Change In Mutual Inductance Research Articles

A fast modeling method of pulsed eddy current with double-coil based on model-driven BP neural network

ABSTRACT The analytical model serves as an important guiding role in practical testing. Currently, there is scarce research on the building of the analytical model for pulsed eddy current (PEC) with double-coil excited by a voltage source. This paper derives a frequency-domain model for PEC from a double-coil’s equivalent circuit. To tackle low modeling efficiency due to complex impedance changes and mutual inductance changes, a BP neural network (BPNN) maps lift-off, thickness, and frequency to impedance changes and mutual inductance changes. Training samples for the BPNN come from analytical models of impedance change and mutual inductance change. The study finds that a BPNN with four hidden layers and Bayesian regularization significantly improves prediction accuracy. Finally, the correctness of the BPNN method is verified. The PEC signals obtained by the BPNN method, the analytical model, and the Comsol finite element method are compared under different thicknesses and lift-offs, and it is found that the consistency of the PEC signals of these three methods is very well. And, the amplitudes of the residual signals between the BPNN method and the analytical model of the PEC signals are relatively small, and the relative errors at the peaks are no more than 0.4%.

Design of Compensation Topology for IPT System Considering Coils’ Parameters and Load Variations for CC or CV Output

The inductive power transfer (IPT) technology is drawing increasing attention. Variations in the height of the secondary coil are inevitable due to the fluctuations in the height of the electrical equipment or the pressure of the tires, which leads to variations in the coils’ parameters (self-inductances and mutual inductance). The coils’ parameters and load variations can dramatically affect the performance of the IPT system. In this paper, a unified mathematical model which can describe multiple compensation topologies is established. A design method is proposed to obtain suitable topology and component parameters based on the unified mathematical model and the non-dominated sorting genetic algorithm II. In addition, not only the stable output voltage/current is achieved, but the efficiency and cost are also improved. Finally, two experimental prototypes were built to verify the effectiveness, which has the output characteristics of constant current (3.5A/600W) and constant voltage (72V/100W), respectively. The results show that the output fluctuations are less than 5.63%, and the maximum efficiency is above 94.69% when the coils’ parameters (the primary self-inductance change from 85.76μH to 102.2μH, the secondary self-inductance change from 86.26μH to 102.35μH, and the mutual inductance change from 38.2μH to 72.1μH) and load (double change) vary.

New Control Method for Receiver-Side DC–DC Converter With Large Stability Margin and Fluctuation Suppression Toward DWPT System

Dynamic wireless power transfer (DWPT) system is applied to electric vehicles, medical treatment, communication and many other fields. Usually, a DC-DC converter is cascaded at the receiver side to suppress output fluctuation caused by mutual inductance change in the moving process. However, there occurs instability in some conditions in the system under conventional topology and control method. This work proposes a new control method based on dual buck-boost converter to handle the above two problems at the same time. It can, in theory, reduce the peak-peak and average values of DC inductor current, meanwhile, increase the converter efficiency. Also, it can improve the stability margin of the whole system. In this paper, we use a simulator to replace the actual DWPT system. Through the simulator, the WPT system can produce the same fluctuating output voltage as that under dynamic conditions to support experiment. The stability of the system is explored by constructing the small signal model of the system. Then, the effectiveness of the method is proved by simulation and experiment results.

Simulation and Theoretical Study on the Mutual Inductance of the B-Dot Used for High-Power Transmission Lines

For the B-dot used for high-power transmission lines, due to its special structure, the current method to obtain its mutual inductance is calibration experiments and there lacks an effective method to estimate its mutual inductance at the design stage. In this paper, the mutual inductance of this kind of B-dot is studied by simulation and theoretical analysis. Through simulation, the frequency response of the mutual inductance is obtained and it is found that the mutual inductance at high frequency which is the main working frequency range of the B-dot is lowest and stable. Through theoretical analysis, the approximate calculation formula of mutual inductance at any frequency is derived. Using the experimental results in previous reference, the theoretical results and the simulation results are verified. The influencing factors of the B-dot’s mutual inductance at high frequency are analyzed. The results show that the number of wire loops, the inner radius of wire loops and the radius of hole are positively related to the mutual inductance, and the height of the center of the wire loops is negatively related to the mutual inductance. Among these four factors, increasing the inner radius of wire loops can improve the mutual inductance more significantly. The work in this paper reveals the physical meaning of the mutual inductance change and provides guidance for the design of the B-dot.

