Dc-dc Efficiency Research Articles

A Design Method of Compensation Circuit for High-Power Dynamic Capacitive Power Transfer System Considering Coupler Voltage Distribution for Railway Applications

Capacitive power transfer (CPT) is a promising method to solve the problems caused by the traditional Pantograph-catenary contact power supply for railway applications. In contrast, the CPT system suffers a broken risk because of the small coupling capacitor. This paper has analyzed the CPT coupler’s voltage distributions for dynamic CPT systems when high power is required in real railway applications. The triangle relationship among the coupler voltages is derived. The circuit of the CPT system to accolated the coupler voltage is analyzed. Then, the compensation parameters are given. With the adopted LCLC-CL topology, the design process is presented by considering the coupler voltages. An experimental setup is conducted to validate the proposed design method. The experimental results show that the system can achieve 3 kW output power with 92.46% DC-DC efficiency and the voltage distribution aggress well with the designed values.

Efficiency Optimization Based Parameter Design Method for the Capacitive Power Transfer System

In this article, a parameter design method is proposed to improve the dc-dc efficiency of the capacitive power transfer (CPT) system. Similar to the inductive power transfer (IPT) system, the capacitive coupler is analyzed by using a T-type model, giving direct insight into the impedance refracted from the secondary side. Compared to the IPT system, the external capacitor of the capacitive coupler introduces extra design freedom, making it easy to realize the optimal load condition by adjusting the external capacitance. To quantify the relationship between the optimal load and the external capacitance, the impedance characteristic of the rectifier is discussed. Then, the efficiency analysis is conducted in detail. Considering the impact of the resonant frequency, and the external capacitance that determines the coupling coefficient, a parameter design method is proposed to improve the dc-dc efficiency. Although the design example is conducted with the double-sided LC compensated CPT system, the analysis and design process can be extended to other compensation networks easily. The effectiveness of the proposed design method is verified with a 100-W output CPT system. The experimental results show that the dc-dc efficiency can reach 89.39% with 10-W output, and reach 93.02% with 100-W output.

A Framework for Code Division Multiple Access Wireless Power Transfer

The availability of energy is one of the major hindrances to unlocking the massive potential of electronic devices. Powering a highly connected network of devices requires multiple access and a wireless power transfer (WPT) solution that is scalable and capable of maintaining a constant power flow regardless of reconfiguration (mutability) and electromagnetic environment (power flow selectivity). In this paper, we present a framework for the implementation of code division multiple access wireless power transfer (CDMA-WPT) for enabling WPT among multiple transmitters and multiple receivers simultaneously. CDMA-WPT maintains power flow selectivity and is easily scalable. An inverter/rectifier topology is presented for the hardware implementation of CDMA-WPT. A design process for practical co-design of high-performance hardware and obtaining a code set is also presented. We demonstrate the hardware implementation of CDMA-WPT using two transmitters and two receivers maintaining a nearly constant 5W operation with nearly 75% dc-dc efficiency, and four transmitters and four receivers maintaining a constant 4W operating with greater than 70% dc-dc efficiency. . This paper is accompanied by a video hardware demonstration in real-time the difference between using orthogonal codes in CDMA versus conventional single-frequency WPT using 4 transmitter-receiver pairs; conventional single-frequency WPT shows up to a 100% deviation from the intended transfer power as opposed to 8.1% for orthogonal codes in CDMA.

Single-Stage Duty-Controlled Half-Bridge Inverter for Compact Capacitive Power Transfer System

Capacitive wireless power transfer (CPT) is becoming a promising alternative to inductive power transfer (IPT) due to low costs and the simplicity of capacitive coupler. This paper presents a new architecture that makes CPT systems even simpler and easier to control. In the proposed scheme, a wide input voltage range is achieved by duty control while the output voltage is inherently load-independent, and this eliminates the need for an extra DC-DC converter. Our system also provides an extended zero-voltage-switching (ZVS) range to deal with both input and load variations. We carried out ZVS analysis for each MOSFET switch and based on this an optimal design was proposed. We implemented a prototype 160 W CPT system based on our design procedure, and its performance was then verified under a universal input voltage with load variations from 200- $1000~\Omega $ . A DC-DC efficiency as high as 88.2% was achieved, showing the value of the proposed topology.

