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A resonant converter with less voltage rating of power switches and wide voltage operation is investigated in this Letter for medium voltage applications. Four active switches and two split capacitors are adopted on the primary side to reduce the voltage rating on power semiconductors. The resonant converter is adopted in the converter to have a wide soft switching operation range. Two flying capacitors are used in the presented circuit to operate as the resonant capacitor and also to achieve voltage balance of two input split capacitors. The variable winding turns are used on the secondary side to overcome the problem of the limited voltage operation in the conventional resonant converter. If the input voltage is in the low-input voltage range, the low turns-ratio of the power transformer is used to increase the voltage gain of the resonant converter. If the input voltage is in a high-voltage range, then the high turns-ratio of the transformer is adopted to reduce the voltage gain. Thus, the proposed converter can achieve wide input voltage operation. Experimental results with a 0.8 kW prototype are provided to confirm the effectiveness of wide input voltage operation from 260 to 800 V.

A high efficiency converter is developed for high-voltage input and low-voltage output such as DC light rail vehicle, industry high power units with three-phase AC input or bipolar DC micro-grid system. The proposed circuit structure is constructed with series DC–DC circuits to lessen voltage rating of power metal oxide semiconductor field effect transistors (MOSFETs). Single transformer is employed with two primary inputs and one secondary output to lessen conduction loss on power MOSFETs and copper loss on transformer windings so that the converter efficiency is improved. Phase-shift duty cycle control is employed to reduce switching loss on MOSFETs. Input voltages balance problem in conventional three-level converters is overcome by using a voltage balance capacitor. The effectiveness and feasibility of the studied structure were evaluated based on 1 kW DC converter with 100 kHz switching frequency.

An input-series output-parallel soft switching resonant circuit with balance input voltage and primary-side current is studied and implemented for direct current (DC) microgrid system applications. Two resonant circuits are connected with input-series and output-parallel structure to have the advantages of low voltage stresses on active devices and low current stresses on power diodes. A balance capacitor is adopted on high voltage side to balance two input capacitor voltages. The LLC (inductor–inductor–capacitor) resonant circuit cells are employed in the converter to have soft switching operation for power semiconductors. The magnetic coupling component is adopted on the primary-side to automatically realize current balance of the two resonant circuits. In the end, a laboratory hardware circuit is built and tested. Experiments demonstrate and prove the validity of the resonant converter.

This paper studies and implements a power converter to have less current ripple output and wide voltage input operation. A three-leg converter with different primary turns is presented on its high-voltage side to extend the input voltage range. The current doubler rectification circuit is adopted on the output side to have low current ripple capability. From the switching states of the three-leg converter, the presented circuit has two equivalent sub-circuits under different input voltage ranges (Vin = 120–270 V or 270–600 V). The general phase-shift pulse-width modulation is employed to control the presented converter so that power devices can be turned on at zero voltage in order to reduce switching loss. Compared to two-stage circuit topologies with a wide voltage input operation, the presented converter has the benefits of simple circuit structure, easy control algorithm using a general integrated circuit or digital controller, and less components. The performance of the presented circuit is confirmed and validated by an 800 W laboratory prototype.

A new hybrid inductor-inductor-capacitor (LLC) converter is investigated to have wide voltage input operation capability and zero-voltage turn-on characteristics. The presented circuit topology can be applied for consumer power units without power factor correction or with long hold-up time requirement, photovoltaic energy conversion and renewable energy power transfer. To overcome the weakness of narrow voltage gain of resonant converter, the hybrid LLC converter with different turns ratio of transformer is presented and the experimental investigation is provided to achieve wide voltage input capability (400 V&ndash, 50 V). On the input-side, the converter can operate as full bridge resonant circuit or half bridge resonant circuit with input split capacitors for high or low voltage input region. On the output-side, the less or more winding turns is selected to overcome wide voltage input operation. According to the circuit structures and transformer turns ratio, the single stage LLC converter with wide voltage input operation capability (400 V&ndash, 50 V) is accomplished. The laboratory prototype has been developed and the experimental waveforms are measured and demonstrated to investigate the effectiveness of the presented hybrid LLC converter.

A soft-switching direct current (DC) to DC converter is studied in this study to achieve benefits: (i) low-primary current (circulating current) loss, (ii) low-switching loss, (iii) low-output filter inductance, and (iv) wide hold-up time. On primary side of the studied converter, a phase-shift pulse-width modulation full-bridge (FB) circuit and a half-bridge (HB) circuit using same lagging-leg switches of FB circuit to reduce the switching losses at light load. Resonant capacitor is adopted on primary side of FB circuit to lessen primary current at freewheeling state so as to reduce conduction losses. The output sides of HB and FB circuits are series connection to create two positive voltages instead of one positive voltage on conventional FB circuit so as to reduce primary current and output filter inductance. To extend hold-up time and avoid using large size of input capacitor when utility power is off, the auxiliary windings are used on secondary side to achieve higher-voltage gain. To verify the performance and effectiveness of the studied converter, the operational principle and equivalent circuits are explained and analysed in detail and a 1440 W prototype is constructed and tested for 300-400 V input and 48 V output applications.

