Soft-switching Conditions Research Articles

Bidirectional ZVS Buck–Boost Converter With Single Auxiliary Switch and Continuous Current at Low Voltage Source

In this article, a bidirectional zero voltage switching buck–boost dc–dc converter with a simple auxiliary circuit is presented. The auxiliary circuit employs only a single switch and a pair of coupled inductors to provide soft switching condition in both power flow directions. Moreover, the soft switching condition is independent of the load variation and duty cycle. Energy storage devices such as batteries and super capacitors are commonly utilized in systems using bidirectional converters as the low voltage source. Batteries require continuous current to prolong their life time and overall system efficiency. The proposed converter has continuous current at low voltage side in both operating modes, unlike the similar converters, which utilize coupled inductors in order to provide soft switching condition. Fully soft switching operation including the zero current switching condition of all diodes at turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> has significantly contributed to the converter overall efficiency. Operating principles, mathematical derivations and the soft switching conditions of the proposed converter are analyzed in both boost and buck operating modes. Furthermore, to confirm the main converter features and the theoretical analysis, a prototype of the proposed converter is implemented at 100 W–100 kHz and the experimental results are presented.

A new soft‐switching multi‐input quasi‐Z‐source converter for hybrid sources systems

This study focuses on a zero voltage transition multi-input quasi-Z-source converter (qZSC). This topology can be used for input sources with different voltages and currents to provide a constant output voltage. In the proposed structure, several qZSCs are combined and the output filter of all stages is eliminated. Therefore, the overall number of circuit elements, cost, volume and weight are reduced in comparison with when they are in a separate operation. In this converter, the soft-switching conditions are provided for all stages by using only one auxiliary circuit. The employed technique provides zero-voltage zero-current switching (ZVZCS) and zero-voltage switching for main switches at turn-on and turn-off instants, respectively. The auxiliary switch turns on under zero-current switching and turns off under ZVZCS. Furthermore, the reverse recovery losses of diodes are reduced. The theoretical foundation of the proposed converter is presented and its performance is simulated by OrCAD software. The obtained results show 3.5% improvement in the efficiency at nominal loads, compared to its hard-switching counterpart. A dual-input prototype of the proposed structure is successfully built to support the validity of the theoretical analysis.

Five-Degree-of-Freedom Modulation Scheme for Dual Active Bridge DC–DC Converter

A five-degree-of-freedom (5-DOF) modulation scheme is proposed in this article for dual active bridge converter to improve its efficiency in a wide operation range. First, the possible operation modes of the converter under the 5-DOF is analyzed. As a result, 11 effective modes are obtained and their steady-state characteristics expressions are solved, including the inductor root-mean-square (rms) current, inductor peak-to-peak current, and transmission power, etc. It is worth mentioning that the inductor peak-to-peak current expression is simple and it can be regarded as an indicator for rms current. Thus, the peak-to-peak current is treated as the objective to obtain the optimal solutions of each mode, and the global minimum peak-to-peak (GMPP) modulation scheme is obtained. However, there are only two switches that can realize soft-switching operation in the low-power range under GMPP, which results in significant switching loss. Therefore, to further expand the soft-switching operation range in the low-power range, the soft-switching conditions are also taken into consideration, and an optimized five-degree-of-freedom (O5-DOF) modulation scheme is proposed. With the proposed O5-DOF, almost all switches can realize soft-switching operation during the whole load range, and the inductor rms current is minimized simultaneously. Finally, the experimental results are presented to validate the theoretical analysis and effectiveness of the proposed modulation scheme.

Multi-Input High Step-Up DC–DC Converter With Independent Control of Voltage and Power for Hybrid Renewable Energy Systems

In this article, a new nonisolated multi-input step-up converter is presented. By implementing a new switching algorithm in the proposed topology, the converter output voltage, as well as the power absorbed from each source, can be controlled independently, resulting in a simple controller, which is a distinctive virtue for this converter in comparison to similar multi-input converters. Current sharing between various sources is achieved independently. There is no need to control the different parameters of switches' gate-source voltage, such as the delay between switches, and thus, independent maximum power point tracking algorithm can be used for each input source. Providing soft-switching condition and transferring power from all inputs to the load independently are the other features of this converter. Operating modes of the converter as well as experimental results obtained for a 300-W prototype for supplying stand-alone load are presented.

