Series-series Research Articles

Analysis of Losses in Two Different Control Approaches for S-S Wireless Power Transfer Systems for Electric Vehicle

This paper presents the study and detailed analysis of converter losses at different stages together with the series-series (S-S) compensating coils in wireless power transfer (WPT) systems, via two distinct approaches to control the power converters. The two approaches towards wireless DC–DC power flow control are termed as the Single Active High-Frequency Wireless Power Transfer (SAHFWPT) system and the Dual Active High-Frequency Wireless Power Transfer (DAHFWPT) system. The operation of converters in SAHFWPT and DAHFWPT are controlled by the extended phase shift (EPS) and dual phase shift method respectively. The general schematic of the SAHFWPT system consists of an active bridge and a passive bridge, while the schematic of the DAHFWPT system consists of both active bridges. The efficiency evolutions of ideal SAHFWPT and DAHFWPT are far away from the real ones. Moreover, this article analyzes the operation and losses of the uni-directional power flow of the WPT system, i.e., from the DC bus in the primary side to the battery load in the secondary side. The loss estimation includes high-frequency switching losses, conduction losses, hard turn on and turn off coil losses, etc. Moreover, the efficiency of the WPT system depends on operation of the converter. A 50 W–3600 W Power range system at a resonant frequency of 85 kHz is implemented in MATLAB/SIMULATION to demonstrate the validity of the proposed method.

Reconfigurable Rectifier-Based Detuned Series-Series Compensated IPT System for Anti-Misalignment and Efficiency Improvement

For an inductive power transfer (IPT) system, mobility is one of the most attractive features, but coupling variations can dramatically affect the system's output. In this article, a reconfigurable rectifier-based detuned series-series (SS) compensated IPT system is proposed to tolerate an extensive coupling range and improve the system efficiency simultaneously. The reconfigurable rectifier, which can operate in a full-bridge rectifier mode or a half-bridge rectifier mode, is used to alter the equivalent ac load from one value to the other so the expected coupling range of the detuned SS topology can be extended. At the same time, the system efficiency is also partly improved because the ac load is changed to get closer to the optimal load of the IPT system. First, a detuned SS IPT system with the reconfigurable rectifier is presented and followed by the analysis of the working modes. Then, a detailed parameter design process and switching control of the reconfigurable rectifier are introduced. Finally, a 400-W prototype was constructed to verify the validity of the proposed method. The experimental results demonstrate that the output power fluctuation of the proposed IPT system is less than 17.5% and the lowest efficiency can be improved from 68.6% to 87.5% with the coupling coefficient varying from 0.1 to 0.4. The proposed method can implement significant antimisalignment and efficiency improvement simultaneously, and it is regarded as a potential solution for low-power IPT applications with high spatial mobility.

Novel Design Method in Wireless Charger for SS Topology with Current/Voltage Self-Limitation Function

This study proposes a novel wireless power transfer (WPT) resonance compensation design method based on the SS topology with a self-limitation function that achieves fault tolerance without additional components when the secondary circuit is in a short and open state. Conventionally, WPT compensation topologies have constant current (CC) or constant voltage (CV) output characteristics. The CC and CV characteristics can lead to overvoltage and overcurrent, respectively. Several control systems have been proposed to counter this issue; however, they tend to increase the cost and weight of the system. The proposed topology has a self-limitation function that limits the voltage–ampere output. Here, the wireless charging system was designed after the parameters were obtained using the proposed analysis. The performance of the proposed design was verified by configuring a 400 W experimental prototype and comparing it with the conventional series–series (SS) topology. Experimental results indicated that the system could effectively limit the output voltage and current resulting from open-or short-circuit states.

