Trap distribution of polymeric materials and its effect on surface flashover in vacuum

The surface trap parameter can significantly affect the development of surface flashover in vacuum,but the effective mode and mechanism are not very clear yet.The trap parameters of three polymeric materials were tested and calculated by means of isothermal surface potential decay.The flashover experiment was developed under different applied voltages.The results show a positive correlation between the withstand voltage and the deep trap,i.e.,the deeper trap energy level is,the higher flashover voltage is.The dynamics process of charge trapping and detrapping was analyzed based on the charge transport model in dielectrics with a single trap level and two discrete trap levels.The time of charge trapping was compared with that of the discharge development.The results show that the charge trapping time is longer than the flashover development time.The way to influence flashover for a trap is not to decrease the secondary electrons in single discharge development,but to change the electric field distribution on the dielectric surface by charge capture.

Discharge Characteristics of SF_6 in a Non-Uniform Electric Field Under Repetitive Nanosecond Pulses

The characteristics of high pressure sulphur hexafluoride（SF6） discharges in a highly non-uniform electric field under repetitive nanosecond pulses are investigated in this paper.The influencing factors on discharge process,such as gas pressure,pulse repetition frequency（PRF）,and number of applied pulses,are analyzed.Experimental results show that the corona intensity weakens with the increase of gas pressure and strengthens with the increase of PRF or number of applied pulses.Spark discharge images suggest that a shorter and thicker discharge plasma channel will lead to a larger discharge current.The number of applied pulses to breakdown descends with the increase of PRF and ascends with the rise of gas pressure.The reduced electric field（E/p） decreases with the increase of PRF in all circumstances.The experimental results provide significant supplements to the dielectric characteristics of strongly electronegative gases under repetitive nanosecond pulses.

Analysis on the capacity degradation mechanism of a series lithium-ion power battery pack based on inconsistency of capacity

The lithium-ion battery has been widely used as an energy source. Charge rate, discharge rate, and operating tem- perature are very important factors for the capacity degradations of power batteries and battery packs. Firstly, in this paper we make use of an accelerated life test and a statistical analysis method to establish the capacity accelerated degradation model under three constant stress parameters according to the degradation data, which are charge rate, discharge rate, and operating temperature, and then we propose a capacity degradation model according to the current residual capacity of a Li-ion cell under dynamic stress parameters. Secondly, we analyze the charge and discharge process of a series power battery pack and interpret the correlation between the capacity degradations of the battery pack and its charge/discharge rate. According to this cycling condition, we establish a capacity degradation model of a series power battery pack under inconsistent capacity of cells, and analyze the degradation mechanism with capacity variance and operating temperature difference. The comparative analysis of test results shows that the inconsistent operating temperatures of cells in the series power battery pack are the main cause of its degradation; when the difference between inconsistent temperatures is narrowed by 5 ℃, the cycle life can be improved by more than 50%. Therefore, it effectively improves the cycle life of the series battery pack to reasonably assemble the batteries according to their capacities and to narrow the differences in operating temperature among cells.

A model-based driving cycle test procedure of electric vehicle batteries

The battery test methods are the key issues to investigate the energy-storage characteristics and dynamic characteristics of electric vehicle(EV) batteries.In this paper,the research advances of existing battery test methods as well as driving cycles are reviewed.An electric vehicle model that consists of EV dynamics model,battery model and electric motor model is built.The dynamic characteristics of the battery in frequency domain are analyzed.Based on the EV model and the frequency domain characteristics of the battery,a driving cycle test procedure of EV battery is proposed.The battery test procedure is able to reflect the real-world characteristics of EV batteries,and can be used as a universal EV battery test method.

Dynamic Characteristics in Subnanosecond Breakdown and Generation of Supershort Avalanche Electron Beam

In this paper,subnanosecond-pulse and one-nanosecond-pulse generators are used to study the breakdowns in highly overvolted gaps in atmospheric pressure air.With different cathodes,we measured the applied voltage and discharge current to investigate the dynamic characteristics in the subnanosecond breakdown during the generation of a supershort avalanche electron beam.Especially,characteristics of dynamic displacement current are presented in the current paper,which is detected between the ionization wave front and a plane anode.It is shown that during a subnanosecond voltage rise time,the amplitude of the dynamic displacement current can be higher than 4 kA.It is demonstrated that the breakdown in the air gap is assisted by ionization processes between the ionization wave front and a plane anode.