Efficient AC-DC power factor corrected boost converter design for battery charger in electric vehicles

With the widespread use of electric vehicles (EVs), the design of a highly quality and efficient battery charger has become an important research topic. In this study, an efficient AC-DC power factor corrected (PFC) boost converter with active snubber cell (ASC) is proposed for the battery charger. ASC integrated into the AC-DC PFC boost converter turns on the main switch with zero voltage transition (ZVT) and turns off with zero current transition (ZCT), which among soft switching techniques for eliminating the switching losses. In addition, it has been provided that other switching elements are operated with soft switching. Soft switching conditions and unity power factor (PF) are achieved from light load to full load conditions. Unlike the soft-switched PFC converter circuits in the current literature, no current and voltage stresses have been observed on any component in the main converter and ASC circuits. The paper also presents the steady-state operating principles and design guidelines of the proposed converter in detail. The efficiency improvement between the hard switched counterpart has been verified by making detailed loss analysis. The proposed converter has been constructed as 3.3 kW and tested according to European efficiency standards with various case studies. The total harmonic distortion (THD) of input current has been measured as less than 5% in compliance with EN 6100-3-2 Class D Limits (A) standards.

Principle and Topology Derivation of Integrated Cascade Bidirectional Converters for Centralized Charge Equalization Systems

This article presents a systematic topology derivation method for developing integrated cascaded bidirectional (ICB) converters, and the centralized charge equalization system can be optimized with the proposed family of converters. On the basis of the traditional centralized system, the proposed ICB converters are generated by integrating the polarity switches and different bidirectional dc–dc converters. Compared with existing methods, the ICB converter-based centralized equalization system obtains the advantages of high voltage gain, high efficiency, high reliability, and low cost, which is more attractive in engineering applications. Since different topology structures have various performances, a half-bridge-based ICB converter with a bidirectional switch is analyzed in detail as an example to validate the feasibility and effectiveness of the proposed topology family. The operation principles, design guidelines, and soft-switching conditions are discussed in more depth. Finally, the experimental results and comparative analysis are conducted to verify the advantages of the proposed ICB converter and prove the evident performance improvement compared with conventional methods.

An LLC-Based Battery Equalizer with Inherent Current Limitation

Automatic battery equalizers require no sensing circuits, which reduces their cost, size, and complexity. However, among existing methods, additional resistors or diodes are used in the balancing paths to ensure safe operation, which degrades the conversion efficiency and balancing speed. To overcome this problem, this article proposes an equalizer architecture based on the half-bridge LLC converter. The inherent current limitation characteristic of the proposed equalizer improves the balancing speed. High conversion efficiency is achieved due to the soft-switching operations of the switches. The circuit topology and working modes are presented first, then the features of voltage equalization, inherent current limitation, and soft-switching conditions are analyzed in detail. Finally, the proposed equalizer is validated by simulation and experiment.

Soft-Switched Three-Port DC-DC Converter With Simple Auxiliary Circuit

In this paper, a new high efficiency soft-switching non-isolated three-port converter (TPC) is proposed. In the conventional TPC, three switches are required to process power in different directions between inputs and output. Providing soft-switching condition for all switches using a low number of auxiliary components is a challenging task. In this paper, the conventional TPC topology is modified by changing its structure and adding a simple auxiliary circuit such that all switches operate under soft-switching condition in all operating modes. To reduce the volume of the converter, the magnetic components are integrated using a coupled inductor in the auxiliary soft-switching cell. In this paper, various converter operating modes are presented, and design considerations are discussed. Finally, a prototype 200 W, 100 V converter is implemented in the laboratory, and the theoretical analysis is validated by the experimental results.

