Switching Transition Research Articles

Experimental Comparison of High‐Speed Gate Driver Design for 1.2‐kV/120‐A Si IGBT and SiC MOSFET Modules

Silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET) is regarded as an attractive replacement for Si insulated gate bipolar transistor (IGBT) in high-power density applications due to its high switching speed and low switching loss. However, to fully utilise these benefits, the gate driver of the SiC MOSFET needs to be optimised to meet its special driving requirements. Fundamentally, both gate drivers for Si IGBT and SiC MOSFET share similar design methodology since these two power devices have the same MOS-gated structure. However, one of the major challenges in the gate driver design for SiC MOSFET is overcoming the electromagnetic interference, which is resulted from the much higher dv/dt and di/dt ratios during the switching transition. In this study, high-speed gate drivers for Si IGBT and SiC MOSFET power modules of similar ratings of 1.2 kV/120 A have been designed. The performances of gate driver have been experimentally evaluated by a double pulse test. The design considerations of gate driver to enable the replacement of Si IGBT by SiC MOSFET have been conclusively investigated and presented in this study.

An Accurate Subcircuit Model of SiC Half-Bridge Module for Switching-Loss Optimization

The increasing demand for high power density requires the power converter to operate in high switching frequency. Silicon carbide (SiC) power module is regarded as one of the most promising candidates for high-frequency applications due to the superior switching speed and low switching loss. With the increase of switching frequency, the switching loss will be the limiting factor of efficiency. Hence, it should be minimized during each switching transition. The optimization of switching loss is normally achieved by the repetitive double pulse test experiments. It is time-consuming to find an optimum gate resistance to achieve the tradeoff between switching loss and electromagnetic interface. In this paper, an accurate subcircuit model for SiC power module is proposed to assist optimization of switching loss in converter design. By considering the device physics and structure, an accurate Miller capacitance model is obtained. Moreover, a parameter extraction procedure is presented, which is based on the datasheet. Good agreements are achieved between the PSpice simulation and experiment.

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

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

A Modulation Strategy to Operate Multilevel Multiphase Diode-Clamped and Active-Clamped DC–AC Converters at Low Frequency Modulation Indices With DC-Link Capacitor Voltage Balance

This paper proposes a modulation strategy for multilevel multiphase diode-clamped dc–ac converters (also applicable to other functionally equivalent topologies) able to keep the dc-link capacitor voltages balanced under passive front ends, low frequency modulation indices (i.e., low number of switching transitions per fundamental cycle), any value of the amplitude modulation index, and any ac-side displacement power factor. A suitable phase voltage pattern with minimum number of switching transitions is presented for the n -level three-phase case. Subsequently, it is extended to higher number of switching transitions per fundamental cycle and to higher number of phases. Simulation results with three, four, and five levels; three and five phases; and several frequency-modulation-index values are presented to validate the proposed modulation strategy. Experimental results obtained with a four-level three-phase dc–ac converter prototype are also provided. The proposed modulation strategy enables the use of this type of converters in applications where the ac fundamental frequency may be close to the switching frequency, such as in high-power systems and variable-speed motor drives.

Threshold effect in the relationship between investor sentiment and stock market returns: a PSTR specification

This article verifies whether the hypothesis of heterogeneous agent modelling and the behavioural heterogeneity framework can reproduce recent stylized facts regarding stock markets (e.g. the 1987 crash, internet bubble, and subprime crisis). To this end, we investigate the relationship between investor sentiment and stock market returns for the G7 countries from June 1987 to February 2014. We propose an empirical non-linear panel data specification based on the panel switching transition model to capture the investor sentiment-stock return relationship, while enabling investor sentiment to act asymmetrically, non-linearly, and time varyingly according to the market state and investor attitude towards risk. Our findings are twofold. First, we show that the hypotheses of efficiency, rationality, and representative agent do not hold in reproducing stock market dynamics. Second, investor sentiment affects stock returns significantly and non-linearly, but its effects vary with the market conditions. Indeed, the market appears predominated by fundamental investors in the first regime. In the second regime, investor sentiment effect is positively activated, increasing stock returns; however, when their overconfidence sentiment exceeds some threshold, this effect becomes inverse in the third regime for a high threshold level of market confidence and investor over-optimism.

