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1.
This paper presents a powerful application of genetic algorithm （GA） for the minimization of the total harmonic current distortion （THCD） in high-power induction motors fed by voltage source inverters, based on an approximate harmonic model. That is, having defined a desired fundamental output voltage, optimal pulse patterns （switching angles） are determined to produce the fundamental output voltage while minimizing the THCD. The complete results for the two cases of three and five switching instants in the first quarter period of pulse width modulation （PWM） waveform are presented. Presence of harmonics in the stator excitation leads to a pulsing-torque component. Considering the fact that if the pulsing-torques are at low frequencies, they can cause troublesome speed fluctuations, shaft fatigue, and unsatisfactory performance in the feedback control system, the 5th, 7th, 1 lth, and 13th current harmonics （in the case of five switching angles） are constrained at some pre-specified values, to mitigate the detrimental effects of low-frequency harmonics. At the same time, the THCD is optimized while the required fundamental output voltage is maintained. 相似文献
2.
INTRODUCTION With the development of super conductor, the PWM-CSC is being increasingly studied in recent years owing to its advanced features including sinu- soidal source current at unity power factor and high quality dc output current (Zhang and Ooi, 1993; Kazerani and Ye, 2002; Vincenti and Jin, 1994; Wang, 2000). However, under unbalanced source voltage, considerable output second harmonics and input low-order harmonics are produced due to negative sequence voltage (Vincenti and… 相似文献
3.
To elucidate the principles of notable torque and flux ripple during the steady state of the conventional direct torque control (DTC) of induction machines, the factors of influence torque variation are examined. A new torque ripple minimization algorithm is proposed. The novel method eradicated the torque ripple by imposing the required stator voltage vector in each control cycle. The M and T axial components of the stator voltage are accomplished by measuring the stator flux error and the expected incremental value of the torque at every sampling time. The maximum angle rotation allowed is obtained. Experimental results showed that the proposed method combined with the space vector pulse width modulation(SVPWM) could be implemented in most existing digital drive controllers, offering high performance in both steady and transient states of the induction drives at full speed range. The result of the present work imphes that torque fluctuation could be eliminated by imposing proper stator voltage, and the proposed scheme could not only maintain constant switching frequency for the inverter, but also solve the heating problem and current harmonics in traditional induction motor drives. 相似文献
4.
评估指标体系的选取是企业信用评估的首要问题，它是一个特征选择问题。文章提出了一种针时SVM组合技术的拆分特征选择方法，其主要思想是时SVM组合中的各个分类器分别进行特征选择，再采用不同的特征子集作为各子分类器的输入，进行组合建模与预测。文章从filter和wrapper相结合的思想出发，进行了子分类器的特征选择；之后，针对企业信用评估问题的特点，采用了二叉树结构作为SVM的组合策略。实验表明，拆分特征选择方法能选出规模较小、具有一定差异的关键指标集，提高了模型的分类性能，并且具有计算简单，运行快速的优点。 相似文献
5.
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
6.
Voltage source converter high-voltage direct current （VSC-HVDC） is a new power transmission technology pref- erable in small or medium power transmission. In this paper we discuss a new control system based on space vector modulation （SVM） without any voltage line sensors. Using direct power control （DPC） SVM and a new double synchronous reference frame phase-locked loop （DSRF-PLL） approach, the control system is resistant to the majority of line voltage disturbances. Also, the system response has accelerated by using a feed forward power decoupled loop. The operation of this control strategy was verified in a SIMULINK/MATLAB simulation environment. To validate this control system, a 5 kV.A prototype system was constructed. Compared to the original controllers, the current total harmonic distortion （THD）, the active and reactive deviations and the DC voltage overshoot were lowered by 2.5%, 6.2% and 8%, respectively. The rectifier power factor in the worst condition was 0.93 and the DC voltage settling time was 0.2 s. 相似文献
7.
MOTIVATION Iris recognition, widely accepted as one of the best biometrics recognition methods in the world because of its stability, uniqueness and noninvasive-ness (Adler, 1965; Daugman, 1993; Ma et al., 2002; Wildes, 1997), has the potential of applications in very wide areas. As a kind of pattern recognition to classify the iris correctly by comparing the similarity between irises, two major works are: (1) to find the appropriate features to represent iris properly; and (2) to classi… 相似文献
8.
INTRODUCTION Automatic face recognition has become a very active research area in the last decade due to the new interest in, and need for, surveillance and security, telecommunication and digital libraries, hu-man-computer intelligent interaction, and smart en-vironments. The small sample size (SSS) problem is often encountered because the number of the samples is much smaller than the dimension of the sample space in face recognition. It results in the singularity of the within-class … 相似文献
9.
An improved automatic voltage coordination control strategy(AVCCS) based on automatic voltage control(AVC) and battery energy storage control(BESC) is proposed for photovoltaic grid-connected system(PVGS) to mitigate the voltage fluctuations caused by environmental disturbances.Only AVC is used when small environmental disturbances happen,while BESC is incorporated with AVC to restrain the voltage fluctuations when large disturbances happen.An adjustable parameter determining the allowed amplitudes of voltage fluctuations is introduced to realize the above switching process.A benchmark low voltage distribution system including PVGS is established by using the commercial software DIg SILENT.Simulation results show that the voltage under AVCCS satisfies the IEEE Standard 1547,and the installed battery capacity is also reduced.Meanwhile,the battery’s service life is extended by avoiding frequent charges/discharges in the control process. 相似文献
10.
