Switching Interval Research Articles

Coded Switching Scheme for Monitoring the Operation of Distribution Capacitors

A novel scheme is proposed to monitor the operation of capacitors scattered in MV distribution systems. It first codes each capacitor with a distinctive switching character by setting a unique combination of a three-phase switching order and time interval. As a result, the transient of the three-phase reactive power during capacitor switching will appear in a unique way. Then, the reactive power disturbances monitored in the substation are decoded to identify which capacitor is being switched on and off . A detailed decoding method is developed to realize this identification without being impacted by the switching interference of loads and other reactive power compensation devices. Moreover, the implementation of the proposed scheme in the field is elaborated, and the resultant three-phase voltage unbalance is analyzed in this paper. Compared with existing methods, this scheme only requires one power quality monitor located at the substation to monitor the operations (energizing or de-energizing) of downstream distribution capacitors without extra communication devices. The operation information is valuable for tackling power quality problems caused by capacitor switching and optimizing the distribution grid operation.

Finite-time annular domain stability of Itô stochastic impulsive systems with markovian jumping under asynchronous switching

ABSTRACT This study examines the finite time annular domain stability (FTADS) and stabilisation of a class of Itô stochastic impulsive systems with asynchronous switching controller. The asynchronous switching means that the controller switching does not accurately coincide with system switching in delayed time interval. The design of the controller depends on the observed jumping parameters, which cannot be precisely measured in real-time because of switching delay. Our results apply to cases where some subsystems of the switched systems are not necessarily stable under the influence of input delay. When the subsystem is stable in the synchronous switching interval and unstable in the asynchronous case, a compromise among the average impulsive interval, the upper bound of delay, and the decay/increasing rate of Lyapunov function in the synchronous/asynchronous switching interval respectively is given. By the mode-dependent parameter approach (MDPA) and allowing the increase of the impulses on all the switching times, the extended FTADS criteria for Itô stochastic impulsive systems in generally nonlinear setting are derived first. Then, we focus on the case when the system in both synchronous and asynchronous switching intervals are unstable. By reaching a tradeoff among average impulsive interval, the upper bound of delay, the magnitude of impulses and the difference between the increasing rate of Lyapunov function in the synchronous and asynchronous switching interval, new sufficient conditions for existence of the state feedback controller are also developed by MDPA. In addition, we consider the effect of different impulsive strengths (harmful and beneficial impulses) and obtained less conservative results because the Lyapunov function may be non-decreasing during switching interval. Moreover, we extend the conclusion from nonlinear stochastic impulsive switching systems to linear case. Finally, we present two examples to illustrate the effectiveness of the results obtained in this study.

Asynchronous Switching Control for Continuous-time Switched Linear Systems with Output-feedback

This paper investigates the asynchronous switching control problem for continuous-time switched linear systems via dynamic output-feedback, where the dynamic output-feedback controller contains an impulsive reset law to reset the controller state. A time-varying multiple Lyapunov-like-function (MLF) approach is employed to analyze the stability and weighted L2-gain of the closed-loop systems. The switching stability criteria for the closed-loop systems are established in terms of linear matrix inequalities (LMIs), which are dependent on the upper and lower bounds of the switching interval and the asynchronous delays. The switching logic is designed to guarantee the closed-loop systems achieving the weighted L2-gain performance. Two numerical examples are provided to show the effectiveness of the proposed method.

Improved quasi-synchronization criteria for delayed fractional-order memristor-based neural networks via linear feedback control

Abstract This paper is concerned with the quasi-synchronization of two delayed fractional-order memristor-based neural networks (FMNNs) with mismatched switching jumps via linear feedback control. The concept of asynchronous switching time interval (ASTI) is introduced first to describe when the drive-response FMNNs update their connection weights asynchronously. Under the framework of fractional-order differential inclusions, two improved quasi-synchronization criteria, expressed by algebraic conditions and LMIs conditions respectively, are established by constructing appropriate Lyapunov functionals in combination with some fractional-order differential inequalities. Different from most previously published works, the synchronization error bound can be estimated without requiring the bound of chaotic trajectories. In addition, it has been shown that the degree of mismatch between the switching jumps has an important influence on the distribution of ASTI as well as the practical synchronization error. Finally, two numerical examples are given to verify the validity and feasibility of the obtained results.

