Contactless Energy Transfer System Research Articles

Impedance Circle Modeling and Dynamic Characteristics Analysis of Contactless Energy Transfer System Under Load Variations in Rotary Ultrasonic Machining

In rotary ultrasonic machining, contactless energy transfer (CET) is developed to transmit energy to the transducer at the series resonant frequency or resonant frequency of the transducer. Specifically, during energy transmission, variations in working conditions such as variable axial forces will change the load of the transducer and introduce undesired dynamic effects into the contactless energy transfer system (CETS). In order to explore the connections between these variations and the working performance more directly and theoretically, a new theoretical model—CETS impedance circle is proposed in this paper to reflect the CETS dynamic characteristics, including the CETS frequency characteristics and the relationships between CETS transfer performances at different frequencies under load variations. With the developed theoretical model, the effect of load variations on the trends of CETS impedance circle is investigated. Moreover, based on the impedance circle and its trends, the CETS frequency characteristics, the effect of primary series compensation, and a comparison of the transfer performances at the two working frequencies are theoretically studied. Finally, the CETS impedance circle theories are experimentally verified, and the experimental results are consistent with the analysis of the theoretical model.

A new efficiency figure of merit for induction heating appliances operating under highly variable operating conditions

Induction heating is an efficient and high-performance heating method which already has a significant market penetration and economic impact due to its benefits inherent to contactless energy transfer systems such as quickness, cleanness, and safety. Efficiency is a key design parameter since it determines not only the appliance performance but also its environmental impact, with significant socio-political implications. However, it is not easy to determine and compare the actual power converter efficiency operating under highly variable conditions typical of IH. This paper proposes an averaged efficiency parameter elaborated based on technical and typical IH usage conditions that offers a useful value to compare power converters operating under realistic operation conditions. The proposed parameter has been evaluated in some of the most significant power converter topologies used in reported state-of-the-art induction heating systems.

Dynamic Compensation Optimization and Frequency Characteristic Analysis for Contactless Energy Transfer Under Load Variations in Rotary Ultrasonic Machining

In rotary ultrasonic machining, contactless energy transfer (CET) converts power from an ultrasonic power supply to the ultrasonic transducers. Two-side compensation circuits improve the efficiency of this process, but the addition of secondary compensation causes problems such as dynamic imbalance. Load changes affect the performance of CET system (CETS) with compensation, and dynamic compensation is needed for good CETS performance, such as high transfer efficiency and output power. This article investigates the frequency characteristics of CETS without compensation under different loads. The effects of two-side compensation on CETS under load variations is studied for the dynamic compensation characteristic. The comparison of mathematical model and performance of CETS with dynamic compensation are investigated to propose the optimized dynamic compensation. The model of CETS with optimized dynamic compensation under load variations is developed. The CETS frequency characteristics with optimized dynamic compensation are studied. The experimental results basically agree with the calculated results. The CETS with optimized dynamic compensation at the series resonant frequency can produce high transfer efficiency, high output power, low input impedance range under load variations in the cutting process of RUM, and solves the problems caused by the secondary side compensation.

Performances of resonant frequency tracking methods and compensation strategies for rotary ultrasonic machining device with contactless energy transfer

As the core component of rotary ultrasonic machining (RUM) device, the ultrasonic transducer is subjected to mechanical loads during processing, leading to variations in its equivalent electrical parameters. For RUM device with contactless energy transfer (CET) system, this phenomenon can cause the mismatch between the compensation parameters and the transient electrical parameters of the transducer, which will further degrade the resonant frequency tracking (RFT) accuracy and the output performance. In this study, bilateral compensation parameters and coil turns of the CET were first calculated for no-load RUM device to gain optimal transfer efficiency and achieve tuning matching and impedance matching. After that, the drift of the transducer electrical parameters under load conditions was quantified by loading experiments. Based on electrical model, the influences of mechanical loads on the impedance characteristics of RUM equipment were revealed. For the four compensation topologies, different RFT methods were employed according to the above analysis. Finally, theoretical analyses and verification experiments were conducted to investigate the performances of various driving configurations for the transducer considering the load effects. The results demonstrate that inappropriate selection of RFT method and compensation strategy can introduce considerable error between the tracking frequency and the resonant frequency of the transducer, causing poor output performance of RUM device. The Series-Series (SS) topology combined with the phase-locked method can gain stable transfer efficiency and high power factor with excellent RFT accuracy. Furthermore, this configuration has load adaptive capability, meaning that the power obtained by the transducer increases as the load increases, which is beneficial to suppress the output amplitude decay during machining. The conclusions presented in this research can provide references for the design of RUM device.

