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This article proposes a novel control for the multiple-input, single-inductor, multiple-output dc–dc converters. It is digitally and discretely implemented, which can have an outstanding performance in low-power applications so that at the power of 10 mW, it has an efficiency of 92.5%. Conventionally, in this power range, an attempt is made to take advantage of an analog design that is flexible. Thus, a fully programmable (software designed) converter with digital design using a microcontroller is in great demand. This converter design basis is to deploy the microcontroller's central processing unit (CPU) as little as possible. Also, it only turns on the CPU when necessary to be employed in low-power, portable systems, e.g., energy-harvesting technologies. Therefore, construction costs are significantly reduced. Depending on the energy level of the inputs, they can simultaneously be utilized to charge the outputs. This article uses stability analysis, time-multiplexing control method, and variable-frequency pulsewidth modulation in the proposed control design. Each output can be charged with different frequencies according to its load, and the maximum switching frequency is equal to 10 kHz. Also, the proposed technique for zero-current switching has been digitally implemented; it can be utilized to determine the optimal value of the inductor discharge duty cycle based on the inductor's left-side voltage. Comparative simulations and experimental results reveal the superiority and practicality of the proposed approach. [ABSTRACT FROM AUTHOR]

In this article, a new efficient soft-switching synchronous rectification (SR) buck converter is proposed, which is without voltage stress increment for all switches and diodes. By introducing an auxiliary circuit to the SR buck converter,the soft-switching condition is achieved within the wide range of load power for the power semiconductor devices. The auxiliary network, which consists of capacitor, inductor, switch, and three diodes, provides a zero-voltage condition for main switch and SR switch at both the turn-on and the turn-off instant. Besides, the auxiliary inductor creates a zero-current turn-on and a zero-voltage turn-off condition for the auxiliary switch. Considering the resonance between the parasitic capacitors of the semiconductor components and the auxiliary inductor, two diodes are designed to avoid the additional voltage stress on power devices. The operating principle of this proposed converter is analyzed. A 600 W prototype is implemented to test the soft-switching operation. The advantage of the proposed converter is demonstrated by the efficiency curve over a wide range of load power against the conventional SR buck converter. [ABSTRACT FROM AUTHOR]

This article introduces a new nonisolated soft-switching coupled-inductor (CI) step-up dc/dc converter. The presented topology utilizes a three-winding CI (TWCI) along with a voltage multiplier circuit to increase the voltage conversion ratio without needing a high duty cycle. Using this circuit, a high voltage gain can be achieved without requiring a large number of turns ratio in the CI. The input current ripple of the introduced converter is very low, which is very desirable for renewable energy sources applications. The TWCI also creates an additional design freedom to increase the voltage gain, which indicates more circuit flexibility. Additionally, the voltage stress across the single power switch is limited with the help of a regenerative clamp capacitor. The leakage inductor of the CI is used to create a resonant tank to reduce power losses further. The leakage inductances help provide the zero-current switching conditions for the single power switch and decrease the reverse-recovery issues for all diodes, leading to an efficiency improvement. The operation principle, steady-state analysis, and design considerations are discussed thoroughly. Finally, the theoretical analysis is validated through experimental results obtained from a 200 W prototype with 250 V output voltage. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel interleaved boost-integrated LC series resonant converter, in which the series resonant tank is located on the secondary side. Moreover, the input and output of the interleaved boost unit are in series directly, which is helpful to reduce the voltage stress of the output filter capacitor of boost unit. With the proposed pulse frequency modulation, except for that the output voltage can be controlled as constant under different input voltages, another feature is that the high-frequency transformer design is related to the series resonant frequency instead of the switching frequency. Hence, the proposed converter can operate under a very wide switching frequency range with a constant maximum magnetic flux density. The zero voltage switching and zero current switching can be achieved for all switches diodes. Finally, a 500-W prototype with a switching frequency range from 60 to 200 kHz is built to verify the operation principles of the proposed converter and modulation. [ABSTRACT FROM AUTHOR]

This article proposes a new single switch trans-inverse high step-up converter applicable in sustainable sources of energies such as photovoltaic (PV) and fuel cell (FC). Through developing a single-ended primary-inductor converter by a three-winding built-in transformer (BIT) mixed with a switched-capacitor voltage multiplier cell, high voltage gains as well as low voltage stress across the mosfet can be achieved to reduce the required duty cycle and the conduction losses. The third winding of the BIT acts in a trans-inverse manner whose turns ratio should be lower than unity. Hence, with a lower number of windings the voltage gain can also be improved. Furthermore, the quasi-resonance operation of the proposed converter, reduces the associated switching losses of the mosfet and also guarantees zero current switching of diodes through the whole switching cycle. Meanwhile, low input current of the proposed converter serves as an interesting feature to maintain PV and FC lifetime. The detailed steady-state analysis of the proposed high-efficiency converter is presented with an extensive performance comparison to explore its advantages. Finally, a 200-W prototype with 20–250-V voltage conversion is developed in the laboratory to examine the carried steady-state analysis. [ABSTRACT FROM AUTHOR]

