Half-Bridge Modulation Strategy for Bidirectional Wireless Power Transfer Based on Efficiency Optimization Under Light Load Conditions

Mobility, continuity and safety are crucial in charging and discharging system of electric vehicles (EV) in smart grid applications. Bidirectional inductive wireless power transfer (BIWPT) system is ideal choice for these services. With accurate and efficient system models in hand, the circuit designers can predict and optimize the system performance. In this paper, an accurate, intuitive, and comprehensive steady-state theoretical model is proposed and implemented in MatLab environment. This model is generalized and can be used for any magnetic design of BIWPT system with the same compensation topology. The model is able to predict the system currents, voltages, power, power factor and equivalent impedance. The proposed model is used to evaluate two different designs for LCL compensation topology based on impedance frequency response analysis. Also, general considerations for the filters design parameters are stated and verified in this paper. A Simulink MatLab model for 1 kW BIWPT system is built to verify the proposed theoretical analysis.

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.

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.

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.

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.

A hybrid modulation strategy is proposed for the LCC-LCC compensated bidirectional wireless power transfer system (LCC-BWPT), which aims to boost the efficiencies in the whole operating range. The basic operating modes of LCC-BWPT with the hybrid modulation strategy are analyzed, and the unified discrete-time model is then established based on the full-mode operation, which can accurately describe the state variables under all operating modes. Based on the model, the criteria for optimal operation are put forward in consideration of three working processes of LCC-BWPT, i.e., the constant current (CC) charging process, the constant voltage (CV) charging process, and the CC discharging process. The optimal control variables in three working processes are derived respectively, which realize full zero-voltage switching (ZVS) operation and minimize the reactive current. On this basis, an optimal modulation strategy featuring high efficiency performance is proposed for LCC-BWPT. Besides, a control method independent of the real-time wireless communication is developed for LCC-BWPT with the optimal modulation strategy. Finally, a 1.2kW prototype is applied, and experimental results verify the effectiveness of the proposed optimal modulation strategy, where the efficiencies are improved in the whole operating range.

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.

Bidirectional Inductive Power Transfer (BD-IPT) is a promising technology that plays a significant role in specific scenarios such as vehicle-to-grid/home/vehicle systems. However, the BD-IPT system requires frequency synchronization between primary and secondary sides. Some researchers utilize a dedicated wireless communication interface to get the synchronization tracking information. But this solution will increase the cost and complexity while decrease the robustness and universality of the system. Therefore, this paper proposes a synthesizer PLL based frequency tracking technique for the BD-IPT system without adopting any communications. Specifically, the proposed controller includes two closed-loops, which decide and calculate the details of the active power, respectively. A proposed synthesizer PLL, which includes the phase detector, low-pass filter and voltage-controlled oscillator, is designed to generate an accurate synchronization signal. Also, the entire system operates in a zero-voltage switching (ZVS) state to achieve the high efficiency. Finally, a 120 W experimental prototype is built to verify the correctness feasibility of the whole system.

Conventional time-domain model of bidirectional inductive power transfer (BIPT) systems highly rely on specific compensation network and lacks universality. To address this issue, we propose a universal time-domain model for voltage-fed BIPT systems. The proposed state-space model applies to all compensation networks and resonant parameters, The input of the state space consists of the output voltage of the H-bridge. While the voltage combinations of the H-bridge are adaptive to different phase shift conditions. Based on the circuit analysis and by solving the state equations, analytical expressions for the state variables can be obtained. The time-domain analytical model is piecewise and accurately predicts the coil currents and capacitor voltages under all fundamental modulation schemes and compensation topologies. The simulation and experimental results of different compensation topologies and modulation strategies are presented, verifying the effectiveness of the proposed model. Compared with commercial software, the computation burden is obviously alleviated. The simulation is accelerated by 64 times than Simulink and 10 times than Psim.

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.

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.

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.

In bidirectional inductive power transfer (BIPT) systems, phase synchronization loop that keeps the secondary-side excitation voltage synchronized with the current is essential for stable power transmission. However, the characteristic of control object in the synchronization loop can vary due to the variation of the operating point parameters (OPPs), which can lead to loop instability. In this article, the transfer functions of the control object and the phase detector in the phase synchronization loop are derived. The influence of the variation of OPPs on the transfer function of the control object is analyzed. The transfer function is mainly affected by one zero that is sensitive to the OPPs and can shift into low-frequency region, while the other poles and zeros are at high frequencies and have less influence. The phase synchronization controller is designed considering the variation of OPPs to ensure the stability of the system in a wide range of OPPs. The sensitivity of the loop to the OPPs is analyzed. Frequency response results from simulation and experiment have verified the correctness of the model, and the stability of the loop. Steady-state and transient experiments prove the stable steady-state performance and fast transient response of the system.

In recent years, a number of bidirectional inductive power transfer systems (BD-IPT) suitable for wireless grid integration of electric vehicles have been developed. These developments have been fueled by the enhanced efficiency and spatial tolerance offered by BD-IPT systems. A typical BD-IPT system utilizes two synchronized full-bridge converters operating at fixed duty cycles to drive the primary and secondary magnetic couplers. However, in order to cater for a wide range of loading conditions, additional circuitry is employed at the expense of cost and power density. As an alternative solution, this paper proposes a novel power converter, named a boost active bridge (BAB), to replace the full-bridge converters. The BAB topology caters to a wide range of loading conditions without the need for any extra switching devices. A comprehensive mathematical model that predicts steady-state currents, voltages, and power transfer is presented to highlight the operating principles of the BAB technology. Experimental results obtained from a 3.5-kW prototype show a nearly constant efficiency under all loading conditions, validating the viability of the proposed BAB topology.