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This study aims to analyze the zero-voltage-switching (ZVS) region of a Triple-Active-Bridge (TAB) converter with five degrees of freedom. A TAB converter is an isolated converter derived from a dual-active-bridge (DAB) converter and composed of three full bridges (FBs) coupled to three winding transformers. To reduce the switching loss of the 12 active switches that compose 3 FBs, the ZVS operation is essential. However, owing to the numerous operation modes derived by five-phase shift ratios, ZVS analysis is complicated, particularly in the time domain. Therefore, this study presents the ZVS analysis model of the TAB converter based on the generalized harmonic approximation (GHA). Through the GHA of a TAB converter, the proposed model consists of unified formulas applicable to all operating ranges of the converter. Unified formulas consider all parameters, such as series inductance, port voltage, parasitic capacitance, transformer voltage, and turn ratio. In the proposed model, the ZVS area is confirmed using five-phase ratios with voltage modulation ratios as variables and verified using MATLAB and experiments. [ABSTRACT FROM AUTHOR]

This study aims to analyze the zero-voltage-switching (ZVS) region of a Triple-Active-Bridge (TAB) converter with five degrees of freedom. A TAB converter is an isolated converter derived from a dual-active-bridge (DAB) converter and composed of three full bridges (FBs) coupled to three winding transformers. To reduce the switching loss of the 12 active switches that compose 3 FBs, the ZVS operation is essential. However, owing to the numerous operation modes derived by five-phase shift ratios, ZVS analysis is complicated, particularly in the time domain. Therefore, this study presents the ZVS analysis model of the TAB converter based on the generalized harmonic approximation (GHA). Through the GHA of a TAB converter, the proposed model consists of unified formulas applicable to all operating ranges of the converter. Unified formulas consider all parameters, such as series inductance, port voltage, parasitic capacitance, transformer voltage, and turn ratio. In the proposed model, the ZVS area is confirmed using five-phase ratios with voltage modulation ratios as variables and verified using MATLAB and experiments.

In this paper, a hybrid-bridge-based dual-active-bridge (DAB) converter with a three-level (TL) half-bridge and a two-level full-bridge is proposed, which can be utilized to interface the medium voltage and low voltage DC. In the proposed converter, there are only eight power switches in total. Compared with the traditional hybrid-bridge-based DAB converter with a neutral-point-clamped (NPC) type TL half-bridge, a fewer power device count and higher efficiency can be realized in the proposed converter due to removing clamping diodes. Thus, a more compact circuit structure and a lower cost can be obtained. Moreover, zero-voltage-switching (ZVS) of all switches in primary-side and secondary-side can be achieved in the proposed converter. The operating principle, performances, and characteristics of the proposed converter are analyzed in detail. Also, a specification design case with a detailed key parameter design is given. Finally, a 1-kW experimental prototype is established to validate the proposed converter, and obtained experimental results are highly consistent with the theoretical analysis.

This article presents a 10-kW novel gallium-nitride (GaN)-based three-phase grid to 48-V battery energy storage system (BESS). The BESS utilizes a single-stage ac–dc dual-active-bridge (DAB) converter with dual-phase-shift (DPS) and variable-frequency (VF) control. 600- and 80-V GaN power transistors, as well as planar magnetics, are used to achieve 96.6% efficiency and 50-W/in $^3$ power density. The operation principle and power transfer characteristics are derived based on time-domain analysis of the DAB inductor current. VF and DPS are utilized to achieve power factor correction and zero-voltage switching simultaneously while minimizing the DAB rms current. An online calculation algorithm is presented with short execution time, which enables the closed-loop control of the BESS. Experimental results are presented to validate the novel control. [ABSTRACT FROM AUTHOR]

In this article, high step-down dc–dc converters are widely employed in data center applications. Due to the higher step-down conversion ratio in the new generation 48 V voltage regulator module, a conventional buck converter is not suitable for such applications. To conquer this problem, a novel dc–dc converter is proposed in this article to achieve an ultrahigh step-down voltage conversion ratio for data centers. The nonisolated topology can be optimally designed to integrate both the switched-capacitor and coupled inductor techniques, which allows zero-voltage-switching (ZVS) of all active switches to be achieved and improves high efficiency. In addition, the converter presents the advantages of lower voltage stress, ultrahigh voltage gain, common ground, and simple control strategy. A comprehensive analysis of the steady-state analysis, derivation of voltage gain, voltage stress, and ZVS condition is presented in detail. Finally, a 30 W, 48-to-1 V experimental prototype is built and tested, which validates the ultrahigh step-down voltage gain and soft-switching characteristic of the proposed converter. The maximum efficiency of the prototype is 89.1% and the efficiency is 81.4% in full-load condition. [ABSTRACT FROM AUTHOR]

This article investigates an immittance-network-based multiport zero-voltage-switching (ZVS) bidirectional converter with power decoupling capability. It has a highly modularized design, bidirectional and decoupled power control for each energy port, high efficiency and easy realization of ZVS, and good compatibility with different types of energy subsystems, which make it a promising topology for renewable energy systems. By connecting the independent current sources to a voltage bus or independent voltage sources to a current bus, the power flow between each energy port is decoupled and can be easily controlled. A current-bus-based multiport converter is discussed thoroughly, including its power control principle, modulation strategy, and ZVS realization. It is shown that the power flow directions of energy ports, as well as the high-order harmonics generated in the resonant tank, have great effects on the ZVS realization at different ports. A modified enhanced-phase-shift modulation by inserting an additional phase shift is proposed to alleviate the negative effects of high-order harmonics generated from energy ports with different power directions without introducing excessive reactive current. A minimum phase shift is derived under the worst-case scenario so that ZVS is ensured at all ports under all power flow conditions. Finally, a 1 kW, 96 V/72 V/300 V prototype is implemented to verify all theoretical analysis. ZVS is ensured under different operation modes and the system efficiency is above 91% over the full load range. [ABSTRACT FROM AUTHOR]

