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The output characteristics and the transfer efficiencies of inductive power transfer (IPT) systems are affected by (but not limited to) the variation of parameters such as, variable load, misalignment between the primary and secondary coils, and resonance frequency detuning. This paper first analyzes the resonant conditions of all voltage-fed compensation topologies in IPT systems to achieve the load-independent voltage transfer characteristic at load-independent zero phase angle frequency. With these conditions, the parameters sensitivity to the key performance factors of the S-SP, LCC-S, LCC-P, and double-sided LCC compensated IPT systems are systematically investigated when considering the losses in coils and compensation networks. Comparisons of the quantitative sensitivity analysis and experimental results for all IPT systems are made in terms of the voltage transfer ratio and efficiency. These analyses can provide guidance for the selection of superior compensation networks to minimize the additional converter effort and simplify the control algorithm of closed-loop IPT systems. [ABSTRACT FROM AUTHOR]

The classical switched-capacitor (SC) equalizer is widely used in battery management systems because of the accurate balancing and ease of implementation. However, it only achieves the adjacent cell-to-cell equalization, and its balancing speed and efficiency become extremely low for multicell series-connected battery strings. Therefore, a delta-structured switched-capacitor equalizer is introduced to achieve a high-speed and high-efficiency any-cells-to-any-cells (AC2AC) equalization at arbitrary imbalanced status for any number of cells. The slow switching limit and fast switching limit impedances of the proposed equalizer are developed to provide a theoretical guidance for the optimized design of the SC equalizers. A prototype for four battery cells was built, and a comparison with existing equalizers was presented. Experimental and comparative results show that the proposed solution exhibits an automatic AC2AC balancing with high reliability and strong robustness. The measured balancing efficiency is up to 94.5%. [ABSTRACT FROM AUTHOR]

The double-sided LCC topology provides a highly efficient compensation method for electric vehicle (EV) wireless charging systems. However, the two compensated coils occupy a large volume. In order to address the volume increase as well as to be compatible with unipolar coil structures, which are widely applied in EV wireless charging systems, an integration method is introduced in this paper. Aspect ratios of the compensated coils are studied to minimize the respective coupling effect. With the proposed integration method, the extra coupling coefficients are either eliminated or decreased to a negligible level. A wireless charging system with the proposed integration method is built and the experimental results show that the system resonates at 85 kHz and delivers 3.09 kW with a dc–dc efficiency of 95.49% at an air gap of 150 mm. Furthermore, a comparison with the integration method into bipolar coil structures is presented and the results demonstrate that the system with the proposed integration method is more immune to front-to-rear and vertical misalignments. [ABSTRACT FROM AUTHOR]

This paper proposes an LC-compensated electric field repeater to extend the transfer distance of a capacitive power transfer (CPT) system. The repeater contains two metal plates connected with an external capacitor and an external inductor. The plates are used to generate electric fields to transfer power. The external inductor and capacitor are used to resonate with the plates in order to increase the voltage levels. The repeater is placed between a transmitter and a receiver, which also contains metal plates compensated by an LC network. The repeater can increase the transfer distance of the CPT system without significantly influencing the system power and efficiency. In this paper, the capacitive coupler structure and dimensions are designed and simulated using Maxwell software. Considering all the capacitive coupling between plates, an equivalent circuit model is derived. The fundamental harmonics approximation method is used to analyze the working principle of the circuit. A 150 W input power CPT system is designed as an example to validate the proposed repeater structure and compensation circuit topology. The system can achieve an efficiency of 66.9% from dc source to dc load, when the transfer distance is 360 mm and the repeater is placed between the transmitter and the receiver. [ABSTRACT FROM AUTHOR]

This paper proposes a four-plate compact capacitive coupler and its circuit model for large air-gap distance capacitive power transfer (CPT). The four plates are arranged vertically, instead of horizontally, to save space in the electric vehicle charging application. The two plates that are on the same side are placed close to each other to maintain a large coupling capacitance, and they are of different sizes to maintain the coupling between the primary and secondary sides. The circuit model of the coupler is presented, considering all six coupling capacitors. The LCL compensation topology is used to resonate with the coupler and provide high voltage on the plates to transfer high power. The circuit model of the coupler is simplified to design the parameters of the compensation circuit. Finite-element analysis is employed to simulate the coupling capacitance and design the dimensions of the coupler. The circuit performance is simulated in LTspice to design the specific parameter values. A prototype of the CPT system was designed and constructed with the proposed vertical plate structure. The prototype achieved an efficiency of 85.87% at 1.88-kW output power with a 150-mm air-gap distance. [ABSTRACT FROM AUTHOR]

