Synchronous Rectifier Research Articles

Online Efficiency Optimization of a Closed-Loop Controlled SiC-Based Bidirectional Boost Converter

This article presents an online efficiency optimization strategy for a digitally controlled, wide operating range silicon carbide based boost converter with bidirectional power flow. The proposed strategy minimizes switching losses at any given operating point by adjusting the converter switching frequency and dead times to optimally set the peak synchronous rectifier turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current. This results in the converter achieving zero-voltage switching quasi-square wave (ZVS-QSW) operation with minimum inductor current ripple. The optimal timing parameters are determined online by fit functions based on sensed input/output voltages and inductor current, and applied to the converter in a low-bandwidth feed-forward loop operating in conjunction with closed-loop regulation of the converter output voltage. The fit functions are developed from multivariate curve fitting of the analytical solutions of the minimum-conduction ZVS-QSW state plane over the complete range of operation. The proposed approach enables bidirectional operation with efficiencies greater than 97.5% for input voltages ranging from 200 to 400 V, step-up conversion ratios up to 2.5, and power levels between 2 and 8 kW. The converter also achieves efficiencies greater than 99% over wide power levels at boost conversion ratios lower than 2.

A Time-Domain-Model-Based Digital Synchronous Rectification Algorithm for CLLC Resonant Converters Utilizing a Hybrid Modulation

For bidirectional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant converters, synchronous rectification (SR) is a key technique that can reduce the conduction losses in rectifying side by replacing the diodes with the switches’ channel. However, existing methods suffer from either complex hardware, or incomplete and imprecise control effect. Aiming at solving these problems, this article proposes a digital sensorless SR algorithm based on the time-domain model under a hybrid modulation for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> converters. The proposed approach can precisely enable the SR drive action within almost the whole load range and without any additional hardware, e.g., antiparallel diode, SR IC, and high bandwidth sensor. Its implementation only needs to measure dc signals (e.g., the output current), rather than any high-frequency resonant signals. Additionally, the presented algorithm can be easily implemented on a digital controller. Finally, experiments have been performed on a prototype to verify the validity and applicability of the presented SR algorithm.

Power-Estimation-Based Synchronous Rectification Solution for Bidirectional DAB-LLC Converter

An LLC-DAB bidirectional converter with reduced switch count as a DC-DC transformer (DCX) is proposed in this paper. It can achieve voltage regulation, full load range zero voltage switching (ZVS) for eight main switches and wide load range ZVS for four auxiliary switches, with consideration of the switch junction capacitors under different power direction. A part portion of total power is transferred through an auxiliary DAB circuit to achieve voltage regulation and bidirectional power conversion. The main power is transferred through LLC circuit with an easy PWM scheme achieving high conversion efficiency. Different from the existing LLC-DAB DCX structure, the two secondary side transformer outputs are in parallel, and connected to the same full-bridge circuit. In this way, the auxiliary DAB circuit can not only adjust the output voltage, but also can inject current into the secondary side to help achieving ZVS of switches without synchronous rectifier (SR) circuit. The converter operation principle is analyzed under different power directions, and ZVS is analyzed with the consideration of all the switch junction capacitors. Based on the analysis, the design consideration is introduced. Finally, a 2-kW prototype with 750V input and 400V output is built up to verify the effectiveness of the proposed solution.

A single input dual output converter with low cross regulation

Nowadays, many applications require multiple power supply voltages for various sub-functional modules, especially in consumer electronics. The single input dual-output (SIDO) converter contains less components is good scheme than adopt two single input single output (SISO) converters. However because of the outputs are coupled with same magnetic component, it would suffer cross regulation problem. This paper presents a cross regulation solution for the SIDO AC/DC converter. By the rectifier diode of upper output winding is replaced with a synchronous rectifier switch and the stacked design of two output windings. The energy of the two output windings can circulate with each other. Therefore cross regulation can be effectively improved. The operation principles, design procedure of the proposed solution are present and descripted. A prototype circuit was built to validate the feasibility of the proposed solution. The main advantages of proposed converter are implemented with low cost analog IC, the synchronous rectification has lower conduction loss, the stacked windings design have less total turns number and lower voltage stress for synchronous rectifier switch.

