Automated Impedance Matching System for Robust Wireless Power Transfer via Magnetic Resonance Coupling
TL;DR: An automated impedance matching (IM) system is proposed to increase the efficiency by matching the resonance frequency of the resonator pair to that of the power source, improving the power transfer efficiency.
Abstract: Recently, a highly efficient midrange wireless transfer technology using electromagnetic resonance coupling has been proposed and has received much attention due to its practical range and efficiency. The resonance frequency of the resonators changes as the gap between the resonators changes. However, when this technology is applied in the megahertz range, the usable frequency is bounded by the industrial, scientific, and medical (ISM) band. Therefore, to achieve maximum power transmission efficiency, the resonance frequency has to be fixed within the ISM band. In this paper, an automated impedance matching (IM) system is proposed to increase the efficiency by matching the resonance frequency of the resonator pair to that of the power source. The simulations and experiments verify that the IM circuits can change the resonance frequency to 13.56 MHz (in the ISM band) for different air gaps, improving the power transfer efficiency. Experiments also verified that automated IM can be easily achieved just by observing and minimizing the reflected wave at the transmitting side of the system.
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TL;DR: With the proposed topology and its tuning method, the resonant frequency is irrelevant with the coupling coefficient between the two coils and is also independent of the load condition, which means that the system can work at a constant switching frequency.
Abstract: This paper proposes a double-sided LCC compensation network and its tuning method for wireless power transfer (WPT). With the proposed topology and its tuning method, the resonant frequency is irrelevant with the coupling coefficient between the two coils and is also independent of the load condition, which means that the system can work at a constant switching frequency. Analysis in frequency domain is given to show the characteristics of the proposed method. We also propose a method to tune the network to realize zero voltage switching (ZVS) for the Primary-side switches. Simulation and experimental results verified analysis and validity of the proposed compensation network and the tuning method. A wireless charging system with output power of up to 7.7 kW for electric vehicles was built, and 96% efficiency from dc power source to battery load is achieved.
768 citations
Cites methods from "Automated Impedance Matching System..."
...mated impedance matching system was designed in [19], and in [21], two ways for tuning the primary tank are introduced: the primary capacitance and inductance....
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...There are two main methods, namely, frequency control [17], [18] and impedance matching [19], [20]....
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TL;DR: A wireless, battery-free platform of electronic systems and haptic interfaces capable of softly laminating onto the curved surfaces of the skin to communicate information via spatio-temporally programmable patterns of localized mechanical vibrations is presented.
Abstract: Traditional technologies for virtual reality (VR) and augmented reality (AR) create human experiences through visual and auditory stimuli that replicate sensations associated with the physical world. The most widespread VR and AR systems use head-mounted displays, accelerometers and loudspeakers as the basis for three-dimensional, computer-generated environments that can exist in isolation or as overlays on actual scenery. In comparison to the eyes and the ears, the skin is a relatively underexplored sensory interface for VR and AR technology that could, nevertheless, greatly enhance experiences at a qualitative level, with direct relevance in areas such as communications, entertainment and medicine1,2. Here we present a wireless, battery-free platform of electronic systems and haptic (that is, touch-based) interfaces capable of softly laminating onto the curved surfaces of the skin to communicate information via spatio-temporally programmable patterns of localized mechanical vibrations. We describe the materials, device structures, power delivery strategies and communication schemes that serve as the foundations for such platforms. The resulting technology creates many opportunities for use where the skin provides an electronically programmable communication and sensory input channel to the body, as demonstrated through applications in social media and personal engagement, prosthetic control and feedback, and gaming and entertainment. Interfaces for epidermal virtual reality technology are demonstrated that can communicate by programmable patterns of localized mechanical vibrations.
500 citations
TL;DR: In this paper, a maximum efficiency point tracking control scheme is proposed to maximize the system efficiency while regulating the output voltage, which is unique and prominent in that it fixes the operating frequency at the receiving-side resonant frequency and converts both the input voltage and the load resistance at the same time.
