Center-tapped Rectifier Research Articles

Implementation of a ZVS Three-Level Converter with Series-Connected Transformers

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.

Zero‐voltage switching full‐bridge DC/DC converter with parallel‐connected output and without output inductor

This study presents a soft-switching converter without output inductor. The features of the proposed converter are zero-voltage switching (ZVS) for all power switches, load current sharing and high circuit efficiency. Full-bridge converter with phase-shift pulse-width modulation (PWM) is adopted to regulate the output voltage. Based on the resonant behaviour by the output capacitance of MOSFETs and the resonant inductance, active switches can be turned on at ZVS during the transition interval. Thus, the switching losses of power MOSFETs are reduced. The voltage stress of power switches is clamped to DC bus voltage. Four transformers are connected in series in the primary side. Each transformer can be operated as an inductor to smooth the output current or a transformer to achieve electric isolation and power transfer from input side to output side. Therefore no output inductor is needed in the secondary side. Two centre-tapped rectifiers connected in parallel are used in the secondary side to achieve load current sharing. Finally, experiments based on a 960 W (48 V/20 A) laboratory prototype are provided to demonstrate the performance of proposed converter.

Analysis and implementation of a new soft switching DC/DC PWM 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 Vin/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.

Soft switching DC/DC converter for high-input voltage and medium-power applications

A new soft switching DC/DC converter for high-input voltage and medium-power applications is presented in this study to achieve zero-voltage switching (ZVS) turn-on for all power switches, implement load current sharing, reduce the voltage stress of switches at Vin/2 and decrease current rating of the rectifier diodes and the output inductors. Three three-level ZVS DC/DC circuits with the same active switches are adopted in order to reduce the current rating of the rectifier diodes and output filter inductors for high-input voltage and high-load current applications. Three centre-tapped rectifiers are connected in parallel 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. Phase-shift pulse-width modulation scheme is used to control four power switches and regulate the output voltage. Based on the resonant behaviour 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. Finally, experiments with 1 kW prototype are provided to verify the effectiveness of the proposed converter.

Analysis on Center-Tap Rectifier Voltage Oscillation of LLC Resonant Converter

The LLC resonant converter employing a center-tap rectifier can suffer from a high voltage oscillation across rectifier diodes owing to a leakage inductance of a transformer secondary. The amplitude of this voltage oscillation is varied according to design parameters, parasitic components, and operation regions, i.e., below-resonant region and above-resonant region. To reduce the diode voltage stress, this paper analyzes the voltage oscillation mechanism and presents the design consideration.

A Current-Driving Synchronous Rectifier for an LLC Resonant Converter With Voltage-Doubler Rectifier Structure

This paper proposes a current-driving scheme for a synchronous rectifier (SR) in an LLC resonant converter with a voltage-doubler rectifier. In the proposed scheme, only one current transformer (CT) with one secondary winding is used to drive two SRs in the voltage-doubler rectifier. Also, the sensed current from the CT can be fed to the output with an energy-recovery circuit. Compared to the conventional center-tapped rectifier, the CT count for the SR drive circuit is reduced, which saves both cost and space. Although the current rating of the SR in the voltage-doubler rectifier is doubled, the voltage rating is well reduced and a lower voltage rating device with lower ON-state resistance can be used to compensate the increased current rating. Furthermore, the SR voltage stress is well clamped to the output voltage under any condition which improves the reliability of the circuit. A prototype with 16 V/5.6 A output was built to verify the theoretical analysis.

Analysis, Design and Implementation of an Interleaved Single-Stage AC/DC ZVS Converters

An interleaved single-stage AC/DC converter with a boost converter and an asymmetrical half-bridge topology is presented to achieve power factor correction, zero voltage switching (ZVS) and load voltage regulation. Asymmetric pulse-width modulation (PWM) is adopted to achieve ZVS turn-on for all of the switches and to increase circuit efficiency. Two ZVS half-bridge converters with interleaved PWM are connected in parallel to reduce the ripple current at input and output sides, to control the output voltage at a desired value and to achieve load current sharing. A center-tapped rectifier is adopted at the secondary side of the transformers to achieve full-wave rectification. The boost converter is operated in discontinuous conduction mode (DCM) to automatically draw a sinusoidal line current from an AC source with a high power factor and a low current distortion. Finally, a 240W converter with the proposed topology has been implemented to verify the performance and feasibility of the proposed converter.