Efficient Multi-Port Bidirectional Converter With Soft-Switching Capability for Electric Vehicle Applications

In this paper, to solve the hard-switching operation problem and the lack of existing a bidirectional power flow path from output to the energy storage device of the conventional three-port converter, a new soft-switched bidirectional multi-port converter is proposed. A large number of switches, different power flow paths which vary in each operating mode, and changing the outputs and their power levels are some of the challenges to provide soft-switching conditions in multi-port converters. In the proposed converter, by changing the topology of the conventional three-port converter, the bidirectional power exchangeability between ports is provided. Moreover, a soft-switching cell is added, which can operate independently from the output power levels. Less number of components with low volume is one of the important features of this multi-port converter. Due to the soft-switching operation of the proposed converter, the size of passive components and heat-sink is reduced. In addition, by the use of coupled inductors in the soft-switching cell, only one magnetic core is used and thus, single-stage power conversion is achieved and conduction loss is reduced. In this paper, the converter operating modes are presented, and design considerations are discussed. Finally, a 200 W–200 V prototype is implemented, and the theoretical analysis is validated by the experimental results.

High step-up isolated forward-flyback DC/DC converter based on resonance with pulse frequency modulation

A high step-up isolated forward–flyback DC–DC converter with pulse frequency modulation (PFM) is presented in this paper. The proposed converter has features of both a forward and a flyback converter and can deliver energy during the turn-on and turn-off intervals in a switching period. In addition, by utilizing resonance it can achieve zero-voltage switching (ZVS) for the primary switches and zero-current switching (ZCS) for the secondary rectifier diodes. All of the power semiconductors operate under soft switching conditions. The structure of the proposed converter is simple and easily implemented. It also provides a high step-up voltage gain. The current stresses of the power devices in PFM are lower than those in pulse width modulation (PWM). Therefore, the converter efficiency in PFM is higher than that in PWM. The operation principle and characteristic of the presented converter are described in detail, and the converter performances for PWM and PFM are compared. A 160 W hardware prototype has been built, and experimental results verify the validity of the theoretical analysis.

Quasi-Resonant Bridgeless PFC Converter With Low Input Current THD

In this article, a quasi-resonant bridgeless power factor correction (PFC) converter is presented. Aiming to improve the input current total harmonic distortion, a single auxiliary switch with low voltage stress than the similar counterparts is employed. Due to resonant operation, the size and value of the passive components are reduced and maximum voltage gain of four is achieved which is higher than that of conventional buck PFC converter. Also, soft switching condition for the main semiconductor elements is realized from 20% of nominal power to full load and entire input voltage range (90 to 130 Vrms) without employing any extra component. The operating modes are explained and the theoretical analysis is discussed in details. A straightforward design procedure for the proposed converter is presented. A 200 W, 160 kHz laboratory prototype is implemented to verify the theoretical analysis and the effectiveness of the proposed topology.

New auxiliary circuit for boost converter to achieve soft‐switching operation and zero input current ripple

In this study, a simple auxiliary circuit is proposed and investigated to provide soft-switching operation in the boost converter. The proposed auxiliary circuit includes only a small auxiliary inductor and two auxiliary capacitors. In this structure, by implementing the auxiliary inductor, a negative current flows through the power switch before its turn-on moment. Therefore, the power switch turns on under zero voltage switching condition. In addition, by properly designing the parallel capacitor of the power switch, a soft-switching condition can be achieved for its turn-off. Furthermore, implementing this simple auxiliary circuit can be helpful to decrease the reverse recovery losses of the diode since the diode turns off under zero current switching condition. Another advantage of the proposed structure is its zero input current ripple. In this study, the performance of the proposed auxiliary circuit with conventional boost converter has been analysed, and designing the methodology of the auxiliary components is presented. Voltage stress and power loss of components, converter voltage gain, and closed-loop model of the converter have been investigated. Moreover, the performance of the proposed auxiliary circuit is compared with previous works and its operation is investigated in a 200 W laboratory prototype.

