Local ageing defects are the main causes of cross-linked polyethylene(XLPE)power cable faults.This research aims at assessing the severity level of typical cable local ageing defects based on the high-voltage frequenc...Local ageing defects are the main causes of cross-linked polyethylene(XLPE)power cable faults.This research aims at assessing the severity level of typical cable local ageing defects based on the high-voltage frequency domain spectroscopy(FDS)non-linearity.Experimentally,typical XLPE cables ageing defect conditions are simulated,with different ageing types,degrees,and local proportions.Then,the high-voltage FDS detection is conducted and the results have been analysed.It has been found that the high-voltage FDS non-linearity is only related to the detection voltage and ageing degree.Especially,it is more sensitive to changes in the ageing severity.Thus,the local ageing defect severity assessment method based on non-linearity has been established.Additionally,the sensitivity has been compared between two diagnostic evaluation methods:the high-voltage FDS and the widely used very-low frequency method(VLF,0.1 Hz).It can be concluded from the comparison result that the proposed assessment method has higher sensitivity than that of the traditional methods.Finally,the effectiveness of the proposed method for evaluating the on-site long cables has been validated.The result demonstrates that the proposed method can assess on-site long cables and has the potential to be formed as quantitative standards.展开更多
The dynamics of network power response play a crucial role in system stability.However,the integration of power electronic equipment leads to amplitude and angular frequency(abbreviated as"frequency")time-va...The dynamics of network power response play a crucial role in system stability.However,the integration of power electronic equipment leads to amplitude and angular frequency(abbreviated as"frequency")time-varying characteristics of the node voltage during dynamic processes.As a result,traditional calcu-lation methods for and characteristics of the power response of the network based on phasor and impe-dance lose their validity.Therefore,this paper undertakes mathematical calculations to reveal the power response of a network under excitation by voltage with time-varying amplitude and frequency(TVAF),relying on the original mathematical relationships and superimposed step response.Then,the multi-timescale characteristics of both the active and reactive power of the network are explored physically.Additionally,this paper reveals a new phenomenon of storing and releasing the active and reactive power of the network.To meet practical engineering requirements,a simplified power expression is presented.Finally,the theoretical analysis is validated through time-domain simulations.展开更多
Under the background of complicated interconnected network,the splitting criterion for accurately capturing the electrical center in real time is the prerequisite of power grid splitting.This paper studies the feature...Under the background of complicated interconnected network,the splitting criterion for accurately capturing the electrical center in real time is the prerequisite of power grid splitting.This paper studies the features of electric quantity in the electrical center in aspect of the instantaneous frequency,and proposes the out-of-step splitting criterion for power systems based on bus voltage frequency.Firstly,through the establishment and solution to the out-of-step model of the power grid,the analytical expression of the voltage frequency at any position is obtained in the out-of-step oscillation,and the voltage frequency features of electrical center and non-electrical center are analyzed in details.Then,this paper constructs the typical scene of migration of electrical center to study the change rules of voltage frequency.Finally,the splitting criterion based on bus voltage frequency is proposed as well as the instruction for use.This criterion is easy to be realized and can adapt to the migration of electrical center.Also it is free from the limits of power network structure and operational mode.Simulation results of CEPRI-36 system and interconnected network example of one actual region verify the accuracy and the effectiveness of the proposed criterion.展开更多
This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency o...This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).展开更多
For the partial discharge test of electrical equipment with large capacitance,the use of lowfrequency voltage instead of power frequency voltage can effectively reduce the capacity requirements of test power supply.Ho...For the partial discharge test of electrical equipment with large capacitance,the use of lowfrequency voltage instead of power frequency voltage can effectively reduce the capacity requirements of test power supply.However,the validity of PD test under low frequency voltage needs to be evaluated.In order to investigate the influence of voltage frequency on corona discharge in the air,the discharge test of the tip-plate electrode under the frequency from 50 to0.1 Hz is carried out based on the impulse current method.The results show that some of the main features of corona under low frequency do not change.The magnitude of discharge in a positive half cycle is obviously larger than that in a negative cycle.The magnitude of discharge and interval in positive cycle are random,while that in negative cycle are regular.With the decrease of frequency,the inception voltage increases.The variation trend of maximum and average magnitude and repetition rate of the discharge in positive and negative half cycle with the variation of voltage frequency and magnitude is demonstrated,with discussion and interpretation from the aspects of space charge transportation,effective discharge time and transition of discharge modes.There is an obvious difference in the phase resolved pattern of partial discharge and characteristic parameters of discharge patterns between power and low frequency.The experimental results can be the reference for mode identification of partial discharge under low frequency tests.The trend of the measured parameters with the variation of frequency provides more information about the insulation defect than traditional measurements under a single frequency（usually 50 Hz）.Also it helps to understand the mechanism of corona discharge with an explanation of the characteristics under different frequencies.展开更多
