Analysis and Design of Load-Independent, Efficient, Transformerless Multilevel Online Inductive Power Transfer System

Inductive power transfer (IPT) and capacitive power transfer (CPT) are mainly two effective ways to achieve wireless power transfer (WPT). IPT system needs capacitor to compensate the system, while the CPT system requires inductor to tune the system. Therefore, IPT coupler can be used to compensate the CPT coupler and vice versa. In this article, an inductive and capacitive hybrid wireless power transfer (HWPT) system is proposed to improve the system coupler antimisalignment ability. The couplers of IPT and CPT are employed together to compensate each other and transfer power together. Superposition theory is used to analyze the system working principle in detail. With the analysis results, a scaled-down system is built to validate the performance of the proposed approach. Experimental results show that the proposed HWPT system can achieve 653 W output power with 87.7% dc–dc efficiency at the well-aligned condition, and the maximum variation of the output power is 8.3% with the coupler misalignment from 0 to 270 mm (halfwidth of the coupler), which agree well with the analysis results.

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.

The increasing development and commercialization of electric and hybrid electric vehicles includes the challenge of enabling an efficient and comfortable charging process of a car‘s battery. A promising solution for this purpose is provided by the use of inductive power transfer (IPT) technologies for a contactless charging with an electric power in the order of several kW [1]. A current driven charging coil (primary coil) is positioned on the floor below the car and coupled via an airgap with a secondary coil attached to the bottom of the car. IPT systems generate magneto-quasistatic fields with frequencies from 80 up to 140 kHz. A person positioned inside or near the car, however, will also be exposed to these magnetic fields. Exposure related changes of the electric field strength inside the human body can lead to stimulations of nerve and muscle tissues. Therefore, limits for the volume-averaged body-internal electric strength are proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [2]. Investigations of the human exposure to magneto-quasistatic fields require the use of high-resolution numerical simulation techniques such as the Finite-Difference Time Domain (FDTD) method. Complex geometries of conductive and/or permeable sheets contained in the IPT system and the car body as well as anatomical body phantoms have to be considered in exposure simulations. Also, potential misalignments between the IPT system’s coils might have an influence on the exposure and need to be taken into account. A high-resolution discretization of such scenarios within commercially available eddy current solvers is often unfeasible as it requires the solution of very high-dimensional and extremely ill-conditioned algebraic systems of equations. As an alternative, three two-step methods have been introduced in [3] and [4] making use of domain decomposition approaches enabling a division of the exposure scenario into two domains: the source area including the influence of shielding geometries and the area occupied by the exposed body. These three two-step methods – the Coupled Scaled-Frequency (SF-)FDTD method, the Co-Simulation SF-FDTD method and the Co-Simulation Scalar-Potential Finite Difference (SPFD) method – are used here for a high-resolution modeling of magneto-quasistatic exposure scenarios including realistic models of various IPT systems, the car and the human body. With the application of the two-step methods a reduction of the memory demands and the simulation time is achieved in comparison to a monolithic application of the SF-FDTD method and the simulations can be performed on a standard computer workstation. Figure 1 a) shows an exposure scenario where a human body model (body phantom Duke [5]) is positioned beside a car model with an IPT system positioned below the car. For an improvement of the coupling between the IPT’s coils, optimization analyses are conducted using an FEM-based magneto-quasistatic field solver included in the software ANSYS Maxwell 3D [6]. Here, different geometry designs are compared to each other regarding an optimization of the coupling coefficient and a reduction of the magnetic leakage fields, coincidentally. The optimized model geometries of different IPT systems are used in exposure analyses carried out with the abovementioned two-step methods. In a first step, the magnetic source field simulation is performed with the software CST Microwave Studio (MWS) [7]. The simulation model includes the IPT system and the car body sheets, but not the human body model, since its interaction with the magnetic source field is negligible. Source field simulations are also carried out considering lateral misalignment of the IPT system’s coils and different values for the thickness of the car body sheets for an analysis of a consequential variation of the leakage fields – and thus the exposure of the human body. Figure 1 b) shows the magnetic flux density in a cross section of the car and in the center of the IPT system with the designated position of the human body model indicated. In a second step, the exposure of the human body is calculated, i.e., the exposure-related distribution of the body-internal electric field strengths, using the previously calculated source fields. Within the two-step SF-FDTD methods this second step is also carried out using CST MWS or, alternatively, using the software Sim4Life [8], whereas within the Co-Simulation SPFD method a discrete Poisson equation is solved using a preconditioned conjugate gradient solver. A high flexibility is achieved by the use of the Co-Simulation SPFD method (as well as with the Co-Sim SF-FDTD method), since the magnetic source field simulation can be computed using any magnetic field simulation tool. Figure 1 c) shows the electric field strength in the median plane of the human body voxel model. The maximum voxel-averaged electric field strength is evaluated for each scenario to analyze the influence of each configuration (different IPT systems, coil misalignments and car body sheet thicknesses) on the exposure and for an exposure assessment according to the ICNIRP guidelines.