This paper proposes a combined inductive and capacitive wireless power transfer (WPT) system with LC -compensated topology for electric vehicle charging application. The circuit topology is a combination of the LCC-compensated inductive power transfer (IPT) system and the LCLC-compensated capacitive power transfer (CPT) system. The working principle of the combined circuit topology is analyzed in detail, providing the relationship between the circuit parameters and the system power. The design of the inductive and capacitive coupling is implemented by the finite-element analysis. The equivalent circuit model of the coupling plates is derived. A 3.0-kW WPT system is designed and implemented as an example of combined inductive and capacitive coupling. The inductive coupler size is 300 mm × 300 mm and the capacitive coupler is 610 mm × 610 mm. The air-gap distance is 150 mm for both couplers. The output power of the combined system is the sum of the IPT and CPT system. The prototype has achieved 2.84-kW output power with 94.5% efficiency at 1-MHz switching frequency, and performs better under misalignment than the IPT System. This demonstrates that the inductive–capacitive combined WPT system is a potential solution to the electric vehicle charging application. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) is an emerging technology that can realize electric power transmission over certain distances without physical contact, offering significant benefits to modern automation systems, medical applications, consumer electronics, etc. This paper provides a comprehensive review of existing compensation topologies for the loosely coupled transformer. Compensation topologies are reviewed and evaluated based on their basic and advanced functions. Individual passive resonant networks used to achieve constant (load-independent) voltage or current output are analyzed and summarized. Popular WPT compensation topologies are given as application examples, which can be regarded as the combination of multiple blocks of resonant networks. Analyses of the input zero phase angle and soft switching are conducted as well. This paper also discusses the compensation requirements for achieving the maximum efficiency according to different WPT application areas. [ABSTRACT FROM PUBLISHER]

This paper compares the characteristics of the series–series and double-sided Inductor-Capacitor-Capacitor (LCC) compensation topologies for electric vehicle (EV) wireless chargers. Both the well-tuned and mistuned topologies for the two compensation methods are analyzed in detail. The mistuning considered here is mainly caused by the variations of the relative position between the primary and secondary sides. The output power displacements caused by mistuning are compared for both compensation topologies, as well as the impacts of the load variations on the performances of the mistuned topologies. The voltage and current stresses on components are also studied. The comparative result shows that the double-sided LCC compensation topology is less sensitive to mistuning. A double-sided LCC-compensated EV wireless charger system with up to 7.7-kW output power is built to verify the analysis results. A peak efficiency of 96% from dc power source to battery load is achieved. [ABSTRACT FROM PUBLISHER]

This paper presents an integrated LCC compensation topology for electric vehicle/plug-in hybrid electric vehicle wireless chargers. The effect of the coupling between the additional coil and the main coil on the LCC compensation topology is studied. The proposed topology will reduce the size of the additional coil and make the system more compact with extremely high efficiency. The basic characteristics of the proposed topology are analyzed based on fundamental harmonic approximation. Furthermore, based on the steady-state model, three categories of operation modes are presented and analyzed. In order to realize zero-voltage switching, the series capacitor C2 on the secondary side is tuned. A numerical method is used to analyze the impact of different values of \Delta C2 on the turnoff current, and the best value of C2 is chosen to build a prototype to verify the analysis. [ABSTRACT FROM PUBLISHER]

This paper proposes a double-sided LCC compensation network and its tuning method for wireless power transfer (WPT). With the proposed topology and its tuning method, the resonant frequency is irrelevant with the coupling coefficient between the two coils and is also independent of the load condition, which means that the system can work at a constant switching frequency. Analysis in frequency domain is given to show the characteristics of the proposed method. We also propose a method to tune the network to realize zero voltage switching (ZVS) for the Primary-side switches. Simulation and experimental results verified analysis and validity of the proposed compensation network and the tuning method. A wireless charging system with output power of up to 7.7 kW for electric vehicles was built, and 96% efficiency from dc power source to battery load is achieved. [ABSTRACT FROM PUBLISHER]