Adaptive Wireless Power Transfer System With Relay Transmission and Communication

Wireless power transmission (WPT) systems have been increasingly utilized for wireless charging of electric vehicles. However, most research efforts or commercial products only address wireless power transmission but not wireless data communication. In addition, limitation of the transmission range is always a gap obstructing its popularity. Accordingly, this article presents a novel WPT scheme incorporating both relay transmission and magnetic field data communication. For power transmission, a resonant inverter with pulsewidth modulation was developed using relay coils to induce longer distance alternating current. For data transmission, a magnetic field communication system based on impedance changes and not reliant on extra radio frequency links was realized. Fuzzy compensation was used to stabilize the transmission of both power and data to counter changes in mutual inductance between coils. Phase-shift keying was utilized to generate digital signals for data transmission. Our experimental prototype was tested and verified to simultaneously transmit power and data in compliance with SAE TIR J2954 specifications using real-world experiments.

Modeling and Experiments of a Wireless Power Transfer System Considering Scenarios from In-Wheel-Motor Applications

This paper presents the design and modeling procedure of a wireless power transfer (WPT) system applied to In-wheel-motor (IWM). The system is designed to transmit over 10 kW of power following the physical constraints faced by the IWM applications. The issues of coil misalignment and load change are discussed as particular scenarios in IWM. The finite element model is built for circular, rectangular, and double-D coils, finding that the rectangular coil has the best performance considering the transmission interval and misalignment resistance. The circuit design procedure is presented, and the analysis of the influence of load and mutual inductance change on the WPT system is addressed. Finally, the performance of the design is verified with experiments on a full-scale prototype. It is proved that the WPT system successfully transmits 10 kW of power with a DC–DC efficiency of over 90% under a transmission interval of 140 mm. The output voltage is stable under 40 mm coil misalignment scenarios and over 50% load change.

Anti-offset performance optimization of coupling coils in wireless power transfer system based on genetic algorithm

With the popularity of electric vehicles (EVs), the application of wireless power transfer (WPT) in EVs has attracted more and more attention. The coupling coil is the key component to realize the stable transmission of electric energy, but in the process of wireless charging, the position of the primary and secondary coils may be misaligned, resulting in the change of mutual inductance and the instability of output current and power. Therefore, the study of the structure of the coupling coil is helpful to improve the transmission performance of WPT. In order to improve the anti-offset ability of the coupling coil, a DS (Double tangent semicircle) coil model based on the DD (Double D) coil is proposed in this paper, which can improve the pick-up ability and anti-offset ability of the receiver coil. Through theoretical analysis, genetic algorithm (GA) optimization, simulation analysis and experiments, it is verified that DS coil is better than DD coil in horizontal offset state and rotary offset state. At the same time, the experiments show when the rotation angle is in the range of −45° to 45° and 135° to 225°, that the current at the receiving end remains stable, and the maximum change rate is only 0.3%. This paper is of great significance to the optimal design of WPT coupling coil.

Periodic Energy Control for Wireless Power Transfer System

Wireless power transfer (WPT) systems are widely applied in many scenes due to their safety, convenience, and flexibility. This letter proposes a novel control strategy named periodic energy control (PEC) in WPT systems. It is suitable for all kinds of compensation topologies of WPT systems. Specifically, it takes the energy input to the resonant network as the control target, which calculates the energy input by measuring the capacitor voltage or the inductor current, thereby controlling the switching action of the inverter. Meanwhile, it not only effectively suppresses the overvoltage (or overcurrent) when system parameters such as load and mutual inductance change, but also features low sensitivity to mutual inductance, which has advantages in the scene where mutual inductance changes. Moreover, this letter presents the principle of PEC and derives the energy input to the resonant network in various compensation topologies of WPT systems. Finally, experiments are presented to verify the effectiveness of this control method.

