Harmonics-based steady-state mathematical model of bidirectional inductive wireless power transfer system in V2G applications

For bidirectional inductive wireless power transfer systems, zero voltage switching (ZVS) of switching devices and system efficiency are always the keys to research. In this paper, the efficiency of the bidirectional dual-LCC compensation topology is firstly modelled, and the optimal bilateral modulation strategy is quantitatively derived. Then, a half-bridge modulation method under light load conditions is proposed. Compared with the full-bridge modulation strategy, the operating efficiency of the system is further improved. Finally, a 3.3 kW two-way wireless power transfer system simulation model is built in MATLAB. Compared with the full-bridge triple-phase-shift modulation strategy, it is proved that the half-bridge modulation scheme proposed in this paper has higher energy transfer efficiency under light load conditions.

Bi-directional Inductive Power Transfer (IPT) systems allow contactless power transfer between two sides and across an air-gap, through weak magnetic coupling. These systems essentially constitute high order resonant circuit and their complexity increases with increasing number of pick-ups. A mathematical model which provides an insight into the behaviour of bi-directional IPT systems with multiple pick-ups would therefore be invaluable at design stage. This paper develops a multivariable dynamic model for bi-directional IPT system with multiple pick-ups. A 1.5 kW bi-directional IPT system with 3 pick-ups is simulated in PLECS and the results are presented with comparisons to demonstrate the validity of the proposed model. Results of the simulation indicate that the proposed model accurately predicts the behaviour of bi-directional IPT system with multiple pick-ups and can therefore be used as a valuable tool for both dynamic analysis and controller design.

This paper presents the design of a bidirectional wireless power and information transfer system. The wireless information transfer is based on near-field technology, utilizing communication coils integrated into power transfer coils. Compared with conventional far-field-based communication methods (e.g., Bluetooth and WLAN), the proposed near-field-based communication method provides a peer-to-peer feature, as well as lower latency, which enables the simple paring of a transmitter and a receiver for power transfer and the real-time updating of control parameters. Using the established communication, control parameters are transmitted from one side of the system to another side, and the co-control of the inverter and the active rectifier is realized. In addition, this work innovatively presents the communication-signal-based synchronization of an inverter and a rectifier, which requires no AC current sensing in the power path and no complex algorithm for stabilization, unlike conventional current-based synchronization methods. The proposed information and power transfer system was measured under different operating conditions, including aligned and misaligned positions, operating points with different charging powers, and forward and reverse power transfer. The results show that the presented prototype allows a bidirectional power transfer of up to 1.2 kW, and efficiency above 90% for the power ranges from 0.6 kW to 1.2 kW was obtained. Furthermore, the integrated communication is robust to the crosstalk from the power transfer and misalignment, and a zero BER (bit error rate) and ultra-low latency of 15.36 µs are achieved. The presented work thus provides a novel solution to the synchronization and real-time co-control of an active rectifier and an inverter in a wireless power transfer system, utilizing integrated near-field-based communication.

Bi-directional Inductive Power Transfer (IPT) systems facilitate contactless power transfer between two sides and across an air-gap, through weak magnetic coupling. These systems constitute a 6th order resonant circuit and, as such, are difficult to design and control. A mathematical model which provides an insight into the behaviour of bi-directional IPT systems would therefore be invaluable at design stage. This paper presents a dynamic model through which the behaviour of bi-directional IPT systems can be accurately predicted. A 1.5 kW bi-directional IPT system is simulated in PLECS, and results are presented with comparisons to demonstrate the validity of the dynamic model. Results indicate that the proposed model accurately predicts the dynamics of the bi-directional IPT system and can therefore be used as a valuable tool for both transient analysis and controller design.

Wireless Power Transfer (WPT) systems have demonstrated their efficiency over a broad frequency spectrum. However, the design and the optimization of multi-MHz frequency WPT systems remain complex due to parasitic components specifically. This paper outlines a methodology for designing and optimizing a compact 13.56 MHz resonant inductive coupling WPT systems based on a GaN Class E inverter. The proposed design approach combines analytical modeling and advanced numerical simulations taking into account parasitic elements. The effectiveness of this approach is experimentally confirmed through a prototype, which shows an efficiency of 78% for a transmitted power of 43 W to a 5.54 cm³ coupler. The advanced modeling results perfectly match with the experimental ones (mismatch of only 2% for the evaluation of efficiency). The WPT system developed thanks to this method shows a power density among the highest ones in the non-mating connectors’ state of the art.