Au/Zn O/n-type Si device is obtained using atomic layer deposition（ALD） for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state（Nss）, barrier height（Φb）, series res...Au/Zn O/n-type Si device is obtained using atomic layer deposition（ALD） for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state（Nss）, barrier height（Φb）, series resistance（Rs）, donor concentration（Nd）, and dielectric characterization depending on frequency or voltage. These parameters are acquired by use of impedance spectroscopy measurements at frequencies ranging from 10 k Hz to 1 MHz and the direct current（DC） bias voltages in a range from-2 V to ＋2 V at room temperature are used. The main electrical parameters and dielectric parameters,such as dielectric constant（ε＂）, dielectric loss（ε＂）, loss tangent（tan δ）, the real and imaginary parts of electric modulus（M and M）, and alternating current（AC） electrical conductivity（σ） are affected by changing voltage and frequency. The characterizations show that some main electrical parameters usually decrease with increasing frequency because charge carriers at surface states have not enough time to fallow an external AC signal at high frequencies, and all dielectric parameters strongly depend on the voltage and frequency especially in the depletion and accumulation regions. Consequently, it can be concluded that interfacial polarization and interface charges can easily follow AC signal at low frequencies.展开更多
Nowadays, the coal mine is more and more demanding for electrical equipment, and the use of high voltage frequency converter in the motor control system has become more and more widespread. The working conditions of c...Nowadays, the coal mine is more and more demanding for electrical equipment, and the use of high voltage frequency converter in the motor control system has become more and more widespread. The working conditions of coal mine have high requirements for the reliability of high voltage frequency conversion equipment, which requires that the equipment can quickly resume operation after failure. However, the fault of frequency converter itself is often difficult to eliminate, resulting in a long troubleshooting time, which has a certain impact on the continuous production of coal mine. At the same time, the application effect of high voltage frequency converter on electric shovel is studied.展开更多
Based on the characteristic of AC-excited variable speed constant frequency(VSCF)wind power generation,the vector control technique was applied in a doubly fed induction generator(DFIG).Maximum wind energy or maximum ...Based on the characteristic of AC-excited variable speed constant frequency(VSCF)wind power generation,the vector control technique was applied in a doubly fed induction generator(DFIG).Maximum wind energy or maximum output power point can be tracked by decoupling control of active power and reactive power.The research result shows that the net power of generation system delivered to grid in maximum wind energy tracking mode is not the most.We presented a novel maximum power point tracking(MPPT)control strategy by analyzing the DFIG mathematic model and power relations which delivered the maximum power to the grid.The maximum power point could be tracked automatically without measuring wind speed in the control strategy and the control was independent of optimal turbine power curve,which had excellent dynamic and static performances and robustness.Simulation and experimental results testify the accuracy and validity of the control strategy.展开更多
A cascade glow discharge in atmospheric helium was excited by a microsecond voltage pulse and a pulse-modulated radio frequency(RF) voltage, in which the discharge ignition dynamics of the RF discharge burst was inves...A cascade glow discharge in atmospheric helium was excited by a microsecond voltage pulse and a pulse-modulated radio frequency(RF) voltage, in which the discharge ignition dynamics of the RF discharge burst was investigated experimentally. The spatio-temporal evolution of the discharge, the ignition time and optical emission intensities of plasma species of the RF discharge burst were investigated under different time intervals between the pulsed voltage and RF voltage in the experiment. The results show that by increasing the time interval between the pulsed discharge and RF discharge burst from 5 μs to 20 μs, the ignition time of the RF discharge burst is increased from 1.6 μs to 2.0 μs, and the discharge spatial profile of RF discharge in the ignition phase changes from a double-hump shape to a bell-shape. The light emission intensity at 706 nm and 777 nm at different time intervals indicates that the RF discharge burst ignition of the depends on the number of residual plasma species generated in the pulsed discharges.展开更多
