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Covariance of the orbital state of a resident space object (RSO) is a necessary requirement for various space situational awareness tasks, like the space collision warning. It describes an accuracy envelope of the RSO’s location. However, in current space surveillance, the tracking data of an individual RSO is often found insufficiently accurate and sparsely distributed, making the predicted covariance (PC) derived from the tracking data and classical orbit dynamic system usually unrealistic in describing the error characterization of orbit predictions. Given the fact that the tracking data of a RSO from a single station or a fixed network shares a similar temporal and spatial distribution, the evolution of PC could share a hidden relationship with that data distribution. This study proposes a novel method to generate accurate PC by combining the classical covariance propagation method and the data-driven approach. Two popular machine learning algorithms are applied to model the inconsistency between the orbit prediction error and the PC from historical observations, and then this inconsistency model is used to the future PC. Experimental results with the Swarm constellation satellites demonstrate that the trained Random Forest models can capture more than 95% of the underlying inconsistency in a tracking scenario of sparse observations. More importantly, the trained models show great generalization capability in correcting the PC of future epochs and other RSOs with similar orbit characteristics and observation conditions. Besides, a deep analysis of generalization performance is carried out to describe the temporal and spatial similarities of two data sets, in which the Jaccard similarity is used. It demonstrates that the higher the Jaccard similarity is, the better the generalization performance will be, which may be used as a guide to whether to apply the trained models of a satellite to other satellites. Further, the generalization performance is also evaluated by the classical Cramer von Misses test, which also shows that trained models have encouraging generalization performance.

Isotope effect on the superconductive transition temperature (T c ) is an essential indicator to examine whether the mechanism of superconductors is conventional or not. Unconventional isotope effect of BiS2-based superconductors have been previously reported in ambient-pressure tetragonal phase, however, to comprehensively explore the nature of superconductivity, investigation of BiS2-based system in high-pressure structure is highly desirable. In this contribution, we present the first-principles calculations of phonon spectra and superconductivity in high-pressure monoclinic phase of LaO0.5F0.5BiS2 with 32S and 34S, and the corresponding isotope coefficient of 0.13 ≤ α ≤ 0.20 is observed. This value is much greater than that of BiS2-based superconductors in ambient-pressure phase, but slightly smaller than that of conventional MgB2. Taking into account the lower calculated T c than experiment results, we finally conclude that the moderate phonon-mediated pairing plays a significant role in the superconductivity of BiS2-based system in high-pressure phase, moreover, the cooperative multiple paring interactions should also be considered.

In a constant-volume chamber, the atomization characteristics of low-viscosity fuel sprays were studied under the effects of mass concentration and injection pressure. Microscopic spray parameters were measured via laser diffraction downstream of the nozzle at various axial and radial positions. The results showed that an increase in the mass concentration suppressed the atomization effect in a linear manner. The increase in injection pressure promoted droplet breakup; however, the trend gradually weakened and became more noticeable at high concentrations. Compared to the concentration, the influence of the injection pressure on the atomization characteristics was dominant. Although low concentration and high injection pressure promoted droplet breakup, they also increased the probability of droplet collision, resulting in droplet aggregation. This was more evident in low-viscosity fuels. The droplet size increased in the axial direction owing to the aggregation. However, the diameter decreased in the radial direction owing to the outward deflection of small droplets caused by air turbulence and entrainment. In addition, the high-velocity airflow significantly promoted droplet breakup near the nozzle and spray axis regions and suppressed the aggregation effect. Nevertheless, lower-viscosity fuels maintained smaller droplet sizes and better atomization throughout the spraying process, which was easier to achieve than that in higher-viscosity fuels. Overall, low concentration, high injection pressure and low viscosity of the fuel have beneficial effects on the droplet breakup. This is important to enhance the atomization effect of the fuel.

The non-volatile resistive switching process of a MoS2 based atomristor with a vertical structure is investigated by first-principles calculations. It is found that the monolayer MoS2 with S vacancy defects (Vs) could maintain an insulation characteristic and a high resistance state (HRS) is also remained. As an electrode metal atom adsorbed on MoS2 monolayer, the semi-conductive filament is formed with the assistance of Vs. Under this condition the atomristor presents a low resistance state (LRS). The ON state current of this semi-filament is increased close to two orders than that of without filament (HRS). The energy barrier for an Au-atom to penetrate the monolayer MoS2 via Vs is as high as 6.991 eV. When it comes to double S vacancy (Vs2), the energy barrier is still amounted to 3.554 eV, which manifests the bridge-like full conductive filaments cannot form in monolayer MoS2 based atomristor. The investigation here promotes the atomistic understanding of the resistive switching properties about the monolayer MoS2 based memristor. The physics behind should also work in atomristors based on other monolayer transitional metal dichalcogenides, like WeSe2 and MoTe2. The investigation here will promote the comprehension of these devices at atomic scale and be a reference for device design or optimization.

