Inductive Power Transfer Prototype Research Articles

Decoupling Optimization of the Three-Coil Coupler for IPT System Featuring High Efficiency and Misalignment Tolerance

The efficiency of an inductive power transfer (IPT) system decreases significantly with misalignment. This paper proposes a parameter optimization method for the three-coil coupler (TCC) to obtain high system efficiency and misalignment tolerance. The magnetic flux distribution of the TCC is compared with the conventional two-coil coupler, based on which the reason for high misalignment tolerance of the TCC is clarified. To reduce the optimization time, the concepts of primary self-inductance decoupling and mutual inductance decoupling are introduced. An IPT prototype using LCC/S (inductor-capacitor-capacitor/series) compensation topology and the optimal TCC was built to verify the validity of the proposed optimization method. The radii of the transmitting and receiving pads of the TCC are 210 and 130 mm, respectively, and the power transfer distance is 100 mm. The system efficiency is 90.106% in aligned case and 85.446% in the most misaligned case (misalignments in X-, Y-, and Z-axis are 75, 100, and 50 mm, respectively). Compared to the output voltage in aligned case, the output voltage in the most misaligned case is only decreased by 39.26%.

Effective Scheme for Inductive Wireless Power Coil Design Using Scan-and-Zoom Optimization

In inductive power transfer (IPT) systems, the coil design is crucial since the power transfer efficiency (PTE) of IPT depends on the coil characteristics such as geometric shape, diameter, wire thickness, etc. The most commonly used technique for the coil is finite element analysis (FEA). Nevertheless, if there are more than two parameters to be designed, FEA design requires a long simulation time since the coil design problem is separated into a series of single-parameter optimization problems. Another issue of conventional FEA is difficulty in interfacing with circuit simulation. To mitigate this issue, a novel co-simulation framework of MATLAB/ANSYS Maxwell is proposed in this paper. In MATLAB, multi-dimensional optimization algorithms like scan-and-zoom are employed to determine geometric parameters to achieve high PTE and minimize the number of FEA executions while Maxwell serves to extract the circuit parameters from the geometric parameters and enhance the accuracy of calculation. The 100 W prototype IPT system is built to verify the proposed coil design scheme in this paper. The performance comparisons with the conventional methods in terms of design accuracy, simulation time, and application flexibility are performed on a pair of designed single-layer circular coils.

Modular Coupler With Integrated Planar Transformer for Wireless EV Charging

A dynamic inductive power transfer (IPT) system is a safe and convenient solution for providing power to electric vehicles (EVs) while they are driving along a roadway. This technology can help reduce the size and cost of the bulky EV batteries without limiting the EV's travelling range. In recent years, practical aspects of dynamic IPT systems have been investigated to advance various IPT technologies from laboratories into roadways. This paper suggest an IPT roadway layout, focusing on a modular IPT system configuration with an integrated semi-loosely coupled planar transformer inside the in-road coupler to mitigate the installation and maintenance concerns of IPT roadways. The proposed configuration keeps the current in the couplers constant and load-independent while providing galvanic isolation between the coupler and the converter, and can be used as a replacement for the conventional LCL and transformer configuration. In order to reduce the number of components used in each module, each in-road coupler is connected to a common H-bridge through a single DC switch to enable individual couplers to be energized independently. Mathematical analysis and simulation results are provided, and validated using a scaled 7.7 kW prototype IPT system employing the proposed configuration.

A self-oscillating series-none inductive power transfer system using a matrix converter

Power density and conversion efficiency are two critical parameters of inductive power transfer (IPT) systems. These parameters are related to the number of components in the power conversion circuit as well as its modulation method. The combination of Midpoint Matrix Converter and pulse-density modulation (PDM) has a potential to improve these parameters, due to a low number of semiconductor switches utilization as well as constant efficiency at the maximum output and partial load operations . In this context, this paper analyzes the performance of a three-phase to single-phase Midpoint Matrix Converter using a Free-wheeling Switch (MMCFS) and the PDM in a high coupling factor series-none IPT application. This converter utilizes on–off control to manage power transfer, which automatically tracks the load resonant frequency. Dynamic and steady-state mathematical equations were derived to represent the converter and the IPT system characteristics. These equations show a relationship between the link efficiency, the link gain, the damping ratio and the coupling factor. A kick-start method and a multistep switching strategy were developed to start and operate the converter, respectively. Additionally, a 150 W MMCFS-based IPT prototype was built to verify the improvement, which demonstrated an efficiency of around 80% at the maximum output and partial load operations.