The perylene （C20H12） layer effect on the electrical and dielectric properties of Al/p-Si （MS） and Al/perylene/p-Si （MPS） diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Exper...The perylene （C20H12） layer effect on the electrical and dielectric properties of Al/p-Si （MS） and Al/perylene/p-Si （MPS） diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Experimental results show that C-V characteristics give an anomalous peak for two structures at low frequencies due to interface states （Nss） and series resistance （Rs）. The increases in C and G/o3 at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant （er） and dielectric loss （e＇） are subtracted using C and G/co data at 1.5 V. The eI and e＂ values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln（o＇ac）-ln（w） for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2-V characteristics, the doping acceptor atom concentration （NA） and barrier height （,~） for Schottky barrier diodes （SBDs） 1.303 ~ 1015 cm-3, and 1.10 and I. 13 eV, respectively. of MS and MPS types are also obtained to be 1.484 ~ 1015展开更多
Energy efficiency has become one of the top design criteria for current computing systems. The Dynamic Voltage and Frequency Scaling （DVFS） has been widely adopted by laptop computers, servers, and mobile devices to...Energy efficiency has become one of the top design criteria for current computing systems. The Dynamic Voltage and Frequency Scaling （DVFS） has been widely adopted by laptop computers, servers, and mobile devices to conserve energy, while the GPU DVFS is still at a certain early age. This paper aims at exploring the impact of GPU DVFS on the application performance and power consumption, and furthermore, on energy conservation. We survey the state-of-the-art GPU DVFS characterizations, and then summarize recent research works on GPU power and performance models. We also conduct real GPU DVFS experiments on NVIDIA Fermi and Maxwell GPUs. According to our experimental results, GPU DVFS has significant potential for energy saving. The effect of scaling core voltage/frequency and memory voltage/frequency depends on not only the GPLI architectures, but also the characteristic of GPU applications.展开更多
Recently,Multicore systems use Dynamic Voltage/Frequency Scaling(DV/FS)technology to allow the cores to operate with various voltage and/or frequencies than other cores to save power and enhance the performance.In thi...Recently,Multicore systems use Dynamic Voltage/Frequency Scaling(DV/FS)technology to allow the cores to operate with various voltage and/or frequencies than other cores to save power and enhance the performance.In this paper,an effective and reliable hybridmodel to reduce the energy and makespan in multicore systems is proposed.The proposed hybrid model enhances and integrates the greedy approach with dynamic programming to achieve optimal Voltage/Frequency(Vmin/F)levels.Then,the allocation process is applied based on the availableworkloads.The hybrid model consists of three stages.The first stage gets the optimum safe voltage while the second stage sets the level of energy efficiency,and finally,the third is the allocation stage.Experimental results on various benchmarks show that the proposed model can generate optimal solutions to save energy while minimizing the makespan penalty.Comparisons with other competitive algorithms show that the proposed model provides on average 48%improvements in energy-saving and achieves an 18%reduction in computation time while ensuring a high degree of system reliability.展开更多
In an autonomous droop-based microgrid,the system voltage and frequency(VaF)are subject to deviations as load changes.Despite the existence of various control methods aimed at correcting system frequency deviations at...In an autonomous droop-based microgrid,the system voltage and frequency(VaF)are subject to deviations as load changes.Despite the existence of various control methods aimed at correcting system frequency deviations at the secondary control level without any communication network,the challenges associated with these methods and their abilities to simul-taneously restore microgrid VaF have not been fully investigated.In this paper,a multi-input multi-output(MIMO)model reference adaptive controller(MRAC)is proposed to achieve VaF restoration while accurate power sharing among distributed generators(DGs)is maintained.The proposed MRAC,without any communication network,is designed based on two methods:droop-based and inertia-based methods.For the microgrid,the suggested design procedure is started by defining a model reference in which the control objectives,such as the desired settling time,the maximum tolerable overshoot,and steady-state error,are considered.Then,a feedback-feedforward con-troller is established,of which the gains are adaptively tuned by some rules derived from the Lyapunov stability theory.Through some simulations in MATLAB/SimPowerSystem Tool-box,the proposed MRAC demonstrates satisfactory perfor-mance.展开更多
The latch-up effect induced by high-power microwave（HPM） in complementary metal–oxide–semiconductor（CMOS） inverter is investigated in simulation and theory in this paper. The physical mechanisms of excess carrie...The latch-up effect induced by high-power microwave（HPM） in complementary metal–oxide–semiconductor（CMOS） inverter is investigated in simulation and theory in this paper. The physical mechanisms of excess carrier injection and HPM-induced latch-up are proposed. Analysis on upset characteristic under pulsed wave reveals increasing susceptibility under shorter-width pulsed wave which satisfies experimental data, and the dependence of upset threshold on pulse repetitive frequency（PRF） is believed to be due to the accumulation of excess carriers. Moreover, the trend that HPMinduced latch-up is more likely to happen in shallow-well device is proposed.Finally, the process of self-recovery which is ever-reported in experiment with its correlation with supply voltage and power level is elaborated, and the conclusions are consistent with reported experimental results.展开更多
