Turn-on Switching Research Articles

Soft-Switching Bidirectional Three-Level DC–DC Converter with Simple Auxiliary Circuit

This paper suggests a soft-switching bidirectional three-level DC–DC converter with a simple auxiliary circuit. The proposed converter uses auxiliary LC resonant circuits so that the power switches operate under a soft-switching condition. The resonant operation of the LC circuits makes power switches turn on at zero voltage, eliminating the turn-on switching power losses. The proposed converter improves the power efficiency, not using complex power switching circuits, but using simple LC resonant circuits. The operation of the proposed converter is described according to its operation modes. Experimental results for a 1.0 kW prototype are discussed to verify its performance. The proposed converter achieved the power efficiencies of 97.7% in the step-up mode and 97.8% in the step-down mode, respectively, for the rated load condition.

Simplified analytical model for estimation of switching loss of cascode GaN HEMTs in totem-pole PFC converters

A practical analytical model to calculate the switching loss of cascode gallium nitride high electron mobility transistors (GaN HEMTs) is proposed. To facilitate analysis and application, the transmission delays introduced by Si MOSFET and interconnection inductances are ignored in modeling. Meanwhile, the nonlinear junction capacitances of the device and circuit stray inductances are also incorporated to increase the accuracy of the model. The turn-on and turn-off switching processes are described in detail and the simplified equations can be easily solved by using mathematical tools. Based on the analytical model, loss evaluation of totem-pole PFC converter is introduced briefly. Finally, the accuracy of the model is validated by comparing the calculated loss and converter's efficiency with experiment results. Peak efficiency of 99.26% is achieved for a 3.6 kW single phase CCM Totem-Pole PFC AC/DC converter switching at 50 kHz based on 650 V cascode GaN HEMTs.

High Step-Up Interleaved dc–dc Converter With Asymmetric Voltage Multiplier Cell and Coupled Inductor

In this article, a novel high step-up interleaved dc-dc converter is presented, which is composed of an interleaved structure, an asymmetric voltage multiplier cell (AVMC), and a passive lossless clamped circuit. Compared to the classical interleaved boost converter, the proposed converter has a higher voltage gain owing to the employment of the AVMC and the coupled inductor. In addition, the input current ripple is limited to low values with the help of the interleaved structure, which gives more lifetime to the input power source. The voltage stresses of main switches are substantially low so that the MOSFETs with low voltage rate and ON-resistance (RDS(ON)) can be used. In addition, the voltage stresses and the reverse recovery problems of diodes are improved dramatically. Moreover, the zero current switching (ZCS) turn-on of switches and the ZCS turn-off of the clamp diodes are realized to reduce the switching losses. The leakage inductor energy is recycled and the voltage spikes are improved greatly by the passive lossless clamped circuit so that the efficiency can be upgraded further. Finally, a 400-W, 40-V-input, 400-V-output prototype is established to demonstrate the performance of this converter. The highest efficiency is about 97.3% and the full-load efficiency is approximately 97%.

An Improved Digital Algorithm for Boost PFC Converter Operating in Mixed Conduction Mode

This article proposes an improved digital algorithm based on predictive control for the operation of a boost power factor correction (PFC) converter in the mixed conduction mode (MCM). The proposed MCM algorithm comprises of a proposed digital conduction mode detection method, a proposed predictive discontinuous conduction mode (DCM) average current controller, a proposed digital compensation technique in DCM to account for the initial nonzero inductor current during switch turn-on and also a predictive continuous conduction mode (CCM) average current controller. The proposed algorithm flow is computationally efficient with no additional sensor/circuit requirements and ensures low harmonic content in the input current. The proposed MCM algorithm is verified experimentally on a 300-W boost PFC converter hardware prototype for converter operation in MCM, pure DCM, and pure CCM within a half line cycle. The proposed MCM algorithm is evaluated experimentally in terms of current tracking, current harmonics, and computation times.

