共查询到20条相似文献,搜索用时 406 毫秒
1.
Francisco GONZ?LEZ-LONGATT Pawel REGULSKI Happy NOVANDA Vladimir TERZIJA 《电力系统自动化》2012,36(8):191-197
Future power system faces several challenges,one of them is the high penetration level of intermittent wind power generation,providing small or even no inertial response and being not contributing to the frequency stability.The effect of shaft stiffness on inertial response of fixed speed wind turbines is presented.Four different drive-train models based on the multi-body system are developed.The small-signal analysis demonstrates no significant differences between models in terms of electro-mechanical eigen-values for increasing shaft stiffness.The natural resonance frequency of drive-train torsion modes shows slightly different values between damped and undamped models,but no significant differences are found in the number-mass models.Time-domain simulations show the changes in the active power contribution of a wind farm based on a fixed speed wind turbine during the system frequency disturbance.The changes in the kinetic energy during the dynamic process are calculated and their contribution to the inertia constant is small and effective.The largest contribution of the kinetic energy is provided at the beginning of the system frequency disturbance to reduce the rate of the frequency change,it is positive for the frequency stability. 相似文献
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In order to improve the performance of the antenna at low frequency, short circuit branch and coupling feed structure are introduced into the folded broadband single antenna in this paper, then resonant frequency is merged into the antenna using method of stagger tuning, finally, a UWB antenna is designed to work between 800MHz~2700MHz. Analysis are conducted to determine the antenna’s properties. The short-circuit wire location, feeding point location and the length of folded strip are discussed in detail. The SAR is calculated by HFSS simulation software while the antenna is close to a 3D human head model. The research results show that the antenna can cover eight commonly used commercial frequency bands at present, and electromagnetic radiation of the antenna has tiny influence on the human head model. 相似文献
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《电气》2012,(3):24-29
Based on real-time digital simulations(RTDS),a laboratory environment similar to the real-time operation situation of the Three Gorges Hydropower Station is established.Then,the causes for the power fluctuation of the second generator by errors in the rotor rotating speed calculation are found,and the tuning method of the speed related parameters are given.The damping and reverse tuning characteristics of power system stabilizers(PSSs)in the digital automatic voltage regulator(AVR)are compared and investigated in the frequency range of 0.18-1.1 Hz.The efficiency of the proposed tuning method for ensuring power system stability is verified by RTDS.Finally,field tests show the validity of the laboratory test results. 相似文献
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To improve the microcrystalline silicon thin film deposition in quality and to increase its microcrystalline silicon content,we numerically investigated the characteristics of homogeneous discharges in hydrogen diluted silane and argon mixed gases at atmospheric pressure using a two-dimensional fluid model.The model takes into account the primary processes of excitation and ionization,sixteen reactions of radicals with radicals in silane/hydrogen/argon discharges,so this model can adequately describe the discharge plasma.The effects of very high frequency(VHF)excitation on the electron density in such discharges are analyzed.The simulation results show that the electron density does not linearly vary with the excitation frequency within from 90150 MHz.he maximum value occurs at an appropriate excitation frequency i.e.the transition frequency.Increasof the excitation frequency would effectively increase the electron density before the transition frequency,but decreases the density afterwards.is.Moreover,the densities of involved particle species,including H2+,H,Ar*,Ar+,SiH3+,SiH3,SiH3,SiH2are closely interrelated. 相似文献
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《电气》2011,(3):35-39,46
