Yanjie Guo

Applying LCC Compensation Network to Dynamic Wireless EV Charging System

Based on the wireless power transfer (WPT) technology, dynamic wireless charging of electric vehicle (EV) is gaining increasing attentions because it promotes the popularization of EV and also serves a new form of clean transportation. In this paper, we introduce the LCC compensation network to WPT system oriented for dynamic wireless EV charging application. First, characteristics of symmetrical T-type network, which is the origin of the favorable LCC compensation network, are summarized. Then, parametric design for both the LCC network used in the secondary side and the LCC network used in the primary side is elaborated theoretically. Furthermore, neighboring effects resulting from the combination of the LCC compensation network and the inevitable inter-coupling between adjacent segments are investigated. Finally, a two-segment LCC compensated dynamic EV charging system is built up and tested with both intra-segment and inter-segment experiments. Spatially averaged output power and dc-dc efficiency of the prototype are measured to be 2.34 kW and 91.3%, respectively. High consistency of the experimental results validates the correctness of the proposed analyses and parametric design method, as well as the suitability of applying LCC network in dynamic wireless EV charging applications.

Improving the Misalignment Tolerance of Wireless Charging System by Optimizing the Compensate Capacitor

In this paper, we present a simple method to extend the feasible rated charging zone of a four-coil coupled wireless charging system (WCS) by optimizing the compensate capacitors of the coils. With the proposed optimizing method, the tolerant lateral misalignment of our WCS prototype has been extended to 44.3% of the coil size, achieving a 38.3% relative improvement.

Systematic Analysis of Conducted Electromagnetic Interferences for the Electric Drive System in Electric Vehicles

There are serious electromagnetic compatibility (EMC) problems in electric vehicles. In order to explain and solve them, a systematic method to analyze conducted interferences of the electric drive system is shown in this paper. This method represents the efiects of the power battery which is the most difierent part between electric drive systems used in electric vehicles and other cases. Also, equivalent models are established from power electronics devices to the entire system by considering both the working mechanism and stray parameters. Firstly, insulated gate bipolar transistor (IGBT) and inverter are studied as the main interference source. A new expression is put forward to estimate the frequency domain features of the inverter disturbances. Then, power battery and electric motor are discussed as the main propagation paths. Their high frequency circuit models are given with parameters obtained from tests and measurements. Finally, the system model is established. The system interferences are analyzed to get their generation causes, in∞uence factors and frequency domain characteristics. Comparisons between simulations and experiments verify the correctness of the models and the method.

Switch-On Modeling and Analysis of Dynamic Wireless Charging System Used for Electric Vehicles

This paper presents an equivalent model to analyze switch-on process of dynamic wireless charging system of electric vehicle (EV). In the model, system initial state before switching is considered and the full response is used to describe the switch-on process. First, the system states before and after switching are discussed, and an approximate method is proposed to calculate the initial value of converter dc-side voltage in switch-on unit. Then, equivalent transient sources and system transfer functions are obtained to establish the switch-on model. So, the switch-on process can be described through full responses of the selected currents under the excitation of equivalent sources. Furthermore, the proposed model is verified by a developed dynamic wireless EV charging prototype. Also, switch-on transient characteristics are investigated through discussions on system parameter and vehicle speed effects. Finally, a simple way to select the suitable switching position is provided based on the analysis of switching position influence, and its effectiveness has been validated by experimental results.

Null-Coupled Electromagnetic Field Canceling Coil for Wireless Power Transfer System

In this paper, we present a kind of null-coupled canceling (NCC) coil to shield electromagnetic fields (EMFs) for wireless power transfer (WPT) systems. The proposed NCC coil is based on the particular zero-mutual-inductance characteristic between two general coils. The working principles, shielding effectiveness, and practical expansions of the proposed NCC coil are illustrated. Furthermore, locating of the zero-mutual-inductance position and determination of the canceling coil current are elaborated, and effects that an NCC coil exerts on the output power, efficiency, and misalignment tolerance of the applied WPT system are theoretically studied. Finally, targeted at our predesigned electric vehicle wireless charging-oriented WPT prototype, a practical NCC coil is built and tested with comparative experiments with the prevalent aluminum (Al) plate shielding. The experimental results show that, with a properly chosen canceling current, the proposed NCC coil could not only shield the EMF more effectively, but also cause a lower efficiency reduction to the applied WPT system than an Al-plate does.

