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This article presents a new common grounded converter based on a switched capacitor. The converter can be used as a suitable interface for single-phase ac or two-wire dc grids. The direct connection between the negative terminal of the input voltage source and the null terminal of the output source enables the elimination of the leakage current in renewable energy systems, especially in photovoltaic power generation. The proposed topology offers voltage-boosting capability, so there is no need for an additional boost converter and it is possible to inject power into the grid at dc input voltages lower than the peak value of the output voltage, which helps improve the efficiency of the converter. In addition, the proposed topology has the ability to handle reverse current, hence, it feeds non-unity power factor loads. The operating modes and design of passive components are described in detail. The performance and advantages of the proposed converter are compared with other converters. Finally, through the experiment on a (3.78 kW/7 kW) converter, the performance of the proposed converter is validated.

In the conventional design of a double-sided LCL compensation network for the capacitive power transfer (CPT) system, two external capacitors are connected in parallel with the horizontal capacitive coupler, or a vertical capacitive coupler is required to reduce the resonant inductances. This approach results in a loosely coupled structure. The compensation inductor resonates with the whole coupler, inducing reactive power transferred from the primary to the secondary side, leading to higher voltage stresses on the plates, which inevitably increases the system complexity and susceptibility to air breakdown. This article proposes a double-sided LCL compensation network design method for the CPT system where no parallel-connected capacitors are required, thereby a strongly coupled structure can be obtained with a constant current (CC) output and input zero phase angle (ZPA) characteristics. By keeping the phase angle difference between the voltage vectors across the primary and secondary plates at 90°, no reactive power is transmitted from the primary to the secondary side. Thus, the voltage stresses across the plates can be minimized. A 500 W prototype with a high coupling coefficient of 0.82 is established to verify the proposed system and an efficiency of 90% is achieved.

For multistorey car parks, this article proposes and implements an integrated sensorless wireless charging (SWC) system of electric vehicles (EVs) using a symmetric high-order network that is designed to mirror the electrical parameters of the onboard receiver and battery. The proposed SWC control can avoid the need of communicating and sensing the receiver's and battery's states. It possesses the competitive advantages of being controller-free, sensor-free, communication-free, converter-free, and switch-free onboard. Given the efficient charging for millions of EVs, this integrated SWC scheme can effectively reduce the electrical and electronic component counts, which aligns with the themes of carbon neutrality and environmental sustainability. By detecting the current threshold and then switching two resonant frequencies, the symmetric high-order network enables the autonomous management of constant-current and constant-voltage charging modes while maintaining the zero-phase-angle operation. The experimental dc-to-dc efficiency can reach 91.8% based on a 2.4-kW proof-of-concept prototype at a 150-mm transfer distance. Software simulation and hardware experimentation are given to verify the feasibility of proposed integrated SWC system using the symmetric high-order network.

This article presents a frequency-domain analysis that models the behavior of Constant-on-Time (COT)-controlled buck converters in wide-input–output-range scenarios. Based on this analysis, a design strategy is proposed to enable robust control with a duty-cycle-independent quality factor, also known as a constant $Q$-value. A constant $Q$-value circuit based on the proposed strategy is then constructed and incorporated with a baseline ultrafast transient COT control scheme to experimentally verify the system stability and optimal load transient response under wide input–output range scenarios. In addition, the design strategy is extended to other COT buck control schemes with simulation and calculation verifications.

Bidirectional ac–dc power converters are essential in emerging smart grids with increasing renewable energy penetration. This article presents a bidirectional ac–dc power converter system comprising modular multilevel converters (MMCs) and dual active bridges (DABs) with medium-frequency transformer isolation designed for linking an ac distribution voltage of 6.6 kV to a dc grid of 800 V for future electric vehicle (EV) charging infrastructure. The novel contributions include: 1) a modular method to power EV charging infrastructures in multistorey carparks without mains-frequency transformers and 2) the incorporation of a front-end control with electric spring (ES) functions that enable the dc power grid with battery energy storage to interact dynamically with the ac power grid at the distribution voltage level to achieve instantaneous power balance and hence system stability. The long-term aim is to use large EV charging infrastructures to stabilize increasing intermittent renewable energy via the proposed ac–dc converter, consequently accelerating the adoption of large-scale renewable energy and EV as a complementary solution to combat climate change. This article focuses on the bidirectional ac–dc converter of this overall idea based on the MMC and DAB technologies as an example. Results on the power converter operation level and ac microgrid level are included.

In this article, a novel load-independent capacitive power transfer (CPT) system with multiple constant voltage (CV) outputs is proposed. The capacitive repeater unit is designed to enhance the power transfer capability, which contains four plates where two plates are used to receive power from its previous unit and the other two plates transfer power to the next unit. Electric coupling between the receiving and transmitting plates in the repeater unit can be eliminated by placing them perpendicularly and employing the split-inductor matching network. The load is connected with each capacitive repeater unit so that multiple loads can be powered simultaneously. Aluminum oxide ceramic is placed between the two adjacent units to enhance their electric coupling. The $L$ -LCL network is adopted to compensate each capacitive repeater unit. Thus, CV outputs can be achieved for all loads, which ensure the independent operation of each load. The output voltages and efficiency are analyzed when considering the parasitic resistances. Finally, a three-load experimental setup is built to verify the effectiveness of the proposed system with an efficiency of 93.21%.

