, introduced worldwide to the RF/microwave community by Nathan O. Sokal [2], as a power inverter and as a rectifier, with very high conversion efficiencies up to microwave frequencies. Recent research advances and implementations of class-E rectifiers and dc-to-dc converters at UHF and beyond are included. Offering competitive performance in terms of efficiency for RF power recovery, together with a wide bandwidth for low-loss power conversion, their potential for some modern applications is highlighted.The authors would like to acknowledge support in part by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2017-83343-C4-1-R projects, co-funded with FEDER, and in part by Lockheed Martin Endowed Chair at the University of Colorado

Emerging Works on Wireless Inductive Power Transfer: AUV Charging from Constant Current Distribution and Analysis of Controls in EV Dynamic Charging

Wireless power transfer through inductive coupling, termed as inductive power transfer (IPT), is one of the important technologies in power electronics that enable transfer of power between entities without physical connections. While it has seen significant growth in the areas such as electric vehicle charging, phone charging and biomedical implants, its emerging applications include charging of autonomous underwater vehicles (AUVs) and dynamic charging of electric vehicles from the roadway. This dissertation addresses a few key challenges in these areas of IPT applications, paving the way for future developments. For the WPT for AUV, the recently developing sea-bed installed marine systems are targeted, which typically gets power from on-shore sources through constant dc low-current distribution. As the present underwater IPT topologies are not suitable for such applications, this dissertation proposes underwater IPT topologies to interface directly with such constant current distribution and provide a constant voltage output supply to the on-board systems inside the AUVs. The considerations for seawater losses and the small-signal models for control purposes are also addressed. Analysis and experimental results are provided for validations of the analytical designs and models. In the area of electric vehicle dynamic wireless power transfer (EV DWPT), the comparison of control performances of different coupler, compensation topologies and control implementations are addressed. The effect of communication latency on control bandwidth are also addressed. The outcomes are presented through analysis and simulations, and based on that future research recommendations are made to pave way for future commercial developments of well regulated and interoperable EV DWPT systems

RF Systems Design for Simultaneous Wireless Information and Power Transfer (SWIPT) in Automation and Transportation

This work presents some recent solutions that exploit the wireless power transfer (WPT) technology for energizing moving vehicles and machinery tools. Such technology is currently experiencing unprecedented interests in non-traditional RF/microwave sectors fields, such the industrial automation and the railway transportation safety. Near-field electromagnetic coupling solutions are presented showing that, in order to obtain efficient performances for broad ranges of operating conditions, the nonlinear electromagnetic co-design of the entire WPT system, from the energy source to the receiver load, needs to be carried out. This technology can be combined with wireless data transfer, thus realizing integrated systems able to simultaneously control the energy transfer and the transmission of data. The adopted operating frequencies are in the MHz range, which is only recently considered for this kind of applications. In particular this work focuses on three different systems: the first one demonstrates the constant powering of “on the move” industrial charts at 6.78 MHz, regardless of the relative position of the transmitter and the receiver sub-systems; the second one presents a novel design of a balise transportation system adopting a high efficiency GaN-based transmitter designed to keep its performance over a wide range of loading conditions; the last one consists of the simultaneous wireless power and data transfer, to a rotating machinery tool, automatically controlled by the powering system based on the coexistence of frequency-diverse inductive and capacitive couplings