As part of the International Asteroid Warning Network's observational exercises, we conducted a campaign to observe near-Earth asteroid 2019 XS around its close approach to Earth on 2021 November 9. The goal of the campaign was to characterize errors in the observation times reported to the Minor Planet Center, which become an increasingly important consideration as astrometric accuracy improves and more fast-moving asteroids are observed. As part of the exercise, a total of 957 astrometric observations of 2019 XS during the encounter were reported and subsequently were analyzed to obtain the corresponding residuals. While the timing errors are typically smaller than 1 s, the reported times appear to be negatively biased, i.e., they are generally earlier than they should be. We also compared the observer-provided position uncertainty with the cross-track residuals, which are independent of timing errors. A large fraction of the estimated uncertainties appear to be optimistic, especially when

Aiming at the emergence of patients with outdoor cardiac arrest, to strive for more golden rescue time, a robot suitable for the rescue of patients with outdoor cardiac arrest is proposed. Combined with the medical research on the human thorax, the dynamic model of the human thorax is established, the kinematics and dynamics of the end effector mechanism are analyzed, and the robot is simulated for cardiopulmonary resuscitation in the human thorax with Adams software. The relationship between the stroke, speed, acceleration, driving torque, and time of the end effector is obtained. Second, the dynamic formula theory is simulated with Matlab software. The difference between the theoretical driving torque and the simulation driving torque is 5.2% and 2.3% respectively. Finally, the feasibility of the CPR operation of the robot is preliminarily verified through experiments.

Realizing single light solitons that are stable in high dimensions is a long-standing goal in research of nonlinear optical physics. Here, we address a scheme to generate stable two-dimensional solitons in a cold Rydberg atomic system with a parity-time (PT) symmetric moiré optical lattice. We uncover the formation, properties, and their dynamics of fundamental and two-pole gap solitons as well as vortical ones. The PT symmetry, lattice strength, and the degrees of local and nonlocal nonlinearity are tunable and can be used to control solitons. The stability regions of these solitons are evaluated in two numerical ways: linear-stability analysis and time evolutions with perturbations. Our results provide an insightful understanding of solitons physics in combined versatile platforms of PT-symmetric systems and Rydberg–Rydberg interaction in cold gases.

We theoretically investigate the frustrated double ionization (FDI) of molecules with different alignment-dependence using a three-dimensional classical ensemble method. The numerical results show that the FDI probability decreases with increasing wavelength, which is similar to the wavelength dependence of the FDI probability of atoms. Tracing the classical trajectories reveals that the contributions to molecular FDI from single-recollision and multiple-recollision mechanisms are equal in the short wavelength regime. In the long wavelength regime, the single-recollision FDI channel dominates in FDI. The nature in which molecular FDI occurs is identified and explained.

Epoxy resin (EP) materials are frequently used in high voltage power equipment because of their excellent electricity, force, and heat properties. However, under the condition of DC high voltage, the surface of EP insulation material is more likely to accumulate charge, which distorts the nearby electric field and causes flashover along the surface. In this article, a nanocomposite coating was prepared by spraying through the nanoparticles (TiO2 with carbon nanotubes) dispersed in the polydimethylsiloxane (PDMS) elastomers solution. Micro-nano porous structures are introduced in the spraying process, which hinders the development of collision ionization and increases the flashover strength of the coating. At the same time, the change in surface morphology makes the hydrophobic properties of the coating improve and enhances the anti-icing and anti-fouling capacity. Spraying nano filler provides a general method for improving hydrophobicity and flashover strength.