A distributed generation network could be a hybrid power system that includes wind-diesel power generation based on induction generators(IGs)and synchronous generators(SGs).The main advantage of these systems is the p...A distributed generation network could be a hybrid power system that includes wind-diesel power generation based on induction generators(IGs)and synchronous generators(SGs).The main advantage of these systems is the possibility of using renewable energy in their structures.The most important challenge is to design the voltage-control loop with the frequency-control loop to obtain optimal responses for voltage and frequency deviations.In this work,the voltage-control loop is designed by an automatic voltage regulator.A linear model of the hybrid system has also been developed with coordinated voltage and frequency control.Dynamic frequency response and voltage deviations are compared for different load disturbances and different reactive loads.The gains of the SG and the static volt-ampere reactive compensator(SVC)controllers in the IG terminal are calculated using the Black Widow Optimization(BWO)algorithm to insure low frequency and voltage deviations.The BWO optimization algorithm is one of the newest and most powerful optimization methods to have been introduced so far.The results showed that the BWO algorithm has a good speed in solving the proposed objective function.A 22%improvement in time adjustment was observed in the use of an optimal SVC.Also,an 18%improvement was observed in the transitory values.展开更多
In this paper, 0.15-μm gate-length In0.52Al0.48As/In0.53Ga0.47As InP-based high electron mobility transistors （HEMTs） each with a gate-width of 2×50 μm are designed and fabricated. Their excellent DC and RF c...In this paper, 0.15-μm gate-length In0.52Al0.48As/In0.53Ga0.47As InP-based high electron mobility transistors （HEMTs） each with a gate-width of 2×50 μm are designed and fabricated. Their excellent DC and RF characterizations are demonstrated. Their full channel currents and extrinsic maximum transconductance （gm,max） values are measured to be 681 mA/mm and 952 mS/mm, respectively. The off-state gate-to-drain breakdown voltage （BVGD） defined at a gate current of-1 mA/mm is 2.85 V. Additionally, a current-gain cut-off frequency （fT） of 164 GHz and a maximum oscillation frequency （fmax） of 390 GHz are successfully obtained; moreover, the fmax of our device is one of the highest values in the reported 0.15-μm gate-length lattice-matched InP-based HEMTs operating in a millimeter wave frequency range. The high gm,max, BVGD, fmax, and channel current collectively make this device a good candidate for high frequency power applications.展开更多
This paper deals with a combined test rig for a traction system in the laboratory environment.An experimental system was designed and implemented to verify the performance of the traction system for a metro train.For ...This paper deals with a combined test rig for a traction system in the laboratory environment.An experimental system was designed and implemented to verify the performance of the traction system for a metro train.For a highly accurate control of the system,a hybrid control algorithm combining vector control and slip frequency control was applied to control the traction inverter.The design method of the flywheels,which represent the equivalent model of the train moment inertia,was elaborated.A train runtime diagnosis system was completed by adopting the multifunction vehicle bus（MVB） protocol.The dynamic performance of the metro power traction system was emulated under the control of the train runtime diagnosis system.Using the combined test rig,the performances of the traction system in traction,braking,temperature rise,etc.,were verified through traction and breaking experiments.展开更多
To apply a quasi-cyclic low density parity check(QC-LDPC)to different scenarios,a data-stream driven pipelined macro instruction set and a reconfigurable processor architecture are proposed for the typical QC-LDPC alg...To apply a quasi-cyclic low density parity check(QC-LDPC)to different scenarios,a data-stream driven pipelined macro instruction set and a reconfigurable processor architecture are proposed for the typical QC-LDPC algorithm.The data-level parallelism is improved by instructions to dynamically configure the multi-core computing units.Simultaneously,an intelligent adjustment strategy based on a programmable wake-up controller(WuC)is designed so that the computing mode,operating voltage,and frequency of the QC-LDPC algorithm can be adjusted.This adjustment can improve the computing efficiency of the processor.The QC-LDPC processors are verified on the Xilinx ZCU102 field programmable gate array(FPGA)board and the computing efficiency is measured.The experimental results indicate that the QC-LDPC processor can support two encoding lengths of three typical QC-LDPC algorithms and 20 adaptive operating modes of operating voltage and frequency.The maximum efficiency can reach up to 12.18 Gbit/(s·W),which is more flexible than existing state-of-the-art processors for QC-LDPC.展开更多
Sampled SPWM is an excellent VVVF method of motor speed control, meanwhile the harmonic components of the output wave impairs its applications in practice. A designated harmonic suppression technology is presented for...Sampled SPWM is an excellent VVVF method of motor speed control, meanwhile the harmonic components of the output wave impairs its applications in practice. A designated harmonic suppression technology is presented for sampled SPWM, which is an improved algorithm for the harmonic suppression in high voltage and high frequency spectrum. As the technology is applied in whole speed adjusting range, the voltage can be conveniently controlled and high frequency harmonic of SP WM is also improved.展开更多