Minimizing the eddy current loss in the chassis when charging an electric vehicle wirelessly

The eddy current loss in the steel chassis of an electric vehicle (EV) is an underestimated problem facing the EV oriented wireless charging system (WCS) designers. In this paper, we have proposed three basic optimizing strategies to develop efficient WCSs with less eddy losses. Finite element simulations are conducted to compare and evaluate the effectiveness of these three methods. Moreover, a 3-kW EV oriented wireless charging prototype is developed, with a steel plate imitating the vehicular chassis, full-load wireless charging experiments are performed. Experimental results match well with the simulation. It shows that minimizing the quadratic sum of the transmit-coil current and receive-coil current is more effective to reduce the eddy current loss.

Analysis of power factor correction circuit for EV wireless charging system

In order to reduce interference on the grid, a power factor correction (PFC) circuit used for electric vehicle (EV) wireless charging system is analyzed in this paper. Firstly, the load of PFC circuit is described considering current source type inverter and energy transfer coils. Then, dynamic model of boost converter used in PFC circuit is established through state space averaging method. Moreover, controllers are taken into count to get system close-loop transfer functions. Based on the system model, PFC circuit is studied under conditions of different charging powers, coil lateral misalignments and load inductances. All the simulation and experimental results have proved that the designed PFC circuit works well on the application of EV wireless charging system.

Rectifier Load Analysis for Electric Vehicle Wireless Charging System

This paper presents the analysis of a rectifier load used for an electric vehicle (EV) wireless charging system, as well as its applications on compensation network design and system load estimation. First, a rectifier load model is established to get its equivalent input impedance, which contains both resistance and inductance components, and can be independently calculated through the parameters of the rectifier circuit. Then, a compensation network design method is proposed, based on the rectifier load analysis. Furthermore, a secondary side load estimation method and a primary side load estimation method are put forward, which adopt only measured voltages and consider the influence of the rectifier load. Finally, an EV wireless charging prototype is developed, and experimental results prove that the rectifier equivalent load can be correctly calculated on conditions of different system load resistances, rectifier input inductances, dc voltages, and mutual-inductances. The experiments also show that rectifier load equivalent inductance will impact system performances, and the proposed methods have good accuracy and robustness in the cases of system parameter variations.

Experimental Study on Asymmetric Wireless Power Transfer System for Electric Vehicle Considering Ferrous Chassis

Steel chassis of an electric vehicle (EV) could reduce the efficiency of a wireless power transfer (WPT) system installed on which. To improve the performance of practical EV-oriented wireless charging systems, asymmetric WPT systems in ferrous environment are studied in this paper. First, inevitable adverse effects of the ferrous chassis on a nearby WPT coil are investigated. Then, impedance matching criteria to achieve the theoretical maximal efficiency of a general WPT system are theoretically elaborated. Further, one common symmetric and two asymmetric EV oriented WPT systems are built and comparative experiments on these three WPT systems are conducted. Vulnerability to ferrous environment, throughput power, efficiency, misalignment sensibility, as well as electromagnetic field radiation of these three WPT systems are assessed and compared in both ideal environment and chassis-emulated ferrous environment. Experimental results indicate that, asymmetric WPT system with a smaller transmitter and a larger receiver is more suitable to be implemented on a real EV for wireless charging.

Effects of operation frequency and current on coil impedance of EV wireless charging system

This paper presents an analysis of operation frequency and current effects on coil impedance and system characteristics of electric vehicle (EV) wireless charging system. Firstly, an equivalent circuit model of EV wireless charging system with dual side LCC compensation networks is established. Also, power loss and system efficiency expressions are given. Then, frequency influence is studied considering Litz wire used for the coils. Furthermore, effects of frequency and current are analyzed based on parameter measurements and tests. Finally, efficiency and output power change curves are given to show the impacts of frequency- and current-dependent coil impedances on system characteristics.