High step‐up interleaved zero‐voltage transition DC–DC converter with coupled inductors

A high step-up DC–DC converter which is applied to a voltage lift capacitor and coupled inductors to increase the voltage gain is proposed in this study. Moreover, the interleaved structure is applied in the converter to decrease the input ripple current. Besides, the voltage stress across the main and auxiliary switches is low. Furthermore, all switches and diodes have the soft-switching condition by using an active clamp auxiliary cell. Consequently, the proposed converter has a high efficiency which is ideal for photovoltaic applications. Energy stored in the coupled inductors is transferred to the voltage lift capacitors and then transmitted to the output. Therefore, no voltage spikes caused by leakage inductors are created on the main switches. The converter operates in continuous current mode and its control remains in pulse width modulation. A 210 W laboratory prototype of the converter with 40 V input voltage and 420 V output voltage under 100 kHz switching frequency is constructed and experimental results confirm the theoretical analysis. Low voltage stress, low input ripple current and high efficiency (96.5%) show the superiority in the operation of the proposed converter in comparison with other similar structures.

Comparison of Wide-Band-Gap Technologies for Soft-Switching Losses at High Frequencies

Soft-switching power converters based on wide-bandgap (WBG) transistors offer superior efficiency and power density advantages. However, at high frequencies, loss behavior varies significantly between different WBG technologies. This includes losses related to conduction and dynamic ON-state resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS(ON)</sub> ) degradation, also charging/discharging of input capacitance (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ISS</sub> ) and output capacitance (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> ). As datasheets lack such important information, we present measurement techniques and evaluation methods for soft-switching losses in WBG transistors which enable a detailed loss-breakdown analysis. We estimate the gate loss under soft-switching conditions using a simple small-signal measurement. Next, we use Sawyer-Tower and nonlinear resonance (NR) methods to measure large-signal C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> energy losses up to 40 MHz. Finally, we investigate the dependence of dynamic R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS(ON)</sub> degradation on OFF-state voltage using pulsed-IV measurements. We demonstrate an insightful comparison of soft-switching losses for various normally OFF gallium nitride (GaN) and silicon carbide (SiC) devices. A p-GaN-gated device exhibits the most severe RDS(ON) degradation and the lowest gate loss. Cascode arrangement increases threshold voltage for GaN devices and reduces gate losses in SiC transistors; however, it leads to higher C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> losses. The study facilitates the evaluation of system losses and selection of efficient WBG devices based on the trade-offs between various sources of losses at high frequencies.

Three‐phase efficient resonant‐pole inverter without auxiliary switches

In order to optimise, the operating efficiency of the three-phase inverter, a new three-phase efficient resonant-pole inverter without auxiliary switches is presented. A set of auxiliary circuits without auxiliary switches is set on each phase bridge arm. When the auxiliary circuit works in the inverter commutation process, the main switch device on the bridge arm can achieve zero-current turn-on and zero-voltage turn-off, and the efficiency of the inverter can be improved by reducing the switching loss. Furthermore, there are no auxiliary switches in the auxiliary circuit, which is conducive to limiting the hardware cost of the auxiliary circuit and improving the reliability of the inverter. This study analyses the working mode of the circuit and the realisation condition of soft switching. The experimental results on the 3 kW prototype indicate that the switching device is in the state of soft switching, and the efficiency of the prototype at the rated output power is equal to 98.9%, which is more than that of other similar soft-switching inverters. Consequently, the presented topology is significant for the research and development of efficient three-phase inverters.

Influence of MOSFET Parasitic Capacitance on the Operation of Interleaved ZVS Boost Converters

Interleaved zero-voltage switching boost converters have been known for over 20 years. However, the influence of parasitic capacitance of transistors has not been described. In this paper the converter is analyzed and the equation for voltage ratio is derived for any number of converter phases. First a general description of the topology, including main voltage and current waveforms, is provided. Subsequently the converter is analyzed and conditions for soft switching are derived. Next the analysis results are compared to measurements of an experimental converter setup. Discrepancies are identified and the influence of parasitic capacitance is analyzed. By considering the parasitic capacitance the difference between experimental and analytical results of voltage ratio is reduced from 0.2 to less than 0.05.