Design and Evaluation of a Laminated Three-Phase Rotary Transformer for DFIG Applications

In doubly fed induction generators (DFIGs), the rotor is excited through slip-ring and brush assemblies. These slip-ring and brush assemblies often require frequent routine maintenance, which affects the reliability of the DFIG. Alternatively, a contact-less energy transfer system, such as a rotary transformer, can be utilized in place of the slip rings. In DFIGs, the rotor frequency is very low, under 5 Hz, and this can lead to a huge rotary transformer since the transformer size is inversely proportional to its operating frequency. However, in a rotor-tied DFIG, whereby the rotor is connected directly to the grid whilst the stator is connected to a back-to-back converter, the rotor frequency becomes the grid frequency and can lead to a reasonably sized rotary transformer. In this paper, the design methodology of a three-phase rotary transformer that can be used in rotor-tied DFIG applications is proposed. The rotary transformer is coupled to the power windings of the rotor-tied DFIG and can improve its reactive power capabilities. The proposed methodology is validated with finite element analysis in 3D and can be used for an efficient design process with the proposed error correction. The proposed methodology is then applied in the design of a 6 kVA rotary transformer. Remarkable practical results are presented to demonstrate the effectiveness of the methodology. The rotary transformer is subsequently coupled to a rotor-tied DFIG and an acceptable performance is demonstrated for the entire system.

State-Space Model of an Electro-Mechanical-Acoustic Contactless Energy Transfer System Based on Multiphysics Networks.

Contactless energy transfer systems are mainly divided into acoustic, inductive, capacitive, and optical, in which main applications are related to biomedical, wireless chargers, and sensors in metal enclosures. When solids are used as transfer media, ultrasound transducers based on piezoelectricity can be used for through-wall power transfer, which can be named as an electro-mechanical-acoustic contactless energy transfer system. This work presents a state-space model derived from a multiphysics network that includes all the multiphysical power conversion without separating the stages and including the real physical elements, like as the piezoelectric parameters and the geometry of the transfer media. The model is compared to the experimental response of the system and evaluated for different scenarios regarding transducers types and solid transfer media. An error analysis has shown that the maximum quadratic error between theoretical and experimental responses is 3.7%.

Design of a contactless powered and piezoelectric-actuated tool for non-resonant low-frequency vibration-assisted machining of brittle-hard materials

Ultrasonic-assisted grinding (UAG) is the state-of-the-art process for machining of brittle-hard materials. In comparison to conventional processes, the main advantages lie in the reduction of tool wear and process forces. Such a vibration system is based on a resonant actuator and a power supply unit generating the alternating current. Both units are interconnected by a contactless energy transfer (CET) system. This system configuration shows one optimal working point at the resonant frequency with maximum amplitude, which is significantly depending on the tool shape. In this work, a piezo-activated tool system is designed to realize non-resonant low-frequency vibrations. Major emphasis is put on the thermal behavior of the piezo drive, particularly on the in-process heating depending on the working frequency. In addition, focus lays on the theoretical and numerical design of the radial operating transducer CET system for a previously set actuator design. As a result, this system configuration offers a fully variable adjustment of the amplitude from under 1 to over 50 μm at frequency range. Outside this range, higher amplitudes can be achieved for short periods to the detriment of the fatigue strength according to FKM.

Design of Sliding Mode Controlled Bi-directional DC-DC Current Source Resonant Converter for an Inductive Contactless Battery Charging Application

The practical use of current source DC-DC resonant converters has an outstanding performance in terms of its robust and fast performance. In this paper, the non-linear behavior during the battery charging application is solved using an adaptive Sliding Mode Control (SMC) technique. The SMC has a robust feature in fast transient responses over large load disturbances. The proposed converter uses Contactless Energy Transfer (CET) system that provides a suitable reactive power compensation for the design. The winding parameters of the inductance are mathematically modeled with low coupling factor to remove the voltage and current harmonics. The designed converter is subjected to input side perturbation for a non-linear disturbance and the output obtained using the Sliding Mode Controller is analysed. The non-linearity at the output voltage is reduced when using the SMC. The controller design show the setting time of the DC voltage under such disturbance is reduced to 97%. The proposed system is mathematically modeled and simulated using MATLAB/Simulink. The prototype model is designed and the results are analyzed.