Research on Efficiency Improvement of High Frequency Transformer in UPS based on Maxwell

On-line UPS occupies a large proportion in today's standby power market due to its rapid dynamic response and clean power output. The bi-directional DC-DC converter can replace the directional DC-DC in both commercial mode and battery mode of UPS, and realize the sharing of power transformer, inductor and power switch components in two DC-DC circuits, so as to achieve the goal of large charging current, high power density and low cost. In UPS, the loss of magnetic components is the main factor affecting the efficiency of bi-directional converter. In order to improve the efficiency of bidirectional DC-DC, a high frequency transformer is designed. Maxwell software is used in this paper to simulate the transformer losses in different winding arrangements, so as to select the optimal winding arrangements, reducing the transformer winding losses and improving the converter efficiency. Finally, the prototype is made and debugged to verify the feasibility of the design.

Experimental installation of wireless power transfer system based on the series resonance technology

<span lang="EN-US">In this work, we aim to install a wireless power transfer (WPT) system experimentally. Series resonance technology was used to achieve zero-voltage switching (ZVS). We investigated the impact of the primary and secondary resonance frequencies (f<sub>p</sub> and f<sub>d</sub>), and inverter frequency switching (fch) on the efficiency (β) and maximum transfer power in a WPT system based on the inductive wireless power transfer (IWPT) technology. An ultrasonic device was utilized as a generator to excite the coil at the primary side. The experimental outcomes showed that there is an optimum unlike f<sub>p</sub> and f<sub>d</sub> can be got to match fch. It was found also that there is a trade-off between the power supplied to the load (PRL) and DC-DC efficiency (β). At an air-gap of 5 cm, the obtained results are recorded as follows; the peak recorded system β is 62% that was obtained at f<sub>p</sub>=19 kHz, f<sub>d</sub>=f<sub>ch</sub>=24 kHz that is corresponding to 101.88W of PRL; whereas the highest PRL resulted i.e. 244W when f<sub>p</sub>=19 kHz, f<sub>d</sub> =24 kHz, f<sub>ch</sub>=21 kHz at 61% of β; in such case, the maximum β* PRL multiplication was achieved i.e. 149. Moreover, the coils’ misalignment was studied. The outcomes showed that the lateral misalignment has worst effect on the PRL and β than the air-gap. The experimental results were validated with simulation ones.</span>

Reduced Ferrite Double D Pad for Roadway IPT Applications

Roadway inductive power transfer presents an opportunity to provide a robust and user friendly system for electric vehicle charging by utilizing magnetic couplers (pads) embedded in the roadway. Roadway pads are expected to have a long service life but existing pads use a large quantity of the brittle magnetic material ferrite, which may break in the harsh environment of a roadway. This article shows what happens when the volume of ferrite material is reduced from an example double D pad to minimize the quantity and size of ferrite that needs to be protected. Also presented are design insights into the placement of a reflection winding that helps shape the field in the absence of the majority of ferrite. The final selected example design reduces the leakage magnetic field where a person may be present by 43%, at the expense of an increase in primary VA of 73% from the original double D pad. The final presented pad reduces the ferrite volume by 86% compared to the original example double D pad, is only 50 mm thick, and is shown to have a measured dc-dc efficiency of 91% when delivering 4.7 kW to an available secondary.

Analysis and Demonstration of a Dynamic ZVS Angle Control Using a Tuning Capacitor in a Wireless Power Transfer System

In this article, a dynamic zero-voltage switching (ZVS) angle control scheme on the wireless power transfer (WPT) system inverter is proposed by implementing a tuning capacitor. High-frequency (HF) and high-power WPT systems are desired in battery charging applications to reduce the battery charging time. Consequently, the power semiconductor devices are subjected to increased voltage, current, and thermal stresses. In this article, the switching losses in the primary-side inverter of a WPT system are suppressed by realizing the ZVS operation during the battery charging process. A dual-loop control strategy is proposed, which involves traditional phase shift control between the inverter phase legs to maintain constant-current (CC)/constant-voltage (CV) at the output and a tuning capacitor to dynamically tune the ZVS angle. The dynamic tuning of the ZVS angle ensures a minimum reactive power requirement from the input source and, therefore, helps to improve the overall efficiency of the system. Closed-loop simulations of the proposed control strategy are carried out using the piecewise linear electrical circuit simulation (PLECS) simulation software. The proposed control strategy is verified on a 10-W WPT prototype by performing the open-loop experimental validations. The maximum efficiency of the proposed control strategy is found to be ~ 87 % during the CC/CV charging modes. The improvement of ~ 10 % in the dc-dc efficiency is achieved with the proposed ZVS control strategy.

