Bidirectional Wireless Power Transfer System Research Articles

A Phase Synchronization Technique Based on Perturbation and Observation for Bidirectional Wireless Power Transfer System

For the bidirectional wireless electric vehicle charging system, when both the primary and secondary converters are active, the phase synchronization between the two converters are necessary to control the power flow direction. This article proposes a new phase synchronization method by tracking the maximum (or minimum, depending on the power flow direction) value of the output current, without auxiliary hardware or the real-time communication between the primary and secondary sides. First, the relationship between the output current and the phase difference of the control signals is derived. It is found that the maximum output current is determined by the relative phase-shift angle (time interval between the middle points of the primary and secondary voltages) and the internal phase-shift angles of the two converters (time interval when the output voltage equals to the dc-link voltage). Second, a new 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. Third, 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. Moreover, the relationship between the internal phase-shift angle and the transfer power is derived to regulate the magnitude of the transfer power, with the dead-time effect taken into consideration. Finally, experimental results verify the validity of the proposed method with different air gaps and power levels. The method is easy to be implemented, helpful for the optimal operation of the static and quasi-static wireless charging system and suitable for the bidirectional power flow.

A Novel Bidirectional Wireless Power Transfer System for Mobile Power Application

This paper presents a bidirectional wireless power transfer system for mobile power applications. A novel 2-switch bidirectional wireless power transfer system with dual-side control is proposed for mobile power applications. Although only two switches are adopted, the energy can be transferred from the transmitter side to the receiver side and vice versa. The term bidirectional means that the power-flow is bidirectional and also that the transmitter is also a receiver and the receiver is also a transmitter. The output energy can be easily controlled by the duty ratios of the two switches. Thus, the proposed bidirectional power transfer system uses only one circuit to achieve bidirectional power transfer. Hence, the system cost and volume can be reduced so that the system is small and convenient for mobile power systems, portable and/or wearable electronic devices. A prototype system is constructed and the experimental results verify the validity of the proposed bidirectional wireless power transfer system.

Dynamic WPT system for EV charging with integrated energy storage

Wireless power transfer (WPT) can be used to charge electric vehicles (EVs) safely and efficiently. Dynamic wireless EV charging systems to charge EVs while moving has been developed but this technology is not yet widespread. One of the key challenges of dynamic charging is the pulsed nature of the transferred power, which may negatively impact battery life and the utility grid. Hybrid energy storage systems have been demonstrated as a potential solution, at the expense of a dedicated converter to interface with the energy storage element. This study presents a possible solution to the problem of adsorption and conditioning of high-power pulses, in the form of a novel converter topology that combines inductive WPT and super capacitor energy storage without the need for an additional converter stage. A suitable switching pattern is presented along with a steady-state mathematical model based on inductive power transfer, providing insight into the operation of the system. Experimental results of a prototype bi-directional WPT system are shown to validate the model and demonstrate the applicability of the proposed converter topology.

Three‐phase bi‐directional wireless EV charging system with high tolerance to pad misalignment

Electric vehicles (EVs), which are becoming increasingly popular, can be charged by either wired or wireless means. The latter, based on wireless power transfer (WPT) technology, is convenient and safe, but pad misalignment is one of the major concerns as it causes a reduction in charging power level, prolonging the charging process. Therefore, wireless charging systems with high tolerance to pad misalignment are necessary. This study proposes a three-phase bi-directional wireless power transfer (BD-WPT) system with a control scheme that offers high tolerance to pad misalignment in EV charging applications. The system uses simple coil designs for pads and utilises the magnetic coupling among pads to compensate for the power variation. A comprehensive mathematical model, incorporating all magnetic cross-coupling effects, is presented to investigate the charging performance of the system under pad misalignment and different pad spacings. To demonstrate the validity of the proposed system, theoretical and simulated results are presented, benchmarking against a single phase WPT system, and in comparison to a prototype 1.3 kW three-phase BD-WPT system. Results are convincing and indicate that the proposed three-phase BD-WPT system with small pad spacing is more tolerant to wide pad misalignment in EV charging applications.