Performances of a Contactless Energy Transfer System for Rotary Ultrasonic Machining Applications

In rotary ultrasonic machining (RUM), the contactless energy transfer (CET) system based on the rotary transformer can replace the well-established slip ring technology to supply power for the revolving ultrasonic vibrator. However, the transfer efficiency and power output capability of the CET system is usually a pair of contradictions. The high voltage of the compensation element is prone to occur, especially in high power applications, which is dangerous. In this paper, for four basic compensation topologies, the mathematical models of the transfer efficiency, the load impedance and the compensation elements' voltages are presented. The compensation elements are optimized for improving the transfer efficiency. The effects of coil turns on the transfer efficiency, the load impedance and the compensation elements' voltages are researched. The coil turns are optimized to control the load impedance of the power supply and the voltages of the compensation elements. The experimental results basically agree with the theoretical results. The optimized CET system not only has high transfer efficiency, but also has high power output capability. At the same time, the high voltages of compensation elements are avoided effectively and the safety of the system is guaranteed.

Contribution to the System Design of Contactless Energy Transfer Systems

In this contribution, a design procedure that is applicable to many kinds of wireless or contactless energy transfer systems is proposed. The design procedure is limited to near field wireless energy transfer systems in resonant operation. For this purpose, the input impedance and voltage transfer function of different natural frequencies are calculated analytically, and moreover, the behavior of the system is described. Following three issues lead to a readily applicable design procedure. First, the knowledge of the transfer functions. Secondly, the knowledge of basic magnetic properties and lastly, the known influence of harmonics according to rectifier and inverter. This design procedure is demonstrated with two hardware setups.

Self-Compensation Theory and Design of Contactless Energy Transfer and Vibration System for Rotary Ultrasonic Machining

In contactless energy transfer and vibration system (CETVS) for rotary ultrasonic machining, the energy is delivered to an ultrasonic transducer equipped with a rotary spindle shank through a loosely coupled transformer (LCT). The purpose of this paper is to present a simplified construct, referred to as self-compensation system, to overcome the drawbacks of external compensation elements occupying the limited shank space during the LCT's leakage inductance compensating and the transducer's capacitance compensating. The advantage of this approach is that the secondary leakage inductive reactance of the LCT and the capacitive reactance of the transducer are mutually compensated without an intermediate element, which conserves the spindle shank space and reduces the operating load of an LCT. In this paper, we first derive the mutual compensation equation between a transducer and an LCT. Then, for a given transducer, the structural parameters of an LCT are designed with theoretical calculations and simulation analysis. Experiments are conducted with the self-compensation system excited by a 50 V ultrasonic signal. The results show that the energy transfer efficiency of LCT reached 92.0%, the amplitude of the transducer reached $10.7\,\mu {\rm{m}}$ , when the CETVS is self-compensated. These results indicate that this self-compensation theory and design are feasible.

Operation of an Electrical Excited Synchronous Machine by Contactless Energy Transfer to the Rotor

This paper deals with the design, the setup, and the operation of a rotating contactless energy transfer (CET) system. The system is used to replace the slip rings of an electrical excited synchronous machine and to transfer energy onto the rotor of the machine without mechanical contact. A compensation topology with an autoresonant circuit to generate the high frequency voltage is presented. Furthermore, the required parameters of the CET system are calculated. Based on these calculations, the system consisting of the power electronics, the compensation network, the magnetic path, the control system, and the electrical excited synchronous machine with controller, is set up. Finally, the calculated parameters are verified by measurements.

Design of Contactlessly Powered and Piezoelectrically Actuated Tools for Non-Resonant Vibration Assisted Milling

This contribution presents a novel design approach for vibration assisted machining (VAM). A lot of research has already been done regarding the influence of superimposed vibrations during a milling process, but there is almost no information about how to design a VAM tool where the tool is actually rotating. The proposed system consists of a piezoelectric actuator for vibration excitation, an inductive contactless energy transfer system and an electronic circuit for powering the actuated tool. The main benefit of transferring the required power without mechanical contact is that the maximum spindle speed is no longer restricted by friction of slip rings. A detailed model is shown that enables for preliminary estimation of the system’s response to different excitation signals. Experimental data are provided to validate the model. Finally, some parts are shown that have been manufactured using the contactlessly actuated milling tool.

Resonant frequency stabilization technique in series-series contactless energy transfer systems

AbstractA technique for stabilization of resonant frequency is proposed in this paper. An additional power circuit, a compensator that allows keeping constant resonance frequency was introduced by the authors. In the presented solution the resonant circuit frequency stabilization is achieved by forcing a zero phase shift between the current and the voltage of the main switching module.