The utilization of wind generation equipment, such as DFIGs （double fed induction generators）, interconnected to islanded power generation and distribution systems is investigated in order to determine their effects...The utilization of wind generation equipment, such as DFIGs （double fed induction generators）, interconnected to islanded power generation and distribution systems is investigated in order to determine their effects on the overall system operating characteristics and stability. The use of a stable power station （with high speed machines） will be critical in achieving fast and reliable transient response to network events, in particular, when large transient loads are expected on a continuous basis, i.e., industrial mining and mineral processing equipment. Simulation results of this paper assist in understanding how small power stations and wind generation equipment respond to large transients in an islanded network. In particular, detailed simulations and analyses will be presented on impacts of distributed wind generation units （1.5 MW DF1G） on the stability of a small weak network. The novelty of this paper is on detailed analyses and simulation of weak networks with interconnects DFIG＇s including their impacts on system stability under various transient operating conditions.展开更多
基金National Key Research and Development Program of China,Grant/Award Number:2023YFB2406900。
文摘Local ageing defects are the main causes of cross-linked polyethylene(XLPE)power cable faults.This research aims at assessing the severity level of typical cable local ageing defects based on the high-voltage frequency domain spectroscopy(FDS)non-linearity.Experimentally,typical XLPE cables ageing defect conditions are simulated,with different ageing types,degrees,and local proportions.Then,the high-voltage FDS detection is conducted and the results have been analysed.It has been found that the high-voltage FDS non-linearity is only related to the detection voltage and ageing degree.Especially,it is more sensitive to changes in the ageing severity.Thus,the local ageing defect severity assessment method based on non-linearity has been established.Additionally,the sensitivity has been compared between two diagnostic evaluation methods:the high-voltage FDS and the widely used very-low frequency method(VLF,0.1 Hz).It can be concluded from the comparison result that the proposed assessment method has higher sensitivity than that of the traditional methods.Finally,the effectiveness of the proposed method for evaluating the on-site long cables has been validated.The result demonstrates that the proposed method can assess on-site long cables and has the potential to be formed as quantitative standards.
基金supported in part by the National Natural Science Fundation of China(52225704 and 52107096).
文摘The dynamics of network power response play a crucial role in system stability.However,the integration of power electronic equipment leads to amplitude and angular frequency(abbreviated as"frequency")time-varying characteristics of the node voltage during dynamic processes.As a result,traditional calcu-lation methods for and characteristics of the power response of the network based on phasor and impe-dance lose their validity.Therefore,this paper undertakes mathematical calculations to reveal the power response of a network under excitation by voltage with time-varying amplitude and frequency(TVAF),relying on the original mathematical relationships and superimposed step response.Then,the multi-timescale characteristics of both the active and reactive power of the network are explored physically.Additionally,this paper reveals a new phenomenon of storing and releasing the active and reactive power of the network.To meet practical engineering requirements,a simplified power expression is presented.Finally,the theoretical analysis is validated through time-domain simulations.
基金This work was supported by State Grid Corporation of China,Major Projects on Planning and Operation Control of Large Scale Grid(No.SGCC-MPLG029-2012)China Postdoctoral Science Foundation(No.2014M552080).
文摘Under the background of complicated interconnected network,the splitting criterion for accurately capturing the electrical center in real time is the prerequisite of power grid splitting.This paper studies the features of electric quantity in the electrical center in aspect of the instantaneous frequency,and proposes the out-of-step splitting criterion for power systems based on bus voltage frequency.Firstly,through the establishment and solution to the out-of-step model of the power grid,the analytical expression of the voltage frequency at any position is obtained in the out-of-step oscillation,and the voltage frequency features of electrical center and non-electrical center are analyzed in details.Then,this paper constructs the typical scene of migration of electrical center to study the change rules of voltage frequency.Finally,the splitting criterion based on bus voltage frequency is proposed as well as the instruction for use.This criterion is easy to be realized and can adapt to the migration of electrical center.Also it is free from the limits of power network structure and operational mode.Simulation results of CEPRI-36 system and interconnected network example of one actual region verify the accuracy and the effectiveness of the proposed criterion.
文摘This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).