In this study, a full-duplex data communication module is designed and developed for sharing information in a contactless power transfer system. It is realized through LC tank circuits with an inductive power transfer (IPT) system. On both the transmitter and receiver sides, one LCC compensation topology is used. Since Phase Shift Keying (PSK) is less susceptible to error and power-efficient digital modulation techniques, this paper proposes to implement PSK digital modulation technique to data signal modulation for full-duplex communication in a wireless EV charger. The proposed scheme ensures stability, transfers load status, charging level, and emergency messages between the source and load sides of the system, and vice versa. The results are compared with the Amplitude Shift Keying (ASK) digital modulation technique. Further, the impedance-based model is developed to analyze the interference between the power and high-frequency information signals. The inductive power and data transfer (IPDT) prototype is developed in the laboratory and results show that the data rate reaches 288 kbps when 46.6 W of power is transferred from source to load.

Along with the technology boom regarding electric vehicles such as lithium-ion batteries, electric motors, and plug-in charging systems, inductive power transfer (IPT) systems have gained more attention from academia and industry in recent years. This article presents a review of the state-of-the-art development of IPT systems, with a focus on low-voltage and high-current electric mobility applications. The fundamental theory, compensation topologies, magnetic coupling structures, power electronic architectures, and control methods are discussed and further considered in terms of several aspects, including efficiency, coil misalignments, and output regulation capability. A 3D finite element software (Ansys Maxwell) is used to validate the magnetic coupler performance. In addition, a 2.5 kW 400/48 V IPT system is proposed to address the challenges of low-voltage and high-current wireless charging systems. In this design, an asymmetrical double-sided LCC compensation topology and a passive current balancing method are proposed to provide excellent current sharing capability in the dual-receiver structures under both resonant component mismatch and misalignment conditions. Finally, the performance of the proposed method is verified by MATLAB/PSIM simulation results.

An inductive power transfer (IPT) system usually consists of four parts: an AC-DC power factor correction (PFC) converter, a high frequency DC-AC inverter, a compensation network comprising a loosely coupled transformer (LCT) and the resonant capacitors, and a rectification output circuit. Due to the relative large air gap, the magnetic coupling coefficient of the IPT system is poor, different from the closely-coupled IPT systems. As a result, the efficiency of the IPT system is always a main concern for different applications. To ensure high power transfer efficiency, these IPT systems should have high tolerance for different gap variation and horizontal misalignment conditions. In this paper, some design considerations to reduce gap and misalignment effects for the IPT system is proposed. By using finite element analysis (FEA) simulation method, the performance of different transmitter and receiver coil dimensions are compared. In order to validate the performance of the proposed design considerations, a hardware prototype is built and the corresponding experiments are carried out. The experimental results shows that the LCT prototype could maintain coupling coefficient between 0.237∼0.212 within 40 mm horizontal misalignment.

