Wide Zero-voltage Switching Research Articles

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 Dual-Transformer-Based Three-Level DC–DC Converter With Wide ZVZCS Switching Range

In this letter, a dual-transformer-based three-level DC-DC converter (TLDC) with wide zero-voltage and zero-current switching (ZVZCS) switching range is proposed. Compared with traditional ZVZCS TLDCs, this converter can achieve zero-voltage switching (ZVS) for the leading switches and zero-current switching (ZCS) for the lagging switches without any extra auxiliary components. By introducing an additional transformer, the energy can be transmitted during the whole switching period, and the current ripple of the output filter inductor can be reduced, resulting in a reduction in output filter inductance. Besides, the control strategy is a traditional simple phase-shift control. The circuit, operation principle and some steady-state characteristics are discussed in this letter. Finally, a 1-kW 650–800 V input and 250 V output experimental prototype is designed to demonstrate the validity and features of the proposed converter.

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.

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.

An improved wide ZVS soft‐switching range PWM bidirectional forward converter for low power applications with simple control circuit

This paper presents a new PWM (Pulse Width Modulation) ZVS (Zero Voltage Switching) bidirectional forward DC-DC converter. The proposed bidirectional forward converter uses two main switches and employs the leakage inductance of the transformer to transfer the power. Two auxiliary capacitors are paralleled with the main switches to provide the ZVS soft-switching condition and to reset the transformer core. Having two main switches, one transformer, and two auxiliary capacitors makes the proposed converter simple and low cost. Compared with the main counterpart, the proposed converter uses PWM which is really simple relative to the phase shift voltage matching control approach. Moreover, to provide the ZVS soft switching conditions, the magnetizing inductance value should be large which decreases the circulating current and increases the efficiency significantly in both boost and buck directions especially at the low power. The ZVS soft-switching conditions can be maintained from low power to full load. The operating modes of the proposed converter along with the design approach and the stress analysis are completely considered. To verify the theoretical results, a prototype is constructed and the theoretical results are compared with the experimental results.

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.

Hybrid DC-DC Converter with Low Switching Loss, Low Primary Current and Wide Voltage Operation

A full-bridge converter with an additional resonant circuit and variable secondary turns is presented and achieved to have soft-switching operation on active devices, wide voltage input operation and low freewheeling current loss. The resonant tank is linked to the lagging-leg of the full bridge pulse-width modulation converter to realize zero-voltage switching (ZVS) characteristic on the power switches. Therefore, the wide ZVS operation can be accomplished in the presented circuit over the whole input voltage range and output load. To overcome the wide voltage variation on renewable energy applications such as DC wind power and solar power conversion, two winding sets are used on the output-side of the proposed converter to obtain the different voltage gains. Therefore, the wide voltage input from 90 to 450 V (Vin,max = 5Vin,min) is implemented in the presented circuit. To further improve the freewheeling current loss issue in the conventional phase-shift pulse-width modulation converter, an auxiliary DC voltage generated from the resonant circuit is adopted to reduce this freewheeling current loss. Compared to the multi-stage DC converters with wide input voltage range operation, the proposed circuit has a low freewheeling current loss, low switching loss and a simple control algorithm. The studied circuit is tested and the experimental results are demonstrated to testify the performance of the resented circuit.

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.

Analysis of a PWM Converter with Less Current Ripple, Wide Voltage Operation and Zero-Voltage Switching

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.

Analysis of a Wide Voltage Hybrid Soft Switching Converter

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.

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.

Hybrid DC Converter with Current Sharing and Low Freewheeling Current Loss

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.