This article introduces a nonisolated, high step-up voltage multiplier cell (VMC)-based dc–dc converter for applications such as module-integrated converter and power optimizers. The VMC combines switched capacitor with autotransformer techniques and active clamp circuit. The autotransformer tertiary winding is employed to increase voltage gain without operating the main switch under extreme duty cycle condition, to reduce the current through the main switch before it turns offand to ensure its zero-voltage switching (ZVS) operation on a wide operation range. The auxiliary switch in the clamp circuit provides ZVS for the main switch and vice-versa. Thus, both switches are turned on with zero voltage and there is no switching loss. Hence, high switching frequency is used to reduce the passive components’ volume and weight. Besides, the low dc-bias and bidirectional magnetizing current allows a smaller magnetizing inductance in the autotransformer to further minimizing the dimensions of the magnetic core. The leakage inductances are used to provide zero-current switching condition for the diodes, eliminating their reverse-recovery losses. The operation principle, steady-state analysis, and design guidelines are depicted and validated through experimental results obtained from a 350-W prototype of the proposed converter. Efficiency of 96.5% at full load is also reported. [ABSTRACT FROM AUTHOR]

In order to break limited step-down ratio range and poor regulation capacity in the conventional resonant switched-capacitor converters for rectifier application, a single-stage ac/dc rectifier based on the dual-resonance switched-capacitor converter is proposed in this article. Through utilizing a dual-resonant structure and nonoverlapping strategy to realize wide continuous voltage gain of the proposed converter, high power factor (PF) and low total harmonic distortion (THD) based on the narrow dead zone are guaranteed by operating at high step-down conversion ratio in this converter topology. Moreover, the voltage gain is concentrated between resonant frequency and double resonant frequency to achieve a narrow switching frequency range for rectifier application. Furthermore, operating at flat voltage stress curves to obtain low voltage stress character. Comprehensive mode analysis, input PF and THD, and stress analysis are given, and analysis results indicate that the proposed power factor correction converter can work with soft turn on and zero-current turn off; high efficiency is realized. Finally, an experimental prototype with 85–130 Vac input and 47 Vdc/44 W output is built and tested for verifying the operation modes and PFC performance, and the comparison between different rectifiers and the proposed one is provided. [ABSTRACT FROM AUTHOR]

In this article, a family of nonisolated zero voltage switching (ZVS) bidirectional dc–dc converters (BDCs) with simple auxiliary circuit and continuous current at low voltage side source ($V_L$) is proposed. The auxiliary circuit is only composed of a single switch, a capacitor, and a small inductor which is applied to all proposed nonisolated BDCs to provide soft switching condition for all semiconductor elements. Thus, in terms of components count, the presented converters are superior to other counterpart BDCs. In addition, the continuous current at $V_L$ is maintained, while the main and auxiliary switches in both operating modes are turned on and off at ZVS. Moreover, all diodes turn off at zero current switching which mitigate the reverse recovery problem. Hence, a suitable overall efficiency is achieved in all proposed BDCs. The proposed bidirectional buck/boost converter is analyzed for both step-up and step-down operating modes in details and a 100 W converter prototype is implemented to verify the main converter features and the theoretical analysis. [ABSTRACT FROM AUTHOR]

A new soft-switching dual-switch forward converter with self-driven synchronous rectifier is presented in this article. The proposed converter operates under discontinuous conduction mode; therefore, compared with the two-switch forward (TSF) converter, one diode along with one inductor is removed from the output side. The leakage inductance of the transformer is employed to transfer the power from the input side to the output side. To provide the zero-current switching (ZCS) condition for all semiconductor devices in both on and off instants, a delay time between the off-command signals of main switches along with a capacitor is used as auxiliary circuit, which eliminates the required additional switch for soft switching. Moreover, the auxiliary circuit in addition to provide soft-switching condition, resets the transformer core, resonantly. Compared with the TSF converter with the help of the new auxiliary circuit, two reset diodes at the input side can be removed. The proposed converter is controlled with duty cycle using the pulsewidth modulation. Also, a winding is added at the output side of transformer to drive the MOSFET of synchronous rectification. Thus, a ZCS TSF converter with the minimum number of components is proposed. 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 implemented and the theoretical results are compared with the experimental results. [ABSTRACT FROM AUTHOR]

Zero-voltage zero-current switching (ZVZCS) phase-shift full-bridge (PSFB) dc–dc converters are candidate converters for high-power switching mode power supply because of their low cost and high efficiency. However, these converters still have some definite weaknesses, e.g., resetting obstacles of high-value currents, extra electrical stress on the power devices. Hence, customers seldom adopt these topologies in high-power applications. This article proposes a new ZVZCS PSFB dc–dc converter to solve the above problems. A clamping circuit with two mosfets, two diodes, and a resetting transformer ensures ZCS of the lagging-leg switches over a wide load range, and no extra electrical stress arises on the primary or secondary components. The clamping circuit has a high current reset ability and can break through the power limitation of conventional ZVZCS PSFB dc–dc converters. The volume of the resetting transformer is small because of the low voltage-second product, and the added mosfets cause low power loss because of the wide soft-switching load range and low on-resistance. The experimental results from a 12-kW prototype prove the rightness and advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

This work presents an offline power supply with fully integrated power stage in 0.18 $\mu \text{m}$ high-voltage (HV) CMOS silicon on insulator (SOI). It supports both ac–dc and dc–dc conversion from 15–400 V input down to 3.3–10 V output and is optimized for applications below 300 mW such as the Internet of Things (IoT), smart home, and e-mobility. An active zero-crossing buffer enables on-chip integration of the HV buffer capacitor. Below 150 V, constant ON-time control is based on voltage intervals, sensed by ten HV threshold-detection circuits. Above 150 V, the converter operates in the resonant mode. It achieves a superior power density of 458 mW/cm3 and 84% peak efficiency. [ABSTRACT FROM AUTHOR]