The eigenface method that uses principal component analysis （PCA） has been the standard and popular method used in face recognition. This paper presents a PCA - memetic algorithm （PCA-MA） approach for feature selection. PCA has been extended by MAs where the former was used for feature extraction/dimensionality reduction and the latter exploited for feature selection. Simulations were performed over ORL and YaleB face databases using Euclidean norm as the classifier. It was found that as far as the recognition rate is concerned, PCA-MA completely outperforms the eigenface method. We compared the performance of PCA extended with genetic algorithm （PCA-GA） with our proposed PCA-MA method. The results also clearly established the supremacy of the PCA-MA method over the PCA-GA method. We further extended linear discriminant analysis （LDA） and kernel principal component analysis （KPCA） approaches with the MA and observed significant improvement in recognition rate with fewer features. This paper also compares the performance of PCA-MA, LDA-MA and KPCA-MA approaches. 相似文献
11.
基于MATCONT的电力系统电压稳定分岔及控制仿真试验 总被引：1，自引：0，他引：1
介绍了电力系统ODE模型中引起电压失稳的常见分岔类型及分岔控制的基本概念;运用基于Matlab的数值分岔分析软件MATCONT对一个经典单机—动态负荷系统进行了分岔分析,验证了PQ动态负荷模型系统存在着鞍结分岔(SNB)现象,而RL动态负荷模型系统并无分岔现象产生.为延迟PQ动态负荷模型系统的鞍结分岔点,在原系统中引入了线性状态反馈控制和SVC控制两种分岔控制方法.MATCONT仿真结果显示,这两种控制方法均能够有效延迟鞍结分岔,从而提高系统的电压稳定性,并可通过选择合理的反馈控制器增益及SVC增益获得理想的分岔控制效果. 相似文献
12.
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
13.
This paper presents a nonlinear robust control design method for a generic rotorcraft unmanned aerial vehicle（RUAV）. The control objective is to let the RUAV track some pre-defined time-varying position and headingtrajectories. The proposed controller employs feedback linearization process to realize the dynamic decoupling controland applies adaptive sliding mode control to compensate for the parametric uncertainties and external disturbances.The global asymptotical stability is proved via stability analysis. Compared with the cascaded controller, the proposedcontroller demonstrates a superior tracking performance and robustness through numerical simulation in the presenceof parametric uncertainties and unknown disturbances. 相似文献
14.
HAN Yan-fang SHI Peng-fei 《浙江大学学报(A卷英文版)》2006,7(6):969-975
INTRODUCTION Visual inspection plays a vital role in assuring the quality of industrial products. Texture surface detection aims at detecting defects such as cracks, stains, broken points, etc. on texture surfaces. Due to the repetitive changes of texture gray values and structures, traditional detection methods based on intensity or edge detection are invalid, which makes texture surface detection one of the most intriguing problems during the past decades. Generally, most of previous a… 相似文献
15.
Feature extraction of electrocardiogram(ECG) is oneof the mostimportanttasksin heart disease diagnosis .Gen-erally,these algorithms include length and energytransfor-mation[1],hidden Markov models[2],neural networks[3],and wavelet transform[4], etc . Howe… 相似文献
16.
对如何提高基于内容三维模型检索中的特征提取方法的效果进行了研究,提出了在特征提取过程中使用分类信息获得内容特征的方法．根据一类模型在内容上存在“大致类似,略有差异”的特点,提出采用有弹性的“本征模型”作为一类模型的代表．探索了本征模型特征的提取,较优本征模型的筛选,给出较为高效的基于本征模型的三维模型检索过程．采用多种评价指标对标准测试库Princeton Shape Benchmark的实验表明,该方法表现优异． 相似文献
17.
This paper proposes novel multi-layer neural networks based on Independent Component Analysis for feature extraction of fault
modes. By the use of ICA, invariable features embedded in multi-channel vibration measurements under different operating conditions
(rotating speed and/or load) can be captured together. Thus, stable MLP classifiers insensitive to the variation of operation
conditions are constructed. The successful results achieved by selected experiments indicate great potential of ICA in health
condition monitoring of rotating machines.
Project supported by the National Natural Science Foundation (No. 50205025) and the Natural Science Foundation of Zhejiang
Province (No. 5001004). 相似文献
18.
INTRODUCTIONRotatingmachinessuchaselectromotor,dy namotor,turbocompressor,etc .areimportantequipmentsinmanyindustryfields.Peoplehadbeenpayingconsiderableattentiontotheircon ditionmonitoringandfaultdiagnosis (Xu ,19 98) .Theoretically ,anyfluctuationofforc… 相似文献
19.
A new three-phase 5-level current-source inverter 总被引：1，自引：0，他引：1
BAO Jian-yu BAI Zhi-hong WANG Qing-song ZHANG Zhong-chao 《浙江大学学报(A卷英文版)》2006,7(12):1973-1978
INTRODUCTION Multilevel converters can offer substantial benefits for higher power applications compared to two level inverters, including reduced harmonics, and increased power ratings because of reduced switching device voltage and current stresses. However, until recently, multilevel voltage source inverters (Peng, 2001) have been the dominant multilevel topology, despite the fact that current-source inverters (CSIs) have many advantages for higher power applications. These include mo… 相似文献
20.
This paper presents a novel low-pass filter （LPF） with sharp rejection, wide stopband and compact size, which are realized by the defected ground structure （DGS） and the defected microstrip structure （DMS）. The equivalent circuit model is proposed and the circuit parameters are extracted by the circuit simulation software. The parameters measured are 3 dB cutoff frequency fc of 5.2 GHz, the insertion loss less than 0.5 dB from DC to 4.0 GHz and S21 less than -20 dB within the wide stopband from 6 GHz to 16 GHz. The results of the circuit optimization agree well with those of the full wave simulation and the measured ones, which validate the effectiveness of the equivalent circuit model. The size of the proposed LPF is decreased compared with normal LPF. This LPF can be applied in rectennas to eliminate high order harmonics. 相似文献