Full-range Zero-voltage Switching Research Articles

Magnetizing Current Injection Based Push-Pull Dual Active Bridge Converter With Optimized Control to Achieve Full Load Range ZVS for the Distributed Generation System

To reduce greenhouse gas emissions, the distributed generation system is an approach worth investigating. With fewer switches, the push-pull circuits are suited for low-voltage and high-current applications, such as the distributed generation system. In this paper, a modified push-pull dual active bridge (PPDAB) dc-dc converter and its optimized control are proposed to achieve full load range zero voltage switching (ZVS). Considering the switch junction capacitors, the added current is injected by the magnetizing inductance to achieve full load range ZVS. Based on the RMS value of transformer current, the optimized control strategy is proposed to enhance the system efficiency with the precondition of achieving full load range ZVS of all switches. The working principles, ZVS region analysis, and design of key parameters are discussed in detail. Finally, the effectiveness of the proposed method for the PPDAB converter is verified by the results of a laboratory prototype.

Current observer-based critical conduction mode control of a bidirectional DC–DC converter in battery charging/discharging applications

A current observer-based digital critical conduction mode control of a bidirectional DC–DC converter with full-range soft switching for battery charging/discharging applications is proposed in this paper. Under the proposed control method, the bidirectional DC/DC converter operates in the critical continuous mode (CRM), the full-range zero-voltage switching (ZVS) can be achieved, and the inductor current ripple can be optimized. The CRM control is achieved by the proposed current observer, and the zero-crossing detection (ZCD) analog circuit or current sampling circuit can be eliminated. Therefore, compared with existing methods, the design complexity of the hardware circuit can be simplified. In addition, the proposed current observer can estimate the inductor current over a wide range of load and voltage variations. Therefore, the proposed control method can be applied to a wide range of charging and discharging applications. Finally, a prototype with 30–60 V input voltage, 24 V output voltage, and 75–150 kHz switching frequency is built. The experimental data and waveforms prove the correctness and advantages of the solutions proposed in this paper.

Dead-Time Optimization and Magnetizing Current Design for a Current-Fed Dual Active Bridge DC–DC Converter to Secure Full Load Range ZVS in Wide Voltage Range

Current-fed dual active bridge (CF-DAB) converters are widely used because of the small input current ripple and high power density. This paper proposes the dead-time optimization methods and the magnetizing current design for a CF-DAB converter under the pulse-width plus phase-shift (PPS) control to achieve full load range zero-voltage-switching (ZVS) in a wide voltage range. In the ZVS analysis, the influence of junction capacitance and dead time is considered, including the dead-time effect on leakage inductance current, which can effectively explain that the CF-DAB converter under PPS control is difficult to achieve ZVS at light load in practice. Based on the analysis, it is first revealed that the CF-DAB converter under PPS control is not sufficient to achieve ZVS only by adjusting the dead time. Based on the new ZVS model and analysis of the dead-time effect, the magnetizing inductance design and dead-time optimization without adding extra control degrees of freedom and auxiliary components are proposed to achieve the full load range ZVS and improve the overall efficiency of the converter in a wide voltage range. Besides, to obtain the low root-mean-square (RMS) current, the design of DC inductance and leakage inductance are also investigated. Finally, a 1 kW prototype is built to verify the effectiveness of the proposed solution.

Towards Full Range Zero-Voltage Switching of DAB Converters: An Improved Multi-Mode Modulation at Light Loads Under Close-to-Unity Voltage Ratio

The soft switching characteristics of ZVS are of great significance for reducing the switching loss and improving the efficiency of the converter. However, affected by non-ideal factors, the DAB converter using the three-phase-shift modulation method has an inherent non-ZVS region. This paper proposes a novel operating mode to fill the non-ZVS area with ZVS operation where the input and output voltage are close to match with. What's more, combined with the existing mixed-mode modulation method and dynamic-process modulation method, the ZVS operation of DAB in full voltage gain range and full power range under all working conditions can be realized.

Improved Control Strategies for Totem-Pole PFC With True Full Range ZVS Operation

Zero voltage switching (ZVS) of power semiconductor devices is an effective way to improve the efficiency and power density of the power electronic converters with extremely high switching frequency. This article aims to analyze and realize the true full-range ZVS operation of a totem-pole power factor correction circuit. The available ZVS control strategies are investigated, and the conditions for the realization of full-range ZVS operation are analyzed. It is revealed that the existed control strategies did not consider the influence of the dead-time, resulting in the failure of ZVS operation in some input voltage ranges. To address this issue, two feasible retrofitted control strategies, namely the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current optimization control and the adaptive dead-time control, are proposed. The merits and drawbacks of the two control strategies are carefully analyzed and compared. It is found that the adaptive dead-time control can not only achieve the true full range ZVS but also significantly reduce the loss of the freewheeling diodes. The design consideration of key parameters is discussed. Finally, the feasibility of the proposed control and the correctness of the theoretical analyses are verified by simulation and experiment.