In this article, an improved soft-switching quadratic boost converter is proposed. Instead of inserting an additional active clamp or auxiliary zero-voltage transition circuit at the switching node, the proposed topology connects the high-voltage switching node to the input diode node by replacing one of the input diodes with a low-rated switch. The proposed topology can attain soft-switching condition for all the switches and input diode turns-off under zero-current switching (ZCS). The operation of input-side switch not only aids zero-voltage switching (ZVS) turn-on for the main switch but also helps in reducing the conduction loss. Also, the input-side switch operates under ZCS turn-on and ZVS turn-off, making it a loss economical solution. An adaptive timing scheme for driving the input switch is proposed, which can ensure soft-switching condition under varying gain and load range. The detailed operational modes, analysis, and design considerations of the proposed topology are presented. A 250 W hardware prototype is built to validate the performance of the proposed converter operating at 100 kHz switching frequency. Results with adaptive soft-switching scheme shows that the converter is modulated to achieve its best efficiency condition under various system conditions. A peak efficiency of 96.1% at 155 W and efficiencies above 95.75% over a wide load range are achieved using all Si devices. [ABSTRACT FROM AUTHOR]

In this article, we propose a high step-up interleaved dc–dc converter with zero-voltage switching, which is based on the coupled-inductor technique and voltage multiplier cell. A capacitor is placed in series with the secondary windings of the coupled inductors to increase voltage gain so low-voltage-rated and on-resistance mosfets can be employed to reduce conduction losses. By using auxiliary switches, soft switching is provided for a wide range of load variations. Due to the presence of the leakage inductor, all diodes are turned off with zero-current switching condition, so the reverse recovery problem is alleviated. Besides, the thermal stress of the phases and the input current ripple are low due to the interleaved structure applied. The operation principle and steady-state analysis of the presented converter are discussed. Finally, in order to verify the operation of the proposed converter, a 28 V input voltage to 460 V output voltage prototype with a rated power of 250 W is implemented and tested in the laboratory. [ABSTRACT FROM AUTHOR]

In this article, a fully soft switched interleaved bidirectional buck/boost converter with high voltage conversion ratio (VCR) and no pulsating current at low voltage source is proposed. Winding cross-coupled inductors technique is employed in order to increase VCR and mitigate current ripple at low voltage side. Moreover, soft switching conditions for all semiconductor devices are provided and the leakage inductances energy of coupled inductors are absorbed in both high step-up/down operating modes. Furthermore, the reverse recovery problem of all diodes is removed due to zero current switching turn off. All the mentioned advantages are achieved for a bidirectional converter with two interleaved phases in both high step-up/down operating modes by only one clamp circuit consisting of a clamp capacitor and two active switches. Also, the body diodes of the main switches are utilized as the main diodes to reduce the element count. The converter performance is validated by theoretical analysis and an 800 W prototype circuit in both operating modes. [ABSTRACT FROM AUTHOR]

Sinusoidal modulation can keep the resonant current in phase with the terminal voltage, and, thus, it is feasible to achieve both zero current switching (ZCS) on/off and eliminate backflow power in a series resonant converter. However, it makes the transfer characteristics inherently dependent on the resonant tank and, thus, challenges power regulation. In this article, a novel intermittent sinusoidal modulation is proposed for a bidirectional series resonant converter (BSRC). Each switching cycle incorporates a sinusoidally modulated resonant period and an intermittent period for the current controllability, while fully ZCS as well as null backflow power can be maintained for high efficiency regardless of load conditions. The BSRC operates as a current source, with the normalized voltage gain being either stepped up or down, to achieve a wide range of output power. Moreover, the output power together with the power loss is proportional to the switching frequency, making the high power efficiency independent of the load. Therefore, fully ZCS, linear current controllability, and load-independent high efficiency can be simultaneously realized throughout a wide load range. A 1-kVA BSRC prototype that interfaces a high-voltage bus ranging from 240 to 480 V and a low-voltage bus of 48 V validates the proposed modulation scheme. [ABSTRACT FROM AUTHOR]

The series-capacitor buck converter doubles the duty ratio and equalizes the current between two phases. A series-resonator buck (SRB) converter is realized by adding a resonant tank in series with the series-capacitor Cs. All switches turn-on at zero voltage, and the low-side switches turn-off at zero current. This article focuses on modeling the steady-state operation of the SRB converter. The steady-state model calculates voltage gain, component peak voltages, and resonant inductor peak current. The understanding of the relationships between the voltage gain, regulating variable, and state variables help to optimize the power stage design. The expectations were validated by a 2-MHz converter with a peak efficiency of 98.5%, 48 V at the input and 7 V, 20 A at the output. [ABSTRACT FROM AUTHOR]

In this article, a high-performance modified Y-source dc–dc converter is proposed. Comparing with traditional Y-source dc–dc converter, the proposed converter can achieve soft switching characteristics. Due to the discontinuous conduction mode operation of one of the coupled inductor windings and the resonant cell constructed by switch parasitic capacitor, the switch can operate in zero voltage switching (ZVS) and diodes realize zero current switching. Also, the voltage gain of the proposed converter is greatly improved. Meanwhile, the control strategy of hybrid pulsewidth modulation and PFM is adopted to guarantee the ZVS operation within a wide range. A 160 W experimental prototype based on planar coupled inductor is built to verify theoretical analysis and efficiency is up to 94.45% under full load condition. [ABSTRACT FROM AUTHOR]