EFFECT OF PULSE WIDTH MODULATION ON DC MOTOR SPEED

Pulse width modulation (PWM) is used to generate pulses with variable duty cycle rate. The rapid rising and falling edges of PWM signal minimises the switching transition time and the associated switching losses. This paper presents a DC motor speed controller system using PWM technique. The PWM duty cycle is used to vary the speed of the motor by controlling the motor terminal voltage.The motor voltage and revolutions per minutes (RPM) obtained at different duty cycle rates. As the duty cycle increases, more voltage is applied to the motor. This contributes to the stronger magnetic flux inside the armature windings and the increasethe RPM. The characteristics and performance of the DC motor speed control system was investigated. In this paper, a PIC microcontroller and a DC-DC buck converter are employed in the DC motor speed controller system circuit. The microcontroller provides flexibility to the circuit by incorporating two push button switches in order to increase and to decrease the duty cycle rate. The characteristics and performance of the motor speed controller system using microcontroller was examined at different duty cycle rate ranging from 19% to 99%.

Interleaved full ZVZCS DC–DC boost converter: analysis, design, reliability evaluations and experimental results

In this study, a new interleaved full soft switching DC-DC boost converter with a high power reliability is proposed. To achieve soft switching, a simple auxiliary circuit consisting of one switch, one diode, one inductor and two capacitors is employed in each single-phase DC-DC boost converter connected in parallel. All switches and diodes, including main and auxiliary ones, operate under soft switching conditions. These soft switching conditions consist of zero voltage and zero current switching (ZVZCS) for all switches and diodes at switching transitions except the output diodes, which turn off only with zero current switching. The soft switching technique used in this study decreases power losses which leads the converter to have higher efficiency and reliability. Also, the auxiliary circuit is located out of the main power path preventing high voltage and current stresses on the switches. In this study, operational modes analysis, design procedure, power reliability evaluations and laboratory prototype results with switching frequency of 20 kHz, input voltage of 48 V and output power of 40 W are presented.

Unified Algorithm for Multilevel Inverters

Multilevel inverters (MLIs) are broadly classified into symmetrical and asymmetrical types based on the DC-link voltage distribution. Asymmetrical MLIs are further classified into binary, quasi-linear and ternary hybrid inverters based on the geometric progression of the DC-link voltages. This study focuses on a new type of random asymmetrical MLIs (RASMLIs) where the DC links voltages are random and randomness is not pertained to any specific geometric progression. This study proposes an optimised vector search algorithm which is unified for symmetrical, asymmetrical and RASMLI. The concept of gradient-intercept equation and its corresponding Gs is the basis of the algorithm for identifying the proximal vectors. The algorithm determines the maximum DC bus utilisation at which the inverter can effectively produce quality output with minimal total harmonic distortion. As the redundant vectors reduce due to randomness the algorithm also aims at reducing the common-mode voltage with minimum switch transition. To validate the proposed algorithm, a T-type converter with H-bridge modules cascaded along each phase is considered. An experimental prototype of the same was developed and random DC voltages were fed using isolated DC supplies with induction motor as load. Nexys-4 field programmable gate array was used to implement the algorithm.

A novel electrostatically doped ferroelectric Schottky barrier tunnel FET: process resilient design

This work investigates a process-variation resilient electrostatically-doped ferroelectric Schottky-barrier tunnel FET (ED-FE-SB-TFET) based on negative capacitance (NC). The key attributes of ED-FE-SB-TFET are perovskite ferroelectric (FE) gate stack-induced NC behavior and electrostatic doping to induce pockets at both source/drain and channel interfaces. The positive feedback among the electric dipoles in FE material leads to intrinsic voltage amplification and enhanced gate controllability, thus it facilitates faster switching transitions. The proposed ED-FE-SB-TFET endeavors to create a substantial reduction in the ambipolar current ( $$I_\mathrm{Amb}$$ ), steep sub-threshold slope, paramount boost in drive current, lower drain-induced barrier-lowering, and enhanced scalability. It also obviates the need for metallurgical doping, hence ion-implantation or dopant segregation techniques employed for planar SB-TFETs pocket-doping are no longer required, and it also modifies effective Schottky barrier height and Schottky tunneling barrier width significantly to enhance the device behavior. It offers a simplified fabrication process, and it is highly resilient towards process variations, doping control issues, and random dopant fluctuations. Moreover, there is a reduced thermal budget that facilitates its fabrication on single crystal silicon-on-glass substrate realized by wafer scale epitaxial transfer. Results reveal its potential as strong candidate for next generation, scaled and low power applications.

