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Non-isolated high-voltage gain soft-switching dc-dc converter is an ideal candidate for distributed generation system converters. This paper proposes a high-voltage gain soft switching quasi-Z-source dc-dc converter. The converter integrates a coupled inductor and switched capacitor into a quasi-Z-source network. Soft switching is achieved for all active devices in the converter by controlling the auxiliary switch Sa. By inheriting the advantages of the quasi-Z-source network and coupled-inductor/switched-capacitor, the converter has high voltage gain, high efficiency, low input current ripple, low voltage spike of main switch, and common ground. In addition, the efficiency of the converter is improved by recycling the energy of leakage inductance, resulting from an inherent active clamp of the main switch. The steady-state operation, voltage relationship, current/voltage stress, and power dissipation of each component of the converter have been analyzed and derived in detail. The properties of the proposed converter are verified by designing a 200 W prototype in the laboratory. When the input voltage is 48 V and the output voltage is 380 V, the converter efficiency reaches 96.92%, while the efficiency is 93% in a hard switching. The key waveforms of the converter obtained from the experiment agree well with the theoretical analysis results.

This paper proposes a high step-up dc-dc converter with a continuous input current which is suitable for sustainable energy systems. A three-winding coupled inductor, two power switches, three diodes, and three capacitors are utilized to perform the functions of active switched inductor and switched capacitor. By charging the two primary windings in parallel, and discharging the two primary windings in series to the intermediate capacitor and the output, the conversion ratio can be further improved with lower voltage stresses and current stresses on its power switches. In addition, the energy stored in the leakage inductance is recycled to reduce the voltage spikes of the power switches. Eventually, a laboratory prototype with an input voltage of 36 V - 48 V, and output voltage of 400 V - 600 V with a rated power of 600 W is implemented to validate the correctness and effectiveness of the theoretical analyses. The maximum efficiency and full load efficiency are 97 % and 96.2 %, respectively.

This paper discusses electrical design optimization of a 3.3 kW, 380 V to 250-380 V, 500 kHz, dual-active-bridge dc-dc converter for on-board chargers, operated with constant-power (CP) charging. In order to operate the converter at 500 kHz without concerns on switching performance and efficiency while also improving power-density, a low-parasitics, PCB-based, wire-bondless full-bridge module featuring bare-die SiC MOSFETs and compact, electro-thermally multi-functional coolers is employed. High switching frequency operation also felicitates realization of the DAB inductor using the transformer’s leakage inductance, thereby enhancing power-density by eliminating the need for a discrete inductor. Design strategy for such magnetic integration in a planar transformer is discussed followed by a systematic design optimization of the transformer, including selection of leakage inductance value, core geometry and number of turns for achieving zero-voltage-switching (ZVS) and maximum average efficiency over the entire charging profile. Experimental validation was performed using a proof-of-concept prototype, which is operated up to 3.3 kW and has a final projected power density of 5.44 kW/L. Results demonstrate operation with ZVS over the entire charging profile with satisfactory high-frequency waveforms and a peak efficiency of 98%.

This article introduces a push–pull series connected (PPSC) ac–dc converter intended for high-voltage direct current applications. The proposed topology requires fewer submodules compared to a standard modular multilevel converter (MMC) to withstand the same dc voltage. Each converter phase unit is connected to its corresponding phase on the ac side via a center-tapped single-phase transformer which also provides the galvanic isolation needed in most applications. The required arm inductance can be merged into the transformer leakage inductance avoiding the need for additional inductors. In this article, both the design and operation of the converter are discussed in detail. Furthermore, a comparison of the PPSC and MMC in terms of energy storage requirements and efficiency is presented. The converter concept and the control strategy proposed is validated by computer simulations using the piecewise linear electrical circuit simulation (PLECS) simulation package as well as through experiments on a small-scale, 300-V, 2-kW laboratory prototype.

This paper presented a high-efficiency push-pull resonant converter solution for auxiliary power supply in 70 kV isolated applications. This power supply consists of a two-stage structure with a resonant push-pull inverter and a buck regulator. A series resonance is introduced in the inverter with its operation and parameter design to achieve high-efficiency voltage isolation. A buck converter with feedforward control is presented with the small-signal model and controller design to regulate the output voltage. Besides, the transformer is another challenge as a crucial part of the voltage isolation. Specifically, the optimization design of toroidal core and sector windings is presented, including the analysis of isolation, loss analysis, and leakage inductance. The paper presents comprehensive converter and transformer models, describing the proposed power supply’s design process. Furthermore, a case study is demonstrated under 70 kV isolation with 36 V-84 V input and 48 V output. A prototype of a 200 W, 1.4 L isolated power supply has been built to demonstrate the design model’s validity and process. Results convincingly indicate that the proposed converter has the highest efficiency of 93.1% and can maintain the 70 kV isolation voltage with good regulation performance.

In this article, a 10 MHz dc/dc converter based on three-dimensional air core transformer with zero-phase difference synchronous driving signals is designed. By using the characteristics of no leakage inductance in the inner winding of the nested toroidal air core transformer, the phase difference between the output voltage of the inverter and the input voltage of the rectifier can be regarded as zero, so that the rectifier and the inverter can use the same driving signal, which simplifies the control of the synchronous rectifier switches, and realizes the reliable and efficient synchronous rectification control at 10 MHz. The prototypes with primary and secondary compensation are proposed and the experimental results verify the feasibility of the proposed control method and numerical design method.

This article proposes a new high step-up DC-DC converter for fuel cell applications. Built-in transformers and voltage multiplier cells are integrated into the structure to step-up the voltage gain. The paper proposes a new topology with common ground. Two of them are connected using the dual boost concept. Thus, the final structure provides input current interleaved that reduces the current ripple, output-series connection that increases the voltage gain and floating ground on the output voltage, which can be a limitation for some applications. Additionally, on designing the built-in transformer with a leakage inductance value much less than the magnetizing inductance value (less than 0:5%), the proposed topology does not need a clamp circuit, which reduces the number of components and increases the efficiency. Operational steps, static gain analysis, and design guide of the new converter are described in details herein. Furthermore, a 1 kW, 48-800 V prototype was built to verify the theoretical analysis. Tests in laboratory reached 94:60% of maximum efficiency at 480 W and 93:00% of efficiency at 1.0 kW (rated power).

