결합계수 및 코일 자기 인덕턴스 변화에 따른 무선전력전송 시스템의 입력 임피던스 변화에 관한 연구

The input impedance of twitch muscle fibres of the Atlantic hagfish has been measured with sinusoidal transmembrane currents. The apparent specific membrane resistance and capacitance decreased markedly with frequency, and were relatively independent of fibre diameter. A model of the T-system based on anatomical observations, was used to predict the input impedance in the normal solution (artificial sea water). The changes in input impedance produced by glycerol treatment, low chloride solution, reduced pH and isotonic solutions with low ionic strength were easily interpreted in terms of the same model. The model predicts severe attenuation of the action potential if conducted electrotonically by the transverse tubules towards the center of the fibre.

High Transmission Capacity P.U.A. Wireless Power Transfer for AUV Using an Optimized Magnetic Coupler

This paper presents the results of an experimental study of user interaction with four types of handset antennas. Results are obtained using 63 volunteers who hold the phone in a completely natural manner. Input impedances are measured with respect to hand positions on the phone. The study reveals typical hand interaction scenarios, the extent of antenna input impedance changes and the relative capabilities of different antennas in handling such interactions. The experimental results presented in this paper agree well with simulations. (6 pages)

An energy-efficient high-powermulti-coil wireless power transfer system (WPT) has been studied in this paper. The proposed system was first analyzed and examined using theoretical modeling; this was followed by finite element analysis and circuit simulation to confirm the goal. As the air gap between the transmitter and receiver coils widens, the coupling coefficient of a WPT system will drop. A large-air-gap WPT system’s coupling coefficient can be raised by adding relay coils between the transmitting and receiving coils. On the other hand, an increased coupling coefficient improves the system’s overall power transfer efficiency. The suggested multi-coil system, which has an air gap of 15 cm and a lateral misalignment of 3 cm between the transmitting and receiving coils, has been simulated and verified using the Maxwell 3-D finite element tool and Ansys Simplorer circuit simulation software.

Transfer efficiency (TE) is an important research topic in the practical application of a wireless power transfer (WPT) system. WPT system is a loosely coupled system; the coupling coefficient changes drastically due to the relative movement of the transmitting and receiving sides. It is difficult to achieve maximum efficiency tracking (MET) only from the research of frequency tracking, impedance matching, and system parameters under a fixed coupling coefficient. This article proposes a novel MET control method of the WPT system with optimized T-type impedance matching network under the real-time identification of a coupling coefficient to realize the MET control. This method synthetically analyzes the nonlinearity of the rectifier circuit, the identification of coupling coefficient, the variation of load resistor, and the controllability of the output voltage, involving the main factors of the MET control. The simulation and experimental results show that the WPT system has a good performance on MET and constant output voltage control; the validity and accuracy of the proposed MET control method are consistently verified.

In this paper, a new approach is proposed to achieve maximum coupling coefficient for the windings in circular Wireless Power Transfer (WPT) systems. The designed magnetic structure has the maximum magnetic coupling coefficient in a specific air gap in order to maximize the system efficiency. Series resonant compensator network is analyzed in frequency domain and proper operating point is selected to achieve constant voltage gain in different loads. This system controls output voltage through a closed loop control via controlling inverter's duty cycle. The design procedure is explained for a 5 kW system. This system can transfer power from 100mm to 200mm air gap by resonant network and magnetic circular coupling that has a 480mm diameter. Efficiency results for output power in various air gaps are presented, where efficiency of the nominal load for 150mm air gap is 93%.

This paper proposes a novel coupling coefficient and load estimation method in wireless power transfer (WPT) systems. First, the relationship among the harmonics of the transmitter side input current, the coupling coefficient, and the load is mathematically derived in detail. Afterwards, a state estimation based parameter identification algorithm is utilized to accurately estimate the coupling coefficient and the load, with full consideration of information redundancy. Compared to the existing methods, the proposed method only requires transmitter side input current, can accurately estimate the coupling coefficient and the load at the same time, and can be applied to rather complex WPT topologies. Simulation and hardware experiments in an example LCC-C compensated WPT system verify the validity of the proposed coupling coefficient and load estimation method.

The coupling coefficient determines the transfer efficiency of the wireless power transfer (WPT) system. The magnetic leakage can be reduced, and the coupling coefficient of the coil can be enhanced by adding a magnetic shield. Thus, the transfer efficiency of the WPT system can be improved. However, when the receiving coil is added with magnetic shield and occurs horizontally misaligned, the coupling coefficients between the coils with the magnetic shield can only be calculated by finite element simulation, and there is no calculation method for the coupling coefficient of two circular coils with bilateral finite magnetic shield at horizontal misalignment. Therefore, based on Maxwell's equations and Bessel's function, the formula of the coupling coefficient between circular coils at coaxial is derived by the subdomain hierarchical analysis (SHA) method. On this basis, the coupling coefficient calculation formula between circular coils at horizontal misalignment is further derived by using the boundary vector equivalence (BVE) method. The results show that the maximum experimental error is not more than 5.58%, and the longest average time of the algorithm is not more than 1.282 s, which verifies the effectiveness and rapidity of the proposed method.