A soft switching three-level pulse-width modulation (PWM) converter is presented for industrial electronics with wide voltage range operation, such as solar power or fuel cell applications. Phase shift PWM scheme is used on the input-side to accomplish the zero voltage turn-on on power switches and improve the converter efficiency. Three-level diode-clamp circuit topology is adopted in the presented circuit to lessen the voltage ratings on active devices for high voltage applications. Three sub-circuits with the different turns-ratio of transformers can be selected in the presented converter in order to achieve 10:1 (Vin,max = 10Vin,min) wide input voltage operation when compared to the conventional multilevel converter. The proposed circuit is a single-stage converter instead of two-stage converter to realize wide voltage operation. Therefore, the presented converter has less component counts. Finally, the design procedure and experiments with a 300W laboratory circuit are presented and discussed to confirm the circuit analysis and converter performance.

This study presents a high-voltage zero-voltage switching converter with balance capacitors in the direct current microgrid. In the proposed converter, full-bridge circuits with primary-series and secondary-parallel connection are used for high-voltage input and high-current output applications. The series connection of full-bridge circuits reduces the voltage rating of power switches in each full-bridge circuit cell. Therefore, high-speed power metal–oxide–semiconductor field-effect transistors are employed to reduce the converter size. Flying capacitors are connected between each full-bridge circuits so that the input split voltages can be balanced automatically in every switching period without using the complexity control scheme. The phase-shift pulse-width modulation scheme is used to regulate the output voltage. The power switches can be turned on at zero voltage due to the energy stored in the output inductors or primary leakage inductors and the switching losses are reduced. The output sides of the full-bridge circuits are connected in parallel to reduce the current ratings of transformer secondary windings and passive power components. Finally, experiments are provided to validate the characteristics and usefulness of the proposed converter in microgrid applications.

This study presents a soft-switching converter for direct current microgrid applications. The studied converter includes n cells of the hybrid full-bridge converter with primary-series–secondary-parallel connection for high-voltage input and large current output applications. Thus, the voltage stress of power switches and the current stress of rectifier diodes are decreased. Therefore, the low-voltage stress and low conduction resistance of power metal–oxide–semiconductor field-effect transistors are utilised in the studied converter to reduce conduction losses on power switches. The flying capacitors are connected between each circuit cell to prevent voltage unbalance on input split capacitors. On each circuit cell, a full-bridge converter with an additional half-bridge circuit is employed to achieve low circulating current losses, less output inductance and a wide range of zero-voltage switching. Finally, the studied converter with 1800 W rated power is constructed and tested to verify the theoretical analysis.

Conventional series resonant converters have researched and applied for high-efficiency power units due to the benefit of its low switching losses. The main problems of series resonant converters are wide frequency variation and high circulating current. Thus, resonant converter is limited at narrow input voltage range and large input capacitor is normally adopted in commercial power units to provide the minimum hold-up time requirement when AC power is off. To overcome these problems, the resonant converter with auxiliary secondary windings are presented in this paper to achieve high voltage gain at low input voltage case such as hold-up time duration when utility power is off. Since the high voltage gain is used at low input voltage cased, the frequency variation of the proposed converter compared to the conventional resonant converter is reduced. Compared to conventional resonant converter, the hold-up time in the proposed converter is more than 40ms. The larger magnetising inductance of transf...

A bidirectional resonant converter is presented and verified in this paper for an electric vehicle battery charger/discharger system. The presented circuit can achieve forward and backward power operation, low switching losses on active devices, and wide output voltage operation. The circuit structure of the presented converter includes two resonant circuits on the primary and secondary sides of an isolated transformer. The frequency modulation approach is adopted to control the studied circuit. Owing to the resonant circuit characteristic, active devices for both forward (battery charge) and backward (battery discharge) power operation can be turned on at zero voltage switching. In order to implement a universal battery charger for different kinds of electric vehicle applications, the DC converter is demanded to have a wide output voltage range capability. The topology morphing between a full bridge resonant circuit and half bridge resonant circuit is selected to obtain high- and low-output voltage range operations so that the 200–500 V output voltage range is realized in the presented resonant converter. Compared to the conventional bidirectional converters, the proposed can be operated under a wide voltage range operation. In the end, a 1 kW laboratory prototype circuit is built, and experiments are provided to demonstrate the validity and performance of the presented bidirectional resonant converter.

A parallel direct current (DC) to DC converter is presented for medium power applications. The studied converter includes three half-bridge circuits with sharing two power switches at high-voltage side to reduce switch counts. Three half-bridge circuits are connected by primary-parallel and secondary-parallel to reduce the current stress of power devices at low-voltage side. Each half-bridge circuit supplies one-third of the total power to the output load. Asymmetric pulse-width modulation is employed to generate the gated signals of the switches and regulate the output voltage. Based on the resonant behaviour of the output capacitance of power switches and the leakage inductance of the transformer, the zero-voltage switching turn-on of power switches can be achieved. Current doubler rectifier topology is adopted at the low-voltage side to have the advantage of low ripple current at output capacitor. A laboratory prototype with 1440 W power is built to verify theory analysis and effectiveness of the studied converter.

