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The movement of a wheeled vehicle is a non-regular dynamic process characterized by a large number of states that depend on the movement conditions. This movement involves a large number of situations where elastic tires skid and slip against the base surface. This reduces the efficiency of movement as useful mechanical energy of the electromechanical drive is spent to overcome the increased skidding and slipping. Complete sliding results in the loss of control over the vehicle, which is unsafe. Processes that take place immediately before such phenomena are of special interest as their parameters can be useful in diagnostics and control. Additionally, such situations involve adverse oscillatory processes that cause additional dynamic mechanical and electrical loading in the electromechanical drive that can result in its failure. The authors provide the results of laboratory road research into the emergence of self-oscillatory phenomena during the rolling of a wheel with increased skidding on the base surface and a low traction factor. This paper reviews the methods of designing an anti-slip control system for wheels with an oscillation damping function and studies the applicability and efficiency of the suggested method using mathematical simulation of the virtual vehicle operation in the Matlab Simulink software package. Using the self-oscillation suppression algorithm in the control system helps reduce the maximum amplitude values by 5 times and average amplitudes by 2.5 times while preventing the moment operator from changing. The maximum values of current oscillation amplitude during algorithm changes were reduced by 2.5 times, while the current change rate was reduced by 3 times. The reduction in the current-change amplitude and rate proves the efficiency of the self-oscillation suppression algorithm. The high change rate of the current consumed by the drive’s inverters may have a negative impact on the remaining operating life of the rechargeable electric power storage system. This impact increases with the proximity of its location due to the low inductance of the connecting lines and the operating parameters, and the useful life of the components of the autonomous voltage inverters.

Nanofluidic devices have turned out to be exemplary systems for investigating fluidic transport properties in a highly restricted area, where the electrostatic interactions or chemical reactions between nanochannel and flowing species strongly dominate the ions and flow transport. Numerous nanofluidic devices have recently been explored to manipulate ion currents and construct electronic devices. Enlightened by electronic field effect transistors, utilizing the electric field effect of nanopore nanochannels has also been adopted to develop versatile nanofluidic devices. Here, we report a nanopore-based nanofluidic unijunction transistor composed of a conical glass nanopipette with the biomaterial polydopamine (PDA) coated at its outer surface. The asfabricated nanofluidic device exhibited negative differential resistance (NDR) and ion current oscillation (ICO) in ionic transport. The pre-doped copper ions in the PDA moved toward the tip as increasing the potential, having a robust shielding effect on the charge of the tip, thus affecting the surface charge density of the nanopore in the working zone. Finite element simulation based on a continuum model coupled with Stokes-Brinkman and Poisson-Nernst-Planck (PNP) equations revealed that the fluctuations in charge density remarkably affect the transport of ionic current in the nanofluidic device. The as-prepared nanofluidic semiconductor device was a ready-to-use equipment that required no additional external conditions. Our work provides a versatile and convenient way to construct nanofluidic electronic components; we believe by taking advantage of advanced surface modification methods, the oscillation frequency of the unijunction transistors could be controlled on demand, and more nanofluidic devices with resourceful functions would be exploited.

Based on the enormous application potential of GaN-based high electron mobility transistors (HEMT) in high-frequency and high-power scenarios, this article focuses mainly on the study of the Gunn oscillation effect of GaN-based HEMT devices. From the perspective of electric field regulation, a sandwich structure GaN HEMT device model with field plate structure is proposed, and a hydrodynamic physical model is established. The negative resistance characteristics in the GaN HEMT are obtained by the finite element method and the influence of the gate field plate on the Gunn oscillation frequency in the device channel is studied. The numerical simulation results show that the suitable field plate structure can modulate the distribution of the channel electric field below the gate, promote the electric field to enter the negative differential mobility region, undergo valley to valley electron transfer, form electron domains, and generate the Gunn oscillation currents in the terahertz band. Meanwhile, the length of the field plate regulates the oscillation current frequency of the device, and the stable and usable terahertz frequency band signal can be realized. This research opens up the possibility for semiconductor solid-state devices to realize terahertz frequency band radiation, and provides the basis for realizing new breakthroughs in HEMT for terahertz applications.