A Bidirectional UPS Inverter Utilising High Frequency Center–Tapped Transformer

A new variation of transformer-isolated inverter for UPS application is proposed. It is basically similar to the circuit proposed by Kourtroulis with the following modifications: 1) a modified modulation technique for the HF PWM interver stage and 2) replacing the full bridge active rectifier witha center-tapped active rectifier. With these modifications, the switches count is reduced, and expectedly, the efficiency is increased. Futhermore, the modified PWM technique will ensure that the transformer can be utilised near to its full potential. This is due to be absence of the low frequency component that can result in transformer saturation. The paper will detail the design considerations for the proposed topology. It will primarily focus on the power circuit, modulation method, and the high frequency transformer design. To prove the concept, a 1–kW prototype inverter was built and tested. Keywords: Inverter, bidirectional, high frequency transformer, pulse width modulation

Implementation of an interleaved resonant converter for high-voltage applications

An interleaved resonant converter for high voltage application is presented in this paper. There are two half-bridge legs connected in series and two split capacitors in the adopted circuit to limit the voltage stress of each active switch at one-half of input voltage. Thus MOSFETs with 600V voltage rating can be adopted for 1200V input voltage application. For each half-bridge leg, two series resonant circuits are operated with interleaved one-half of switching period. The secondary windings of two transformers are connected in series in order to balance the transformer primary currents and to share the input current. Thus the sizes of the transformer core and bobbin are reduced. The centre-tapped rectifier is used on the output side to reduce the conduction loss with one diode voltage drop. Based on the resonant behaviour, MOSFETs are turned on at ZVS, and rectifier diodes can be turned off at ZCS if the switching frequency is less than the series resonant frequency. Two half-bridge legs are operated with one-fourth of switching period such that the ripple currents at input and output sides arc reduced. Finally, experiments with a 960W prototype, verifying the effectiveness of the proposed converter, are described.

ZVS Resonant Converter With Series-Connected Transformers

This paper presents a new series-resonant converter with series-connected transformers in order to realize zero voltage switching (ZVS) for power switches, zero current switching (ZCS) for rectifier diodes at full load, less transformer secondary winding with a full-wave rectifier, and load current sharing. Two series-resonant converters using the same switches are operated with interleaved half switching cycle. The secondary windings of transformers are connected in series in order to ensure that the primary side currents are balanced to share load current. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is adopted on the output side such that the voltage stress of the rectifier diodes is equal to the output voltage, rather than being two times the output voltage as in a conventional center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at ZVS, and rectifier diodes are turned off at ZCS if the switching frequency is less than the series resonant frequency. The proposed converter can be applied for the power supply unit of all-in-one PCs, liquid crystal display (LCD) TVs and servers, and dc-dc converters for fuel-cell power system. Laboratory experiments with a 1000-W prototype, verifying the effectiveness of the proposed converter, are described.

ZVS Resonant Converter With Parallel–Series Transformer Connection

A new series resonant converter with a parallel-series transformer connection is proposed in order to achieve zero voltage switching (ZVS) for all power switching, zero current switching (ZCS) for rectifier diodes at a full load, and less transformer secondary winding with a full-wave rectifier. For high-output-voltage applications, the primary windings of two transformers are connected in parallel in order to share the input current and reduce the root-mean-square rms current on the primary windings such that the copper losses on the transformers are reduced. The secondary windings of the two transformers are connected in series in order to ensure that the primary side currents are balanced and the secondary winding turns are also reduced. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is used on the output side. Thus, the voltage stress of the rectifier diode is equal to the output voltage rather than being two times the output voltage as that in a center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at the ZVS, and the rectifier diodes are turned off at the ZCS if the operating switching frequency is less than the series resonant frequency. The laboratory experiments with a 660-W prototype, verifying the effectiveness of the proposed converter, are described.

