Chunsen Tang

Load Detection Model of Voltage-Fed Inductive Power Transfer System

Detecting load parameters in the inductive power transfer (IPT) system is essential to establishing a stable and efficient wireless power supply of good quality for kitchen appliances. This paper presents an effective load detection approach, namely transient load detection model, to detect load conditions by utilizing the energy injection mode and free resonant mode. To realize the proposed model, the differential equation of the primary resonant current under the free resonant mode was used. Besides, real-time sampled data, including the operating frequency in the free resonant mode and peak value of the primary resonant current were collected. Imitating the wireless power supply for kitchen appliances, simulation and experimental results with the full-bridge SS-type voltage-fed IPT system have shown that this transient load detection model is accurate and reliable.

Dynamic parameters identification method for inductively coupled power transfer system

In inductively coupled power transfer (ICPT) system, due to load and coupling parameters dynamic variation, primary resonant system parameters often drift from inherent operating point and lead to drastic decrease of power transfer capability and efficiency. In order to identify dynamically variation of system parameters, this paper put forwards system dynamics parameters identification method based on energy analysis. The method sets up energy supply, storage and dissipation function and energy equilibrium equations in primary resonant tank. And system reflection impedance solving function is given in analytic form as well. Furthermore, with the reflection impedance identification, this paper presents load parameters identification method. The identification methods are derived from energy perspective to avoid complex system modeling and requirements of high speed sampling system. Only zero crossing points sample data of resonant variables are required in system identification process. The identification is beneficial for system controller design. The identification methods are verified by experiments results.

Frequency bifurcation phenomenon study of a soft switched push-pull contactless power transfer system

This paper studies a frequency bifurcation phenomenon of a soft-switched push-pull contactless power transfer (CPT) system with parallel tuned pick-up and short-circuit decoupling power flow control. An extended stroboscopic mapping method is applied to obtain the possible zero voltage switching (ZVS) operating points first, then the fundamental resonant operating points are defined, and the system softswitching stability is analyzed according to the eigenvalues of the Jacobi matrix of the Poincare mapping model of the system. An example system with multiple resonant frequency points is studied and verified by simulation results. Frequency hopping phenomenon is identified and discussed in the system when the switch of the decoupling power flow controller is turned on and off with a very low frequency. The results are very useful for guiding the design of practical CPT systems, and the proposed method can also be applied to analyze nonlinear behaviors in other switch-mode resonant converters.

Energy Efficiency Analysis of U-Coil Wireless Power Transfer System

In order to improve the power transfer efficiency and ensure the space cleanliness of power transfer direction in inductive coupled wireless power transfer (WPT) system, a new U-coil WPT system is proposed. Based on the mutual inductance coupling theory, a new methodology for ensuring that a U-coil system is more energy efficient than a two-coil counterpart is presented in this paper. The theoretical proof and the conditions for meeting the objective are derived and practically verified in a practical prototype. The experimental results show: 1) comparing with two-coil system, power transfer efficiency can be improved more than ten times by using U-coil system; and 2) with the same power transfer efficiency principle, the dimension of primary and load coils in U-coil system shrinks at least 66% comparing with that of two-coil system. The U-coil system not only improves power transfer efficiency but also ensures the cleanliness of the space along the energy transfer direction.

Extended stroboscopic mapping (ESM) method: A soft-switching operating points determining approach of resonant inverters

This paper proposes an extended stroboscopic mapping (ESM) method for analyzing soft-switching operating points of resonant inverters. The essential idea of the proposed method is treating the operating period of traditional stroboscopic mapping model as a variable and employing fixed-point theory to find the soft-switching operating points. The method consists of four simple and easy-to-implement steps and can accurately determine the periods and steady-state responses of all possible steady-state soft-switching operating points of resonant inverters. A series tuned inductively coupled power transfer (ICPT) system is taken as an example to test the proposed method. Both simulation and experimental results have proved the validation of the proposed ESM method.