In this paper, an inductor–inductor–capacitor (LLC) resonant dc–dc converter design procedure for an onboard lithium-ion battery charger of a plug-in hybrid electric vehicle (PHEV) is presented. Unlike traditional resistive load applications, the characteristic of a battery load is nonlinear and highly related to the charging profiles. Based on the features of an LLC converter and the characteristics of the charging profiles, the design considerations are studied thoroughly. The worst-case conditions for primary-side zero-voltage switching (ZVS) operation are analytically identified based on fundamental harmonic approximation when a constant maximum power (CMP) charging profile is implemented. Then, the worst-case operating point is used as the design targeted point to ensure soft-switching operation globally. To avoid the inaccuracy of fundamental harmonic approximation approach in the below-resonance region, the design constraints are derived based on a specific operation mode analysis. Finally, a step-by-step design methodology is proposed and validated through experiments on a prototype converting 400 V from the input to an output voltage range of 250–450 V at 3.3 kW with a peak efficiency of 98.2%. [ABSTRACT FROM PUBLISHER]

This paper presents a novel topology for a nonisolated bidirectional dc–dc converter with soft-switching capabilities, which usually operates at a zero-voltage-switching (ZVS) condition. A nonisolated dc–dc converter combines a buck converter and a backward boost converter into one circuit, which consists of a half-bridge power switch, an inductor, and capacitors. In order to realize ZVS conditions, the proposed converter utilizes a coupled inductor, a small independent inductor, and auxiliary switches and diodes. Due to ZVS, switching stress on switch components is reduced, and the reverse recovery problem of MOSFET antiparallel body diodes is also eliminated. Moreover, the operating modes of the proposed converter can be switched between a ZVS mode and a conventional hard-switching mode on the basis of load conditions. The soft-switching mode is for heavy loads, and the hard-switching mode is for light-load conditions. Therefore, the highest efficiency can be obtained at almost all load ranges. The detailed theoretical analyses in each mode are presented, and a 1-kW prototype is also built to verify the principle of the circuit and the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This letter presents a novel topology for a buck dc–dc converter with soft-switching capability, which operates under a zero-current-switching condition at turn on and a zero-voltage-switching condition at turn off. In order to realize soft switching, based on a basic buck converter, the proposed converter added a small inductor, a diode, and an inductor coupled with the main inductor. Because of soft switching, the proposed converter can obtain a high efficiency under heavy load conditions. Moreover, a high efficiency is also achieved under light load conditions, which is significantly different from other soft-switching buck converters. The detailed theoretical analyses of steady-state operation modes are presented, and the detailed design methods and some simulation results are also given. Finally, a 600 W prototype is built to validate the theoretical principles. The switching waveforms and the efficiencies are also measured to validate the proposed topology. [ABSTRACT FROM AUTHOR]

This paper presents a simple circuit for balancing series-connected battery cells. The circuit is composed of one low-voltage metal–oxide–semiconductor field-effect transistor (MOSFET) for each cell and a symmetrical multiwinding transformer for a group of cells. Only one control signal is needed for all MOSFETs, and energy can be directly transferred from higher voltage cells to lower voltage cells. A small capacitor is added to form a resonant circuit with the transformer magnetizing inductance so that soft switching can be achieved in some operation range to obtain high efficiency. The circuit balance function and soft-switching condition are analyzed and verified by simulation and experiments. A circuit for balancing a 4- and 12-cell battery group is tested. The experimental results showed the effectiveness of the circuit. The energy transfer efficiency between cells can reach up to 93%. The circuit can be easily scaled to battery strings containing up to 12 battery cells, directly applicable to consumer electronics application where the number of cells is typically less than 12. A battery pack containing a large number of battery cells, such as the ones used in electric vehicles, can be balanced in groups, for example, in modules containing 12 cells each and with one additional circuit to balance among the modules. [ABSTRACT FROM AUTHOR]