A Circumferential Coupled Dipole-Coil Magnetic Coupler for Autonomous Underwater Vehicles Wireless Charging Applications

Inductive power transfer is a practical approach to recharging the autonomous underwater vehicles (AUVs). The performance of the magnetic coupler determines the system transfer capacity. The annular magnetic coupler is widely utilized in the underwater wireless charging system. However, this magnetic coupler has limitations on magnetic field distribution. The flux linkage occupies the center of the AUV, and hence, the electronics inside the AUV are susceptible to electromagnetic interference. Additionally, the weight of the annular magnetic coupler greatly increases the burden on AUV power supply. In this paper, the magnetic coupler structure evolution is analyzed and a dipole-coil-based magnetic coupler with a novel circumferential coupling manner is presented. The magnetic flux is perfectly confined by the coupling manner, and the magnetic coupler weight is reduced by dimension optimization. To implement the magnetic coupler, the Fe-based nanocrystalline soft magnetic material is taken into consideration. To validate the proposal, a wireless charging system is built. Experimental results show that the system transfers 630W under water with a DC-DC efficiency of 89.7%.

Fault-Tolerant Wireless Power Transfer System With a Dual-Coupled LCC-S Topology

A dual-coupled inductor-capacitor-capacitor and series (LCC-S) compensated wireless power transfer (WPT) system with a compact receiver size is proposed in this paper to improve the misalignment performance and achieve fault tolerant operation as well as a stable output power. The compensation coil and the main coil are integrated as two decoupled unipolar coils on the transmitter side, while they are both coupled with the receiver coil. The two mutual inductances among the two decoupled coils and the receiver coil have opposite impacts on the output power when they both increase or decrease. Therefore, the output power can remain stable when the misalignment increases. The short- and open-circuit characteristics are analyzed, which demonstrates that the proposed topology can achieve both short- and open-circuit protection. A prototype was built and the experimental results verified the theoretical analysis and simulations. The system can deliver from 297 W to 321 W when the x-misalignment increases from 0 mm to 90 mm, with a dc-dc efficiency of 92.78% to 93.56%. The proposed WPT system can be used for the wireless charging of e-mobility scooters and autonomous underwater vehicles. The system can provide a stable output and can tolerate both short- and open-circuit faults at the output.

Single-Turn Air-Core Coils for High-Frequency Inductive Wireless Power Transfer

The efficiency of megahertz-frequency inductive wireless power transfer designs is currently limited by the quality factor of the resonant tanks and the coils. In this article, we use two-dimensional finite-element analysis to optimize the cross section of single-turn air-core inductors for this application and demonstrate coils for wireless power at high-frequency and very-high-frequency industrial, scientific, and medical (ISM) bands. Our resonant tanks achieve diameter-normalized quality factors (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) that are 25%-70% better than the state of the art for air-core coils at 6.78 MHz (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> = 73 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and 13.56 MHz (102), and we show significant improvements at the 27.12 MHz (123) and 40.68 MHz (137) ISM bands. We highlight the importance of capacitor selection and the tank configuration for designing high-Q resonant tanks and recover the increase of Q with frequency that is missing from the existing literature. Furthermore, we show that maximizing height is not ideal for wireless power transfer applications and build high-performance coils at small heights. We integrate these coils into a wireless power transfer system at 6.78 MHz and 500 W output power, showcasing a maximum dc-dc efficiency above 89% with a gap (3 cm) equal to the coil radius, a significant efficiency improvement over existing work.

Design of coaxial coupled structure for distance-insensitive wireless power transfer.