Modeling and Development of Wireless Power Transmission System for Electric Vehicles

The main objective of this paper is to develop a sustainable Wireless power transmission (WPT) model. WPT is the technique of transferring electric energy from a power source to a load without any contact between them. This process can be done through different methods using different topologies, which include Series Series (SS), Series Parallel (SP), Parallel Series (PS), and Parallel Parallel (PP). One of the most widely used methods in WPT is inductive power transfer. The main advantages of WPT – it allows charging for multiple devices, has high charging speeds, low cost, less maintenance, and higher efficiency than wired charging. Despite significant advancements in charging solutions, the system still has various issues, such as coil position, the number of receiving coils, the distance between transmitter and receiver coils, high initial cost, and impacts on its sustainability. This paper discusses the simulation model of the WPT model using SS topology in the JMAG software and analyzes the effect of the position of coils and distance between transmitter and receiver coils on the output. This simulation model can further be used to build a prototype for charging EV batteries.

Power Factor Correction Modulated Wireless Power Transfer System With Series-Series Compensation

Power factor correction (PFC) is usually realized with a boost converter in a traditional power converter. This paper introduces a PFC modulated WPT method which can realize PFC function through phase-shift modulation of the primary-side inverter of a series-series (SS) WPT system. A close-loop control method of the phase-shift modulated system is also proposed for practical implementations. Without using a PFC converter, the structure of a WPT system can be simplified. Theoretical analysis and experimental results are provided to verify the idea.

Inductor-Aid Step-Up LLC Resonant Wireless Power Transfer

An inductor-aid step-up LLC wireless power transfer (WPT) system is proposed in this paper. It could step up the WPT output voltage beyond the conventional LLC series-series (SS) compensation method. Employing a parallel inductor with the transmitter coil to lessen the circuit impedance thus the inverter exhibits a new gain curve. The constant frequency operation and simple control of two series active switches in the parallel inductor branch shows a practical improvement of conventional constant frequency LLC WPT system, in terms of voltage demand, new standards and applications. Even the frequency modulation LLC WPT system could be benefited from this enhanced topology rather than to deteriorate the inverter current stress and unnecessary over-rating of magnetic components. The receiver side compensation tank has no additional voltage drop and overcurrent. A 300W prototype has been constructed to validate the concept and performed at 90% efficiency.

An Underwater Inductive Power Transfer System with a Compact Receiver and Reduced Eddy Current Loss

Inductive power transfer (IPT) technology is widely used in autonomous underwater vehicles (AUVs) to achieve safety and flexibility. However, the eddy current loss (ECL) will be generated in the seawater due to the high-frequency alternating current in the transmitter and receiver. An underwater IPT system with a series-none (SN) compensation topology is proposed in this paper to achieve a compact receiver for AUVs and reduce the ECL. The analytical model of the IPT system is built to analyze its transfer performance. The phase difference between the transmitter and receiver current of the SN compensation topology is larger than 90° compared to that of the conventional series-series (SS) topology, which can significantly decrease the magnitude of the electric field caused by coil currents; thus, the eddy current loss is reduced. Moreover, the optimal load resistance of the seawater IPT system is lower than that in the air, and the SN compensation topology has a more compact receiver with no compensation capacitor in the receiving side, which can save the internal space in the AUVs. An experimental prototype based on the SN topology is built, and the experimental results have verified the analysis.

A Review of Compensation Topologies and Control Techniques of Bidirectional Wireless Power Transfer Systems for Electric Vehicle Applications