This study introduces a new modified high-gain single-switch single-ended primary-inductor converter-based dc/dc converter. The low input ripple of the proposed converter makes it very suitable for renewable energy applications. In the proposed topology, a three-winding coupled-inductor and a voltage doubler rectifier are used to achieve high voltage gain without needing an extreme duty cycle. This circuit can provide an ultra-high voltage conversion ratio without requiring a large number of the turns ratio of the three-winding coupled-inductor (TWCI). Due to a regenerative clamped circuit, the leakage energy of the coupled-inductor is recycled; thus, the maximum voltage spike across the single-power switch is restricted. Therefore, mosfet with a low maximum voltage rating can be utilized, which can alleviate the conduction power dissipations of the converter. Here, the switching power losses have been reduced significantly due to the circuit's soft-switching operation for the switch and all diodes. The steady-state analysis of the proposed converter is discussed thoroughly. Finally, the theoretical analysis is verified through the experimental results from a sample prototype (400-W, 25-400 V). [ABSTRACT FROM AUTHOR]

In the last thirty years, the integrated gate-commutated thyristor (IGCT) has been employed in medium voltage $\,\mathrm{M}\mathrm{W}$ power level converters and has demonstrated some of the lowest conduction losses of any actively controlled device in traditional hard-switched, sub- $\,\mathrm{k}\mathrm{Hz}$ applications. Extending the use of the device to medium frequency applications, such as dc transformers is possible through soft-switched operation, where low turn-off current and zero-voltage turn-on significantly reduce switching losses. For this purpose, this article explores the tradeoffs in the transition between zero-voltage and zero-current switching conditions of reverse conducting IGCTs. Switching conditions resulting in minimal switching loss are identified for standard commercial devices and engineering samples subjected to increased electron irradiation to reduce switching energy at the expense of on-state voltage. The operation of the IGCTs at the record frequency of 5 $\mathrm{k}$ $\mathrm{Hz}$ is thermally validated under load in the identified switching conditions. [ABSTRACT FROM AUTHOR]

Active power decoupling (APD) technology is an effective solution to store the double-line frequency ripple power in the single-phase system and remove the bulky aluminum electrolytic capacitors. However, APD introduces power loss because of adding extra switches operating at high frequency, which hurts the system efficiency inevitably. Addressing this issue, this article proposes an improved boost power factor correction (PFC) rectifier with a buck-type APD cell. An auxiliary circuit, composed of a resonant inductor and a diode, is added. With the developed modulation strategy, zero voltage switching of the switches both in the PFC and APD circuits is achieved, which improves the system efficiency significantly. This article first describes operating modes and then analyzes the soft-switching condition of each switch. Finally, a 300 W prototype is built and the experimental result shows that the efficiency is increased by 4%. [ABSTRACT FROM AUTHOR]

The inherent dead angles of the input line current in buck power factor correction (PFC) converter deteriorates the power factor (PF). This article introduces a new bridgeless single-phase buck (PFC) converter with reduced components. This converter is designed to operate in discontinuous conduction mode (DCM) to achieve inherent PFC with a simple structure. The DCM operation gives additional advantages, such as low turn-on losses and reduced complexity of the control circuitry. Unlike the buck PFCs, in which dead angle is the main drawback, in the proposed converter the PF is improved and the dead angle is eliminated by applying an auxiliary switch. Besides, the efficiency is further improved by employing the bridgeless structure. The switching losses are eliminated due to achieved zero current switching (ZCS) at the turn-on and turn-off of the main switches, and also ZCS at the turn-on and zero voltage switching at turn-off of the auxiliary switch. The proposed topology is successfully implemented on a 120 W prototype converter at 110 Vrms input voltage and 48 V output voltages, and its performance is experimentally verified. The results show the total harmonic distortion of 5.3% and efficiency of 93.1% at the rated load. [ABSTRACT FROM AUTHOR]

In this article, a new simple buck converter with zero voltage switching (ZVS) performance and almost zero output current ripple is proposed. The proposed structure's auxiliary circuit contains a capacitor and an inductor without any switches, which makes it possible to minimize the switching losses and eliminate other additional losses. The main power diode also turns off under zero current switching condition and the reverse recovery losses of the power diode is minimized. Eliminating the switching losses and the reverse recovery losses allows the converter to operate with high power efficiency, which makes it a good option for high power efficiency-required applications. In this article, five operational modes are explained. The design section includes the designing criteria of the components. Also, the efficiency analysis, control system for stabilizing the output voltage, and applying a variable inductor to ensure the soft-switching operation are analyzed. The comparison results are also discussed. Moreover, an experimental prototype of the proposed structure at 200 W output power and 75 kHz frequency is built to prove the above-mentioned advantages. Finally, the soft-switching waveforms are obtained for different output powers with various duty cycles and equal switching frequency to verify the ZVS performance of the converter at different loads and changes in input voltage and duty cycle. [ABSTRACT FROM AUTHOR]

Traditional phase-shift full-bridge converters are popular in industrial applications due to the advantages of simple design, fixed-frequency control and soft switching. However, a large duty cycle variation range is required in applications with a wide input voltage range, which can cause loss of soft switching range, excessive circulating currents and output current ripple. This article introduces a three-leg converter that is a hybrid combination of two full-bridges. The current and power of the two transformers in the converter are shared automatically by adopting the symmetrical structure and modulation, and output current ripple is suppressed by the superposition of the two transformer voltages. The circulating current is minimized in the proposed converter that the conduction loss is reduced. By adding two auxiliary switches on the secondary side, zero-voltage switching and zero-current switching of all switches can be achieved to maintain high efficiency in a wide range. An experimental prototype rated at 1 kW is designed to convert 220–460 V input to 100 V output. The experimental results show that the proposed converter can achieve high efficiency over a wide input voltage and load range. [ABSTRACT FROM AUTHOR]