Coaxial coupled structure of wireless power transfer, applied to high-precision instruments in aerospace, can eliminate interference sources by spatial isolation. For the optimization of the electromagnetic structure, a C-shaped magnetic structure is presented for both shielding electromagnetic simulation and improving coupling. By comparing of spiral and coaxial structures, an analysis is presented and validated in the effect of positional offset on inductive coupling, voltage gain, and efficiency. To obtain a stable and sufficient power supply, the prototype is implemented based on primary series-secondary series compensation topology with a maximum output power of 200 W, and a DC-DC efficiency of 82% is achieved.

Analysis and design of hybrid inductive and capacitive wireless power transfer for high‐power applications

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.

A Rotation-Resilient Wireless Charging System for Lightweight Autonomous Underwater Vehicles

This paper presents a rotation-resilient wireless charging system with a reversely wound receiver that supports efficient charging for lightweight autonomous underwater vehicles. By employing a two-part reversely wound receiver coil structure, the total mutual inductance of the proposed coil structure remains relatively constant when rotational misalignment between the transmitter and receiver coils occurs, thereby ensuring wireless charging power is nearly continuous during rotational misalignment. Finite element analysis was performed with ANSYS Maxwell to verify the proposed coil structure. Double-sided LCC compensation topology was applied and circuit analysis was conducted via a mesh current method. A prototype of the rotation-resilient wireless charging system with the proposed coil structure was built and tested. Experimental results are well-matched to simulations, demonstrating that the system can deliver 745 Watts at a dc-dc efficiency of 86.19% when the system is fully aligned, and efficient under worst-case rotational misalignment.

Textile-Based Flexible Coils for Wireless Inductive Power Transmission

Wireless inductive power transmission systems can potentially supply wearable devices. Power cables or batteries can be eliminated by implementing a wireless power transfer system, making the wearable devices less obtrusive to users. However, rigid coils can cause discomfort to users in wearable applications. The novel screen-printed flexible coils on textiles reported here are intended to be a low-cost and comfortable solution when integrated into clothing. A constant-width circular-spiral flat coil has been designed to minimize the detrimental effect of the low conductivity of the screen-printed flexible conductors on the efficiency of the wireless power transfer system. The coils are printed on 65/35 polyester/cotton textile with a screen-printed Fabink-UV-IF1 interface layer coating. The interface layer provides a relatively flat and smooth surface to prevent the permeation of the conductive paste into the textile and allows the printing of finer-profile coils. A 5 V 1.2 W DC output has been achieved by a wireless power transfer system using the printed flexible coils with Qi standard circuitry; a DC-DC efficiency of 37% has been measured.

Selection of Inductor and Snubber Capactor to Optimize the Size and Efficiency of DC-DC Switching Power Converter

This paper presents a selection of inductor and snubber capacitor in non-isolated synchronous DC-DC switching power converter. The circuit is made to operate in Synchronous Discontinuous Conduction Mode (SDCM)/Forced Continuous Conduction Mode (FCCM) of operation for minimum inductor value, to reduce the size, weight and cost of the converter. The turn off loss of the switch induced by SDCM of operation is minimized by connecting snubber capacitor across the transistor switch. Before the switch is turned ON, snubber capacitor requires certain amount of energy must be stored in the inductor to discharge the capacitor energy [1]. The question is how much capacitor and inductor value is required. A series of MATLAB script are executed to find minimum inductor value for FCCM of operation and to select snubber capacitor for maximum efficiency. Complementary gate signals are used to control the ON and OFF of main and auxiliary switch. SDCM of operation due to complementary control gate signal scheme, minimum turn on loss of the transistor switch and low diode reverse recovery loss are achieved. Thus the Zero Voltage Resonant Transition (ZVRT) of transistor switch is realized, both turn on and turn off loss is minimized and also removes the parasitic ringing in inductor current.