Bilayer Predictive Power Flow Controller for Bidirectional Operation of Wirelessly Connected Electric Vehicles

This paper presents a comprehensive solution that allows a wirelessly connected electric vehicle (EV) to be autonomously charged and discharged, during long-term parking and/or transient stops. A bilayer power flow controller for bidirectional wireless power transfer system (BWPTS) in EVs applications is proposed. The proposed controller can manage the power flow between the EV and surrounding infrastructures, such as utility grid, home micro-grid, building micro-grid, road, or another vehicle. It consists of two control layers; the first is responsible for communicating with the surrounding infrastructures and gathering information from the vehicle operator, charging station, utility grid, and battery management system. These data are analyzed to generate the reference power signal with information about the mode of operation (charge, discharge, or abstain) and rate. The second layer receives the reference signal and predicts the control parameters for the resonant converters (on both the vehicle and grid sides) to track the desired power. The proposed algorithm is adaptively estimating the mutual inductance to consider the misalignments in the system, based on a new simple real-time mutual estimation algorithm using a single voltage measurement from the vehicle side. The second control layer is designed based on an accurate analytical model for the BWPTS's power flow. For verification purposes, a prototype for BWPTS was built and driven by the proposed controller, which was implemented using a field-programmable gate array integrated circuit. Also, a vehicle-level simulation was performed to validate the operation of the proposed controller in quasi-dynamic wireless charging at traffic signals. The proposed controller shows fast and stable response during both the transient and steady-state operation in comparison with the conventional proportional-integral controller.

Frequency regulation strategy for private EVs participating in integrated power system of REs considering adaptive Markov transition probability

The active power imbalance caused by renewable energies (REs) and loads is usually viewed as a main reason for the grid frequency variation. Private electric vehicles (EVs) participating in integrated power system frequency regulation of REs has great realistic significance, the bidirectional wireless power transfer system for EVs is analyzed in this paper, a fuzzy adaptive PI controller is proposed to achieve the charge and discharge control of EVs at any power value. Then a Markov model with adaptive Markov transition probability is developed to analyze the stochastic distribution of EVs. Considering the basic travel demands of the owners and the EV battery state of charge (SOC), a new advanced frequency regulation strategy is further proposed, and the regulation ability of EVs is quantitatively described. Finally, the effectiveness of the proposed frequency regulation strategy is verified by simulation results.

Hybrid Bidirectional Wireless EV Charging System Tolerant to Pad Misalignment

Electric vehicles (EVs) are becoming increasingly popular as a means of future transport for sustainable living. However, wireless charging of EVs poses a number of challenges related to interoperability, safety, pad misalignment, etc. In particular, pad misalignments invariably cause changes in system parameters which in turn lead to increase in losses as well as reduction in power throughput, making the charging process long and inefficient. Consequently, wireless charging systems that are less sensitive to pad misalignments have become preferable. This paper, therefore, presents a hybrid wireless power transfer (WPT) system that charges EVs at constant rate despite large misalignments between charging pads. The proposed charging system uses a combination of two different resonant networks to realize a constant and efficient charging process. A mathematical model is also developed, showing as to how the two resonant networks can be combined to compensate for pad misalignments. To demonstrate the validity of the proposed concept as well as the accuracy of the mathematical model, theoretical performance is compared with both simulations and experimental results of a prototype 3.3 kW hybrid bidirectional WPT system. Results clearly indicate that the proposed hybrid WPT system is efficient and offers a constant charging profile over a wide range of spatial (three-dimensional) pad misalignments.