To increase the specific capacitance of supercapacitors, polyaniline (PANI) has been chosen as additive electrode material for the pseudocapacitive performance. Here, we synthesize a molecular-level uniform reduced graphene oxide/PANI (rGO/PANI) composite film with high flexibility and conductivity via self-assembly and specific thermal reduction, which performs great potential in flexible supercapacitors with high areal capacitance. Particularly, the electrode of rGO/PANI-42.9% exhibits a high specific areal capacitance (1826 mF cm−2 at 0.2 mA cm−2), and it also presents a good cycling stability (it remains 76% of its initial capacitance after 10 500 cycles). Moreover, the specific gravimetric capacitance of rGO/PANI-33.3% reaches up to 256.4 F g−1 at 0.2 A g−1, showing greatly enhanced performance compared with the pure rGO electrode (183 F g−1). The results of various characteristic analysis demonstrate that electrochemical performance of the as-prepared rGO/PANI film is closely associated with the uniform distribution of PANI in rGO/PANI composite. Overall, our reported method is convenient and environmental-friendly, and could be beneficial for the development of high-performance capacitive energy storage materials.

Quantum steering ellipsoid (QSE) can faithfully characterize arbitrary bipartite state, and provide a new method to visually investigate and capture various quantum nonlocalities. Note that the dissipation of quantum nonlocalities can be accelerated by the coupling between the system and the decoherence channel, which induces great challenges in detecting quantum nonlocalities. Herein, considering the scenario in which the subsystem of a two-qubit system is coupled with a decoherence channel, the quantum discord (QD) and concurrence are visually characterized and detected by employing the QSE. The results reveal that the QSE y and z semiaxes are responsible for the traits of the QD and concurrence under the bit flip channel. The x and y semiaxes dominate and visualize the QD and concurrence under the phase damping channel. Of particular note is that one can realize the detections of the QD and concurrence via the shape of the QSE. To be clearer, the disappearance of the QD can be ascertained according to a needle-shaped QSE or a vanishing QSE in the Bloch sphere. In contrast, one can witness the concurrence if the total semiaxis length is greater than one. Beyond this, our results visually reveal that quantum entanglement is a stronger quantum nonlocality than the QD from the perspective of geometry, and thus deepens the understanding of the quantum nonlocality.

Diamond-silicon carbide (SiC) composite stacks are composed of two kinds of wide-bandgap materials, each of which has excellent thermal, electronic, optical, and mechanical properties, and is considered an ideal material for heat dissipation. For optimal application, the interface between the two materials needs to be almost void-free and of high-quality growth. Traditional methods such as sintering and liquid/vapor phase infiltration have many problems, but the preparation of diamond-SiC composites by the microwave plasma chemical vapor deposition (MPCVD) method can effectively solve these problems, overcome the interface defects, and break through the size limitation. In this review, various techniques for preparing diamond-SiC composites by MPCVD will be discussed. It mainly includes the co-deposition of diamond and cubic polytype β-SiC, deposition of diamond films on β-SiC/Si substrates, and deposition of diamond films on 4H-SiC and 6H-SiC substrates. The implementation methods, research progress, and application trend of each approach are reviewed in detail.

By studying the structure and functional characteristics of five-axis linkage CNC machine tool, design five-axis CNC machine tool with X, Y, Z linear motion axes, B and C rotation axes. The virtual simulation system of miniature five-axis machine tool is built based on the VERICT, and an impeller part was simulated and processed as an example. Check whether the state of each moving axis in the machine tool movement is correct, and judge the rationality of the structure design of the machine tool based on the error information such as interference and collision in the processing. It is proved by simulation that the machine can realize five-axis linkage machining within the design range and meet the design requirements.

Aluminum alloy has limited its application due to low hardness and poor wear resistance. Therefore, surface modification by electroplating is beneficial to improving hardness and wear resistance properties. Hence, Ni/W–ZrO2 coating was organized on aluminum alloy by electro-deposition method in this paper. The optimum organization parameters were obtained. The impact of different ZrO2 additions on the hardness and friction wear properties of Ni/W–ZrO2 coatings were further investigated. The SEM, Vickers examiner and wear examination are used to analyze the micromorphology, micro-hardness as well as friction and wear resistance properties, respectively. The results show that when the addition of ZrO2 was 40g/L in the deposition bath, the Ni/W–ZrO2 coating possesses the optimum micro-hardness of 384HV. This is mainly attribute to the dispersion-enhancing effect of ceramic particles. This work offers a new approach to surface strengthening technology for aluminum alloys.

In this paper, models of hot carrier degradation (HCD) in nMOSFET and nFinFET, combined with the physical mechanism and reaction-diffusion framework and considering saturation effect, are proposed. The HCD data of different technology nodes of nMOSFET and nFinFET are used to verify the accuracy of the models. The results show that the prediction errors of device parameter degradation under different stress voltages are less than 10% for several types of short channel devices, which is better than the existing reported research results. Furthermore, the models have simple analytical expressions that allow them to not only be applied to device HCD prediction, but also be extended to circuit level HCD prediction tool more easily.

