A self-tuning variable frequency control for multi-level contactless Electric Vehicle charger

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.

A self-tuning controller for contactless electric vehicle (EV) charging systems based on inductive power transfer (IPT) with multiple power levels is proposed. The multiple charging levels (consisting of ten charging levels) are achieved by controlling the energy injection frequency of the transmitter coil of the IPT system. The proposed controller is capable of self-tuning the switching operations to the natural resonance frequency of the IPT system, and it benefits from soft-switching operations (zero-current switching), which ensures the maximum performance of the IPT system. The proposed controller has such a simple design, which can be implemented based on a simplified control circuit. The simulation of the proposed controller for an inductive charging system at different charging levels is carried out in MATLAB/Simulink. Also the proposed controller with an ac/dc/ac converter is implemented experimentally on an IPT charging system to verify the effectiveness of the controller at different charging levels. The experimental test results conform with the simulation results and verify that the proposed controller effectively enables self-tuning capability and soft-switching operations at different charging levels for IPT-based contactless EV charging systems.

Based on the current-mode switching cell (CMSC), an inductive power transfer (IPT) system with dual-output is proposed in this letter. In the proposed IPT system, two CMSCs are inversely connected in series at the Rx side. Two CMSCs operate in the positive half-cycle and in the negative half-cycle of the Rx coil current, respectively. The dual output voltages can be regulated independently. The circuit structure of the CMSC is quite simple and helps to make the Rx side more compact. The control scheme is based on Rx-side real-time regulation and thereby wireless communication links are not required. Additionally, zero voltage switching is ensured for all switches. In order to verify the theoretical analysis, an experimental prototype with 20 V/3.3 A and 5 V/3 A outputs is fabricated, and the maximum efficiency can reach 92.8%.

To improve misalignment tolerance for an inductive power transfer (IPT) system, a third-coil is employed to reversely connect with the primary coil of the loosely coupled transformer (LCT) in series. The LCT with a third-coil (LCT-TC) not only can improve the misalignment performance in x - and y -directions, but also does not affect the inherent output characteristics (such as constant current or voltage output) of original compensation topologies. In addition, the proposed approach can keep the IPT system operating with relatively high efficiency against misalignment. Then, a detailed design method of LCT-TC is presented. Finally, a double-side LCC-compensated IPT system is chosen as an example to verify the feasibility of proposed LCT-TC. A 3.4-kW prototype is constructed, and experimental results show that the proposed method has a good misalignment performance. The LCC-LCC IPT system with LCT-TC can retain 96% of the well-aligned power at 40% misalignment, and the end-to-end (dc–dc) overall system efficiency is at least 92%. Besides, the fluctuation of the output current is [–2%, 5%] while the load varies from 15 to 34 Ω within 40% misalignment.

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.

SummaryRectifier load in inductive power transfer system has nonlinear characteristics. However, the traditional analysis method equates it to a pure resistor, which leads to a certain deviation between the theoretical analysis and the actual circuit. This will reduce the accuracy of the inductive power transfer (IPT) system model and affect the soft switching operation of the inverter. In this paper, the IPT system with S‐type topology on the secondary side is studied. Firstly, the resistance–inductance characteristics of the rectifier load are analyzed by simulation, and then a second‐order circuit response model is established to solve the time‐domain expression of voltage and current. Then, the fundamental component of voltage and current is extracted by Fourier transform to calculate the impedance value of the rectifier load, and the mathematical calculation model of the rectifier load is established. On this basis, the influence of the inductive component of the rectifier load on the input impedance of the IPT system is analyzed. Then, a parameter design method for zero voltage switching is proposed for S‐S and LCC‐S topologies. Finally, an experimental platform of S‐S and LCC‐S IPT system is built. The correctness and effectiveness of the theoretical analysis and the proposed parameter design method are verified by experiments.