The reasons of introducing cold air into pulverizer are analyzed for boilers with large capacity and high parameters. The temperature rises of the exhaust gas are calculated when varying the amount of the cold air. The hot primary air heater, a new technology, is developed to eliminate the cold air from the pulverized coal system. The applications, advantages and disadvantages are introduced in detail for the new device and system. It is concluded that introducing cold air into pulverizer is one of the major factors that causes the exhaust gas temperature of boilers with large capacity to be high. The amount of the cold air could be reduced signif icantly, even to zero in some cases by adopting the hot primary air heater, which drops the exhaust gas temperature of the boiler effectively. The hot primary air heater, which could play part roles of the steam-air heater or the hot air recirculation system, could also be used to adjust the exhaust gas temperature within the range of 20 ℃ by controlling the flow rate of the cooling medium. Moreover, the startup period of the steam-air heater or the hot air recirculation system will be shortened, which is a unique advantage of the hot primary air heater among the measures to drop the exhaust gas temperature. 相似文献
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Time–frequency multiresolution of fault-generated transient signals in transmission lines using a morphological filter 下载免费PDF全文
Juan Carlos Quispe John Morales Eduardo Ordun Carlo Liebermann Michael Bruhns Peter Schegner 《电力系统保护与控制》2023,8(2):349-362
The ongoing transformation of electrical power systems highlights the weaknesses of the protection schemes of traditional devices because they are designed and configured according to traditional characteristics of the system. Therefore, this work proposes a new methodology to study the fault-generated high frequency transient signals in transmission lines through multiresolution analysis. The high frequency components are determined by a new digital filtering technique based on mathematical morphology theory and a spectral energy index. Consequently, wide spectra of signals in the time–frequency domain are obtained. The performance of this method is verified on an electrical power system modeled in ATP-Draw, where simulation and test signals are developed for different locations, fault resistances, inception angles, high frequency noises, sampling frequencies, types of faults, and shapes of the structuring element. The results show the characteristics of the fault such as the traveling wave frequency, location, and starting time. 相似文献
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The radio frequency(RF)modes of reverberation chamber(RC) in different frequency ranges are calculated to develop frequency-stirring techniques for RCs.An experimental system is built with a two-port vector network analyzer,of which one port is connected to a transmitting antenna located in a corner of a RC,and the other port is connected to a receiving antenna located in the working area of the RC.The parameter S21 is obtained in eight different locations of the receiving antenna for discussing the number of RF modes and the stirring bandwidth.It is found that the lowest useable frequency of a RC is determined by the RC’s dimension:the larger the dimension is,the lower the lowest useable frequency is.S21 at the lowest useable frequency is about-20 dB,and it is more stable than that at lower frequencies when the frequency increases.Increasing the bandwidth would result in a smoother dependence of S21 on frequency,which shows that frequency stirring is effective.In a RC with frequency stirring,the standard deviations of three individual field components and the total field are within the specified tolerance,i.e.the electric field distribution is uniform.Meanwhile,the electric field’s magnitude is characterized by the Chi-distribution with two degrees of freedom or the Rayleigh distribution,and the square of the magnitude is characterized by the Chi-square distribution with two degrees of freedom or the exponential distribution.Therefore,both good uniformity and good behavior of the electric field can be obtained if the RF modes in the RC are sufficient. 相似文献