The equivalent input impedance of power system usually needs to be obtained by an impedance scanning test in practical applications, i.e., a harmonic generator is utilized to emit fully controllable disturbing signals, and response is recorded to calculate the input impedance. However, in those high voltage application scenarios, the leakage inductance of a boosting transformer of the harmonic generator will reduce the harmonic current generation capacity heavily. This paper proposes an enhanced harmonic current injecting method based on the virtual impedance methodology for impedance tests in the traction power supply system (TPSS) of electric railways. By impedance shaping, converters of the harmonic generator can be regarded as a virtual capacitance. Its capacitive reactance can offset partial inductive leakage reactance of the boosting transformer at high frequencies. With this proposed method, a larger harmonic current can be injected into the TPSS under test at 25kV high voltage level more easily. Simulation results and experimental results based on StarSim Hardware-in-the-loop (HIL) platform confirm the effectiveness of the proposed method. The results show that the injected harmonic current at 2600 Hz at 25kV was increased by 133%.

The variation of load resistance and coupling coefficient are two key factors affecting the output characteristics of wireless power transfer system during the charging process. Both the variation of coupling coefficient caused by the position deviation of primary and secondary devices and the variation of load resistance during charging will result in the low output power and efficiency of the wireless charging system. In view of the above problems, this paper studied the constraint conditions of the compensation network of several wireless power transfer systems, and analyzed the output characteristics of the wireless power transfer system of each compensation network under the variation of load and coupling coefficient. The LCL-LCL type compensation network structure was selected for optimization design and according to the variation characteristics of output power and efficiency with load and coupling coefficient, the method of optimizing the compensation network parameters was proposed. The output power value of the design system was further optimized by adding a dc-dc converter circuit. Finally, the effectiveness of the proposed optimization design method was verified through the system simulation.

At present, wireless power transfer systems based on magnetic resonance, parity-time symmetry, and fractional order have received more and more attention, especially in wireless charging applications of mobile phones, electric vehicles, and other products. However, the consequent electromagnetic radiation safety issues are becoming increasingly prominent. Therefore, this paper compares and studies the magnetic field distribution of magnetic resonance, parity-time symmetric and fractional-order wireless power transfer systems, and uses ANSYS simulation software to simulate and comparative analyze. The simulation results show that under the condition of equal output power, the magnetic field distribution of the parity-time symmetric wireless power transfer system is more concentrated when the coupling coefficient is small, while the magnetic field distribution of the magnetic resonance wireless power transfer system is more concentrated when the coupling coefficient is large, but it is significantly smaller than that of the fractional-order wireless power transfer system. In addition, the safety range of the parity-time symmetric wireless power transfer system is significantly larger than that of the magnetic resonance and the fractional-order wireless power transfer system at different output power. Remarkably, the magnetic field distribution of fractional-order wireless power transfer system will also change with different order, which implies that the safety range of the fractional-order wireless power transfer system can be designed according to the requirements to achieve the ideal safety range.

Coupling coefficient calculation and optimization of positive rectangular series coils in wireless power transfer systems

This paper presents a theoretical analysis, an optimal design method, and experimental results for a wireless power transfer (WPT) system with an intermediate coil. The analytical expression of the dc voltage transfer function is presented and discussed. In a two-coil WPT system, which has low coupling coefficient, the intermediate coil boosts the apparent self-inductance and magnetizing inductance of the primary side at around the resonance frequency of the intermediate coil, so that the apparent coupling coefficient is compensated. The coupling coefficient makes the system efficiency increase and induces bifurcation phenomenon. From the analysis, this paper proposes an optimal design method using the second resonance frequency operation with the bifurcation phenomenon and presents design procedure for high efficiency. A prototype of the WPT system with the intermediate coil is implemented and experimented to verify the validity of the analysis and the proposed design method. The prototype operates at 100 kHz switching frequency and has an air gap between primary and secondary side of 200 mm. An overall system efficiency of 95.57% has been achieved at 6.6 kW of output power.

Wireless power transfer (WPT) systems’ efficiency is significantly impacted by non-monotonic variations in the coupling coefficient. For very short distances or strong-coupling cases, the WPT efficiency is minimal at the natural resonant frequency, with two peaks around this frequency, known as the frequency splitting phenomenon. On the other hand, WPT capability decreases for long distances or weak coupling cases. Therefore, adaptive matching is required for WPT systems with varying distances, like wireless charging systems for electric vehicles (EVs). This paper first presents a detailed analysis of the frequency splitting phenomenon by studying the root locations of the WPT system’s transfer function. Then, a real-time fixed-frequency adaptive impedance matching (IM) method is proposed, in which the amplitude and phase of the input impedance is estimated using the average active power, the average reactive power, and the amplitude of input voltage. Unlike traditional search-and-find techniques, the proposed method calculates the optimal IM network parameters only in a single iteration, which improves the convergent speed. A scaled-down 20-Watt prototype controlled by the TMSF2812 is fabricated and used to validate the effectiveness of the proposed method over a wide range of coil-to-coil distances.

A wireless power transfer (WPT) system via magnetic resonance coupling method is attracting attention to high convenience. A WPT system has problems such as power transmitting loss and output voltage fluctuation due to the change in the coupling coefficient and the load state. In previous method, sliding mode control system as a tracking controller considering nonlinearity and uncertainty has been proposed, but the output of this control system had bias and chattering. This paper proposes operator-based nonlinear sliding mode control system to reduce chattering and bias simultaneously for a WPT system using buck converter. First, the model of the WPT system using rectifier and buck converter is explained and dynamics formulas are derived. Next, the proposed operator-based nonlinear sliding mode control system design for the WPT system is described and tracking performance is confirmed. Finally, the result of simulation of constant voltage control and comparison with the previous method is shown.