In this article, we propose a bilaterally transmitted domino-type multiload inductive power transfer (IPT) system for constant-voltage (CV) outputs, low voltage attenuation, and high efficiency. There are three major contributions. First, the series–series/parallel (S–SP) topology is developed to design the multiload IPT system, which can realize the load-independent CV outputs without using compensation inductors, enabling a compact IPT system. Second, a bilateral IPT structure is proposed with two parallel power transfer routes to mitigate the practical output voltage attenuation issue, resulting in a better CV property. Third, system efficiency is improved by the proposed bilateral IPT structure. With the bilateral S–SP compensated multiload IPT design, the output voltage attenuation analysis and system efficiency are investigated considering parasitic resistances. A 70 W six-load bilateral IPT prototype is implemented and compared with the unilateral counterpart. With <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 0.26 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> = 300, the proposed bilateral IPT system validates an improved CV output with a small attenuation rate of 10.22%, which is much lower than the unilateral one. The maximum efficiency achieves 90.39%, showing 5.17% higher than the unilateral IPT system in the identical load condition.

Inductive power transfer (IPT) systems are often designed to achieve their highest efficiency at a fixed load value and at a fixed coil separation distance and misalignment. A variation in the position of the coils or the load value tends to drastically affect the efficiency, and therefore makes the designed IPT system not practical for applications that are mobile with variable loading conditions such as dynamic wireless charging for electric vehicles. This paper presents a novel design approach for loosely-coupled IPT systems that can inherently maintain efficient operation against changes in the system's characteristics, coil geometries and loading conditions. The transmitting-end of the proposed IPT system consists of a Load-Independent Class EF inverter that provides a constant amplitude current in the transmitting-end coil and achieves zero-voltage switching (ZVS) independent of the coupling factor and the load resistance. A Class D rectifier with a resistance compression network (RCN) was implemented for the receiving-end of the IPT system to ensure that the reflected resistance to the transmitting-end is at its optimum value with minimal dependence on the output load resistance. The combination of the features of the inverter and rectifier allow the IPT system to operate efficiently across a wide range of air gaps, without retuning. Experimental results show a maximum DC-DC efficiency of 83% with a coil separation of one coil diameter and 85 W output power. A weighted average DC-DC energy transfer efficiency (where the coils move through zero alignment, to full alignment, and back to zero alignment at constant velocity), was measured at 73%.

This paper introduces the working principle of the inductive power transfer (IPT) system from the perspective of the electromagnetic field. Using Maxwell’s equations, the analytical solution for the electromagnetic field, synthesized by the primary and secondary circular coils in an IPT system, is deduced in detail to obtain the electric field in the IPT system, and the derivation process is easy to understand for researchers engaged in IPT. The final solutions are obtained by combining analytical derivation and the numerical integration method to find the induced voltage in the secondary coil. Finally, by comparison, the simulation results from the finite element software are in a good agreement with those from the analytical analysis. Moreover, an IPT system is set up to validate the analytical and simulation results, and the maximal relative error is under 6% in different working conditions, which shows that it is feasible to understand the working principle of IPT systems from the viewpoint of the electromagnetic field.

This study proposed a hybrid inductive and capacitive wireless power transfer system to achieve high‐power transfer by combining inductive power transfer (IPT) and capacitive power transfer (CPT). A traditional IPT system imposes a high voltage on the transmitter because of resonance. Meanwhile, high voltages are required to establish an electric field to deliver power to the CPT system. Therefore, they can be combined to a hybrid system to achieve high‐power transfer by utilising two power transfer paths. A general model of the hybrid IPT and CPT coupler is analysed in detail. With a series–series compensation topology, 1.1 kW hybrid system with equal power transferred by two paths is simulated and set up to evaluate the performance of the proposed method. An experimental prototype is built under various conditions, and the result shows that the hybrid system achieved 1.1 kW output power through both of magnetic path and of electric path successfully with 91.9% DC–DC efficiency.