Herein, we present a self-resonant boost converter integrated circuit (IC) for ultra-wide range source tracking of a photovoltaic generator (PVG). The tracking is efficiently achieved using a self-controlled resonant frequency generator (SRFG). The SRFG, which is realized using a harmonic oscillator, defines the switching frequency of the converter by operating under three conditions: underdamping, overdamping, and critical damping. The maximum power point tracking (MPPT) controller, which synchronously operates with the SRFG, tracks the light irradiance of the PVG over a 75 $\times $ operating range of source resistance (20–1500 $\Omega $). The MPPT is achieved by controlling the ON-time of the power switch using a programmable delay controller (PDC). The proposed SRFG and the MPPT controller are realized using 31 and 38 nW, respectively. The zero current switching (ZCS) controller is realized using 20 nW. The total power consumption of the converter is 125 nW. The converter IC is fabricated in a 180-nm CMOS process with a 2- $\mu \text{m}$ -thick top-metal option. Measured results show that the boost converter achieves tracking efficiencies > 90% over an ultra-wide range of source resistance (20–1500 $\Omega $), corresponding to the illuminance range (3000–5 lux). The measured peak end-to-end efficiency is 86% at 250-mV input and 20- $\Omega $ source resistance. Using a commercial PVG module, the converter delivers the maximum output power of 120 $\mu \text{W}$ with a peak conversion efficiency of 89%. The boost converter performs a self-startup at 80-mV input using an on-chip transformer-based startup circuit (OTSC). [ABSTRACT FROM AUTHOR]

This letter introduces a fully integrated inductive power converter for thermal energy harvesting using the thermoelectric generator (TEG). With a three-step self-start block, the power converter can cold-start from 83 mV. After self-start, the minimum input voltage to sustain the power converter operation is only 6.4 mV. An integrated maximum power point tracking block keeps impedance matching at the TEG output. A novel low-power zero-current switching block realizes accurate switching with little overhead. The proposed power converter is implemented in a 55-nm CMOS process and achieves 81% peak end-to-end efficiency. [ABSTRACT FROM AUTHOR]

In this article, the output voltage control strategy of modular multilevel resonant dc converters (MMRDC) for medium-voltage wide-input-range applications is studied. First, the feasibility and influence of the switching frequency regulation and modulation index regulation are investigated in detail. It is found that the switching frequency choice has a significant effect on the voltage stress of arm inductors and the transformer. Then, based on these considerations, the modulation index regulation plus switching frequency regulation based design and control optimization is proposed. With the proposed design and control method, the switching frequency range for adapting to a wide input range is further reduced, especially under light load operating conditions. Besides, the high voltage stress on arm inductors is avoided and the high voltage dv/dt on the transformer is also eliminated. Finally, a laboratory prototype with 8–16 kV input and 375 V/60 kW output has been built and the experimental validation under a wide input range has been done. The efficiency over 96.4% under the wide input range proved the effectiveness of the optimized control methods. [ABSTRACT FROM AUTHOR]

Current-fed half bridge converter with bidirectional switches on ac side and a full bridge converter on dc side of a high frequency transformer is an optimal topology for single stage galvanically isolated ac–dc converter for onboard vehicle charging application. The ac side switches are actively commutated to achieve zero current switching (ZCS) using single phase shift modulation (SPSM) and discontinuous current phase shift modulation (DCPSM). Furthermore, zero voltage turn-on (ZVS) is achieved for dc side switches. Compared with SPSM, DCPSM maintains a constant peak current in the converter throughout the grid cycle of ac mains voltage. However, constant peak current contributes to a high circulating current near the zero crossings of ac mains voltage and also at light load conditions. This article proposes an improved discontinuous current phase shift modulation to increase the efficiency of the converter across different loading conditions. A dual control variable is adopted to actively reduce the circulating current while maintaining soft switching of both ac and dc side switches across the grid cycle of ac mains voltage. A 1.5-kW laboratory prototype has been developed to experimentally validate the analysis, design, and improvement in performance for different loading conditions. [ABSTRACT FROM AUTHOR]

Multilevel circuits can achieve high-voltage level, power density, and performance. This article considers a dual active bridge (DAB) based on the active neutral-point-clamped (ANPC) three-level circuit (ANPC–DAB). The soft-switching characteristics of the ANPC circuit during the switching process between switching states are analyzed, and the conditions for enabling all 12 switching devices to achieve zero-voltage switching (ZVS) on all the turn-on switching transitions are obtained. Based on this, the distribution of hard-switching turn-off and conduction losses of power devices is further analyzed, and an optimized switching strategy that can balance the loss distribution of power devices is proposed by the evaluation of all zero states and analysis of a switching-state sequence. Moreover, this article examines the effect of the proposed switching strategy by analyzing the loss distribution of power devices and efficiency of the ANPC–DAB. Finally, experiments are conducted using a 1-kW prototype. The simulation and experimental results show that the proposed switching strategy can effectively improve the loss distribution of power devices while all the power devices realize ZVS. [ABSTRACT FROM AUTHOR]

Critical conduction mode (CRM) or discontinuous conduction mode (DCM) boost power factor correction (PFC) converter is widely used in low power applications for its advantages of zero-current turn-on of the switch, no reverse recovery in diode, and simple control. The input current of fixed switching frequency control CRM boost PFC converter and the input current of constant duty-cycle control DCM boost PFC converter mainly contain third harmonic. Moreover, the phase of the third harmonics is opposite. This article proposes a harmonic elimination parallel control to connect these two converters in parallel. The input current third harmonic of the parallel converter can be eliminated completely so as to improve the PF to nearly unity in the whole input voltage range. This parallel method is an interesting way to extend power, and is different from the existing method of parallel DCM boost PFC converter or parallel CRM boost PFC converter. The experimental results verify the accuracy of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Due to the contradiction between [ABSTRACT FROM AUTHOR]