Dynamic model development and control for multiple‐output flyback converters in DCM and CCM

SummaryMultiple‐output flyback converters are widely used in switching power supplies due to their low component count and cost‐effective structure. The main problem of this structure is how to balance output voltages in different load conditions. This paper proposes a new approach for single‐input multiple‐output flyback converters operating in DCM and CCM by a small‐signal averaged model. The averaged model is derived by presenting the piecewise‐linear waveform for the inductor currents inside the converter. In DCM, the magnetizing current and currents through the output windings reach zero when the switch is turned off. In CCM, the magnetizing current of the converter is continuous over a switching interval and this possibility exists that only some of the output diodes completely conduct when the switch is off. The proposed model of the converter can be used in a wide range of operations within identical and non‐identical loading conditions. Using a laboratory prototype, several case studies and input‐to‐output transfer functions are considered to verify the proposed model. The controller design is performed for the both CCM and DCM, and then dynamic characteristics of the overall system are evaluated.

Synchronization Thresholds in an Ensemble of Kuramoto Phase Oscillators with Randomly Blinking Couplings

We consider a network of Kuramoto phase oscillators with randomly blinking couplings. Applicability of the averaging method for small switching intervals is rigorously substantiated. Using this method, we analytically estimate the threshold coupling force for synchronizing the ensemble oscillators. The threshold synchronization is studied as a function of the switching interval for various network sizes. The effect of preserving synchronization for a significant increase in the switching interval is found, which is the key feature of the system since a slight increase in this interval usually leads to the synchronization failure. The intermittent-synchronization possibility for small network sizes and large switching intervals is shown. An increase in the network size is shown to result in a stability increase due to the decreasing probability of appearance of uncoupled configurations. The regions corresponding to the global synchronization of oscillators are singled out in the system-parameter space.

Vector Lyapunov Function based Input-to-State Stability of Stochastic Impulsive Switched Time-Delay Systems

In this paper, the input-to-state stability is studied for stochastic impulsive switched time-delay systems. Using the vector Lyapunov function, average dwell time, and the properties of $M$ -matrix, different types of sufficient conditions are established. Both the case that the continuous dynamics is stable and the case that the discrete dynamics is stable are addressed, and the stability conditions are obtained. In the obtained stability conditions, different components of the vector Lyapunov function are allowed to be coupled; the information in consecutive impulsive switching intervals is also allowed to be coupled. Therefore, the magnification on the corresponding coupling items is avoided and the obtained results are more general and less conservative than the existing results. Furthermore, we investigate the relationships among the vector Lyapunov function approach, the approach based on the comparison principle and the scalar Lyapunov function approach. According to the vector Lyapunov function, the comparison system is constructed and the scalar-Lyapunov-function-based stability conditions are established. Finally, the applicability of our results is illustrated through two examples from neural systems and the synchronization problem of chaos-based secure communication systems.

Sea-level changes vs. organic productivity as controls on Early and Middle Devonian bioevents: Facies- and gamma-ray based sequence-stratigraphic correlation of the Prague Basin, Czech Republic

Abstract The Devonian marine stratigraphic record is characterized by a number of bioevents – overturns in pelagic and benthic faunal assemblages, which are associated with distinct changes in lithology. The coincidence of lithologic and biotic changes can be explained by the causal link between biotic evolution, carbonate production and relative sea-level changes. To gain insight into the sea-level history of Early and Middle Devonian bioevents (the Lochkovian/Pragian Event, Basal Zlichovian E., Daleje E., and Chotec E.) we carried out a sequence-stratigraphic analysis of carbonate-dominated successions in the Prague Basin (peri-Gondwana), a classic area of Devonian bioevents. The study is based on a basin-wide correlation of facies and field gamma-ray spectrometry (GRS) logs from 18 sections (Lochkovian to Eifelian), supported by element geochemistry and published biostratigraphic and carbon isotope data. Devonian carbonate deposition in the Prague Basin alternated between two end-member modes: an oligotrophic, homoclinal ramp (Praha and Daleje-Třebotov Formations) and a mesotrophic, distally steepened ramp (Lochkov, Zlichov, and Chotec Formations). They show contrasting facies, particularly the absence/presence of gravity-flow deposits, allochem composition, U/Th ratios, and geochemical composition (productivity proxies such as P/Al, Si/Al, Zn/Al, TOC and stable carbon isotopes). The mesotrophic systems reflect an increased availability of nutrients on the shelf during the late Lochkovian, early Emsian (Zlichovian), and Eifelian periods when sea surface temperature, pCO2, and silicate weathering rates were higher. The oligotrophic systems deposited during the Pragian–to-earliest Emsian and late Emsian (Dalejan) periods reflect reversed palaeoclimatic trends. We identified three depositional sequences (DS), DS1 (base of Pragian to early Emsian); DS2 (early Emsian to mid Emsian); and DS3 (mid Emsian to mid Eifelian). These sequences were integrated into a peri-Gondwana relative sea-level curve, which was then compared with the Euramerican sea-level curve of Johnson et al. (1985). The bioevents coincided with several sequence stratigraphic surfaces, representing variable limbs of the relative sea-level curve. On the other hand, their conspicuous coincidence with the switching intervals between the colder oligotrophic and warmer mesotrophic modes suggests that organic production linked to global climate was the primary control on biotic overturns, while sea-level fluctuations may have only amplified its effects.