Self-Driven Current-Doubler Synchronous Rectifier and Design Tuning for Maximizing Efficiency in IPT Systems

A novel driving circuit for a current-doubler synchronous rectifier (SR) to inductive power transfer (IPT) applications is proposed in this article using only auxiliary windings in the existent rectifier output filter inductors to drive active switches. The proposed SR overcomes the limitations of the traditional driving schemes because it does not require any processing, analog circuits, gate driver circuits, or current measurement, normally used in the conventional SR applied to IPT systems. The proposed configuration presents a simple and robust operation considering usual parametric variation in IPT systems, such as coupling factor, misalignment, load variation, and component tolerances. Moreover, the same size and weight of the conventional diode rectifier board are maintained due to the simplicity of the self-driven circuit. The proposed configuration allows increasing the global efficiency by reducing the conduction losses of the output rectifier and previous stages. A resonant circuit design procedure using an iterative process to find the maximum efficiency point considering the self-driven SR is proposed to maximize the global system efficiency. A 100-W resonant series–parallel IPT prototype is developed to validate the performance of the proposed self-driven SR circuit presenting a maximum global efficiency equal to 94.8%.

A Bidirectional Symmetrical C4LC-DCX Resonant Converter With Power Limitation Capability

To achieve the maximum efficiency of resonant converter under wide voltage conversion gain range, two stage conversion, which adopts the resonant converter operating at resonant frequency to work as a dc–dc transformer (DCX) in isolation stage, is a preferred solution. This article proposes a bidirectional C4LC resonant converter to work as a DCX. The structure of the topology is totally symmetrical, and two auxiliary inductors are used to achieve full load range zero-voltage-switching (ZVS) for all the power switches under bidirectional power flow. Unlike conventional ZVS analysis, the ZVS of the proposed converter is analyzed with considerations of all the switch junction capacitors and load. The clamping diodes are also combined in the topology which can help achieve natural power limitation in case of overload and limit the startup current. Even though four inductors and one transformer are illustrated in the topology, all these magnetic components can be simplified and manufactured with one external inductor and one conventional transformer. Meanwhile, the converter operates at a fixed frequency and adopts the synchronous pulsewidth modulation (PWM) modulation, which can achieve constant voltage gain and automatically change the power direction without synchronous rectifier (SR) current detection. Finally, the experimental results from a 1-kW prototype verify the effectiveness of the proposed converter.

An LLC-DAB Bidirectional DCX Converter With Wide Load Range ZVS and Reduced Switch Count

An LLC dual active bridge (DAB) bidirectional converter with reduced switch count as a dc–dc transformer (DCX) is proposed in this article. It can achieve voltage regulation, full load range zero voltage switching (ZVS) for eight main switches and wide load range ZVS for four auxiliary switches, with consideration of the switch junction capacitors under different power direction. A part portion of total power is transferred through an auxiliary DAB circuit to achieve voltage regulation and bidirectional power conversion. The main power is transferred through LLC circuit with an easy PWM scheme achieving high conversion efficiency. Different from the existing LLC -DAB DCX structure, the two secondary side transformer outputs are in parallel, and connected to the same full-bridge circuit. In this way, the auxiliary DAB circuit can not only adjust the output voltage, but also can inject current into the secondary side to help achieving ZVS of switches without synchronous rectifier circuit. The converter operation principle is analyzed under different power directions, and ZVS is analyzed with the consideration of all the switch junction capacitors. Based on the analysis, the design consideration is introduced. Finally, a 2-kW prototype with 750 V input and 400 V output is built up to verify the effectiveness of the proposed solution.