A new single-stage high frequency-link three-phase $LLC$ ac–dc converter is proposed in this article. The proposed converter is featured by a boost full-bridge topology-based phase module with power factor correction (PFC) for the three-phase utility frequency ac  to single-phase high-frequency ac  conversion without a smoothed dc link, which brings the simplicity, cost-effectiveness, excellent modularity, and high efficiency into the power supply. The soft switching commutation can achieve over the wide range of load power with the assist of magnetizing current of a high frequency transformer in the $LLC$ topology. The load power and voltage can be regulated by pulse frequency modulation  and phase-shift pulsewidth-modulation  depending on the load conditions. The effectiveness of the proposed converter is investigated by simulation and experiment of a 2 kW–50 kHz preliminary prototype, thereby the single-stage frequency conversion, PFC and zero voltage soft-switching  are revealed from a practical point of view. [ABSTRACT FROM AUTHOR]

To address the hard-switching issue of conventional buck converter and high-voltage/current stress issue of soft-switched converter like resonant cross-commutated buck converter, a new soft-switched dc–dc topology with two-phase operation is proposed in this article. The ac current generated from the floating half bridge of one phase is injected into the switching node of another phase to realize zero-voltage switching for all MOSFETs and zero-current switching for the low-side MOSFETs. This method is named as active cross-commutation (Acc). The benefits of AccBuck converter include soft switching, low-voltage stress of low-side switches, low current stress for all switches, and fixed switching frequency. The operation principles with and without parasitic output capacitance (Coss) are analyzed by using the state-plane method. Clamped diodes are added to reduce the Coss-related ringing. The analytical formula of voltage gain is derived, which is related to the duty ratio, Coss, inductance, load current, and switching frequency. A prototype was fabricated to demonstrate the proposed converter. During the fixed-duty-ratio operation, the converter achieves 97.8% peak efficiency and 1410 W/in3 power density at 50 A output current, 54 V input, and 9 V output. The calculated load line and regulation capability are also verified experimentally. [ABSTRACT FROM AUTHOR]

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-off 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. [ABSTRACT FROM AUTHOR]

This article presents a novel concept of switch-mode dc–dc boost converters with reduced switching losses. The converters use an auxiliary switching cell to achieve zero voltage switching during the turn-off of a transistor. The novel concept facilitates an increase in the efficiency or switching frequency of an IGBT-based boost converter. This article discusses the converters topology, the principle of operation, and issues related to the reduction of power losses, the range of optimal operation, and selection of components. The concept of the converter was verified through simulation and a series of experiments that demonstrate the process of zero-voltage turn-off and the efficiency of the converter. [ABSTRACT FROM AUTHOR]

This letter presents a novel solution to attenuate the electromagnetic emission of power switching circuits due to the resonance of the loop parasitic inductances with the parasitic capacitances of the power devices. A resonant snubber based on the magnetic coupling of a power parasitic loop causing unwanted oscillations with another one inserted at the printed circuit board level purposely and loaded by a dissipative element, is presented. A design method is proposed and used to damp the unwanted oscillations affecting the switching voltage and current in a prototype, which was specifically designed and fabricated to validate the proposed solution. The conducted emission delivered by such a prototype equipped with the resonant snubber, with an RC snubber, and without any snubber are compared. [ABSTRACT FROM AUTHOR]

Soft-switching technique contributes to higher conversion efficiency and switching frequency for transformerless grid-connected inverters (TLIs), which is beneficial to improve power density and reduce cost. However, existing soft-switching TLIs can only operate with unity power factor; as a consequence, they could not supply reactive power required by newly technical standards. In order to solve this issue, a novel zero-voltage-transition (ZVT) scheme has been proposed in this article, and two resonant tanks with a compact structure are applied in H6-type topology. The derived ZVT inverter enables high-frequency switches of both positive and negative power regions to be turned on and off under zero-voltage conditions, as well as all auxiliary switches can be turned on with zero-current switching. Meanwhile, unipolar differential-mode voltage and constant common-mode voltage characteristics are also maintained. Finally, comprehensive experiment results from a 100-kHz/1-kW prototype are provided to verify the correctness of the proposed inverter. [ABSTRACT FROM AUTHOR]

This article introduces a new nonisolated full soft-switching step-up dc/dc converter based on single-ended primary inductor converter (SEPIC) structure. The proposed topology utilizes a three-winding coupled-inductor (TWCI) to increase the voltage gain, but unlike other coupled-inductor-based converters, its voltage gain is increased by reducing its magnetic turns ratio. Moreover, the secondary and tertiary turns ratios of the TWCI can be used as an additional design freedom to extend the voltage gain, which indicates more converter flexibility. Due to the continuous input current, the proposed converter can be used for many types of renewable energy sources. Also, the leakage energy from the TWCI has further been recycled and transferred to the output with the help of a regenerative passive clamp circuit. Due to the soft-switching performance, the proposed converter has no switching losses at the turn-on instant for the power switch and reverse recycling losses of the diodes. Furthermore, the use of a small number of components along with the soft-switching performance offer high efficiency. Steady-state analysis and design considerations are discussed thoroughly. Finally, a 200-W prototype with 200 V output voltage is provided to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Three-port converters with high voltage gain are desirable solutions for integrating renewable energy and energy storage devices into high voltage dc bus. A high gain three-port converter with soft switching is proposed in this paper, which can realize zero voltage switching for all switches and zero current switching for all diodes in various operating modes. Single coupled inductor is used to achieve high voltage gain and to reduce the voltage stress of switches so that switches with low on-resistance can be selected to reduce the conduction loss. In addition, the advantages of fewer components, higher voltage gain, and very low switch voltage stresses make the proposed converter more suitable for application in renewable energy systems than similar solutions. Various operating modes, performance analysis, design considerations, efficiency analysis, and control method of the proposed converter are discussed. A laboratory prototype with 30 V renewable energy source, 48 V energy storage device and 400 V output is designed to verify the performance of the proposed three-port converter. [ABSTRACT FROM AUTHOR]