Investigation of Nanosecond Pulsed Discharge and Its Audio Characteristics in Atmospheric-pressure Air

There was no well-resolved mechanism of audible noise caused by corona discharge on UHV transmission lines. Hence we measured the sound pressure of pulsed discharges between needle-plane electrodes under different discharge conditions in air, for revealing the intrinsic relationship between discharge and its audible noise(AN). The relationship between discharge parameters and audio characte- ristics was drawn from the analysis of the electric and sound signals obtained in experiments. Experiment results showed that nanosecond pulsed discharges produce the sound pressure with a microsecond pulse lagging behind the discharge pulse in their waveforms. The peak value of the sound pulse decreases and its high frequency component gradually attenuates, when the measuring distance from discharges increases. The sound pulses correlate with the discharge current and voltage significantly, especially the current. The audible noise produced by repetitive pulsed discharge increases with the strength, duration, and pulse repetition rate of discharge.

Technical Approaches Towards Ultra-High Power Density SiC Inverter in Electric Vehicle Applications

Along with the rapid growth in electric vehicle(EV)market,higher power density and more efficient motor drive inverters are required.It is well known that silicon carbide(SiC)has advantages of high temperature,high efficiency and high switching frequency.It is believed that the appropriate utilization of these merits can pave the way to ultra-high power density inverters.This paper presents issues about SiC chip’s current-carrying capability enhancement which is crucial for a compact inverter of tens and hundreds of kilowatts.Technical approaches towards ultra-high power density EV inverter including SiC module packaging,dc-link capacitor function analysis and system level integration are discussed.Different PWM algorithms which may improve efficiency and help to reduce the inverter volume are also studied.

A Study on the Conducted Interference of Capacitor Charging Power Supply

In this paper, a mathematical analysis of the EMI (Electromagnetic Interference) for a 20 kHz/10 kV capacitor charging power supply in frequency-domain is presented, and a related circuit model considering the transient switching interference is proposed. Due to the high working frequency and the device-switching transitions, the conducted EMI caused by the charging circuit which includes the harmonics of grid frequency, working frequency and device-switching transition frequencies. Thus under certain working situations or loads parallel power supply, the interference may cause charging failure. To solve this problem, a high frequency transformer modeled with stray capacitances and an approximation of the device-switching transition is applied in the Spice-based simulation model, and a mathematical analysis in frequency-domain is presented.

Online Monitoring Method for Junction Temperature of SiC MOSFETs based on Temperature Sensitive Electrical Parameter

Compared to Si devices,the junction temperature of SiC devices is more critical due to the reliability concern introduced by immature packaging technology applied to new material.This paper proposes a practical SiC MOSFET junction temperature monitoring method based on the on-state voltage$\\boldsymbol{V}_{\\mathbf{ds}(\\mathbf{on})}$measurement.In Section II of the paper,the temperature sensitivity of the on-state voltage$\\boldsymbol{V}_{\\mathbf{ds}(\\mathbf{on})}$is characterized.The hardware of the measurement system is set up in Section III,which consists of an On-state Voltage Measurement Circuit(OVMC),the sampling and isolation circuit.Next,a calibration method based on the self-heating of the SiC MOSFET chip is presented in Section IV.In the final Section,the junction temperature is monitored synchronously according to the calibration results.The proposed method is applied to a Buck converter and verified by both an Infrared Radiation(IR)camera and a Finite Element Analysis(FEA)tool.

Generation of X-ray Emission in Repetitive Nanosecond-pulse Discharge at Atmospheric Pressure

Pulsed discharges can generate high power densities and high equivalent electric fields in plasma to emit X-rays,which is closely related to discharge mechanism.In this paper,discharge characteristics and X-ray emission of typical nanosecond-pulse discharges(corona,diffuse,spark or arc)are reviewed.Especially,the diffuse discharges are observed at pulse repetition frequencies up to 1 kHz.Factors influencing the discharge characteristics and X-ray emission are analyzed,such as the gap spacing,parameters of the applied pulse(amplitude,pulse repetition frequency),anode and cathode materials,and curvature radius of cathode.It is concluded that the maximum X-ray intensity is obtained in a diffuse discharge,and the X-ray intensity is affected by the pulse repetition frequency,applied voltage,anode material,and curvature radius of cathode.For example,X-ray intensity increases with the pulse repetition frequency and the atomic numbers of the anode material,but it decrease with the increase of curvature radius.It is also shown that the cathode material has no obvious influence on the X-ray intensity.

