Wide Zero-voltage Switching Range Research Articles

Maximum Efficiency Tracking and ZVS Realization for Wide Output Voltage Range Employing Segmented TPS Modulation Scheme

The efficiency of wireless power transfer (WPT) systems is highly dependent on the load and dc voltage gain, which may change in a wide range in electric vehicle (EV) charging applications. Besides, existing control triple-phase-shift (TPS) strategies aimed at power regulation, zero-voltage switching (ZVS) realization and maximum efficiency point tracking (MEPT) have limitations when applied to the wide output voltage application. To fill this gap, a segmented TPS modulation scheme is proposed. Considering wide-range ZVS, three different working modes are derived to achieve MEPT over the wide output voltage range. The proposed modulation scheme employs closed-loop control by integrating different working modes. In addition, the efficiency-oriented seamless transition method among different working modes is described, which can avoid the transient oscillation at the boundary of the mode transition. The proposed modulation scheme's on-state loss and switching loss are compared to the traditional TPS modulation scheme. Finally, a 1.5 kW prototype has been built to verify effectiveness of the proposed modulation scheme within the wide voltage range, and the measured efficiency can be increased by up to 0.82% in the deep buck mode and 2.20% in the deep boost mode.

Analysis of Grid Current Distortion and Waveform Improvement Methods of Dual-Active-Bridge Microinverter

Due to its merits of fewer power switches, a wide zero-voltage switching range, and high efficiency, the dual-active-bridge (DAB) microinverter is drawing growing interest. However, it has an inherent issue of grid current distortion and spikes, which deteriorate the total current distortion. Existing literature mainly focuses on modulation strategies and barely analyzes the underlying causes, let alone the methods to improve grid current quality. This article fills this blank by revealing the dead-time effect on grid current distortion from two aspects. Several methods are proposed to improve the grid current quality and are compared in detail. Besides, a complete set of grid current closed-loop control methods is proposed based on the DAB microinverter modeling. The control method not only provides the correct control logic but also eliminates the immanent time-varying and condition-dependent features of the control loop, making the proposed current control method self-adaptive and universal. The analyses and the proposed control method are all validated by experimental results.

A Closed-Loop High-Frequency Current Shaping Method to Achieve Trapezoidal Transformer Current in a Current-Fed Dual Active Half-Bridge Converter for Minimum RMS Current and Wide-Range ZVS

This article proposes the use of primary and secondary side duty ratio control along with the phase shift control in a current-fed dual active half-bridge (DAHB) converter to achieve trapezoidal transformer current, which results in zero voltage switching (ZVS) of all the switches and minimum rms current even at light loads, for a wide range of input voltage. The high-frequency transformer current is directly sensed at specific transition instants by a delay-adjusted sampling strategy to be used as control variables in a current control structure. This is better because the voltage control of capacitor voltages would have required more expensive sensors. A simple and accurate small-signal model of the converter is developed, and the relevant transfer functions are derived. The controller design details are provided. Finally, experimental results on a 1-kW laboratory prototype demonstrate the effectiveness of the closed-loop duty ratio control in achieving trapezoidal transformer current resulting in improved efficiency and ZVS of the switches, compared to a simple phase shift control.

An Independent Dual-Coil Driving Topology for Wireless Power Transfer

The existing dual-coil driving topology mostly adopts two inverters or additional switching circuit, which increases the cost and size, and the complexity of the wireless power transfer (WPT) system. In this letter, a novel inverter topology with independent dual-coil driving capability is proposed for WPT applications, where the main switch and auxiliary switch can drive two independent coils. Moreover, this topology not only offers wide zero voltage switching range and compact size, but also improves the output power and coil utilization. Meanwhile, a quadruple D square (QDS) coil with uniform magnetic field is discussed with the dual-coil driving topology. The detailed parameters design of the proposed topology is discussed and the QDS coil is compared with other coils in terms of magnetic flux intensity. Finally, a 1MHz and 220W wireless power transfer system is built to verify the proposed topology and coil structure.

