Wide Soft-switching Range Research Articles

An Isolated DC–DC Converter for 800 V Electric Vehicle with Wide Soft-Switching Range and Low Voltage Stress on Power Switches

An Isolated DC–DC Converter for 800 V Electric Vehicle with Wide Soft-Switching Range and Low Voltage Stress on Power Switches

Ripple-Free Bidirectional DC–DC Converter With Wide ZVS Range for Battery Charging/Discharging System

A ripple-free bidirectional dc-dc converter (BDC) with wide soft-switching range is proposed for battery charging/discharging application in this paper. On battery side, the current ripple can maintain zero by two-phase interleaving technology in spite of the battery voltage and transfer power variation. Through series connection, high voltage conversion ratio and reduced voltage stresses of switches can be achieved effectively. The built-in transformer technology allows for a small magnetic component size, due to its inherent saturation avoidance. With the proposed control law, the control variables can be decoupled. The duty cycle is fixed by battery side voltage while the transfer power can be regulated monotonously by phase-shift angle. Theoretical derivation illustrates that soft switching can be obtained in all switches by adopting proper parameter design. Furthermore, comparative analysis shows the proposed converter is suitable for battery charging/discharging applications. The experimental verification proves the merits of the proposed converter by a 40-60V/400V 1 kW prototype.

Optimized Bidirectional DC-DC Converter Adapted to High Voltage Gain and Wide ZVS Range

As a key component connecting dc microgrid and energy storage system, dual active bridge (DAB) converter has some inherent problems under high gain conditions. To solve the problems, this article proposes a half-bridge cascaded DAB converter with partial switch sharing. The converter combines the advantages of high voltage gain, wide soft switching range and less reactive backflow loss, under a hybrid modulation strategy based on pulsewidth modulation control and phase-shift control. In this article, the output power, soft switching characteristic and reactive backflow loss are analyzed in detail. By using the Karush–Kuhn–Tucker function method to achieve multiobjective optimization, the system can achieve the zero voltage switch (ZVS) turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and reduce the reactive backflow loss. Moreover, the coupled relationships among variables are clarified clearly, and the system can achieve high voltage gain at low turns ratio. A 500 W, 100 kHz experimental prototype is built to verify the correctness of the theoretical analysis.

Variable Saturation Inductor-Based Full Bridge Converter With Wide ZVS Range and Reduced Duty Cycle Loss

A phase-shifted full-bridge (PSFB) converter is widely used in various applications due to its soft-switching characteristics. However, one of the recognized shortcomings of the PSFB converter is that it cannot simultaneously have a wide soft switching range and a small secondary-side duty cycle loss. The shortcoming hinders the high frequency and high efficiency of the converter. In this article, the change of the energy demand of the converter on the external series inductor with input voltage and load is analyzed. On this basis, a variable saturation inductor with controllable energy is proposed to meet the energy demand and solve the problem of core heating. The controllable change characteristics of the inductor energy are studied directly instead of the controllable change of the inductance value. By adjusting the inductor energy, the PSFB can not only achieve soft switching under light loads, but also reduce duty cycle loss under heavy loads. Theoretical analysis and experimental verification are carried out on the soft switching and duty cycle loss of the converter. Since the transformer ratio can be increased due to thesmaller duty cycle loss. The efficiency of the converter can be further improved.

Efficiency-oriented circuit parameter optimization of dual active bridge converter

The power carbon neutrality path is to build a new power system with new energy as the main body. Dual active bridge (DAB) converter is considered as the core topology of new power system mode due to its galvanic isolation, bi-directional power capability, and wide soft-switching range, which is responsible for inter-connection between DC buses of different voltage levels and various DC loads. However, the lack of fast and accurate quantitative circuit parameter optimization design methods in DAB converter affects the improvement of the full working domain efficiency. In this paper, a hierarchical filtering method considering the control parameter is proposed to avoid the full range exhaustive search, and the effectiveness and correctness of the method are verified experimentally. First layer circuit characteristics must fulfill output power and inductor current requirements. The second layer filters poor inductor RMS current and soft-switching parameters. The last layer filters out weak steady-state circuit characteristics and identifies optimal regions. The proposed method improves the efficiency while reducing the area of the circuit parameter region for calculating the loss function by 85% compared with the traditional full-scale search method based on the loss analysis model, thus improving the optimization speed. The optimal circuit parameter solving process provides a graphical representation of the relationship between DAB operating characteristics and the optimal parameter area, ensuring proper optimization. Besides, the idea of hierarchical filtering can be well applied to the optimal design of other converters, and better guide the industrialization of products. • Using hierarchical filtering method can speed up the design. • Visualization of parameters can ensure the correctness of optimization results. • The design of other converters can also use the hierarchical filtering method. • Optimal design of parameters can ensure the normal operation of the device and also improve the steady-state characteristics.