Nanosecond Repetitively Pulsed Dielectric Barrier Discharge in Air at Atmospheric Pressure

Dielectric barrier discharge （DBD） between two cylindrical glass containers with salt water generated by a nanosecond repetitively pulsed power generator is reported. The electrical parameters, luminous images and spectrum diagnosis are presented. It is shown that the DBD possesses a large discharge current and an intense optical emission from the nitrogen second positive system below 400 nm. The gas temperature remains very close to room temperature regardless of pulse polarity. Luminous photographs with a short exposure time down to 2 ns indicate that no filament is observed and the discharge is homogeneous.

Deposition of SiCxHyOz thin film on epoxy resin by nanosecond pulsed APPJ for improving the surface insulating performance

Non-thermal plasma surface modification for epoxy resin（EP）to improve the insulation properties has wide application prospects in gas insulated switchgear and gas insulatedtransmission line.In this paper,a pulsed Ar dual dielectrics atmospheric-pressure plasma jet（APPJ）was used for Si CxHyOzthin film deposition on EP samples.The film deposition was optimized by varying the treatment time while other parameters were kept at constants（treatment distance：10 mm,precursor flow rate：0.6 l min-（-1）,maximum instantaneous power：3.08 k W and single pulse energy：0.18 m J）.It was found that the maximum value of flashover voltages for negative and positive voltage were improved by 18%and 13%when the deposition time was3 min,respectively.The flashover voltage reduced as treatment time increased.Moreover,all the surface conductivity,surface charge dissipation rate and surface trap level distribution reached an optimal value when thin film deposition time was 3 min.Other measurements,such as atomic force microscopy and scanning electron microscope for EP surface morphology,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy for EP surface compositions,optical emission spectra for APPJ deposition process were carried out to better understand the deposition processes and mechanisms.The results indicated that the original organic groups（C–H,C–C,C=O,C=C）were gradually replaced by the Si containing inorganic groups（Si–O–Si and Si–OH）.The reduction of C=O in ester group and C=C in p-substituted benzene of the EP samples might be responsible for shallowing the trap level and then enhancing the flashover voltage.However,when the plasma treatment time was longer than 3 min,the significant increase of the surface roughness might increase the trap level depth and then deteriorate the flashover performance.

Improvement of Spatial Uniformity of Nanosecond-Pulse Diffuse Discharges in a Multi-Needle-to-Plane Gap

Large-scale non-thermal plasmas generated by nanosecond-pulse discharges have been used in various applications, including surface treatment, biomedical treatment, flow con- trol etc. In this paper, atmospheric-pressure diffuse discharge was produced by a homemade nanosecond-pulse generator with a full width at half maximum of 100 ns and a rise time of 70 ns. In order to increase the discharge area, multi-needle electrodes with a 3~3 array were designed. The electrical characteristics of the diffuse discharge array and optical images were investigated by the voltage-current waveforms and discharge images. The experimental results showed that the intensity of diffuse discharges in the center was significantly weaker than those at the margins, resulting in an inhomogeneous spatial uniformity in the diffuse discharge array. Simulation of the electric field showed that the inhomogeneous spatial uniformity was caused by the non-uniform distribution of the electric field in the diffuse discharge array. Moreover, the spatial uniformity of the diffuse discharge array could be improved by increasing the length of the needle in the centre of the array. Finally, the experimental results confirmed the simulation results, and the spatial uniformity of the nanosecond-pulse diffuse discharge array was significantly improved.

Advances in Inductively Coupled Power Transfer Technology for Rail Transit

Traditional power supply method for moving electric railway vehicles is based on contact type power collection technology.This sometimes cannot meet the requirements of modern rail transportation.A new wireless power transfer(WPT)technology can offer significant benefits in modern rail transportation particularly in some stringent environments.This paper reviews the status and the development of rail transit power supply technology,and introduces a new challenging technology--inductive power transfer(IPT)technology for rail transit.Tesla established the underpinning of IPT technology and creatively and significantly demonstrated power transfer by using highly resonant tuned coils long time ago.However,only in recent years the IPT technology has been significantly improved including the transfer air-gap length,transfer efficiency,coupling factor,power transfer capability and so on.This is mainly due to innovative semiconductor switches,higher control frequency,better coil designs and high performance material,new track and vehicle construction techniques.Recent advances in IPT for rail transit and major milestones of the developments are summarized in this paper.Some important technical issues such as coupling coil structures,power supply schemes,segmentation switching techniques for long-distance power supply,and bidirectional IPT systems for braking energy feedback are discussed.