Single-Phase GaN-Based T-Type Totem-Pole Rectifier With Full-Range ZVS Control and Reactive Power Regulation

This article proposes a high-efficiency single-phase GaN-based rectifier with reactive power transfer for use in front-end power supplies as an efficient alternative to centralized reactive power compensation. A full-range zero-voltage switching (ZVS) modulation for both unity power factor (PF) operation and nonunity PF operation is proposed for the GaN-based rectifier in critical conduction mode (CRM) operation. A frequency limitation method is also developed to limit the peak frequency during the ac current zero-crossing. Also, a GaN-based T-type totem-pole rectifier is proposed to overcome the control challenge in CRM during the ac voltage zero-crossing. Meanwhile, a digital-based control scheme is developed to implement ZVS operation and reactive power regulation. The proposed rectifier and ZVS control have the advantages of simple topology, high efficiency, straightforward control implementation, and capability of flexible reactive power regulation. A 1.6-kVA prototype of the GaN-based CRM T-type totem-pole rectifier is built and demonstrated with full-range ZVS operation, 98.9% full-load efficiency, and flexible reactive power regulation with smooth dynamic response.

A Modulation Scheme With Full Range ZVS and Natural Power Factor Correction for Bridgeless Single-Stage Isolated AC–DC Converter

The ac side structure of a bridgeless single-stage isolated ac–dc converter reduces the number of components by sharing power switches between the bridgeless rectifier and the dual-active-bridge (DAB) dc–dc converter. However, it also makes it more difficult to achieve zero-voltage switching (ZVS) for the ac side switches. Therefore, a modulation scheme is proposed to achieve ZVS for all switches over the full ranges of the grid voltage and load. A quasi-fixed switching frequency control method is also applied, in which the switching frequency is constant during a half-cycle of the grid voltage. By adjusting the switching frequency, the grid side inductor can operate in critical conduction mode without a zero-current-detection circuit, which facilitates the ZVS realization of the ac side switches. In addition, a natural power factor correction can be realized without the grid-side current sensors. Finally, a 500 W prototype was built to validate the theoretical analysis and the effectiveness of the proposed modulation scheme.

VSFPWM Based on Circulating Current Ripple Prediction for ZVS in Two Paralleled Grid-Tied Inverters With Coupled Inductors

Zero voltage switching (ZVS) control is an effective and promising way to further improve the power density, efficiency and electromagnetic interference for the two paralleled silicon carbide inverters with coupled inductors. In this article, focusing on the popular 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> interleaved pulsewidth modulation (PWM), the circulating current ripple prediction model is first derived as a function of operating conditions in the time-domain. With the assistance of this model, the actual trajectory of phase-leg currents can be reconstructed by superposition of sampling fundamental current and predicted circulating current ripple, without adding any high-frequency current sensor or auxiliary circuit. By carefully considering the ZVS requirement of all switches, a variable switching frequency PWM (VSFPWM) for full range ZVS control is proposed in this article. The proposed VSFPWM shows a good performance of ZVS realization in various load situations, as well as a good dynamic response of the inverter during current step change. In addition, due to the real-time variation of switching frequency, the proposed VSFPWM demonstrates the obvious advantage in conductive EMI reduction. Both the simulation and experimental results are presented to verify the effectiveness of the analysis and proposed method.

A Novel Full-Bridge Step Density Modulation for Wireless Power Transfer Systems

Aiming for wireless power transfer (WPT) systems with high efficiency demands inverters under zero-voltage switching (ZVS) conditions. This letter presents a novel full-bridge step density modulation (FB-SDM) for WPT systems based on the step density averaging principle, which can achieve full-range ZVS operation. Compared with existing ZVS modulation schemes, such as pulse density modulation and hybrid frequency pacing, the proposed modulation scheme has the ability of balancing power device losses and the minimum low frequency output fluctuation. Simulation and experimental results prove that FB-SDM is one of the most potential ZVS modulation schemes for WPT systems.