A dc-dc converter with asymmetric pulse-width modulation is presented for medium voltage applications, such as three-phase ac-dc converters, dc microgrid systems, or dc traction systems. To overcome high voltage stress on primary side and high current rating on secondary side, three dc-dc circuits with primary-series secondary-parallel structure are employed in the proposed converter. Current doubler rectifiers are used on the secondary side to achieve low ripple current on output side. Asymmetric pulse-width modulation is adopted to realize soft switching operation for power switches for wide load current operation and achieve high circuit efficiency. Current balancing cells with magnetic component are used on the primary side to achieve current balance in each circuit cell. The voltage balance capacitors are also adopted on primary side to realize voltage balance of input split capacitors. Finally, the circuit performance is confirmed and verified from the experiments with a 1.44 kW prototype.

A hybrid PWM converter is proposed and investigated to realize the benefits of wide zero-voltage switching (ZVS) operation, wide voltage input operation, and low circulating current for direct current (DC) wind power conversion and solar PV power conversion applications. Compared to the drawbacks of high freewheeling current and hard switching operation of active devices at the lagging-leg of conventional full bridge PWM converter, a three-leg PWM converter is studied to have wide input-voltage operation (120–600 V). For low input-voltage condition (120–270 V), two-leg full bridge converter with lower transformer turns ratio is activated to control load voltage. For high input-voltage case (270–600 V), PWM converter with higher transformer turns ratio is operated to regulate load voltage. The LLC resonant converter is connecting to the lagging-leg switches in order to achieve wide load range of soft switching turn-on operation. The high conduction losses at the freewheeling state on conventional full bridge converter are overcome by connecting the output voltage of resonant converter to the output rectified terminal of full bridge converter. Hence, a 5:1 (600–120 V) hybrid converter is realized to have less circulating current loss, wide input-voltage operation and wide soft switching characteristics. An 800 W prototype is set up and tested to validate the converter effectiveness.

A new hybrid high-frequency link pulse-width modulation (PWM) converter using voltage balance capacitor and current balance magnetic coupling is proposed to realize low freewheeling current loss and wide load range of soft switching operation. Series-connected H-bridge converter is adopted for high voltage applications. In addition, a voltage balance capacitor and a current balance magnetic coupling core are employed for achieving voltage and current balance. To extend zero-voltage switching (ZVS) range of switches at lagging-leg of phase-shift PWM converter, soft switching LLC converter is linked to the lagging-leg of phase-shift PWM converter. Therefore, the wide ZVS load operation is realized in the presented hybrid converter. The other high freewheeling current disadvantage in conventional phase-shift PWM converter is improved by a snubber circuit used on low-voltage side. Thus, the primary current during the freewheeling state is decreased and close to zero. In addition, the conduction losses on primary-side components of studied converter are reduced. The secondary-sides of phase-shift PWM converter and LLC resonant converter are series-connected to achieve power transfer between input and output sides. Experimental results using a laboratory prototype are provided to demonstrate the effectiveness of the studied circuit and control algorithm.

A new soft switching three-level converter with two DC/DC circuits in the primary side and current double rectifiers in the secondary side is presented to realize the zero-voltage switching operation, reduce the transformer secondary winding turns and the output current ripple, and lessen the voltage rating of rectifier diodes. Two DC/DC pulse-width modulation circuits sharing same power switches with interleaved half switching cycle are adopted in the proposed converter to reduce the current rating of transformer primary windings. Two inductors and four diodes are adopted in the secondary side to achieve current double rectifier, reduce output ripple current, and decrease the transformer secondary winding turns. Based on the pulse-width modulation scheme, the power switchers can be turned on at zero-voltage switching operation. Laboratory experiments with a 1.44kW prototype are provided to verify the theoretical analysis. Copyright © 2016 John Wiley & Sons, Ltd.

A new full-bridge converter is presented to have the advantages of low conduction loss and wide zero-voltage switching (ZVS) range. The proposed converter includes two dc–dc converters connected in parallel to reduce the current stresses of power components. Each dc–dc converter integrates a phase-shift pulse-width modulation full-bridge circuit and an un-regulated half-bridge circuit sharing the lagging-leg switches in order to reduce the switch counts. The un-regulated half-bridge circuit is adopted to extend the ZVS range of the lagging-leg switches to improve the drawback of the narrow ZVS range in conventional full-bridge converter. Two dc–dc converters share the lagging-leg switches so that the switch counts in the proposed converter are less than the switches in conventional parallel full-bridge converters. The resonant capacitors are used on the primary side of full-bridge converters to reduce the primary current to zero at the freewheeling state. The secondary windings of full-bridge and half-bridge converters are connected in series to generate two positive voltage levels at the secondary rectified voltage. Therefore, the output inductor voltage at the freewheeling state is decreased and the output inductor size is reduced. Finally, the effectiveness of the proposed converter is verified by the experiments.

A zero-voltage switching (ZVS) converter with five resonant circuits with shared switches is presented to achieve the functions of less switch counts, low switching losses and low current stress of passive components at low-voltage side. For medium input voltage case, four split capacitors and four active switches with V in/2 voltage stress are adopted at high-voltage side. Two balance capacitors are used to automatically balance input capacitor voltages in every switching cycle. Five resonant circuits are adopted in the proposed converter to share load current and reduce the current stress of passive components. On the basis of the circuit characteristics of resonant converter, power switches are turned on at ZVS from zero to full load. Rectifier diodes can be turned off at zero-current switching if the switching frequency is less than the series resonant frequency. Hence, the reverse recovery losses on the rectifier diodes are improved. Experimental verifications with a 1.92 kW prototype are provided to demonstrate the effectiveness of the proposed converter.

