共查询到19条相似文献，搜索用时 390 毫秒
1.
A novel control strategy for the load converter supplying the unbalanced AC load in a DC isolated distribution system is presented. The control algorithm results in balanced and sinusoidal load voltages under unbalanced AC loading. The unbalanced load is characterized in the d-q-0 rotating coordinate based on symmetrical sequence components. Also, the mathematical model of the load converter in both a-b-c and d-q-0 coordinates is derived by using the average large signal model. Then, two control strategies for the load converter are presented. The first one uses the conventional d-q-0 controller to ensure the voltage and current regulation. The second one is a newly proposed control strategy based on the decomposition of the voltage and current into in- stantaneous positive, negative, and zero sequences. These three sequences are controlled independently in their own reference frames as DC signals. The performance of the load converter using these two control strategies is compared. Simulation results show the validity and capability of the newly proposed control strategy. 相似文献
2.
This paper proposes a current control scheme for a grid-connected pulse width modulator （PWM） voltage source converter （GC-VSC） under imbalanced and distorted supply voltage conditions. The control scheme is implemented in the positive synchronously rotating reference frame and composed of a single proportional integral （PI） regulator and multi-frequency resonant controllers tuned at the frequencies of 2ω and 6ω, respectively. The experimental results, with the target of eliminating the active power oscillations and current harmonics on a prototype GC-VSC system, validate the feasibility of the proposed current control scheme during supply voltage imbalance and distortion. 相似文献
3.
PWM逆变器载波方式的选择 总被引：1，自引：2，他引：1
In this paper the influence of different carrier waveforms upon the output characteristics of PWM inverter is described in detail. When a triangular carrier waveform is used in hard-switching PWM inverters, harmonics exist in the neighborhood of the output frequency of the inverter output voltage and current due to the dead time. The triangular carrier waveform used in soft-switching PWM inverter will cause difficulties in controlling resonance-trigger time, higher loss in the resonant circuit, and less utilization of the DC bus voltage. If a sawtooth carrier is used in hard-switching PWM inverter, there will be severe distortion in the current waveform. When sawtooth carriers with alternate positive and negative slopes are used in soft-switching PWM inverters, the resonancetrigger time is easy to control, and distortion in the output voltage and current caused by the dead time will not appear. 相似文献
4.
This paper proposes an analysis and a direct power control （DPC） design of a wind turbine driven doubly-fed induction generator （DFIG） under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions. 相似文献
5.
A new PWM converter based on soft-switching is introduced.The converter uses a minimum number of devices,and requires less switching operations than conventional techniques,Switching is realized solely in a ZVS)zero voltage switching)mode,therefore the loss is reduced and EMI(electromagnetic interference)is suppressed.The paper analyzes the operation of ZVS,and discusses the methods for maintaining a unit power factor and constant DC voltage.Changing the modulation index M and the phase angle θ keeps the input current in phase with the voltage.It also keeps the current sinusoidal,and ensures a constant output voltage. 相似文献
6.
A differential cross-coupled regulated cascode(RGC)transimpedance amplifier(TIA)is proposed. The theory of multi-stage common-source(CS) configuration as an auxiliary amplifier to enhance the bandwidth and output impedance of RGC topology is analyzed. Additionally, negative Miller capacitance and shunt active inductor compensation are exploited to further expand the bandwidth. The proposed RGC TIA is simulated based on UMC 0.18 μm standard CMOS process. The simulation results demonstrate that the proposed TIA has a high transimpedance of 60.5 d B?, and a-3 d B bandwidth of 5.4 GHz is achieved for 0.5 p F input capacitance. The average equivalent input noise current spectral density is about 20 p A/Hz~(1/2) in the interested frequency, and the TIA consumes 20 m W DC power under 1.8 V supply voltage. The voltage swing is 460 m V pp, and the saturation input current is 500 μA. 相似文献
7.
The major aim of power quality （PQ） enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network. The dynamic voltage restorer （DVR） is a device used to mitigate voltage sags to regulate load voltage. This paper presents a mathematical model for leading series voltage injection to mitigate sags thereby achieving the improvement of the utility power factor as well as power sharing between the DVR and utility. The power sharing will be as per requirement to compensate the sags considering the available distributed generation （DG）. The approach of mitigating voltage sags using the concept of leading series voltage injection is suitable for those locations where phase shift in the voltage will not cause any problem. The MATLAB/SIMULINK SimPowerSystem toolbox has been used to obtain simulation results to verify the proposed mathematical model. 相似文献
8.
Partial discharge test on a transformer is carried out according to the items in IEC 60.During the test,unproved measuring system is calibrated by proved system at a voltage no less than 50% the rated testing voltage.The result is then extrapolated linearly,leading to an error related to the distribution of stray capacitance,which varies with the testing frequency,especially to large transformers.In this paper a factor,named the capacitive rise fact,is introduced to assess the rise.The factor can be adjusted to some extent by changing the reactance that is connected to the LV side of the testing circuit to lower the capacity of the power source.However,the factor changes when the voltage divider on the high voltage side is removed after the voltage ratio has been calculated,and a great error is resulted under unfavorable conditions. 相似文献
9.
