Switching Transition Research Articles

LV Converters: Improving Efficiency and EMI Using Si MOSFET MMC and Experimentally Exploring Slowed Switching

Widespread adoption of electric vehicles will require ac power distribution systems to accommodate high penetrations of power electronic loads, placing increasing demands on the power quality of grid-connected converters. Recent developments in devices and circuit topologies have the potential to improve the intrinsic power quality of these grid interface inverters, reducing the need for passive filters and associated reactive power consumption. Wide bandgap devices, such as SiC, have recently gained much attention due to their low switching losses facilitating raised pulsewidth modulation frequencies. However, the high cost of SiC together with electromagnetic interference (EMI) resulting from very rapid switching transitions necessary to realize low switching losses cause concern. Previous research in Si MOSFET modular multilevel converters (MMC) suggests a high-efficiency alternative with potential for lower EMI. Si MOSFET MMC benefits are enhanced with parallel-connected devices and slowed switching, made possible by low effective switching frequency. This paper uses experimental results to explore the impact of parallel connection and slowed switching on Si MOSFET MMC losses, and presents improved Si MOSFET switching loss models to resolve inaccuracies observed with conventional Si MOSFET models. EMI is then compared between SiC and Si MMC using carefully controlled relative measurements of radiated EMI.

Highly Optimized Complementary Inverters Based on p-SnO and n-InGaZnO With High Uniformity

Oxide semiconductors are desirable for large-area and/or flexible electronics. Here, we report highly optimized complementary inverters based on n-type indium–gallium–zinc oxide and p-type tin monoxide thin-film transistors. Oxide-based inverters with a record voltage gain of 142 have been achieved. The switching point voltage has also been tuned to reach the ideal value, namely half value of the supply voltage. A narrow transition width of 1.04 V (13% of the supply voltage) is achieved which offers a strong anti-jamming ability to avoid logic errors. Rail-to-rail output voltage swing has been achieved. The inverters still maintain high performance at a low supply voltage of 6 V. A very large number of inverters have been fabricated and showed excellent uniformity in a working area of 1 cm $\times $ 1 cm. The switching point voltage and transition width show very small standard deviations of only 0.55% (0.022 V) and 2.3% (0.024 V), respectively, demonstrating promises for large-scale circuit integration.

Monolithically integrated power circuits in high‐voltage GaN‐on‐Si heterojunction technology

This study presents monolithically integrated power circuits, fabricated in a high-voltage GaN-on-Si heterojunction technology. Different advanced concepts are presented and compared with solutions found in the literature. High switching transition slew rates are demonstrated by means of a monolithic power circuit with integrated gate driver. A highly linear temperature sensor is integrated in a GaN-high-electron-mobility transistor (HEMT) power device for the 600 V class and on-state resistance of 53 mΩ. An area-efficient HEMT structure with integrated freewheeling diodes is presented. This structure is applied in a monolithic multilevel converter chip, as well as in a 600 V class half-bridge chip. The multilevel chip is integrated by an advanced printed circuit board embedding technology and tested in inverter operation with a mains voltage output of 120 V RMS . The performance of the half-bridge is demonstrated in a synchronous buck converter operation from 400 to 200 V and with a switching frequency of 3 MHz.

Hybrid DC Circuit Breaker and Fault Current Limiter With Optional Interruption Capability

Since most of renewable energy resources are dc type, dc microgrids find more attention in deregulated power systems for improvement of reliability and efficiency of the system. In dc microgrids, there is no zero-crossing in current and voltage; so the circuit breaking and fault current limiting are serious concerns. Conventional thyristor-based dc fault current limiters are attractive solutions for tackling this problem. However, they impose permanent interruption on the system in case of temporary fault. In this paper, a novel hybrid circuit breaker (HCB) is proposed to improve power quality of the system by adopting different limiting behaviors for permanent and temporary faults. The proposed HCB transfers load power through a mechanical circuit breaker (MCB) under normal condition. Upon fault occurrence in both sides of the HCB, the fault current is transferred from the MCB to a current limiting path incorporating a zero voltage switching (ZVS) transition mechanism. The HCB limits the fault current for a predefined duration and then interrupts the faulty feeder. In case of temporary fault, the current is returned to the MCB in ZVS. The HCB operation principle is discussed in different operation modes. Capabilities of the proposed HCB are tested and verified by different experiments carried out on a prototype.