A New Current-Driven Synchronous Rectifier for Series–Parallel Resonant ( $LLC$) DC–DC Converter

A new synchronous rectifier (SR) driving method is proposed using primary current sensing in this paper. Because the magnetizing current of transformer is included in the primary winding of transformer, it cannot be used to generate the driving signals of SRs directly. A current-compensating winding in current transformer (CT) is used to cancel out the magnetizing current and generate suitable driving signals for SR. Therefore, one CT is used to generate two driving signals for two SRs in LLC converter with a center-tapped rectifier. This current-driven method is simple and low cost for high-output-current dc-dc application. A 150-W dc-dc prototype using LLC half-bridge converter with the proposed SR circuit is built up to verify the theoretical analysis.

Analysis of two resonant converters with the same converter leg

A new series resonant converter composed of two resonant circuits with the same converter leg is presented to achieve the zero-voltage switching (ZVS) turn-on of power switches at a wide range of input voltage and load conditions and zero-current switching (ZCS) turn-off of rectifier diodes in a low input voltage case. Thus, the switching losses of power switches and reverse recovery current on rectifier diodes are improved. If the minimum dc voltage gain of the proposed converter is properly selected, the output voltage can be regulated at no-load condition. Two resonant converters using the same power switches are operated by the phase shift half-switching cycle. Thus, the current ripple at the input terminal capacitor can be reduced. In order to reduce the current stresses of output diodes, the output sides of two resonant converters are connected in parallel. The root mean square currents on transformer secondary windings, transformer copper losses and thermal losses can be further reduced. The output voltage doubler topology is adopted in the output side such that the voltage stress of rectifier diodes is equal to the output voltage instead of two times the output voltage in the conventional centre-tapped rectifier topology. Based on the resonant behaviour, all switches are turned on at ZVS and rectifier diodes are turned off at ZCS if the switching frequency is less than the series resonant frequency. The laboratory experiments with a 1000 W prototype are provided to verify the effectiveness of the proposed converter.

Implementation of a series resonant converter with series–parallel transformers

This study presents a series resonant converter with series–parallel transformers in order to achieve zero voltage switching (ZVS) turn-on of MOSFETs, zero current switching (ZCS) turn-off of rectifier diodes, less voltage stress of rectifier diodes, less secondary winding with a full-wave rectifier and load current sharing. Two series resonant modules with the same switches are operated with the phase-shifted half switching cycle. In each resonant converter, primary windings of two transformers are connected in parallel in order to share the input current and reduce the root-mean-square (rms) current on primary windings such that copper losses of the transformers are reduced. The secondary windings of two transformers are connected in series in order to ensure that the primary currents are balanced to share load current. Thus the sizes of the transformer core and bobbin are reduced. Two full-wave diode rectifiers are adopted on output side such that the voltage stress of rectifier diodes is clamped to output voltage, rather than being two times the output voltage as in a conventional centre-tapped rectifier topology. Laboratory experiments with a 1000 W prototype were provided to describe the effectiveness of the proposed converter.

Practical Evaluations of a Novel Asymmetrical ZCS-PWM DC-DC Converter with High-Frequency Transformer-Link

This paper presents a novel Zero Current Switching (ZCS)-PWM controlled half-bridge DC-DC converter with High-Frequency (HF)-link. The newly-proposed soft switching DC-DC converter consists of a multi-resonant half-bridge HF-isolated inverter controlled by an asymmetrical PWM scheme and a center-tapped diode rectifier with a choke input filter. In order to attain the wide range of soft-commutation under the condition of constant switching frequency, the single Active Edge-Resonant Cell (AERC) that is composed of a lossless inductor and a switched resonant capacitor is originally employed for the half-bridge inverter arm, providing and assisting ZCS operations in the switching power devices. The ZCS-PWMDC-DC converter treated here is evaluated in experiments using the 800 W-55 kHz prototype. The practical effectiveness of the proposed soft switching DC-DC converter is actually demonstrated and discussed with the experimental results under open loop and closed loop configurations. Finally, the feasibility of the DC-DC converter topology is discussed from the view points of the high efficiency and high power density.