Owing to the constantly rising energy demand, Internal Combustion Engine (ICE)-equipped vehicles are being replaced by Electric Vehicles (EVs). The other advantage of using EVs is that the batteries can be utilised as an energy storage device to increase the penetration of renewable energy sources. Integrating EVs with the grid is one of the recent advancements in EVs using Vehicle-to-Grid (V2G) technology. A bidirectional technique enables power transfer between the grid and the EV batteries. Moreover, the Bidirectional Wireless Power Transfer (BWPT) method can support consumers in automating the power transfer process without human intervention. However, an effective BWPT requires a proper vehicle and grid coordination with reasonable control and compensation networks. Various compensation techniques have been proposed in the literature, both on the transmitter and receiver sides. Selecting suitable compensation techniques is a critical task affecting the various design parameters. In this study, the basic compensation topologies of the Series–Series (SS), Series–Parallel (SP), Parallel–Parallel (PP), Parallel–Series (SP), and hybrid compensation topology design requirements are investigated. In addition, the typical control techniques for bidirectional converters, such as Proportional–Integral–Derivative (PID), sliding mode, fuzzy logic control, model predictive, and digital control, are discussed. In addition, different switching modulation schemes, including Pulse-Width Modulation (PWM) control, PWM + Phase Shift control, Single-Phase Shift, Dual-Phase Shift, and Triple-Phase Shift methods, are discussed. The characteristics and control strategies of each are presented, concerning the typical applications. Based on the review analysis, the low-power (Level 1/Level 2) charging applications demand a simple SS compensation topology with a PID controller and a Single-Phase Shift switching method. However, for the medium- or high-power applications (Level 3/Level 4), the dual-side LCC compensation with an advanced controller and a Dual-Side Phase-Shift switching pattern is recommended.

Design Space of Sub-Resonant Frequency- Controlled Series–Series-Compensated Inductive Wireless Power Transfer Links Operating With Constant Output Current Under Frequency Constraints

Output current of inductive wireless power transfer links (IWPTLs) with battery loads is influenced by coupling coefficient and input–output voltage. To regulate the output current while keeping the operational frequency near resonance, dc–dc converters are often added at IWPTL input and/or output, increasing system complexity and dimensions while reducing lifetime and reliability. On the other hand, a sub-resonant frequency control method was shown to eliminate the need for dc–dc converters addition as well as preventing IWPTL overrating. The technique is based on imposing bifurcation (or frequency splitting) and varying the operational frequency within certain region below resonance to regulate IWPTL output current. Due to the fact that some applications restrict the operational frequency band, methodology for deriving the design space of sub-resonant frequency-controlled series–series (SS)-compensated IWPTL (SS-IWPTL) operating under frequency constraints with constant current (CC) output is proposed in this work. The algorithm identifies all feasible combinations of loosely coupled transformer (LCT) coils self-inductances and coupling coefficients for expected ranges of input–output voltages and prescribed operational frequency band, allowing to maintain CC output. Simulations and experiments are carried out to verify the proposed methodology.

Output Power Regulation of a Series-Series Inductive Power Transfer System Based on Hybrid Voltage and Frequency Tuning Method for Electric Vehicle Charging

In the inductive charging scenario of an electric vehicle (EV), the charger should have the capability to flexibly regulate the output power regardless of the misalignment and EV battery voltage. This article proposes a hybrid voltage and frequency tuning strategy for a series-series (SS) inductive power transfer (IPT) system to regulate power through 0 to 3.3 kW at any battery voltages and misalignment conditions without using additional converters. A voltage tuning is used to achieve full-power of 3.3 kW and partly contribute to reducing the power. When the input voltage achieves the lower limit, a frequency tuning is used to further decrease the power to 0 W, achieving the regulation through 0 to full power. The practical charging region is specified by 110 mm airgap, 100 mm misalignment in both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> directions, and 180–240 V battery voltage range. Experiments are carried out at various conditions, and it shows that with an input voltage range of 180–380 V and a frequency of 82.5–87.9 kHz, the charging power can be regulated between 100 W and 3.3 kW at any case in the specified working region. In addition, a peak dc-dc efficiency of 95.7% is achieved at 3.29 kW.

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.

Misalignment-Tolerant Dual-Transmitter Electric Vehicle Wireless Charging System With Reconfigurable Topologies

Wirelesscharging for electric vehicles (EVs) enjoys many benefits, such as convenience, safety, and automation. One of the major issues concerning EV wireless charging is misalignment tolerance along the door-to-door direction of the EV. This letter proposes a misalignment-tolerant dual-transmitter EV wireless charging system with a reconfigurable topology. At central positions, the system can be reconfigured to the S-S (series-series) topology where the two transmitting coils are connected in series to feed the load. At boundary positions, the two transmitting coils form the LCCC-S (inductor-capacitor-capacitor-capacitor-series) topology to enhance power transfer capability and tolerate weak couplings. In this way, not only the output power can be smoothed with door-to-door misalignment, but also wireless charging is guaranteed at weak couplings. Experimental results reveal that within the cover area of the transmitting coils, high-efficiency stable output can be achieved.