(18-Crown-6)K][Fe(1)Cl(1)4 ]0.5 [Fe(2)Cl(2)4 ]0.5 : A Multifunctional Molecular Switch of Dielectric, Conductivity and Magnetic Properties.

Multifunctional materials that exhibit different physical properties in a single phase have potential for use in multifunctional devices. Herein, we reported an organic-inorganic hybrid compound [(18-crown-6)K][Fe(1)Cl(1)4 ]0.5 [Fe(2)Cl(2)4 ]0.5 (1) by incorporating KCl and FeCl3 into a 18-crown-6 molecule, which acts as a host of the six O atoms providing a lone pair of electrons to anchor the guest potassium cation, and [FeCl4 ]- as a counterion for charge balance to construct a complex salt. This salt exhibited a one-step reversible structural transformation giving two separate high and low temperature phases at 373 K, which was confirmed by systematic characterizations including differential scanning calorimetry (DSC) measurements, variable-temperature structural analyses, and dielectric, impedance, variable-temperature magnetic susceptibility measurements. Interestingly, the structural transformation was coupled to both hysteretic dielectric phase transition, conductivity switch and magnetic-phase transition at 373 K. This result gives an idea for designing a new type of phase-transition materials harboring technologically important magnetic, conductivity and dielectric properties.

One current adaptive switching strategy for DC/DC converter with spike limitation

In this study, a new current adaptive switching strategy with the spike limitation applied in DC/DC converter is proposed. With this switching strategy, the switching speed of the power switch can be regulated adaptively with the change of the load. The turn-on/turn-off current is inversely proportional to the load. So, at the light load, the switching speed of the power switch is faster and the switching losses are lower. In addition, all of the control should be based on one principle that the current/voltage spike across power switch under a smaller load cannot exceed that under a rated load. The switching characteristics of power switch with the proposed switching strategy and the relationship between current/voltage spike, turn-on/turn-off current and power loop stray inductance during the switching transition is discussed in this study. Moreover, the drive circuit is designed in detail. Finally, a boost converter prototype with 200 V DC input voltage/380 V output voltage/1 kW output power is established to verify the proposed method. The tested results show that the efficiency of the converter adopted the proposed method rises by 1.5% comparing with that used a conventional switching strategy at the light load.

Analysis and Optimization of Variable-Frequency Soft-Switching Peak Current Mode Control Techniques for Microinverters

This paper presents a detailed power loss model for a microinverter with three different zero voltage switching boundary conduction mode (BCM) current modulation methods. The model is used to calculate the optimum peak current boundaries for each modulation method. Based on the power loss model, a dual-zone modulation method is proposed to further improve the microinverter efficiency. The proposed modulation method provides two main benefits: the addition of one more soft switching transition and low inductor peak current. The additional soft switching transition reduces switching losses by means of zero current switching. The lower peak current boundary reduces inductor rms current and conduction losses as well as allowing the output filter inductor to be smaller and more efficient. An improved BCM peak current control method was proposed and implemented on a microinverter prototype. The control circuit provides a highly accurate representation of the filter inductor current waveform and also provides galvanic isolation that simplifies control circuit design. The experimental results on a 400-W three-phase half-bridge microinverter validate the theoretical analysis of the power loss distribution and demonstrate that further improvement in efficiency can be achieved by using the proposed dual-zone modulation method.