A New Optimal Thermal-Based Adaptive Frequency Control for Bidirectional DC–DC Converter with Full-Range ZVS

A new, optimal thermal-based adaptive frequency control (OTC) for a bidirectional DC–DC converter with full-range zero-voltage switching (ZVS) is presented in this paper. The proposed OTC achieves ZVS for a bidirectional DC–DC converter without any zero-crossing detection (ZCD) circuit or current sensor. In order to ensure a ZVS over a wide voltage and load range, the optimal switching frequency was adjusted by detecting and tracking the lowest junction temperature of the semiconductor device. Because the proposed OTC does not need a ZCD circuit, the complexity of the circuit and the susceptibility of the sampling noise are reduced. Additionally, compared with the expensive current sensor, the proposed method of temperature detection by the NTC thermistor decreases the cost. In addition, the proposed OTC does not need accurate circuit parameters and voltage or current sampling results, so the dependence on the parameters is reduced. Moreover, the temperature of the switch is directly monitored in the proposed OTC, which can effectively protect the device. A prototype with 16–32 V input and 48 V output was built, and the experiment results prove the effectiveness and feasibility of it.

A Hybrid Extended Phase Shift Modulation Strategy for DAB Converter With DC Blocking Capacitor to Extend ZVS Range and Reduce RMS Current

This article is aimed at enlarging the zero-voltage switching (ZVS) range and reducing current stress for the dual-active-bridge (DAB) converter with dc blocking capacitors (DCBCs). A hybrid extended phase shift modulation strategy (HEPSMS) is proposed, which makes the converter switch between the full-bridge mode and the half-bridge mode to obtain multivoltage matching operation points. Thus, the root mean square (rms) current and the burden of achieving full load range ZVS are reduced. In addition, the voltage–second of the leakage inductor is controlled to achieve equivalent voltage matching under wide voltage output, thereby simplifying the control law and achieving full load range ZVS under a wide voltage range. The operation principle, ZVS range, and rms current are analyzed and compared with the conventional modulation method. Finally, a 1-kW experimental prototype with a 200-V input and a 100–400-V output was built to verify the feasibility and effectiveness of the proposed method.

7.2 kV Three-Port SiC Single-Stage Current-Source Solid-State Transformer With 90 kV Lightning Protection

This article proposes a multiport modular single-stage current-source solid-state transformer (SST) for applications like photovoltaic, energy storage integration, electric vehicle fast charging, data center, etc. The 7.2 kV 50 kVA current-source SST consists of five input-series output-parallel modules, each based on 3.3 kV SiC reverse-blocking <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> -plus-diode modules. The proposed SST has some unique features. First, compared with the voltage-source or matrix converter-based SSTs, the current-source SST has a unique advantage of single-stage isolated ac/dc or ac/ac conversion with an inductive dc link, but no medium-voltage (MV) ac experiments have been reported. This article for the first time demonstrates MV ac current-source SST up to 7.5 kV peak. Second, the multiport SST has a buffer port for active power decoupling (APD) or energy storage integration. The double-line-frequency power ripple from single-phase ac grid normally results in a large capacitor size in MV SSTs. The APD scheme is proposed in MV applications for the first time to enable a reduced dc link and the electrolytic capacitor-less SST with high reliability. Third, for a direct grid-connected converter without line-frequency transformer, insulation and protection are critical. A medium-frequency transformer design passes 55 kV basic-insulation level (BIL) and 60 kV high potential dielectrics withstand test with only 0.09% leakage inductance. Importantly, a lightning protection scheme is presented to protect the SST itself from 90 kV BIL impulse. Fourth, the proposed current-source SST topology is a modular soft-switching solid-state transformer (M-S4T) with full-range zero-voltage switching and controlled <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> for low electromagnetic interference. These concepts are verified in a three-port M-S4T prototype with forced oil cooling under single-module, stacked-module, steady-state, and dynamic operations.