This paper proposes a new design concept of small air-gap bidirectional Wireless Power Transfer (WPT) system using Dual Active Bridge (DAB) topology. The wireless charging coils are considered as a weakly coupled transformer having relatively high leakage inductance, and thus the new design can obtain soft switching without implementing resonant capacitor or external inductor. This design has a simple construction and can enable bidirectional inductive power transfer with superior performance compared to the traditional large air-gap system. The new system can transfer high power via a compact coil structure thanks to smaller air gap. Moreover, soft-switching operation enables significant improvement in efficiency. The proposed design enables electrical vehicles and smart wheels to use batteries for supporting grid silently and seamlessly. This paper considers the application of smart wheel charger and presents an analytical design of the system using finite element analysis and circuit simulation. As a result, the design can achieve 97% efficiency at 3-kW, 85-kHz operation.

Bi-directional inductive power transfer (BD-IPT) systems are suitable for applications such as wireless integration of Electric Vehicle (EV) with the utility grid. This paper presents a comprehensive study of the most widely used BD-IPT systems in EV applications - a series tuned inductor-capacitor (LC) type BD-IPT system. The system parameters used in the paper have been set according to SAE J2954 guidelines for wireless electrical vehicle charging. Mathematical and simulation models of the system have been developed to investigate the behavior and sensitivity of the system to variations in circuit parameters. The validity of the mathematical models is verified and the efficiency of each system is investigated using simulated results based on a 3.7 kW simulated systems. Both frequency and relative phase modulation between converters are being considered for performance optimization of the systems. Nearly a 4% improvement in efficiency can be observed with these optimum modulations values.

For the bidirectional wireless power transfer (BWPT) system, when both the primary and secondary converters become active, the phase synchronization between their control signals are necessary to control the power flow direction. Generally, the synchronization is realized by the real-time wireless communication devices or the auxiliary windings, which calls for high requirements of the hardware for sampling and controlling as well as increases the cost. Therefore, this paper proposes a new phase synchronization method without the real-time communication or auxiliary hardware. Firstly, the relationship between the output current and the phase differences of the control signals is derived. It is found that the extreme value of the output current is determined by the relative phase-shift angle between the primary and secondary converters and the internal phase-shift angles of the two converters. Secondly, a scheme for generating the control signals is proposed to ensure that the relative phase-shift angle is not influenced by the internal phase-shift angles. Thirdly, based on the perturbation and observation method, a procedure is proposed to track the extreme value of the output current and obtain the target relative phase-shift angle for the phase synchronization state. Finally, simulation and experimental results verify the validity of the proposed method. The method is easy to be implemented, and useful for the bidirectional power flow of the static BWPT system.

Depletion of fossil fuels and growing concerns about climate change have resulted in an increasing trend towards the use of sustainable technologies such as electric vehicles (EVs). As a result, effective means of charging EVs and managing EVs has become one of the most researched topics in the past few years. Among the many solutions proposed, inductive power transfer (IPT) systems, especially bi-directional IPT systems, are gaining popularity as an effective method to wirelessly interface EVs with the utility grid for charging as well as dynamic demand management. To enable wide spread use of bi-directional IPT technology for interfacing EVs with the gird essentially requires low cost and efficient magnetic couplers. As such, this paper investigates three new low cost magnetic designs, as alternatives to commonly used circular couplers. The proposed designs along with a standard circular coupler with similar ratings are modeled and simulated on JMAG studio to compare the performance. Based on the simulation data and experimental results gathered from a prototype implementation, the most effective design that yields a good coupling for the lowest cost has been identified as a possible solution for magnetic couplers used in bi-directional IPT systems.