Bidirectional Current-Fed Half-Bridge (C) (LC)–(LC ) Configuration for Inductive Wireless Power Transfer System

This paper contributes to the analysis and development of a new power electronics system for bidirectional wireless power transfer (WPT). The major focus is the analysis and implementation of a new current-fed resonant topology with current-sharing and voltage-doubling features. A new bidirectional WPT system with current-fed half-bridge voltage-doubler circuit is proposed and analyzed with series–parallel and series resonant networks. Traditionally used parallel L–C resonant tank in transmitter circuit with current-fed WPT topology causes higher voltage stress across the inverter devices to compensate the reactive power consumed by the loosely coupled coil. In the proposed topology, this is mitigated by adding a suitably designed capacitor in series with the transmitter coil; thus, developing a series–parallel CLC tank. Detailed analysis and design is reported for both grid-to-vehicle and vehicle-to-grid operations. The power flow is controlled through variable frequency modulation. Soft switching of the devices is obtained irrespective of the load current. A proof-of-concept experimental hardware prototype rated at 1.2 kW is developed and tested. Experimental results are presented to verify the analysis and demonstrate the performance of the system with bidirectional power flow.

Modeling and Feasibility Analysis of Quasi-Dynamic WPT System for EV Applications

In this paper, a new bidirectional wireless power transfer (WPT) charging and discharging concept is analyzed for its feasibility in integration at traffic signals. Classified as quasi-dynamic WPT (QDWPT), a string of coils are proposed to be installed beneath the road surface to provide grid-to-vehicle and vehicle-to-grid (V2G) services to battery electric vehicles (BEVs) while stopped. An experimentally verified lithium-ion battery array and Bidirectional Wireless Power Transfer system are combined to provide a comprehensive simulation under three proposed scenarios. First, four fixed standardized WPT charging levels are evaluated under a Federal Test Procedure-72 city driving profile. Second, a variable charging scenario autonomously adjusts the charging level based on the BEV state of charge. Third, an algorithm is proposed to toggle between charging and discharging based on the BEV psychological and grid retail price to evaluate V2G service viability. For each scenario, a comparison over the maximum driving range per drive cycle and range gained for each consumed kWh is quantified. Moreover, the effect of WPT coil misalignment over the driving performance is investigated and evaluated. This paper concludes that QDWPT at traffic signals is a promising solution to substantially extend the driving range and operating time for city driving especially at high charging levels.

A bidirectional wireless power transfer system for an electric vehicle with a relay circuit

In order to extend the transfer distance, enhance the tolerance for coil misalignment, and improve the capability of energy feedback and power transfer efficiency of conventional wireless power transfer (WPT) systems for electric vehicles, this paper presents a bidirectional WPT topology with a relay circuit. In the proposed topology, the primary and pickup circuits are implemented with virtually identical structures, which can operate in both magnetic field excitation and magnetic field receiving modes to facilitate bidirectional power flow between the primary side and the pickup side. A relay circuit is introduced to achieve high transfer efficiency under special conditions such as long distance or coil misalignment. The mathematical model of the system is established to describe its working mechanism in detail. Both the direction and amount of power flow can be regulated by controlling the shift phase voltages generated by primary and pickup switches. At the same time, the power and efficiency of system are analyzed, which provides a reference to optimize the parameters. The viability of the proposed system is verified by experiments, and the results suggest that the relay bidirectional WPT system is a reliable and efficient system for electric vehicle charging systems.

Inverter-Rectifier Using SiC Power Devices for Bidirectional Wireless Power Transfer System of Electric Vehicles

The bidirectional wireless power transfer system will have many advantages to charge the batteries of the electric vehicles. In their power supply circuit, the efficiency of the inverter and rectifier is important for total system efficiency. The inverter-rectifier, which is a type of power supply circuit in this system, performs inverter operation and rectifier operation. To reduce the loss of operation modes of both, we decided to use SiC power devices that are able to reduce switching loss. However, there is a problem of high conduction loss caused by the use of SiC power devices in rectifier operation. We propose the method of parallelizing SiC-MOSFET and diode of low forward voltage, and achieved a higher efficiency.