We have studied generation of electromagnetic oscillations in the long-wavelength part of the terahertz range by diode structures with active side border. Diodes represent planar structures 1.28 (m long, 0.32 (m wide. They include a conductive channel placed on a semi-insulating InP substrate, two contacts, and an active side boundary (ASB) in the form of an n-type region located between the InP channel and the metal electrode connected to the ohmic contact of the anode. Donor concentration in a channel is 6·1022 m – 3. The article considers two different ASB on the bases of InP and InGaAs and analyses generation efficiency of diodes. We carried out a simulation by the Ensemble Monte Carlo technique. The characteristics of the diode are compared with the characteristics of common InP diodes with the same parameters. We found out that the I-V characteristic of diodes does not contain a region with negative differential conductivity. However, there are high frequency current oscillations. The operation regime is close to trapped domain mode. In the course of the research, we determined the efficiency and frequency properties of the diode. The frequency range of diodes is established to be in the range from 100 to 350 GHz. Maximum generation efficiency of diodes with InP-based ASB is about 2.5 % at a frequency of 160-180 GHz. The article highlights the effect of increase in cutoff frequency in the case of using ASB to compare with a common InP diode. In particular, using InP-based ASB, gives current oscillation in the range from 300 to 350 GHz when ASB position is near the anode contact. Nevertheless, this effect is absent if InGaAs-based ASB is applied. Thus, we assume that frequency properties can be improved due to enhanced energy relaxation in ASB.

А study of electromagnetic oscillations in the longwave part of the terahertz range by graded-band diodes based on InPAs has been carried out. These diodes contain an InP cathode layer and an InPAs graded-band layer using InP0.2As0.8 on the anode contact. Diodes with a length of 500, 640 and 1280 nm were considered. A donor concentration in the active region of the diode is 1017 cm – 3. The direct current characteristics of diodes were determined and their frequency properties in the oscillation generation mode were evaluated. The simulation was carried out using the Ensemble Monte Carlo Technique with consideration of impact ionization. Characteristics of diodes were compared with those obtained for diodes without accounting for impact ionization.It was shown that the I-V characteristic of short graded-band diodes does not contain areas with negative differential conductivity. Under the condition of impact ionization, these diodes exhibit an increase in current. While these diodes remain stable, they demonstrate charged layer current instabilities and oscillation generation in resonant circuits. The study revealed that the maximum generation efficiency is approximately 10 %, observed in diodes with a length of 1280 nm at a frequency of 100 GHz. In shorter diodes, the efficiency decreases to 3.9 % and 2.0 % in diodes with lengths of 640 and 500 nm, respectively. The cut-off frequency of generation was around 400 GHz in diodes with a length of 500 nm. Impact ionization was found to lead to a decrease in efficiency without compromising the frequency properties of diodes. Conversely, in the case of a 1280 nm diode, it improved frequency properties, supporting the application of graded diodes with impact ionization for achieving maximal frequencies.

Discharge current oscillation in Hall thrusters can cause noise or, in the worst case, severe damage to the satellite. An amplitude detection system senses the discharge current and can shut off the thruster if excessive oscillations occur. The system divides a waveform 100 ms long and sampled at 1 MHz into 1000 segments and calculates the current amplitude in each segment. Next, a Power Processing Unit (PPU) calculates the number of segments where the current threshold is exceeded and determines whether the thruster should stop running. The proposed system was installed in a PPU2, PPU for 6 kW thrusters, and PPU Technology Development Unit 2 (PPU-TDU2) for 1 kW thrusters. In a test of the PPU2, the system detected 905 peaks over the threshold of 5.1 A during the 100 ms period, which has acceptable agreement with the actual number of peaks, 931. In addition, the thruster can be automatically changed to a state with a low-amplitude discharge current by changing the magnetic field. In a test of the PPU-TDU2, the maximum amplitude of 4.3 A calculated by the system agreed well with the peak value of 4.07 A calculated from the current waveform on an oscilloscope. These results reveal that the amplitude detection system is sufficiently accurate for thrusters of different power levels.