Controllable DC-link bridge-type FCL for low voltage ride-through enhancement of converter interfaced DG systems

Recently penetration level of converter-interfaced distributed generation (DG) systems has been increased in utility and will be more so in the future. To avoid grid instability, converter-interfaced DG should have low voltage ride through (LVRT) capability considering grid codes. An efficient scheme is proposed to enhance the LVRT capability of converter-interfaced DGs. The proposed LVRT technique employs a single phase controllable DC-link bridge type fault current limiter (CD-BFCL), which is placed in DC side of the converter. During normal condition, the CD-BFCL does not affect overall operation of converter-interfaced DG; whereas, during all AC faults including balanced, unbalanced, and transient repeated network faults, converter output AC currents are limited to a desired level. In this way, the converter-interfaced DG is capable to ride through faults even at the zero grid voltage during the AC grid faults. Analytics and modes of operation of the CD-BFCL are presented during switching intervals to demonstrate the efficiency of the proposed approach in limitation of converter over-current. The operation of the proposed method is proved through simulation studies in PSCAD/EMTDC. Also, a laboratory prototype is developed to validate the possibility of practical implementation of the CD-BFCL.

Breakdown Enhancement and Current Collapse Suppression by High-Resistivity GaN Cap Layer in Normally-Off AlGaN/GaN HEMTs

In this letter, a device structure of high-resistivity-cap-layer HEMT (HRCL-HEMT) is developed for normally-off p-GaN gate HEMT toward high breakdown voltage and low current collapse. It demonstrates that the breakdown capability and current collapse of the device were effectively improved due to the introduction of a thick HR-GaN cap layer. The fabricated HRCL-HEMT exhibits a high breakdown voltage of 1020 V at ${I}_{\text {DS}} = 10~\mu \text{A}$ /mm with the substrate grounded. Meanwhile, the dynamic ${R}_{\text {on}}$ is only 2.4 times the static ${R}_{\text {on}}$ after off-state ${V}_{\text {DS}}$ stress of 1000 V with the substrate grounded (the OFF to ON switching time interval is set to $200~\mu \text{s}$ ).

Robust adaptive tracking control of uncertain slowly switched linear systems

In this paper, robust adaptive tracking control schemes for uncertain switched linear systems subject to disturbances are investigated. The robust adaptive control problem requires the design of both adaptive and switching laws. A novel adaptive law is proposed based on an extended leakage approach, which does not require knowledge of the bounds of the uncertainty set. Two switching laws are developed based on extended dwell time (DT) strategies: (a) mode-dependent dwell time (MDDT); (b) mode–mode-dependent dwell time (MMDDT). MDDT exploits the information of the known reference model for every subsystem, i.e., the dwell time is realized in a subsystem sense. MMDDT is a variant of MDDT that can guarantee stability under faster switching than MDDT, provided that the next subsystem to be switched on is known. The proposed adaptive schemes can achieve global uniform ultimate boundedness for shorter switching intervals than state-of-the-art adaptive approaches based on DT. In addition to global uniform ultimate bounded stability, transient and steady-state performance bounds are derived for the tracking error. The numerical example of a highly maneuverable aircraft technology vehicle is adopted to demonstrate the effectiveness of the proposed adaptive methods.

Frequency-domain light intensity spectrum analyzer based on temporal convolution.

We propose and experimentally demonstrate a new type of all-optical radio frequency (RF) spectrum analyzer based on temporal convolution and cross-phase modulation (XPM) that can be regarded as the frequency-domain counterpart of a conventional light intensity spectrum analyzer (LISA). The XPM effect converts the intensity envelope of an optical signal to the phase of the probe signal, while the temporal convolution helps to enable the RF spectrum to be temporally resolved with a high frame rate. This frequency-domain LISA (f-LISA) has experimentally demonstrated an 800-GHz observation bandwidth with 1.25-GHz resolution (1GHz for a single frequency) and a 94-MHz frame rate. To showcase its potential applications, this analyzer has successfully characterized the dynamic RF spectrum of an ultrafast wavelength-switching signal with a 10-ns switching interval. We believe that it is promising for some ultrafast dynamic RF spectrum acquisition applications, e.g., fast tuning lasers and real-time channel monitoring.

