Actual vs textbook transformers

The current in the secondary coil of a transformer acts to oppose the flux generated by current in the primary coil, by Lenz’s law. According to most physics textbooks, the total flux is then zero, so transformers should stop working. Something is missing in the textbook accounts.

An Enhanced Method of Contactless Charging of Railway Signaling Torch Light

Wireless charging, also known as contactless charging (for shorter range), is a method of supplying energy to electrical devices by sending electricity via an air gap. Wireless charging methods have advanced recently, and commercial solutions have been developed, providing a potential option to overcome the energy bottleneck of typically portable battery-powered gadgets. Due to its simplicity and improved user experience, this technology is attracting a wide range of applications, from low-power gadgets to high-power electric cars. However, including wireless charging into the systems raises a number of difficult challenges in terms of implementation, scheduling, and power management. One such application is to convert the existing system of traditional battery powered railway signaling torchlight into a rechargeable type contactless charging system. This provides a better way of increasing the life time of the product and has better compactness. A rechargeable Li-ion battery must be installed in lieu of the old non-rechargeable battery. To achieve satisfactory efficiency, the magnetic resonance coupling technology of contactless charging can be utilized. Through a shorter air gap, electrical power is transmitted from the charging module (main coil) to the Torchlight (secondary coil). Overall, the present system's cost, size are reduced and lifetime is increased.

Design of circular inductive pad couple with magnetic flux density analysis for wireless power transfer in EV

As the population grows, people will consume more natural resources. This issue will lead to a low petrol supply for all land transportation, especially supplies for car consumption. Therefore, the electric vehicle (EV) has been introduced to overcome this issue. Currently, wired charging of EVs has been implemented in most of the developed country, including Malaysia. However, some drawbacks have been found from this technology. Therefore, wireless charging comes into the picture to solve this issue. Charging pad on the road and at the car are required for both wired and wireless charging. Various designs of charging pad are available. However, this paper will only focus on the circular design. There is many software that can be used to design the coil pad. Each software has a different procedure and steps to design the coil pad. In this paper, JMAG Designer software will be used to design the circular coil pad. Then, three coil pair were simulated using JMAG Designer to investigate the magnetic flux density between primary and secondary coil when varying the misalignment of 0 cm, 4 cm and 8 cm. From the simulation, there is no specific trend in the relationship between magnetic flux density and misalignment.

Misalignment and Range Adaptive Wireless Charging System with Constant Current/Constant Voltage Output Based on Coupling Coefficient Estimation

Compared with the traditional plug-in charging system, wireless power transfer (WPT) system has the characteristics of electrical and mechanical isolation. A wireless system is proposed suitable for battery charging under misalignment or range variation, and the constant current (CC) and constant voltage (CV) charging are realized by the estimation of coupling coefficient. Firstly, two different operating frequencies based on SS basic compensation structure are designed to realize CC output and CV output respectively. After circuit analysis, CC and CV output cannot be achieved when the position of the secondary coil changes. To solve this issue, when the coil is under misalignment or range variations, the required system parameters are measured, and the coupling coefficient in the charging process is estimated by using the transconductance amplitude equation. Then the corresponding input voltage or working frequency is calculated and fine-tuned. Therefore, the CC and CV charge of the battery can be realized under misalignment or range variation. Finally, experimental results are presented to verify the feasibility and correctness of this method.

DC Current Limiting Characteristics of Flux-Coupled Type SFCL Using Superconducting Element Connected in Parallel in a DC System

In this paper, the fault current limiting (FCL) characteristics of a flux-coupled type superconducting fault current limiter (SFCL) with parallel connection between two windings in a DC system were analyzed. The flux-coupled type SFCL was composed of two coils connected in parallel and a superconducting element (SE), which was connected in series with the secondary coil. The flux-coupled type SFCL works in DC systems similar to those in AC systems. Before a fault occurs, the respective magnetic fluxes generated by the two coils connected in parallel offset each other, maintaining the voltage induced in the two coils at zero. In case of a fault, however, resistance is generated in the SE, preventing the magnetic fluxes generated by the two coils from offsetting each other. Thus, some voltage is induced in the two coils, and this starts to limit the fault current. DC short circuit tests were conducted, and the test results confirmed that the flux-coupled type SFCL with the two parallel connected coils was effective in limiting the fault current in a DC system. Additionally, the effect of the wiring direction of the two coils on the SFCL’s FCL performance and operating current, limiting impedance, and instantaneous power load was further analyzed, and as a result, the performance conditions of the SFCL in a DC system were determined.