A Full Load Range ZVS Isolated Three-Level DC/DC Converter with Active Commutation Auxiliary Circuit Suitable for Electric Vehicle Charging Application

The isolated three-level DC/DC converter (ITLDC) can be used to charge electric vehicles. During the constant current charging stage, the ITLDC can be designed to realize nature zero voltage switching (ZVS). However, during the constant voltage charging stage, the charging current is small; thus, nature ZVS cannot be realized. This paper presents an active commutation auxiliary circuit (ACAC) for the ITLDC to realize the full load range ZVS. With the proposed ACACs, all the main switches achieve zero-voltage turn-on and quasi zero-voltage turn-off, and the auxiliary switches realize zero current turn-on and zero-voltage turn-off; thus, the efficiency will be high. The auxiliary currents generated by the ACACs are controllable. During the constant current charging stage, the ITLDC realizes nature ZVS and the auxiliary currents are controlled to zero; thus, the ACACs do not result in high current stress or bring in additional losses, and the efficiency will be high. During the constant voltage charging stage, the charging current decreases with charging time and the charging current is too small to realize nature ZVS. Thus, the ITLDC can work with the proposed ACACs and the auxiliary currents can be controlled within a suitable value to realize ZVS. With the proposed ACACs, the ITLDC can realize ZVS during the whole charging process; thus, the efficiency will be high. The structure and operating principle of the ITLDC with ACACs are introduced and the performance of the proposed TLDC is experimentally verified on a 1.5 kW prototype converter.

Coupled-Inductor-Based Dual Active Bridge Converter With Soft Switching Capability and Low Component Count

A coupled-inductor-based dual active bridge (DAB) converter with soft switching capability and low component count is proposed in this article. Under wide-input voltage range application, it only utilizes four active switches to achieve voltage regulation and can behave like the current-fed DAB (CF-DAB) converter. In addition, three magnetic components, including the input dc inductor, the transformer, and the leakage inductor, can all be integrated into one coupled inductor, thus reducing the magnetic component count. With the coupled-inductor structure, the voltage of the half bridge capacitor at the output side can be automatically changed according to different duty cycle. Consequently, the voltage matching at the two ports of the equivalent leakage inductor will always be satisfied by controlling the input capacitor voltage with the adopted pulsewidth modulation (PWM). Based on the detailed analysis of the working modes, power transfer characteristics, and zero-voltage switching (ZVS) conditions, full load range ZVS can be mathematically obtained, which shows that the full load range ZVS capability is an intrinsic feature of the proposed converter and is not related to the converter inductance values. Furthermore, the magnetic integration and parameter design are analyzed in detail. Finally, experimental results are provided to demonstrate the effectiveness of the proposed solution.

Three Winding Coupled Inductor-Based Dual Active Bridge DC-DC Converter With Full Load Range ZVS Under Wide Voltage Range

In this article, a three winding coupled inductor-based dual active bridge (TWCI DAB) dc-dc converter is proposed. Similar to the current-fed DAB converter, the proposed TWCI DAB has small input current ripple and wide input voltage range. In addition, the zero-voltage switching (ZVS) of all switches in the full load range under wide input voltage variation can be realized. With the magnetic integration structure, the size of the total magnetics can be reduced, and the efficiency is also increased compared with the discrete magnetic case. To better analyze the working principle of the three winding coupled inductor, a general analysis method based on magnetic reluctance model is first introduced to obtain the expressions of high frequency current. Furthermore, ZVS analysis and inductor design to obtain low inductor root mean square (rms) current and full load range ZVS based on the ZVS conditions, maximum power transfer and rms current are presented. Finally, the validity of the proposed topology and design are verified by experimental results from a 1-kW laboratory prototype.

Modified Three-Port DAB Converter Employing Voltage Balancing Capability for Bipolar DC Distribution System

To construct the bipolar low-voltage dc distribution system, a dual-active-bridge (DAB) converter and a voltage balancer are needed. However, this conventional two-stage circuit is bulky and shows low efficiency. Besides, when a short circuit fault occurs at one of the bipolar dc poles, the conventional topology cannot balance the other normal dc pole voltage due to its single closed circuit, which eventually loses the high reliability of the bipolar system. To mitigate those issues, a modified three-port DAB converter is proposed. The proposed converter is an enhanced topology of the three-port DAB converter, which can balance the bipolar voltage levels without additional voltage balancers. In addition, each bipolar output has an independent closed circuit to balance the normal dc pole under the short circuit fault at one of the dc poles, thereby improving the system reliability. Moreover, constant duty-cycle modulation and magnetizing inductance design are proposed to obtain full-range zero voltage switching (ZVS) of all switches. Since the proposed ZVS modulation uses a constant duty-cycle value, its control can be easily implemented in a digital signal processor. Finally, a 2-kW prototype is developed to validate the effectiveness of the proposed converter.