Photodetachment microscopy in time-dependent fields

Photodetachment of negative ions in combined laser and low-frequency fields is investigated. The time-dependent Green's function method is used for calculation of electron flux at a macroscopic distance from the photodetachment source, typical for a photodetachment microscopy experiment. In calculating the electron flux, we use the stationary phase method for the time integral, equivalent to the semiclassical approximation, to compute the time-dependent wave function. The stationary points ${t}_{1}^{(i)}, i=1,...,n$ correspond to time instances of launching of classical trajectories arriving at the detector at a given spacetime point $(\mathbf{r},t)$. The number of trajectories $n$ contributing to the electron flux at any point in the classically allowed spacetime domain can be controlled by varying the switching interval of the high-frequency laser which initiates the photodetachment process. The divergences inherent in the electron flux in the semiclassical treatment are removed by using the uniform Airy approximation near the caustics.

A High-Efficiency 6.78-MHz Full Active Rectifier With Adaptive Time Delay Control for Wireless Power Transmission

This paper presents a full active rectifier consisting of GaN devices and a CMOS controller designed for wireless power transmission in high-power consumer devices. An adaptive time delay control circuit is developed to maximize the conduction interval of the GaN switch, which can significantly reduce the power loss caused by the forward voltage imposed by the diode. The proposed control algorithm also eliminates the reverse leakage current of the rectifier, and thus further improves its power transfer efficiency. The controller implemented based on a high-voltage 0.18- $\mu \text{m}$ CMOS process and the power stage consisting of four GaN transistors are assembled on the same printed circuit board (PCB) board. The proposed rectifier provides a maximum output current of 3 A at 5 V, with a 6.78-MHz ac input voltage. Its peak power transfer efficiency is 91.8%.

Voltage THD Reduction for Dual-Inverter Fed Open-End Load With Isolated DC Sources

In this paper, the near-state pulse width modulation (NSPWM), adapted to be used in dual-voltage source inverter (VSI) fed open-end load, is introduced primarily aiming to appreciably minimize the voltage total harmonic distortion (THD). Within the framework of the proposed method, the active time of pulses at the second inverter is relatively adjusted within switching interval (compared to the first VSI). The phase voltage harmonics are formulated for dual-inverter modulated by NSPWM; then, optimal adjustment is identified via a three-dimensional curve of phase voltage THD versus modulation index (MI) and phase angle displacement (PAD). Due to the limitation of MI in NSPWM, the desired output voltage is synthesized with modifying not only MI but also PAD between references of two VSIs. Furthermore, NSPWM inherently takes advantage of better efficiency compared to conventional space vector modulation due to switching only two phases within an interval (by clamping one phase to positive/negative dc-rail). The dual-VSI supplied by two isolated dc sources is assembled in the laboratory to experimentally evaluate the THD reduction feature of the proposed method; also, the simulation results obtained by means of a MATLAB/Simulink environment show close agreement with experimental data.

A DC-to-Three-Phase Boost–Buck Inverter With Stored Energy Modulation and a Tiny DC-Link Capacitor

Three-phase voltage-source inverters typically feature a significant amount of dc energy storage to maintain a stiff dc bus. In these cases, the dc-link capacitor is sized to store enough energy to maintain several tens of cycles of ac output at the rated power. In this paper, we propose to reduce the size of the dc-link capacitor dramatically to store enough energy to provide just one high-frequency switching cycle of the ac output power. The dc bus is no longer stiff, and hence, classical sinusoidal pulse-width modulation cannot be used. However, the stored energy modulation (SEM) proposed herein synthesizes high-quality sinusoidal output voltage waveforms, even with such tiny dc-link capacitors. In SEM, the switching intervals of the interconnecting switches are carefully determined nonlinear functions of various operating parameters such as reactive component sizing, switching frequency, load levels, etc. This paper presents the analytical and detailed design development of the SEM approach along with circuit simulation, experimental results, and comparative evaluation of a dc-to-three-phase system example.