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Audible noise from high voltage transmission lines’ corona discharge has become one of the decisive factors affecting design of high voltage transmission lines, thus it is very important to study the spatial propagation characteristics of audible noise for its accurate pre- diction. A calculation model for the propagation of audible noise is presented in this paper, which is based on the basic equation of the sound wave and can involve the influences of the atmosphere absorption and ground effects. The effects of different ground impedances and the atmospheric attenuation on the distribution of sound pressure level are discussed in this paper. The results show that the atmospheric absorp- tion may increase the attenuation of the audible noise, and the ground surface affects both the amplitude and phase of the sound. The spatial distribution fluctuates considering the ground effects. The atmospheric attenuation and the ground effect are closely related to the frequency of the noise. In the frequency range of the audible noise, the influence of atmospheric attenuation on the spatial propagation characteristics is more obvious in high frequency while ground has significant influences in low frequency. 相似文献
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Efficient and High Accuracy 2-D DCT and IDCT Architecture for Image Compression Based on Improved CORDIC 下载免费PDF全文
WU Hao SONG Helun LIU Nan DING Peng WU Fei LI Zhenyao WANG Zhengguang JI Yu RU Zhanqiang 《国外电子测量技术》2022,9(4):49-57
Discrete Cosine Transform (DCT) is the most widely used technique in image and video compression. In this paper, the structure of DCT and Inverse DCT (IDCT) algorithm is split in the form of COordinate Rotation DIgital Computer (CORDIC) rotation matrix. The two-dimensional (2-D) 88 DCT/IDCT units based on the improved rotation CORDIC algorithm is proposed. The shift and addition operations of the CORDIC algorithm are used to replace the cosine multiplication operations in the algorithm. The design does not contain any mul-tiplier unit, which reduces the complexity of the hardware unit. The row-column transform unit composed of register arrays connects two 1-D 8-point DCT units to complete the calculation of 2-D 88 DCT. The pipeline latency of proposed architecture is 28 clock cycles. The proposed efficient two-dimensional DCT architecture has been synthesized on the Xilinx’s Kintex-7 FPGA. The resource utilization is 17.36 % for Slice LUTs, 3.49 % for Slice Registers, and the maximum operating frequency is 172 MHz. It takes only 0.161s to complete a process of block of 88 samples. A frame of image is processed by the designed DCT unit and then recon-structed by the IDCT unit to verify the function. The Peak Signal to Noise Ratio (PSNR) can reach 51.99 dB. 相似文献
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《继电器》2018,(2)
The cost of Energy Storage System (ESS) for frequency regulation is difficult to calculate due to battery’s degradation
when an ESS is in grid-connected operation. To solve this problem, the influence mechanism of actual operating
conditions on the life degradation of Li-ion battery energy storage is analyzed. A control strategy of Li-ion ESS
participating in grid frequency regulation is constructed and a cost accounting model for frequency regulation
considering the effect of battery life degradation is established. The estimated operating life and annual average
cost of the Li-ion ESS under different dead bands and SOC set-points are calculated. The case studies show that the
estimated operating life of the Li-ion ESS under the actual operating condition differs significantly from the nominal
life provided by the manufacturer under the standard condition and the full discharge mode. This paper provides
an accurate costing method for the ESS participating in grid frequency regulation to help the promotion of the ESS
to participate in the ancillary service market. 相似文献
11.
基于电力网络一次调频动态模型建立及仿真 总被引:4,自引:0,他引:4
传统一次调频(PFR)模型忽略网络和电厂炉侧主蒸汽压力约束;不计主蒸汽压力对发电机出力影响,认为发电机功率-频率响应是线性关系。充分考虑锅炉、汽机、负荷、电网之间相互配合和制约关系,考虑发电机频率响应的非线性因素并建立了基于实际电力网络的PFR动态模型。该模型可用于分析电力网络各环节PFR动态响应对频率稳定的贡献,体现发电机、负荷和电网动态PFR综合能力。通过对IEEE 30节点系统进行仿真,分析了网络、炉侧对PFR的影响、约束对PFR的影响和线路跳线故障,并得出结论:当机组运行在上限、限载或部分机组没有并入PFR都会使电网的PFR能力下降;系统管理者应正确管理PFR服务,加强参数管理,合理调度潮流,使机组尽量不在接近约束的情况下运行,确保机组在需要时能释放出PFR容量抑制频偏;频偏出现后,系统管理者应合理调度二次调频(SFR)使频率尽快返回基值,并使系统整体PFR能力得到恢复。 相似文献
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基于DDS的软件变频控制 总被引:1,自引:0,他引:1
分析了采用分频方法实现变频控制的频率分辨率及精度,介绍了基于DDS的软件变频控制工作原理及实现方法,并分析了这种方案对变频控制性能的改善。 相似文献
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提出在外场使用环境下的频率测量系统的设计方法,用于外场复杂测试环境,设计满足机动化、一体化测量要求。系统采用连续采样的频差倍增法,采用双平衡混频器实现混频模块、滤波电路,提高测量分辨能力,根据GPIB接口特点,采用D7210C和75160BN,75161BN芯片实现计算机与仪器与测量仪器间的双向、异步、准确可靠的数据通信任务,编写软件,采用自动化测量方式,完成外场环境下原子频标的频率测量。通过对实验室和外场的比对试验数据得出系统满足测试要求,设计的系统1s比对不确定度指标达到4×10E-13。 相似文献
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开关电源电磁干扰抑制的频率控制方法比较 总被引:3,自引:0,他引:3
在开关电源开关器件的开关过程中 ,寄生器件 (如寄生电容、寄生电感等 )中能量的高频变化会产生大量的电磁干扰。除了采用无源缓冲或滤波电路的干扰抑制方法外 ,实际中还常利用控制开关频率的有源方法来抑制干扰。在此介绍和比较了随机频率法和调制频率法这两种常用的干扰抑制方法 相似文献