Decoupled EPS Control Utilizing Magnetizing Current to Achieve Full Load Range ZVS for Dual Active Bridge Converters

A decoupled extended phase shift control is proposed to decrease the control complexity and achieve full load range zero voltage switching (ZVS) for dual active bridge (DAB) dc–dc converters. In the proposed solution, full load range ZVS is achieved by adding an extra small fixed duty cycle and utilizing the magnetizing current. In addition, the two control variables are decoupled, since the control of the duty cycle is only determined by the voltage conversion ratio and is independent of the phase shift angle, which avoids the detection of operation mode and switching of control laws. The ZVS model considering junction capacitors and magnetizing inductance, ZVS region under full load range, and derivation of control law are analyzed in detail. Finally, the effectiveness of the proposed solution is experimentally verified on a 500-W, 250kHz GaN-based prototype.

Hybrid SPS Control for ISOP Dual-Active-Bridge Converter Based on Modulated Coupled Inductor With Full Load Range ZVS and RMS Current Optimization in DC Transformer Applications

The Input-serial-output-parallel (ISOP) dual-active-bridge (DAB) converter is an attractive solution to be used as a DC transformer (DCT) in the DC power distribution system. However, due to zero-voltage-switching (ZVS) limitation and large circulating current, the efficiency of the converter will be reduced. To improve the efficiency, an ISOP DAB converter based on a modulated coupled inductor, and a corresponding hybrid SPS control are proposed in this paper. With the hybrid SPS control strategy, the equivalent leakage inductance of modulated coupled inductor can be controllable. The large inductance is adopted at light load and the small inductance for the transformer is applied at heavy load to reduce circulating current and extend the ZVS range. By optimizing the root-mean-square (RMS) current of two operation modes of the converter, a control boundary of the hybrid SPS control can be obtained to modulate the coupled inductor. Meanwhile, the additional magnetizing inductance is utilized to achieve ZVS for all switches. The analysis based on the RMS current optimization and ZVS condition is given. Based on the conditions of the full load range ZVS and small RMS current, the parameters of the modulated coupled inductor, the turn ratio of the transformer, and magnetizing inductance are designed. Finally, a 250kHz, 800/400V, 2000W ISOP DAB prototype is built to verify the effectiveness of the proposed method. Meanwhile, a comparison experiment with the conventional individual leakage inductors solution is given, which shows performance improvements of the proposed solution.

Current-Source Solid-State DC Transformer Integrating LVDC Microgrid, Energy Storage, and Renewable Energy Into MVDC Grid

Solid-state dc transformer to integrate low-voltage dc (LVdc) microgrid, wind turbine (WT) generator, photovoltaic (PV), and energy storage (ES) into medium-voltage (MV) direct-current (MVdc) distribution grids is attractive. This article proposes current-source dc solid-state transformer (SST) for MVdc collection system in WT, PV, and ES farms or as an interface between the MVdc grid and the LVdc microgrid. Compared to conventional current-source converter (CSC) based SSTs, a switch reduction scheme on reverse-blocking device bridges is proposed to reduce device count and the number of devices on the dc-link current path. Importantly, the proposed switch reduction scheme is generic and can be applied to the dc ports of dc–ac, ac–dc, or dc–dc hard-switching or soft-switching CSC-based SSTs. Based on this scheme, the proposed current-source dc SSTs are derived, which have reduced electrolytic-capacitor-less dc-link. The proposed dc SSTs also achieve single-stage isolated dc–dc or dc–ac conversion, full-range zero-voltage switching (ZVS) for main switches, zero-current switching (ZCS) for resonant switches, and controlled <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ dv/dt $</tex-math></inline-formula> . The proposed dc SSTs, operating principles, predictive control method, the ZVS, and the controlled <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ dv/dt $</tex-math></inline-formula> under voltage buck-boost ranges are verified with MV simulations and an experimental prototype based on SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfets</small> , diodes, and a nanocrystalline transformer.

Dynamic Level Changing for Full Range ZVS in Flying Capacitor Multi-Level Converters

This paper presents a control technique for flying capacitor multi-level (FCML) converters to achieve zero-voltage switching (ZVS) across the full range of duty cycles, with application in high power density and high efficiency power converters. Previous works have used variable frequency control to enable ZVS at specific duty cycles in FCML converters, but have not been able to use these methods to enable ZVS across the full range. This work uses dynamic level selection and variable frequency control to increase inductor current ripple at duty cycle ranges for which ZVS was previously unattainable. An experimental 5-level FCML prototype has been built using GaN devices on a single-sided PCB to demonstrate this control technique. We demonstrate 4-level and 5-level operation with ZVS at duty cycles that are not possible with 5-level operation alone, as well as a dynamic level transition with active capacitor voltage balancing.