Experimental Study of High-Temperature Switching Performance of 1.2kV SiC JBSFET in Comparison with 1.2kV SiC MOSFET

The high-temperature switching performance of a 1.2kV SiC JBSFET is compared with a 1.2kV SiC MOSFET using a clamped inductive load switching circuit representing typical H-bridge inverters. The switching losses of the SiC MOSFET are also evaluated with a SiC JBS Diode connected antiparallel to it. Measurements are made with different high-side and low-side device options across a range of case temperatures. The JBSFET is observed to display a reduction in peak turn-on current – up to 18.9% at 150°C and a significantly lesser turn-on switching loss – up to 46.6% at 150°C, compared to the SiC MOSFET.

Discovery of Environment-Sensitive Fluorescent Agonists for α1-Adrenergic Receptors.

A series of novel fluorescent agonists were well developed herein with turn-on switch for α1-adrenergic receptors (α1-ARs) by conjugating the environment-sensitive fluorophore 4-chloro-7-nitrobenzoxadiazole with phenylephrine. Overall, these probes exhibited efficient binding and apparent fluorescence intensity changes (up to 10-fold) upon binding with α1-ARs. Moreover, these probes have been successfully applied for selectively imaging α1-ARs in the living cells. The dynamic process of α1-ARs internalization was traced successfully with these newly designed fluorescent agonists. Fluorescence polarization assay demonstrated specific interactions between these probes and α1-ARs. With these new probes, a bioluminescence resonance energy transfer binding assay has been well established and applied to the high-throughput screening of unlabeled α1-ARs agonist and antagonist. It is expected that these environment-sensitive fluorescent turn-on agonists may provide useful new tools in studying pharmacology and physiology of α1-ARs during drug discovery.

Superior Short Circuit Performance of 1.2kV SiC JBSFETs Compared to 1.2kV SiC MOSFETs

The high-temperature switching performance of a 1.2kV SiC JBSFET is compared with a 1.2kV SiC MOSFET using a clamped inductive load switching circuit representing typical H-bridge inverters. The switching losses of the SiC MOSFET are also evaluated with a SiC JBS Diode connected antiparallel to it. Measurements are made with different high-side and low-side device options across a range of case temperatures. The JBSFET is observed to display a reduction in peak turn-on current – up to 18.9% at 150°C and a significantly lesser turn-on switching loss – up to 46.6% at 150°C, compared to the SiC MOSFET.

Analysis and Design Considerations of Efficiency Enhanced Hierarchical Battery Equalizer Based on Bipolar CCM Buck–Boost Units

Compared with the conventional hard switching battery equalizers, hierarchical battery equalizer based on the bipolar continuous-conduction mode buck-boost units could effectively reduce the switching loss and improve the conversion efficiency. This paper mainly addresses the key technical challenges associated with the optimal design of this battery equalizer. The inductor current is controlled to enter into the negative region. Thus, the mosfet body diode provides a freewheeling path for the inductor current during the dead band. This ensures zero-voltage switching turn-on of both power mosfets in each buck-boost unit without auxiliary snubbers. Therefore, the switching losses are significantly reduced. Meanwhile, the integral of the inductor negative current is precisely controlled to minimize the circulating current. This guarantees both minimized conduction losses and suitable equalization speed. Furthermore, an equalization algorithm, which compensates the battery internal resistance induced state-of-charge error, is proposed to improve the equalization accuracy. The operating principles and design considerations are analyzed in detail. An experimental prototype to balance four series-connected lithium-ion battery cells is implemented. The experimental results validate the design of the equalizer and demonstrate obvious efficiency enhancement over the conventional method.

An adjustable dual-emission fluorescent metal-organic framework: Effective detection of multiple metal ions, nitro-based molecules and DMA.