This article proposes a bridgeless push–pull resonant ac–dc converter featuring naturally balanced switching loss at the primary side. The proposed converter employs a current-fed push–pull structure and two rectifier diodes at the primary side and a series resonance circuit at the secondary side. By incorporating two rectifier diodes, a diode bridge can be removed from the grid side of the proposed converter, and thereby that the number of components and primary-side conduction loss are reduced. One major advantage of the proposed converter is balanced loss distribution over one cycle of grid voltage, which guarantees high power transfer capability with enhanced overall switch utilization. The series-resonant circuit provides zero-current switching turn-off at the output diode, thereby reducing the reverse recovery loss. The operating principles and theoretical derivations of the converter are discussed in detail. The validity and performance of the proposed converter are verified using a prototype with 1.65 kW output power. [ABSTRACT FROM AUTHOR]

This article proposes a dual-inverter pulsewidth modulation (PWM) scheme for dc-biased vernier reluctance machines (dc-biased-VRMs) with reduced switching frequency capable of zero-sequence current regulation. The dc-biased-VRM utilizes the additional dc bias current in armature winding to construct the rotor flux. To regulate the dc bias current, two sets of three-phase inverters with common dc bus are used to provide dc current flow path. In each switching cycle, the number of switching actions is doubled compared with the conventional three-phase inverter. There is still a certain optimization space for adjusting the dc bias current and reducing the switching loss. The proposed scheme reconfigures the zero voltage vector based on the discontinuous PWM (DPWM) scheme, it effectively reduces the switching actions, thus reducing the switching frequency and ensuring the low switching loss of the inverter. In addition, an inserted zero voltage vector regulation method is associated with the proposed DPWM scheme, and it assures the zero-sequence current regulation ability. Besides, by adopting complementary zero voltage vector distribution in odd and even sectors, the balanced voltage stress of upper and lower switching devices in each bridge arm is realized. The proposed dual-inverter PWM scheme does not require any additional devices, and it provides an effective solution to improve the efficiency of the dc-biased-VRM drive system. Finally, the effectiveness of the proposed scheme is verified experimentally. [ABSTRACT FROM AUTHOR]

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 $ dv/dt $. The proposed dc SSTs, operating principles, predictive control method, the ZVS, and the controlled $ dv/dt $ under voltage buck-boost ranges are verified with MV simulations and an experimental prototype based on SiC mosfets, diodes, and a nanocrystalline transformer. [ABSTRACT FROM AUTHOR]

In this article, an interleaved high-voltage gain dc–dc converter is proposed for use with photovoltaic (PV) systems. By integrating two three-winding coupled inductors (CIs) with switched capacitor cells, the voltage gain is further extended. Through passive diode-capacitor clamp circuits, the energy stored in the leakage inductances is absorbed; additionally, the voltage stress of the power switches is clamped to a value far lower than the output voltage, which enables designers to select switches with low-voltage ratings. Due to the interleaved structure of the proposed converter, the input current has a small ripple, which leads to the increased lifespan of the PV panels. In addition, the current stress on the components is reduced. Thanks to the leakage inductances of the CIs, the zero-current switching condition is intrinsically provided for the diodes; accordingly, the adverse impact of the diodes’ reverse-recovery is alleviated. The operating principles, steady-state analyses, and design considerations of the proposed converter are presented in this article. A comparison with other similar converters is carried out to verify the merits of the proposed converter. Finally, the theoretical analyses are confirmed through the experimental results of a 400-W prototype with an output voltage of 400 V. [ABSTRACT FROM AUTHOR]

This article proposes a load-independent zero-current switching (ZCS) parallel-resonant inverter along with its analytical expressions and a design method. The proposed inverter achieves constant output voltage amplitude and ZCS against load variations, which are called the load-independent operation in this article. The analytical expressions provide design equations for achieving the load-independent operation. The analytical expressions and the design equations were verified from the quantitative agreements between the experimental measurements and analytical predictions. [ABSTRACT FROM AUTHOR]

A switched resonator converter having continuous buck gain is presented in this article. The converter has a single energy transfer capacitor and distributed inductors. As a result, converter operation is based on the multiple resonators. The ratio between the inductors can be adjusted to vary the regulation range. In that range, converter gain can be varied modulating either pulsewidth of the control signals or its frequency. To this end, one of the inductors is operated in both resonant and linear modes. Hence, the converter has a multiresonant and multimode operation. The resonant operation helps turn on and off the switches having zero-current, and it is load-independent. However, switches connected to the inductor that changes its operation in between resonant to linear modes have hard-switching at that instant. The converter operation is analyzed, and it is verified using experimental results in this article. [ABSTRACT FROM AUTHOR]

A high step-up dc–dc converter with multiple magnetic devices and switched-capacitor voltage multiplier cell (SC VMC) is proposed in this article. By simultaneous implementation of a coupled inductor (CI) and a built-in transformer (BIT), the voltage gain is flexibly increased with an additional degree of freedom in comparison with the converters with only BIT or CI. To further increase the voltage gain, the secondary winding of the CI is inserted in series with the primary winding of the BIT. This new architecture leads to multiplication of the turns ratios of the CI and BIT in the voltage gain expression, as well. The SC VMC not only extends the voltage gain but also reduces the voltage stress across the MOSFETs. To have a better device utilization, the blocking capacitor is participated in voltage gain improvement. Moreover, through active clamp circuit, the leakage energy of the magnetic devices is recycled and zero voltage switching (ZVS) performance is obtained for the main and auxiliary MOSFETs. In such a case, the switching frequency can be increased to reduce the volume of the converter. Finally, a 400-W laboratory prototype with 25– 400 V voltage conversion is fabricated to demonstrate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