Plasma power supply is an important equipment to output an adjustable radio-frequency voltage for generating capacitively coupled plasma (CCP). Nowadays, radio-frequency power amplifier (RFPA) is popular for implementing plasma power supply. However, a bulky matching network is needed to be located between the RFPA and CCP, resulting in low power density and high system complexity. In this article, a buck-type inverter is proposed to directly power CCP, which not only outputs an RF ac voltage with low harmonics, but also realizes zero-voltage-switching for power switch over a wide capacitive load range. The derivation of the buck-type inverter is presented, and a step-by-step parameters design approach is proposed. Finally, a 13.56-MHz, 28-W prototypeis fabricated and a CCP discharge experiment is carried out. The experimental results are provided to verify the effectiveness of the proposed buck-type inverter and parameters design approach. The power density of prototype is 15 W/in3, which is much higher than traditional plasma power supply with 0.06 W/in3. [ABSTRACT FROM AUTHOR]

Recent developments of fast-charging power delivery protocols are driving ac–dc adapters to 100-W power ranges. Conventional solutions in this power range employing a two-stage topology and a big twice-line frequency buffer capacitor are generally costly and bulky. This article presents a patent-pending modulation method for an active-clamp flyback converter, allowing for a single-stage adapter design with reduced capacitance requirements and higher efficiency. This is achieved by exploiting the inherent energy storage capability of the clamping capacitor while turning it into an active power buffer. No hardware modifications are needed, while all salient features of active-clamp flyback converter, i.e., soft switching and leakage recycling, are retained. Operating principles and detailed controller design are discussed, and a 100-W laboratory prototype is built. The prototype achieves 94% peak efficiency and up to 92% size reduction of the buffer capacitor. The experimental evaluation shows that the new single-stage solution enabled by the proposed modulation method is superior to the conventional two-stage and single-stage solutions in terms of cost, conversion efficiency, and power density. [ABSTRACT FROM AUTHOR]

Traditional wireless power transfer (WPT) systems usually adopt the triple-phase-shift control method to maintain a constant output voltage, track the maximum system efficiency point (MEPT), and achieve zero-voltage-switching (ZVS) operation for various applications. However, these three targets are achieved at the cost of high reactive power on both primary and secondary sides, especially under light-load conditions, leading to low efficiency. This has become one of the challenges that hinder a further deployment of WPT technologies in practice. To address this vital problem, in this article, how the reactive power lowers the system efficiency is revealed based on a mathematical model established. Then, a hybrid modulation control strategy based on a proper selection between the full-bridge and half-bridge modes of the inverter and active rectifier is developed. An experimental prototype is constructed to verify the effectiveness of the proposed control method. Experimental results show that the proposed method can reduce the reactive power, maintain a constant output voltage, and realize the MEPT and ZVS operation, with high efficiencies up to 94.29% in a wide load range. [ABSTRACT FROM AUTHOR]

Conventional energy storage systems (ESSs) such as super-capacitors and lithium-ion batteries require voltage equalization systems to eliminate voltage imbalances, and bidirectional dc-dc converters to complete the charging process. These separated systems require some sensors, inductors, switches, and transformers. Consequently, the ESSs volumes, prices, and their complexity are dramatically increased by increasing the required series connected batteries count. Here, a self-equalized battery charger is proposed for lithium-ion batteries by combining a voltage multiplier (VM) and a phase-shifted full-bridge (PSFB) dc-dc converter. In the proposed self-equalized battery charger, the voltage multiplier eliminates the voltage imbalances and the PSFB dc-dc converter carries out the charging process. By combining the voltage equalizing and the charging systems into a single system, an integrated converter is obtained which leads to simultaneous charging and equalization operations, power and control sections simplicity, as well as low volume and price. By utilizing the phase-shift control method, zero-voltage-switching (ZVS) operation of power MOSFETs is obtained which leads to high efficiency and low EMI noise. The experimental results for 8 battery modules including 48 lithium-ion cells, are in good agreement with the given mathematical analyses and simulations and clearly show the simultaneous charging and voltage equalizing operations, as well.

To reduce the switching losses in high‐power inductive power transfer (IPT) system, this paper focuses on the zero‐voltage‐switching (ZVS) control strategy for a parallel multi‐inverter IPT system. First, the mathematical models of the parallel multi‐inverter IPT system are studied. Then, the compensation network parameters of the parallel multi‐inverter are designed, and the ZVS angles of #1 and #2 inverters are derived. Finally, a 1.2‐kW IPT system with parallel two‐inverter was built for experimental verification. The experimental results show that the ZVS angles of #1 and #2 inverters are equal whether at different Udc or different Po. This conclusion can provide a reference for the ZVS of the IPT system supplied by parallel multi‐inverter. To reduce the switching losses in high‐power IPT system, this paper focuses on the ZVS control strategy for a parallel multi‐inverter IPT system. A 1.2‐kW IPT system with parallel two‐inverter was built for experimental verification. The experimental results show that the ZVS angles of #1 and #2 inverters are equal whether at different Udc or different Po. [ABSTRACT FROM AUTHOR]

In this article, an efficiency-oriented control strategy is proposed for LCC–LCC-compensated wireless power transfer (WPT) system to achieve zero-voltage-switching (ZVS) operation over a wide current regulation range, in which full-bridge (FB) and half-bridge (HB) modes are combined and switchable based on requirements from load. The harmonic-considered time-domain models for FB and HB modes are first built to calculate current through the switches at the turn-off moment accurately. Then, focused on the constant voltage charge stage with variable output current, the ZVS boundaries are identified in HB and FB modes as the preferable control trajectories, which determines the desired current output with joint considerations of frequency, phase-shift angle, and duty ratio. Next, a least squares optimization method is introduced to fit the theoretical control trajectories into a smooth curve that is practical for implementation on microcontrollers. Finally, a 4.4-kW WPT prototype is built to verify the feasibility and validity of the proposed control strategy. Results show that a high system efficiency can be achieved over a wide output current range, with an efficiency of 94.68% even at 20% rated power. [ABSTRACT FROM AUTHOR]