A Current-Sharing Compensation Method for High-Power-Medium-Frequency Coils Composed of Multiple Branches Connected in Parallel

In inductive power transfer (IPT) systems, the coils with paralleled multiple branches are commonly used in high power applications where the frequency range is between 20 and 90 kHz. The traditional compensation method takes multiple branches as a whole and the compensation capacitors are connected outside the coils, which suffers from current unbalance among multiple branches, but currently few researchers analyze it. Therefore, this article illustrates the current-unbalance mechanism and proposes a current-sharing compensation method for IPT coils. The current-unbalance characteristics of coils with paralleled multiple branches are illustrated to prove the current-sharing necessity. Then, based on the relation between the impedance of branch and current unbalance, a compensation capacitor with a specially designed value is connected in each branch, so that the current unbalance can be suppressed by the increased branch impedance. Besides, the cost, volume, and weight of IPT systems remain unchanged approximately. Finally, a 30-kW IPT prototype is built up to verify the availability of the proposed method, and the currents and temperatures of multiple branches are equally distributed within wide power range with this method.

A Family of Hybrid IPT Couplers With High Tolerance to Pad Misalignment

The transfer performance of inductive power transfer (IPT) systems is greatly affected by the inevitable magnetic pad misalignment. Practical IPT converters are expected to operate satisfactorily under considerable pad misalignments. Current design, control, and optimization of IPT circuits have achieved limited pad misalignment tolerance. In this article, a family of hybrid IPT couplers, which combine a conventional bipolar coupler and a simple series&#x2013;series topology, are proposed to achieve high tolerance to pad misalignments. The proposed hybrid IPT couplers are applicable to all IPT compensation topologies. In addition, overcurrent protection is inherently provided in the event of removal of the secondary coil and load. This article also provides the design principle of this family of hybrid couplers with different coil winding polarities to achieve a given coupling tolerance. Being a universally applicable IPT coupler with high tolerance to pad misalignment, the family of hybrid IPT couplers can be used in any IPT topology. An S-<i>LCC</i> compensation topology is used to illustrate the design of the IPT system with load-independent constant-voltage output under load and coupling variations. Finally, a 3-kW IPT prototype using a hybrid coupler and the S-<i>LCC</i> topology is built to verify the analytical findings.

Self-Driven Current-Doubler Synchronous Rectifier and Design Tuning for Maximizing Efficiency in IPT Systems

A novel driving circuit for a current-doubler synchronous rectifier (SR) to inductive power transfer (IPT) applications is proposed in this article using only auxiliary windings in the existent rectifier output filter inductors to drive active switches. The proposed SR overcomes the limitations of the traditional driving schemes because it does not require any processing, analog circuits, gate driver circuits, or current measurement, normally used in the conventional SR applied to IPT systems. The proposed configuration presents a simple and robust operation considering usual parametric variation in IPT systems, such as coupling factor, misalignment, load variation, and component tolerances. Moreover, the same size and weight of the conventional diode rectifier board are maintained due to the simplicity of the self-driven circuit. The proposed configuration allows increasing the global efficiency by reducing the conduction losses of the output rectifier and previous stages. A resonant circuit design procedure using an iterative process to find the maximum efficiency point considering the self-driven SR is proposed to maximize the global system efficiency. A 100-W resonant series–parallel IPT prototype is developed to validate the performance of the proposed self-driven SR circuit presenting a maximum global efficiency equal to 94.8%.

Common Mode Noise Analysis for Inductive Power Transfer System Based on Distributed Stray Capacitance Model

This article reveals the significant stray capacitances in inductive power transfer (IPT) coil, and offers two methods for modeling the stray capacitance effect: concentrated model and distributed model. Both analytic formulas and FEM simulation are introduced to estimate the value of parasitic capacitances, and experimental measurements on an 11 kW IPT coil prototype are conducted to verify the correctness of both methods. The common-mode noise propagation circuit of the IPT system is derived and simulated based on these two models. The results show that parasitic capacitance between Litz wire winding and shielding metal on the transmitter side plays a dominant role in CM noise propagation and the distributed model has higher fidelity because of its asymmetric structure. Besides, to mitigate conductive CM noise, an EMI filter, and HF isolation transformer are introduced. Finally, the conductive EMI tests are performed in an 11kW IPT prototype. The experimental results validate the accuracy of the proposed CM noise model with stray capacitances of the IPT coil. And the combination of EMI filter and HF isolation transformer can suppress CM noise greatly and render the CM noise spectrum below the CISPR 32 Class-B limit.