基金supported by the National Key R&D Program of China(2017YFB0902704)the Science and Technology Project of SGCC(GY71-15-048)
文摘For the partial discharge test of electrical equipment with large capacitance,the use of lowfrequency voltage instead of power frequency voltage can effectively reduce the capacity requirements of test power supply.However,the validity of PD test under low frequency voltage needs to be evaluated.In order to investigate the influence of voltage frequency on corona discharge in the air,the discharge test of the tip-plate electrode under the frequency from 50 to0.1 Hz is carried out based on the impulse current method.The results show that some of the main features of corona under low frequency do not change.The magnitude of discharge in a positive half cycle is obviously larger than that in a negative cycle.The magnitude of discharge and interval in positive cycle are random,while that in negative cycle are regular.With the decrease of frequency,the inception voltage increases.The variation trend of maximum and average magnitude and repetition rate of the discharge in positive and negative half cycle with the variation of voltage frequency and magnitude is demonstrated,with discussion and interpretation from the aspects of space charge transportation,effective discharge time and transition of discharge modes.There is an obvious difference in the phase resolved pattern of partial discharge and characteristic parameters of discharge patterns between power and low frequency.The experimental results can be the reference for mode identification of partial discharge under low frequency tests.The trend of the measured parameters with the variation of frequency provides more information about the insulation defect than traditional measurements under a single frequency（usually 50 Hz）.Also it helps to understand the mechanism of corona discharge with an explanation of the characteristics under different frequencies.
文摘Au/Zn O/n-type Si device is obtained using atomic layer deposition（ALD） for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state（Nss）, barrier height（Φb）, series resistance（Rs）, donor concentration（Nd）, and dielectric characterization depending on frequency or voltage. These parameters are acquired by use of impedance spectroscopy measurements at frequencies ranging from 10 k Hz to 1 MHz and the direct current（DC） bias voltages in a range from-2 V to ＋2 V at room temperature are used. The main electrical parameters and dielectric parameters,such as dielectric constant（ε＂）, dielectric loss（ε＂）, loss tangent（tan δ）, the real and imaginary parts of electric modulus（M and M）, and alternating current（AC） electrical conductivity（σ） are affected by changing voltage and frequency. The characterizations show that some main electrical parameters usually decrease with increasing frequency because charge carriers at surface states have not enough time to fallow an external AC signal at high frequencies, and all dielectric parameters strongly depend on the voltage and frequency especially in the depletion and accumulation regions. Consequently, it can be concluded that interfacial polarization and interface charges can easily follow AC signal at low frequencies.
文摘Nowadays, the coal mine is more and more demanding for electrical equipment, and the use of high voltage frequency converter in the motor control system has become more and more widespread. The working conditions of coal mine have high requirements for the reliability of high voltage frequency conversion equipment, which requires that the equipment can quickly resume operation after failure. However, the fault of frequency converter itself is often difficult to eliminate, resulting in a long troubleshooting time, which has a certain impact on the continuous production of coal mine. At the same time, the application effect of high voltage frequency converter on electric shovel is studied.
基金Funded by the National Natural Science Foundation of China(No.60974049)the Science and Technology Support Industrial Project of Jiangsu Province(No.BZ2008031,No.BE2008074,and No.BE2009090)+1 种基金the Nantong International Cooperative Project(No.W2009003)the Natural Science Foundation of Nantong University(No.08Z022 and No.08Z025).
文摘Based on the characteristic of AC-excited variable speed constant frequency(VSCF)wind power generation,the vector control technique was applied in a doubly fed induction generator(DFIG).Maximum wind energy or maximum output power point can be tracked by decoupling control of active power and reactive power.The research result shows that the net power of generation system delivered to grid in maximum wind energy tracking mode is not the most.We presented a novel maximum power point tracking(MPPT)control strategy by analyzing the DFIG mathematic model and power relations which delivered the maximum power to the grid.The maximum power point could be tracked automatically without measuring wind speed in the control strategy and the control was independent of optimal turbine power curve,which had excellent dynamic and static performances and robustness.Simulation and experimental results testify the accuracy and validity of the control strategy.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11875104 and 12175036)。
文摘A cascade glow discharge in atmospheric helium was excited by a microsecond voltage pulse and a pulse-modulated radio frequency(RF) voltage, in which the discharge ignition dynamics of the RF discharge burst was investigated experimentally. The spatio-temporal evolution of the discharge, the ignition time and optical emission intensities of plasma species of the RF discharge burst were investigated under different time intervals between the pulsed voltage and RF voltage in the experiment. The results show that by increasing the time interval between the pulsed discharge and RF discharge burst from 5 μs to 20 μs, the ignition time of the RF discharge burst is increased from 1.6 μs to 2.0 μs, and the discharge spatial profile of RF discharge in the ignition phase changes from a double-hump shape to a bell-shape. The light emission intensity at 706 nm and 777 nm at different time intervals indicates that the RF discharge burst ignition of the depends on the number of residual plasma species generated in the pulsed discharges.