Abstract: With a good balance between power transfer distance and efficiency, wireless power transfer (WPT) using magnetic resonant coupling is preferred in many applications. Generally, WPT systems are desired to provide constant output voltage with the highest possible efficiency as power supplies. However, the highest efficiency is not achieved by the reported closed-loop WPT systems that maintain constant output voltage against coupling and load variations. In this paper, an efficiency evaluation method is put forward to evaluate the closed-loop control schemes. Furthermore, a maximum efficiency point tracking control scheme is proposed to maximize the system efficiency while regulating the output voltage. This control scheme is unique and prominent in that it fixes the operating frequency at the receiving-side resonant frequency and converts both the input voltage and the load resistance at the same time. Thus, the maximum efficiency point on the constant output voltage trajectory can be tracked dynamically. Therefore the system's output voltage can be maintained constant and its efficiency is always the highest. The experimental results show that the maximum efficiency point is tracked and a very high overall efficiency is achieved over wide ranges of coupling coefficient and load resistance.
463 citations
TL;DR: In this paper, a perturbation-and-observation-based tracking system is developed through additional hardware such as a cascaded boost-buck dc-dc converter, an efficiency sensing system, and a controller.
Abstract: All the wireless power transfer (WPT) systems share a similar configuration including a power source, a coupling system, a rectifying circuit, a power regulating, and charging management circuit and a load. For such a system, both a circuit- and a system-level analyses are important to derive requirements for a high overall system efficiency. Besides, unavoidable uncertainties in a real WPT system require a feedback mechanism to improve the robustness of the performance. Based on the above basic considerations, this paper first provides a detailed analysis on the efficiency of a WPT system at both circuit and system levels. Under a specific mutual inductance between the emitting and receiving coils, an optimal load resistance is shown to exist for a maximum overall system efficiency. Then, a perturbation-and-observation-based tracking system is developed through additional hardware such as a cascaded boost-buck dc-dc converter, an efficiency sensing system, and a controller. Finally, a 13.56-MHz WPT system is demonstrated experimentally to validate the efficiency analysis and the tracking of the optimal load resistances. At a power level of 40 W, the overall efficiency from the power source to the final load is maintained about 70% under various load resistances and relative positions of coils.
264 citations
Cites background from "Automated Impedance Matching System..."
...A tunable impedance matching before the coupling coils was studied in order to reduce the reflected power due to a varying coil distance [26]....
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...network when the load is changing over time [26]....
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TL;DR: In this paper, an active single-phase rectifier (ASPR) with an auxiliary measurement coil (AMC) and its corresponding control method are proposed to track the maximum system efficiency under varied loads and detuning conditions in real time.
Abstract: The efficiency of wireless power transfer (WPT) systems is highly dependent on the load, which may change in a wide range in field applications. Besides, the detuning of WPT systems caused by the component tolerance and aging of inductors and capacitors can also decrease the system efficiency. In order to track the maximum system efficiency under varied loads and detuning conditions in real time, an active single-phase rectifier (ASPR) with an auxiliary measurement coil (AMC) and its corresponding control method are proposed in this paper. Both the equivalent load impedance and the output voltage can be regulated by the ASPR and the inverter, separately. First, the fundamental harmonic analysis model is established to analyze the influence of the load and the detuning on the system efficiency. Second, the soft-switching conditions and the equivalent input impedance of ASPR with different phase shifts and pulse widths are investigated in detail. Then, the analysis of the AMC and the maximum efficiency control strategy are provided in detail. Finally, an 800-W prototype is set up to validate the performance of the proposed method. The experimental results show that with 10% tolerance of the resonant capacitor in the receiver side, the system efficiency with the proposed approach reaches 91.7% at rated 800-W load and 91.1% at 300-W light load, which has an improvement by 2% and 10% separately compared with the traditional diode rectifier.
243 citations
Cites background from "Automated Impedance Matching System..."
...system’s resonance, the capacitor arrays are utilized in [24] and [25] by switching the connection of the capacitors so that the system can be maintained resonant....
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References
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TL;DR: A quantitative model is presented describing the power transfer of self-resonant coils in a strongly coupled regime, which matches the experimental results to within 5%.
Abstract: Using self-resonant coils in a strongly coupled regime, we experimentally demonstrated efficient nonradiative power transfer over distances up to 8 times the radius of the coils We were able to transfer 60 watts with ∼40% efficiency over distances in excess of 2 meters We present a quantitative model describing the power transfer, which matches the experimental results to within 5% We discuss the practical applicability of this system and suggest directions for further study
5,284 citations
"Automated Impedance Matching System..." refers background or methods in this paper
...It has efficiencies of approximately 90% within 1 m and 45% at 2 m [10], [11]....