A novel multifunctional Pb(II)-based MOF, [Pb1.5(DBPT)]2·(DMA)3(H2O)4 (1), with excellent chemical stability, was successfully assembled by connecting {Pb2O10} unit with a multi-topic polycarboxylate ligand of 3-(3,5-dicarboxylphenyl)-5-(4-carboxylphenyl)-1-H-1,2,4-triazole (H3DBPT). It exhibits dual fluorescence emissions at 380 nm (λex = 280 nm) and 540 nm (λex = 380 nm), respectively. Through the adjustable dual fluorescence emissions, it could act as a turn-off and turn-on switch for detecting N,N-dimethylacetamide (DMA) molecule. Moreover, Fe3+ ions exert luminescence quenching role on compound 1 at both excitation lengths in water, among which the quenching at λex = 280 nm is of high sensitivity (KSV = 1.2 × 105), and the quenching at λex = 380 nm is of wide-range. The sensing for metal ions of In3+, Zr4+, and Al3+ is also effective at λex = 280 nm, with the KSV constants of 1.6 × 105, 1.6 × 105, and 4.3 × 104, respectively. More importantly, a series of nitroaromatic compounds (TNP, 2,4,6-trinitrophenol; 4-NA, 4-nitroaniline; NB, nitrobenzene) and nitro-based drugs (MNZ, metronidazole; DMZ, dimetridazole) could be detected at both excitation lengths, demonstrating the advantage of broad range response of fluorescence sensing. Thanks to the excellent chemical stability and unusual dual emission luminescence properties for chemical detection of various metal ions, nitro-based molecules and DMA solvent, the Pb-based MOF reported in this work is, therefore, a very promising multi-response sensor.

Effects of gamma irradiation on the electrical characteristics of trench-gate non-punch-through insulated gate bipolar transistor

We studied the effects of gamma-ray irradiation on the static and dynamic electrical characteristics of a trench-gate non-punch-through insulated gate bipolar transistor (IGBT) device. The threshold voltage and breakdown voltage decreased after irradiation, whereas the collector leakage current increased. Turn-on and turn-off switching times decreased and increased, respectively, with the irradiation dose. The irradiation-induced changes in the electrical characteristics can be attributed to the buildup of the positive oxide-trapped charges in the gate oxide by gamma irradiation. The evaluated characteristics data were compared with the data for gamma-irradiated planar-gate IGBTs reported in the literature. It was found that a significant degradation occurred in the shift of the threshold voltage and switching times for trench-gate IGBTs.

A simple dead-time compensation strategy for grid-connected voltage-sourced converters semiconductor switches

This paper presents a simple strategy to compensate the distorted currents synthesized by a grid-connected voltage source converter due to dead-time, turn-on and turn-off time delays of the semiconductor switches. The algorithm consider only the polarity of the fundamental component of the currents flowing through the converter terminals and the values of the time delays and voltage drops supplied by the manufacturers to the semiconductors devices. The presented compensation belongs to the group classified as average value compensation technique methodology since it does not change the pulse pattern of the converter's semiconductor switches. A simplified mathematical description of the effects caused by these unwanted time delays is presented and used to derive a correction factor to be added, in real time, to the converter output controller in order to compensate for its terminal voltages. The asymptotic stability and robustness of the proposed methodology is investigated redrawing the converter current controllers, designed in dq-reference frame, as proportional-resonant ones, in the abc coordinates, and adding the effect of the compensating signal in the feedback loop using the concept of describing function. In addition, the minimum value of the DC bus voltage necessary is also evaluated to ensure the operation of the converter in the linear modulation region when the compensation algorithm is active. Experimental results are presented to validate the theoretical analysis and to demonstrate the effectiveness of the proposed strategy for three different operation conditions of a grid-connected converter: (i) active power injection; (ii) active power consumption and (iii) reactive power support.

A Novel Zero-Current-Switching PWM Buck Converter with Magnetic Coupling Effect

In this paper, a novel zero current switching PWM buck converter with magnetic coupling effect is proposed. The main switch in this topology turns on with zero current switching and turns off with zero current transition condition. Furthermore, the auxiliary switch turns on and turns off with zero current switching condition as well. And the main diode operates at zero voltage switching turn-on and zero current switching turn-off. In addition, extra efficiency is improved because part of the resonant energy stored in auxiliary windings of the coupled inductor could be transmitted to output load, and the resonant current is also suppressed. The soft-switching operation of the proposed converter is realized in a wide load range. The operating principles and the soft-switching conditions are analyzed in detail. Finally, a 1-kW experiment prototype is set up to validate the theoretical analysis. The related experiment results at 50 and 100 kHz are also given to verify the proposed topology.