In order to deal with the challenges in establishing a high input voltage high step-down auxiliary power supply (APS) for modular converters, a flyback converter utilizing series-connected silicon carbide (SiC) MOSFETs is proposed in this article. With the aid of a novel snubber circuit structure, the used series-connected SiC MOSFETs can switch with nearly perfect dynamic voltage sharing. Besides, the snubber circuit acts as voltage clamping circuit for the flyback converter, so voltage overshoot caused by transformer leakage inductance can be effectively controlled. Furthermore, the snubber circuit helps to power the control, gate driver, and startup circuits of the APS, leading to a reduction in system complexity and improvement in efficiency. Detailed circuit analysis and design considerations of the APS are presented. Finally, hardware of a 4 kV/120 W APS is established and experimentally verified.

Purpose Despite its well-founded criticism and lack of proper justification under core saturation conditions, the T-equivalent transformer model (Steinmetz scheme) is obviously championing in the literature. This educational paper aims to explain in a simple manner the limitations of the T-model of a low-frequency transformer and critically analyses some attempts to improve it. Design/methodology/approach Using a simplified examination of magnetic fluxes in the core and windings and using the modeling in ATPDraw, it is shown that transient transformer models with the indivisible leakage inductance allow circumventing the drawbacks of the T-model. Findings The authors show the absence of valid grounds for subdividing the leakage inductance of a transformer between its primary and secondary windings. The connection between the use of individual leakage inductances and inaccurate prediction of inrush current peaks is outlined as an important example. Practical implications The presented models can be used either as independent tools or serve as a reference for subsequent developments. Social implications Over generations, the habitual transformer T-equivalent is widely used by engineers and Electromagnetic Transients Program experts with no attention to its inadequacy under core saturation conditions. Having studied typical winding configurations, the authors have shown that neither of them has any relation to the T-equivalent. Originality/value This educational paper will contribute to the correct understanding of the transients occurring in a transformer under abnormal conditions such as inrush current or ferroresonance events, as well as during an out-of-phase synchronization of step-up generator transformers.

An isolated high step-up converter, which is derived from the reverse structure of a regular LLC resonant converter, is proposed in this article. The proposed converter consists of an inverter stage, a secondary-side resonant tank, and an active voltage-doubler rectifier. An additional input diode is introduced into the regular push–pull inverter so as to make the magnetizing inductance free from being always clamped by the input voltage and make up new voltage gain features. The leakage inductance, which always shows a significant value when reflected to the secondary side in a high step-up transformer, can be used to make up the resonant tank. Under a simple pulse-frequency-modulation control with 0.5 duty ratios for both the primary-side and secondary-side switches, a high step-up function can be easily realized by the converter with good load regulation ability. Meanwhile, synchronous rectification (SR) can be naturally achieved by the secondary-side switches. The additional input diode can be replaced by a MOSFET with an analog SR chip to further improve the efficiency, without changing the original control scheme. The validity of the study is confirmed by a 500-W prototype with 36–42 V input and 380-V output. The peak efficiency can reach 96.9%.

A current-fed dual-inductor resonant full-bridge dc–dc isolated boost converter is proposed. The converter is most suitable for applications that demand wide input voltage and load ranges. It can be used as a front-end dc–dc converter that can boost variable low voltage from a power source [battery (home/industrial inverter/industrial UPS application), fuel-cell, or solar-PV] and interface it to a high-voltage dc-link, which typically feeds an inverter. It removes all major drawbacks of conventional current-fed isolated dc–dc converters, namely high-voltage spikes across the switches due to transformer leakage inductance, need for additional start-up circuit, and difficulty in converter tripping in case of faults. Soft-switching of rectifier didoes and clamping power switches is load independent leading to good efficiency over entire load range. Converter can be operated with D < 0.5, making it suitable for wide input voltage range applications. A detailed comparative analysis with state-of-the-art converters for wide input voltage range applications considering the major important factors, such as power device utilization, transformer utilization, inductive energy requirement, and dc capacitors utilization, confirms the superiority of the proposed converter. Experimental results for a 2.5 kVA inverter application with an input dc voltage range of 90–160 V and output ac voltage of 230 V are provided.

Bidirectional dc–dc converters with storage devices and high-voltage conversion ratio are widely utilized in renewable energy systems in order to manage power flow between renewable sources, storage devices, and load. One of the most important parameters in these converters, which affects the lifetime of storage devices, is the pulsating current flowing through them. This article presents a bidirectional buck/boost converter that employs a coupled inductors technique to increase the voltage conversion ratio while the current in low-side voltage source is continuous. Furthermore, only an active clamp circuit, including a clamp capacitor and an auxiliary active switch, is utilized to create soft-switching conditions for the main switches and absorb the leakage inductance energy of coupled inductors for both high step-up/step-down operating states. In this converter, the soft-switching condition is provided for all switches without any extra element in the power flow direction. Also, all diodes turn off at the ZCS condition, which removes the reverse recovery problem. A low number of elements and fully soft-switching condition for all semiconductor devices have contributed to the converter efficiency. Theoretical analysis of the proposed converter in both operating states is presented in detail, and a 500-W prototype circuit is implemented to verify the validity of the theoretical analysis and converter performance.