This article proposes a high step-up quasi-resonant converter that minimizes switching loss over a wide range of input voltages. By employing a bidirectional switch and corresponding switching modulation, the proposed converter achieves the main switch with almost zero voltage, and therefore incurs very little switching loss at all active switches. Moreover, no instantaneous reactive current flows through the circuit under wide variations of input voltages and loads. The duty cycle of primary-side switches is fixed to 0.5; then, the input and clamp capacitor voltages become identical, and thereby the following resonant capacitor voltages remain in balance. As a consequence, the proposed converter becomes compact and achieves high boost-ratio and high efficiency over a wide range of input voltages. The operating principle of the converter is presented along with its design procedure. 400-W/380-V prototype of the proposed converter has been implemented and tested at 40–60 V to verify its effectiveness. [ABSTRACT FROM AUTHOR]

This article presents load independent zero-voltage-switching (ZVS) parallel resonant Class E inverter, which is based on parallel resonant Class E inverter. A new detailed analysis and design procedure at any duty ratio are introduced. This circuit can maintain ZVS and a constant amplitude ac output current over a wide range of load resistance from a nominal value to short circuit without additional elements or feedback control. A prototype circuit was designed with the proposed equations at the nominal load resistance 20.0  $\Omega$ , the output power 10.0 W, the output current 1 A, and the operating frequency 1.00 MHz. In circuit simulation using PSIM and in circuit experiments, ZVS and constant amplitude ac output current were confirmed at the load resistance 1.00, 5.00, 10.0, 15.0, and 20.0  $\Omega$. [ABSTRACT FROM AUTHOR]

Light load efficiency and output voltage regulation of a low-Q LLC resonant converter is a critical problem for wide input voltage and load range applications. Parasitic capacitances such as rectifier diode junction capacitance (Cj) degrade the soft switching performance. Compact size, high density, and high transformer turns-ratio requirements for microinverter applications add significant distributed capacitance (Cd) of the low-profile transformer, worsening the output regulation and zero-voltage-switching (ZVS) capability at light loads. Wide switching frequency requirement for regulation at light loads, which increases core losses and turn-off switching losses in power MOSFETs, further degrades the power conversion efficiency. The conventional phase-shift modulation causes a high circulating current and loss of ZVS at light loads. Therefore, a hybrid adjustable switching-frequency-duty-cycle modulation technique for improving the light load efficiency is proposed and analyzed for a full-bridge LLC resonant converter. Accurate loss analysis for the proposed modulation scheme, including the effect of parasitic capacitances, is performed using time-domain equations. The proposed methodology precalculates the optimal duty cycle at light load conditions for the required input voltage range such that minimum power losses are incurred. Variation in switching frequency at the preselected duty-cycle value regulates the output voltage. ZVS over a wide range of operating conditions is observed. An experimental prototype for a 20–40 V input, 380-V/300-W output LLC converter is tested for the validation of theoretical analysis. [ABSTRACT FROM AUTHOR]

A self-current balancing structure of the dual-transformer-based triple-port active bridge (DT-TAB) converter with the reduced component count is proposed in this article for future sustainable energy system applications. The proposed topology inherits good characteristics of the conventional triple-port active bridge (TAB) with even power sharing in an open loop as a newly added function. It can achieve high power density over the existing TAB converters that possess current-balancing function because the need for an auxiliary magnetic circuit or sophisticated control scheme in equalizing the shared power is eliminated. Besides, the demagnetization and magnetic short-circuit problems associated with the conventional TAB converters that are been eradicated, decoupled power flow management is achieved at all conditions. Moreover, the phase shift between the input H bridges gives an additional control degree of freedom that permits the control of the output power or offers independent control of voltage magnitude during the reverse power flow, thereby extending the system-operating range. The proposed DT-TAB converter has been adapted for the two-port operation. All the power switches achieved zero-voltage-switching turn-on. Finally, the robust operation performances of the proposed DT-TAB converter have been verified by the laboratory prototype assembled and tested up to 1 kW. The experimental results presented at the end are the proof-of-concept. [ABSTRACT FROM AUTHOR]

This article presents a novel isolated dc–dc converter circuit topology, which is able to offer high performance for a wide range of operating conditions. The prominent features of the proposed circuit topology include its direct power transfer (DPT) capability, quasi-rectangular waveform for the input current, and soft-switching performance for a wide range of operating conditions. The amount of power processed by the power switches and transformer is reduced through DPT. In addition, the quasi-rectangular waveform of the input current decreases its peak and root-mean-square values, leading to reduced conduction losses associated with the magnetics and power semiconductors. In the proposed structure, the power switches benefit from zero-voltage-switching characteristics, while the output diodes operate under zero-current-switching conditions. Thus, the proposed topology minimizes both the conduction and switching losses, thereby improving the overall efficiency. Extensive simulation and experimental results are provided to verify the feasibility of the proposed circuitry and demonstrate its superior performance. [ABSTRACT FROM AUTHOR]

Three-phase inverters are usually required to output reactive power in electric machine drives, renewable energy generation, static var generators, and other power electronic systems. Therefore, the inverter may operate within wide power factor angle range. However, the traditional zero-voltage-switching space vector modulation (ZVS-SVM) method for three-phase inverters is only applicable when power factor angle is between −π/6 and +π/6. In this article, a general ZVS-SVM method for three-phase inverter with arbitrary output is proposed. The principles for vector selection and vector sequence arrangement are discussed in detail. With only one switching operation of the auxiliary switch in each switching cycle, ZVS of all switches can be achieved. Operation stage analyses and ZVS condition of the inverter with the proposed method are introduced. In addition, the resonant parameters design considerations and loss analyses are investigated. Finally, the proposed ZVS-SVM method is verified by the experiment. [ABSTRACT FROM AUTHOR]

This article proposes a novel sawtooth-carrier based pulsewidth-modulation (SCPWM) method for quasi-Z-source inverter (qZSI) with the zero-voltage-switching (ZVS) operation to reduce the total harmonic distortion (THD) and inductor current ripple. The conventional variable-duty pulsewidth-modulation (VDPWM) method has been being used for qZSIs because it causes the low switching loss. However, this method has the limitation not only to improve the THD of output current but also to reduce the size of inductor when it is applied to the qZSI. To figure it out, the proposed SCPWM method uses the sawtooth-carrier signal while keeping the benefit from the use of variable duty. In particular, the ZVS operation occurs whenever the edge of sawtooth-carrier signal is located in the time interval of shoot-through state. This allows to increase the carrier frequency of qZSI without any additional switching loss. Thus, both the THD of output current and the inductor current ripple can be reduced while keeping the high efficiency of system. The operating principle of the proposed SCPWM method is first explained in detail. Thereafter, its performance is mathematically analyzed and compared with that of conventional VDPWM method. Finally, its practical effectiveness is verified by the hardware experimental test. [ABSTRACT FROM AUTHOR]

