Yugang Su

Steady-State Load Identification Method of Inductive Power Transfer System Based on Switching Capacitors

An online steady-state load identification method is proposed to solve the problems related to frequency drift, system robustness deterioration, difficulties in controller design due to the uncertainties in load and mutual inductance variations of an inductive power transfer (IPT) system. Take a Series-Series-type IPT system as an example, an additional capacitor is added into the system to make the system work in two operating modes, and a mathematical model is established according to the two modes for the system identification. Simulation and experimental results have verified the proposed online load identification method. It has demonstrated that the method is accurate and reliable for identifying uncertain loads and magnetic coupling variations if other system parameters are known. The method can be used to improve the system performance with precise control.

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.

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.

Z-Impedance Compensation for Wireless Power Transfer Based on Electric Field

Capacitive power transfer (CPT) has been investigated as an alternative wireless power transfer technology based on electric field coupling. The coupling interface of CPT is formed by a pair of “capacitors” in series with the power source and load. The effective capacitance ranges from tens to a few hundreds of picofarads, yielding high impedance. Therefore, in most CPT systems, a tuning inductor is connected in series with the coupling interface for circuit compensation and power transfer capability enhancement. However, this compensation method suffers from high voltage spikes from the inductor if the secondary side load is removed suddenly causing electrical and health hazards. To address the issue, this paper proposes a CPT system based on a Z-impedance compensation network with inherent open-circuit and short-circuit immunity. It also has the voltage boost capability as a Z-source inverter. Its operating principle is described and a set of design equations are given. Both simulations and experimental results from a 5 W low power design have demonstrated that the proposed compensation method using the Z-impedance matching network exhibited open-circuit and short-circuit immunity, could boost up the output voltage by 50% with power efficiency exceeding 80%.

Discrete time mapping modeling and bifurcation phenomenon study of a ZVS converter

The varying period and complex commutation conditions make the classic mapping modeling method based on fixed switching period no longer fit for soft switching circuit analysis. This paper proposes a discrete time mapping method for modeling variable frequency resonant circuits. The analysis begins with the derivation of a sixth-order iterative map for a ZVS converter used in ICPT (inductively coupled power transfer) systems and then the model developed is employed to analyze the instability and sub-harmonic operation of the converter.

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.

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.