A fault current limiter (FCL) may be applied to assist the low-voltage ride-through (LVRT) of a doubly fed induction generator (DFIG). FCLs with fixed impedance, lack the flexibility to adjust their impedance to adapt to different LVRT scenarios. The direct switch-in and -out of the fixed-impedance FCL yields transient electromagnetic oscillations in the DFIG, which need to be addressed. In this paper, a variable-impedance FCL is implemented at the stator side of the DFIG to assist its LVRT, and a novel methodology is proposed to control the impedance of the FCL, with which the stator current oscillation is effectively constrained and the smooth switch-out of the FCL is realized to avoid continued active power consumption of the FCL and to restore the DFIG to its pre-fault working condition. Analysis of the LVRT transient is carried out, which lays the foundation for the control methodology to determine the impedance of the FCL based on calculation of the optimization goal. The feasibility and effectiveness of the control to the variable-impedance FCL are verified by the numerical analysis results, which compare the LVRT simulation results with the application of the fixed-impedance and the variable-impedance FCLs.

Summary With the occurrence of the oscillation current (OC) in the direct current (DC) traction network of rail transit, malfunctions appear in the relay protection system frequently. For the purpose of improving the reliability of the protection system, more effective feature extraction methods are expected to be taken into consideration. Thus, in this paper, a novel approach to feature extraction is proposed to make a distinction between the short‐circuit fault current (FC) and the OC, combined ensemble empirical mode decomposition (EEMD) and sample entropy (SampEn). Firstly, on the basis of EEMD method, the feeder current signal is disassembled, and a range of intrinsic mode functions can be derived. Then the SampEn value of each intrinsic mode functions component is calculated. Finally, all the SampEn values are summed up to serve as the feature vector that involves information on the operation state of DC traction network. In accordance with the simulation results of typical feeder current signals, it is proved that the proposed method is capable of distinguishing the FC and OC effectively. The measured data calculation results show that the proposed method can control the misjudgment rate below 5%. Therefore, the proposed method can provide a good reference for identifying the operation state of the DC traction network.

This study presents a practical method to construct a high-frequency equivalent circuit model for AC motors in Spice-like simulation software. This model can be used to analyse the characteristics of the motor and predict the conducted electromagnetic noise in an adjustable speed drive system. The modelling is based on measured data of the impedance and vector fitting technique. The procedure of the modelling is elaborated in this study and verified by comparing simulated data with experimental data on a 200 kW induction motor in the frequency range from 10 kHz to 10 MHz. This modelling method can be extended to model other types of motors irrespective of the power rating of the motors. Applications of the motor modelling to study common mode voltage in the system and current oscillation in motor winding are presented.

In this paper, the flow injection (FI) technique combined with a partially-closed electrode (PCE) was used to manipulate the physicochemical microenvironment at the electrode/electrolyte interface so as to study the effects of chloride ions (Cl− ions) and nitrate ions (NO3− ions) on the anodic dissolution of the Fe/0.5 mol dm−3 H2SO4 system. The anodic dissolution is modified by injecting various composition-containing solutions into the vicinity of the PCE, and then, the electrodissolution processes are analyzed by comparing the j–t curves before and after the injections. At the initial stage of the passive region, it is found that NO3− ions promote the anodic dissolution of iron by creating more active sites on the surface of the electrode when CNO3−/CCl− = 1:1; however, they inhibit the anodic dissolution by making the film more compact for the strong oxidized characteristics of NO3− ions when CNO3−/CCl− = 10:1.