A Novel High-Frequency Transformer-Linked Soft-Switching Half-Bridge DC–DC Converter With Constant-Frequency Asymmetrical PWM Scheme

This paper presents a novel soft-switching half-bridge dc-dc converter with high-frequency link. The newly proposed soft-switching dc-dc converter consists of a single-ended half-bridge inverter controlled by an asymmetrical pulsewidth-modulation scheme and a center-tapped diode rectifier. In order to attain the wide range of soft commutation under constant switching frequency, the single active edge-resonant snubber cell composed of a lossless inductor and a switched capacitor is employed for the half-bridge inverter leg, providing and assisting zero-current-switching operations in the switching power devices. The practical effectiveness of the proposed soft-switching dc-dc converter is demonstrated by the experimental results from an 800 W - 55 kHz prototype. In addition, the feasibility of the dc-dc converter topology is proved from the viewpoints of the high efficiency and high power density.

Analysis, Design, and Implementation of a Parallel ZVS Converter

A soft-switching converter is presented in this paper to achieve a zero-voltage-switching (ZVS) turn on for all switches. Two half-bridge converters with asymmetric pulsewidth-modulation scheme are connected in parallel to control the output voltage at the desired value and achieve load-current sharing. Based on the output capacitance of power switches and the resonant inductance, including the external inductance and the transformer leakage inductance, the resonance can be achieved at the transition interval of power switches. Therefore, the ZVS turn on of power switches can be realized. The peak voltage of the power switches is limited to input dc voltage. The center-tapped rectifier is adopted at the transformer secondary side to achieve a full-wave rectification. Operation principles, steady-state analysis, and design equations of the proposed converter are discussed in detail. Finally, experimental results based on a 240-W prototype are provided to verify the performance and the feasibility of the proposed converter.

Low Voltage and Current Stress ZVZCS Full Bridge DC–DC Converter Using Center Tapped Rectifier Reset

An improved zero-voltage and zero-current-switching (ZVZCS) full bridge dc-dc converter is proposed based on phase shift control. With an auxiliary center tapped rectifier at the secondary side, an auxiliary voltage source is applied to reset the primary current of the transformer winding. Therefore, zero-voltage switching for the leading leg switches and zero-current switching for the lagging leg switches can be achieved, respectively, without any increase of current and voltage stresses. Since the primary current in the circulating interval for the phase shift full bridge converter is eliminated, the conduction loss in primary switches is reduced. A 1 kW prototype is made to verify the theoretical analysis.

Asymmetrical pulse-width modulation bidirectional DC–DC converter

System analysis of a bidirectional DC–DC converter for a fuel cell electric vehicle driving system is presented. The proposed converter is based on a zero voltage switching (ZVS) half-bridge converter with centre-tapped rectifier at the secondary side of the transformer. The asymmetrical pulse-width modulation is used in the converter to achieve ZVS feature of power switches and to regulate the output voltage at the desired value. The proposed converter has the advantages of high efficiency, low circuit components and simple circuit configuration. The operating principle and the system analysis are described and discussed in detail. Finally, the experimental results for the proposed converter are provided to verify the theoretical analysis.

A Rectification Topology for High-Current Isolated DC-DC Converters

This paper presents a novel current tripler rectification (CTR) topology for secondary-side rectification in high-current low-voltage isolated dc-dc converters. Compared with the conventional center-tapped and current doubler rectifiers, the CTR topology has three filter inductors to share the output current, and thus higher current capability and better thermal management can be achieved. Theoretical analysis and experimental results verify that the proposed CTR is a good candidate for rectification topology in high-current dc-dc converters.