An analysis of the effect of investor sentiment in a heterogeneous switching transition model for G7 stock markets

In line with Chiarella and He (2000) and Boswijk et al. (2007), this study examines the stock market dynamics in a behavioural heterogeneity framework. In particular, we analyse the stock return dynamics in G7 countries over recent decades while considering the effect of heterogeneous investor sentiment. We develop an empirical and nonlinear heterogeneous stock price specification allowing for the presence of two types of investors (arbitrageurs and noise traders) and two regimes. With reference to the heterogeneous smooth transition regression model, we enable the price to switch smoothly between regimes after accounting for an endogenous change in investor sentiment. Our findings do not reject the hypothesis of the nonlinear investor sentiment effect on stock returns. Further, we show that two regimes characterize the stock price dynamics for which the price is closely governed by fundamentals in the first one, while investor sentiment drives the price in the second one. Our model, therefore, captures the main stylized facts observed in the market and shows good in- and out-of-sample forecasting power.

Achieving Efficiencies Exceeding 99% in a Super-Junction 5-kW DC–DC Converter Power Stage Through the Use of an Energy Recovery Snubber and Dead-Time Optimization

A highly efficient 5-kW bidirectional dc–dc converter power stage operating from a 400-V supply implementing super-junction (SJ) metal–oxide–semiconductor field-effect transistor (MOSFETs) is presented. SJ MOSFETs have low on-state resistances and low switching losses. However, their application in voltage-source converters can be compromised by the reverse recovery behavior of their intrinsic diodes and their highly nonlinear output capacitances. A series switching-aid circuit is used to control the output capacitance charging current. The dead times between switching transitions are assessed and optimized in order to deactivate the intrinsic diodes. The combination of these techniques enables very high efficiencies to be attained. Calorimetric measurements indicate a full-load efficiency of 99.1% for the prototype 5-kW dc–dc converter power stage. A loss reduction of approximately 50% is achieved with the prototype converter power stage when compared to an equivalent insulated-gate bipolar transistor (IGBT)-based power stage. Lastly, a loss versus duty cycle function is experimentally determined, which can be used to inform the design of a maximum efficiency point tracking system.

Characterizing the Switching Transitions of an Adsorbed Peptide by Mapping the Potential Energy Surface.

Peptide adsorption occurs across technology, medicine, and nature. The functions of adsorbed peptides are related to their conformation. In the past, molecular simulation methods such as molecular dynamics have been used to determine key conformations of adsorbed peptides. However, the transitions between these conformations often occur too slowly to be modeled reliably by such methods. This means such transitions are less well understood. In the study reported here, discrete path sampling is used for the first time to study the potential energy surface of an adsorbed peptide (polyalanine) and the transition pathways between various stable adsorbed conformations that have been identified in prior work by two of the authors [ Mijajlovic , M. ; Biggs , M. J. J. Phys. Chem. C 2007 , 111 , 15839 - 15847 ]. Mechanisms for the switching of adsorbed polyalanine between the stable conformations are elucidated along with the energetics of these switches.

Combining Sharp and Smooth Transitions in Volatility Dynamics: A Fuzzy Regime Approach

SummaryVolatility in financial markets is characterized by alternating persistent turmoil and quiet periods, but also by a slowly varying average level. This slow moving component keeps open the question of whether some of its features are better represented as abrupt or smooth changes between local averages of volatility. We provide a new class of models with a set of parameters subject to abrupt changes in regime (Markov switching) and another set subject to smooth transition changes. These models capture the possibility that regimes may overlap with one another (fuzzy). The empirical application is carried out on the volatility of four US indices. It shows that the flexibility of the new model enables a better overall performance over either Markov switching or smooth transitions and provides a local average volatility measure as a parametric estimation of the low frequency component.

Analog Synaptic Behavior of a Silicon Nitride Memristor.

In this paper, we present a synapse function using analog resistive-switching behaviors in a SiNx-based memristor with a complementary metal-oxide-semiconductor compatibility and expandability to three-dimensional crossbar array architecture. A progressive conductance change is attainable as a result of the gradual growth and dissolution of the conducting path, and the series resistance of the AlOy layer in the Ni/SiNx/AlOy/TiN memristor device enhances analog switching performance by reducing current overshoot. A continuous and smooth gradual reset switching transition can be observed with a compliance current limit (>100 μA), and is highly suitable for demonstrating synaptic characteristics. Long-term potentiation and long-term depression are obtained by means of identical pulse responses. Moreover, symmetric and linear synaptic behaviors are significantly improved by optimizing pulse response conditions, which is verified by a neural network simulation. Finally, we display the spike-timing-dependent plasticity with the multipulse scheme. This work provides a possible way to mimic biological synapse function for energy-efficient neuromorphic systems by using a conventional passive SiNx layer as an active dielectric.