Mössbauer and Magnetization study of polycrystalline multiferroic [formula omitted

The present work reports the preparation of polycrystalline SmFeO3 (SFO) and its characterization using bulk magnetization, 57Fe Mössbauer spectroscopy and ferroelectric polarization measurements. Temperature dependent bulk magnetization study shows crossover between zero-field cooled (ZFC) and field cooled (FC) curves at 4K and slope variation of ZFC curve in 200–300K region due to the spin switching transition which is found to be tunable with the applied magnetic field as observed in recent literature on single crystal SFO sample. From the temperature dependent Mössbauer measurements, transition from antiferromagnetic to paramagnetic state at about 708K and signatures of temperature induced spin reorientation of Fe3+ are observed in quadrupole shift (QS) and A23 hyperfine parameters in the temperature range 450–500K. The least square fitting to the temperature variation of Hint gives the critical exponent (β)≈0.327±0.001 suggesting the 3D Heisenberg magnet like behavior. The presence of ferroelectric ordering is shown from ferroelectric and PUND (Positive Up Negative Down) data measured at low temperatures (200K).

Resource-Efficient Gradient Methods for Model Predictive Pulse Pattern Control on an FPGA

We demonstrate that an optimization-based model predictive pulse pattern controller can be designed with a complexity in terms of hardware resource usage on a field-programmable gate array (FPGA) that is comparable to that of a conventional controller. The keys to the superior performance and resource usage over existing solution methods for model predictive pulse pattern control are an appropriate problem reformulation and a newly derived result for the projection on the truncated monotone cone that composes the feasible set in this application. Using a coldstarted classic gradient method in fixed-point arithmetic, a numerically stable implementation is shown to require less than 300 clock cycles to meet the stringent accuracy specification for problems with at most three switching transitions per phase. For the case of four (five) transitions, only about 550 (690) cycles are required. At the same time, merely two digital signal processor (DSP)-type multipliers on an FPGA are used for all problem sizes. These results indicate a speed improvement of ten times and a resource reduction by 17 times in terms of DSP-type multipliers for the case of three transitions per phase compared with an existing solution method. When there are four or five transitions per phase, the resource reduction is even more impressive.

Signatures of a macroscopic switching transition for a dynamic microtubule

Characterising complex kinetics of non-equilibrium self-assembly of bio-filaments is of general interest. Dynamic instability in microtubules, consisting of successive catastrophes and rescues, is observed to occur as a result of the non-equilibrium conversion of GTP-tubulin to GDP-tubulin. We study this phenomenon using a model for microtubule kinetics with GTP/GDP state-dependent polymerisation, depolymerisation and hydrolysis of subunits. Our results reveal a sharp switch-like transition in the mean velocity of the filaments, from a growth phase to a shrinkage phase, with an associated co-existence of the two phases. This transition is reminiscent of the discontinuous phase transition across the liquid-gas boundary. We probe the extent of discontinuity in the transition quantitatively using characteristic signatures such as bimodality in velocity distribution, variance and Binder cumulant, and also hysteresis behaviour of the system. We further investigate ageing behaviour in catastrophes of the filament, and find that the multi-step nature of catastrophes is intensified in the vicinity of the switching transition. This assumes importance in the context of Microtubule Associated Proteins which have the potential of altering kinetic parameter values.