Non-Linear Switching Circuit for Active Voltage Rectification and Ripples Reduction of Piezoelectric Energy Harvesters

This paper describes an improved non-linear switching circuit (INLSC) for active rectification of voltage and reduction of ripples in the voltage waveform for the piezoelectric energy harvesting (PEH) system. The proposed converter controls the alternating current (AC) generated by the piezoelectric device (PD) under mechanical vibration. The proposed circuit combines the boost and buck-boost processes through a switching process, which functions in both positive and negative cycles. In addition, it controls the voltage and frequency of the load capacitor. In this process, the passive components in the circuit are energised by being short with the AC voltage using switching signals, which facilitates the active rectification of ultra-low AC voltage. Design considerations, theoretical analysis, simulations and experimental results are presented. It was shown that the circuit was able to control the switching signal and to convert low AC voltage (0.44 Vi) to high direct current (DC) voltage (6.5 Vdc) while achieving an output power of 469 µW which outperforms the existing similar circuits and synchronous rectifier circuit. The ripples in the rectified voltage were also comparatively less. Application-wise, the proposed circuit could power a manually connected 7-segments display, commonly used for traffic applications.

Synchronous Rectification Based on Resonant Inductor Voltage for CLLC Bidirectional Converter

Synchronous rectification (SR) is an effective method to reduce the secondary side conduction loss of CLLC bidirectional resonant converter and improve its efficiency, but the SR driving signal in CLLC converter is hard to determine. Existing SR signal generating methods can be divided into three categories: theoretical calculation, voltage detection, and current detection. Compared with the other two methods, the current detection method has wider applicability and is insensitive to parasitic parameters, but usually requires lossy, bulky and costly current sensors, increasing the cost and size of the converter. This article proposed a SR scheme based on resonant inductor voltage. The polarity of the resonant current is obtained indirectly through the inductor voltage, thereby avoiding the use of current sensors. To handle the false pulses problem caused by parasitic oscillation, a corresponding SR control strategy is proposed. The SR driving signal is then adjusted according to the delay and transient requirements. Experimental results on a 380V/270V 3kW CLLC converter prototype were presented to verify the effectiveness of the proposed SR method.

An Isolated High Step-Up Converter Based on the Active Secondary-Side Quasi-Resonant Loops

Resonant converter is a good solution as the isolated high step-up converter due to its soft-switching features and less component count. However, since the resonant tank is placed on the primary side (low-voltage side) in most traditional resonant converters, large input current still leads to a big proportion of power loss. Besides, synchronous rectification (SR) is also a big issue. The diode conducting time in a resonant converter is hard to be predicted so a current transformer or an analog SR chip is usually employed to detect the current zero-crossing point when the higher efficiency is required. In this article, an isolated high step-up converter with active secondary-side quasi-resonant tank is proposed. Since the whole resonant tank is placed on the high-voltage side, the current stress of the resonant capacitors and their power loss can be greatly alleviated. Besides, the analytical solution of the diode conducting time is derived and two SR control schemes are proposed, without the need to detect the current zero-crossing point. All the switches and diodes achieve the soft-switching so this leads to a good efficiency performance. The validity is confirmed by the experimental results of a 500 W prototype with 36–48 V input and 380 V output.

Synchronous rectification control method of AC/DC converters based on the response surface algorithm

In order to improve the stability and anti-interference ability of synchronous rectification control of AC/DC converter, a synchronous rectification control method of AC/DC converter based on response surface algorithm is proposed. A high speed and low power comparator is designed to compare input and output signals. The AC/DC converter optimisation model is constructed by response surface algorithm. Logic control is implemented through synchronous rectification logic and synchronous rectification control. The control part of power supply and drive AC/DC converter is designed to realise the synchronous rectification control of AC/DC converter. The performance of synchronous rectifier control of AC/DC converter under the application of the proposed method was tested. The test results show that the output waveform of the converter trigger pulse is very stable and regular. It has good phase shifting characteristic; the method has strong anti-interference ability and achieves the original design goal.