Implementation of zero current switch turn-ON based buck-boost-buck type rectifier for low power applications

ABSTRACTA single-stage single-switch AC–DC integrated converter is proposed in this paper, as a tight DC voltage regulator with unity input power factor for the fundamental component of the input current. Proposed converter is formed by the integration of buck-boost configuration with a buck converter operated by a single switch. The buck-boost section of the proposed configuration is operated in current discontinuous conduction mode (DCM) to get unity input power factor at the supply terminals and the buck section is operated up to boundary current conduction mode (BCM). The features acquired by the converter operating in complete discontinuous conduction mode (DCM) are unity input power factor, zero-current turn-ON for the Switch, fast and good DC output voltage regulation with extensive conversion range and low voltage stress on the switch. Additionally, the intermediate capacitor voltage stress is independent of converter load variations and so the switch also is subjected to constant peak voltage stress. A comprehensive study is carried out to obtain the necessary design equations. A design model is implemented using simulation and hardware. The results confirm the performance of the proposed configuration.

Turn-On Mode Fluorescence Switch by Using Negative Photochromic Imidazole Dimer.

The development of fluorescence switchable molecules in several polar and apolar environments has been required for fluorescence imaging of nanostructures. Photochromic molecules are an important class for the reversible light-triggered fluorescence switching. Although many studies of fluorescence switching by using photochromic reactions have been reported, the report of photochromic molecules reversibly showing turn-on mode fluorescence switching has been limited in spite of their importance. Herein, we report the photoactivatable fluorescence based on negative photochromism, where the absorption spectrum of the compound after irradiation is blue-shifted relative to that before irradiation. We introduced naphthalimide units as a green fluorophore to the negative photochromic binaphthyl-bridged imidazole dimer. The fluorescence of the naphthalimide unit is efficiently quenched in the initial colored isomer (fluorescence quantum yield: Φfluo. = 0.01) by Förster resonance energy transfer. In contrast, the fluorescence quantum yield increases up to 0.75 in the transient isomer formed by the negative photochromic reaction. The fluorescence intensity thermally decreases with the thermal back reaction to form the original stable colored form. These results indicate that the negative photochromic molecules are suitable for turn-on mode fluorescence switches and will give an attractive insight for the development of reversible fluorescence switching molecules.

High Step-Up Nonisolated ZVS/ZCS DC–DC Converter for Photovoltaic Thin-Film Module Applications

Photovoltaic (PV) thin-film modules normally present higher voltages at the maximum power points than crystalline silicon ones. This feature makes the usage of low-voltage MOSFETs (≤100 V) unfeasible in high step-up boost-based converters. In order to solve this drawback, this paper proposes a novel high step-up nonisolated dc–dc converter based on the classical synchronous buck converter with coupled inductor and voltage multiplier techniques. Besides reducing the voltage stress on the active switches, the proposed converter also requires a coupled inductor with lower core-window product, allowing the use of a smaller magnetic device. The resonant operation mode of the proposed converter enables zero-voltage-switching turn-on of active switches and zero-current-switching turn-off of diodes, which increases its efficiency. A 150-W prototype, able to work with a large variety of commercial PV thin-film modules, with 55–85-V input and 400-V output voltages, is built to verify the developed analysis. Experimental results show that the maximum obtained efficiency is nearly 98%, and the weighted California Energy Commission efficiencies are greater than 96.7% over the whole input voltage range.

Parallel current‐fed resonant converter with balance current sharing and no input ripple current

This studies a parallel current-fed resonant converter with the advantages of the balance current sharing and no input ripple current. The basic structure of the developed circuit includes a boost converter and half-bridge resonant converter with the same power switches to reduce switch counts. Two boost-type converters with an interleaved pulse with modulation are used in the front stage to eliminate input ripple current and reduce the size of boost inductor. Parallel resonant converter with magnetic coupling current balancing cell is adopted in the rear stage to automatically balance two resonant circuits and realise the zero-voltage turn-on switching for power devices. The voltage doubler circuit is employed on the secondary-side to achieve high-voltage output. The developed converter can be used for current-type input source and voltage-type output. Finally, experiments with 1 kW laboratory prototype are provided to confirm the feasibility of the proposed converter.