A 50-kW High-Frequency and High-Efficiency SiC Voltage Source Inverter for More Electric Aircraft

High power density is required for power converter in more electric aircraft due to the strict demands of volume and weight, which makes silicon carbide (SiC) extremely attractive for this application. In this paper, a prototype of 50-kW SiC two-level three-phase voltage source inverter is demonstrated with a gravimetric power density of 26 kW/kg (without inclusion of filter). A gate assisted circuit is introduced to reduce the switching loss. In addition, the ringings of voltage and current due to parasitic parameters during the switching transition can also be mitigated. A mathematical model with consideration of various parasitic parameters is developed, which illustrates the parasitic effects in high-speed switching SiC power module. The converter is operated at a switching frequency up to 100 kHz and a narrow dead band of 250 ns. The measured efficiency is 97.91%.

Rotational Magnetization Lag-Angle Plots Using the Anisotropic Stoner–Wohlfarth Model

A numerical implementation of the classical Stoner-Wohlfarth (SW) model to simulate the magnetization angle of an assembly of SW particles with an effective axis of anisotropy under a rotating applied field is presented. Using an angular distribution for the angle each SW particle is making with the medium's reference axis, the proposed model successfully simulated lag-angle plots exhibiting the same rotational magnetization behavior measured for different ellipsoidally magnetizable media in the literature. The developed algorithm provides a simple tool for rotational-energy-loss calculations, preserves the physical intuition of the classical SW model, and is computationally faster compared to the Preisach-Stoner-Wohlfarth models. The effect of the angular distribution parameters on the switching transition angle and the algorithm's potential for modeling additional anisotropies through using different angular distributions are discussed.

Digital to analog resistive switching transition induced by graphene buffer layer in strontium titanate based devices

Resistive switching behaviour can be classified into digital and analog switching based on its abrupt and gradual resistance change characteristics. Realizing the transition from digital to analog switching in the same device is essential for understanding and controlling the performance of the devices with various switching mechanisms. Here, we investigate the resistive switching in a device made with strontium titanate (SrTiO3) nanoparticles using X-ray diffractometry, scanning electron microscopy, Raman spectroscopy, and direct electrical measurements. It is found that the well-known rupture/formation of Ag filaments is responsible for the digital switching in the device with Ag as the top electrode. To modulate the switching performance, we insert a reduced graphene oxide layer between SrTiO3 and the bottom FTO electrode owing to its good barrier property for the diffusion of Ag ions and high out-of-plane resistance. In this case, resistive switching is changed from digital to analog as determined by the modulation of interfacial resistance under applied voltage. Based on that controllable resistance, potentiation and depression behaviours are implemented as well. This study opens up new ways for the design of multifunctional devices which are promising for memory and neuromorphic computing applications.

Exponential stability and [formula omitted]-gain analysis for positive time-delay Markovian jump systems with switching transition rates subject to average dwell time

The paper deals with the problems of exponential stability and L1-gain analysis for positive time-delay Markovian jump systems (MJSs) with switching transition rates. Another set of useful regime-switching model is given, which extends fixed transition rates to time-varying transition rates. By resorting to the linear co-positive Lyapunov function and average dwell time, sufficient conditions for exponential stability are proposed in terms of standard linear programming. Based on the obtained results, L1-gain performance is analyzed. Finally, an example is proposed to illustrate the validity of the main results.