Adaptive Modulation of Resonant DAB Converters for Wide Range ZVS Operation With Minimum Reactive Circulating Power

Resonant mode dual active bridge (DAB) bidirectional dc–dc converters using either an inductive–capacitive–inductive ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> ) or a capacitive–inductive–capacitive ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLC</i> ) ac-port network offer several performance benefits compared to more conventional nonresonant filter DAB topologies. This includes a reduction in the circulating power between the two bridges, which consequently enables the conduction loss to be minimized and the physical converter volume to be reduced. However, these gains also require that soft-switching is maintained, which is very challenging to achieve across all operating conditions, particularly at light loads. This article investigates the zero-voltage-switching (ZVS) capability of resonant mode DAB converters, applying Fourier analysis to the converter modulation patterns to quantify the ZVS boundaries analytically. The resulting analytic formulations also quantify the DAB real and reactive power flows, which subsequently enables the identification of modulation conditions that improve the converter's soft-switching and reactive circulating power flow behavior. The analysis is verified using detailed time-domain PSIM simulations matched to experimental DAB converters equipped with both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLC</i> filters.

A 1-kW and 100-cm Distance Magnetically Coupled Resonant WPT System Achieving 80% Efficiency

For the magnetically coupled resonant wireless power transfer (MCR WPT) applications with high-power level and medium-range distance, the low coupling coefficient brings severe challenges to the system efficiency and reliability, as the coil loss and the voltage/current stress on compensation components are both considerable; meanwhile, the high operating frequency that contributes to improve the power density will result in high switching loss and related electromagnetic interference. In this article, a parameter design methodology for high-power and medium-range-distance MCR WPT applications was proposed to achieve high system efficiency. The accurate time-domain system model was built to obtain the relationship among voltage/current stresses on the compensation components, zero-voltage-switching (ZVS) conditions of power switches and system parameters. The key parameters, including the switching frequency, the coil self-inductance, and the compensation inductance, are designed to realize wide-range ZVS and reduce voltage/current stresses. Double-layer coil configuration was adopted instead of the traditional single-layer coil to reduce coil losses, and the series compensation capacitors in TX and RX coils were split to achieve current sharing between double-layer coils. Meanwhile, the LCCL-TT compensation network was used to achieve the optimal load and maximize the system efficiency. Finally, a 1-kW MCR WPT prototype within 100-cm transmission distance was implemented in the laboratory for experiments, and the system efficiency under the rated condition is 80.62%.

Zero-Voltage Switching Full-Bridge Converter With Reduced Filter Requirement and Wide ZVS Range for Variable Output Application

In this article, a novel zero-voltage switching (ZVS) full-bridge converter is proposed to overcome the disadvantages of traditional phase-shifted full-bridge (PSFB) converter. In the proposed converter, a half-bridge (HB) converter with center-tap rectifier (CTR) is integrated into the traditional PSFB converter by sharing the lagging-leg switches and output filter. The HB converter operates with full duty cycle to ensure continuous energy transmission and the output voltage is regulated by adjusting the phase-shifted time of full-bridge (FB) converter. The proposed converter has many advantages such as reduced filter requirement, wide ZVS range and low primary circulating current. In addition, the rectifier in the proposed converter is composed of a full-bridge rectifier section and a CTR section. This feature makes the proposed converter well appropriate for the medium output voltage applications. Key operation principle and characteristics are fully discussed in this article. The effectiveness of proposed converter is verified using a 1.2 kW prototype circuit with 280 V input voltage and 60–120 V output voltage.

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.

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.

A Dual-Bridge DC–DC Resonant Converter Using Extended PWM and Phase-Shift Control

To enhance the overall efficiency of a dual-bridge resonant converter, a new asymmetric pulsewidth modulation (PWM) control named extended pulsewidth modulation (EPWM) with both variable pulsewidth and variable symmetry is introduced in this article, which is applied to the high-voltage-side bridge of the converter and is combined with phase-shift control to form a 3-D gating scheme. A specified control strategy based on the 3-D gating scheme is then derived for the purpose of minimum tank current operation. Thanks to the flexibility brought by EPWM, full zero-voltage switching (ZVS) operation range is maintained as large as that of a conventional PWM-based minimum current trajectory, and only one switch loses ZVS at light load. The modulated voltage pulsewidth is kept at high level in a wide load range, which compromises the by-effect of high-order harmonics due to asymmetric modulation. Besides, the backflow power on both sides is almost minimized naturally. Therefore, the proposed control trajectory can have better performance in a light-load region than previous reported solutions. Experimental results prove the accuracy and effectiveness of the proposed minimum current operation with wide ZVS range and show the improvement of overall conversion efficiency.