This article studies magnetic forces between transmitter (Tx) and receiver (Rx) coils in an inductive power transfer (IPT) system aiming to use those forces to align the coils and, consequently, improve power transfer. Due to its popularity, the analysis is conducted on a series–series compensated IPT system with planar spiral coils. The proposed method utilizes the bifurcation operation mode of the system and unloaded resonating receiver to maximize attractive force between magnetic couplers. Three-dimensional finite-element method simulations indicate that high-power IPT systems can develop enough attractive force to align coils even under nominal current. Regardless of the coil shape, e.g., spiral or Double-D (DD), the attractive forces tend to align the coils. Hence, a smart charging station can be devised based on self-aligning capability. Furthermore, this article proposes a mechanical structure to facilitate the attractive lateral force for the alignment of high power applications, i.e., wireless fast-charging stations. The forces are analyzed, modeled, and simulated for a 100-kW IPT system with an operating frequency of 20 kHz, while the self-aligning capability is experimentally verified on a downscale 11-kW prototype.

Inductive power transfer (IPT) technology becomes highly attractive option for wireless battery charging applications. To fulfill the charge profile of battery packs, wide output voltage regulation is always necessary. In this paper, an improved LCC-S compensated IPT system utilizing variable frequency switched capacitor control is put forward. Compared with the traditional LCC-S compensation topology, an extra capacitor is connected in series with the compensation inductor to form a symmetrical T-network. Switched capacitor is utilized to regulate the equivalent capacitance of the middle branch of T-network, which has the advantages of low voltage stress. In the proposed control method, the variation range of switching frequency is in compliance with SAE J2954 Standard and frequency bifurcation can be avoided. The detuning issue at receiver side caused by switching frequency variation is solved by using the variable inductor. The proposed IPT system is able to realize nearly unity power factor with high efficiency in the whole voltage range. Finally, a 592 W prototype with 112-168V output voltage is built to verify the proposed IPT system. Experimental results show that the peak efficiency of the improved LCC-S compensated IPT system reaches 94.6% at full load when the coupling coefficient <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> =0.2.

SummaryMultistring arrays of LED in parallel connection are widely applied in lighting fields. Active control and passive methods are utilized to guarantee equal current sharing between different strings with a common voltage source. Compared with active control, the passive methods that adopt purely passive components without real power dissipation are good candidates. Currently, an inductive power transfer (IPT) converter providing a constant voltage (CV) line, followed by some immittance networks that convert the CV line to constant current (CC) outputs, is commonly used to drive multiple LED strings. However, in such a two‐conversion‐stage scheme, the component count is as many as , where is the number of LED strings, which deviates from compact, low‐cost, and simple design ideas. To address it, this paper aims to develop a single‐immittance‐network‐based IPT system to drive multistring LEDs with the current balance. The proposed IPT system can directly provide a CV to CC conversion to drive multistring LEDs with the benefits of simplifying the circuit design, size, and cost. The proposed IPT system also features programmable luminous power, zero‐phase‐angle (ZPA) input, IPT technology, and load‐independent‐current (LIC) output. Detailed analysis, implementation, and experiment are presented in this paper.

A dynamic inductive power transfer (IPT) system is a safe and convenient solution to address the issues related to the limited battery capacity and travel distance of electric vehicles (EVs). In recent years, practical aspects of dynamic IPT systems have been investigated to advance various IPT technologies from laboratories to roadways. This paper suggests a configuration to mitigate some of the installation and maintenance concerns of IPT roadways by proposing a switchable inductively coupled connector. Besides providing galvanic isolation, the inductively coupled connector helps maintain a constant and load-independent current in the primary coupler. Moreover, each primary coupler is connected to a common H-bridge through a single DC switch minimizing the number of components required to energize each coupler independently. A mathematical analysis and simulation results have been provided to validate a scaled 3.3kW prototype IPT system employing the proposed configuration.

Variable parameter (VP) or variable frequency (VF) methods for load‐independent output current or output voltage in inductive power transfer (IPT) systems have been widely studied. This study proposes an IPT system based on series‐series compensation topology with VP and VF methods to achieve constant‐current–constant‐voltage (CC–CV) charging for electric bicycles (EBs). The proposed IPT system can operate in CC and CV modes regardless of load conditions at two different operating frequencies with corresponding values of compensation capacitors. The rating current/voltage of the proposed method is configurable by altering the compensation capacitor and operational frequency. Therefore, one charging stand can be shared by various EBs to save the space and to cut the overall cost. Only one capacitor is needed for one EB specification. The proposed IPT system can achieve zero‐voltage switching under all load conditions. An experimental prototype with two ratings of 48 V/3A and 60 V/4A is built to verify the feasibility of the proposed method. The experimental results demonstrate the feasibility of the proposed method.