Research on Characteristics of Wireless Power Transfer System Based on U-Type Coupling Mechanism

Aiming at the power supply problem of high-speed rotating equipment, a wireless power transfer system based on U-shaped core coupling mechanism with a primary coil is proposed. Firstly, the transfer model of the U-type coupling mechanism wireless power transfer system is established. The expressions of transfer power and transfer efficiency are obtained by theoretical calculation, and the factors affecting the transfer characteristics of the system are analyzed. At the same time, the magnetic field distribution of the system and the coupling parameters change when the relative position of the primary and secondary coils changes through simulation analysis. Finally, an experimental platform is established for experimental verification. The results show that the system can obtain 1.72 w output power with 51.19% transfer efficiency when the distance between the secondary coil and U-core is 15 mm and 30 mm, respectively. The transmission efficiency and power of the primary coil and secondary coil under different misalignments are tested and compared. It is proved that the wireless power transfer system based on U-type coupling mechanism can effectively realize the stable power supply of the rotating equipment monitoring system.

WIRELESS CHARGING TROLLEY WITH VEHICLE-PILE COLLABORATION

Most of the built carts will use a combination of lithium batteries, but the types of lithium battery connectors are cumbersome and their charging time is too long. In this project, a Faraday capacitor is used instead of the car's power source to store power in a wireless charging mode, by providing DC power to the transmitter coil along the road to induce a certain voltage to the secondary coil carried by the car to achieve the effect of storing power for the Faraday capacitor. A camera module openmv in the centre of the track captures images and uses a target detection algorithm to intelligently identify the position of the car to control the activation and deactivation of the coils to improve efficiency.

Mutual inductance calculation of the one-primary multiple-secondary coil system

It is of great significance to accurately calculate the mutual inductance of one-primary multiple-secondary coil system (OPMSC) in order to improve energy transmission efficiency, measurement accuracy of magnetic sensor, etc. In this paper, a method based on time harmonic field to calculate such mutual inductance is proposed. Both the high frequency alternating current model and the time-harmonic electromagnetic field calculation method are used to ensure engineering practicability of the method. The current of each coil and the relative position between coils are considered in the proposed method. Moreover, according to the full derivation of a new analytical method. the extremum phenomenon of mutual inductance is described. And this method is verified by both finite element simulations and experiments, which proves that the method is effective for optimizing the relative position of the multiple coils when mutual influence among all the coils is taken into account.

Non-Destructive Evaluation for Sectional Loss of External Tendon of Prestressed Concrete Structures Using Total Flux Leakage

A non-destructive evaluation method is proposed to identify the sectional loss of the external tendon of prestressed concrete structures by detecting the change of the magnetic flux in the external tendon exposed to a magnetic field. The method uses a solenoid-shaped device with two coils: a primary coil for producing magnetic field and secondary coil for damage detection, wrapping the external tendon. A current applied to the primary coil in the device causes the magnetic field. Then, the change in the magnetic flux by the damage in the external tendon is detected by the variation of the voltage in the secondary coil in the device as the device moves along the tendon. An alternating current is applied to the primary coil to minimize the effect of the moving speed of the device. As a result, the damaged area can be detected with a low-level energy current. In addition, a wrapping solenoid-shaped device that is easy to disassemble and assemble was developed for in situ inspection. The measured signal from the secondary coil has a sinusoidal form with the same frequency as the applied current to the primary coil, and the peak curve of the measured signal provides enough information to detect the damage. It is shown that the proposed method can quantitatively identify one or multiple damaged-tendon locations as well as damages of at least 2 cm.

A low-power prototype of contactless field power controlled BLAC and BLDC motors

In this paper, a new design configuration has been proposed in which a prototype of resonant inductive power transfer-based contactless power transfer to wound rotor has been developed which provides field power to brushless alternating current (BLAC) or brushless direct current (BLDC) motors without the use of permanent magnets in the rotor. Further, wound field in the rotor of DC motor can be powered without carbon brushes. The proposed design facilitates motor performance improvement by adding an extra dimension of field flux control, while the armature circuit is conventionally fed from position detection and commutation schemes. It contains a primary multilayer concentrated coil fed with high-frequency resonating AC supply or switched mode supply. A single layer helical secondary coil coaxially fixed on the shaft receives high frequency wireless AC power transmitted from primary coil. Fast rectifier inside the hollow shaft and DC filter provides the transferred DC power to field terminals in the rotor. It has been verified that rotor power can be varied linearly with linear variation in input DC power with the highest efficiency at the resonant frequency. Available power to the rotor remains invariable with rotational speed and angle, which is a necessary requirement for rotor field. DC voltage on the rotor terminals can be effectively controlled during standstill as well as during rotation at any speed.