Soft Switching Interleaved High Step-Up Converter With Multifunction Coupled Inductors

This article presents an efficient interleaved soft switching dc-dc converter for high step-up applications. In the proposed converter, two multifunction coupled inductors are employed to increase the voltage gain, accomplish soft switching operation for all semiconductors in a wide range of load variations, and smooth the input current. Besides, the leakage inductance energy is recovered to enhance the voltage gain and efficiency while assisting soft switching condition for the switches and diodes. In addition, no auxiliary switch or extra magnetic element is employed in the proposed converter while the voltage stress of switches and diodes is rather low. These have led to simple structure, high density, low cost, and improved efficiency. Theoretical analysis and design considerations for the proposed converter are presented. Moreover, the experimental results of a 48 to 500 V laboratory prototype approve the effectiveness of the proposed topology.

Research on a Novel High-Efficiency Three-Phase Resonant Pole Soft-Switching Inverter

A high-efficiency three-phase resonant inverter is presented to optimize the performance of the inverter. When the auxiliary resonant circuit on each phase bridge arm works in the commutation process of the inverter, the voltage across resonant capacitors in parallel with main switches will form zero state periodically. In this case, main switches can achieve zero-voltage soft-switching. Meanwhile, auxiliary switches can achieve zero-current turn on and zero-voltage turn off during the operation of the auxiliary resonant circuit. Soft-switching can reduce switching loss and make the inverter work efficiently. The novelty of the inverter mainly reflects in the simple structure of the auxiliary circuit and the simple control method of auxiliary switches. This article analyzes the working mode of the circuit and the realization condition of soft-switching. Meanwhile, it discusses theoretical calculation of the power loss of the auxiliary circuit. The experimental results on the 3-kW prototype show that switching devices work in the soft-switching state. The efficiency of the prototype under the rated output power reaches 98.7%, which is higher than that of the same type of other soft-switching inverter. Therefore, the topology is valuable for the research and development of the high-performance three-phase inverter.

Fully Soft-Switched High Step-Up Nonisolated Three-Port DC–DC Converter Using GaN HEMTs

In this article, a soft-switched nonisolated high step-up multi-input dc–dc converter is proposed. The proposed converter has overcome the hard switching problem of the conventional boost three port converter (boost-TPC) by providing zero-voltage-switching condition for all switches at various operating modes. The proposed converter uses coupled inductors technique to enhance the voltage gain and utilizes the leakage inductance energy and the energy storage device power path to provide soft switching condition. In addition, the voltage stress of the main switch is reduced which has led to utilizing low R ds(ON) switches. Various converter operating modes are presented and design considerations are discussed. To evaluate the proposed converter performance, two prototypes of the proposed converter are implemented utilizing the latest generation gallium nitride high electron mobility transistors and the mature Si MOSFETs technology. The results show that the proposed converter efficiency is enhanced in comparison with the conventional boost-TPC converter.

A Family of Soft-Switching DC–DC Converters With Two Degrees of Freedom

Switching losses including reverse recovery losses, have a significant impact on total losses of DC–DC converters especially in high voltage applications. This article introduces a new family of DC–DC converters with two degrees of freedom, which can handle the mentioned issue. The proposed family of DC–DC converters contains a bidirectional and a unidirectional cell, and provides an additional control parameter. This parameter can be adjusted so that there are soft switching conditions for all the switches of the converter within the entire range of loading. In addition, properly tuning the new parameter can decrease the circulating current and consequently decrease the conduction losses considerably. Besides, the unidirectional cell contributes to power transfer, especially under full load condition. Moreover, the filter capacitor is one fourth in comparison with the conventional dc-dc converters. The proposed converter is modeled and its operation modes are studied. Also, in order to verify the findings, a 500 W prototype with a frequency of 100 kHz is implemented, and the results are compared.