Some advantages of the SEPIC buck-boost converter makes it stand out from other configurations. It makes possible to obtain from a unipolar input voltage both unipolar and bipolar output voltage with a good symmetry between positive and negative output voltages. It also provides efficient performance as well as circuit simplicity in unipolar and bipolar topology owing to the use of a single switch which can be operated by available integrated controllers of boost converters. The article considers the topologies of a SEPIC buck-boost converter built according to the traditional scheme (with two inductors) and according to the scheme on magnetically coupled chokes. To analyze the processes and factors affecting the converter operation efficiency, a circuit simulation has been done using the Electronics Workbench. The results of the investigation of a pulsed DC converter of input voltage to unipolar or bipolar output voltage using SEPIC buck-boost topology are presented. The circuit simulation enables to specify the switching process characteristics, to estimate the ripple level of the input current and its spectral characteristics, and to develop recommendations concerning the choice of parameters of converters elements and generation of control signals. Based on the simulation results, the load, control, and noise characteristics of the converter are obtained. The level of symmetry of positive and negative output voltage is investigated for the converter on discrete and magnetically coupled chokes. The assessment of the effect of leakage inductance on converters with magnetic coupling of inductive elements is given. Examples of practical implementation of converters built according to the SEPIC topology are shown. It is found that the resistance of the choke windings, which is less than 0.5 Ohm, has practically no effect on the efficiency of the converter, retaining the factor of about 0.9 in a wide range of load currents, while the main source of conversion losses is a passive diode switch. Synchronous converter circuits of a number of manufacturers are more efficient, but require more complex controllers for active switches with elements for protection against through currents.

This article proposes a novel bidirectional isolated dc–dc converter with high voltage gain and wide input voltage, which can be applied to bidirectional power conversion systems. The proposed topology is composed of a bidirectional buck-boost converter and a forward-flyback converter; it has the advantage of higher voltage gain and has continuous current characteristic of the low-side port in step-up and step-down mode. In addition, the proposed topology also has the function of leakage inductance energy recovery, which can improve the efficiency of the converter, reduce the voltage surges on switches, and have the characteristics of zero voltage switching on certain switches. Finally, this paper implements a 500-W bidirectional dc–dc converter to verify the feasibility of the proposed topology. The low-side voltage of the proposed topology is 24, 48, and 55 V; the maximum efficiency in step-up mode are 94.2%, 95.6% and 96.9%, and the maximum efficiency are 92.6%, 94.2% and 94.5% in the step-down mode, respectively.

A high gain nonisolated dc–dc converter is proposed for the distributed generation systems. High voltage gain is achieved by integrating different methods with reduced duty ratio. Inductive voltage spikes across MOSFET s are alleviated and stress is reduced with inclusion of a passive-clamp circuit. Thus, lower voltage rating (small ${R}_{\text{ds}({\textsc {ON}})}$ ) active devices can be adopted. Using this clamp, zero-voltage switching over wide load range is achieved for both the MOSFET s. In addition, leakage energy of the coupled inductor is recycled without using auxiliary switch and thus, the gain get further improved. Zero-current switching is obtained for all the diodes using quasi $-$ resonance principle, which diminishes voltage spikes across the diode caused by the parasitic ringing between leakage inductance and diode's stray capacitance. Therefore, snubbers are not necessary to protect the diodes and to mitigate reverse-recovery losses. Overall efficiency improves because of lower switching and conduction losses of the semiconductor devices. A 600 W prototype working at 75 kHz is built in the laboratory to verify the performance. The peak efficiency is nearly 96.5% and is above 95% for wide load range.

In order to avoid the bus voltage spikes caused by leakage inductance endangering the normal operation of the inverter, based on the improved Y-source inverter, the traditional clamping structure and voltage peak absorption circuit are introduced, and a high step-up and low-voltage stress improved Y-source inverter with the capability of absorbing bus voltage spike is proposed. This topology fully utilizes the structural characteristics of the improved Y-source inverter itself, and further increases the DC-side voltage gain on the basis of ensuring the busbar voltage peak absorption capacity, while reducing the capacitor voltage stress. This paper demonstrates the superiority of the proposed topology over improved Y-source inverter topology by analyzing its working principle and voltage gain, simulation and experiment platform are constructed to perform the circuit simulation and experiment, and the correctness of the theoretical analysis of the proposed inverter and the effectiveness of the busbar voltage peak absorption capacity are verified.

In this article, we propose a novel interleaved high step-up converter. The proposed converter integrates the built-in transformer voltage multiplier cell (VMC) to the interleaved boost converter with voltage lift capacitor. The voltage gain is increased by both of the turns ratio of the built-in transformer and the voltage lift capacitor. Hence, there is no need to operate the converter around unity duty cycles to obtain high voltage gains. Meanwhile, the voltage stress across semiconductors is reduced considerably, facilitating the utilizing of mosfet s with low on -state resistance and diodes with low forward voltage drop decreasing the conduction losses. The leakage inductance of the built-in transformer not only provides zero current switching (ZCS) for mosfet s but also controls the falling current rate of the diodes alleviating the reverse current recovery problem. In addition, the energy of the leakage inductance is recycled by the clamp capacitor avoiding high spikes across switches. In comparison with the recently published converters, the proposed converter introduces all of the abovementioned advantages with a low number of components that make it an interesting solution for high efficiency and high step-up applications. Finally, a 40-V to 580-V prototype with 930 W power is fabricated to explore the merits of the proposed converter.

This paper deals with a control system and an algorithm of Lithium-ion battery fast charging. Charger structure consists of an electromagnetic filter, two parallel full-bridge DC-DC converters with low-pass filter. The parallel full-bridge DC-DC converter has two isolated transformers. Sometimes, changes are observed in the transformer ratio and the leakage inductance due to a fault caused by partial short circuit in the transformer. In addition, a transformer is rarely open circuit by a fault or out of service for maintenance. So, a control system which is based on sliding mode control is used for covering the uncertainties of transformer ratio and its leakage inductance. The transformer ratio has an important role in state-space equation of the charger circuit and has important effects on the control system in constant current and constant voltage modes. Therefore, this paper analyses the impact of the parameters of isolated transformer and the control system on the reference signal tracking and the accuracy of current sharing between two parallel DC-DC converters. The simulation results show the effectiveness of the proposed control system.