Multiple-Input Soft-Switching DC–DC Converter to Connect Renewable Energy Sources in a DC Microgrid

This paper presents a new multiple-input soft-switching DC-DC Ćuk converter for clean and renewable energy sources. The proposed converter can buck and boost the different voltages of renewable energy sources to produce a constant DC output voltage in a DC microgrid. In the proposed converter, edge-resonant soft-switching modules are used to perform better than the conventional multiple-input Ćuk converter. All switches in the edge-resonant soft-switching modules can realize zero-current switching turn-on and zero-voltage switching turn-off. By using these modules, the proposed converter can achieve lower current stress of the switches, wider soft-switching range, and higher power efficiency than the conventional multiple-input Ćuk converter. These advantages are achieved in the edge-resonant modules, which optimize soft-switching states and costs. In addition, the soft-switching states can be easily achieved because the edge-resonant soft-switching modules have a wide soft-switching range. Furthermore, the proposed converter can independently transfer the generated power from renewable energy sources to the DC microgrid. In this article, the operation principles and performance of the proposed converter are discussed in detail. The theoretical analysis is validated by experimental results obtained from a laboratory-scale prototype and full-scale real-time hardware-in-the-loop experiments.

Optimization of LLC Resonant Converter With Two Degrees of Freedom Based on Operation Stage Trajectory Analysis

LLC resonant DC-DC converter has been widely used in high power density and high efficiency applications. Pulse frequency modulation (PFM) is commonly applied due to its wide soft-switching range. In some special cases, phase shift modulation (PSM) is applied to widen voltage regulation range, improve light-load efficiency, or implement a soft start-up process. Because LLC is with 2 control degrees of freedom (2DOFs), switching frequency and duty ratio, a unified analysis and optimization for LLC with 2DOFs is desired. This paper makes an effort to present a unified time domain operation stage trajectories (OSTs) analysis of LLC. On this basis, a unified numerical optimization method is proposed with arbitrarily designed optimization objectives. With the proposed optimization method, the optimized LLC with 2DOFs is with better performance compared to conventional PFM and PSM, which is verified by the experimental results.

Communication-Free Power Management Strategy for the Multiple DAB-Based Energy Storage System in Islanded DC Microgrid

Along with the development of the renewable energy, such as the photovoltaics and the wind turbine, the energy storage system (ESS) is becoming as a critical part for the renewable-based microgrids. In this article, dual-active-bridge (DAB) dc-dc converter with bidirectional power flowing ability, wide soft-switching range, and ultrafast dynamic characteristic is adopted for integrating multiple energy storage units (ESUs) for balancing the power flowing between the renewable energy and the loads in a islanded dc microgrids. For the multiple DAB-based ESS, a communication-free power management strategy is proposed in this article to maintain the dc-link voltage for the islanded dc microgrid, and high robustness of the dc-link voltage can be ensured when the output voltage of energy storage equipment, the load condition, and the power sharing performance of the ESS are changed. The proposed strategy also ensures seamless ESU plug-in or plug-out operations. Finally, the small-scale simulation model and experimental platform are both employed to verify the effectiveness of the proposed communication-free power management scheme.

A Coupling-Insensitive X-Type IPT System for High Position Tolerance

The output characteristic of an inductive power transfer (IPT) system is highly susceptible to variations in magnetic coupling. In this article, a primary-side X-type compensation topology is proposed to acquire stable output characteristics against a wide range of magnetic coupling without resorting to tight control and coil design. By introducing the concept and derivation principle for the coupling-insensitive compensation topologies, the X-type network is presented to provide self-regulation ability for primary coil current against variable coupling, thereby enabling steady power transfer in a highly dynamic environment. The design considerations for the passive parameters are elaborated, followed by the comparison with regular compensation methods. Owing to its unique structure and design flexibility, the X-type compensation exhibits a stable output characteristic that is beneficial in enhancing the tolerance to position shifts. Moreover, it also features a wide soft-switching range and more flexible design for the output level range than previous topologies. Experimental results show stable power transfer over a coupling factor of 0.14-0.28, where the power fluctuation is less than 20%. The presented method is seen as a potential solution for low power IPT systems, where high mobility is demanded.

Peak Current Control and Feed-Forward Compensation of a DAB Converter

The double active bridge (DAB) converter has been proposed in different applications due to its advantage of wide soft-switching range and power flow regulation capability. Applications like hybrid or electric vehicles and avionics systems require a fast dynamic response since the demanded power depends on the driving, which becomes an important factor for safety. Additionally, due to unbalance in the components, a dc offset may be applied to the transformer; therefore, the risk of saturation is possible. This article presents a double band current control for the DAB converter that permits to avoid the risk of transformer saturation. Additionally, feed-forward compensation is employed to achieve a very fast transient response under load and input voltage variations. The proposal is described, analyzed, designed, simulated, and experimentally tested.