Capacitive Power Transfer System With a Mixed-Resonant Topology for Constant-Current Multiple-Pickup Applications

Capacitive power transfer (CPT) systems based on high-frequency electric field coupling have attracted much attention recently due to their simplicity and low eddy-current losses. This paper proposes a mixed-resonant topology consisted of a Π-CLC resonant circuit on the primary side and a T-CLC circuit on the secondary side for multiple pickups constant current output applications. The voltage gain, current gain, and zero phase angle frequency at different operating modes of Π-CLC and T-CLC circuits are analyzed by fundamental frequency approximation, and the conditions leading to a constant output current independent of loads are determined. Based on the analysis, a design method to determine the resonant network parameters is proposed according to the required output current of each pickup. A prototype with three pickups has been designed and built, and both simulation and experimental results have demonstrated that the proposed multiple-pickup CPT system can output a constant current at each operating power pickup against the load variations of itself and others.

The Recognition and Control of Nonideal Soft-Switching Frequency for Wireless Power Transfer System Based on Waveform Identification

Nonideal frequency problems can occur in a wireless power transfer system due to multiple soft-switching frequencies and frequency bifurcation. To make the system work at an ideal frequency with high-power transfer capability and efficiency, a method based on waveform identification is proposed. First, the space state model of a SP type WPT system is built, and the waveforms at ideal and nonideal working frequencies are obtained based on the stroboscopic mapping theory. Second, according to the characteristics of these waveforms, the swing door algorithm is improved by waveform distortion rate and fast Fourier transformation, which is used to recognize nonideal waveforms. Then, a control strategy based on “online self-determined optimization” is proposed to deal with the problem. Finally, the results of simulation and experiments show that the method proposed in this paper can identify the waveforms at nonideal frequency and find an ideal working frequency for the WPT system.

A Shared Channel Design for the Power and Signal Transfers of Electric-field Coupled Power Transfer Systems

Electric-field coupled power transfer (ECPT) systems have been proposed as an alternative wireless power transfer (WPT) technology in recent years. With the use of capacitive plates as a coupling structure, ECPT systems have many advantages such as design flexibility, reduced volume of the coupling structure and metal penetration ability. In addition, wireless communications are effective solutions to improve the safety and controllability of ECPT systems. This paper proposes a power and signal shared channel for electric-field coupled power transfer systems. The shared channel includes two similar electrical circuits with a band pass filter and a signal detection resistor in each. This is designed based on the traditional current-fed push-pull topology. An analysis of the mutual interference between the power and signal transmission, the channel power and signal attenuations, and the dynamic characteristic of the signal channel are conducted to determine the values for the electrical components of the proposed shared channel. Experimental results show that the designed channel can transfer over 100W of output power and data with a data rate from 300bps to 120 kbps.

An embeddable transmitter coil applied to electric vehicles powered by IPT system

Transmitter coil is one of the most critical part in an inductive power transfer (IPT) system for electric vehicles (EVs) application. For the traditional transmitter coils, due to the switch process between the adjacent coils, two serious problems of pick up voltage fluctuation and high power loss on the windings affect the stability and efficiency of the wireless EV charging. In order to solve these problems, this paper proposes a novel segmented transmitter coil for wireless power transfer on EV. A mutual inductance model is established based on the Neumanns Formula, moreover, a key parameters selection method and turns ratio optimization method of the proposed segmented transmitter coils are also presented to keep the mutual inductance in a constant level while the transmitter coils switching one by one. Both of the simulations and experimental results verify the validity and effectiveness of the proposed transmitter coils and its key parameters selection method.

Full-Duplex Communication on the Shared Channel of a Capacitively Coupled Power Transfer System

This paper proposed a novel wireless power transfer system with full-duplex communication on a shared channel for capacitively coupled power transfer systems. For the analysis of power and signal transmission, a frequency-domain model of the power and signal channels is established. Based on this model, the signal transfer characteristic of the channel and the influence of power flow on the signal channel are analyzed. Moreover, to ensure the power and signal transfer without unacceptable interference or attenuation, a parameters selection method of the communication channel is developed. In addition, an interference suppression strategy by taking the interference from the ipsilateral channel into consideration is proposed. To suppress the interference effectively, an estimation of the ipsilateral channel output signal is made. Then, the signal from the opposite channel is demodulated by removing the estimated values of the interference. Both simulation and experimental results showed have proven the correctness and effectiveness of the proposed wireless power and signal transfer method. Finally, it has demonstrated that the designed channel can transfer 100 W of power, and a full-duplex communication can be well achieved with different data rates in two directions when both two data rates are set within 200 kb/s.