Comprehensive Analysis of Electrical Parameters Degradations for SiC Power MOSFETs Under Repetitive Short-Circuit Stress

The degradations of electrical parameters for silicon carbide power MOSFETs under repetitive short-circuit (SC) stress are investigated in detail in this paper. It demonstrates that the generation of negative charges along the gate–oxide interface of the channel region is the dominant degradation mechanism, which results in the increase in the threshold voltage ( ${V}_{\text {th}}$ ) and the rise of ON-state resistance ( ${R}_{\text {dson}}$ ) under low gate voltage bias condition. Furthermore, degradations of dynamic characteristics including gate charge ( ${Q}_{\text {g}}$ ) and switching behaviors of the device after the repetitive SC stress are extracted and analyzed for the first time. It illustrates that the increased ${V}_{\text {th}}$ contributes to the rise of the Miller plateau voltage ( ${V}_{\text {gp}}$ ), which further leads to the increase in gate–source charge ( ${Q}_{\text {gs}}$ ). Meanwhile, the increase in the turn-ON time and the reduction of turn-OFF time are observed, which are also resulted from the positive shifts of ${V}_{\text {th}}$ and ${V}_{\text {gp}}$ , leading to the rise of turn-ON switching energy ( ${E}_{{ \text {on}}}$ ) and the decline of turn-OFF switching energy ( ${E}_{\text {off}}$ ), respectively.

A Switched-Capacitor Bidirectional DC–DC Converter With Wide Voltage Gain Range for Electric Vehicles With Hybrid Energy Sources

A switched-capacitor bidirectional dc–dc converter with a high step-up/step-down voltage gain is proposed for electric vehicles with a hybrid energy source system. The converter presented has the advantages of being a simple circuit, a reduced number of components, a wide voltage-gain range, a low voltage stress, and a common ground. In addition, the synchronous rectifiers allow zero voltage switching turn-on and turn-off without requiring any extra hardware, and the efficiency of the converter is improved. A 300 W prototype has been developed, which validates the wide voltage-gain range of this converter using a variable low-voltage side (40–100 V) and to give a constant high-voltage side (300 V). The maximum efficiency of the converter is 94.45% in step-down mode and 94.39% in step-up mode. The experimental results also validate the feasibility and the effectiveness of the proposed topology.

A Quasi-Resonant ZVZCS Phase-Shifted Full-Bridge Converter with an Active Clamp in the Secondary Side

A novel Pulse-Width-Modulation (PWM) quasi-resonant active-clamp phase-shifted full-bridge converter is presented and analyzed in this paper. In the proposed topology, an active-clamp switch and a clamp capacitor that resonates with the leakage inductance of transformer are employed at the secondary side. The active-clamp circuit helps all of the primary switches in achieving both zero-voltage switching (ZVS) turn-on and nearly zero-current switching (ZCS) turn-off over the entire load range, and resets the primary current during the freewheeling interval. The operation of the active-clamp circuit eliminates voltage ringing across the rectifier. In addition, the secondary diodes can achieve ZCS turn-off, which removes the reverse recovery problem of diodes, and the active-clamp switch can achieve ZCS turn-on. A 3.5-kW prototype was built to verify the performance of the proposed converter. A maximum efficiency of 97.6% was achieved under a 2-kW load, and an efficiency of more than 96% was achieved even under a light load.

SiC MOSFETs for Offshore Wind Applications

Space and weight are critical factors for offshore wind applications during the construction, operation, and maintenance phases. Superior material properties of silicon carbide enable the development of power devices capable of switching fast as well as handling high power. Thus, this paper performs the quantitative evaluation of the total converter loss and efficiency at different switching frequencies in order to observe the potential performance gains that SiC MOSFETs can bring over Si IGBTs for such applications. When simulating the detailed converter losses in a three-phase, two-level topology; the turn-on and turn-off switching energy losses obtained from the laboratory measurement and the conduction losses acquired from the datasheet are used as a look-up table input. Additionally, the simulated results are compared with the analytical and the numerical solutions. In conclusion, this analysis gives an insight into how SiC MOSFET outperforms Si IGBT over all switching frequency ranges with the advantages becoming more visible at higher frequencies.