The Design and Coupler Optimization of a Single-Transmitter Coupled Multireceiver Inductive Power Transfer System for Maglev Trains

Inductive power transfer (IPT) is an effective energy supply solution for maglev trains that depend on current collectors to obtain enough electricity. This article proposed a system optimization that combines the compensation parameter and coupler optimization. The Pareto theory is employed to optimize an IPT system with a single-transmitter coupled multireceiver for maglev trains. The circuit model of the multipickup system and the finite element model of the coupler are given. A scale-down 1-kW prototype is built as the benchmark for the optimization. Then, the proposed system optimization is presented. The efficiency, pickup power density, and system cost are selected as the design objectives, and an optimal solution is selected from the Pareto fronts. A further coupler optimization is presented, and the optimization result is discussed and compared with other Maglev IPT coupler designs. Finally, an 8.5-kW IPT prototype based on the final optimized solution is built, and it is compared with other two different solutions to validate the method.

High-Efficiency Bilateral S–SP Compensated Multiload IPT System With Constant-Voltage Outputs

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.

Coupled electromagnetic-thermal analysis of roadway inductive power transfer pads within a model pavement

Inductive Power Transfer (IPT) technology is a promising solution for wireless charging of Electric Vehicles (EVs). Given the expected uptake of IPT technology for both stationary and in motion in-road charging, many technical challenges regarding the electromagnetic field and thermal aspects need to be overcome to generate cost-effective and reliable solutions. One particular design constraint of in-road IPT systems is the occurrence of local increases in temperature during operation due to power losses in the wireless charging pads. In this paper, safe operating conditions of an enclosed wireless power transfer pad within a pavement model were identified. This aspect has been studied less rigorously compared with the electromagnetic design. This paper presents a numerical thermal analysis of a double-D (DD) prototype IPT primary pad based on two possible configurations; flush-mounted or buried, within a model pavement. A coupled electromagnetic-thermal simulation has been developed to aid in the development of thermally robust in-road IPT systems. In order to validate the proposed two-way coupled electromagnetic-thermal Finite Element (FE) simulations, experiments were performed to capture the evolving thermal field within an IPT primary pad under continuous and periodic duty cycles. This method made possible analysis of the heating patterns and so the identification of internal hotspots within an IPT pad in a roading structure. A thermal camera was used to provide detailed surface temperature distributions, while suitable application of non-metallic Fiber Bragg Grating (FBG) sensing technology enabled a robust technique to measure temperatures within the intense magnetic fields of a high frequency wireless power transfer system to be developed. Comparisons at steady state of the pavement surface temperature distribution, as well as point measurements with the pad and sand, demonstrate good accuracy. The maximum steady state surface temperature occurs at the centre of the sand surface where the IPT pad is placed and is approximately 87 °C and 100 °C for buried and flush-mounted pads, respectively. Moreover, for a 2/3 duty cycle loading, the maximum temperature of the pad tended to an average of approximately 76 °C, while at constant operation the average temperature is 105 °C. Therefore, a 5 min cooling period significantly reduced operating temperatures within the studied model IPT system. In the future, the methodologies proposed in this paper can also be used to improve the design of higher power IPT pads by identifying hotspots and maximum thermal stresses and determination of optimal charging patterns for heat dissipation.

Analysis and Design of Cubic Magnetic Coupler for High Distance-to-Diameter Ratio IPT Systems

This article proposes a kind of cubic-magnetic coupler (CMC) for inductive power transfer (IPT) system, which has huge application potential in the charging field of moving targets. The CMC can still maintain sufficient coupling coefficient when used for long-distance wireless power transfer, it also has great capability of misalignment tolerance. Distance-to-diameter ratio (DDR) is defined to eliminate the impact of coil size and make the comparison between different couplers fairer and easier. This article optimizes the parameters and shape of the CMC. Then, the proposed coupler is compared with several existing couplers employed in long-distance IPT systems. Double-sided <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> compensation topology is chosen to limit the current flowing through the coupling coils. A CMC with an outer size of 180×180×180 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> was made, based on which an IPT prototype was built. The superiorities of the proposed coupler were verified by a series of experiments. When the DDR equals 3, the coupling coefficient of the CMC is 0.00985, and the maximum dc–dc and ac–ac efficiencies are 64.9% and 72.8%, respectively.