This paper presents a inductor&ndash, inductor&ndash, capacitor (LLC) resonant converter with variable winding turns to achieve wide voltage operation (100&ndash, 400 V) and realize soft switching operation over the entire load range. Resonant converters have been developed for consumer power units in computers, power servers, medical equipment, and adaptors due to the advantages of less switching loss and better circuit efficiency. The main disadvantages of the LLC resonant converter are narrow voltage range operation owing to wide switching frequency variation and limited voltage gain. For computer power supplies with hold-up time function, electric vehicle battery chargers, and for power conversion in solar panels, wide input voltage or wide output voltage operation capability is normally demanded for powered electronics. To meet these requirements, the variable winding turns are used in the presented circuit to achieve high- or low-voltage gain when Vin is at low- or high-voltage, respectively. Therefore, the wide voltage operation capability can be implemented in the presented resonant circuit. The variable winding turns are controlled by an alternating current (AC) power switch with two back-to-back metal-oxide-semiconductor field-effect transistors (MOSFETs). A 500-W prototype is implemented and test results are presented to confirm the converter performance.

A phase-shift pulse-width modulation converter is studied and investigated for railway vehicle or solar cell power converter applications with wide voltage operation. For railway vehicle applications, input voltage range of dc converters is requested to have 30&ndash, 40% voltage variation of the nominal input voltage. The nominal input voltages of dc converters on railway vehicles applications may be 37.5 V, 48 V, 72 V, 96 V and 110 V. Therefore, a new dc converter with wide input voltage operation from 25 to 150 V is presented to withstand different nominal input voltage levels such as 37.5&ndash, 110 V on railway power units. To realize wide input voltage operation, an auxiliary switch and auxiliary transformer windings are used on output side of conventional full-bridge converter to have different voltage gains under different input voltage values. Phase-shift pulse-width modulation is adopted in the developed dc converter to accomplish soft switching operation on power switches. To confirm and validate the practicability of the presented converter, experiments based on a 300 W prototype were provided in this paper.

A hybrid soft-switching converter including two resonant circuits and an un-regulated dc–dc pulse-width modulation (PWM) circuit is presented. Two split capacitors with four active switches are used at primary side to limit power switches at V in/2. The variable frequency operation is adopted to regulate output voltage. Two flying capacitors are also adopted at the primary side to automatically balance two input split voltages. One un-regulated PWM converter shared the same power switches of two resonant circuits is used to reduce the output current ripple. Therefore, the power rating of power semiconductors and passive components are reduced. The operation principles, performance and effectiveness are illustrated and verified on a 1.44 kW (48 V/30 A) prototype circuit.

This paper presents three soft switching converters in future dc microgrid system applications. The studied circuits are consisted of series-connection of half-or full-bridge circuits with a single transformer to convert high-voltage input to low-voltage output. On high-voltage side, $\mathbf{n}$ converters are series connection to reduce the voltage rating of power switches into $\mathbf{V}_{\mathbf{in}}/\mathbf{n}$ . Thus, the low voltage stress MOSFETs with low turn-on resistance can be used in each converter modules to reduce conduction loss, increase switching frequency and reduce circuit size. The control scheme of the studied circuits are using the general asymmetric PWM scheme, phase-shift PWM scheme and frequency control scheme to control load voltage stable. Power devices in these three control approaches are all turned on at zero-voltage switching such that the switching losses are reduced and high circuit efficiency is predicted. Finally, the performance of the proposed circuit was demonstrated by the prototype circuits.

This paper studies a parallel full-bridge converter with less ripple current and balance load current for low voltage DC microgrid applications. Two full-bridge circuits use same active switches at lagging-leg. Therefore, the zero-voltage switching range of lagging-leg switches is improved. Current doubler rectifiers are adopted to decrease ripple current on output inductor and capacitor. The output voltage regulation and low switching loss are achieved by using phase-shift pulse-width modulation operation. The performance of the studied circuit is verified by experiments with a laboratory prototype rated 1.92 kW.

This paper studies a parallel soft switching converter with less switch counts for medium power application. The studied converter includes three half-bridge circuits with sharing two power switches at high voltage side to reduce switch counts. Three half-bridge circuits are connected by primary-parallel and secondary-parallel to reduce current stress of power devices at low voltage side. Each half-bridge circuit supplies one-third of total power to output load. Asymmetric pulse-width modulation is employed to generate the gated signals of the switches and regulate output voltage. Based on the resonant behavior by the output capacitance of power switches and the leakage inductance of transformer, the zero-voltage switching turn-on of power switches can be achieved. Current doubler rectifier topology is adopted at low voltage side to have the advantage of low ripple current at output capacitor. A laboratory prototype with 1440W rated power is constructed and experiments are provided to verify the theory analysis and demonstrate the effectiveness of the studied converter.

A high efficiency dc–dc converter is studied for light rail transportation applications on DC microgrid systems. The adopted structure includes two series-connected resonant circuits with single isolated transformer from input 750 V to output 48 V. Two half-bridge resonant circuits and one voltage balance capacitor are used to reduce voltage rating of active devices and to realize split voltages balance. Two series resonant circuits are connected with input-series by single transformer to reduce primary root-mean-square currents. Therefore, power devices with low voltage rating are selected in studied circuit to reduce power loss on sower devices and transformer winding of the isolated transformer. Frequency control approach is adopted to adjust load voltage under different voltage condition and current variations. Since the equivalent resonant tank of the studied circuit is activated under inductive load, active devices are easily operated at zero-voltage switching over wide voltage and current operation range. The feasibility of the studied circuit has been verified with a 1 kW prototype.