Triple active bridge (TAB) as an isolated multiport converter is a promising integrated energy system for smart grids or electric vehicles. This article aims to derive and analyze zero voltage switching (ZVS) regions of TAB, in which both switching losses are reduced, and electromagnetic interference issues are mitigated. In the proposed closed-form solution of ZVS criteria, parameters such as the parasitic capacitance of the switches, the leakage inductance of the transformer, the switching frequency, the port voltage, the phase-shift inside and between the full-bridges are all taken into account. The analysis shows how the five degrees of freedom can be used to maintain ZVS operation in various operating points. The analysis and derived closed-form ZVS criteria are experimentally verified using a laboratory prototype. The derived analytical ZVS criteria are a powerful tool to study and optimize the operation of TAB converters.

Solid-state transformers (SSTs) are a promising solution photovoltaic (PV), wind, traction, data center, battery energy storage system (BESS), and fast charging electric vehicle (EV) applications. The traditional SSTs are typically three-stage, i.e., hard-switching cascaded multilevel rectifiers and inverters with dual active bridge (DAB) converters, which leads to bulky passives, low efficiency, and high electromagnetic interference (EMI). This article proposes a new soft-switching solid-state transformer (S4T). The S4T has full-range zero-voltage switching (ZVS), electrolytic capacitor-less dc link, and controlled dv/dt , which reduces EMI. The S4T comprises two reverse-blocking current-source inverter (CSI) bridges, auxiliary branches for ZVS, and transformer magnetizing inductor as a reduced dc link with 60% ripple. Compared with the prior S4T, an effective change on the leakage inductance diode is made to reduce the number of the devices on the main power path by 20% for significant conduction loss saving and retain the same functionality of damping the resonance between the leakage and resonant capacitors and recycling trapped leakage energy. The conduction loss saving is crucial, being the dominating loss mechanism in SSTs. Importantly, the proposed single-stage SST not only holds the potential for high power density and high efficiency but also has full functionality, e.g., multiport dc loads integration, voltage regulation, and reactive power compensation, unlike the traditional single-stage matrix SST. The S4T can achieve single-stage isolated bidirectional dc–dc, ac–dc, dc–ac, or ac–ac conversion. It can also be configured input-series output-parallel (ISOP) in a modular way for medium-voltage (MV) grids. Hence, the S4T is a promising candidate for the SST. The full functionality, e.g., voltage buck–boost, multiport, etc., and the universality of the S4T for the dc–dc, dc–ac, and ac–ac conversion are verified through the simulations and experiments of two-port and three-port MV prototypes based on 3.3 kV SiC mosfet s in dc–dc, dc–ac, and ac–ac modes at 2 kV.

This article presents the design of a dual-mode V-band power amplifier (PA) that enhances the efficiency at power back-off (PBO) using load modulation. The PA utilizes a reconfigurable two-/four-way power combiner to enable two discrete modes of operation–full power and back-off power. The power combiner employs two techniques to further improve the PA efficiency at PBO: 1) usage of transformers with non-uniform turns ratios to reduce the difference in impedance presented to the PA cores between the two modes and 2) utilize a proposed switching scheme to eliminate the leakage inductance associated with the disabled path in back-off power mode (BPM). The two-stage PA achieves a peak gain of 21.4 dB with a fractional BW (fBW) of 22.6% (51–64 GHz). At 65 GHz, the PA has a Psat of +17.9 dBm with an OP1 dB of +13.5 dBm and a peak power added efficiency (PAE) of 26.5% in full-power mode. In BPM, the measured Psat, OP1 dB, and peak PAE are +13.8 dBm, +9.6 dBm, and 18.4%, respectively. The PAE is enhanced by 6% points at a 4.5-dB back-off. The PA is capable of amplifying a 6 Gb/s 16-QAM modulated signal with an EVMrms of −20.7 dB at an average Pout/PAE of +13 dBm/13.6%, respectively. This PA was implemented in 16-nm FinFET, occupies a core area of 0.107 mm2, and operates under a 0.95-V supply.

This article proposes a high-power density 1.8 kW auxiliary power module (APM) for electric vehicles (EVs) based on gallium nitride devices. A design procedure for the high-frequency phase-shift full-bridge with current-doubler rectifier using printed circuit board (PCB)-based planar magnetics is proposed. Leakage inductance analysis of the high-frequency pulsewidth-modulation converter is given to achieve both regulation and zero-voltage-switching turn- on . Then, the magnetics optimization procedure for the customized planar core is proposed with a magnetic figure-of-merit concept to meet the high-power density target. Technical considerations are detailed to meet the extreme temperature constraint imposed on the EVs components. Finally, the proposed APM is demonstrated with a switching frequency of 700 kHz and a power density of 8.1 kW/L (132.8 W/in3).

Nowadays the use of electronic equipment finds a progressive development in the modern world. Hence it becomes a mandate to check whether the harmonic content of line current of any electronic device which is connected to the ac supply meets the appropriate standards. This demand is satisfied by implementing the Power Factor Correction (PFC) circuit in order to make the input current to be in sinusoidal in nature and in-phase with the input voltage. Numerous solutions are available to make the line current almost sinusoidal. This paper describes an isolated power factor corrected power supply that utilizes the leakage inductance of the isolation transformer to provide boost inductor functionality. The bulk capacitor is in the isolated part of the power supply allowing for controlled startup without dedicated surge limiting components. A control method based on switch timing and input/output voltage measurements is developed to jointly achieve voltage regulation and input power factor control.