A Compact Gate Control and Voltage-Balancing Circuit for Series-Connected SiC MOSFETs and Its Application in a DC Breaker

This paper presents a novel compact circuit combining function of gate control and voltage balancing for series-connected silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET). Two series-connected SiC MOSFETs with the proposed circuit only require a single standard gate driver to achieve the gate control and voltage balancing during both steady-state and switching transition. Moreover, the proposed circuit is only composed of ten passive components. Therefore, the proposed circuit provides a low-cost and highly reliable method to increase the blocking voltage of the SiC MOSFET. The operation principles of the proposed circuit are theoretically analyzed. In addition, the high-blocking-voltage device is not only required in switching-mode power supply (SMPS) but also in dc-breaker applications. The proposed circuit is then modified to make it suitable to the dc-breaker applications. The simulation and experimental results validate the effectiveness and superiority of the proposed circuit in both SMPS and dc-breaker applications.

Improve Control to Output Dynamic Response and Extend Modulation Index Range With Hybrid Selective Harmonic Current Mitigation-PWM and Phase-Shift PWM for Four-Quadrant Cascaded H-Bridge Converters

The selective harmonic current mitigation pulsewidth modulation (SHCM-PWM) technique can be used in cascaded multilevel converters to extend the harmonic reduction spectrum, reduce the coupling inductance and increase the efficiency. The offline SHCM-PWM technique has small number of switching transitions as its switching angles can only change once in a fundamental cycle and relatively long time delays because it uses FFT. As a result, its dynamic response has a lot to desire. As it will be proven in this paper, in four-quadrant power converters, to have a good transient dynamic response, both active and reactive power must be controlled at least two times in a fundamental cycle. In this paper, a hybrid modulation technique is introduced. The proposed technique uses SHCM-PWM under steady state and phase-shift PWM (PSPWM) under transient. In addition, in order to extend the modulation index range and ensure that SHCM-PWM can process four-quadrant active and reactive power, the constraints of the switching angles for the SHCM-PWM are modified. Simulations and experiments are conducted on a seven-level cascaded H-bridge converter to verify the proposed technique.

A tuning-less model predictive control for modular multilevel converter capable of unbalanced grid fault

This paper focuses on a tuning-less model predictive control (MPC) strategy with unbalanced fault-ride-through capability for a three-phase modular multilevel converter (MMC). Three individual control stages are designed to cater for the multiple control objectives in MMC without the need for any weighting factor tuning. A conceptually simple power regulation approach which requires neither synchronous coordinate transformation nor grid-voltage phase angle detection is introduced into the proposed MPC. Meanwhile, two alternatives are proposed to the power regulation stage to adapt to the special needs under unbalanced grid fault. Neither of the alternatives involves any tuning work. In addition, a modified sorting algorithm is presented to resolve the problem of unnecessary switching transitions, which is inherent in conventional sorting algorithm. The proposed tuning-less MPC is capable of direct active and reactive power control, circulating current minimization, submodule capacitor voltage balancing, switching frequency reduction, and great resilience under balanced and unbalanced grid conditions. The presented simulation results confirm the effectiveness and feasibility of the proposed control method.

Resistive Random Access Memory Cells with a Bilayer TiO2/SiOX Insulating Stack for Simultaneous Filamentary and Distributed Resistive Switching

In order to fulfill the information storage needs of modern societies, the performance of electronic nonvolatile memories (NVMs) should be continuously improved. In the past few years, resistive random access memories (RRAM) have raised as one of the most promising technologies for future information storage due to their excellent performance and easy fabrication. In this work, a novel strategy is presented to further extend the performance of RRAMs. By using only cheap and industry friendly materials (Ti, TiO2, SiOX, and n++Si), memory cells are developed that show both filamentary and distributed resistive switching simultaneously (i.e., in the same I–V curve). The devices exhibit unprecedented hysteretic I–V characteristics, high current on/off ratios up to ≈5 orders of magnitude, ultra low currents in high resistive state and low resistive state (100 pA and 125 nA at –0.1 V, respectively), sharp switching transitions, good cycle‐to‐cycle endurance (>1000 cycles), and low device‐to‐device variability. We are not aware of any other resistive switching memory exhibiting such characteristics, which may open the door for the development of advanced NVMs combining the advantages of filamentary and distributed resistive switching mechanisms.