Switching Transition Research Articles

Impact of $RC$ Snubber on Switching Oscillation Damping of SiC MOSFET With Analytical Model

As the most popular wide bandgap (WBG) power device, the silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET) has been widely adopted in the power electronics applications and brings in the benefits, including reduced switching losses, enhanced switching frequency, and improved power density. However, the switching oscillation and the electromagnetic interference (EMI) become more serious due to the rapid switching speed of SiC MOSFET. Thus, adding $RC$ snubber branch is considered as an effective method to suppress such unwanted oscillation in the early works. In this article, the switching transient of SiC MOSFET with $RC$ snubber is investigated with an analytical model based on the finite-state machine (FSM). The accuracy of the proposed analytical model can be verified by comparisons between the calculated and measured waveforms during the switching transition. In addition, the impacts of the $RC$ snubber on switching oscillation, switching loss, and high-frequency (HF) EMI noise have been comprehensively investigated based on the model, which shows that the added $RC$ snubber can effectively avoid the switching oscillation and reduce the level of HF EMI without increasing switching loss.

An Adaptive Multistep Balancing Modulation Technique for Multipoint-Clamped Converters

In this article, a new pulsewidth modulation technique is proposed for the output voltage control and the dc-bus capacitors voltage balancing of a multipoint-clamped multilevel converter. The voltage equalization is achieved by allowing each converter's leg voltage to switch through multiple levels in a single modulation period (multistep operation). The approach is generalized with respect to the number of levels and phases and can be applied regardless of the converter operating conditions. Nevertheless, the multistep behavior generally leads to an increase of the average switching transitions rate. In the proposed method, this drawback is mitigated with an online adaptive selection of the number of switching levels. The algorithm is validated through an extensive hardware-in-the-loop testing and compared to other approaches.

Current-driven magnetization switching and dynamic spin reorientation transition in magnetic tunnel junctions

We present theoretical results on electrically induced magnetization dynamics in CoFeB/MgO/CoFeB tunnel junctions connected to a constant-current source. Our calculations take into account both the spin-transfer torque (STT) created by a spin-polarized current and a voltage-controlled magnetic anisotropy (VCMA) associated with the CoFeB|MgO interface. It is shown that the current-driven spin dynamics in an ultrathin free layer of such junction is not limited by the magnetization precession and switching, but also can have the form of a dynamic spin reorientation transition, which is caused by the combined action of STT and VCMA and gives rise to a steady precessional state. Critical current densities necessary for the appearance of different types of magnetic dynamics are calculated as functions of the free-layer thickness and in-plane aspect ratio. The spin current pumped into a normal-metal overlayer by the tunnel junction with the precessing magnetization is also evaluated.

Model Predictive Control Based on Optimized Pulse Patterns for Modular Multilevel Converter STATCOM

This article considers a medium-voltage static synchronous compensator (STATCOM) that is based on a delta-connected modular multilevel converter (MMC) and operates at switching frequencies of 150 Hz or less. Offline computed optimal pulse patterns (OPPs) facilitate the shaping of the grid current spectrum at such low switching frequencies. However, STATCOM applications require the injection of harmonics and negative-sequence currents, as well as fast power transients. In order to achieve this, a model predictive controller is designed, which modifies the switching transitions of the OPPs, inserts additional pulses if required, and controls the circulating current in the delta-connected MMC.

Film-Nanostructure-Controlled Inerasable-to-Erasable Switching Transition in ZnO-Based Transparent Memristor Devices: Sputtering-Pressure Dependency

We found that the write-once-read-many-times (WORM, inerasable)-to-rewritable (erasable) transition phenomenon results from the different structures of the filament, which is determined by the grain orientations of the deposited films. The conduction mechanism of this switching transition and its impact on the synaptic behavior in various ZnO nanostructures are also discussed. Furthermore, our WORM devices have a programmable physical damage function that can be exploited for use in security systems against data theft, hacking, and unauthorized use of software/hardware. This work proposes ZnO-based nonvolatile memory for invisible electronic applications and gives valuable insight into the design of WORM and rewritable memories.