Dielectric barrier discharge (DBD)-based plasma reactor and lamp are widely used for the growing areas of medical science, bacterial disinfection, pollution control, surface treatment, and so on. In this article, a simplified high-frequency, high-voltage short-pulse power modulator (HV-SPPM) is proposed for DBD plasma sources that are effectively capacitive loads. An energy discharge circuit (EDC) has been devised in the HV-SPPM to terminate the high-voltage pulses increase indefinitely for a capacitive load, which causes damage to the pulse power modulator. The HV-SPPM is using a wide bandgap (WBG) device without having a dissipative snubber circuit on primary side and magnetic compression circuit. The performance of the HV-SPPM has been validated experimentally by using a suitable DBD plasma-UV load. In the proposed HV-SPPM, a series diode with resistor has been introduced across the DBD plasma-UV lamp to damp out the sinusoidal oscillations between DBD capacitance and leakage inductance of the transformer. The HV-SPPM is capable to generate negative voltage pulses up to 6 kV and pulse width 800 ns with frequency variation up to 50 kHz. The proposed arrangement makes the HV-SPPM more compact, lightweight, simple, and highly efficient with very short rise and fall times voltage pulses suitable for the DBD plasma applications.

A novel hybrid cascaded dc–dc converter is proposed for high voltage gain applications in this article, which is characterized by the hybrid series-parallel connection based on coupled inductors and voltage multiplier cells. The input current ripple is decreased due to the interleaved operation and the voltage stress of the switches is only 1/6 of the output voltage when the turn ratio is 1. So the high-performance MOSFETs with low ON-state resistance can be used to reduce the conduction losses. The reverse-recovery problem of the output diode can be suppressed by the leakage inductance of the coupled inductors. The leakage inductance energy of the coupled inductors is absorbed and recycled to the output, which can largely improve the efficiency of the proposed converter. The working principle and steady-state characteristics of the converter are analyzed in detail. Finally, the correctness of the theoretical analysis is verified through experimental results of a 400-W laboratory prototype.

Soft switching based on resonant operation, through mitigating switching loss and alleviating electromagnetic interference, is essential to high-frequency operation to achieve high power density. To overcome the obstacles of high switch voltage stress and ease the contradiction between voltage stress and conduction loss for traditional single-switch resonant converters, a family of zero-voltage-switched (ZVS) isolated resonant converters is proposed which utilizes a novel resonant switch. The converters enable parasitic components, including transformer leakage inductance, switch output capacitance, and diode junction capacitance to act as a part of resonant components, which facilitates ZVS and zero-current-switching operation and pushes up switching frequency. The specific derivation of the topologies is expounded, and one of the proposed converters is taken for example to perform in-depth analysis, whose mode analysis, operation principles, and parameter design method are minutely presented. Synchronous rectification is employed to further improve efficiency. A prototype was built in the laboratory and the experimental results validate the theoretical analysis well.

Three-level isolated DC-DC converter is an attractive topology in high input voltage applications, which can provide the voltage stress of the power devices to only a half of the dc voltage and also reduce the size of dc filter requirement. But major limitations in the existing three level ZVS converter topologies are brought out with an increased inductance in the primary side and it required to provide complete ZVS of all primary devices down to light loads. By employing an external inductance in the primary of the transformer, total leakage inductance of the transformer increases which is required for realization of soft switching of the converter switches but there are some disadvantages of connecting external inductance in the primary of the transformer. To overcome all these drawbacks, the three-phase three-level isolated DC-DC soft switching converter has been proposed in order to reduce voltage and current stresses. This converter topology requires less number of control switches and operates with an asymmetrical duty cycle control. The proposed three level DC-DC converters provide two- level voltage waveform before dc output filter, which significantly reduce the size of dc output filter. The proposed work has been implemented using MATLAB/SIMULINK and the performance of the proposed converter is verified through simulation results.

Compared to Si FETs, when the main GaN FET is in full zero voltage switching condition, maximum switching loss reduction can be achieved. Therefore, in this article, an active clamp flyback converter with GaN devices that implements fast ZVS by using the proposed dynamic resonant period control (DRPC) technique can reduce large transformer leakage inductance energy loss on the active resonant circuit. As the loading changes, the DRPC technique can dynamically adjust the on -time in auxiliary switch to prevent large voltage stress on the components in the primary side. In full load condition, the leakage energy loss can be reduced, thereby transferring more energy to the secondary side with maximum efficiency up to 94%.

Wound-core transformers are characterized by their economical and efficient design and are therefore widely used in power distribution systems; for this reason it is of paramount importance to determine their electrical characteristics. One of the most important parameters in these transformers is leakage reactance, since this is what largely determines short-circuit currents and voltage regulation. And yet the authors have found a conspicuous gap in the scientific literature concerning analytical formulations for the calculation of leakage reactance in wound-core transformers. In order to fill this gap, the authors propose a formula in terms of leakage areas and the Rogowski’s height of the windings. A geometric model of the active part of the transformer is proposed which allows for the exact calculation of the leakage areas. The results of the proposed formula are compared with simulations with the finite element method in 3D (FEM3D) and with measurements in eight real case studies. It is concluded that although the FEM3D calculates the closest results to measurements, the proposed formula reported sufficiently accurate results for transformer design purposes.

This paper discusses an isolated switching mode power supply (SMPS) with an AC 30 kVrms insulation capability for application to the solid-state transformers (SSTs) in railway vehicles. The insulation capability of the SMPS should be higher than AC 25 kVrms for application at the SSTs in railway vehicles. The proposed highly isolated SMPS is superior to commercial isolated power supplies with low insulation capability, which is normally less than 20 kV. The input side of the proposed isolated SMPS is physically separated from its output side by a specially designed miniature high-frequency (HF) transformer to obtain high insulation capability. The core of the miniature HF transformer is separated by insulation material. The primary and secondary coils are wound around each separated core. A CLLC resonant converter that consists of a primary resonant capacitor (C), two inductors (LL), and a secondary resonant capacitor (C) is applied as the proposed isolated SMPS topology to improve the output voltage regulation performance, which varies due to a large leakage inductance derived from the airgap of the proposed miniature HF transformer. Experiments are carried out to verify the CLLC resonant converter of the proposed isolated SMPS. Electrostatic finite element method (FEM) simulations and high potential (HiPot) tests are carried out to verify the AC 30 kVrms insulation capability of the proposed isolated SMPS. The electrostatic FEM simulations demonstrate the DC 42.43 kV insulation capability, and the HiPot tests verify the insulation capability from AC 5 kVrms to AC 30 kVrms.

