Chunbo Zhu

Simulation and experimental analysis on wireless energy transfer based on magnetic resonances

Wireless energy transfer based on coupled magnetic resonances is a new technology which energy can be transferred via coupled magnetic resonances in the non-radiative near-field. A simple energy transfer system structure was proposed in this paper. Based on this structure, the back electromotive force (back-EMF) in the receiving coil related with different transfer distance and with driving frequency was simulated and analyzed. Experimental results shows that the power can be transmitted is up to 50 W, the transfer efficiency is more than 60%, the distance of energy transfer is longer than 1 meter. The energy transferring is able to go through various non-metallic objects. The prospective applying fields are wide, such as EV charging, industrial robot, aerospace, wireless sensor networks, and RFID technology.

Super-Capacitor Stacks Management System With Dynamic Equalization Techniques

Super capacitor has the advantage of quick charge, large power density, and long cycle life. The shortage is the lower energy density compared with electrochemistry batteries. These features make it suitable for a short-distance electric bus used in the city. Because of the capacitance difference between the capacitor cells, after a number of deep discharging/charging cycles, the voltage difference between cells will be enlarged. This will accelerate the aging of the weak super capacitors and affect the output power. So, a management system with an equalization function is essential. In this paper, a practical super-capacitor stacks management system with dynamic equalization techniques is proposed. The function of the management system includes: monitoring the current, voltage, and temperature of the stacks, control of charge, and discharge with equalization online. A switched-capacitor equalization approach is adopted showing a low-cost way to meet the accuracy requirements. The dynamic equalized charging and discharging circuit is described. The algorithm to increase the operation speed and the precision is analyzed. By dynamically redistributing the current, the equalization procedure can be quicker and more efficient. This approach has been verified by experiments

Research on the topology of wireless energy transfer device

Aiming at the practical applications of novel wireless energy transfer, the mathematical model for wireless energy transfer devices based on intermediate frequency resonant is established in this paper. Based on the electromagnetic fields sine-band theory, the transfer scheme using lumped parameters is designed. It is proved that using the resonator with a high quality factor value and coupling coefficient matched resonant frequency leads to a bigger transfer energy and a longer distance. A correction method in this band is proposed based on the analysis of the resonator characteristics in the intermediate frequency electromagnetic field. The method makes it possible to transfer more energy over a longer distance. It is demonstrated that about 23 W electric power can be transferred with the distance of 0.7 m in the experiment.

Design and Loss Analysis of Loosely Coupled Transformer for an Underwater High-Power Inductive Power Transfer System

To prevent magnetic flux leakage to the maximal extent, increase the coupling coefficient of high-power inductive power transfer (IPT) system, and reduce the electromagnetic radiation in water medium, a novel underwater loosely coupled transformer (LCT) based on the semiclosed magnetic core structure is proposed in this paper. Power loss of the devised LCT is investigated comparatively in three media including air, freshwater, and seawater. It is shown that winding loss and core loss in the three media are basically identical. However, additional eddy current (AEC) loss in various water media is different for the sake of the difference in conductivity. In particular, AEC loss is extremely low in freshwater and relatively significant in seawater. Furthermore, when the operating frequency exceeds a certain value, AEC loss will be greater than core loss and winding loss, and become the major factor in restricting transmission efficiency of LCT in seawater. Finally, theoretical analysis and simulation are demonstrated by the underwater experiment on an IPT prototype system, which can transfer 10 kW at 91% maximal transmission efficiency and over a 25 mm air gap.

Design of battery and ultracapacitor multiple energy storage in hybrid electric vehicle

Combination of battery and ultracapacitor as energy storage of hybrid electric vehicles is considered a good way to improve overall vehicle efficiency and battery life. Coordinated power distribution and bi-directional DCDC converter control are challenges. Method to determine distribution of ultracapacitor and battery is proposed based on a specific hybrid electric bus. A bi-directional DCDC converter is interface of two energy storage to control power flow. Metrics of converter are determined from vehicle simulation. To downsize the converter and get high efficiency, bi-directional DCDC converter operates under complementary DCM condition and soft-switching.