A Hybrid Inductive Power Transfer System with High Misalignment Tolerance Using Double-DD Quadrature Pads

Inductive power transfer (IPT) has been widely adopted as an efficient and convenient charging manner for both static and in-motion EVs. In this paper, a new hybrid topology is presented to improve the coupling tolerance under pad misalignment. The double inductor–capacitor–capacitor (LCC-LCC) network and series hybrid network combining the LCC-LCC topology and series-series (SS) topology are connected in parallel to provide better tolerance against self- and mutual inductance changes, particularly with a large Z-axis transmission distance. A double-DD quadrature pad (DD2Q) consists of a Q pad, and double orthogonal DD pads are analyzed in detail, which are employed to decouple the cross-mutual inductance. Moreover, a parametric design method based on the misalignment characteristics of the DD2Q pads is also proposed to maintain relatively constant power output. A 650-W hybrid topology with a fixed operating frequency of 85 kHz was built to verify the system’s feasibility. The size of the DD2Q pads was 280 mm × 280 mm, and the air gap was 100 mm. The results clearly show that the proposed hybrid topology can achieve a fluctuation within 5% in the output current with load varying from 100% full load to 25% light load conditions when the Z-axis transmission distance varies from 80 mm to 150 mm, and the maximum efficiency can reach 91% when the Z-axis transmission distance is 80 mm.

Research on Control Method and Variable Topology Design of Wireless Power Transmission System with Coil Offset

Aiming at the coil offset of magnetic coupling wireless power transmission (WPT) system with the Series–Series (SS) resonance structure, in order to stabilize the transmission efficiency above 80% according to SAE J2954, Control method and variable topology design with the maximum lateral offset of 20 cm are researched on. In this paper, the mutual inductance theory is adopted to establish an equivalent circuit model of the system. The expressions of the transmission characteristics with coil offset are derived and the influence of coil offset on transmission characteristics is analyzed. According to the difference offsets, a bilateral control method with phase‐shift control on primary side and double closed‐loop control on secondary side for small offset (0, 10 cm) for constant voltage output at 200 V is adopted. In addition, a double‐sided LCC topology structure is developed for larger offset (10, 20 cm) with the maximum efficiency transmission method by parameter configuration. The simulation platform and the experiment platform are developed and the output characteristic experiments with different loads and different coupling coefficients under different offsets are finished to verify the results and provide a reference for the anti‐offset research of the system. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Design methodology for S-S compensated sub-resonant controlled inductive wireless power transfer link with range of CV loads under frequency constraints

Coupling coefficient of inductive wireless power transfer Link (IWPTL) varies with changes in vertical distance and misalignment between primary and secondary coils. This poses a challenge in system design when a certain geometrical positioning uncertainty is introduced. System design must take this into consideration allowing operation over a range of coupling coefficients rather than a single value. Furthermore, in instances such as electrical vehicle (EV) charging, frequency constraints are introduced such as the bounds in SAEJ2954 standard. This paper proposes a design methodology for seriesseries (S-S) compensated IWPTL with sub-resonant frequency control allowing for operation over a range of coupling coefficients. Example system is validated by simulation and experimental results.

Compensation topologies for wireless power transmission system in medical implant applications: A review

This review paper addresses and discusses the challenge of selecting the best topology for a wireless power transmission (WPT) system for a medical implant application in order to improve power transfer efficiency (PTE). WPT systems using inductive and magnetic resonance coupling (MRC) have been introduced in recent years as a convenient and secure alternative to traditional wired charging systems. Compensation topologies are essential in MRC-WPT system to improve the PTE over certain distances. The fundamental topologies comprising series-series (SS), series-parallel (SP), parallel-series (PS), parallel-parallel (PP), and Series-Non resonant secondary (SN) or primary side series (PSS) are all explored and discussed. The theoretical analysis of power transfer efficiency using reflected impedance theory, as well as the selection of the most relevant topology depending on system requirement and application, are studied and addressed. Resonance frequency selection is necessary to identify the compensation capacitor for magnetically coupled WPT system. IEEE and ICNIRP safety regulations and guidelines for biomedical applications are reviewed and addressed.