High-power isolated bidirectional dc–dc converters with wide voltage range are attracting increasing attention in many applications. The bidirectional three-phase current-fed dc–dc converters are known to be suitable for wide voltage range applications compared to dual active bridge based converters, having advantages of reduced device current ratings and prevention of transformer saturation due to high impedance nature. However, when the duty cycle becomes lower than 0.33 or higher than 0.66, power transfer capability is limited, and the efficiency is significantly reduced due to increased circulating current, which has rarely been discussed so far. In this article, a hybrid dual-asymmetrical pulsewidth modulation (DAPWM) and pulsewidth modulation plus phase-shift (PPS) switching method is proposed for efficiency improvement of the bidirectional three-phase push–pull converter with very wide voltage range. A seamless mode change method between PPS and DAPWM is also proposed for minimizing the transient state. Further, through current waveform and power flow analysis, the leakage inductance along with transformer turn ratio are designed to minimize the root mean square (rms) current of devices, while having the capability of transferring the desired power and limiting the slew rate of transformer winding current under wide voltage range operation. Experimental results from a 22-kW prototype are provided to validate the proposed concept.

In this article, a new single-input multioutput high step-up dc–dc converter is proposed, which is suitable for sustainable energy applications. Basically, the presented converter consists of an interleaved and a modified single-ended primary inductor converter, which uses coupled-inductor and switched-capacitor-voltage-multiplier techniques. Each stage generates a different output voltage using only one input voltage source and one duty ratio. The output voltage gains are effectively increased at low duty ratios by employing coupled-inductors and voltage multiplier cells. Moreover, because of using low voltage rated MOSFETs, the voltage stresses on power switches are very low. Therefore, the conduction losses are reduced and the conversion efficiency will be improved. In order to lighten the reverse recovery problems of the output diodes, the leakage inductance of the coupled inductors can be beneficial. The maximum efficiency that is achieved by the proposed converter is 97.5% and 96.2%, respectively, for both output loads. The operating principles and steady-state analysis are discussed in detail. Finally, experimental results for a prototype of the proposed topology that is implemented under 24 V for input voltage source, 286 and 390 V, respectively, for both output ports are presented to assess the effectiveness of the proposed converter.

This paper proposes a non-isolated three-port converter which integrates the input port, battery port, and load port into one converter for renewable energy applications. The coupled inductor and switched capacitor are used to achieve high voltage gain and three power switches can be utilized to realize the power flows between the sources, the battery, and the load. The energy stored in the leakage inductance is recycled to reduce the voltage stress of the power switch. In addition, various operating stages are analyzed and design considerations are presented. Compared to the relevant converters, the proposed converter can realize power flows and achieve high voltage gain by using few components. Finally, a laboratory prototype of the proposed converter with input port voltage 24 V, battery port voltage 48 V, and output voltage 400 V with 200 W rated power is implemented to validate the feasibility and effectiveness of the theoretical analyses.

LLC resonant converter has the advantages of high frequency and high efficiency, and has been developed rapidly and widely used in recent years. However, due to the presence of multiple magnetic components in the circuit, the improvement of power density is limited. To solve this problem, integrated magnetic transformer is usually designed to replace the discrete magnetics. While, the leakage inductance of the transformer cannot be controlled, the loss of the converter increases. In this paper, a magnetic integrated LLC resonant converter with independent inductance winding is proposed. The resonant inductance and magnetizing inductance are integrated with the transformer in the same magnetic core by using the decoupling integration method. Compared with the existing solution of magnetic integrated LLC resonant converter, this method can reduce the leakage inductance between the transformer windings and decrease the magnetic saturation of the integrated magnetics, thereby reducing the magnetic core loss and improving the efficiency of the converter. Compared with the discrete magnetics, the volume and weight of the magnetic components are reduced by 25.68% and 43.82% respectively, making the power density of the converter effectively improved. Finally, an experimental prototype of integrated magnetic LLC resonant converter with operating frequency of 350kHz and output power of 400W is built. The experimental results verify the correctness of the design scheme.

Funding Information: This work was supported by FinElib, Finland, through the FinELib consortium's agreement with IEEE. Publisher Copyright: © 2013 IEEE. In this paper, a new family of ultra-high step-up DC-DC converters based on a center-tapped coupled inductor (CI) is proposed. These single-switch converters employ different inductive and capacitive power transfer techniques by utilizing multi-winding CIs, intermediate capacitor links and simple switched-capacitors to improve the transferred power rate, harvest magnetizing and leakage inductance energies, and enhance power density. Achieving high voltage gain in low duty cycle values enables the proposed converters to operate under wide output voltage ranges; meanwhile, distributing the output voltage on two or three output ports alleviates the voltage stress on output terminal components. Low input current ripple, simple pulse width modulation control, low switch voltage stress and operation without circulating current can be listed as other features. In this paper, the proposed family is introduced, theoretically analyzed and compared with other state-of-the-art researches. Finally, the accuracy of analyses are evaluated with some experimental tests of a 1.25 kW experimental prototype.