GaN Active Rectifier Diode

Active or synchronous rectification is used today to further increase the efficiency of mass-market power supplies by eliminating the turn-on voltage of rectifier diodes, thus reducing conduction losses. However, the active rectification is usually realized by two devices: a power MOSFET and a control circuit to imitate an ideal diode behavior. This paper presents a GaN active rectifier diode consisting of a 600 V power transistor, a control circuit with gate driver, and a supply generation, all monolithically realized in a GaN power integrated circuit (IC). This enables a true two-terminal device that can directly replace a rectifier diode. In order to evaluate the proposed conduction loss reduction by replacing a rectifier diode by an active diode, the theoretical limits at circuit level and at semiconductor level are analyzed. The GaN active rectifier diode is demonstrated in a half-wave rectification (110/230 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</sub> , 50/60 Hz) up to a forward current of 6 A. A single-device realization of low-loss GaN active rectifier diodes is more cost-efficient than a multi-chip or package-integrated solution.

Comprehensive Review of KY Converter Topologies, Modulation and Control Approaches With Their Applications

In current scenario, the challenging task in designing a DC-DC converter has high voltage gain and small output ripple waves, which researchers deal with highly complicated. Because of its topological and Continuous Conduction Mode (CCM), the KY converters have developed a better converter than all the traditional DC-DC converters to overcome this intricacy of voltage transfer gain and output ripple waves. The KY converters had comparative and various qualities when compared with the boost converter with Synchronous Rectifier (SR). The KY converter is used in photovoltaic and sustainable power applications, which are examined in this study. KY converter incorporates mode-1 and mode-2 operation and its types, for example, one plus D and one plus 2D where the KY can deliver the N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> type of KY converters. This article provides a comprehensive review and investigation of the KY converters, which incorporates their topology with control methodologies, Pulse Width Modulation (PWM) techniques, working activity of KY converters, and types for mode-1 and -2; it interprets the few strategies the KY converter is executed and its applications.

Switched inductor based bidirectional DC-DC converter for high voltage gain

A switched inductor based bidirectional DC-DC converter (BDC) for high voltage gain is designed for electric vehicle (EV) and solar PV installation applications. The global energy crisis has increasingly intensified due to the increased population, the government is compelled to reduce the use of fossil fuels due to global warming and are forced to utilise renewable sources of energy. One of the major challenges with EV and PV installation are the interface between the energy storage unit and the DC link. The proposed BDC can solve this problem and achieves a high step-up/step-down conversion ratio. This converter operates at a switching frequency of 100 kHz and obtain a high voltage gain without having extreme duty ratio values. Zero voltage switching (ZVS) improves the performance of synchronous rectifiers by allowing them to switch on and off more easily with improved efficiency. A comparison between conventional buck-boost converter, high voltage gain BDC and switched inductor based BDC is done. The performance study and analysis of BDC is also carried out with MATLAB/SIMULINK R2020b.

Design of a High Efficiency High Step-Up/Step-Down Bidirectional Isolated DC–DC Converter

This paper presents a novel bidirectional DC–DC converter, equipped with a three-winding coupled inductor, that can be applied to high-voltage, bidirectional DC–DC energy conversion and meet battery charging and discharging requirements. The architecture consists of a semi-Z-source converter and a forward–flyback converter featuring a three-winding coupled inductor with an iron core. This proposed topology retains the current continuity characteristics of the low-voltage side, all switches possess the zero-voltage switching feature, and the switches on the low-voltage side in the step-down mode have a synchronous rectification function. A 500-W bidirectional converter is implemented to examine the practicality and feasibility of the proposed topology. The relatively streamlined design of the converter can greatly reduce production costs. In the step-up and step-down modes, the maximum energy conversion efficiencies are 95.74% and 96.13%, respectively.

Dual-Side Phase-Shift Control for Strongly Coupled Series–Series Compensated Electric Vehicle Wireless Charging Systems

Wireless power transfer (WPT) for electric vehicles is an emerging technology and a future trend. To increase power density, the coupling coefficient of coils can be designed to be large, forming a strongly coupled WPT system, different from the conventional loosely coupled WPT system. In this way, the power density and efficiency of the WPT system can be improved. This paper investigates the dual-side phase-shift control of the strongly coupled series–series compensated WPT systems. The mathematical models based on the conventional first harmonic approximation and differential equations for the dual-side phase-shift control are built and compared. The dual-side phase-shift angle and its impact on the power transfer direction and soft switching are investigated. It is found that synchronous rectification at strong couplings can lead to hard switching because the dual-side phase shift in this case is over 90°. In comparison, a relatively high efficiency and soft switching can be realized when the dual-side phase shift is below 90°. The experimental results have validated the analysis.