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...There are many methods to conduct this such as impedance matching (IM) [19], [20], frequency matching [21], coupling manipulation [11], [22], and changing the resonator parameters [23]....
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...The magnetic resonant coupling phenomenon has been explained in detail using the mode coupling method [10], [11]....
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TL;DR: A circuit model is presented along with a derivation of key system concepts, such as frequency splitting, the maximum operating distance (critical coupling), and the behavior of the system as it becomes undercoupled, including the introduction of key figures of merit.
Abstract: Wireless power technology offers the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as data are transmitted through the air. Initial work on the use of magnetically coupled resonators for this purpose has shown promising results. We present new analysis that yields critical insight into the design of practical systems, including the introduction of key figures of merit that can be used to compare systems with vastly different geometries and operating conditions. A circuit model is presented along with a derivation of key system concepts, such as frequency splitting, the maximum operating distance (critical coupling), and the behavior of the system as it becomes undercoupled. This theoretical model is validated against measured data and shows an excellent average coefficient of determination of 0.9875. An adaptive frequency tuning technique is demonstrated, which compensates for efficiency variations encountered when the transmitter-to-receiver distance and/or orientation are varied. The method demonstrated in this paper allows a fixed-load receiver to be moved to nearly any position and/or orientation within the range of the transmitter and still achieve a near-constant efficiency of over 70% for a range of 0-70 cm.
1,630 citations
"Automated Impedance Matching System..." refers methods in this paper
...There are many methods to conduct this such as impedance matching (IM) [19], [20], frequency matching [21], coupling manipulation [11], [22], and changing the resonator parameters [23]....
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TL;DR: In this article, the physical phenomenon of long-lifetime resonant electromagnetic states with localized slowly-evanescent field patterns was investigated to transfer energy efficiently over non-negligible distances even in the presence of extraneous environmental objects.
1,628 citations
"Automated Impedance Matching System..." refers background or methods in this paper
...It has efficiencies of approximately 90% within 1 m and 45% at 2 m [10], [11]....
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...The magnetic resonant coupling phenomenon has been explained in detail using the mode coupling method [10], [11]....
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...Recently, a highly efficient midrange WPT technology using magnetic resonance coupling (MRC) was rediscovered and proposed [10]–[12] and has received much attention due to its high efficiency and practical midrange [13]–[15]....
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TL;DR: This paper overviews theoretical and practical design issues related to inductive power transfer systems and verifies the developed theory using a practical electric vehicle battery charger.
Abstract: This paper overviews theoretical and practical design issues related to inductive power transfer systems and verifies the developed theory using a practical electric vehicle battery charger. The design focuses on the necessary approaches to ensure power transfer over the complete operating range of the system. As such, a new approach to the design of the primary resonant circuit is proposed, whereby deviations from design expectations due to phase or frequency shift are minimized. Of particular interest are systems that are neither loosely nor tightly coupled. The developed solution depends on the selected primary and secondary resonant topologies, the magnetic coupling coefficient, and the secondary quality factor.
1,389 citations
"Automated Impedance Matching System..." refers background in this paper
...Recent researches include WPT for small electronic devices such as mobile appliances [3], [4] and medical implants [5]–[7] and bigger high-power devices such as EVs [8], [9]....
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TL;DR: In this paper, the physical meaning and prop-erties of the power waves defined by [Equation], [ Equation] where V/sub i/ and Z/sub I/ are the voltage at and the current flowing into the ith port of a junction and the impedance of the circuit connected to the it h port.
Abstract: This paper discusses the physical meaning and prop-erties of the waves defined by [Equation], [Equation] where V/sub i/, and Z/sub i/, are the voltage at and the current flowing into the ith port of a junction and Z/sub i/, is the impedance of the circuit connected to the ith port. The square of the magnitude of these waves is directly related to the exchangeable power of a source and the reflected power. For this reason, in this paper, they are called the power waves. For certain applications where the power relations are of main concern, the power waves are more suitable quantities than the conventional traveling waves. The lossless and reciprocal conditions as well as the frequency characteristics of the scattering matrix are presented. Then, the formula is given for a new scattering matrix when the Z/sub i/'s are changed. As an application, the condition under which an amplifier can be matched simultaneously at both input and output ports as well as the condition for the network to be unconditionally stable are given in terms of the scattering matrix components. Also a brief comparison is made between the traveling waves and the power waves.
906 citations