The parasitic inductor can be used as resonant component to increase the power density in resonant converters. However, the parasitic inductance value of PCB copper traces is not large enough to achieve zero current switching in low and medium switching frequency conditions. To tackle this problem, a novel integration method to increase parasitic inductance value is proposed in this letter. The proposed method is based on direct coupling, which utilizes lateral structure and vertical structure to increase equivalent inductance between two parasitic inductors. The proposed method not only can achieve high efficiency, high power density, and very low profile design, but also can save the cost and space of discrete inductors for the designed prototype in low and medium frequency range. The comparison and design procedure of both lateral and vertical structures of the parasitic inductor are presented in details. Two 100-W prototypes employing gallium nitride devices are built to compare the discrete inductor solution with the proposed parasitic inductor integration method. The power density of the prototype using parasitic inductor is 62.5% higher than discrete inductance and has achieved a peak efficiency of 93.4%. [ABSTRACT FROM AUTHOR]

Multiphase interleaved boost diode-capacitor (MIBD) converters, as the combination of multiphase interleaved input and voltage multiplier cells (VMCs), provide a preferred solution for both high voltage gain and high-efficiency application. This article proposes a universal zero-voltage transition (ZVT) circuit design method for a family of MIBD converters with different VMC structure and cell number. Compared with other soft-switching (SS) design methods, there is no extra voltage stress for all the semiconductor devices. An auxiliary circuit consisting of two low-voltage rating switches, two diodes, two capacitors, and one small inductor is integrated into the hard-switching (HS) two-phase interleaved boost diode-capacitor (TIBD) converters to provide zero-voltage switching (ZVS) turn-on and turn-off for the main switches and zero-current switching (ZCS) turn-off for all the diodes. Besides, the auxiliary switches turn on under ZCS. All the SS is accomplished within a wide duty cycle and power rating. From the comprehensive comparison, the constructed converters’ performance exceeds that of ZVS converters published in the recent literature. Furthermore, the extendable high voltage gain, low input current ripple, low voltage stress, and simple parameter design characteristics of HS MIBD converters are also conserved. Finally, a 320-W laboratory prototype is implemented to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

To meet the requirements of higher current ratings and lower thermal impedances, paralleling power field-effect transistor (FET) discretes or modules is often a cost-effective or even an unavoidable solution. While paralleling FETs allows for a significant reduction in conduction loss, the switching loss is increased in hard-switching applications. This article proposes a generic soft-switching modulation scheme for parallel power FET bridge legs. Part of the paralleled FET legs is chosen as an auxiliary leg that is turned on prior to the remaining main legs. A resonant commutated pole (RCP) mode is then created, which enables the high-side FET of the auxiliary leg to achieve zero-current switching (ZCS) or quasi-ZCS and the remaining FETs to achieve zero-voltage switching. Thus, we can significantly reduce the switching loss that normally dominates the total power loss of high-frequency hard-switching converters particularly at partial and light loads. Experimental results from three parallel GaN high-electron-mobility transistor legs validate the effectiveness of this RCP-enabled solution in reducing switching losses and improving power conversion efficiencies. This article is accompanied by supplementary JIF and PDF files demonstrating the operational details of the RCP mode. [ABSTRACT FROM AUTHOR]

An integrated boost-LC-resonant-flyback multimode converter with a wide voltage gain is proposed in this article. With three different pulsewidth modulation strategies, the proposed converter can realize three modes including high-, medium- and low-voltage-gain (LG), by multiplexing inductors and power switches. In the high-voltage-gain mode, it has better load characteristics than the conventional LLC converter through an extra energy storage stage. In the medium-voltage-gain mode, the working condition is similar to that of the conventional LLC converter, but the issues of current reflow and circulation can be addressed than reducing the conduction loss. In the LG mode, the proposed converter works as a flyback converter, and it has a higher conversion efficiency and simpler operation state than the conventional LLC converter. Additionally, all power switches can realize zero-current switching over a wide load range. The operating principle, voltage gain, design methodology, and control scheme are fully presented in this article. Finally, a laboratory prototype with 110 V input voltage, 0–5 A output current, and 24–165 V output voltage was conducted and verified the proposed solution. [ABSTRACT FROM AUTHOR]

A phase-shift modulated converter with two full bridges at primary side and rectifier diodes in hybrid combination at secondary side is proposed in this article. Due to the proposed symmetrical modulation strategy, two full-bridges always equally share the total system power rating, and thus the VA rating of two transformers is minimized. The circulating currents decay to zero in the zero state, contributing to reduce the conduction loss and duty-cycle loss. Zero-voltage or zero-current switching is achieved for all switches over whole input voltage range with an auxiliary inductor. The rectifier output voltage is synthesized of two controlled transformer secondary voltages all the time, which achieves the same output current ripple suppression effect as the conventional input-parallel output-parallel full-bridge converters with interleaved control scheme, and reduces the voltage stress of rectifier diodes. These advantages make the converter suitable for wide input voltage range applications. In this article, the operation principle and steady-state analysis of the proposed converter are illustrated in detail. Experimental results with 220–460 V input voltage are demonstrated to verify the advantages. [ABSTRACT FROM AUTHOR]