Design of Inductive Power Transfer (IPT) for Low-Power Application

Inductive power transfer (IPT) is preferred for numerous applications nowadays, ranging from microwatt bio-engineering devices to high power battery charging system. IPT system is based on the basic concept of electromagnetics induction which able to transfer the power from a source of electrical to the load without using any type of physical interconnection. This paper present a low-cost designed and implementation of IPT system via magnetic resonant coupling. NI Multisim 14.0 software was used to simulate the circuit diagram and the hardware prototype was developed for testing

A 13.56 MHz bidirectional IPT system with wirelessly synchronised transceivers for ultra-low coupling operation

This paper presents a high-frequency inductive power transfer (HF-IPT) system with bidirectional capability employing a new wireless synchronisation method. Synchronisation is achieved by transmitting a reference ultra high frequency tone (433.92 MHz) that is stepped down to 13.56 MHz in each transceiver. This allows the operating frequency to be locked across the two sides of the system. Afterwards, a phase search is performed looking for maximum power throughput, determining the phase at the point of resonance (i.e., no reflected reactances). The experimental implementation is achieved with two back-to-back Class EF coil-drivers driven by independent synchronisation circuits. In the experimental setup a constant input voltage is set for each of the two coil-drivers by implementing a source-sink configuration, emulating a bidirectional DC-DC conversion stage at each side. Experimental results show successful transceiver synchronisation, and 4 W were transferred from one end to the other and conversely at an ultra-low coupling of 1.6%. This proves that the combination of the load-independent Class EF transceivers and the synchronisation technique introduced herein is suitable for applications that require large tolerance to misalignment and air gaps larger than one coil diameter, such as in micro e-mobility

Induced voltage estimation from class EF switching harmonics in HF-IPT systems

One of the advantages of high-frequency inductive power transfer systems is the high tolerance to misalignment and large air-gaps. However, the inherently large magnetic field volumes can lead to coupling of additional foreign objects with the primary, causing possible detuning of the system and heating of the objects. These foreign objects and the conditions of the local environment can load the transmitter, which changes the induced voltage on the primary side. Unfortunately, the induced voltage is not directly measurable in an operating transmitter and the most straightforward way of calculating this variable, through a measurement of primary coil current and voltage, can cause a significant decrease in quality factor which reduces system performance. An integrated solution capable of estimating the induced voltage through other less invasive measurements in the primary is needed to ensure safety of operation through foreign object detection. Knowledge of the induced voltage can also be used to correct tuning mismatches where both sides of the link are active (i.e., in synchronous rectification and bidirectional systems). In this article, multiple candidate variables for estimating the induced voltage are assessed based on factors such as measurement practicality and estimation accuracy. It is demonstrated for the first time that a solution which is based on the measurement of only two variables, the amplitude of the fundamental frequency of the switching waveform and input current, can achieve state-of-the-art induced voltage estimation accuracy. These two variables, which can be obtained using simple cost-effective analogue circuitry, are used in a Gaussian process to generate a regression model. This is used to estimate induced voltages at any angle in an approximate magnitude range of 0–20 V with a normalized root-mean-square error of 1% for the real part and 1.5% for the imaginary part. This corresponds to detecting a plastic container with 1 kg of saline so..

Communication‐less Synchronous Rectification for In Motion Wireless Charging

This thesis puts forward a control scheme to allow for synchronous rectification for dynamic wireless power transfer. The automotive industry is transitioning away from internal combustion engines (ICEs) and towards electric vehicles (EVs). This transition is spurred by the environmental and economic benefits EVs offer over ICEs. However, further improvements can still be made to how electric vehicles operate. One of these improvements is the technology of in motion wireless charging or dynamic wireless power transfer. In motion wireless charging offers the ability to remove existing range anxiety concerns for EVs. It also offers the potential for a reduction in battery sizes for EVs, which are the primary cost of EVs, this in turn decreases the total costs of mass EV adoption. Traditional implementations of in motion wireless charging utilize passive rectification to simplify controls between embedded primary pads and the vehicle. However, this solution while effective, limits the potential benefits of wireless charging. The use of synchronous or active rectification techniques, offer improved performance, control techniques, and bidirectional capabilities. However, the reason synchronous rectification is not already used in in motion charging is the complexity of synchronization over wireless communication. To move past this challenge, this thesis investigates a synchronization scheme that can be achieved without communication by taking advantage of induced free resonant currents in the vehicle’s tuning network to synchronize the switching transitions to receive power. In this thesis a traditional in motion wireless charging system utilizing passive rectification is designed and built as a benchmark for dynamic charging. Simulations of this control scheme are presented. Practical considerations are addressed for hardware realization. Finally, the control approach is validated through hardware in static and dynamic applications

Design and development of a test rig for 13.56 MHz IPT systems with synchronous rectification and bidirectional capability