Extension of ZVS Region of Series–Series WPT Systems by an Auxiliary Variable Inductor for Improving Efficiency

To maintain a stable output voltage under various operating conditions without introducing extra dc/dc converters, phase-shift (PS) control is usually adopted for wireless power transfer (WPT) systems. By using this method, however, zero-voltage switching (ZVS) operation cannot be guaranteed, especially in light-load conditions. To achieve high efficiency and reduce electromagnetic interference, it is significant for WPT systems to achieve ZVS operation of all switching devices in the whole operation range. In this article, an auxiliary variable inductor, of which the equivalent inductance can be controlled by adjusting the dc current in its auxiliary winding, is designed for series–series-compensated WPT systems under PS control to mitigate the loss arising from hard switching. As a result, a wide ZVS operation range of all switching devices can be achieved. A laboratory prototype is built to verify the theoretical analysis. The experimental results show that, under load and magnetic coupling variations, ZVS operation at fixed operation frequency as well as a constant dc output voltage can be maintained. Compared to the conventional method with only PS control, the proposed WPT can achieve higher overall efficiency in a wider load range owing to the wide ZVS operation range.

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.

Wide ZVS operation of a semi‐dual‐bridge resonant converter under variable‐frequency phase‐shift control

A secondary phase-shifted dual-bridge converter with semi-active rectifier is able to perform buck–boost dc–dc conversion with soft-switching. However, it can not maintain zero-voltage switching (ZVS) operation for all switches in a wide load range. Besides, the root mean square/peak tank current increases inversely with the decreasing of load in the light load region. To alleviate these problems and extend its load range, a hybrid varying-frequency phase-shift (VFPS) control is proposed to manipulate the power for a semi-dual-bridge converter with the primary half-bridge and secondary semi-active rectifier topology. Steady-state analysis of the converter under VFPS control is performed using the fundamental harmonic approximation approach. A detailed design procedure is given then to find a full ZVS trajectory with a fixed ZVS margin at light load. Experimental results proved that the VFPS control can effectively extend the operation range with full ZVS and maintain high efficiency at light load for the semi-dual-bridge resonant 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 High Gain Multiport DC–DC Converter for Integrating Energy Storage Devices to DC Microgrid

Interfacing multiple low-voltage energy storage devices with a high-voltage dc bus efficiently has always been a challenge. In this article, a high gain multiport dc–dc converter is proposed for low voltage battery-supercapacitor based hybrid energy storage systems. The proposed topology utilizes a current-fed dual active bridge structure, thus providing galvanic isolation of the battery from the dc bus, wide zero voltage switching (ZVS) range of all the switches, and bidirectional power flow between any two ports. The dc bus side bridge uses voltage multiplier cells to achieve a high voltage conversion ratio between the supercapacitor (SC) and the dc bus. Moreover, as the proposed topology employs only one two-winding transformer to achieve a three-port interface, the number of control variables are reduced, which decreases control complexities. The operation of the proposed converter is analyzed in detail, including the derivation of ZVS conditions for the switches and transformer power flow equations. A decoupled closed-loop control strategy is implemented for the dc bus voltage control and energy management of the storage devices under different operating conditions. A 1-kW laboratory prototype is built to verify the effectiveness of the proposed converter, along with the control scheme.

Hybrid full‐bridge converter with wide output voltage for high‐power applications

A hybrid full-bridge converter that consists of a secondary-side phase-shift full-bridge converter (SPS-FBC) and a full-bridge LLC converter is proposed in this study. The wide zero-voltage switching (ZVS) range of the primary switches can be achieved and the series inductor of the SPS-FBC converter does not need to be specially designed to help achieving the soft switching operation with a set of shared high frequency inverter circuits. The dual outputs of the proposed hybrid converter are connected in series, reducing the voltage stress of the power device in the secondary side. The whole dc-output voltage can be regulated by primary-side phase-shift and secondary-side phase-shift dual-mode control scheme within the desired voltage range, by which the two output voltages are regulated independently and free from cross-regulation. Therefore, the proposed converter is suitable for high voltage, high power and wide output voltage range applications. The working principle and steady-state characteristics of the proposed converter are presented and verified in experiment of a 3 kW prototype. The experimental results show that the proposed converter maintains high efficiency throughout the voltage range, and the peak efficiency is 97.43%.