Cascaded Common Nodal Point Multi-level Inverter Topology

Recent trends in the multi-level inverter (MLI) technology demand reduced number of switches, driver circuits, isolated DC sources, peak inverse voltage (PIV), appreciable number of voltage level, and lower total harmonic distortion. This paper presents an improved cascaded MLI configuration. Each module comprises ten switches, two isolated DC sources, and two capacitors; it can generate a maximum of 9-level output voltage waveform. Optimized switching sequence is developed that ensures minimum switching transitions and is implemented through single-carrier pulse width modulation for the control of the proposed topology. The classical cascaded H-bridge inverter and some recently developed MLI configurations were compared with the proposed inverter circuit. Results show that the proposed inverter configuration generates high number of output voltage levels with reduced number of power switches and PIV. It also has a lower per-unit power loss profile. Unit capacitor voltage balancing scheme is developed, which ensures proper control of the unit step voltage level in each of the cascaded modules, at extreme loading condition. For two cascaded inverter modules, simulation and experimental verifications are carried out on the proposed inverter for an R–L load. Simulation results of the output voltage waveforms and its harmonic spectrum are in conformity with experimental results.

A Zero-Voltage-Transition HERIC-Type Transformerless Photovoltaic Grid-Connected Inverter

A zero-voltage-transition highly efficient and reliable inverter concept (ZVT-HERIC) in transformerless photovoltaic grid-connected applications is derived from proposed basic resonant cells. By integrating resonant tanks and freewheeling switches, a compact resonant network is originated to make the switching transitions of high-frequency main switches softening. By utilizing the diode clamping scheme, the potential of the freewheeling loop of the ZVT-HERIC is suppressed on half of the input voltage and to restrict the leakage current. The derived inverter has the advantages of ZVT soft-switching, diode reverse-recovery alleviating, unipolar differential-mode voltage with low dv / dt , and constant common-mode voltage. The steady-state operation of the derived inverter is analyzed, and the circuit performance is discussed to explore the soft-switching region, voltage gain, as well as voltage and current stresses. Finally, the experimental results from a 3-kW prototype at 100-kHz switching frequency are provided to verify the effectiveness of the derived inverter.

Frequency Limitation Due to Switching Transition of the Bias Current in Bidirectional RSFQ Logic

Switching time limitations of the ac bias current of Josephson junctions in bidirectional rapid single flux quantum (RSFQ) logic circuits are investigated in order to determine the limits to the maximum possible operating frequency. We introduce a new approach based on modifying the bias current parameters and determining the inductance values in the circuit for reducing the switching transition time of the bias current through the junctions. We have simulated and optimized the timing and the operation of the bidirectional nondestructive readout and Josephson transmission line cells in this respect to demonstrate the results of utilizing the proposed approach. We successfully reduced the unwanted spike-type signals across the inductances which are made through the transitions during the fast switching times limiting the operation frequency. This is while we have also removed the consequent destructive spikes at the output. We have included the effects of other determining parameters of the circuit in this investigation and found their relatively optimal values to improve the temporal behavior of the bidirectional RSFQ cells. The results of the proposed approach leading to the fastest possible operation of the considered gates obtained in this work are thoroughly reported.

Paracoccidioides spp. catalases and their role in antioxidant defense against host defense responses

Dimorphic human pathogenic fungi interact with host effector cells resisting their microbicidal mechanisms. Yeast cells are able of surviving within the tough environment of the phagolysosome by expressing an antioxidant defense system that provides protection against host-derived reactive oxygen species (ROS). This includes the production of catalases (CATs). Here we identified and analyzed the role of CAT isoforms in Paracoccidioides, the etiological agent of paracoccidioidomycosis. Firstly, we found that one of these isoforms was absent in the closely related dimorphic pathogen Coccidioides and dermatophytes, but all of them were conserved in Paracoccidioides, Histoplasma and Blastomyces species. We probed the contribution of CATs in Paracoccidioides by determining the gene expression levels of each isoform through quantitative RT-qPCR, in both the yeast and mycelia phases, and during the morphological switch (transition and germination), as well as in response to oxidative agents and during interaction with neutrophils. PbCATP was preferentially expressed in the pathogenic yeast phase, and was associated to the response against exogenous H2O2. Therefore, we created and analyzed the virulence defects of a knockdown strain for this isoform, and found that CATP protects yeast cells from H2O2 generated in vitro and is relevant during lung infection. On the other hand, CATA and CATB seem to contribute to ROS homeostasis in Paracoccidioides cells, during endogenous oxidative stress. CAT isoforms in Paracoccidioides might be coordinately regulated during development and dimorphism, and differentially expressed in response to different stresses to control ROS homeostasis during the infectious process, contributing to the virulence of Paracoccidioides.