Characteristics Investigation of Single-Sided Ironless PMLSM Based on Halbach Array for Medium-Speed Maglev Train

This paper investigates characteristics of ironless permanent magnet linear synchronous motor(PMLSM)based on Halbach array used for medium-speed(200km/h)maglev train.Long primary ironless coil is laid in the middle of track and the Halbach permanent magnet array is attached to the bottom of each bogie as a source of traction,U-shape electromagnets at the both sides of the train for levitation.Two dimensional analytical model of single-sided ironless PMLSM based on Halbach array is established,using linear overlay method,the no-load air gap magnetic field is calculated firstly,winding current density distribution is obtained for calculating the characteristics of thrust and normal force against power angle,including force characteristics with equal and unequal pole pitch,the influence of steel sleeper,etc.Besides,the mathematical model for this type motor is built by 3D finite element method,the traction characteristics of medium-speed maglev under maximum speed 200km/h are calculated.The characteristics of this type motor are satisfactory owing to there is no detent force in the motor and thrust force reach maximum meanwhile normal force can be eliminated.Calculation method is verified by comparing finite element results,experimental result on a 200kW type motor further validates the accuracy of calculation and some important conclusions are obtained.

Generation of Atmospheric Pressure Plasma by Repetitive Nanosecond Pulses in Air Using Water Electrodes

Dielectric barrier discharge （DBD） excitated by pulsed power is a promising method for producing nonthermal plasma at atmospheric pressure. Discharge characteristic in a DBD with salt water as electrodes by a home-made unipolar nanosecond-pulse power source is presented in this paper. The generator is capable of providing repetitive pulses with the voltage up to 30 kV and duration of 70 ns at a 300 Ω resistive load. Applied voltage and discharge current are measured under various experimental conditions. The DBD created between two liquid electrodes shows that the discharge is homogeneous and diffuse in the whole discharge regime, Spectra diagnosis is conducted by an optical emission spectroscopy. The air plasma has strong emission from nitrogen species below 400 nm, notably the nitrogen second positive system.

A Novel Voltage Balancing Method of Modular Multilevel Converters

In this paper, a novel voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides the voltages of sub-module capacitors in each arm into several groups and the voltage balancing is based on these groups. The proposed method can save sorting time greatly compared with the conventional method. Simulation results on a MMC based three-phase inverter show validity of the proposed method.

A Graphical Analysis on Compensation Designs of Large-gap CPT systems for EV Charging Applications

Capacitive power transfer(CPT)technology is a newly emerging research focus for EV charging applications.Due to the absence of eddy current loss and light weight of the capacitive coupling metal plates,CPT technology is considered to be a promising alternative to the inductive power transfer(IPT)technology.In this paper,the recent designs of large-gap CPT systems designed for EV charging applications are summarized.And a graphical method based on Smith chart is proposed to analyze the characteristics of the compensation designs.With the design objectives graphically represented,the Smith chart can be used to visually analyze the performance of a compensation design,which could be helpful in multi-objectives design of the CPT system.The graphic features of three major design objectives on the Smith chart are investigated.Several guidelines of a good compensation design are concluded.

Recursive modeling and online identification of lithium-ion batteries for electric vehicle applications

For safe and reliable operation of lithium-ion batteries in electric vehicles,the real-time monitoring of their internal states is important.The purpose of our study is to find an easily implementable,online identification method for lithium-ion batteries in electric vehicles.In this article,we propose an equivalent circuit model structure.Based on the model structure we derive the recursive mathematical description.The recursive extended least square algorithm is introduced to estimate the model parameters online.The accuracy and robustness are validated through experiments and simulations.Real-road driving cycle experiment shows that the proposed online identification method can achieve acceptable accuracy with the maximum error of less than 5.52%.In addition,it is proved that the proposed method can also be used to estimate the real-time SOH and SOC of the batteries.

Research on Multi-Parameter Evaluation of Electric Vehicle Power Battery Consistency Based on Principal Component Analysis

Electric vehicle power battery consistency is the key factor affecting the performance of power batteries. it is not scientific to evaluate the consistency of the battery depending on voltage or capacity. In this paper, multi- parameter evaluation method for battery consistency based on principal component analysis is proposed. Firstly, the characteristic parameters of battery consistency are analyzed, the principal component score can be used as the basis for evaluating the consistency of the battery. Then, the function that multi-parameter evaluation of battery consistency is established. Finally, battery balancing strategy based on fuzzy control is developed. The basic principle of fuzzy control is to fuzzy the input quantity based on expert knowledge, and the fuzzy control auantitv is obtained bv fuzzy control rule_ Th~ re.~nlt.~ ~ro v^rlfiocl hv t,~t