A high-performance capacitive power transfer (CPT) system is expected to achieve the load-independent constant output, near-zero reactive power, and soft switching of power switches simultaneously, resulting in a reduced power stage, simple control circuitry, and minimum component ratings. However, a well-compensated CPT system still suffers very-high-voltage stresses among not only the main coupled plates but also the leakage coupled plates due to the small coupling and edge emission, which increases the risk of air breakdown and deteriorate the electromagnetic interference (EMI) issue. To solve this problem, the voltage stresses among such coupler plates should be predesigned at an acceptable level. This article systematically analyzes the characteristics of a double-sided $LCLC$ -compensated CPT converter that is proven to have enough design freedom providing predesigned voltage stresses for two kinds of coupled plates. Also, three operating frequencies with load-independent constant current (CC) output and input zero-phase angle (ZPA) are found. Without reactive power in the circuit, a parameter design method is proposed for the double-sided $LCLC$ -compensated CPT converter at each frequency to satisfy the desired CC output and the predesigned voltage limitations. In this way, the breakdown and EMI issues can be well mitigated by the intended design, and this method can also be extended to other CPT circuits. Finally, a CPT prototype is built to verify the theoretical analysis with the predesigned voltage stresses among the coupler plates.

To embrace a carbon neutrality future, we are witnessing the paradigm shift from internal combustion engine vehicles to electrified vehicles. The mainstream electric vehicles (EVs) are equipped with a high-voltage battery pack. Charging infrastructure plays a pivotal role in the era of electrified transportation. Its power determines the speed and convenience of recharging, its energy efficiency directly affects the mileage cost of EVs, and its performance impacts the lifespan of the battery. In addition, vehicle-to-grid (V2G) technology requires chargers to have bidirectional power transfer capabilities. This Special Issue aims to provide the latest solutions for the advanced charging of next-generation EVs. The system includes the onboard charger, offboard charging pile, wireless charging, fast charging and charging scheduling, etc. Key emerging research areas covered include innovative power conversion topologies, modeling techniques, control strategies, and energy management algorithms. These advancements are characterized by enhanced features, such as greater intelligence, higher efficiency, increased power density, improved thermal management, extended lifespan, and reduced costs.

A near-field communication capacitive power transfer (NFC-CPT)-combined coupler with a series-none compensation topology is proposed for metal-cover smartphone applications. To achieve capacitive power transfer through metal cover, the metal cover itself is used as the receiving metal plates. To realize NFC through metal cover, the cross slot including a slim horizontal slot and a rectangular slot is embedded on the metal cover, which mitigates the eddy current loss and increases the inductive coupling for the NFC antenna. Besides, the cross slot divides the metal cover into two separate metal plates, which is necessary for capacitive power transfer. Considering the space limitation and safety requirement, no compensation components are integrated inside the smartphone and only a series inductance is integrated on the transmitter side. A prototype of the proposed NFC-CPT-combined coupler has been built. The wireless power transfer and NFC through metal cover have been validated through experiment. The experimental results show that the prototype achieves 5-W output power with a 93.5% circuit efficiency at 6.78 MHz, and the detection range of the NFC antenna is 61 mm.

Wireless power transfer (WPT) technology has become a developing trend with the advantages of flexibility and security. However, WPT systems also face some challenges, such as output power fluctuations caused by misalignment or dynamic charging, accurate modeling of high-order systems, system integration, load estimation, and simultaneous transmission of power and data. Therefore, advanced topologies and magnetic coupler design for WPT systems are becoming critical topics. This Special Section on Advanced WPT Systems With High Efficiency and Misalignment Tolerance Characteristics in IEEE Transactions on Power Electronics (TPEL) provides an insight into some of the newly emerging challenges and potential solutions to overcome those issues. For this Special Section, 120 submissions were received. Twenty-three are published in the October issue. The rest of the papers will be published in the November and December issues of TPEL.

This paper proposes a wireless power repeater system for long-distance and multiple-load applications with equal power load at each repeater. Each repeater performs as a power relay that not only receives and transmits power but also supplies power to its local load. The main contribution of this paper is to provide the design methodology of a distributed power-relay system. First, it provides the mathematical model of the power distribution among the power relays, indicating that the inductances and resistances can affect the power distribution. Second, it provides the power transfer capability of a power-relay system based on the quality factor and efficiency requirement, indicating the maximum achievable number of power relays in a system. Aiming at practical applications, this paper provides the guideline for the circuit parameter design to achieve equal power distribution. Two typical examples are proposed to realize equal power distribution. The identical Mn and different Rn examples are selected for implementation. The coil size is 400 mm × 400 mm, and the eight power relays achieve a transfer distance of 3.2 m with a total power of 760 W and an efficiency of 70%. Experimental results validate that equal power distribution is achieved for the multiple loads across a long distance. Each power relay dissipates about 95-W power in its local load with a power variation limited to ±2%.