Isolated Series-Capacitor-Based Full-Bridge Converter With Reduced Circulating Losses and Wide Soft Switching Range

Aiming at the limitations of traditional full-bridge dc/dc converters, such as, narrow soft switching range, large circulating loss during the freewheeling period, and voltage oscillation on the rectifier diodes, in this paper, a series capacitor-based full-bridge dc/dc converter is presented to reduce the voltage stress of power switches to half of input voltage, and by introducing the asymmetric pulsewidth modulated (APWM) scheme to the proposed converter, zero-voltage switching for all the switches in the proposed converter can be obtained. Moreover, due to the reduced voltage turned-OFF stress for switches, the energy of commutation process for switches is reduced and turned-OFF switching losses can be decreased. Therefore, wide soft switching range for the proposed converter could be achieved on the condition of variable input voltage and load power. Furthermore, a simple auxiliary circuit on the secondary side of the transformer is utilized to clamp the voltage stress of rectifier diodes and voltage oscillation is eliminated. Moreover, during the freewheeling period, the current through the primary side of the transformer can be decay to zero; circulating losses are eliminated and zero current switching for the lagging switches could be achieved. The circuit configuration, operating principle, and relevant analysis results of the proposed converter are analyzed, and a design example is given in this paper. Finally, experimental results from a 400-W 300–380-V/42-V prototype are presented to verify the analysis of the proposed converter.

Asymmetrical hybrid‐controlled half‐bridge LCC resonant converter with low conduction loss and wide ZVS operation range

An asymmetrical hybrid-controlled half-bridge LCC resonant converter which integrated a buck–boost converter and a half-bridge LCC resonant converter is proposed. It benefits with wide soft switching range, low conduction loss and high power density. By utilising an asymmetrical hybrid control strategy, its switching frequency and duty ratio can be adjusted simultaneously. The proposed LCC resonant converter maintains output voltage regulation and zero-voltage switching of switches in wide input voltage and load variation range. Experiment results of a 500 W prototype are provided to verify the theoretical analysis results.

A Family of True Zero Voltage Zero Current Switching (ZVZCS) Nonisolated Bidirectional DC–DC Converter With Wide Soft Switching Range

This paper proposes a true zero voltage zero current switching (ZVZCS) nonisolated bidirectional dc–dc converter with reduced component count. An auxiliary resonant network—which comprises of an inductor, capacitor, diode, and two switches—provides the zero voltage switching transitions of the main switches at turn on and turn off instants. In addition, a pair of auxiliary inductors, which act as inductive snubbers, aids the zero current switching transitions. The proposed configuration is able to provide soft commutation for the main switches for a wide range of input voltage, switching frequency, and load current variations—thus significantly improving the efficiency profile over a wide operating window. Besides, the auxiliary switches are also soft commutated, while the reverse recovery loss induced by the high side diode is eliminated. The ZVZCS soft switching operation is demonstrated by a 150 W prototype converter; it is proven consistent with the waveforms derived from the theoretical analysis. Its performance is evaluated against the standard hard-switched boost, buck, and several other leading soft switching converters published in the recent literature. The maximum full load efficiency at 100 kHz is recorded at 98.2% and 97.5% in the boost and buck modes, respectively.

Hybrid DC–DC Converter With Phase-Shift or Frequency Modulation for NEV Battery Charger

This paper suggests a new hybrid dc–dc converter for a neighborhood electric vehicle battery charger. The proposed converter is based on the conventional phase-shift full-bridge (PSFB) converter with center-tap rectifier. By integrating an $LLC$ series resonant converter into the conventional PSFB converter, the proposed converter has many advantages like wide soft-switching range without duty-cycle loss, zero-current-switching operation of rectifying diodes, minimized circulating current, reduced size of filter inductor, and much better transformer utilization than before presented hybrid dc–dc converters. The proposed converter can be modulated in phase-shift manner or frequency variation. The feasibility of the proposed converter has been verified with the experimental results under an output voltage range of 36–72 V dc at 1 kW.

A Passive Lossless Snubber Cell With Minimum Stress and Wide Soft-Switching Range

A passive lossless snubber cell and its dual structure for reducing the switching loss of a range of switching converters are presented. The proposed snubber cell has several advantages over existing snubbering techniques. First, it provides zero-current-switching and zero-voltage-switching conditions for turning on and off, respectively, the switch over a wide load range. Second, it does not introduce extra voltage stress on the switch. Third, by taking the ripple current through the switch into account, the peak switch current during the snubber resonance period is designed to be less than the designed switch current without the snubber. Hence, the proposed snubber does not introduce extra current stress on the switch. The operating principle, procedure of designing the values of the components, and soft-switching range of the snubber will be given. The connections of the snubber cells to different switching converters will be illustrated. A performance comparison among the proposed snubber and a prior-art snubber will be addressed. The proposed snubber has been successfully applied to an example of a 200-W, 380-V/24-V, 100-kHz two-switch flyback converter. Experimental results are in good agreement with the theoretical predictions.