Design and analysis of decoupled tetra‐polar ring‐coils for wireless power transfer in rotary mechanism applications

Decoupling of same-sided coils is a critical issue for multi-input and/or multi-output inductive power transfer (IPT) systems. The mutual inductance between the same-sided coils may lead to the system detuning and the decrease of power transfer capacity and efficiency. In this study, a tetra polar ring coils (TPR-coils) and its decoupling method are proposed for IPT systems applied to rotary mechanism. Firstly, an analytical expression, which illustrates the relationship between the mutual inductance and geometric parameters of coaxial cylindrical helical coils, is given. Then the equivalent circuit model of TPR-coils is established, and the mutual inductance constraints for the decoupling of TPR-coils are proposed. Combined with the expression of mutual inductance, a geometric parameter solution of decoupled TPR-coils is derived. The correctness of theoretical analysis is verified by finite element method simulations and experiments. The experimental results show that the mutual inductance between the same-sided coils can be reduced to 0.6 μH, and the effectiveness of TPR-coils is also verified on an IPT prototype with 231 W power and over 86% efficiency.

Secondary-Side Voltage Control via Primary-Side Controller for Wireless EV Chargers

In inductive power transfer (IPT) system, the magnetic coupling has significant effects on power and system efficiency. The voltage and current on the secondary side are coupling dependent. Load measurements are not possible through sensors on the primary side. This article proposes the secondary-side voltage controller based on the primary-side control by means of bifurcation approach. The main advantage of operation under bifurcation is that the coupling and load on the secondary have no effect on the voltage gain. This enables the secondary voltage control through the primary voltage. With the proposed sensing coil on the primary side, the bifurcation detection is possible. The proposed control can utilize the frequency split phenomenon and track the bifurcation frequency to ensure maximum efficiency in various coupling conditions. In addition, the design guidelines of the parallel-parallel compensation configuration are introduced for a desired load profile and transfer distance. The constant voltage gain with respect to conditions of magnetic coupling variation is verified by using finite element analysis and experimental study. A 1-kW IPT prototype is constructed to validate the proposed bifurcation detection and voltage control. Experimental results show that the proposed IPT can achieve up to 90% of maximum efficiency while maintaining constant secondary voltage.

An LCC-SP Compensated Inductive Power Transfer System and Design Considerations for Enhancing Misalignment Tolerance

This paper proposes a novel LCC-SP compensation topology for inductive power transfer (IPT) system and its tuning methods to enhance misalignment tolerance. The impedance condition and the constant current output characteristic of the newly proposed topology are analyzed, followed by a detailed derivation of compensation parameters based on the discussion about resonant tank. The realization of zero voltage switching (ZVS) and reactive power demand are discussed by theoretical deduction and numerical simulation. Then, the parameters detuning method to enhance misalignment tolerance is presented and it is found that a stable output current is maintained over a wide misalignment. Compared to traditional compensation topologies, the newly proposed compensation topology provides the advantages of easy achievement of ZVS, high design freedom and high misalignment tolerance. Finally, the IPT prototype with the LCC-SP compensation network is built and tested. The experimental results match well with the calculations, validating the correctness of theoretical analysis.

Design of LCC-S Compensation Topology and Optimization of Misalignment Tolerance for Inductive Power Transfer

This paper proposes a novel parameter tuning method topology for inductive power transfer (IPT) system with excellent load-independent current output. Based on LCC-S compensation topology, detailed derivations of parameters to realize load-independent current output is systematically analyzed. The realizations of zero voltage switching (ZVS) and reactive power demand are discussed by theoretical deduction and numerical simulation. Moreover, from the perspective of maintaining stable transmission power, the parameters detuning method to enhance misalignment tolerance is presented. Theoretical analysis shows that the appropriate detuned resonant tank is advantageous in performance, especially the smoothing of current output to variation of coupling coefficient. The novel LCC-S compensation topology holds high design freedom and high efficiency, while the robust power characteristic against wide misalignment region minimizes the need of complex control. Finally, the IPT prototype is built and test to validate the feasibility of the proposed topology. The efficiency of system is always higher than 86% in tuned parameters and 73% in detuned condition. The fluctuation of current is less than 7.5% when the coupling coefficient varies almost 170% (from 0.293 to 0.5).