A 10 MHz DC/DC Converter With Zero-Phase Difference Synchronous Driving Signal

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.

A Dual-transformer DC–DC with Variable frequency modulation Technique

For renewable power production systems to use less energy overall, power converters with improved efficiency over a wider load range are crucial. We introduce an unique dual-transformer DC-DC converter with many resonant components. With the right choice of resonance parameters, the converter can achieve a broad DC voltage gain range thanks to several resonance features. More resonance frequencies are included in the proposed converter as well, which will allow the load to receive more of the tertiary active power. Diodes achieve soft-switching or quasi-soft-switching during both the on and off periods, and all power switches are capable of on-soft switching. The proposed and analysis of variable frequency modulation (VFM) are achieved. By providing soft switching throughout the whole load range, the suggested modulation approach can lower switching losses. Additionally, the center-tapped bridge implementation of the synchronous rectifier further reduces conduction losses while the proposed modulation technique ensures soft switching of all devices. We installed a 500W prototype in the laboratory to confirm the theoretical analysis. According to the findings of the experiments, the suggested converter can maintain a relatively high efficiency (95%) throughout a wide load range. Starting with 300W, the highest efficiency is 95.4%.

A High-Efficiency High-Power-Density On-Board Low-Voltage DC–DC Converter for Electric Vehicles Application

The on-board low-voltage dc-dc converter (LDC) in electric vehicles (EVs) is used to connect the high-voltage battery with the low-voltage auxiliary system. With the advancement of auxiliary equipment in EVs, the output current of the LDC can be hundreds of amperes, which will cause high-conduction loss and severe thermal concern. In this article, a high-efficiency high-power-density on-board LDC is presented. To reduce current stress and improve efficiency, three-phase interleaved LLC dc-dc converters are paralleled to provide 270 A load current. Synchronous rectifier is used to reduce secondary conduction loss. zero-voltage-switching (ZVS) turn-on of primary switches and ZCS turn-off of secondary switches are achieved, thus switching loss can be reduced significantly. Moreover, phase-shedding technology is used to improve light load efficiency. Switch-controlled capacitor (SCC) technology is used to achieve accurate load current sharing among the three phases, which protects the devices against high-current stress, reduces the conduction loss, and improves the reliability of the system. As SCC switches achieve ZVS turn-on and turn-off by its nature, the loss of the SCC circuit is of less concern with regard to the rated output power. In addition, GaN HEMTs are used in the primary side to improve the power density and eventually help achieving light weight. A 3.8-kW (14 V/270 A) LDC prototype is developed and tested. Experimental results show good current balancing among the three phases. A peak efficiency of 96.7% at 140 A load and a full load efficiency of 95.8% are achieved with 3 kW/L power density and 1.5 kg weight.

Current-Fed LC Series Resonant Converter With Load-Independent Voltage-Gain Characteristics for Wide Voltage Range Applications

This article proposes a current-fed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant converter, which integrates a two-phase interleaved boost circuit with a full-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant converter. All switches can achieve zero voltage switching (ZVS) under full load range without utilizing a magnetizing inductor or an auxiliary inductor, and synchronous rectification (SR) can be realized without SR driving detection. With the proposed modulation, the resonant current is discontinuous without circulating current. Moreover, the voltage gain of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant conversion is fixed, which is independent of load; therefore, the design of voltage regulation range and related parameters can be simplified. The integrated boost circuit works in the critical current mode to achieve ZVS for all the switches. Meanwhile, digital adaptive frequency modulation is presented to ensure ZVS realization and to minimize the boost inductor current ripple. The working characteristics and design considerations for the key parameters of the proposed modulation are also presented in detail in this article. Finally, a 600-W prototype with 27–54 V input and 360 V output is built, and experimental results validate the effectiveness and the advantages of the proposed solution.