Nanoseconds Switching Time Monitoring of Insulated Gate Bipolar Transistor Module by Under-Sampling Reconstruction of High-Speed Switching Transitions Signal

An insulated gate bipolar transistor (IGBT) is one of the most reliable critical components in power electronics systems (PESs). The switching time during IGBT turn-on/off transitions is a good health status indicator for IGBT. However, online monitoring of IGBT switching time is still difficult in practice due to the requirement of extremely high sampling rate for nanoseconds time resolution. The compressed sensing (CS) method shows a potential to overcome the technical difficult by reducing the sampling rate. To further improve the efficiency and reduce the computational time for IGBT online condition monitoring (CM), an under-sampling reconstruction method of an IGBT high-speed switching signal is presented in this paper. First, the physical mechanism and signal characteristics of IGBT switching transitions are analyzed. Then, by utilizing the sparse characteristics of IGBT switching signal in the wavelet domain, the wavelet basis is used for sparse representation. The stagewise orthogonal matching pursuit (StOMP) algorithm is proposed to enhance the convergence speed for switching signal reconstruction. Experiments are performed on not only a double-pulse test rig but also a real Pulse-Width Modulation (PWM) converter. Results show that the IGBT high-speed switching transitions signal can be accurately recovered with a reduced sampling rate and the nanoseconds switching time change can be monitored for IGBT CM.

Switching Loss Balancing Technique for Modular Multilevel Converters Operated by Model Predictive Control Method

The sorting algorithm is the most widely accepted capacitor voltage balancing strategy for a modular multilevel converter. This strategy offers to keep the balance among submodule capacitor voltages under all of the modular multilevel converter working conditions. However, this method generates unnecessary switching transitions in submodules, which results in high switching frequency and switching loss, and uneven distribution of switching transitions and switching loss among submodules (SMs). In this paper, a simplified switching loss balancing control strategy was proposed in order to handle these issues. The proposed approach adjusted the submodule selection process of the sorting algorithm by taking into consideration the number of switching transitions in addition to the capacitor voltages. Even distribution of switching transitions and switching loss was achieved, and the average switching loss was reduced at the cost of slightly increasing the capacitor voltage fluctuations. The effectiveness of the proposed approach was verified through both simulation and experimental results.

Structural changes during the switching transition of chalcogenide selector devices

Ovonic threshold switches are a favored choice for chalcogenide-based amorphous (a-) GeSex selector devices used in cross-point arrays of nonvolatile memories. Previous models of their nonlinear high-field conduction proposed a largely electronic-only switching mechanism, within a fixed density of electronic states. Here, we use a density functional molecular-dynamics supercell calculation to show that the high-current excited state configuration of a-GeSex has structural changes such as additional Ge-Ge bonds and overcoordinated Ge sites, giving lower effective mass, more delocalized conduction states, and a lower ON resistance.

A Physics-Based Compact Model of Stochastic Switching in Spin-Transfer Torque Magnetic Memory

Spin-transfer torque random-access memory (STT-RAM) is gaining momentum as a promising technology for high-density and embedded nonvolatile memory. Owing to random thermal fluctuations, switching transitions generally display statistical variations from cycle to cycle. Stochastic variations are critical to the hindering of memory and computing applications of STT-RAM. To enable the design of STT-RAM circuits for memory and computing, there is a need for accurate compact models capable of predicting the stochastic behavior. Here, we present a detailed model accounting for the anomalous thermal regime of switching deviating from the Neel–Brown thermal model below 200 ns. Anomalous switching is explained by the nonlinear lowering of the energy barrier associated with the perpendicular magnetic anisotropy (PMA). The model is extensively verified against the write-error-rate (WER) data as a function of applied voltage and pulsewidth and experimental switching time-delay distributions.

Event Driven Control of Voltage and Current Gradients of Medium Voltage IGBTs

Medium voltage insulated gate bipolar transistors are fast switching devices that require low gate drive power. They inherently generate high voltage and current gradients during switching transitions. These are generally limited by retarding the changes of the gate charge. Additional gate resistors are usually installed for this purpose. The drawback is high switching losses. A novel method is described in this article that aims at controlling the voltage and current gradients during switching transitions. The gate charge of the input MOS device is controlled by injected gate currents. These follow particular command functions that are predefined and stored in a memory. The method requires reacting within microseconds, which traditional closed-loop control cannot do. Specific time events are therefore defined to trigger the respective command function. These functions depend on the instantaneous values of the collector current or the collector–emitter voltage, variables that are identified without delay, knowing their predefined gradients and counting the time from the respective event to reach their final values. Experimental results show the performance of event driven control. Low current and voltage gradients are enforced while the switching losses are reduced.

Common mode voltage suppression in three‐phase voltage source inverters with dynamic load

This study proposes a novel pulse width modulation (PWM) algorithm to mitigate the common mode voltage (CMV) in a multi-level voltage source inverter feeding an electric machine. Dead-time effect frequently prevents the CMV not to reach zero in several switching periods. Then the electromagnetic interference noise is generated and causes bearing failure and overvoltage stress on winding insulations. The proposed strategy compensates the dead-time effect that alleviates the high-amplitude rectangular pulses with extreme range of variations during high-frequency switching transitions. The existing PWM methods reduce the CMV to ±V dc /6, however by utilising the presented approach, CMV can be reduced to zero. However, the total harmonic distortion will be increased 0.3% at fundamental current harmonic rather than conventional state PWM method, which could be neglected. Simulation results and efficiency analysis imply on worthy performance of the proposed strategy to eliminate the CMV.