Zero-voltage-switching (ZVS) has been widely applied in widebandgap devices based on high-switching-frequency converters, for instance, dual-active-bridge isolated dc–dc converter, which consists of two H-bridges. To secure ZVS for all eight switches, previous literature mostly focuses on half-bridge to analyze switching transitions, which, however, is rather incomplete due to ignoring the impact of modulation strategies and cannot fulfill all circumstances. In this letter, the whole H-bridge is used as a unit to analyze the ZVS transient process, addressing the ZVS setting in different modulation strategies. The minimal initial inductor energy to complete the ZVS process is also quantified, which in return can reduce the transformer current, thereby enhancing the efficiency. Furthermore, the accurate ZVS transition time is derived incorporating with the nonlinearity of switch output capacitance, which can be further used to set the dead-band time. An H-bridge prototype with SiC devices is built up to verify the theory proposed in this letter. [ABSTRACT FROM AUTHOR]

The silicon carbide (SiC) devices have attracted more and more attention due to the capability of withstanding higher blocking voltage, higher switching frequency, and higher temperature. However, challenges for SiC devices applied in voltage-source-inverter fed motor drives such as electromagnetic interference (EMI) issues and limited over-current capability still limit the further application of SiC devices. In this article, a novel SiC devices based zero-voltage-switching (ZVS) current-source-inverter (CSI) is proposed for permanent-magnet synchronous motor (PMSM) drive. The key is to propose an auxiliary resonant circuit, which achieves ZVS conditions for all switches in power circuits and reduces the dv/dt of high speed SiC devices. The resonant capacitor in the auxiliary circuit can clamp overvoltage caused by possible open-circuit faults. To further reduce the EMI, the random switching frequency pulsewidth modulation is designed for the proposed CSI motor drive. The system configuration, working principle, circuit design, and control schemes are described in detail. Both simulations and experiments are presented to verify the effectiveness of the proposed ZVS-CSI fed PMSM drive system. [ABSTRACT FROM AUTHOR]

Single-phase zero-voltage-switching (ZVS) inverter with wide bandgap devices has higher efficiency and power density. However, the dc-side capacitor of the inverter will suffer double line frequency ripple and reduces the lifetime of the dc bus capacitor. Active power decoupling (APD) is an effective method to replace the short lifetime electrolytic capacitor with a smaller film capacitor. In order to help achieving the ZVS condition for ZVS inverter and the additional APD circuit, this article presents a ZVS topology for single-phase full-bridge inverter with APD circuit by adding an auxiliary branch between the dc source and the bridge legs. The auxiliary branch is composed of a clamping capacitor, an auxiliary switch, and a resonant inductor. A ZVS pulsewidth modulation scheme is proposed for a single-phase inverter with APD. The gate drive pulses are designed to realize the ZVS turn-on for the main switches of both APD circuit and single-phase full-bridge inverter. Circuit operation stages are analyzed and ZVS conditions are given. Finally, the proposed ZVS inverter with APD circuit is verified on a 1.5-kW inverter prototype. [ABSTRACT FROM AUTHOR]

Although the silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET) is superior to the conventional silicon (Si) insulated gate bipolar transistor in terms of switching performance, the switching losses of SiC devices increase rapidly by hard switching when the switching frequency (fsw) increase to hundreds of kilohertz (kHz). This paper proposes an auxiliary zero-voltage-transition circuit to realize zero-voltage-switching for all of the high-frequency main switches of the active neutral point clamped (ANPC) inverter based on a SiC/Si hybrid device, and zero-current-switching for all of the auxiliary switches. Through soft switching, the switching losses and anti-parallel diode reverse recovery losses of high-frequency SiC MOSFET switches can be further reduced. First, the circuit topology and the operation principle of the soft switching are detailed followed by the design procedure of the parameters. Then, the efficiencies of hard switching and soft switching ANPC inverters are compared with fsw changing from 10 to 200 kHz. To further improve the efficiency of the soft-switching inverter, two improved methods are proposed. The two proposed methods are auxiliary switches paralleling the external diode and utilizing synchronous rectification technology. Finally, a 1 kW, up to 200 kHz frequency ANPC inverter has been built to validate the above analysis. [ABSTRACT FROM AUTHOR]

Efficiency of wireless power transfer systems, based on inductive power transfer (IPT) technology, suffers significantly due to coil misalignment and load variations. Although numerous control strategies have been proposed in the past to improve the efficiency under these conditions, a technique that utilizes all freedoms of control simultaneously to maximize efficiency is yet to be reported. This article therefore proposes a multivariable control strategy that uses the optimal combination of all control variables to maximize the efficiency of IPT systems when regulating power and even under large coil misalignments and load variations. The article presents a comprehensive mathematical model, describing the underlying theory of the proposed optimal control philosophy, and investigates the performance and limitations of the proposed technique under wide range of operating conditions. To demonstrate the improvement in performance, theoretical results are presented in comparison to those obtained from a 1-kW prototype bidirectional IPT system, and also benchmarking against conventional control techniques. Results convincingly indicate that the proposed optimal control strategy regulates power at maximum efficiency despite large coil misalignments and load variations. [ABSTRACT FROM AUTHOR]

In battery equalization systems, string-to-cell (S2C) and cell-to-cell (C2C) structures each has its unique advantages and disadvantages regarding efficiency, components count, energy-flow-path length, and circuit extendibility. In this article, a novel hybrid battery equalizer combining the advantages of both S2C and C2C structures is proposed. The proposed hierarchical equalizer is based on half-bridge LLC resonant converter in the string-to-module layer and buck–boost converter in the two-level C2C layer. The characteristics of LLC converter are analyzed to fit the voltage equalization applications. The design considerations of LLC converter and buck–boost converter are addressed to ensure zero-voltage-switching among all mosfets and the optimal operation of each layer. Therefore, high conversion efficiency can be achieved in both layers. Comparing with other equalization techniques, the proposed hybrid structure achieves a good compromise among efficiency, components count, energy-flow-path length, and circuit extendibility. To validate the concept, a high switching frequency experimental platform is designed and tested to balance eight series-connected batteries. The experimental results well validate the theoretical analysis and the proposed design methodology. [ABSTRACT FROM AUTHOR]