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 relatively large air gap, the magnetic coupling coefficient of the IPT system is significantly lower than that with tightly coupled transformer. As a result, the efficiency of the IPT system is always a main concern for applications with possible gap variation or misalignment condition. To ensure high power transfer efficiency, these IPT systems should have high tolerance for different gap variation and horizontal misalignment conditions. In this paper, the effect of coupling coefficient deviation to compensation network efficiency is analyzed, and design considerations to reduce gap and misalignment effects for the IPT system are proposed. By using finite-element analysis simulation method, the performance of different transmitter and receiver coil dimensions is compared. In order to validate the performance of the proposed design considerations, a 100-W hardware prototype with two sets of LCT is built and the corresponding experiments are carried out. As compared to the symmetrical LCT architecture, the proposed asymmetrical LCT prototype improves the coupling coefficient reduction from 68% to 28% when the gap varies from 6 to 20 mm and from 89% to 31% when the misalignment ranges from 0 to 50 mm. Therefore, the efficiency deviation for the asymmetrical LCT is maintained within 3.5% over the entire tested gap variation and misalignment ranges.

The efficiency of an inductive power transfer (IPT) system is greatly affected by lateral misalignment between the transmitter and receiver coils. This study proposes a hexagonal arrangement of multi-coil configuration IPT system to improve misalignment tolerance while maintaining the transfer efficiency. Key parameters including equivalent self and mutual inductance of various coil connections are examined. The magnetic characteristics including flux distribution and density, and mutual inductance are simulated using COMSOL Multiphysics software package. Experimental results of the proposed multi-coil IPT system are given and compared with the conventional two-coil IPT system. Simulation and experimental results have shown that the proposed multi-transmitter coil configuration can increase misalignment tolerance compared with conventional system.

Inductive power transfer (IPT) is a promising solution to replace the plug-in charging system for electric vehicles (EVs) owing to its safety and convenience. However, the efficiency and output stability of the IPT system will decrease when misalignment happens. In this work, a two-dimensional misalignment-tolerant IPT system based on a three-arm voltage doubler (VD) rectifier is proposed. When the receiver moves to different positions, receiver coils can transmit energy in three kinds of operation modes, i.e., transmitting power by three, two or one receiver coils. According to different receiver positions, the proposed system can automatically switch between three operating modes to obtain a constant voltage (CV) output even if the receiver moves in lateral and longitudinal directions simultaneously. A 1.6kW experiment setup is built. The experiment results show that, under the situation of different receiver positions and variable loads (40-80Ω), the proposed IPT system can confine the output voltage variation within 5% when the receiver is located in a specific area, which occupies more than 72 % of a square with a side length of 400mm. Besides, in this area, the system efficiency of the proposed IPT system is from 90.66% to 95.11 %.

The single resonant inverter is widely employed in typical inductive power transfer (IPT) systems to generate a high-frequency current in the primary side. However, the power capacity of a single resonant inverter is limited by the constraints of power electronic devices and the relevant cost. Consequently, IPT systems fail to meet high-power application requirements, such as those in rail applications. Total harmonic distortion (THD) may also violate the standard electromagnetic interference requirements with phase shift control under light load conditions. A power regulation approach with selective harmonic elimination is proposed on the basis of a parallel multi-inverter to upgrade the power levels of IPT systems and suppress THD under light load conditions by changing the output voltage pulse width and phase shift angle among parallel multi-inverters. The validity of the proposed control approach is verified by using a 1,412.3 W prototype system, which achieves a maximum transfer efficiency of 90.602%. Output power levels can be dramatically improved with the same semiconductor capacity, and distortion can be effectively suppressed under various load conditions.