This letter proposes a novel primary-side parameter estimation method for bidirectional inductive power transfer (BD-IPT) systems. This method can estimate mutual inductance at startup and monitor secondary-side phasor information continuously during operation. The proposed method can be used to simplify existing optimal control methods in BD-IPT systems by providing necessary feedback information without a wireless communication link. Besides, it helps to implement new control methods to further improve system performance. A current decoupling concept is utilized to estimate both the mutual inductance and secondary phasor information. A circuit model based on the superposition principle is presented to describe the current decoupling concept. The validity and accuracy of the proposed estimation method are demonstrated using the measured results of a 1-kW prototype BD-IPT system.

Matrix converter (MC) based grid connected bi-directional inductive power transfer (BD-IPT) systems are preferable for numerous applications such as electric vehicle (EV) charging and vehicle-to-grid (V2G) systems due to their single-stage grid integration as opposed to two-stage grid integration of conventional BD-IPT systems. However MC based BD-IPT systems essentially produce harmonics which can have adverse effects on power quality of the utility grid. This paper presents a new control technique, through which the grid side harmonic distortion of MC based BD-IPT systems can be improved. A theoretical analysis is presented with simulations to show that the proposed approach is viable, and results suggest that the presented technique improves the power quality of the system significantly by minimizing the grid side harmonic distortion.

In an inductive wireless power transfer system, unavoidable lateral misalignment between the transmitter and the receiver leads to reactive power, which reduces the powertransfer-efficiency and limits the maximum output power under given input voltage. A tunable capacitor provides access to achieve low reactive power and maintain high power-transfer-efficiency. In this paper, the effects of misalignment on power transfer performance is investigated. A conventional capacitor tuning method is analyzed, and its limitations are identified. An innovative low loss online capacitor tuning method is proposed to automatically achieve low reactive power and maintain high power-transfer-efficiency under misalignment. The proposed designs are evaluated via simulation.

This work reveals and analyzes an unfamiliar bifurcation in weakly-coupled inductive wireless power transfer systems (IWPT) employing diode rectifier. This paper firstly provides a local analysis calculating the required RF source power, based on the rectifier ac-dc conversion gain and the two-port analysis of the coupled coils. The local analysis is supported by measured results on silicon. Successively, we demonstrate that if the secondary coil and the diode rectifier have a high quality factor, the rectifier diode varactor can create a turning-point bifurcation in the solution curve of the output dc voltage versus the RF source power. With the bifurcation, the local analysis becomes invalid and a higher source power is required. Bifurcation analysis based on large-signal capacitor modeling and conversion matrix analysis are provided, substantiating the results. The introduced bifurcation analysis is verified by three IWPT examples on PCB. A proposed design with an auxiliary nonlinear varactor is proposed to mitigate the bifurcation with improved performance.

Bidirectional wireless power transfer (BWPT) is an emerging technology within the wireless power transfer field of research, which allows the same device to receive power and it can transmit power to other compatible devices. In practical applications, due to the distance of the coil, the lateral misalignment and the angular misalignment, it is difficult to achieve constant power transmission. This paper proposes an adaptive adjustment scheme, which detects the output power of the circuit in real-time through a closed-loop feedback method, uses ergodic sampling to obtain the best duty cycle, and adaptively adjusts the duty cycle of the inverter pulse width modulation signal, to compensate for the reduction in load power. Furthermore, the validity and feasibility of the scheme are verified by simulation and prototype experiments. A maximum constant power transmission of 4W is achieved within the range of 5 cm in longitudinal distance, 4 cm in lateral displacement and 60° of angular misalignment. The maximum BWPT efficiency can be achieved, up to 66.17%. The proposed method improves the quality of BWPT.

For Inductive Power Transfer (IPT) system, the bi-directional power transfer mode is designed for energy feedback from receiver to transmitter. It will be helpful to improve system efficiency in high power application. In order to realize power flow from low voltage side to high voltage side, the paper gives voltage gain analysis method. On the basis, aiming at the power flow control, the paper proposes a dynamical control method. Based on switching between energy injection and free-running mode, the there is no needed of additional auxiliary circuit. As the control method is only based on logistical computing, the control method is simple and easy for implementation. Finally, simulation and experimental results verify the control method.