When corona discharge occurs around the wire, it will be accompanied by the movement of space charge, and then generate corona discharge effects such as radio interference and audible noise. In order to reveal time domain characteristics of the electric field of radio interference generated by corona discharge, a set of time domain measurement systems for radio interference, including oscillator antenna, sampling resistance, and data acquisition system, is developed. Based on the characteristics of corona-generated radio interference and antenna theory, the size of the antenna, the equivalent circuit model, and the selection of sampling resistance are discussed carefully to satisfy the requirements for the measurement of corona-generated radio interference. To verify the effectiveness of the measurement system, an experimental platform with a single corona source is built, and the time domain waveforms of corona current and radio interference are simultaneously measured. Besides, the attenuation law of radio interference is obtained by using a time domain measurement system. The results show that the amplitude of the measured voltage of radio interference decreases exponentially with distance. The time domain measurement system presented in this paper can lay a solid foundation for the time-domain evaluation of the radio interference level generated by corona discharge.

This paper proposes micro-ROS-based mobile robot system development and 2D mapping. Micro-ROS uses the micro-XRCE-DDS middleware to communicate with ROS2 in an extremely resource-constrained microcontroller environment. The mobile robot control system adopts a layered control method. The x64 PC equipped with Ubuntu ROS foxy is used as the main control platform, the olimex-stm32-E407 equipped with micro-ROS is used as the motion control layer, and the stm32F103 microcontroller is the underlying driver core. The forward and inverse kinematic equations are obtained through the analysis of the robot kinematics model. Through the interaction between the ROS2 nodes in the micro-ROS environment and the ROS2 nodes on the PC side, the cartographer algorithm is used to verify the effectiveness of the micro-ROS-based mobile robot system.

In this paper, the vehicle track tunnel coupling dynamic model is established by using finite element software, and the model is verified. Based on this, the vibration characteristics of the vehicle and track system caused by the settlement of the tunnel foundation are studied. The calculation results show that: (1) the short wave in the tunnel settlement wavelength has a great influence on the dynamic characteristics of vehicles and track structures, and the vibration characteristics of vehicle track system decrease with the increase of wavelength, so it is suggested to control the wavelength above 25 m. (2) The dynamic index of the vehicle and track increases significantly with the increase of amplitude, which affects the driving stability and track operation. Through calculation, it is recommended to control the amplitude below 20 mm. (3) The influence of tunnel base settlement on driving is related to speed. The greater the train speed is, the greater the influence on driving will be. So the train speed should be controlled. (4) Higher running speed will endanger the safety of train operation and the stability of the track structure, so the train running speed should be lower than 200 km/h. The above research provides some theoretical guidance for track maintenance and operation.

With the continuous promotion of domestic 4G network construction and the gradual arrival of 5G networks, the requirements of mobile communication networks on capacity and coverage are constantly improving, and the number of communication base stations is also increasing. Therefore, the “shared tower” with the function of a communication base station added to the existing high-voltage transmission line tower is becoming a new resource-sharing mode. There is no systematic study on the installation location of the shared tower base station on the high-voltage tower, which is not conducive to the application and promotion of “shared tower”. In this paper, the finite element simulation model of the tower installed with the base station is built. The electric field distribution near the tower with the base station, the electric field distribution characteristics under different base station installation quantities and different positions of the base station are mainly studied, and the electric field distribution near the surface of the base station is obtained. Combined with the electrical safety distance limit of communication equipment and iron tower, the influence of the installation location and quantity of the base station on the electric field near the base station is evaluated.

The photonic spin Hall effect (PSHE), characterized by two splitting beams with opposite spins, has great potential applications in nano-photonic devices, optical sensing fields, and precision metrology. We present the significant enhancement of terahertz (THz) PSHE by taking advantage of the optical Tamm state (OTS) in InSb-distributed Bragg reflector (DBR) structure. The spin shift of reflected light can be dynamically tuned by the structural parameters (e.g. the thickness) of the InSb-DBR structure as well as the temperature, and the maximum spin shift for a horizontally polarized incident beam at 1.1 THz can reach up to 11.15 mm. Moreover, we propose a THz gas sensing device based on the enhanced PSHE via the strong excitation of OTS for the InSb-DBR structure with a superior intensity sensitivity of 5.873 × 104 mm/RIU and good stability. This sensor exhibits two orders of magnitude improvement compared with the similar PSHE sensor based on InSb-supported THz long-range surface plasmon resonance. These findings may provide an alternative way for the enhanced PSHE and offer the opportunity for developing new optical sensing devices.