An Interleaved Phase-Shift Full-Bridge Converter with Dynamic Dead Time Control for Server Power Applications

A compact and high-efficiency power converter is the main business of today’s power industry for server power applications. To achieve high efficiency with a low-output ripple, an interleaved phase-shift full-bridge (PSFB) converter is designed, built, and tested for server power applications in this study. In this paper, dynamic dead time control is proposed to reduce the switching loss in the light load condition. The proposed technique reduces the turn-off switching loss and allows a wide range of zero-voltage switching. Moreover, the current ripple of the output inductor can be reduced with the interleaved operation. To verify the theoretical analysis, the proposed PSFB converter is simulated, and a 3 kW prototype is constructed. The experimental results confirm that the conversion efficiency is as high as 97.2% at the rated power of 3 kW and 92.95% at the light load of 300 W. The experimental transient waveforms demonstrated that the voltage spike or drop is less than 2 V in the fast-fluctuating load conditions from 0% load to 60% load and 40% load to 100% load.

Optimized Control for Modified Push-Pull Dual Active Bridge Converter to Achieve Wide ZVS Range and Low Current Stress

Compared with the traditional dual active bridge (DAB) converter, the push-pull DAB converter can reduce the number of switching devices and is suited for low voltage applications. In order to extend the zero voltage switching (ZVS) range and reduce the current stress within wide voltage range, this paper modifies output rectifier circuit, and proposes an optimized control strategies for push-pull DAB converters. Unlike conventional modulation that only utilizing the primary duty cycle and phase shift angle to adjust the power, the duty cycle for the secondary side is also utilized for the PWM modulation. With the modified PWM modulation, a control law for achieving minimum root mean square (RMS) current within the precondition of achieving wide range ZVS is proposed. The working modes under the modified PWM modulation, current and power analysis and optimized control law are analyzed in depth. Finally, the experimental results using a 1 kW prototype verify the effectiveness of the proposed converter.

High-Efficiency WPT System for CC/CV Charging Based on Double-half-bridge Inverter Topology with Variable Inductors

Efficiency remains a key challenge in wireless charging in academia and industry. In this article, a new wireless power transfer (WPT) system based on a double-half-bridge (DHB) inverter with two variable inductors (VIs) is proposed. Compared with conventional full-bridge (FB) inverters, the DHB inverter can reduce the current through the mosfet s under the same output power and thus, reduce the conduction loss. Next, by adjusting the inductances of the VIs instead of using phase shift (PS) method, the output voltage or current can be controlled, while the circulating current can be eliminated and wide-range zero voltage switching operation can be achieved. Consequently, the power loss can be further reduced. Circuit analysis, VI design, as well as hardware implementation, are provided in detail. A laboratory prototype is built to verify the feasibility of the proposed method. Close agreement is obtained between simulation and experimental results. The maximum efficiency can reach 92.4%, which is 3.65% higher than traditional PS control.

Inductor‐based auxiliary circuit‐assisted ZVS in full‐bridge dc–dc converter for EV applications

This study proposes an efficient soft-switched full-bridge DC/DC converter (FBDC) topology operated with modified pulse width modulation (MPWM) for electric vehicle (EV) battery chargers, as the role of DC/DC converter is more prominent in on-board charging. The proposed auxiliary circuit offers zero voltage switching (ZVS) turn-on to all the active switches of the converter during full battery charging range. In consequence, the losses associated with the proposed FBDC are minimal and offer maximum efficiency as compared to available benchmark topologies operated with different gating schemes. The size of magnetic elements used in the proposed topology also reduced as to conventional FBDC operating with trailing edge pulse width modulation and phase shifted modulation gating techniques. A detailed designing and analysis of the MPWM operated ZVS FBDC is presented. Besides, the rationale behind the selection of switching frequency in order to ensure wide-range ZVS is detailed. Further the proposed topology is compared with the other competent topologies for proving its significant merits. Simulation of the proposed configuration is performed at 3.3 kW. Following which, the experimental results obtained from a laboratory prototype of 500 W, 80 kHz validating the operability and feasibility of the proposed converter are presented.

Hybrid LLC Converter with Wide Range of Zero-Voltage Switching and Wide Input Voltage Operation

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–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–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.