Recent studies on compact and lightweight electronic devices have demonstrated that the LLC resonant converter (LRC) can facilitate achieving high efficiency and high power density. Moreover, employing a planar transformer can further improve the overall system power density. Although the planar transformer can assist in reducing the size of the converter, its high magnetic coupling makes the leakage inductance too small for a resonant inductor in the LRC. Therefore, an extra inductor must be employed separately, leading a considerable decrease in the power density. From this reason, significant research on integrated magnetics has been conducted to combine a transformer and external inductor into a single core. However, they require additional wires or magnetic sheets, and their structures are complex and costly. To overcome these limitations, the integrated magnetics planar transformer (IMPT) for a high power density LRC is proposed in this paper. In the proposed approach, since the primary wire is split into each side leg of the EE-type magnetic core and each operates as a transformer and a resonant inductor alternatively, an external inductor or additional wires are unnecessary. In addition, since the magnetic flux density of the IMPT is approximately equivalent to that of conventional transformer, the core size and the number of turns are almost the same. Therefore, the proposed IMPT features higher efficiency and power density without additional size and costs. To confirm the validity of the proposed IMPT, the operational principles, theoretical analysis, design considerations, and experimental results from a 350 W prototype are presented.

This article presents an efficient interleaved soft switching dc–dc converter for high step-up applications. In the proposed converter, two multifunction coupled inductors are employed to increase the voltage gain, accomplish soft switching operation for all semiconductors in a wide range of load variations, and smooth the input current. Besides, the leakage inductance energy is recovered to enhance the voltage gain and efficiency while assisting soft switching condition for the switches and diodes. In addition, no auxiliary switch or extra magnetic element is employed in the proposed converter while the voltage stress of switches and diodes is rather low. These have led to simple structure, high density, low cost, and improved efficiency. Theoretical analysis and design considerations for the proposed converter are presented. Moreover, the experimental results of a 48 to 500 V laboratory prototype approve the effectiveness of the proposed topology.

This paper proposes a high-performance isolated single-ended primary inductor converter (SEPIC) that is integrated with a non-dissipative snubber for a light-emitting diode (LED) driver. The proposed LED driver employs the snubber circuit to minimize any switching overvoltage caused by parasitic leakage inductance of the high-frequency transformer in the isolated SEPIC converter. This paper also presents a detail theoretical analysis of the proposed LED driver including its operating modes and design calculation. The experimental results of the proposed LED driver at the rated power of 18 W shows that it has a high-power factor, low harmonics, employs non-electrolytic capacitors, low switching stress, high reliability and high efficiency.

In this article, a new single-switch buck converter (without considering the synchronous rectifier) with extended duty cycle and continuous output current is proposed. The presented converter employs a self-driven synchronous rectifier with gate energy recovery, which leads to efficiency improvement and simplicity of the converter and the gate drive circuit. The extended duty cycle results in lower current stress of the high-side MOSFET and reduced voltage stress across the synchronous rectifier. Furthermore, the reverse recovery losses of synchronous rectifier are dramatically decreased due to the applied coupled inductors. The introduced converter also provides shoot-through protection and load protection when the high-side MOSFET remains on . In order to clamp the drain–source voltage spikes of the main switch and recover the leakage inductance energy, a lossless snubber circuit is added, which reduces the turn- off drain–source voltage and consequently decreases the turn- off switching losses of the main MOSFET . Moreover, the main switch turns on under zero current switching (ZCS), which results in efficiency improvement. A 150-W prototype of the proposed converter is implemented to verify the theoretical analysis and confirm its efficiency improvement and advantages.

Recently, transformers with toroidal core have received much attention. The compactness and weight of these kinds of transformers make them suitable for power electronics applications. In some areas, it is necessary to have a toroidal transformer with particular parasitic elements such as leakage inductance. So, there is a need for a precise method to calculate the exact amount of leakage inductance for designing the desired system. This article presents a pure analytical method based on Maxwell’s equations to accurately determine the leakage inductance of a toroidal transformer which its windings are wounded separately. The proposed expression for the leakage inductance calculation considers the influence of the core specifications, such as dimensions and material. In order to validate the presented method, 3-D finite-element simulation and experimental results of the prototype transformer have been done.

A zero voltage switching (ZVS) interleaved high step-up converter with coupled inductor and built-in transformer voltage multiplier cell is introduced in this study. A more flexible design is provided by increasing the voltage conversion ratio by utilising the turns ratios of the coupled inductor and built-in transformer. The ZVS operation of the metal-oxide-semiconductor field-effect transistors (MOSFETs) and absorption of the leakage current are realised through active clamp circuits. Furthermore, the voltage stress across the switching devices is minimised that give rises to implementation of low voltage rated MOSFETs and consequently low conduction losses. Meanwhile, the diode reverse current problem is alleviated by the leakage inductance of the coupled inductor and built-in transformer. All of the abovementioned advantages make the proposed converter as a high efficiency candidate for high current and high step-up applications. Finally, a 600 W, 48–700 V voltage conversion with the conversion efficiency of 97% is fabricated to probe the merits of the proposed converter.

Boost dc/dc converters are widely used in renewable energy systems. With growing demand for high efficiency and high voltage gain, many new topologies have been published. This article proposes a novel zero current switching (ZCS) boost converter with a tapped inductor and active edge-resonant cell (AERC). To achieve high voltage gain, the tapped inductor was implemented in the structure of the converter, and by employing an AERC, ZCS of transistors was attained. Subsequently, by employing a resonant operation current, overshoots by leakage inductance were eliminated. This article presents an analysis, mathematical derivations, and laboratory test results. Finally, a 30–50 V input, 380 V output, and 750 W output power laboratory model operating with 45–100 kHz switching frequency was built and tested. The maximum reported efficiency was 96.6%. Soft switching of semiconductors was achieved in the whole output power range.

A comprehensive design methodology is required to maximize the power capacity, the efficiency, and the power density of medium-frequency transformer (MFT), while complying with material, insulation, leakage inductance, and temperature limits. Different from the previous work, an analytical expression for the optimum conductor size of rectangular litz-wire conducting harmonic currents, which ensures best use of the available copper is proposed. A method to tune the leakage inductance with different winding configurations is presented. An insulation design scheme considering the influence of short-term power frequency sinusoidal wave and long-term square wave voltage excitations is put forward. Method to acquire the optimal dimension of fin array heat exchanger under forced air-cooling condition is presented. On this basis, the design methodology is established using the multiobjective nondominated sorting genetic algorithm II. A 1 kV, 200 kVA, 10 kHz nanocrystalline core MFT is designed and prototyped for a 10 kV, 2.5 MW solid-state transformer. The optimal design achieves an efficiency of 99.45%, a power density of 8 MW/m3, and a forced air-cooling temperature of 62 °C.