This paper studies and presents a series-connected high frequency DC/DC converter connected to a DC microgrid system to provide auxiliary power for lighting, control and communication in a DC light rail vehicle. Three converters with low voltage and current stresses of power devices are series-connected with single transformers to convert a high voltage input to a low voltage output for a DC light rail vehicle. Thus, Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) with a low voltage rating and a turn-on resistance are adopted in the proposed circuit topology in order to decrease power losses on power switches and copper losses on transformer windings. A duty cycle control with an asymmetric pulse-width modulation is adopted to control the output voltage at the desired voltage level. It is also adopted to reduce switching losses on MOSFETs due to the resonant behavior from a leakage inductor of an isolated transformer and output capacitor of MOSFETs at the turn-on instant. The feasibility and effectiveness of the proposed circuit have been verified by a laboratory prototype with a 760 V input and a 24 V/60 A output.

This paper presents a new resonant converter to achieve the soft switching of power devices. Two full-bridge converters are connected in series to clamp the voltage stress of power switches at Vin/2. Thus, power MOSFETs with a 500V voltage rating can be used for 800V input voltage applications. Two flying capacitors are connected on the AC side of the two full-bridge converters to automatically balance the two split input capacitor voltages in every switching cycle. Two resonant tanks are used in the proposed converter to share the load current and to reduce the current stress of the passive and active components. If the switching frequency is less than the series resonant frequency of the resonant tanks, the power MOSFETs can be turned on under zero voltage switching, and the rectifier diodes can be turned off under zero current switching. The switching losses on the power MOSFETs are reduced and the reverse recovery loss is improved. Experiments with a 1.5kW prototype are provided to demonstrate the performance of the proposed converter.

A DC/DC converter with parallel input and parallel output circuit topology is presented to achieve the main features of reduced switch count and medium power level compared with conventional parallel half-bridge resonant converter. The proposed converter has three resonant circuits to share load currents and reduce the current stress of circuit components. These three resonant circuits use the same power switches to deliver power from input side to output load so that the switch counts are reduced compared with the conventional parallel resonant converter. The rectifier diodes at the secondary side of three resonant circuits are partially used in common so that the diode counts are also reduced. Since three resonant circuits are connected in parallel, the sizes of the transformers and active and passive components are reduced. The switching frequency of the proposed converter is operated to be less than the series resonant frequency. Thus, active switches are turned on under zero voltage switching and rectifier diodes are turned off under zero current switching. A 1.6 kW laboratory prototype is designed and constructed to demonstrate the feasibility and performance of the proposed circuit.

This article presents a new dc/dc converter to perform the main functions of zero voltage switching (ZWS), low converter size, high switching frequency and low-voltage stress. Metal–oxide–semiconductor field-effect transistors (MOSFETs) with high switching frequency are used to reduce the converter size and increase circuit efficiency. To overcome low-voltage stress and high turn-on resistance of MOSFETs, the series half-bridge topology is adopted in the proposed converter. Hence, the low-voltage stress MOSFETs can be used for medium-input voltage applications. The asymmetric pulse-width modulation is used to generate the gating signals and achieve the ZWS. On the secondary side, the parallel connection of two diode rectifiers is adopted to reduce the current rating of passive components. On the primary side, the series connection of two transformers is used to balance two output inductor currents. Two flying capacitors are used to automatically balance the input split capacitor voltages. Finally, experim...

This paper presents a 1.92 kW resonant converter for medium voltage applications that uses low voltage stress MOSFETs (500V) to achieve zero voltage switching (ZVS) turn-on. In the proposed converter, four MOSFETs are connected in series to limit the voltage stress of the power switches at half of the input voltage. In addition, three resonant circuits are adopted to share the load current and to reduce the current stress of the passive components. Furthermore, the transformer primary and secondary windings are connected in series to balance the output diode currents for medium power applications. Split capacitors are adopted in each resonant circuit to reduce the current stress of the resonant capacitors. Two balance capacitors are also used to automatically balance the input capacitor voltage in every switching cycle. Based on the circuit characteristics of the resonant converter, the MOSFETs are turned on under ZVS. If the switching frequency is less than the series resonant frequency, the rectifier diodes can be turned off under zero current switching (ZCS). Experimental results from a prototype with a 750-800 V input and a 48V/40A output are provided to verify the theoretical analysis and the effectiveness of the proposed converter.

This paper presents a new three-level converter to achieve the advantages of zero-voltage switching of power switches, low voltage and current stresses of rectifier diodes, less transformer secondary winding turns, and low output current ripple. Two three-level circuit cells shared same active switches to reduce current stresses of passive components on the primary and secondary sides and to increase output power. In each circuit cell, two filter inductors and four rectifier diodes are used on secondary side to lessen output ripple current and transformer secondary winding turns. Half-bridge circuit shared the lagging-leg switches of three-level converter are adopted to achieve wide zero-voltage switching range. Two transformers are used in the half-bridge circuit to balance output currents of two three-level circuit cells. The circuit performance of the proposed converter are verified by laboratory experiments.