This paper presents the development of a test rig for bidirectional 13.56 MHz wireless power using identical back-to-back Class EF converters. Theoretical principles of bi-directional wireless power are described and an operating chart representing the range of admissible complex voltages induced on the active transmit side is introduced. The implementation is achieved by driving the gate signals of two Class EF coil-drivers from a signal generator, allowing the relative phase of the currents in each coil to be controlled. The rig sets a constant input voltage for each of the two coil-drivers by implementing a source-sink configuration, emulating a bidirectional DC-DC conversion stage at each side. This setup can also be used to test for tuning mismatches and different loading conditions in the back-to-back Class EF configuration. Experimental results include bidirectional wireless power transmission of 20 W across a 13.56 MHz link with 6.56% coupling. The combination of low coupling factors and moderate power levels enables new classes of applications that require large air gaps and tolerance to misalignment such as in micro e-mobility. High efficiency can be maintained despite changes in coupling factors and load since active rectification ensures operation at the resonant point in both tanks

Design Optimization of Inductive Power Transfer Systems for Contactless Electric Vehicle Charging Applications

Contactless Electric Vehicle (EV) charging based on magnetic resonant induction is an emerging technology that can revolutionize the future of the EV industry and transportation systems by enabling an automated and convenient charging process. However, in order to make this technology an acceptable alternative for conventional plug-in charging systems it needs to be optimized for different design measures. Specifically, the efficiency of an inductive EV charging system is of a great importance and should be comparable to the efficiency of conventional plug-in EV chargers. The aim of this study is to develop solutions that contribute to the design enhancement of inductive EV charging systems. Specifically, generalized physics-based design optimization methods that address the trade-off problem between several key objectives including efficiency, power density, misalignment tolerance, and cost efficiency considering critical constraints are developed. Using the developed design methodology, a 3.7kW inductive charging system with square magnetic structures is investigated as a case study and a prototype is built to validate the optimization results. The developed prototype achieves 93.65% efficiency (DC-to-DC) and a power density of 1.65kW/dm3. Also, self-tuning power transfer control methods with resonance frequency tracking capability and bidirectional power transfer control are presented. The proposed control methods enhance the efficiency of power converters and reduce the Electromagnetic Interference (EMI) by enabling soft-switching operations. Several simplified digital controllers are developed and experimentally implemented. The controllers are implemented without the use of DSP/FPGA solutions. Experimental tests show that of the developed simplified controllers can effectively regulate the power transfer around the desired value. Moreover, the experiments show that compared to conventional converters, the developed converters can achieve 4% higher efficiency at low power levels. Moreover, enhanced matrix converter topologies that can achieve bidirectional power transfer and high efficiency with a reduced number of switching elements are introduced. The self-tuning controllers are utilized to design and develop control schemes for bidirectional power transfer regulation. The simulation analyses and experimental results show that the developed matrix converters can effectively establish bidirectional power transfer at the desired power levels with soft-switching operations and resonance frequency tracking capability. Specifically, a direct three-phase AC-AC matrix converter with a reduced number of switches (only seven) is developed and built. It is shown that the developed converters can achieve efficiencies as high as 98.54% at high power levels and outperform conventional two-stage converters

Synchronous operation of high frequency inductive power transfer systems through injection locking

High frequency inductive power transfer systems can be designed for operation with high tolerance to misalignment and large air-gaps, making it possible to operate in highly dynamic environments. Most examples in the literature use a single active transmitter and a single passive receiver (active-passive approach). Such systems are limited to unidirectional power flow and are susceptible to detuning of the transmitter due to changes of reflected reactance stemming from diode non-linearities. This also limits the range of coupling over which the system can be operated efficiently. Therefore there is significant potential for expanding the range of applications of inductive power transfer systems by moving to an active-active configuration. This will enable bidirectional power flow, power routing through several nodes and on-the-fly retuning to eliminate reflected reactances. One of the greatest challenges in achieving an active secondary in an IPT system is obtaining a stable frequency and phase reference for the synchronous rectifier/transceiver with respect to the transmitter coil current and hence magnetic field. Various methods for synchronisation have been proposed in the literature, but they either require a separate, out of band communication link, or are difficult to scale to MHz operation. This paper describes an alternative to the existing solutions, using an injection locked oscillator to provide optimal phase tracking. A series of candidate feedback configurations are also proposed to provide high system resilience. In this work the basic principles of injection locking are described as applied to synchronous IPT transceivers and experimental results are presented demonstrating its application to a bidirectional back-to-back Class-EF configuration operating at 13.56 MHz, with coupling factors ranging from 1.9 % to 8.4 % and power levels of up to 25 W

Wireless power and data transfer via a common inductive link using frequency division multiplexing

For wireless power transfer (WPT) systems, communication between the primary side and the pickup side is a challenge because of the large air gap and magnetic interferences. A novel method, which integrates bidirectional data communication into a high-power WPT system, is proposed in this paper. The power and data transfer share the same inductive link between coreless coils. Power/data frequency division multiplexing technique is applied, and the power and data are transmitted by employing different frequency carriers and controlled independently. The circuit model of the multiband system is provided to analyze the transmission gain of the communication channel, as well as the power delivery performance. The crosstalk interference between two carriers is discussed. In addition, the signal-to-noise ratios of the channels are also estimated, which gives a guideline for the design of mod/demod circuits. Finally, a 500-W WPT prototype has been built to demonstrate the effectiveness of the proposed WPT system