Dynamic tests of three bonded and two unbonded full-prestressed concrete beams were carried out.The purpose was to seek the relation between prestressing force and natural frequency.Test results indicate that the frequency of prestressed concrete(PSC)beam increases with the increase in prestressing force approximately.The results are different from the dynamic characteristics of isotropic material beam subjected to compressive axial force which were put forward by Clough et al.The reason is that the beams were considered as isotropic,homogeneous,linear elastic material in the traditional analysis method.However,more accurate results are required in the analysis of frequency of PSC beam.The constitutive mode of PSC member is analyzed based on microstructure of concrete in this paper.The orthotropic linear elastic mode is used to analyze the relation between dynamic frequency and prestressing force of concrete beam,at the same time the equivalent stiffness of prestressed tendon relating to the prestressing force is added to the bending deformation stiffness of the beam.The analytical value agrees well with the test result,indicating that the current analysis method in this paper is feasible to full-prestressed concrete beam. 相似文献
10.
Based on planar Si dual-base transistor conception, a novel mesa dual-base heterojunction bipolar transistor （ HBT） is designed and fabricated. Molecule beam extension, selective wet chemical etching, common contact photolithography and metal lift-off technique are adopted in the process. The device has particular and distinct voltage-controlled negative differential resistance （NDR） and photo-controlled NDR. The highest peak-to-vally current rate of the voltage-controlled NDR is larger than 148 and the peak current varies with the increase of collector voltage. The device features high speed and high frequency characteristics derived from HBT and intrinsic bistability and self-latching characteristics due to NDR. A single dual-base HBT can be seen as an integration of NDR device, HBT and photoconductive device. Compared with common HBT,the groove is the key factor producing NDR. 相似文献
11.
张鉴 《黄冈职业技术学院学报》2007,9(4):21-25
本文应用超磁致伸缩材料(GMM)构建FBG的电流传感探头,与ASE光源谱特性解调系统共同组成了交流电流测量系统,对50Hz的交流电流进行测量,并通过温度解调传感实验先对ASE光源谱特性解调进行了定标。通过实验标定ASE光源谱特性解调应变灵敏度系数,最终将交流电流形成的布拉格波长漂移量解调成交变的电压信号输出。该信号与输入电流信号相对应,并且包含了输入电流信号的幅值、频率和相位信息。从示波器测得的输入和输出信号的相似性表明,实验结果与理论分析是一致的,验证了ASE光源谱特性动态解调方法的可行性。 相似文献
12.
张桐 《宜宾师范高等专科学校学报》2013,(12):54-56
设计一种旋转驻波超声电机振子驱动定位齿,可以实现对超声电机预先调整振子齿位置,达到精确定位.通过使用有限元分析软件对电机振子振动模态进行分析,设计了振子的尺寸,并制作了原理样机.实现了输入电压260 V,共振频率为40.55 kHz时,输出力矩17N＆#183;m. 相似文献
13.
郭宝会 《渭南师范学院学报》2012,(6):29-32
为了获得质量较好,经济实惠的扫描隧道显微镜针尖,设计了利用电化学腐蚀法制备针尖的控制电路.该电路包括直流腐蚀控制电路和交流腐蚀控制电路,以及利用比较器实现直流控制电路向交流电路跳转的控制电路.经过计算机仿真实验表明随着腐蚀进行,预设实际电压大于预设参考电压时,可以实现比较器反转和交流腐蚀,达到预设的功能,说明该控制电路可以制备理想的扫描隧道显微镜所用的钨针尖. 相似文献
14.
研究了交变电场对从绿豆叶片中提取的过氧化物酶活性的影响.交变电场电压为600 mV,频率为5MHz的条件下,处理时间在1~3 min范围内酶活性显著提高,1 min时最高为55.68;频率为5 MHz,改变电压处理5 min时,随着电压升高酶活性由抑制到促进逐渐增强,电压为600 mV时酶活最高达57.18;电压值为600 mV,改变频率处理5 min时,低频情况下过氧化物酶活性较低甚至被抑制,频率为2 MHz时酶活性最低为41.7,当频率为4 MHz时酶活性最强达60.54. 相似文献
15.
许胜辉 《武汉职业技术学院学报》2011,10(1):69-71,82
对交流（AC）信号进行同步采样,如电网电压和有功功率均方根值,为了测量计算的非同步交流信号（在文10-6[1]的部分）。提出了一种估值测量的数学表达式,它可测量非同步基频交流信号。用该方法测量的结果与高精密仪器测量的结果进行了比较。最后通过仿真实验证实了此方法的有效性和实用性。 相似文献
16.
研究了双磁垒量子结构中,磁场强度和偏压大小对电子自旋极化输运的影响。结果表明:零偏压下,电子在反平行等强磁垒结构中输运不会产生自旋极化;电子传输的阈值能量随磁场强度或偏置电压的增大而增大;在一定的磁场强度和偏压大小下,比较由半导体InAs和GaAs两类材料构成的量子结构中电子输运自旋极化度,发现它们的电子输运自旋极化度都随入射能量的增大而呈振荡衰减趋势,朗德有效因子高的InAs材料比GaAs的自旋极化度高出一个数量级。 相似文献
17.
自旋为1粒子在旋转磁场中的演化及几何相 总被引：1，自引：0，他引：1
讨论了自旋为1粒子在旋转磁场中的演化.利用尝试波函数法求出了它的演化波函数.讨论了该系统在完成一个演化周期后的几何相. 相似文献
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19.
宋波 《内江师范学院学报》2010,25(4):42-45
以葡萄糖为唯一碳源,研究了细菌Y—BAC在交流电的刺激下细胞的生长和葡萄糖降解的过程．研究表：明对细菌施加交流电20min后,采用50-300Hz的交流电对细菌的脱氢酶没有明显的刺激效应;当对细菌施加交流电12h后时,细菌的脱氢酶和葡萄糖的降解和细菌细胞的通透性没有明显的变化． 相似文献