This paper presents a soft switching converter with the advantages of wide zero-voltage switching range, low primary conduction loss, less output inductance and power transfer within the whole switching cycle. Half-bridge circuit is connected to the lagging-leg power switches of full-bridge converter to improve the soft switching load range. Passive snubber is connected on the secondary side of full-bridge converter. One positive rectified voltage is generated on the secondary side in order to reduce the primary current to zero during the freewheeling state. Therefore, the primary conduction loss is reduced. Since the output inductor voltage at the freewheeling state is also decreased, the output inductance of full-bridge converter can be reduced. The output sides of the full-bridge converter and the half-bridge converter are series connection so that the proposed converter delivers energy from the input voltage to the output load within the whole switching period. The performance of the proposed converter is verified by the experimental verifications with a 1.92kW prototype.

A new DC/DC converter with three circuit cells has been presented. For high input voltage applications, two-input split capacitors with four active switches are used in the proposed converter to limit the voltage stress of each power switch at one-half of input voltage. Thus, power metal-oxide semiconductor field-effect transistors (MOSFETs) with 500 V voltage rating can be adopted for 1000 V input voltage applications. Two balance capacitors are adopted in the proposed circuit to automatically balance two split input capacitor voltages in each switching cycle. Three resonant tanks are used at primary side of the proposed converter to share the load current and reduce the current stress of passive components. Thus, the sizes of the magnetic core and bobbin are reduced. If the operating switching frequency is less than the series resonant frequency, power MOSFETs are turned on at zero-voltage switching and rectifier diodes can be turned off at zero current switching. Thus, the switching losses on power semiconductors are reduced. Finally, experiments with a 1.5 kW prototype are provided to verify the effectiveness of the proposed converter.

A new DC/DC converter with zero voltage switching is proposed for applications with high input voltage and high load current. The proposed converter has two circuit modules that share load current and power rating. Interleaved pulse-width modulation (PWM) is adopted to generate switch control signals. Thus, ripple currents are reduced at the input and output sides. For high-voltage applications, each circuit module includes two half-bridge legs that are connected in series to reduce switch voltage rating to Vin/2. These legs are controlled with the use of asymmetric PWM. To reduce the current rating of rectifier diodes and share load current for high-load-current applications, two center-tapped rectifiers are adopted in each circuit module. The primary windings of two transformers are connected in series at the high voltage side to balance output inductor currents. Two series capacitors are adopted at the AC terminals of the two half-bridge legs to balance the two input capacitor voltages. The resonant behavior of the inductance and capacitance at the transition interval enable MOSFETs to be switched on under zero voltage switching. The circuit configuration, system characteristics, and design are discussed in detail. Experiments based on a laboratory prototype are conducted to verify the effectiveness of the proposed converter.

This paper presents a new three-level zero-voltage switching (ZVS) dc/dc converter for high input voltage applications. There are two ZVS circuits in the proposed converter to share load current. Thus, the size of the output chokes is reduced. These two circuits use the same power switches. Thus, the proposed converter has less switch counts compared with the conventional parallel three-level ZVS dc/dc converter. In the proposed converter, each circuit combines one half-bridge converter and one three-level converter. The transformer secondary windings of two converters are connected in series to reduce the size of output inductor. The voltage stress of each power switch is limited at one-half of input voltage due to three-level circuit topology. Based on the resonant behavior by the output capacitance of active switches and the leakage inductance (or external inductance) at the transition interval, power switches are turned on at ZVS within the desired load range. Experiments based on a 1.5 kW prototype are provided to demonstrate the performance of the proposed converter.

A new soft switching resonant converter is presented in this study to reduce the switching losses on power metal oxide semiconductor field effect transistors (MOSFETs) and overcome the reverse recovery losses on rectifier diodes. Two half-bridge legs connected in series and two split capacitors are adopted to limit the voltage stress of each MOSFET at half-input voltage and to reduce the current rating of transformer windings and passive components at output side. A flying capacitor is connected between two half-bridge legs in order to automatically balance two input capacitor voltages. Therefore MOSFETs with low-voltage stress can be used at high-input voltage applications. The resonant converter is adopted in each half-bridge circuit to reduce the switching losses of active devices. Finally, experiments based on a laboratory prototype are provided to verify the circuit performance.

A new zero-voltage switching (ZVS) DC converter with less power switches is presented in this study. The proposed converter includes three subcircuits connected in parallel with the same switches to share load current. Thus, the proposed converter has less switch counts compared with the conventional parallel ZVS DC/DC converter and the output filter inductances and the transformer windings are reduced. Three-level diode clamped converter is used to reduce the voltage stress of switches at V in/2. The input two capacitor voltages are automatically balanced by adding two flying capacitors in three-level DC/DC converter. The current doubler rectifiers are used at the output side to reduce the output current ripple. The output capacitances of metal oxide semiconductor field effect transistors (MOSFETs) and resonant inductances are resonant at the transition interval. Thus, MOSFETs can be turned on under ZVS. Finally, experiments are provided to verify the effectiveness of the proposed converter.