Based on the BL09 terminal of China Spallation Neutron Source (CSNS), single event upset (SEU) cross sections of 14 nm fin field-effect transistor (FinFET) and 65 nm quad data rate (QDR) static random-access memories (SRAMs) are obtained under different incident directions of neutrons: front, back and side. It is found that, for both technology nodes, the “worst direction” corresponds to the case that neutrons traverse package and metallization before reaching the sensitive volume. The SEU cross section under the worst direction is 1.7–4.7 times higher than those under other incident directions. While for multiple-cell upset (MCU) sensitivity, side incidence is the worst direction, with the highest MCU ratio. The largest MCU for the 14 nm FinFET SRAM involves 8 bits. Monte–Carlo simulations are further performed to reveal the characteristics of neutron induced secondary ions and understand the inner mechanisms.

The low-frequency landing gear walk of aircraft during braking processis studied. Firstly, by virtual of LMS Virtual.Lab motion software, the multi-body dynamic model of the landing gear is established, the motion pair and internal and external loads are applied, and the torsion spring is set at the connection between the landing gear and the fuselage to simulate the flexibility of the landing gear. Then, the variation of friction coefficient of brake discis considered in the model of braking pressure and torque. When the braking control system works, if the braking pressure is less than the limit value, the gear walk is less affected by the friction characteristics of the brake disc. If the braking pressure reaches the limit value, the law of gear walk is the same as that of the pilot's manual control of the braking pressure. At this time, the gear walk is only affected by the positive and negative slope of the friction coefficient of the brake disc. If the friction coefficient curve of the brake disc presents a negative slope, it may cause gear walk, and the greater the absolute value of the slope, the more obvious the gear walk is. Improving the friction characteristics of brake discs can provide a new strategy forgear walk control.

High-pressure structural searches of superhydrides CeBeH8 and CeBH8 were performed under ambient pressure up to 300 GPa. We identify F m 3 ‾ m -CeBeH8 with a superconducting transition temperature T c of 56 K at 10 GPa. Two more phases with spacegroup R 3 ‾ m and C 2 / m , were investigated within the increasing pressures. CeBH8 shows a similar phase transition process as CeBeH8 but with higher transition pressures and higher T c . F m 3 ‾ m -CeBH8 is predicted to be superconducting above 120 GPa with a maximum T c of 118 K at 150 GPa. R 3 ‾ m -CeBH8 and C 2 / m -CeBH8 are dynamically stable above 120 GPa and 100 GPa, respectively. The maximum T c is 123 K at 195 GPa for R 3 ‾ m -CeBH8, and 115 K at 350 GPa for C 2 / m -CeBH8. Our work enriches the family of ternary hydrides and may provide a useful guideline for further search for superconducting hydrides at low and moderate pressures.

Organic–inorganic halide perovskites have been intensively investigated as potential photovoltaic materials due to their exceptional optoelectronic properties and their successful applications in perovskite solar cells (PSCs). However, a large number of defect states still exist in the PSCs so far and are detrimental to their power conversion efficiencies (PCEs) and stability. Here, an effective strategy of incorporating single-crystalline graphene quantum dots (GQDs) into the perovskite films is proposed to passivate the defect states. Intriguingly, the GQD-modified perovskite films exhibit purer phase structure, higher quality of morphology, and higher electrical conductivity when compared with the control perovskite films. All of the advantages caused by the incorporation of the GQDs lead to fast carrier separation and transport, long carrier lifetime, and low nonradiative recombination in the PSCs based on the GQD-modified perovskite films. As a result, this kind of PSC displays an increase in all photovoltaic parameters, and its PCE shows an enhancement of more than 20% when compared with the control PSC. Moreover, this novel PSC is demonstrated to have long-term stability and resistibility against heat and moisture. Our findings provide an insight into how to passivate the defect states and enhance the electrical conductivities in the perovskites and pave the way for their further exploration to achieve higher photovoltaic performances.