文摘The perylene （C20H12） layer effect on the electrical and dielectric properties of Al/p-Si （MS） and Al/perylene/p-Si （MPS） diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Experimental results show that C-V characteristics give an anomalous peak for two structures at low frequencies due to interface states （Nss） and series resistance （Rs）. The increases in C and G/o3 at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant （er） and dielectric loss （e＇） are subtracted using C and G/co data at 1.5 V. The eI and e＂ values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln（o＇ac）-ln（w） for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2-V characteristics, the doping acceptor atom concentration （NA） and barrier height （,~） for Schottky barrier diodes （SBDs） 1.303 ~ 1015 cm-3, and 1.10 and I. 13 eV, respectively. of MS and MPS types are also obtained to be 1.484 ~ 1015
文摘Energy efficiency has become one of the top design criteria for current computing systems. The Dynamic Voltage and Frequency Scaling （DVFS） has been widely adopted by laptop computers, servers, and mobile devices to conserve energy, while the GPU DVFS is still at a certain early age. This paper aims at exploring the impact of GPU DVFS on the application performance and power consumption, and furthermore, on energy conservation. We survey the state-of-the-art GPU DVFS characterizations, and then summarize recent research works on GPU power and performance models. We also conduct real GPU DVFS experiments on NVIDIA Fermi and Maxwell GPUs. According to our experimental results, GPU DVFS has significant potential for energy saving. The effect of scaling core voltage/frequency and memory voltage/frequency depends on not only the GPLI architectures, but also the characteristic of GPU applications.
文摘Recently,Multicore systems use Dynamic Voltage/Frequency Scaling(DV/FS)technology to allow the cores to operate with various voltage and/or frequencies than other cores to save power and enhance the performance.In this paper,an effective and reliable hybridmodel to reduce the energy and makespan in multicore systems is proposed.The proposed hybrid model enhances and integrates the greedy approach with dynamic programming to achieve optimal Voltage/Frequency(Vmin/F)levels.Then,the allocation process is applied based on the availableworkloads.The hybrid model consists of three stages.The first stage gets the optimum safe voltage while the second stage sets the level of energy efficiency,and finally,the third is the allocation stage.Experimental results on various benchmarks show that the proposed model can generate optimal solutions to save energy while minimizing the makespan penalty.Comparisons with other competitive algorithms show that the proposed model provides on average 48%improvements in energy-saving and achieves an 18%reduction in computation time while ensuring a high degree of system reliability.
文摘In an autonomous droop-based microgrid,the system voltage and frequency(VaF)are subject to deviations as load changes.Despite the existence of various control methods aimed at correcting system frequency deviations at the secondary control level without any communication network,the challenges associated with these methods and their abilities to simul-taneously restore microgrid VaF have not been fully investigated.In this paper,a multi-input multi-output(MIMO)model reference adaptive controller(MRAC)is proposed to achieve VaF restoration while accurate power sharing among distributed generators(DGs)is maintained.The proposed MRAC,without any communication network,is designed based on two methods:droop-based and inertia-based methods.For the microgrid,the suggested design procedure is started by defining a model reference in which the control objectives,such as the desired settling time,the maximum tolerable overshoot,and steady-state error,are considered.Then,a feedback-feedforward con-troller is established,of which the gains are adaptively tuned by some rules derived from the Lyapunov stability theory.Through some simulations in MATLAB/SimPowerSystem Tool-box,the proposed MRAC demonstrates satisfactory perfor-mance.
基金Project supported by the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology,China Academy of Engineering Physics(Grant No.2015-0214.XY.K)
文摘The latch-up effect induced by high-power microwave（HPM） in complementary metal–oxide–semiconductor（CMOS） inverter is investigated in simulation and theory in this paper. The physical mechanisms of excess carrier injection and HPM-induced latch-up are proposed. Analysis on upset characteristic under pulsed wave reveals increasing susceptibility under shorter-width pulsed wave which satisfies experimental data, and the dependence of upset threshold on pulse repetitive frequency（PRF） is believed to be due to the accumulation of excess carriers. Moreover, the trend that HPMinduced latch-up is more likely to happen in shallow-well device is proposed.Finally, the process of self-recovery which is ever-reported in experiment with its correlation with supply voltage and power level is elaborated, and the conclusions are consistent with reported experimental results.
文摘A distributed generation network could be a hybrid power system that includes wind-diesel power generation based on induction generators(IGs)and synchronous generators(SGs).The main advantage of these systems is the possibility of using renewable energy in their structures.The most important challenge is to design the voltage-control loop with the frequency-control loop to obtain optimal responses for voltage and frequency deviations.In this work,the voltage-control loop is designed by an automatic voltage regulator.A linear model of the hybrid system has also been developed with coordinated voltage and frequency control.Dynamic frequency response and voltage deviations are compared for different load disturbances and different reactive loads.The gains of the SG and the static volt-ampere reactive compensator(SVC)controllers in the IG terminal are calculated using the Black Widow Optimization(BWO)algorithm to insure low frequency and voltage deviations.The BWO optimization algorithm is one of the newest and most powerful optimization methods to have been introduced so far.The results showed that the BWO algorithm has a good speed in solving the proposed objective function.A 22%improvement in time adjustment was observed in the use of an optimal SVC.Also,an 18%improvement was observed in the transitory values.