This study presents an interleaved pulse-width modulation (PWM) converter to achieve the functions of zero-voltage switching (ZVS) for all power switches and zero-current switching (ZCS) for rectifier diodes at the secondary side. A three-level hybrid DC converter is adopted to reduce the voltage stress of power switched at one-half of the DC bus voltage and automatically balance the two input capacitor voltages. Therefore MOSFETs with 600 V voltage stress can be used at the second stage DC/DC converter after the three-phase power factor correction circuit. The fixed frequency PWM is used in three-level PWM resonant converter to regulate output voltage. Since the selected switching frequency is less than the series resonant frequency, MOSFETs can be turned on at ZVS and rectifier diodes can be turned off at ZCS. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. Interleaved PWM scheme is adopted to share load current and further cancel current ripple at output capacitor side. Thus, output capacitance can be reduced. Finally, experiments are provided to verify the effectiveness of the proposed converter.

A new zero-voltage switching (ZVS) dc converter for high input voltage and high output current applications is presented in this paper. Two three-level pulse-width modulation (PWM) circuits with the same active switches connected in parallel at the output side are adopted to achieve load current sharing and to decrease current stress of rectifier diodes. The center-tapped rectifiers are adopted at the secondary side to have only one diode conduction loss in the forward current path. The series resonant tank of three-level converter is used to achieve ZVS turn-on for all power switches and zero-current switching for all rectifier diodes within nearly entire load range. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. In order to overcome the drawback of a wide range of switching frequency in conventional series resonant converters, the fixed frequency pulse-width modulation is adopted to regulate the output voltage. The series-connected transformers are used in the primary and secondary sides to share and balance the load current. Finally, experiments based on a laboratory prototype are provided to verify the operation principle and demonstrate the effectiveness of the proposed converter.

A dc/dc pulse width modulation (PWM) circuit was investigated to realize the functions of reduced primary current loss and balanced voltage and current distribution. In the presented dc/dc converter, two full bridge pulse width modulation circuits were used with the series/parallel connection on the high-voltage/low-voltage side. The flying capacitor was adopted on the input side to achieve voltage balance on input split capacitors. The magnetic coupling element was employed to achieve current sharing between two parallel circuits. A capacitor-diode passive circuit was adopted to lessen the primary current at the commutated interval. The phase-shifted duty cycle control approach was employed to regulate load voltage and implement soft switching characteristics of power metal-oxide-semiconductor field-effect transistors (MOSFETs). Finally, the experimental results using a 1.68 kW prototype converter were obtained to confirm the performance and feasibility of the studied circuit topology.

This paper presents a new soft-switching dc/dc converter with series-connected transformers to implement the features of zero-voltage switching (ZVS), load current sharing, low voltage stress for MOSFETs, and low current rating for the rectifier diodes and the output inductors. The proposed converter includes two half-bridge circuits connected in series to limit the voltage stress of MOSFETs at one-half of the input voltage. The output sides of the two circuits are connected in parallel to reduce the current rating on the rectifier diodes and the output inductors and to achieve load current sharing. In order to balance two output inductor currents, series-connected transformers at the low-voltage side are adopted. Thus, the output power is equally distributed by the two half-bridge circuits. The output capacitances of MOSFETs and the resonant inductances are resonant at the transition instant such that MOSFETs can be turned on at ZVS. Finally, experiments based on a laboratory prototype with 1-kW rated power are provided to demonstrate the performance of the proposed converter.

This paper presents a new interleaved three-level soft-switching converter with series-connected transformers to achieve zero-voltage switching for all MOSFETs, less transformer secondary windings, and partial ripple current cancellation. Two circuit modules are adopted in the proposed circuit to share the load current and reduce the ripple currents at the input and output capacitors with the interleaved pulse-width modulation (PWM). In each circuit module, two three-level PWM circuits with the same MOSFETs are operated with the phase-shift by one-half of switching period to reduce the input ripple current. The voltage stress of all switches is clamped at Vin/2. The secondary windings of two transformers are connected in series to balance the primary side currents. The current doubler rectifiers are adopted on the secondary side to partially cancel output inductor ripple current. Experiments with a 1-kW prototype, verifying the effectiveness of the proposed converter, are described.

This paper proposes a new soft-switching circuit for high-input-voltage applications to achieve zero voltage switching (ZVS), implement load current sharing, reduce the voltage stress of switches at $V_{\rm in}$ /2, and decrease current rating of the rectifier diodes and the output inductors. Two three-level pulse-width modulation (PWM) circuits with the same active switches are operated with the phase-shift PWM scheme. Two center-tapped rectifiers are adopted at the secondary side such that the current rating of the transformer windings, rectifier diodes, and output filter inductors are reduced and have only one diode conduction loss in the forward current path. Based on the resonant behavior by the output capacitance of active switches and the leakage inductance (or external inductance), all power switches are turned ON at ZVS. The operation principle, circuit analysis, and design example are discussed in detail. Finally, experiments with 1-kW prototype are provided to verify the effectiveness of the proposed converter.

This paper studies a soft switching DC/DC converter to achieve zero voltage switching (ZVS) for all switches under a wide range of load condition and input voltage. Two three-level PWM circuits with the same power switches are adopted to reduce the voltage stress of MOSFETs at Vin/2 and achieve load current sharing. Thus, the current stress and power rating of power semiconductors at the secondary side are reduced. The series-connected transformers are adopted in each three-level circuit. Each transformer can be operated as an inductor to smooth the output current or a transformer to achieve the electric isolation and power transfer from the input side to the output side. Therefore, no output inductor is needed at the secondary side. Two center-tapped rectifiers connected in parallel are used at the secondary side to achieve load current sharing. Due to the resonant behavior by the resonant inductance and resonant capacitance at the transition interval, all switches are turned on at ZVS. Experiments based on a 1kW prototype are provided to verify the performance of proposed converter.