On-Line Foreign Object Detection Using Double DD Coils in an Inductive Wireless Power Transfer System.

This paper proposes an on-line method for foreign object detection in a double DD coil system. The foreign object is detected by real-time measurement of the mutual inductance between the transfer pads. Measurement of the mutual inductance between coils can be performed at the start, during initialisation, or during the wireless power transfer. The coils in the double DD coil structure can be used separately; one coil can be used for power transfer and the other can be used for the mutual inductance measurement. The mutual inductance measurement is based on the voltage measurement across the open circuit receiver coil. The measured value of mutual inductance between the transmitter and the receiver pad can be used in a control algorithm and in a foreign object detection algorithm. Additionally, a 2DDq coil structure can be used as a replacement for the double DD coil structure, which increases the power transfer density. The DD coils in the double DD coil structure can also be driven using two phase-shifted voltages, which enables better location and detection of foreign objects. The method also helps to differentiate the mutual inductance change due to the distance change from the mutual inductance change due to the presence of a foreign object.

Low-Cost Inductive Sensor and Fixture Kit for Measuring Battery Cell Thickness Under Constant Pressure

This study investigates the application of inductive proximity sensors for accurately measuring battery expansion. Previous research has obtained high accuracy sensing using strain gauges, displacement sensors, and load cells, but has been limited by sensor cost. A proximity sensor based on changes in mutual inductance with a metal target sensor benefits from low cost, high accuracy, simple design, and ease of installation, calibration, and measurement; all allowing for better scalability for testing many cells simultaneously. Initial testing demonstrated that the inductance sensor readings were linearly proportional to displacement at multiple cycling temperatures. Further tests were conducted comparing the performance of the inductance sensor with highly accurate displacement sensors (1µm at $2000). Our sensor demonstrates a 3.2 µm maximum error at less than $20 cost, highlighting the cost-effectiveness of the proposed sensor. Thus, the proposed sensing platform will enable low-cost, high throughput testing of cell expansion.

Optimization Design of Resonance Coils With High Misalignment Tolerance for Drone Wireless Charging Based on Genetic Algorithm

The misalignment between the transmitting (Tx) coil and the receiving (Rx) coil is an urgent problem in the drone charging system using wireless power transfer technology. The coupling coefficient is so low when the resonance coils is not aligned, which degrades the drone wireless charging performance. In this article, the optimization processes of the coupling mechanism are presented in detail. First, we illustrate the great superiority of unequally spaced Tx coil, compared with traditional uniformly spaced one. Then, a genetic algorithm to optimize the side lengths of the Tx coils is highlighted by discussing the main design considerations and methods in a comprehensive manner. Furthermore, the Rx coil with varying radius size per turn is proposed in terms of the distribution of magnetic field generated by the optimized Tx coil. Experimental results show that the optimized coils have better coupling performance due to small mutual inductance change under the condition of misalignment. Power transfer efficiencies in different misalignment situations are measured and the best power transfer efficiency improvement achieved by the proposed system can reach 56.23% in contrast with traditional coils. This drone charging system can transfer a maximum power of 100 W with the remarkable transfer efficiency of 92.41%.

Macromodeling of Mutual Inductance for Displaced Coils Based on Laplace’s Equation

Magnetic coupling is applied in a vast of different applications like sensors or medical imaging. Especially for inductive position sensors, magnetic coupling is a main aspect. Hereby, the position information is coded in the mutual inductance between a coil and a target. Consequently, the change of mutual inductance according to the relative position of coupled coils is of special interest in such applications. In this contribution, a new generalized method is presented which can be used to derive a macro model describing the mutual inductance with respect to a relative position of a pair of coils. In contrast to the known procedures, the presented method can be applied for complex coil geometries since no analytic solution of the mutual inductance is necessary. For this purpose, it is utilized that the mutual inductance for a pair of coils can be treated as a potential function that obeys Laplace’s equation. By solving Laplace’s equation, a physics-based approach for a macro model is derived, which explicitly describes the behavior of the mutual inductance based on the relative position of the coils. With this macro model, further analysis can be performed in circuit design or performance analysis of the sensor for example. For evaluation, the accuracy of the procedure is presented for different coil geometries, which are applied in industrial and biomedical applications to emphasize the broad applicability of the presented method.