A Simplified 3-D NLM-Based SVPWM Technique With Voltage-Balancing Capability for 3LNPC Cascaded Multilevel Converter

The nearest level modulation (NLM)-based space vector pulsewidth modulation (SVPWM) algorithms have attracted a great deal of interest since they can provide various degrees of freedom, i.e., optimized switching sequences and adjustable duty cycles. This article proposes a simplified three-dimensional (3-D) NLM-based SVPWM algorithm in a 3-D coordinate system. Compared with the generalized two-dimensional (2-D) NLM-based SVPWM schemes, the proposed method not only provides identical degrees of freedom to optimize switching patterns and obtain adjustable duty cycles, but also presents better digital implementation and lower hardware occupancy to achieve the real-time PWM generation. In addition, based on the NLM-based principle, a method of addressing the issue of unbalanced voltages in a three-phase 3-level neutral point clamped cascaded multilevel converter (3LNPC-CMC) is introduced. The presented method possesses the optimized voltage-balancing capacity and equalizes the unbalanced inner cell and mutual cell voltages in the 3LNPC-CMC with minimum number switching transition. Finally, the whole proposed process is verified by simulation and experimental results.

Analytical Modeling of the Silicon Carbide (SiC) MOSFET during Switching Transition for EMI Investigation

Analytical Modeling of the Silicon Carbide (SiC) MOSFET during Switching Transition for EMI Investigation

Spin switching in single crystal PrFeO3 and spin configuration diagram of rare earth orthoferrites

We report the low field spin switching and spin reorientation transition in rare earth orthoferrite PrFeO3 single crystal grown by optical floating zone method. Applied magnetic fields can regulate the spin switching in a quite wide range of temperatures. The effective magnetic moments of Fe3+ and Pr3+ sublattices undergo parallel to antiparallel configurations in field-cooled-cooling processes, which produce an abrupt drop in magnetization at low temperatures. The reverse spin switching show a magnetization recovering jump at a rather higher temperature in the field-cooled-warming regime, even above 300 K under very low fields. These intriguing magnetic phase transitions are due to the intrinsic 3d-4f electron interactions between Fe3+ and R3+ sublattices, which dominate the interesting magnetic behaviors in RFeO3. In particular, PrFeO3 shows a great sensitivity to weak field even at room temperature, which makes it a controllable candidate for potential application in spintronic devices by using very low field. Finally, we summarize the spin configuration diagram of the RFeO3 family.

An Improved Low-Power Coding for Serial Network-On-Chip Links

In the fast nanosilicon revolution era, network-on-chip (NoC) architecture offers a significant research solution to on-chip multiprocessor-based real-time applications. As the number of cores increases, power consumption of the resources of NoC also increases. Links are the major power dissipator in NoC architecture owing to switching activity of data bits communicated through them. The performance of data communication links in NoC is strongly dependent on the factor of power dissipation. An efficient coding method is needed to reduce both coupling and self-switching activity of data bits of NoC links. In this work, an improved low-power encoding algorithm for serial links is proposed to reduce switching transition for any random data pattern making them more suited to real-time applications. The proposed encoding algorithm is coded, simulated and verified its area and power performance using Synopsys tools utilizing UMC 90 nm technology. Experimental results have shown that it provides on average 48.83% of switching activity reduction for any real-time applications.

Towards general network architecture design criteria for negative gas adsorption transitions in ultraporous frameworks

Switchable metal-organic frameworks (MOFs) have been proposed for various energy-related storage and separation applications, but the mechanistic understanding of adsorption-induced switching transitions is still at an early stage. Here we report critical design criteria for negative gas adsorption (NGA), a counterintuitive feature of pressure amplifying materials, hitherto uniquely observed in a highly porous framework compound (DUT-49). These criteria are derived by analysing the physical effects of micromechanics, pore size, interpenetration, adsorption enthalpies, and the pore filling mechanism using advanced in situ X-ray and neutron diffraction, NMR spectroscopy, and calorimetric techniques parallelised to adsorption for a series of six isoreticular networks. Aided by computational modelling, we identify DUT-50 as a new pressure amplifying material featuring distinct NGA transitions upon methane and argon adsorption. In situ neutron diffraction analysis of the methane (CD4) adsorption sites at 111 K supported by grand canonical Monte Carlo simulations reveals a sudden population of the largest mesopore to be the critical filling step initiating structural contraction and NGA. In contrast, interpenetration leads to framework stiffening and specific pore volume reduction, both factors effectively suppressing NGA transitions.