Atmospheric effects have significant influence on the performance of a free-space optical continuous variable quantum key distribution (CVQKD) system. In this paper, we investigate how the transmittance, excess noise and interruption probability caused by atmospheric effects affect the secret-key rate (SKR) of the CVQKD. Three signal wavelengths, two weather conditions, two detection schemes, and two types of attacks are considered in our investigation. An expression aims at calculating the interruption probability is proposed based on the Kolmogorov spectrum model. The results show that a signal using long working wavelength can propagate much further than that of using short wavelength. Moreover, as the wavelength increases, the influence of interruption probability on the SKR becomes more significant, especially within a certain transmission distance. Therefore, interruption probability must be considered for CVQKD by using long-signal wavelengths. Furthermore, different detection schemes used by the receiver will result in different transmission distances when subjected to individual attacks and collective attacks, respectively.

We have studied the high-pressure compression behavior of molybdenum up to 60 GPa by synchrotron radial x-ray diffraction (RXRD) in a diamond anvil cell (DAC). It is found that all diffraction peaks of molybdenum undergo a split at around 27 GPa, and we believe that a phase transition from a body-centered cubic structure to a rhombohedral structure at room pressure has occurred. The slope of pressure–volume curve shows continuity before and after this phase transition, when fitting the pressure–volume curves of the body-centered cubic structure at low pressure and the rhombohedral structure at high pressure. A bulk modulus of 261.3 (2.7) GPa and a first-order derivative of the bulk modulus of 4.15 (0.14) are obtained by using the nonhydrostatic compression data at the angle ψ = 54.7° between the diffracting plane normal and stress axis.

Most of the traditional flow standard devices are fixed, with very large volumes. When the enterprise has the measurement demand, the client needs to remove all the flowmeters and send them to the location of the standard device, take them back after testing and reinstall them on the production line, resulting in low production efficiency. However, while pursuing the mobility of the device, the overall space, weight, and layout of the device are bound to be limited, thus affecting the stability of the water source and measurement accuracy. Therefore, this paper analyzes the characteristics of mobile devices, in the pursuit of lightweight at the same time design and building water source loop, branch, the overall electrical system, and write the host computer calibration software, and finally through the automatic adjustment of the solenoid valve with PID control scheme to adjust the flow, to improve the stability of water sources.

The dynamic polarizabilities of 3 s 2 1 S 0 and 3 s 3 p 3 P 0 o states of Al+ are calculated using the hybrid configuration interaction and many-body perturbation theory method, and multiconfiguration Dirac–Hartree–Fock method in this work. Five ultraviolet magic wavelengths for the Al+ clock transition 3 s 2 1 S 0 – 3 s 3 p 3 P 0 o are predicted. Although the suitable lasers are not available presently, the potential precision measurement on these magic wavelengths for the Al+ clock transition would be used to extract the ratios of several certain transition matrix elements with high accuracy, and then help to improve the precision and reliability of the estimate of the BBR shift of the Al+ clock transition. The differential dynamic polarizabilities at certain wavelengths are evaluated, which are useful to assess the ac Stark shift of the Al+ clock transition frequency and helpful in the clock experiments to suppress the ac Stark shift of the clock transition as possible as it can.

Lithium batteries have been widely used in portable electronic devices and other electric products. To ensure safety and long life, a lithium battery needs to be equipped with a protection chip. A novel voltage protection method for three-cell lithium-ion battery protection IC (Integrated Circuit) is proposed in this paper. A new voltage protection circuit structure and a three-cell lithium battery voltage sampling circuit are presented to improve the circuit performance of the chip and reduce the dynamic power consumption and chip area of the system. With a new time-division multiplexing circuit structure, the area and power consumption of the chip are greatly reduced. Moreover, this solution can be extended to any number of lithium battery packs connected in series for voltage protection. Testing results show that the overcharge detection accuracy can achieve better than ±15mV, the over-discharge detection accuracy can achieve ±7.5mV, the power consumption of the voltage protection module is 1.7μA, and the area is 300μm×500μm2.

Line commutated converter based high voltage direct current (LCC-HVDC) transmission system is prone to suffer commutation failure, which can lead to the increase of DC current and the interruption of DC transmission power. Furthermore, the increase of DC current might lead to subsequent commutation failure. Based on the reactive power balance of the inverter AC bus, this paper studies the functional relationship between DC current and commutation voltage. The DC current reference value is obtained by using the DC current acquired from the above functional relationship, and combining with the DC current order given by voltage dependent current order limiter (VDCOL). This calculation method can adjust the DC current reference value in time according to the commutation voltage, thus limiting the increase of DC current. In order to verify the commutation failure suppression ability of the proposed method, several simulations are conducted based on CIGRE benchmark HVDC model in PSCAD/EMTDC. Simulation results show that the proposed method can not only suppress commutation failure successfully, but also improve the fault recovery performance of the LCC-HVDC system.