In a wireless power transfer (WPT) system, voltage tuning and frequency tuning are two major methods to control the output power. For the design of a WPT system at the rated power, it is crucial to understand the characteristics of a WPT system with a constant-power load (CPL) under voltage tuning and frequency tuning. The model of a series–series compensated WPT system with a CPL is established based on the Thevenin equivalent circuits. The conditions to achieve the maximum coil-to-coil efficiency for the two tuning methods are obtained. For frequency tuning, the tuning zone above the resonant frequency is selected because of its wide tuning range and zero-voltage switching. The maximum output power at different operating frequencies is derived, and the required inverter dc voltage and the tuning range for a target output power can be obtained accordingly. With a strong coupling, the maximum efficiency of frequency tuning can be as high as that of voltage tuning; while with a weak coupling, the efficiency of frequency tuning is much smaller than that of voltage tuning. The model with a CPL is helpful for the design and optimization of a WPT system with the rated power.

In the wireless charging of high-power electric buses or low-power consumer electronics, the charging distance is normally very small, leading to a strong coupling. Current distortion occurs for a wireless power transfer (WPT) system with a strong coupling. This paper investigates the strongly coupled series–parallel (SP)-compensated WPT system, where the first harmonic approximation (FHA) is no longer valid. A mathematical model of an SP-compensated WPT system based on differential equations is built. There are two sinusoidal components with significantly different frequencies existing in the transmitter and receiver currents, which cause the current distortion. The proposed model and FHA are compared, and the proposed model is more accurate than FHA. The estimations of the current root-mean-square values from FHA tend to be smaller than those from the proposed model and the measured values. In addition, it is found that with the increasing rectifier dc current, the system transits from zero voltage switching to zero current switching. The critical rectifier dc current decreases with the increasing operating frequency. The experimental results verify the effectiveness of the proposed model. The proposed model promotes a better design of an SP-compensated strongly coupled WPT system.

The connected and automated hybrid electric vehicles (CAHEVs) have the potential to improve safety and mitigate traffic congestions. A crucial problem of the CAHEVs is that the lithium-ion batteries are highly temperature sensitive, whose output power is severely limited at low temperatures. Moreover, the cells may be premature aging at high operating temperatures and even result in an explosion, seriously threatening the human safety. Consequently, a practical and energy-efficient battery thermal management (BTM) strategy is required with the minimum possible cooling/heating energy consumption. To achieve the multiple objectives, a finite-set based model predictive control (FSMPC) strategy is presented for the BTM in CAHEVs. Since the thermoelectric model of the BTM system is highly nonlinear and time variant, an extended state observer is implemented for accurate system state estimation and prediction so that the parameter uncertainties inherent in the system can be compensated. The hardware-in-the-loop validation of the proposed strategy is conducted on the urban dynamometer drive schedule-based on a Toyota Prius plug-in HEV model. The results demonstrate that the proposed BTM strategy can maintain the battery pack in the CAHEV operating at the optimum temperature and save 30% BTM energy compared to the conventional method even under 50% parameter uncertainty.

Wireless power transfer (WPT) using magnetic resonance is the technology which could set human free from the annoying wires. In fact, the WPT adopts the same basic theory which has already been developed for at least 30 years with the term inductive power transfer. WPT technology is developing rapidly in recent years. At kilowatts power level, the transfer distance increases from several millimeters to several hundred millimeters with a grid to load efficiency above 90%. The advances make the WPT very attractive to the electric vehicle (EV) charging applications in both stationary and dynamic charging scenarios. This paper reviewed the technologies in the WPT area applicable to EV wireless charging. By introducing WPT in EVs, the obstacles of charging time, range, and cost can be easily mitigated. Battery technology is no longer relevant in the mass market penetration of EVs. It is hoped that researchers could be encouraged by the state-of-the-art achievements, and push forward the further development of WPT as well as the expansion of EV.

This paper investigated the losses and thermal characteristics of induction motors operated from pulse width-modulated (PWM) voltage supply in comparison to that operated from sinusoidal voltage supply. It was concluded that due to the abundant harmonics in the PWM waveforms, significant losses are induced in the motor by the inverter supply. The temperature ascends correspondingly. Switching frequencies of the PWM inverter at 3.5 kHz to 9 kHz were investigated to evaluate their effect on the excessive losses. Experiments were conducted with no load and with load conditions. The losses and thermal characteristics were calculated using finite-element analysis (FEA) and validated by the experiments.

Wireless power transfer has been an increasingly attractive topic because it is convenient, clean, and safe. Its applications include industry clean rooms, electric vehicles (EVs), mobile phones, smart pads, medical devices, defense equipment, and robots. The wireless power transfer may mitigate the heavy reliance of a device on the battery that is heavy, expensive, and have a short operating time. The power level of wireless power ranges from a few milliwatts for medical implants and wireless sensors to several hundred kilowatts for EV charging. The distance of wireless power transfer varies from submillimeters to several meters, while the application areas are persistently expanding. Recently, we witness increasing demands for the electrification of public transportation and convenient charging of mobile devices.