Detecting driving stress in physiological signals based on multimodal feature analysis and kernel classifiers

Abstract Monitoring driving status has great potential in helping us decline the occurrence probability of traffic accidents and the aim of this research is to develop a novel system for driving stress detection based on multimodal feature analysis and kernel-based classifiers. Physiological signals such as electrocardiogram, galvanic skin response and respiration were record from fourteen drives executed in a prescribed route at real drive environments. Features were widely extracted from time, spectral and wavelet multi-domains. In order to search for the optimal feature sets, Sparse Bayesian Learning (SBL) and Principal Component Analysis (PCA) were combined and adopted. Kernel-based classifiers were employed to improve the accuracy of stress detection task. Analysis I used features from 10 s intervals of data which were recorded during well-defined rest, highway and city driving conditions to discriminate three levels of diving stress achieving an averaging accuracy over 99% at per-drive level and 89% in cross-drive validation. Analysis II made continuous stress evaluation throughout a complete driving test attaining a high coincidence with the true road situation especially at the switching interval of traffic conditions. Experimental results reveal that different levels of driving stress can be characterized by specific set of physiological measures. These physiological measures could be applied to in-vehicle intelligent systems in various approaches to help the drivers better manage their negative driving status. Our design scheme for driving stress detection could also facilitate the development of similar in-vehicle expert systems, such as driver's emotion management, driver's sleeping onset monitoring, and human-computer interaction (HCI).

AlGaN/GaN MIS-HEMTs of Very-Low ${V}_{\sf {{th}}}$ Hysteresis and Current Collapse With In-Situ Pre-Deposition Plasma Nitridation and LPCVD-Si3N4 Gate Insulator

In this letter, we report an in-situ predeposition plasma nitridation process, which is adopted to remove the GaN surface oxygen-related bonds and reduce surface dangling bonds by forming Ga-N bonds prior to the low-pressure chemical vapor deposition (LPCVD)Si 3 N 4 deposition. It demonstrates that the Vth hysteresis and current collapse of the device were dramatically improved due to high-quality LPCVD-Si 3 N 4 /GaN interface. The MIS-HEMTs using this in-situ pre-deposition plasma nitridation exhibit a very-low Vth hysteresis of 186 mV at VG-sweep = (-30 V, +24 V), a high breakdown voltage of 881 V with the substrate grounded. Meanwhile, the MIS-HEMT dynamic RON is only 18% larger than the static RON after OFF-state VDS stress of 600 V (the OFF to ON switching time interval is set to 200 μs).

Stability, $l_{2}$ -Gain, and Robust $H_{\infty }$ Control for Switched Systems via ${N}$ -Step-Ahead Lyapunov Function Approach

Unlike the traditional analysis and synthesis approach of a switched system that requires a monotonic decrease of Lyapunov function (LF), this paper investigates an ${N}$ -step-ahead LF approach. Such an approach allows a non-monotonic behavior both at the switching instants and during the running time of each subsystem but guarantees an average decrease at every ${N}$ sampling steps. The asymptotic stability criterion is improved as well as the capability of disturbance attenuation. By introducing a series of auxiliary variables, the future knowledge of states and exogenous noises can be properly used to derive sufficient conditions for the existence of a robust ${H}_{\infty }$ controller in the form of a set of numerical testable conditions. Note that ${N}$ has direct impact on the number of inequality constraints. The essential difficulty is to construct an exponential damping law of the decreasing points of LF, i.e., to find the joint point between the switching interval and the predictive horizon. Moreover, the relationship between ${N}$ -step time difference of LF and switching rate, i.e., the average dwell time constraint, is thoroughly discussed. An ecology system is employed to demonstrate practical potentials of the presented design framework.

Low voltage ride-through enhancement of DFIG-based wind turbine using DC link switchable resistive type fault current limiter

Doubly-fed induction generator (DFIG)-based wind turbines utilise small-scale voltage sourced converters with a limited overcurrent withstand capability, which makes the DFIG-based wind turbines very vulnerable to grid faults. Often, modern DFIG systems employ a crowbar protection at the rotor circuit to protect the rotor side converter (RSC) during grid faults. This method converts the DFIG to a squirrel cage induction generator, which does not comply with the new grid codes. The recent grid codes need wind turbines to stay connected to the utility grid during and after power system faults, especially in high penetration level of wind power. Furthermore, the crowbar switch is expensive. This paper proposes a novel DC-link switchable resistive-type fault current limiter (SRFCL) to improve the LVRT capability of the DFIG. The proposed SRFCL is employed in the DC side of the RSC. The SRFCL solves crowbar protection activation problems and eliminates subsequent complications in the DFIG system. The proposed SRFCL does not have any significant impact on the overall performance of the DFIG during normal operation. Whenever the fault, whether symmetrical or asymmetrical, occurs, the SRFCL not only limits rotor over-currents but also prevents rotor speed acceleration and restricts high torque oscillations even during zero grid voltage, as recommended by some grid codes. To prove the effective operation of the SRFCL on the RSC fault current limitation, analytical analysis is performed in each switching interval. The proposed approach is compared with the crowbar-based protection method. Simulation studies are carried out in PSCAD/EMTDC software. In addition, a prototype is provided to demonstrate the main concept of the proposed approach.