In this article, a quasi-resonant (QR) flyback converter has been proposed for capacitor charging in a pulsed plasma thruster (PPT) of a nano-satellite. The energy in the transformer leakage inductance can be recycled to the resonant capacitor, suppressing the switch-off voltage spikes on the semiconductor power switch. The power switch is turned on with a hybrid switching mode. In this mode, valley-voltage-switching (VVS) is applied until the zero-voltage stress on the power switch is obtained, and zero-voltage-switching (ZVS) is used in the remaining charging process. Consequently, the switching-on loss is reduced, and charging efficiency is improved. When a capacitor bank of $2\mu \text{F}$ is charged to 1.5 kV (i.e., 2.25 J), the switching loss contribution of QR flyback converter using hybrid switching approach is reduced significantly to 0.61% while a flyback converter using hard-switching technique has a switching loss contribution of 15.24%. As a result, the proposed QR flyback converter improves the charging efficiency by 2.43%, from 72.69% to 75.12%. Moreover, the diode in the secondary side can be turned-on with zero-voltage and off with zero-current. Hence, the turn-on overshoot voltage and recovery loss are reduced. [ABSTRACT FROM AUTHOR]

In inductive power transfer (IPT) systems, zero-voltage-switching (ZVS) operation within wide power range is an urgent requirement to improve system efficiency and reduce electromagnetic interference. The combination of phase shift (PS) control and variable frequency control is usually adopted to realize ZVS operation. However, in inductor-capacitor-capacitor-series (LCC-S) systems, the abovementioned hybrid strategy cannot be used directly due to nonnegligible harmonics, which result in detection difficulties or imprecise calculation of turn-off current. To solve this problem, this article proposes an optimal variable frequency phase shift (VFPS) control strategy for LCC-S systems to realize ZVS operation within wide power range. The universal harmonic-considered time-domain model of LCC-S system is deduced, and thus, the switching-moment current of power switches can be calculated accurately. Based on this value, an optimal working trajectory for ZVS operation with minimum frequency variation is presented. Finally, a 2.2-kW IPT prototype is built up to verify the universality of the deduced model and the validity of the proposed optimal VFPS control. Compared with PS control and the VFPS control based on fundamental-harmonic-approximation method, the systems realizes ZVS operation under wide power range with efficiency increase of 2.6%–6.9% and 0.8%–8.8%, respectively, and a peak efficiency of 96.4% is achieved. [ABSTRACT FROM AUTHOR]

Featured with simple topology and easy realization of zero-voltage-switching, the Class E dc–dc converter is preferable for very high-frequency application. In this article, a multipower-level (MPL) hysteresis control is proposed for the Class E dc–dc converter, in which, multiple switching frequencies are selected for obtaining multiple input power levels, and the two adjacent input powers closest to the load power are chosen to synthesize the load power. Compared with the on–off control, which has only two input power levels, i.e., the input power in on mode and zero power in off mode, the MPL hysteresis control reduces the modulation frequency, and thus reducing the mode transition losses. Meanwhile, the conduction losses are also reduced. As a result, the efficiency of the converter is greatly improved. The parameters design and the switching frequencies selection for the Class E dc–dc converter with MPL hysteresis control are presented. Finally, a prototype of 10-W Class E dc–dc converter with 9–18 V input is fabricated and tested in the lab, and the experimental results are provided to verify the effectiveness of the proposed MPL hysteresis control scheme. [ABSTRACT FROM AUTHOR]

This article presents a fully zero-voltage-switching (ZVS) method and an optimal variable on-time (VOT) control for the predictive boundary conduction mode (BCM) boost power factor correction (PFC) converter. The operation analysis of the BCM boost PFC converter, which considers the parasitic capacitances, is performed. Based on the analysis, a novel Taylor approximation method to derive the equations of switching off-time for achieving fully ZVS is proposed. Then, an inductor current approximation method is applied to derive the VOT equation in order to reduce the input current total harmonic distortion (THD). A calculation method for selecting the accurate parasitic capacitance is proposed. Most importantly, the derived equations for achieving ZVS and VOT control are simple and take short calculation time in a DSP controller, and, thus, they can be applied to the predictive control. Experimental results demonstrate that the fully ZVS operation can be achieved by the proposed ZVS method. The input current THD is indeed improved by the optimal VOT control. [ABSTRACT FROM AUTHOR]

Multi-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) technology can fulfill the requirements of time-varying spatial positions of loads in mid-range applications, as it can generate a rotating magnetic field around sending coils, and effectively reduce the limits of spatial positions on transfer characteristics including output power and transfer efficiency. Nevertheless, the design of coils parameters and control strategies put a great influence on the realistic transfer characteristics, which should be considered elaborately in practice. In this paper, a three-phase MCR WPT system with cylinder-shaped coils is investigated, the equivalent circuit model is built to carry out the theoretical analysis. Based on that, the influence on zero-voltage-switching (ZVS) conditions of power switches and the output power of the system, resulting from different phase-shifted angles between each phase, coil turns and angular misalignments of the receiving coil, is analyzed comprehensively. Detailed discussions on relationships among coil turns, the angular misalignment, ZVS conditions, and the output power are completed under different phase-shifted angles. Furthermore, the parametric optimization of coil turns, as well as phase-shifted angles, are proposed to ensure the power switches realize ZVS and ensure the system realize stable output power within the full range of angular misalignment. Finally, experiments are carried out to evaluate the accuracy of theoretical analysis and confirm the validity of the proposed optimal design. [ABSTRACT FROM AUTHOR]