Compact Double-Sided Decoupled Coils-Based WPT Systems for High-Power Applications: Analysis, Design, and Experimental Verification

Wireless power transfer (WPT) system is a practical and promising way for charging electric vehicles due to its security, convenience, and reliability. The requirement for high-power wireless charging is on the rise, but implementing such a WPT system has been a challenge because of the constraints of the power semiconductors and the installation space limitation at the bottom of the vehicle. In this paper, bipolar coils and unipolar coils are integrated into the transmitting side and the receiving side to make the magnetic coupler more compact while delivering high power. The same-side coils are naturally decoupled; therefore, there is no magnetic coupling between the same-side coils. The circuit model of the proposed WPT system using double-sided LCC compensations is presented. Finite-element analysis tool ANSYS MAXWELL is adopted to simulate and design the magnetic coupler. Finally, an experimental setup is constructed to evaluate the proposed WPT system. The proposed WPT system achieved the dc-dc efficiency at 94.07% while delivering 4.73 kW to the load with a vertical air gap of 150 mm.

Six-Plate Capacitive Coupler to Reduce Electric Field Emission in Large Air-Gap Capacitive Power Transfer

This paper proposes a six-plate capacitive coupler for large air-gap capacitive power transfer to reduce electric field emissions to the surrounding environment. Compared to the conventional four-plate horizontal structure, the six-plate coupler contains two additional plates above and below the inner four-plate coupler to provide a shielding effect. Since there is a capacitive coupling between every two plates, the six-plate coupler results in a circuit model consisting of 15 coupling capacitors. This complex model is first simplified to an equivalent three-port circuit model, and then to a two-port circuit model which is used in circuit analysis and parameter design. This six-plate coupler can eliminate the external parallel capacitor in the previous LCLC topology, which results in the LCL compensation and reduces the system cost. Due to the symmetry of the coupler structure, the voltage between shielding plates is limited, which reduces electric field emissions. Finite element analysis by Maxwell is used to simulate the coupling capacitors and electric field distribution. Compared to the four-plate horizontal and vertical structures, the six-plate coupler can significantly reduce electric field emissions and expand the safety area from 0.9 to 0.1 m away from the coupler in the well-aligned case. A 1.97 kW prototype is implemented to validate the six-plate coupler, which achieves a power density of 1.95 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a dc-dc efficiency of 91.6% at an air-gap of 150 mm. Experiments also show that the output power maintains 65% of the well-aligned value at 300 mm X misalignment, and 49% at 300 mm Y misalignment.

Plan and analysis of synchronous buck converter for UPS application

DC-DC converters occupies very significant role in the field of industries or daily life applications. To charge batteries of low voltage connected to uninterrupted power supply (UPS), DC-DC converters are needed. Batteries requires low voltage and the available voltage at the source is to be step-down to the required level of voltage at the point of utility (PoU). While designing DC-DC converters, efficiency and simplicity of the circuit is very much important. Simply for the UPS applications, Buck converter can deliver the voltage at required level which is very simple in operation but the increased losses in diode can be addresses by using a synchronous Buck converter. By using synchronous Buck converter, the diode conduction losses in Buck converter can be minimized, thus improving the efficiency of the converter. In this paper, Synchronous Buck converter is used to charge the batteries of UPS. In this paper Design, modeling of synchronous Buck converter for UPS application was done and its results were obtained by using Matlab/Simulink. A hardware prototype was also developed and the hardware results were also shown.

A Maximum Efficiency Point Tracking Control Scheme Based on Different Cross Coupling of Dual-Receiver Inductive Power Transfer System

One of the most promising inductive power transfer applications is the wireless power supply for locomotives which may cancel the need for pantographs. In order to meet the dynamic and high power demands of wireless power supplies for locomotives, a relatively long transmitter track and multiple receivers are usually adopted. However, during the dynamic charging, the mutual inductances between the transmitter and receivers vary and the load of the locomotives also changes randomly, which dramatically affects the system efficiency. A maximum efficiency point tracking control scheme is proposed to improve the system efficiency against the variation of the load and the mutual inductances between the transmitter and receivers while considering the cross coupling between receivers. Firstly, a detailed theoretical analysis on dual receivers is carried out. Then a control scheme with three control loops is proposed to regulate the receiver currents to be the same, to regulate the output voltage and to search for the maximum efficiency point. Finally, a 2 kW prototype is established to validate the performance of the proposed method. The overall system efficiency (DC-DC efficiency) reaches 90.6% at rated power and is improved by 5.8% with the proposed method under light load compared with the traditional constant output voltage control method.