Enhanced Scan Segmentation for Low Power DFT

Excessive test power dissipation during scan testing of an SOC may cause reliability and yield concerns for the circuit under test (CUT). We propose an enhanced scan segmentation method using logic cluster controllability (LoCCo) technique for scan chain stitching to reduce test power efficiently. After LoCCo based scan stitching, since the trailing edge of scan chains contain very less switching transitions, we optimize the number of segments needed. This enables segmentation hardware reduction and still achieve lower power scan test compared to conventional method. Test cases prepared from ITC’99 standard circuits and industrial designs in 40nm CMOS and 28FDSOI technology were used for comparison. LoCCo based scan segmentation gave a shift power reduction of up-to 21.7% over conventional scan segmentation. Up-to 8.6%, shift power gain was observed even with 25% reduced segmentation when enhanced scan segmentation technique is used.

'Mini-interval gait' switching: understanding the positive implications of a novel training regime.

The neuromechanical reorganization required to change gaits imposes an energetic cost 75% greater than either a walking or running step at the same speed. By combining walking and running with the requisite gait switching transition steps, an exercise protocol can be generated with virtually any desired metabolic output even at relatively slow treadmill speed. Gait switching increases metabolic demand through discrete events, which can be tolerated more easily by individuals recovering from health problems, just as interval training allows greater work production for healthy individuals. In addition to cardio-respiratory benefits, ‘mini-intervals’ with frequent gait switching also provides positive effects and attributes such as distributing muscle group activation, re-training neural coordination, and avoiding repetitive joint overloading. It has the added benefit of developing stability during transitions while a safety hand rail is present which can lead to greater stability in more complex natural environments. Finally, increased mental focus may help avoid the monotony of usual treadmill workouts, aiding adherence to an exercise program. We review evidence for the cost increase of the gait transition step and explain the mechanisms involved. We also discuss literature supporting the range of benefits for mini-interval gait switching as a training and rehabilitation tool.

An Accurate Calorimetric Loss Measurement Method for SiC MOSFETs

An accurate measurement of conduction and switching losses in the power semiconductor devices is necessary in order to design and evaluate the thermal management system of modern converter systems. Conventionally, electrical measurement methods, such as the double-pulse tests (DPTs), are used for measuring the switching losses. However, with the advent of wide-bandgap (WBG) devices that have fast switching transients, it is rather difficult to capture the waveforms accurately during switching transitions, and consequently, the measurement of switching loss becomes inaccurate. In addition, the measurement of switching waveforms depends on the voltage and current probes, as well as the oscilloscope used for the measurement, which makes this method prone to errors. This necessitates the use of measurement methods, which can provide much higher accuracy than the existing conventional electrical methods. Calorimetric methods are based on comparatively slow temperature measurements and do not rely on the measurements of fast switching transitions of voltages and currents, thus eliminating the demand for measuring fast switching transitions. This paper presents an accurate calorimetric method for measuring the device losses, which can be used to determine individual loss components accurately (conduction, turn-on, and turn-off losses). In addition to the turn-on and turn-off losses, this method can evaluate the charging and discharging losses of the device. The novelty of the method lies in the fact that a single setup can be used to measure all possible losses that can occur in a device during converter operation. The calorimetric test setup is described, and a novel modulation scheme is introduced, which enables the segregation of the individual losses. The experimental test setup is built and the method is verified by measuring the losses of a 900-V, 23-A Wolfspeed C3M0120090D SiC MOSFET.

Hard-Switching 650-V GaN HEMTs in an 800-V DC-Grid System With No-Diode-Clamping Active-Balancing Three-Level Topology

For any voltage above 600-V dc, it is usually recommended to use 900–1200-V SiC MOSFETs instead of GaN high-electron-mobility transistors (HEMTs), given presently commercial GaN HEMTs have the maximum voltage rating up to 650 V. This paper is an attempt of employing 650-V E-mode GaN HEMTs to build a three-level bidirectional dc/dc converter, with the input as an 800-V battery, the output as the ~400-V dc grid, and half of the switches working at the hard-switching mode. The active-balancing control instead of using clamping diodes in the conventional neutral-point clamping topology is adopted, aiming at higher efficiency. Simulation based on the double-pulse test results shows that such a design strategy with GaN has a better efficiency over the conventional 1200-V SiC MOSFET-based buck/boost converter. Two bottom-cooled GaN HEMTs are in parallel to enhance the power capability and efficiency, which require the special focus on the parasitic parameters. The effects of parasitics, especially the stray inductance in the current commutating loop and the gate drive loop during switching transitions, have been comprehensively analyzed in this paper. Experimental results under 800-V bus voltage are presented to verify the proposed solution.