A Family of Hybrid IPT Topologies With Near Load-Independent Output and High Tolerance to Pad Misalignment

Inductive power transfer (IPT) systems have many unique benefits compared to conventional plugged-in systems. The coupling pads in IPT systems are inevitably misaligned in many practical applications, thus leading to variations of the transferred power and efficiency that necessitate the use of complicated control for output regulation. A common solution is to use two IPT converters with opposite trends of output to pad misalignment, so that the total output voltage or current could be kept near constant for large coupling variations. However, methods for deriving effective configurations for such hybrid IPT converters and their achievable tolerance to the misalignment are still missing. This article constructs a family of hybrid IPT topologies, including input-parallel-output-parallel, input-parallel-output-series, input-series-output-parallel (ISOP), and input-series-output-series for delivering a constant current (CC) or a constant voltage (CV). Design principles and characteristics for all the hybrid systems with near load-independent output and high tolerance to pad misalignment are derived and discussed in detail. Based on this family of configurations, this article also combines some existing IPT topologies and derives multiple hybrid converters for CC or CV output by using a simple duty cycle control. Finally, a 3.5-kW hybrid IPT prototype converter based on the ISOP structure is built to verify the theoretical analysis.

An Optimal Variable Frequency Phase Shift Control Strategy for ZVS Operation Within Wide Power Range in IPT Systems

In inductive power transfer (IPT) systems, zero-voltage-switching (ZVS) operation within wide power range is an urgent requirement to improve system efficiency and reduce electromagnetic interference. The combination of phase shift (PS) control and variable frequency control is usually adopted to realize ZVS operation. However, in inductor-capacitor-capacitor-series (LCC-S) systems, the abovementioned hybrid strategy cannot be used directly due to nonnegligible harmonics, which result in detection difficulties or imprecise calculation of turn-off current. To solve this problem, this article proposes an optimal variable frequency phase shift (VFPS) control strategy for LCC-S systems to realize ZVS operation within wide power range. The universal harmonic-considered time-domain model of LCC-S system is deduced, and thus, the switching-moment current of power switches can be calculated accurately. Based on this value, an optimal working trajectory for ZVS operation with minimum frequency variation is presented. Finally, a 2.2-kW IPT prototype is built up to verify the universality of the deduced model and the validity of the proposed optimal VFPS control. Compared with PS control and the VFPS control based on fundamental-harmonic-approximation method, the systems realizes ZVS operation under wide power range with efficiency increase of 2.6%-6.9% and 0.8%-8.8%, respectively, and a peak efficiency of 96.4% is achieved.

Frequency and Phase-Shift Control of Inductive Power Transfer for EV Charger with LCCL-S Resonant Network Considering Misalignment

In inductive power transfer (IPT) systems for electric vehicle applications, the coupling coefficient k and self-inductances of the pads can vary depending on the misalignment and vertical distance due to the presence of loosely coupled pads. Furthermore, the operating frequencies of IPT systems are restricted by a Society of Automotive Engineers standard. These frequencies lead to increases in volt-ampere rating and switching losses. Therefore, this paper proposes a control method for operation in a zero voltage switching region close to the zero phase angle frequency for a low volt-ampere rating considering k and the self-inductance variation in a limited operating frequency range. A mathematical analysis is performed, and the critical coupling coefficients of the proposed control are derived. Simulation and experimental results using a 3.3 kW IPT prototype are presented so as to verify the numerical analysis.

Modular Parallel Multi-Inverter System for High-Power Inductive Power Transfer

In order to provide high and extendable power levels for inductive power transfer (IPT) system, a parallel multi-inverter system based on modular inverter is presented. Various power requirements can be implemented by an adjustment of the number of paralleled inverters, which provides a high modularity. A master−slave scheme is employed for the switching-driver signals of parallel inverters, where one acts as a leader while others act as followers. Despite the master−slave scheme, the proposed circuit topology has natural robustness because of the equality in terms of the hardware configuration of each modular inverter. For proper parameters, the output phase (current lagging corresponding voltage) of an inverter is lower than the average of output phase of all inverters, when its output voltage lags behind others, and vice versa . Based on this approach, PI controllers are designed to implement phase synchronization for output voltages of all inverters. An IPT prototype supplied by the proposed parallel multi-inverter with three inverters was designed, built, and tested. Experiments show that the proposed parallel multi-inverter system has not only good circulating current suppression capacity but also excellent performance of phase synchronization. The maximum dc−dc efficiency was 94% at a 35.1 kW receiving power. This paper is accompanied by a Matlab/Simulink file demonstrating phase synchronization control.