Development of Experimental Bench for Wireless Power Transfer

Wireless-power-transfer (WPT) for powering low-power devices has increased in recent years. The inductive resonant coupling method is the most used technique for this application and consists of taking advantage of the magnetic field generated in a coil so that there is current circulation in another nearby coil. In this work, using this technique, the series-series (SS) compensation topology was used to develop a test bench that should supply a load of up to 10W. Therefore, a brief explanation of the topic, calculations used, defined parameters, and we presented preliminary results of the proposed system.

Frequency and Parameter Combined Tuning Method of LCC–LCC Compensated Resonant Converter With Wide Coupling Variation for EV Wireless Charger

The characteristics of inductive power-transfer (IPT) systems are sensitive to the variation of the coupling coefficient caused by misalignment conditions or different gaps. This results in a reduction in transferred power and efficiency. The output characteristics considering frequency modulation applied in series–series (SS), inductor–capacitor–capacitor (LCC)-S and LCC–LCC compensated IPT systems have been explored, revealing that high-order compensation topologies hold limited power regulation ability if coupling varies significantly. The parameter sensitivity of LCC–LCC-compensated topology is investigated through the singular values (SVs) analysis. It is found that the variation of the parallel-compensated capacitors has the greatest impact on the output power. Aiming at alleviating the power drop caused by the coupling variation, a parameter offline tuning method realized by switching the parallel-compensated capacitance for a detuned LCC–LCC resonant converter is proposed for electric vehicle (EV) wireless charging. Analytical expressions have been derived in aiding the design of modified value of capacitance ensuring primary zero voltage switching (ZVS) operation. Thus, the detuned parameter combinations, which deliver rated power even with the worst coupling, are obtained. Finally, a 6.6-kw prototype has been built to verify the validity of the proposed topology, which can deliver 6.1 kW with an efficiency of 94% even when the coupling drops from 0.3 to 0.15.

A Comparative Analysis of S-S and LCCL-S Compensation for Wireless Power Transfer with a Wide Range Load Variation

Wireless power transmission (WPT) has great potential for charging electric vehicles. Constant voltage (CV) and constant current (CC) are two major types of battery charging modes. In this paper, we analyze the output characteristics of series-series (S-S) topology and double capacitances and inductances-series (LCCL-S) topology. Voltage gain variation is achieved in the LCCL-S compensation structure without additional components, and the system is still kept in resonant condition. A WPT experimental platform was also built and tested based on the theoretical analysis. When the load resistance is 300 Ω, a voltage gain of 0.7 or 2.22 is achieved for the LCCL-S with a compensating inductor of 100 μH or 33 μH, respectively. The experimental results fit the theoretical analysis. The CC/CV output characteristics and efficiencies of S-S and LCCL-S topologies in a wide load resistance range are also demonstrated. Moreover, zero voltage switch (ZVS) is also implemented in both two systems.

Investigation on Coil Geometry in WPT Systems for Charging EVs Applications

This paper investigates different coil geometries for designing wireless power transfer (WPT) system for electric vehicle (EV) applications. the system model depend on the lumped parameters model using series- series (SS) compensation topology is briefly discussed. The investigations adopted on comparing the coupling coefficient using Finite Element method (FEM) software when the two coils are laterally and vertically misaligned. Moreover, investigations comprising the electromagnetic flux density distributions. One turn coreless circular planar and square planar coils are simulated and the results depicted and compared for the same wire length. The results show that the circular coil gained higher coupling coefficient and generates more electromagnetic flux density than the square coil.