An optimized resonant converter with zero-voltage switching over an extensive range of loading is proposed to integrate renewable energy sources to an onboard charger. In conventional resonant circuit, high-frequency transformer (HF) parasitic components are used as tank circuit, this degrades the performance due to non-optimal magnetic components. Here, the HF transformer is fabricated with optimized resonant tank circuit shunt branch inductance ($L_p$) as magnetizing inductance, hence eliminating the need for shunt branch inductance. The proposed resonant converter circuit design is optimized for minimum kilovoltampere rating and better voltage regulation with both duty cycle and frequency control (mixed control method). Furthermore, the performance of the converter at a very light load is improved using the proposed control method. Incorporating a low- $R_{\text{DS}}(\text{ON})$ silicon carbide mosfet and softly turning off the switches for a wide load variation minimizes conduction and switching losses and improves efficiency. Using powder core for the design of the tank circuit reduces magnetic losses. A 3-kW prototype of the converter is built to verify the performance from no load to full load. The highest efficiency of the proposed converter is 98.6%, attained at 50% full load. [ABSTRACT FROM AUTHOR]

In this paper, a novel zero-voltage and zero-current switching (ZVZCS) interleaved two switch forward converter is proposed. By using a coupled-inductor-type smoothing filter, a snubber capacitor, the parallel capacitance of the leading switches and the transformer parasitic inductance, the proposed converter can realize soft-switching for the main power switches. This converter can effectively reduce the primary circulating current loss by using the coupled inductor and the snubber capacitor. Furthermore, this converter can reduce the reverse recovery loss, parasitic ringing and transient voltage stress in the secondary rectifier diodes caused by the leakage inductors of the transformer and the coupled inductance. The operation principle and steady state characteristics of the converter are analyzed according to the equivalent circuits in different operation modes. The practical effectiveness of the proposed converter was is illustrated by simulation and experimental results via a 500W, 100 kHz prototype using the power MOSFET. [ABSTRACT FROM AUTHOR]

The efficiency improvement of the on–off controlled Class E dc–dc converter operated at 20 MHz switching frequency is investigated in this paper. It is found that with the on–off control, the input power of the converter during the on mode increases with the increase of the input voltage, and it can be reduced by increasing the switching frequency. With this discovery, a variable switching frequency (VSF) on–off control is proposed, which slightly increases the switching frequency when the input voltage increases, maintaining the input power during the on mode slightly higher than the rated output power over the entire input voltage range, and thus highly improving the efficiency of Class E dc–dc converter at high input voltage. A prototype of 9-V–18-V input, 10-W Class E dc–dc converter has been fabricated and tested in the lab. The experimental results show that the proposed VSF on–off control improves the conversion efficiency of the Class E dc–dc converter by 4%–10% compared to the constant switching frequency on–off control. [ABSTRACT FROM AUTHOR]

A novel single-stage high-frequency link three-phase ($3\phi$) inverter along with a modulation strategy is presented in this paper. The topology is targeted for grid integration of utility scale renewable and alternative energy sources like solar, fuel cell, and wind, where the power flow is unidirectional (from dc to ac). The primary side converter has a $3\phi$ voltage source inverter (VSI) structure along with an additional half-bridge leg. Sinusoidal pulsewidth modulation is implemented in the primary side converter. The three legs of the primary side VSI are zero voltage switched (ZVS) for most part of the line cycle. The additional half bridge leg is ZVS over the complete line cycle. The active switches in secondary side converter are line frequency switched and thus results in negligible switching loss. The converter switching process is described in detail to show the soft-switching of the primary side converter using the device capacitances and leakage inductances of the high-frequency transformers (HFTs). The HFT galvanic isolation results in high power density. A 4-kW laboratory scale hardware prototype is built and tested with the proposed modulation strategy. The experimental results are presented to verify the converter operation. [ABSTRACT FROM AUTHOR]

Zero-voltage-switching (ZVS) mosfet grid inverter has distinct advantages such as higher efficiency and higher power density. However, the ZVS inverter may lose ZVS condition during startup stage if it does not start properly. It may increase the voltage stress on mosfets and even destroy the power semiconductor device. In order to achieve the ZVS condition for ZVS inverter during the startup stage, this paper proposes a safe startup method with an auxiliary clamping capacitor pre-charging circuit and designed ZVS pre-charging pulse sequence. The pre-charging circuit is enabled only at the startup stage. Theoretical analysis shows that the proposed method is capable of reducing the voltage stress during the startup stage for the ZVS inverter. Finally, the proposed safe startup method is verified on a 3 kW grid inverter. [ABSTRACT FROM AUTHOR]

The pulse-density-modulation (PDM) zero-voltage-switching (ZVS) full-bridge converter is a promising power converter for wireless power transfer (WPT) systems. The converter has the advantages of both direct conversion ratio control and load-independent soft switching. These advantages reduce the overall system complexity and power loss. However, the converter suffers from the limitations of large low-frequency subharmonics, a narrowed modulation range, and a large modulation delay. These limitations are caused by the existing PDM strategy, which was designed to generate a symmetric ZVS current to ensure the ideal ZVS for minimizing the switching loss. This paper finds that even with an asymmetric ZVS current, the ideal ZVS can still be ensured by the negative feedback effect of the dead-time voltage. Based on this finding, a PDM strategy that allows asymmetric ZVS currents is proposed to overcome the aforementioned limitations. In experiments, a ZVS full-bridge converter was modulated by the existing and the proposed PDM strategies, respectively. The converter performances and responses were compared and the results showed that the proposed PDM strategy can overcome the limitations while achieving ZVS. The proposed PDM strategy was also tested in a WPT system for verification. [ABSTRACT FROM AUTHOR]