One of the fundamental drawbacks of the conventional LCL resonant inductive power transfer (IPT) system is the inverter highly distorted ac-current. As a consequence, the on-state and switching losses are increased. In order to overcome these disadvantages, this paper introduces an improved IPT system. The proposed improvement comprises notch filters, along with LCL filter in the inverter side of the IPT system. The performance of the conventional and the proposed IPT system is verified by simulation results. Heavy load and light load operation conditions are taken into account. In the end, a detailed power loss analysis of the inverter is presented for both IPT systems. Simulation results as well as power loss analysis verify that the proposed IPT system reduces the switching losses, the on-state losses, the RMS value and the total harmonic distortion of the converter current.

The Inductive power transfer (IPT) systems' efficiency is determined by kinds of parameters. Aim at maximum the power transfer efficiency for Inductive power transfer (IPT) system, the efficiency of four basic topology IPT systems is analyzed. Based on the analysis, genetic algorithms (GA) are used to optimize IPT systems parameters to achieve the maximum of the power transfer efficiency. Before the GA optimization process, the IPT systems are compensated in a resonance condition which can achieve to minimize VA rating of the power supply and maximum power transfer. In the process of GA optimization, to ensure the final solutions achieving bifurcation-free operation, the solutions that generate bifurcation phenomenon (multi zero phase angle frequency) are excluded. The simulation results verify that the GA can find the best optimal solutions for all topology IPT systems.

This paper presents an improved communication architecture with increased data rate for inductive power transfer (IPT) systems. The main challenge is to enable robust and reliable communication within the noisy environment of the power transfer. Therefore, the communication channel, consisting of the coupled pair of coils of the inductive power transfer system is analysed. From this, a frequency band with an excellent available signal to noise ratio has been identified. It is exploited using phase shift keying or higher-order digital modulation schemes as n-th quadrature amplitude modulation to increase the data rate. Furthermore the bandwidth of the system shall be extended by the utilisation of an equalizer. The implementation using a software defined radio will be presented in this paper and it will be shown that reliable and fast communication is possible in a harsh industrial environment.

A key requirement in inductive power transfer (IPT) systems is primary high-frequency voltage generation. Until recently, two power conversion stages (AC-DC-AC) were required to generate high-frequency voltage in the IPT systems. These systems are usually costly and cumbersome. Matrix AC- AC converters, highlighted by the absence of bulky DC link storage elements, are considered as a potential alternative. The removal of one power conversion stage enhances the system performance in term of efficiency, reliability, size, weight, and cost. Now, AC-AC buck, half-bridge, and full-bridge converters are gaining popularity in IPT applications. However, highly accurate analysis of their performance in the IPT systems is a challenge. In this paper, a simple and accurate mathematical analysis for the AC-AC buck converter supplying a series-series compensated IPT system is given. Performance indicators used for analysis are input power factor and power transfer capability. The accuracy of the analysis is validated through simulation. The analytical results presented in this paper can also be employed to analyze the series-series IPT system fed from other AC-AC matrix converters.

Considering the coupling relationships between transfer power and efficiency in continuous-mode inductive power transfer (IPT) systems, this paper presents a pulse energy injection inverter for IPT systems. With a new topology and parameters tuning, the pulse energy injection IPT system with the proposed inverter can work in switch-mode to decouple transfer power with efficiency. Moreover, the transfer power is only decided by the duty ratio of the semiconductor switch, rather than affected by the transmitting resonator, receiving (Rx) resonator, and load. In this way, the pulse energy injection IPT system holds an operating frequency much lower than the resonant frequency to reduce switch loss and improve transfer efficiency. Experiments verify that the IPT system with proposed inverter maintains a high level efficiency within the middle range and realizes nearly 80% supply to load transfer efficiency even in a weak coupling coefficient ( $k=0.044$ ). Finally, experimental analysis implies that the pulse energy injection inverter is suitable for full-range transmission, and high-Q IPT systems with uncertainty in Rx circuits or load.