Variable Structure H∞ Controller for Aircraft

This paper proposes a new synthesis method and tuning procedure for a variable structure H∞ multivariable controller for fixed wing aircrafts attitude control, which consists in switching from one-degree of freedom controller (1-DOF) to two degrees of freedom controller (2-DOF), and vice versa, with a method for bump-less transfer in switching transitions. The proposed method is tested using robustness analysis based on frequency domain and time analysis computer simulations based on a nonlinear mathematical model of the F-16 aircraft published by the NASA, from which satisfactory results are obtained.

Investigations on Optimal Pulse Width Modulation to Minimize Total Harmonic Distortion in the Line Current

High-power and high-speed motor drives have only a few switching transitions in each line cycle. Pulse width modulation (PWM) waveforms with positive voltage transition at the positive zero crossing of the fundamental voltage (type-A) are generally considered for PWM waveform with an even number of switching angles per quarter, whereas waveforms with negative voltage transition at the positive zero crossing (type-B) are considered for an odd number of switching angles per quarter. Optimal switching angles to minimize the total harmonic distortion (THD) in motor current are reported for both type-A and type-B waveforms of pulse numbers ( $P$ ) of 5, 7, 9, and 11. Based on simulation and experimental studies on a $3.7$ kW induction motor (IM) drive, optimal type-A and type-B PWM methods are shown to be better than each other in different modulation ranges for each pulse number. The space vector based analysis of optimal type-A and type-B waveforms brings out the optimal vector sequence at any modulation index for a given $P$ . Findings of the space vector based analysis lead to a new approach for determining optimal switching angles with much reduced computational effort. Compared to sine-triangle PWM, deployment of optimal vector sequences in an IM drive, having a maximum switching frequency of 250 Hz, leads to significant reduction in both THD of line current as well as motor losses over a wide range of speeds and load conditions.

A high-efficiency DC-DC converter with LC resonant in the load-side of HFT and voltage doubler for solar PV systems

This paper presents the implementation of a prototype phase-shift soft-switching full-bridge PWM DC-DC power converter isolated by a high-frequency transformer (HFT). This circuit topology is based on a new concept of series resonant principle in the secondary side. The step-up HFT and the voltage doubler rectifier make this circuit suitable for low-voltage renewable sources such as fuel cell or PV applications. Meanwhile, all semiconductor switches can achieve zero-voltage soft-switching (ZVS) with the assistance of transformer leakage inductances and lossless capacitive snubbers. The new contribution of this work is that the passive semiconductor switches (diodes) on the secondary side can also perform ZVS and zero-current switching (ZCS) transitions with the assistance of voltage doubler capacitance. The theory of operation and the experimental setup of the proposed circuit with a rated output of 5 kW are presented and discussed. A comparison between simulation and experimental results is explored and illustrated.

A high-efficiency DC-DC converter with LC resonant in the load-side of HFT and voltage doubler for solar PV systems

This paper presents the implementation of a prototype phase-shift soft-switching full-bridge PWM DC-DC power converter isolated by a high-frequency transformer (HFT). This circuit topology is based on a new concept of series resonant principle in the secondary side. The step-up HFT and the voltage doubler rectifier make this circuit suitable for low-voltage renewable sources such as fuel cell or PV applications. Meanwhile, all semiconductor switches can achieve zero-voltage soft-switching (ZVS) with the assistance of transformer leakage inductances and lossless capacitive snubbers. The new contribution of this work is that the passive semiconductor switches (diodes) on the secondary side can also perform ZVS and zero-current switching (ZCS) transitions with the assistance of voltage doubler capacitance. The theory of operation and the experimental setup of the proposed circuit with a rated output of 5 kW are presented and discussed. A comparison between simulation and experimental results is explored and illustrated.