A novel zero-voltage switching (ZVS) DC/DC converter with series connected transformers for high input voltage application is presented. Two series half-bridge legs and two split capacitors are adopted in order to limit the voltage stress of active switches at V in/2. Two resonant converter modules are used to reduce current stress on active switches and rectifier diodes. Based on the series resonant tank, the active switches are turned on at ZVS and rectifier diodes are turned off at zero-current switching. Thus, the switching loss of active switches and reverse recovery problem of rectifier diodes are reduced. The secondary windings are connected in series to ensure that the primary winding currents are balanced. Finally, experiments are provided to verify the effectiveness of the proposed converter.

An interleaved series resonant converter with fixed frequency pulse-width modulation (PWM) is presented to achieve load current sharing, ripple current cancelation, zero-voltage switching (ZVS) for power switches and zero-current switching (ZCS) for rectifier diodes. Two three-level DC converters with clamped diodes and flying capacitor are adopted to share load current. The voltage stress of power switches is clamped at one-half of DC bus voltage. The interleaved PWM scheme is used to control two converters in order to reduce the output current ripple and size of output capacitor. The series resonant tank in three-level PWM converter is adopted to realise ZVS turn-on for all power switches andZCS for rectifier diodes. Thus, the switching losses of active switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. The fixed frequency PWM operation is adopted to regulate output voltage, so that the drawback of a wide range of switching frequency in the conventional series resonant converters is overcome. Finally, experiments based on a scale-down prototype are provided to verify the effectiveness of the proposed converter.

This study presents a new DC/DC converter with series-connected transformers to achieve zero voltage switching (ZVS) for power switches, less transformer secondary winding and partial ripple current cancellation. Two three-level circuits using the same active switches are operated with interleaved half switching cycle. The voltage stress of all switches is clamped at V in/2. The transformers secondary windings are connected in series to balance the primary side currents. The current-doubler rectifier is adopted on the output side. Thus, the output inductor ripple currents can be partially cancelled each other and the resultant ripple current at the output capacitor is reduced compared with the output ripple current of the centre-tapped rectifier topology. Based on the resonant behaviour by the output capacitance of active switches and the leakage inductance (or external inductance), all power switches are turned on at ZVS. Laboratory experiments with a 1 kW prototype, verifying the effectiveness of the proposed converter, are described.

An interleaved DC/DC converter with series-connected transformers is presented to implement the features of zero voltage switching (ZVS), load current sharing and ripple current reduction. The proposed converter includes two half-bridge converter cells connected in series to reduce the voltage stress of the switches at one-half of the input voltage. The output sides of the two converter cells with interleaved pulse-width modulation are connected in parallel to reduce the ripple current at the output capacitor and to achieve load current sharing. Therefore, the size of the output chokes and the capacitor can be reduced. The output capacitances of the MOSFETs and the resonant inductances are resonant at the transition instant to achieve ZVS turn-on. In addition, the switching losses on the power switches are reduced. Finally, experiments on a laboratory prototype (24V/40A) are provided to demonstrate the performance of the proposed converter.

An interleaved DC-DC converter with soft switching technique is presented. There are two converter modules in the adopted circuit to share the load power. Since the interleaved pulse-width modulation PWM is adopted to control two circuit modules, the ripple currents at input and output sides are naturally reduced. Therefore the input and output capacitances can be reduced. In each circuit module, a conventional boost converter and a voltage doubler configuration with a coupled inductor are connected in series at the output side to achieve high step-up voltage conversion ratio. Active snubber connected in parallel with boost inductor is adopted to limit voltage stress on active switch and to release the energy stored in the leakage and magnetizing inductances. Since asymmetrical PWM is used to control active switches, the leakage inductance and output capacitance of active switches are resonant in the transition interval. Thus, both active switches can be turned on at zero voltage switching. The resonant inductance and output capacitances at the secondary side of transformer are resonant to achieve zero current switching turn-off for rectifier diodes. Therefore, the reverse recovery losses of fast recovery diodes are reduced. Finally, experiments based on a laboratory prototype rated at 400W are presented to verify the effectiveness of the proposed converter. Copyright © 2012 John Wiley & Sons, Ltd.

An interleaved PWM converter is proposed to implement the features of zero voltage switching (ZVS), load current sharing and ripple current reduction. The proposed converter includes two ZVS converters with a common clamp capacitor. With the shared capacitor, the charge balance of the two interleaved parts is automatically regulated under input voltage and load variations. The active-clamping circuit is used to realize the ZVS turn-on so that the switching losses on the power switches are reduced. The ZVS turn-on of all of the switching devices is achieved during the transition interval. The interleaved pulse-width modulation (PWM) operation will reduce the ripple current and the size of the input and output capacitors. The current double rectifier (CDR) is adopted in the secondary side to reduce output ripple current so that the sizes of the output chokes and capacitor are reduced. The circuit configuration, operation principles and design considerations are presented. Finally experimental results based on a 408W (24V/17A) prototype are provided to verify the effectiveness of the proposed converter.