The Class E dc–dc converter, with a simple topology and zero-voltage-switching (ZVS) for the power switch, can operate at a switching frequency of up to megahertz. In this paper, an optimized ZVS operation condition for minimizing the switch voltage stress, switch rms current, and switch voltage harmonic components is derived for the on‐off controlled Class E dc–dc converter by optimizing the time instant at which the switch voltage resonates back to zero. Based on this result, a step-by-step parameter design approach is proposed for a Class E dc–dc converter with a large input inductor, which avoids time-consuming simulations or complex numerical calculations. Then, a capacitance compensation approach is further proposed to extend the design results to a Class E dc–dc converter with a resonant input inductor. Furthermore, an adaptive duty-cycle adjustment scheme is proposed for reducing the reverse conduction loss of the power switch, thereby improving the conversion efficiency over the entire input voltage range. Finally, a prototype of a 20-MHz 10-W Class E dc–dc converter is built and tested in the laboratory, and experimental results are presented to verify the effectiveness of the proposed optimized parameter design approach and the adaptive duty-cycle adjustment scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active-clamp forward converter (ACFC) with a lossless-snubber on the secondary-side, which combines a resonant capacitor and a clamping diode with an output inductor in parallel. The conventional ACFC achieves zero-voltage-switching on switches of the primary-side during dead time for reducing the switching loss and voltage spike. Unfortunately, on the secondary-side of transformer, the voltage spike damages the free-wheeling diode and rectifier diode due to the reverse recovery current and junction-capacitor of the diode and leakage inductance of the transformer. This paper proposes a lossless-snubber on the secondary-side operation for reducing the voltage spike on the free-wheeling diode and forward-rectifier diode. Therefore, the converter proposed in this paper is suitable for high-output-current applications. Experimental results are shown to verify the analysis and design procedure of the proposed forward converter. [ABSTRACT FROM AUTHOR]

A zero-voltage-switching (ZVS) sinusoidal pulsewidth modulation (SPWM) method for a three-phase four-wire inverter is proposed in order to achieve higher efficiency and power density. With the proposed modulation scheme, the ZVS operation of all switches, including the main switches and the auxiliary switch, can be realized. Besides, all seven switches operate at a fixed frequency. The ZVS SPWM scheme is introduced by considering the various combinations of the polarities in three-phase filter inductor currents and the analysis of operating stages is presented. ZVS condition of the ZVS SPWM scheme is derived and discussions of ZVS condition for typical three-phase loads are also provided. In addition, the resonant parameters design and loss analysis are briefly investigated. Finally, the proposed ZVS SPWM scheme is verified on a 10-kW inverter prototype with SiC mosfet devices. [ABSTRACT FROM AUTHOR]

Although SiC-mosfet has significant advantages on switching performance over traditional Si-IGBT, the switching loss of SiC-mosfet devices at hard switching rises quickly with the increment in the switching frequency. This has narrowed down further possibilities of improving efficiency and power density of the grid inverter. Zero-voltage-switching (ZVS) space-vector-modulation (SVM) technique is introduced to further push the power density of SiC-mosfet inverter. This paper focuses on the impact of applying the ZVS-SVM to three-phase two-level SiC-mosfet inverter. With the same efficiency requirement the ZVS-SVM SiC inverter can operate at a much higher switching frequency, which gives the opportunity to further reduce the size of passive components. The loss distributions, conversion efficiencies, and volumes of passive components of both a 20-kW SiC-mosfet hard-switching inverter and a 20-kW SiC-mosfet ZVS-SVM inverter have been compared under switching-frequency range from 50 to 300 kHz. Meanwhile, a new metric called “efficiency stiffness” is proposed to compare different inverters with respect to the efficiency performance against switching-frequency characteristics. In addition, high voltage overshoot of SiC-mosfet and high thermal stress of resonant inductor are the two critical issues in the SiC-mosfet ZVS-SVM inverter with high switching frequency. A power module including seven SiC-mosfet bare dies with low stray inductance is designed for ZVS-SVM inverter instead of the existing seven discrete TO-247 package SiC-mosfets to reduce the voltage overshoots on the switches. Besides, to reduce the power loss of the resonant inductor caused by large amplitude of current at hundreds of kHz excitation frequency, design of the inductor with distributed air gap and optimal winding thickness are studied. A 20-kW SiC-mosfet ZVS-SVM grid inverter prototype is built to verify the proposed design. [ABSTRACT FROM AUTHOR]

The utilization of wide band gap devices has enabled high frequency operation of totem pole bridgeless PFC rectifier. However, most of the designs reported in the literature with frequency higher than 100 kHz operate under discontinuous conduction mode or critical mode to reduce the switching loss. This paper proposes a zero-voltage-transition (ZVT) technique for totem-pole PFC rectifier under continuous conduction mode operation which enables efficient operation at switching frequencies well above 100 kHz. A simple auxiliary circuit consisting of a small auxiliary inductor and two active switches is placed in parallel with the main input filter inductor to achieve zero-voltage-switching of the main switches. The auxiliary switches operate with zero-current-switching (ZCS) and conduct current as short resonant pulses only during the critical turn-on transition which results in very low losses in the auxiliary circuit. The timing of the auxiliary switches is adaptively controlled with respect to the grid voltage angle for optimized overall efficiency. The effectiveness of the proposed ZVT scheme has been validated through experiments based on a 2.4 kW 400 kHz hardware prototype with 98.35% peak efficiency. [ABSTRACT FROM AUTHOR]

This study presents a new portable eight-output light emitting diode (LED) driver. The eight output-channels are divided into two equal groups, and their output powers can be controlled individually by three active switches. In addition, a simple capacitor-based passive current balancing circuit (CBC) is employed in each port to guarantee that the currents of the four LEDs are the same. When compared with the conventionally used separate two-output isolated converters, the proposed one uses one less active switch. Moreover, zero-voltage-switching (ZVS) is achieved, which improves the power efficiency of the driver. Finally, a highly compact prototype is built, which can reach an efficiency of 94.6%. [ABSTRACT FROM AUTHOR]

LLC resonant converter is a soft switching frequency modulated dc–dc topology with its switching frequency near the resonant frequency. However, in applications where a wide output voltage is desired, it is extremely difficult to tune its operation close to the resonant frequency. In this paper, a novel pulsewidth modulated LLC type resonant converter based on voltage quadrupler rectifier is proposed. The proposed converter always operates at the resonant frequency and is able to achieve a wide output voltage range by modulating the duty cycle of the secondary side auxiliary mosfet. This brings the benefits of the decreased circulating current and corresponding conduction loss, as well as the simplification of the parameters selection and magnetic component design. Zero-voltage-switching and zero-current-switching are realized among all power mosfets and all power diodes, respectively. Detailed circuit operation principles and modeling method are presented. A 1.3-kW converter prototype, generating 250–420 V output from 390-V dc-link is designed. Both the circuit functionality and the theoretical analysis are verified in the experimental results. [ABSTRACT FROM AUTHOR]