Adaptive Bidirectional Inductive Power and Data Transmission System

For the research of wireless power transfer, loosely coupled inductive power transfer (LCIPT) is one of the widely adopted technologies. There are already various researches focusing on development of high-efficiency LCIPT. However, when the transmission and receiver coils are misaligned, the power transfer efficiency will be significantly dropped. This article considers the change of mutual inductance when two induction coils are misaligned. A fuzzy control approach to solve for this problem by adaptively adjusting operational frequency is introduced. Experiments show that it can reduce the power transferring efficiency drop by 11% when two conduction coils are misaligned up to 50 mm. This research also supports adaptive maximum power transfer using tracking mechanism. Before conducting power transmission, the system can choose G2V or V2G according to the vehicle battery capacity via handshaking communication without the need of radio frequency links. In addition, the phase shift pulsewidth modulation technique is proposed for simultaneous data transmission enabling binary quadrature amplitude modulation for digital signal transmission. Fast over current protection is incorporated for power transfer safety when current overload happens. The transmission frequency of this article is controlled to meet the frequency specified by SAE TIR J2954.

Coil Positioning for Wireless Power Transfer System of Automatic Guided Vehicle Based on Magnetic Sensing.

As an auxiliary function of the wireless power transfer (WPT) system, coil positioning can solve the power and efficiency degradation during power transmission caused by misalignment of the magnetic coupler. In this paper, a Hall sensor array is used to measure the change of magnetic flux density. By comparing the multisensor data fusion results with the preset data obtained from the coil alignment, the real-time accurate positioning of the receiving coil can be realized. Firstly, the positioning model of the receiving coil is built and the variation of magnetic flux density with the coil misalignment is analyzed. Secondly, the arrangement of the Planar 8-direction symmetric sensor array and the positioning algorithm based on data fusion of magnetic flux density variations are proposed. In order to avoid coil positioning misalignment caused by the unstable magnetic field distribution which is actually affected by the change of mutual inductance during automatic guided vehicle (AGV) alignment, the constant current strategy of primary and secondary sides is proposed. Finally, the coil positioning experimental platform is built. The experimental results show that the coil positioning method proposed in this paper has high accuracy, and the positioning error is within 4 cm.

Research on the Characteristics of Wireless Power Transfer in Non-ferromagnetic Metal Pipe

With the development of various electronics, the way of transmitting energy by wire has brought increasingly negative effects on the operability and convenience of products. As wireless power transfer (WPT) technology requires no transmission lines, it has received increasingly wide attention. Most of the previous research on the technology of magnetic resonant coupling WPT mainly focused on the transmission of energy in the air. This paper establishes the wireless power transfer system model under non-ferromagnetic metallic environment and studies the effect of non-ferromagnetic metallic environment on coil self-inductance L, mutual inductance M and coil resistance R of WPT system. On this basis, the study on the relationship between coil diameter and mutual inductance is carried out for aluminium pipe, and the relationship between coil diameter and diameter of metal pipe at the maximum mutual inductance is fitted. Besides, experimental verification is conducted for the change of mutual inductance between the coils of WPT system in the aluminium pipe, presenting that the actual measurement results of mutual inductance in the aluminium pipe are consistent with the theory.

Passivity-Based Control for Movable Multi-Load Inductively Coupled Power Transfer System Based on PCHD Model

A passivity-based control strategy for movable multi-load inductively coupled power transfer (ICPT) system based on PCHD (Port-Controlled Hamiltonian Dissipation, PCHD) model is proposed, which can effectively suppress mutual inductance and load interference. During the movement of the secondary coil of the movable multi-load ICPT system, due to the change of mutual inductance and the randomness of the multi-load, it will cause the transmission power and efficiency to oscillate and generate harmonics. Firstly, in view of the above problems, this paper analyzes the ICPT system under movable multiple loads. The DQ transformation method was used to establish the large-signal mathematical model of the system, and PCHD mathematical model in the DQ domain was established to decouple the active and reactive power. Secondly, the passivity-based controller (PBC) is designed by using the principle of interconnection and damping assignment passivity-based control (IDA-PBC). After that, the second method of Lyapunov function is used for stability analysis, and further verifies the asymptotic stability of the closed-loop system. Finally, the proposed method was verified by MATLAB/Simulink simulation. The simulation results show that the passivity-based controller has stronger robustness in both steady and movable states compared with the PI controller, which effectively suppresses the oscillation and total harmonic distortion caused by the change of mutual inductances and the randomness of the loads.