基金Project supported by the National Basic Research Program of China(Grant Nos.2010CB327502 and 2010CB327505)the Advance Research Project(Grant No.5130803XXXX)
文摘In this paper, 0.15-μm gate-length In0.52Al0.48As/In0.53Ga0.47As InP-based high electron mobility transistors （HEMTs） each with a gate-width of 2×50 μm are designed and fabricated. Their excellent DC and RF characterizations are demonstrated. Their full channel currents and extrinsic maximum transconductance （gm,max） values are measured to be 681 mA/mm and 952 mS/mm, respectively. The off-state gate-to-drain breakdown voltage （BVGD） defined at a gate current of-1 mA/mm is 2.85 V. Additionally, a current-gain cut-off frequency （fT） of 164 GHz and a maximum oscillation frequency （fmax） of 390 GHz are successfully obtained; moreover, the fmax of our device is one of the highest values in the reported 0.15-μm gate-length lattice-matched InP-based HEMTs operating in a millimeter wave frequency range. The high gm,max, BVGD, fmax, and channel current collectively make this device a good candidate for high frequency power applications.
基金supported by the Innovation Funds for Technology Based Firms (09C26214301971)
文摘This paper deals with a combined test rig for a traction system in the laboratory environment.An experimental system was designed and implemented to verify the performance of the traction system for a metro train.For a highly accurate control of the system,a hybrid control algorithm combining vector control and slip frequency control was applied to control the traction inverter.The design method of the flywheels,which represent the equivalent model of the train moment inertia,was elaborated.A train runtime diagnosis system was completed by adopting the multifunction vehicle bus（MVB） protocol.The dynamic performance of the metro power traction system was emulated under the control of the train runtime diagnosis system.Using the combined test rig,the performances of the traction system in traction,braking,temperature rise,etc.,were verified through traction and breaking experiments.
基金the National Key Research and Development Program of China(2019YFB1803600)the Key Scientific Research Program of Shaanxi Provincial Department of Education(22JY059)the China Civil Aviation Airworthiness Center Open Foundation(SH2021111903)。
文摘To apply a quasi-cyclic low density parity check(QC-LDPC)to different scenarios,a data-stream driven pipelined macro instruction set and a reconfigurable processor architecture are proposed for the typical QC-LDPC algorithm.The data-level parallelism is improved by instructions to dynamically configure the multi-core computing units.Simultaneously,an intelligent adjustment strategy based on a programmable wake-up controller(WuC)is designed so that the computing mode,operating voltage,and frequency of the QC-LDPC algorithm can be adjusted.This adjustment can improve the computing efficiency of the processor.The QC-LDPC processors are verified on the Xilinx ZCU102 field programmable gate array(FPGA)board and the computing efficiency is measured.The experimental results indicate that the QC-LDPC processor can support two encoding lengths of three typical QC-LDPC algorithms and 20 adaptive operating modes of operating voltage and frequency.The maximum efficiency can reach up to 12.18 Gbit/(s·W),which is more flexible than existing state-of-the-art processors for QC-LDPC.
文摘Sampled SPWM is an excellent VVVF method of motor speed control, meanwhile the harmonic components of the output wave impairs its applications in practice. A designated harmonic suppression technology is presented for sampled SPWM, which is an improved algorithm for the harmonic suppression in high voltage and high frequency spectrum. As the technology is applied in whole speed adjusting range, the voltage can be conveniently controlled and high frequency harmonic of SP WM is also improved.
文摘The utilization of wind generation equipment, such as DFIGs （double fed induction generators）, interconnected to islanded power generation and distribution systems is investigated in order to determine their effects on the overall system operating characteristics and stability. The use of a stable power station （with high speed machines） will be critical in achieving fast and reliable transient response to network events, in particular, when large transient loads are expected on a continuous basis, i.e., industrial mining and mineral processing equipment. Simulation results of this paper assist in understanding how small power stations and wind generation equipment respond to large transients in an islanded network. In particular, detailed simulations and analyses will be presented on impacts of distributed wind generation units （1.5 MW DF1G） on the stability of a small weak network. The novelty of this paper is on detailed analyses and simulation of weak networks with interconnects DFIG＇s including their impacts on system stability under various transient operating conditions.