Research on the model of magnetic-resonance based wireless energy transfer system

The key of magnetic-resonance based wireless energy transfer technology (MRBWET) is the magnetic coupling system which composed of driving and receiving coils, of which the mathematical model is important to the research of the transmission principle and the optimization of mechanism structure and parameters. Based on calculating the radiation level of typical coil, a magnetic-coupled-coil model was built based on analyzing the magnetic dipole used in the experimental system. According to the model, the quantitative relationship between the power contained in the receiving coil and parameters of resonances was discussed. The optimization method of parameters matching for maximal power transfer is proposed. Simulation and experimental results validate the correction and feasibility of the theoretical analysis.

A review on fault mechanism and diagnosis approach for Li-Ion batteries

Li-ion battery has attracted more and more attention as it is a promising storage device which has long service life, higher energy, and power density. However, battery ageing always occurs during operation and leads to performance degradation and system fault which not only causes inconvenience, but also risks serious consequences such as thermal runaway or even explosion. This paper reviews recent research and development of ageing mechanisms of Li-ion batteries to understand the origins and symptoms of Li-ion battery faults. Common ageing factors are covered with their effects and consequences. Through ageing tests, relationship between performance and ageing factors, as well as cross-dependence among factors can be quantified. Summary of recent research about fault diagnosis technology for Li-ion batteries is concluded with their cons and pros. The suggestions on novel fault diagnosis approach and remaining challenges are provided at the end of this paper.

Improved Study of Temperature Dependence Equivalent Circuit Model for Supercapacitors

The supercapacitor, because of its advantages of high specific power, quick charging or discharging with high current rates, and long cycle life, is an interesting choice for energy storage for applications where high power is needed for only a few seconds, such as pulse-power supply systems. Based on the use of supercapacitors all around the world, more and more attention is focused on the effects of temperature on their performance metrics such as capacitance, internal resistance, and efficiency. To predict the terminal voltage of supercapacitors at different temperatures, a three-branch RC equivalent circuit model is improved in this paper, and it can predict the terminal voltage up to 5 to 10 min after completion of charging or discharging. Initially, a typical three-branch RC equivalent circuit model without temperature parameter is used to simulate the pulse charging and discharging behavior of a specific commercial supercapacitor. Next, with the pulse charging and discharging experiment results under -40°C, -20°C, 0°C, and 20°C, all parameters in the circuit model are reset to a function of temperature, and the temperature dependence of parameters is discussed in detail and determined numerically. Finally, for the purpose of validating the correctness and the accuracy of the improved model, compared study of simulation results and experiment curves is done. Comparison results show that the fitting accuracy of the improved equivalent circuit model is satisfied in pulse charging and discharging at different temperature.

Energetic Macroscopic Representation based modeling and control for battery/ultra-capacitor hybrid energy strorage system in HEV

Electrical energy storage system plays an important role in hybrid electric vehicles. In this paper a simulation model for battery/ultra-capacitor hybrid energy storage system is presented by using Energetic Macroscopic Representation (EMR). Based on the model a control strategy for the hybrid energy storage system is developed with a goal of improving battery life and increasing the performance of HEV drive train. The simulation results under different urban driving cycles show the validity of the model.

A high efficiency isolated bidirectional equalizer for Lithium-ion battery string

Equalization for battery pack to enhance its usage life and performance is important for xEVs. In this paper, an isolated bidirectional equalizer based on full-bridge for Lithium-ion battery string is proposed. If a battery charge is excessive, the equalizer transfer charge from this cell to battery string; if a battery charge is insufficient, the equalizer will charge this cell from battery string. Closed-loop control keeps the equalization current constant, allowing precise control of the transferred charge. On the basis of considering OCV hysteresis, we proposed an equalization strategy based on SOC estimation for the equalizer. The equalizer features small size, high efficiency, and high accuracy. Experimental results confirm the applicability of the equalization scheme.