Load Segment Tracking Control of IPT System Based on Power Efficiency Optimization

In the induction electric energy transmission system applied to fix point charging of vehicles, the mutual inductance change caused by position deviation or air gap change, and the equivalent load change caused by power demand change will make the output power and efficiency fluctuate, thus affecting the output stability of the system. In order to ensure the reliability of the charging process of the system and at the same time have a strong power output capacity, this paper proposes a load segmental tracking control strategy based on the optimal power efficiency. This control strategy adjusts the equivalent load to track different power efficiency indicator curves according to different mutual inductance states of the system and power demand when the vehicle is static charging, so that it can always maintain the optimal power efficiency state according to different charging conditions and improve the system performance. Finally, simulation and experimental verification are carried out under different states of mutual inductance. The results show that this method can achieve the equivalent load segmental tracking under different mutual inductance states, and always maintain the optimal power efficiency output.

Electromagnetic Induction Position Sensor Applied to Anti-Misalignment Wireless Charging for UAVs

Misalignment of wireless power transfer (WPT) system's transmitting and receiving ends can cause severe efficiency degradation and electromagnetic radiation. In this paper, a novel parallel transmission (TX) coil matrix structure was proposed to improve the performance of the WPT in the misalignment condition. The receiving (RX) coil's position measurement method was innovated by investigating the magnetic field and the mutual inductance change caused by the relative position change between RX and TX coils. Both theory and experiments confirmed that the phase difference between signal coil and detector coil can be featured as the parameter to represent the magnetic field's change. Based on this principle, a 4×4 TX coil matrix was made which verified the proposal and the sensitivity of the sensor. It was found that the position measurement result was sufficient to decide which TX coil to gate to facilitate the wireless charging in misalignment conditions. The structure and the size of the TX coil matrix could be further optimized to enhance the sensor's reliability and sensitivity.

Output power stabilization control strategy of WPT systems based on secondary side circuit

In the wireless power transfer (WPT) system, the output power is sensitive to the change of mutual inductance and load resistance. It is necessary to keep the output power stable quickly through effective control methods when the receiving coil and transmitting coil are offset or the load equivalent impedance changes. Based on the analysis of the WPT system with DC/DC converter on the secondary side, the relationship between mutual inductance and load voltage and load current, as well as the relationship between duty cycle of DC/DC converter and load demand power are given. A mutual inductance identification method based on load voltage and load current detection is proposed to monitor mutual inductance changes in real time. The output power stability control strategy based on DC/DC converter is also proposed. Finally, the effectiveness and correctness of the theoretical analysis and control strategy in this paper were verified by simulation and experiment.

A New Coil Structure to Reduce Eddy Current Loss of WPT Systems for Underwater Vehicles

Wireless power transfer systems in seawater inevitably suffer some energy loss as a consequence of eddy current loss. Here, we present a coil structure utilizing two transmitter coils placed symmetrically adjacent to each side of the receiver coil. This coil arrangement, termed a 1 × 1 × 1 structure, yields improved power transfer efficiency. The eddy current loss caused by the transmitter coils in a 1 × 1 × 1 system can be reduced to roughly half of that in a 1 × 1 system, with one transmitter coil and one receiver coil. The experimental results show that the power transfer efficiency from the transmitter to the receiver is improved by nearly 10%. After the introduction of equivalent eddy current loss impedance into the circuit, two arrangements of the 1 × 1 × 1 circuit topology are investigated. They consist of a shared or separately compensated capacitance topology. It is found that the shared-compensated capacitance topology is more robust to the change of mutual inductance than the separately compensated capacitance topology. This kind of structure is very useful in underwater vehicle applications.