A stator winding tap changer has been studied for a permanent magnet synchronous motor (PMSM) drive for speeds exceeding the base speed range. At low speeds, all stator windings are configured to fulfill the high output torque; at high speeds, a portion of the stator windings are configured to relieve the burden of the stator winding turns, i.e., large inductive impedance, back electromotive force (BEMF), and field-weakening current. The conventional solid-state tap changers for the PMSMs require snubber capacitors and bleeder resistors. The snubber capacitor is necessary for providing an inductor current path during the stator winding tap-change period. However, it induces long transition times and energy losses. In this article, a snubberless solid-state tap changer is proposed for PMSMs. The proposed mechanism is composed of only three-switches for each tap and controls the leakage inductance current by employing an appropriate switching sequence. With the proposed tap changer, the transition period is reduced and energy loss by bleeder resistance is eliminated. The results of a simulation and an experiment are used to validate the proposed scheme.

Impedance source converters (ISC) based on the magnetic coupling can enhance their voltage gains by maintaining lower shoot-through duty ratios and reduced passive component count. However, the nonzero leakage inductance in the practical ISC generates high switching voltage spikes resulting in poor voltage regulation. Therefore, an absorbing circuit with additional components is crucial to reduce these voltage spikes and to absorb the energy stored in leakage inductances. This article presents a family of differential-mode Y-source converters (DMYSCs) as an alternative to the latest Y-source converter that mitigates the switching voltage spikes without increasing the number of components. The proposed converters DMYSC-I, DMYSC-II, and improved Γ-type Y-source converter are derived from the original Y-source impedance network by altering the winding orientation. In this article, the respective topologies with their working principles are studied and the characteristics are compared with other Y-source converters. Simulation and experimental results have confirmed the abilities of the proposed converters to mitigate their switching voltage spikes.

Full-bridge zero-current-switching (FB-ZCS) dc–dc converters realize quasi-resonant soft-switching and smooth current commutation by utilizing the leakage inductance of high-frequency transformer and a resonant capacitor. The following two types of resonant capacitor configurations are proposed in the literature: First, shunt-connected across the transformer-secondary and, second, series-connected with the transformer-primary. Shunt-connected capacitor has the drawbacks of storing full-load-rated resonant energy irrespective of converter loading. This results in large duty-cycle loss and consequently regulation loss at light-loads. Series-connected capacitor addresses this issue but suffers from higher peak-voltage stress across components and insufficient voltage for resonance at light-loads. To address these limitations, a dual-capacitor resonant circuit is proposed in this article. Series-capacitor facilitates current-adaptive resonant energy storage and shunt-capacitor is designed only for a fraction of full-load-rated resonant energy, which lowers the duty-cycle loss and supports soft-switching at light-loads. This combination also reduces the series-capacitor voltage required for resonance, thereby reducing the peak-voltage stress. Steady-state analysis of converter operation is presented and the advantages over existing converters are demonstrated through simulations for medium-voltage dc application. Experimental results from a scaled-down prototype are presented to validate the proposed converter.

In this article, a soft-switched nonisolated high step-up multi-input dc–dc converter is proposed. The proposed converter has overcome the hard switching problem of the conventional boost three port converter (boost-TPC) by providing zero-voltage-switching condition for all switches at various operating modes. The proposed converter uses coupled inductors technique to enhance the voltage gain and utilizes the leakage inductance energy and the energy storage device power path to provide soft switching condition. In addition, the voltage stress of the main switch is reduced which has led to utilizing low R ds(ON) switches. Various converter operating modes are presented and design considerations are discussed. To evaluate the proposed converter performance, two prototypes of the proposed converter are implemented utilizing the latest generation gallium nitride high electron mobility transistors and the mature Si MOSFETs technology. The results show that the proposed converter efficiency is enhanced in comparison with the conventional boost-TPC converter.

A new alternative circuitry for the transformer-coupled LC inversion generator (TCLCG) is presented. In principle, a TCLCG consists of one in-phase 1:1 transformer and two capacitors per elementary stage. First, the two capacitors will be charged via the primary winding of the transformer in opposite polarity. Afterward, voltage multiplication is being achieved by a closing switch which shortcuts the two capacitors. The odd-numbered capacitor discharges slowly through the primary inductance of the transformer, whereas the even-numbered capacitor discharges fastly through only the leakage inductance of the transformer and, thus, inverts. However, one of the main drawbacks of the classical “textbook” TCLCG circuitry is caused by the fact that connection of the transformers of the higher generator stages is done through the transformers of the lower stages. Consequently, compensation techniques must be applied, i.e., adjustment of the even capacitors and/or transformer inductance values, in order to ensure effective voltage multiplication by means of constructive superposition of each stage. This limits the maximum practical generator stage number and rise time. In the alternative TCLCG circuit principle, the connections to the primary and secondary inputs of the transformers of the higher stages are being done directly from the closing switch. Now, the transformers are in parallel to each other, not in series as in the classical TCLCG circuitry. As a result, the even-numbered capacitors see the same leakage inductance and compensation techniques are no longer necessary. The first experimental verification was done by direct comparison of the classical circuitry and alternative circuitry for two compact two-stage TCLCGs with identical transformers and capacitances. The results showed that the alternative circuitry leads to a fast generator rise time of 25 ns, about 38% faster than the classical circuitry, while still reaching the same generator efficiency of 67%. Additionally, rise time proved to stay constant at 25 ns even if adding the third stage to the TCLCG with the new alternative geometry. This version was still 46% faster than an optimized classical three-stage TCLCG using the asymmetric compensation method.