Yabiao Gao

Safety and efficiency of the wireless charging of electric vehicles

Wireless power transfer is a promising method to address the concerns over charging an electric vehicle. Since wireless charging stations operate without large cables or above-ground stations, they can be conveniently installed in public locations without the risk of vandalism or weather-inflicted damage, improving the lifespan of the electric vehicle charging station. In order for wireless charging stations to become widespread, possible health effects regarding exposure to the strong electromagnetic fields present during wireless power transfer must be investigated. This work examines, first, the potential human safety hazards, second, the electronic device interference, and, third, the thermal heating effects of wireless charging systems. A 3.3 kW wireless power transfer prototype was built in order to examine these effects. Changes in the wireless power transfer efficiency due to the coil misalignment were also investigated using an automated three-axis platform. Design considerations for electric vehicle wireless charging systems and safety recommendations are presented.

Investigating safety issues related to Electric Vehicle wireless charging technology

Electric Vehicles (EV) have gained popularity due to environmental concerns, increasing prices of fossil fuel, and a subsequent desire to move toward renewable energy sources; however, it also raises many concerns associated with connections between EV and charger, EV infrastructure and maintenance, as well as its vulnerabilities to inclement weather and vandalism. Wireless Charging (WC), which operates on magnetic resonance for Wireless Power Transfer (WPT), allows these problems to be alleviated. This paper investigated the safety issues associated with thermal effects, electromagnetic (EM) interference voltages induced by the magnetic field near, inside and at the center of an EV WC system, and magnetic field strength.

Uniform-gain frequency tracking of wireless EV charging for improving alignment flexibility

Wireless power transfer is a promising alternative option for electric vehicle charging due to its non-contact operation. However, the magnetic coupling variation caused by misaligned coils limits its practical application. The output voltage can significantly drop due to the coupling change, lowering the power transfer capability. A uniform-gain frequency tracking control is proposed to keep the output voltage stable within a large misalignment. The uniform-gain control is achieved through voltage gain and impedance analysis across the frequency domain. Experimental results demonstrate that the voltage variation of uniform gain control is within 3.3% across the misalignment range of 200mm, while it is 57.2% for the same misalignment range under fixed frequency control.

Misalignment effect on efficiency of wireless power transfer for electric vehicles

In order to consistently provide efficient EV wireless charging, changes in efficiency caused by coil misalignment should be investigated. This body of work uses a vector network analyzer to record the power transmission coefficients then calculate the efficiency and coupling factors. An automated 3-axis platform was built for coil motion control. The test result shows that the efficiency can remain at 90% as long as the misalignment ratio is within 0.5 and the air gap ratio is from 0 to 0.25.

EV usage and city planning of charging station installations

Electric vehicles (EVs) are becoming popular in the United States. Battery EVs, powered exclusively by electricity, draw more attention because they emit zero exhaust fumes, transfer energy efficiently and can be more economical compared with internal combustion automobiles. This paper presents a comprehensive analysis of the real-world charging, driving and energy consumption patterns of electric vehicles and charging stations deployed in a college town over a period of ten months. Data collection approaches include data from charging stations and from Nissan CARWINGS telematics services. Results indicate that most charging events last fewer than three hours and most battery EVs are used locally within Athens, GA. Based on this EV usage analysis, potential impacts of wireless EV charging stations as well as a list of practical factors are discussed when implementing wireless charging stations across the city.

A Simple and Inexpensive Stereotactic Guidance Frame for MRI-Guided Brain Biopsy in Canines

A magnetic resonance imaging (MRI) guided stereotactic system was developed to provide veterinarians a method to accomplish minimally invasive stereotactic brain biopsies and procedures involving the cerebrum in canines. While MR-guided procedures are prevalent for humans, they are less common in animal practices. The system was designed to minimize fabrication costs in an effort to make such procedures more accessible in the veterinary field. A frame constrained the head without the need for punctures and supported registration and guidance attachments. Location data for registration and relevant structures were selected by the clinician, and a reverse kinematic analysis program generated the settings of the stereotactic arch to guide a needle to the desired location. Phantom experiments and three cadaver trials showed an average targeting error of <3u2009mm using the system.