In conventional LLC-based plug-in electric vehicle (PEV) onboard chargers, the battery pack voltage varies in a wide range with the change of state of charge. This makes it difficult to optimally design the pulse frequency modulated LLC resonant converter. Besides, the voltage regulation of the LLC converter is highly dependent on the load conditions. In this paper, a modified pulse width modulated (PWM) LLC type resonant topology (PWM-LLC) is proposed and investigated in PEV charging applications. The switching frequency of the primary LLC network is constant and equal to the resonant frequency. The voltage regulation is achieved by modulating the duty cycle of the secondary side auxiliary mosfet. Compared with the conventional LLC topology, the proposed topology shrinks the magnetic component size and achieves a wide and fixed voltage gain range independent of load conditions. Meanwhile, zero-voltage-switching and zero-current-switching are realized among all MOSFETs and diodes, respectively. A 100-kHz, 1-kW converter prototype, generating 250–420 V output from the 390-V dc link, is designed and tested to verify the proof of concept. The prototype demonstrates 96.7% peak efficiency and robust performance over wide voltage and load ranges. [ABSTRACT FROM AUTHOR]

This paper presents a new topology for a fully bidirectional soft-switching solid-state transformer (S4T). The minimal topology, featuring 12 main devices and a high-frequency transformer, does not use an intermediate dc voltage link, and provides sinusoidal input and output voltages. The S4T can be configured to interface with two- or multiterminal dc, single- or multiphase ac systems. An auxiliary resonant circuit creates zero-voltage-switching conditions for main devices from no-load to full-load, and helps manage interactions with circuit parasitic elements. The modularized structure allows series and/or parallel stacking of converter cells for high-voltage and high-power applications. [ABSTRACT FROM PUBLISHER]

A novel zero-voltage-switching (ZVS) bidirectional dc/dc converter for energy storage system is proposed in this paper. The primary side is the improved push–pull topology adding one switch to achieve ZVS and the secondary side is a full-bridge topology. Compared with the conventional dual-active-bridge (DAB) dc/dc converter, the proposed converter applies a three-switch topology substituting for the full-bridge structure in the low-voltage side of transformer with seven switches in all. With minimum switch, the cost of the driving circuit can also be saved and the stability of the whole system can be better guaranteed. Most of all, the proposed converter can realize the advantages of DAB, such as bidirectional power transmission and ZVS. Besides, it has no increase in power losses and transformer volume reaching relatively the same effect of the DAB. The operation principles, comparative analysis, design, and control strategy are presented in detail. A 500-W laboratory prototype is built to verify the theoretical analysis and demonstrate the validity of the converter. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel multi-element resonant converter with self-driven synchronous rectification (SR). The proposed resonant converter can achieve a zero-voltage-switching (ZVS) operation from light load to full load, meanwhile, the zero-current-switching (ZCS) can achieve rectifiers of a secondary-side. Therefore, the switching losses can be significantly reduced. Compared with an LLC resonant converter, the proposed resonant converter can be effective to decrease the circulating energy through the primary-side of the transformer to output a load and provide a wide voltage gain range for over-current protection as well as decreasing the inrush current under the start-up condition. Moreover, the proposed converter uses a simple current detection scheme to control the synchronous rectification switches. A detailed analysis and design of this novel multi-element resonant converter with self-driven synchronous rectification is described. Finally, a DC input voltage of 380-VDC and an output voltage/current of 12-VDC/54-A for the resonant converter prototype is built to verify the theoretical analysis and performance of the proposed converter.

Direct and quadrature (DQ) rotating magnetic-field-based transmitting (Tx) coils for wireless charging of multiple internet of things (IoT), which are broadly distributed over three-dimensional (3D) spaces, are newly proposed in this paper. The proposed Tx coils provide a uniformly distributed DQ magnetic field environment so that numerous IoT, such as active radio frequency identification (RFID) tag, electric shelf label (ESL), appliances, and various sensors connected to internet, are charged with 3-D omnidirectional wireless charging. By virtue of the generated DQ magnetic field, six degrees of freedom (6-DoF), regardless of their three-axes positions and directions, are achieved by the proposed Tx coils with plane receiving (Rx) coils, which is essential for the proposed ubiquitous wireless power environment. Therefore, the proposed wide-range ubiquitous inductive power transfer (IPT) is highly recommended for adoption in practical applications, where volumetric structures with large size of core are not allowed. The optimum distance between the DQ lines of the proposed Tx coils dw was found by magnetic field analysis to deliver maximum magnetic field Bt at a target distance of $z_{{1}}$. To generate DQ currents and guarantee zero-voltage-switching operation of the main switches, detailed static analysis of the proposed DQ Class D inverter based on an imaginary gyrator model is presented. The effective area ratio of an Rx coil having a ferrite core is derived and experimentally found in this evenly distributed magnetic field condition. 1:20 and 1:1 scaled-prototypes for d_{l}\,= \,{\text{10}}\;\text{m} and 5 m DQ line cases, respectively, were installed on the ceiling and experimentally verified for the uniformity of magnetic field and the highest wireless power delivery freedom. Experimental results showed that the proposed IPT has 78% of uniformity for magnetic field and Rx coils are freely charged with a 6-DoF characteristic. Two hundred of Rx coils, which are arbitrarily distributed over 3-D space, can be simultaneously charged with 16.2 W of total received load power and 9.3% of power efficiency. [ABSTRACT FROM AUTHOR]

This paper presents an isolated LLC series resonant DC/DC converter with novel frequency adaptive phase shift modulation control, which suitable for wide input voltage (200–400 V) applications. The proposed topology integrates two half-bridge in series on the primary side to reduce the switching stress to half of the input voltage. Unlike the conventional converter, this control strategy increases the voltage gain range with zero-voltage-switching (ZVS) to all switches under all operating voltage and load variations. Adaptive frequency control is used to secure ZVS in the primary bridge with regards to load change. To do so, the voltage gain becomes independent of the loaded quality factor. In addition, the phase shift control is used to regulate the output voltage as constant under all possible inputs. The control of these two variables also significantly minimizes the circulating current, especially from the low-voltage side, which increases the efficiency as compared to a conventional converter. Experimental results of a 1-Kw prototype converter with 200–400-V input and 48-V output are presented to verify all theoretical analysis and characteristics. [ABSTRACT FROM AUTHOR]