Implementation of a Wide Input Voltage Resonant Converter with Voltage Doubler Rectifier Topology

A new circuit structure of LLC converter is studied and implemented to achieve wide zero-voltage switching range and wide voltage operation such as consumer power units without power factor correction and long hold up time demand, battery chargers, photovoltaic converters and renewable power electronic converters. The dc converter with the different secondary winding turns is adopted and investigated to achieve the wide input voltage operation (50–400 V). To meet wide voltage operation, the full bridge and half bridge dc/dc converters with different secondary turns can be selected in the presented circuit to have three different voltage gains. According to input voltage range, the variable frequency scheme is employed to have the variable voltage gain to overcome the wide input voltage operation. Therefore, the wide soft switching load variation and wide voltage operation range are achieved in the presented resonant circuit. The prototype circuit is built and tested and the experiments are demonstrated to investigate the circuit performance.

A Hybrid Control Strategy of LCC-S Compensated WPT System for Wide Output Voltage and ZVS Range With Minimized Reactive Current

To regulate the output voltage of inductor–capacitor–capacitor-series ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -S) compensated wireless power transfer (WPT) system, a hybrid control strategy of phase shift modulation (PSM) and a switch-controlled capacitor is presented in this article. In the proposed hybrid control strategy, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -S compensated WPT system can realize wide output voltage regulation with zero voltage switching (ZVS), and the reactive current in a resonant tank can be minimized in the whole voltage range. Besides, the current in the primary coil of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -S compensated WPT system can be regulated with PSM, which helps to reduce the power loss of the primary coil at light load. Compared with conventional dual-loop hybrid control, the proposed hybrid control can regulate two control variables with one feedback loop simultaneously. To verify the theoretical analysis, a 500-W prototype with 400-V input voltage, 100−250-V output voltage is built. The experimental results show that the inverter can realize ZVS within the whole voltage range and a peak efficiency of 94.7% can be obtained.

Zero-Voltage and Zero-Current Switching Dual-Transformer-Based Full-Bridge Converter With Current Doubler Rectifier

A novel dual-transformer-based full-bridge (DT-FB) converter with a current doubler rectifier (CDR), which can solve the drawbacks of existing FB converters, is proposed in this article. In the primary side of the proposed converter, two switching legs, two transformers, and two blocking capacitors form two half-bridge inverters. The secondary side composes of two output filter inductors and four power diodes, which connect with the form of the CDR. By employing this structure, a wide range of zero-voltage switching for leading-leg and zero-current switching for lagging-leg can be achieved. In the proposed converter, the output power is shared by two small-sized transformers and inductors instead of large-sized ones, which contributes to the improvement of power density and efficiency. Compared with the traditional FB converter, the proposed converter can obtain higher voltage gain, better rectified voltage, and lower current ripple. The operation principle, theoretical analysis, and design considerations of the proposed converter are described in this article. A prototype with 300-380 V input and 100 V/ 10 A output is designed and tested to confirm the effectiveness of the proposed converter.

An LCL-Based SS Compensated WPT Converter With Wide ZVS Range and Integrated Coil Structure

In this article, a zero-voltage switching (ZVS) series–series compensated wireless power transfer (WPT) converter with phase shift modulation is proposed, which can realize output current regulation over wide range. In the proposed WPT converter, an auxiliary LCL resonant network is connected between two midpoints of the H-bridge legs of inverter to provide the peak current for ZVS operation during the dead time, with low rms current to decrease the conduction losses. To reduce the volume of the auxiliary network, an integrated coil structure is applied and the magnetic saturation is avoided due to the orthogonal coil currents. Time-domain analysis and ZVS operation of the proposed WPT converter are performed. Design and optimization of the LCL network are performed. Experimental results of a prototype with 8−20 A adjustable output current confirm the feasibility of the proposed method.

A Dual-Transformer-Based Bidirectional DC–DC Converter of Using Blocking Capacitor for Wide ZVS Range

In order to improve the efficiency of battery charging and discharging in a wide conversion gain, a dual-transformer-based full bridge converter using a block capacitor was proposed. By adding the blocking capacitor in the primary side of one transformer, an extended zero voltage switching (ZVS) range is obtained in a wide output voltage range, which is achieved by regulating the secondary voltage of the transformers to match the output voltage according to the voltage-second balance in both boost and buck modes. Besides, a mirror-symmetrical modulation is introduced in reverse power flow to avoid a limited ZVS range of the traditional dual-transformer converter. The power characteristics and ZVS range are analyzed in detailed. The analysis results and transformer current are compared with the published dual-transformer converter and the conventional dual active bridge (DAB) converter to demonstrate the advantages. Finally, a 300W prototype was built and tested to verify the effectiveness of the proposed converter.