Analysis, design and implementation of a residential inductive contactless energy transfer system with multiple mobile clamps

This study presents the analysis, design and implementation of a simple and cost-effective residential inductive contactless energy transfer system with multiple mobile clamps. The topology is based on the cascaded connection of a buck converter and a high-frequency resonant inverter loaded by several output passive rectifiers. The proposed system includes a sliding transformer to supply the mobile loads, leading to a safe and flexible location of loads. The theoretical analysis and design of the proposed system is based on a mathematical model derived using the first harmonic approximation. Selected experimental results are included to verify the system features. In comparison with conventional topology, the proposed system significantly improves efficiency, complexity and cost.

Power Transfer Performance and Cutting Force Effects of Contactless Energy Transfer System for Rotary Ultrasonic Grinding

In rotary ultrasonic grinding (RUG), a rotating transformer can be used to replace the established slip ring technology and provide a contactless power supply to the revolving transducer. Such contactless energy transfer (CET) is safe, and high rotation speeds are possible. Compared with a closely coupled transformer, the transfer efficiency of the rotating transformer is lower. Compensation of the windings is necessary to improve efficiency. In addition, the cutting force in RUG is not constant; this will influence the power transfer performance, which in turn affects the vibration amplitude of the tool. In this paper, by considering the distinct capacitive and mechanical behavior of the transducer and the equivalent series resistances (ESRs) of the compensation elements, mathematical models are developed to identify the transfer efficiency and the output power of the rotating transformer. A general mathematical compensation model is developed for maximum transfer efficiency. The effects of the cutting force on the transfer efficiency, the output power, and the power factor are also researched. The experimental results basically agree with the calculated results. A CET system that can produce high efficiency, a high power factor and adaptive output power that adapts to the variations of cutting force in the RUG is therefore possible.

Analytical Model of the Half-Bridge Series Resonant Inverter for Improved Power Conversion Efficiency and Performance

Resonant power conversion is a key enabling technology of dc–dc conversion, inverters and contactless energy transfer systems. This paper presents an analytical model of the series resonant half-bridge topology aimed at improving the design, control, and efficiency of resonant power converters. The main contribution is a closed-form expression of the main converter waveforms as well as output power and efficiency. This model enables a fast design-space exploration, as well as the implementation of advanced control techniques using adaptive control or real-time emulation, significantly improving the converter operation. The analytical expressions presented have been applied and verified through a half-bridge series resonant inverter applied to induction heating applications, proving the accuracy and effectiveness of the proposed model.

Realisation of stable output for contact-less energy transfer system with multiple loads

A contact-less energy transfer system (CETS) delivers electric energy to loads without direct physical connection, showing many advantages over conventional method, while its output, either voltage or current, varies simultaneously with the load. In this paper, a novel method is proposed to realise stable output voltage for systems with multiple receiving coils. As the detachable transformer has weak magnetic coupling, resonant compensation is adopted to improve the power factor and reduce the voltage and current stresses on devices. Mutual inductance model is introduced and later simplified by proposing some key parameters, that is, coupling coefficient k, self-inductance ratio between primary and secondary coil n, secondary circuit’s quality factor Qs. Primary-parallel-secondary-series compensated CETS is suitable for multi-load application as it shows stable output voltage characteristics under certain conditions, which are studied. A prototype of contact-less cell-phone charging platform with up to four loads is implemented to verify the design theory. Experimental results indicate that the charging voltage can keep stable when the load number varies, and the transfer efficiency of the separable transformer is high even though the coupling coefficient is fairly low.

Bidirectional Current-Fed Resonant Inverter for Contactless Energy Transfer Systems

This paper presents a bidirectional current-fed parallel resonant push-pull inverter (CFPRPI) for contactless energy conversions. In conventional CFPRPIs, each switch is in series with a blocking diode. Direct zero voltage switching (ZVS) is proposed to remove the series blocking diodes for higher efficiency and boosting ratio. In addition, the modified inverter has bidirectional power flow capability when these blocking diodes are omitted. Resonant tuning of the system is investigated by using a phase-locked loop and a new self-oscillating switching technique (SST). By using the new SST, the inverter has direct ZVS in a wide range of operating frequencies, which is necessary for inductively coupled power transfer systems. Finally, a laboratory prototype with an input voltage of 12 V and a maximum output power of 60 W has been implemented.

Inductance Calculation Nearby Conducting Material

This paper presents the modeling of inductances nearby conducting material. A 3-D magnetic model is derived based on Fourier analysis in which the diffusion equation is incorporated. The model is applied to calculate the mutual inductance in a contactless energy transfer system between four primary coils and a single secondary coil for different positions of the secondary coil. The calculated values are compared with finite element simulations and measurements. A difference of maximum 7% is obtained among the different methods.