Wearable Virtual White Cane: Assistive Technology for Navigating the Visually Impaired

Thirty-eight million people are visually impaired in the world. They encounter many disadvantages in mobility due to vision loss, which poses significant challenges when navigating unstructured environments. Conventional travel aids conveying simple tactile feedback to the visually impaired, such as fixed-length canes, provide limited ability to detect obstacles in a relatively limited distance. As a result, it can be difficult for the visually impaired to navigate smoothly using a cane. Much research effort has been focused on developing electronic travel aids (ETAs). Computer vision-based ETAs [1–5] aim to help guide the user using specialized landmarks or predetermined features. The robustness of such devices is still questionable; for instance, the devices fail to provide navigation in scenarios lacking visual cues or repetitive features [1]. ETAs based on different sensing principles have been presented in literature to overcome these drawbacks. Palleja et al. recently developed a hand-held laser sensor based ETA device. The object detection signal is converted to pressure feedback generated by a belt on the user’s wrist [6]. The limited scanning angle reduces region of interest for navigation. For other ETA devices like Miniguide [7] and the Nurion Laser Cane [8], the user needs intense focus and must intentionally sweep the device over the environment. To ease this inconvenience, Sonic Pathfinder [9,10] mounts an ultrasonic sonar ETA on a headband. The Pathfinder gives audio feedback in the form of notes on a musical scale, based on the proximity to objects ahead the user. Similar to other audio feedback designs [11,12], the major drawback is that audio signals can mask important environmental sounds. Although more complex to implement, devices relying on tactile sensation may thus present advantages. In this work, we present a wearable and miniaturized ETA, called a wearable virtual cane network (WVCN). The device is hands-free and convenient for daily use, aiming to provide consistent and reliable guidance in various conditions.

3-D Coil Positioning Based on Magnetic Sensing for Wireless EV Charging

Wireless power transfer (WPT) via magnetic resonance coupling is considered a promising outlet for electric vehicle (EV) charging due to the noncontact method. Unlike a traditional transformer, with WPT, the relative spacing and lateral distance between the primary and secondary coils are highly variable, which can affect the wireless power delivery and lower the efficiency. A magnetic positioning approach that shares the wireless charging structure is proposed to solve the misalignment issue associated with wireless EV charging. The proposed alignment sensing system employs multiple auxiliary minor coils on the secondary side to position the charging pad. The positioning principle and equivalent circuit were analyzed. The 108 samples were tested and they were distributed throughout the detection range of 70 cm. The experimental results demonstrate that >92% of those samples have positioning errors of <2 cm and 98% of them have positioning errors of <3 cm.

An online LiFePO 4 battery impedance estimation method for grid-tied residential energy storage systems

There has recently been a significant interest directed towards residential battery storage systems mainly motivated by high penetration of renewables, the low cost and high efficiency of power electronic devices, and the advancements in the safety and energy density of the batteries, especially Lithium-Ion (Li-Ion) batteries. Furthermore, the possibility for the end user to become a utility-independent entity with the capacity to overcome power outages and tariff rises is even further propelling this fast growing industry. Lithium iron phosphate (LiFePO4) battery is one of those technologies chosen to take the lead in residential battery storage due to its intrinsic safe performance, good energy density and price. This paper describes an online method for estimating the impedance of LiFePO4 batteries when they are used in residential single phase energy storage systems. Single phase power systems have the intrinsic characteristics of delivering power at twice the frequency of the grid; by energy conservation principle, this pulsating characteristics is transferred directly to the current in the DC stage of the battery storage system. The proposed method takes advantage of this phenomenon and, without interrupting the energy conversion process or adding any external perturbation to the system, is able to characterize, in situ, the AC impedance behavior of the battery. Experimental results are provided to validate the proposed method and simulations show the potential applicability of this method in the assessment of the actual battery aging state.

Analytical method for mutual inductance and optimum frequency calculation in a series-series compensated inductive power transfer system

The switching frequency of inductive power transfer (IPT) is sensitive to the air gap between the primary and secondary coils. The mutual inductance might change significantly for different air gaps, resulting in a shift for the switching frequency. The mutual inductance is usually acquired through experimental measurement, finite element analysis, or frequency tracking control. In this paper, Neumanns formula is simplified to compute the mutual inductance of two coils. A frequency-gap model is presented to offer a simple way to calculate the unity-gain frequency for a symmetrical series-series (SS) IPT. Finite element simulation and experiment were conducted to verify the model. The experimental results show that the unity-gain frequency can be output within an average computational time of 9.8ms, and the gain fluctuates from 0.95 to 1.05 when the air gap changes from 7.5cm to 25cm.