The efficiency of wireless power transfer (WPT) systems is highly dependent on the load, which may change in a wide range in field applications. Besides, the detuning of WPT systems caused by the component tolerance and aging of inductors and capacitors can also decrease the system efficiency. In order to track the maximum system efficiency under varied loads and detuning conditions in real time, an active single-phase rectifier (ASPR) with an auxiliary measurement coil (AMC) and its corresponding control method are proposed in this paper. Both the equivalent load impedance and the output voltage can be regulated by the ASPR and the inverter, separately. First, the fundamental harmonic analysis model is established to analyze the influence of the load and the detuning on the system efficiency. Second, the soft-switching conditions and the equivalent input impedance of ASPR with different phase shifts and pulse widths are investigated in detail. Then, the analysis of the AMC and the maximum efficiency control strategy are provided in detail. Finally, an 800-W prototype is set up to validate the performance of the proposed method. The experimental results show that with 10% tolerance of the resonant capacitor in the receiver side, the system efficiency with the proposed approach reaches 91.7% at rated 800-W load and 91.1% at 300-W light load, which has an improvement by 2% and 10% separately compared with the traditional diode rectifier.

Inductive power transfer (IPT) for battery charging applications has significant advantages over the traditional plug-in system. Since misalignment between the primary and secondary windings is inevitable, it is of significance to improve the misalignment tolerance of IPT systems with constant-current (CC) and constant-voltage (CV) outputs for battery charging. In this paper, the load-independent output characteristic of the hybrid topology and the function switching between CC and CV of the reconfigurable topology are analyzed. Besides, a hybrid and reconfigurable IPT system with 3-D misalignment tolerance for CC and CV outputs is proposed, simplifying or even canceling control schemes. Moreover, a novel parametric design method is given for the IPT system, which can suppress the fluctuation of the output voltage/current within a certain range of misalignment. In order to validate the performance of the proposed topology, a 1-kW prototype is built, and the corresponding experiments are carried out. In the CC/CV mode, the system can operate with the longitudinal misalignment to 50% when the load varies from 36 to 480 Ω, and the fluctuation of the output current/voltage is within 5%. Similarly, the misalignment in Y- and Z-axis is 12.5% and 33.3%, respectively.

Dynamic wireless power transfer is a promising solution to address electric vehicle range anxiety and to reduce the ca-pacity and the cost of the on-board batteries. In the traditional DWPT system, the mutual inductances among transmitters make the design of compensation networks very complex. Besides, the power null phenomenon and the power pulsation phenomenon cause a fluctuating DC output voltage or current on the receiver side. To address these issues, this paper proposes a new magnetic coupler. Unipolar and bipolar coils are laid alternately to form segmented transmitters, which are turned ON or OFF according to the position of the overhead receiver coil. LCC compensations, whose inputs are connected in parallel to a common inverter for cost reduction, are adopted. At the receiver side, unipolar and bipolar coils are overlapped in the same plate in order to effec-tively smooth out the mutual inductance variations and hence, reduce the output voltage or current fluctuations. Also, a con-figurable resonant circuit is designed on the receiver side to achieve constant voltage (CV) charging and constant current (CC) charging. Moreover, an optimization design by using Fi-nite-element analysis software Maxwell is developed to choose the best turns of the receiver coil to further improve the output quality. A laboratory prototype with 4-A charging current and 96-V charging voltage, using 85kHz operation frequency, is con-structed to verify the proposed DWPT system. The experimental results show that constant output voltage and current can be achieved within 2% fluctuation, and the overall efficiency is 90.37%.

In order to improve misalignment tolerance for an inductive power transfer (IPT) system, a third-coil is employed to reversely connect with the primary coil of the loosely coupled transformer (LCT) in series. The LCT with a third-coil (LCT-TC) not only can improve the misalignment performance in x- and y-directions, but also do not affect the inherent output characteristics (such as constant current or voltage output) of original compensation topologies. In addition, the proposed approach can keep the IPT system operating with relatively high efficiency against misalignment. Then, a detailed design method of LCT-TC is presented. Finally, a double-side LCC compensated IPT system is chosen as an example to verify the feasibility of proposed LCT-TC. A 3.4kW prototype is constructed, and experimental results show that the proposed method has good misalignment performance. The LCC-LCC IPT system with LCT-TC can retain 96% of the well-aligned power at 40% misalignment, and the end-to-end (dc-dc) overall system efficiency is at least 92%. Besides, the fluctuation of the output current is [-2%, 5%] while the load varies from 15 Ω to 34 Ω within 40% misalignment.

This paper presents an impedance-based model to systematically investigate the interaction performance of multiple trains and traction network interaction system, aiming to evaluate the serious phenomena, including low-frequency oscillation (LFO), harmonic resonance and resonance instability. The train-network interaction mechanism is therefore studied and one presents a detailed coupling model for investigating the three interactive phenomena and their characteristics, influential factors, analysis methods and possible mitigation schemes. In the Part I of the two-part paper, the measured waveforms of such three phenomena are firstly characterized to indicate their features and principles. An interactive model of the train-traction network system for investigating the three problems is then presented. In order to reveal the interaction mechanism, the all-frequency impedance behaviors of the electric trains and traction network are equally modeled. In which, an impedance-based input behavior of the train is fully investigated with considering available controllers and their parameters in DQ-domain. While, the entire traction network, including traction transformer, catenary, supply lines, is represented in a frequency-domain nodal matrix. Furthermore, the impedance-frequency responses of both electric train and traction network are measured and validated through frequency scan method. Finally, a generalized train-network simulation and experimental systems are proposed for verifying the theoretical results of the two-part paper.

The design of operating frequencies and compensation topologies for load-independent output current or output voltage in two-coil wireless power transfer (WPT) system has been widely studied. The three-coil WPT system has been proven to be more efficient and shows a better performance compared to the two-coil WPT system with an increasing transmission distance. However, the research on load-independent output voltage or output current of the three-coil WPT system is still at pilot stage. This paper systematically investigates the load-independent output voltage and output current characteristics of a three-coil WPT system to achieve a constant output voltage (CV) and constant output current (CC) with near zero reactive power, which can simplify the control. The CV and CC characteristics are achieved by welldesigned passive parameters of the receiver side compensation. Additionally, a hybrid receiver side compensation with two additional switches for the three-coil WPT system is developed to charge the electric vehicle (EV) battery by combining the CC and CV characteristics. Finally, a scaled-down experimental setup with 4A charging current and 96V cell voltage is constructed to verify the proposed approach. The experimental results agree well with the theoretical analysis.