Application of differential evolution for cascaded multilevel VSI with harmonics elimination PWM switching

Harmonic elimination pulse width modulation (HEPWM) method has been widely applied to multilevel voltage source inverter (MVSI) to remove low frequency harmonics from its output voltage. However, the computation of the HEPWM switching angles for MVSI is very challenging due to several constraints, namely angle sequencing, very tight angular spacing and the numerous possibilities of angles distribution ratio. Realizing the potential of Differential Evolution (DE) to handle complex problems, this work proposes its application to solve the HEPWM problem for cascaded MVSI. Its emphasis is on improving the availability of HEPWM for higher output voltage by extending the maximum range of modulation index (M). It also removes the discontinuities in the switching angles and reduces the number of distribution ratio required to obtain the required solution. Compared to the most advanced (similar) work, i.e., 7-level MVSI with seventeen switching angles, DE covers a wider range of M; the maximum achievable M is 2.80. Furthermore, it exhibits very low second order distortion factor (DF₂): for the worst case, the value of DF₂ is 0.0014%. To verify the viability of the proposed algorithm, simulation is carried out and hardware prototype is constructed. Both results show very good agreement with the theoretical prediction.     

支持向量机及其在径流预测中的应用

给出了支持向量机方法(SVM)的思路、特点及关键之处,探讨了SVM在径流预测中的可能性,并与基于遗传算法的门限回归模型(TR) 进行了对比分析。径流预测实例分析表明,在拟合阶段,SVM模型要好于TR模型;在预留检验阶段,SVM模型与TR模型接近。同时SVM模型适合于小样本情况且能达到全局最优。SVM模型用于径流预测是可行的、优越的。     

Minimized Thompson NFA

The problem of converting a regular expression to nondeterministic finite automaton (NFA) is a fundamental problem that has been well studied. However, the two basic construction algorithms: (1) Thompson, (2) McNaughton–Yamada and Glushkov, both have disadvantages. In this article: first, a ‘smart’ parsing algorithm is developed which constructs a parse tree with at most (3l???1) nodes form a regular expression with l literals; second, we propose an algorithm that works on the resulting NFA from Thompson's construction, eliminating as many auxiliary states as possible while maintaining Thompson's properties. It is shown that the resulting NFA is minimized. This means that no auxiliary states can be eliminated without violating the defining properties of Thompson NFA. The time and space requirements for the above algorithms are linear with respect to the length of the regular expression.     

基于旋转扩展和稀疏表示的鲁棒遥感图像目标识别

针对含有残缺图像的遥感图像目标识别问题,提出一种基于旋转扩展和稀疏表示的目标识别方法.首先对训练集进行旋转扩展,使得测试图像能近似用训练集稀疏表示,然后通过求解一个l1范数最小化问题得到测试图像相对于训练集的一个稀疏表示,进而根据不同类对应的稀疏表示对测试图像的近似程度进行识别.与代表性的方法进行比较,实验结果与分析表明,该方法识别率优于已有方法,对残缺图像的识别有较好的鲁棒性,且在小样本、低采样率情况下也能保持较好的识别性能.     

最少量化在实验研究产生的放射性废物管理中的实施

通过源项的引入控制、实践正当化、安全与防护最优化、废物产生的课题化管理、分类收集分别处理等措施的实施，落实废物最少量化在核科研中的实施，减少对环境的危害，降低废物处理处置费用，促进核技术的发展应用。     

Transient performances of the gas turbine recuperating waste heat through hydrogen rich fuels

Operational rules and control strategies of the chemically recuperated gas turbine (CRGT) in the marine propulsion are investigated in this paper. The Minimization of Gibbs free energy method is used to calculate the diesel-steam reforming reaction which products synthetic hydrogen rich fuels, and a universal model of the chemical regenerator which is easily applied to different application environments is created. The hydrogen production and hydrogen molar fraction are investigated to verify that the CRGT improve the combustion performances under low working conditions. Off-design calculations are performed to derive proper operational rules, and transient calculations are performed to investigate the best control strategies for the systems. The modelling approach of the chemical regenerator can be generally used in the chemically recuperated gas turbine. The elaborate operational rules can greatly improve the thermal efficiencies under every working condition. The system using synchronous control strategies have better regulation speed and operation stability than that using asynchronous control strategies.     

Rational approach for the analysis of segmental reinforced soil walls based on kinematic constraints

The paper presents an analytical method for the solution of reinforced soil walls in which the wall facing has a structural role. The three-component (soil–reinforcement–wall) system is statically indeterminate, and hence cannot be solved by equilibrium equations alone. The paper follows up on the work of Baker and Klein [2004. An integrated limiting equilibrium approach for design of reinforced soil retaining structures part I – formulation. Geotextiles and Geomembranes 22, 119–150] where an interaction model, incorporating factors that divide forces between the reinforcement layers and the wall, was introduced to solve the statically indeterminate system. In the current work, the division factors are resolved such that the kinematic constraints of compatibility between the reinforcement layers and the wall are satisfied. This is achieved by solving an optimization problem in which the objective function includes the relative displacement between the reinforcement layers and the wall. The resultant system is fully coupled whereby upper reinforcement layers are affected by the behavior of lower layers. As such, the method overcomes the limitation of the original framework in which the top-down procedure omits such coupling. A non-dimensional parametric study was conducted on walls with 10 face blocks (9 reinforcement layers). Results are given in a normalized manner for cases in which the reinforcement pullout stiffness is uniform and linearly increasing with depth. Analysis results show that in cases where the wall is relatively stiff compared to the reinforcement, the upper reinforcement layers are clearly affected by the lower layers (this is a direct outcome of the fully coupled system). On the other hand, when the relative stiffness of the wall is low, the system behavior tends towards that of a hinged system, which is statically determinate. In this case the solution becomes independent of the reinforcement pullout stiffness. Analysis results indicate that current design codes, which do not explicitly consider the structural role of the facing in the calculation procedure, may be overconservative in certain cases. This result supports the argument for introducing the structural role of the facing into design procedures.     

Waste Minimization At A Nitrocellulose Manufacturing Facility

This paper describes how a nitrocellulose manufacturing facility, the Taiwan Nitrocellulose Industrial Company (TNC), applied the waste minimization assessment methodology developed by USEPA to reduce, recycle and recover the wastes generated at one of its satellite plant located Taoyuan, Taiwan. Since implementing the waste minimization program in the late 1980's, the company not only has solved waste disposal problems associated with the production and met the stringent environmental regulations, but also improved the nitrocellulose productivity over 20% and maintained a top five position despite harsh international competition.     

Frequency security constrained short-term unit commitment

In island grids and weakly interconnected power systems, a loss of a large proportion of generation will cause the system frequency to fall dramatically. In order to ensure a stable operation with the lowest impact on the system, the disturbed power balance must be equalized within a short specified time by activating the seconds reserve of on-line units or by load shedding or both. This paper presents a frequency security constrained short-term scheduling. The procedure commits and optimizes units, calculates necessary seconds reserve capability, and allocates them among the available on-line units to provide emergent frequency regulation following a loss of generation. By means of the low-pressure pre-heater interruption (LPHI) implemented into thermal power plants, seconds reverse provision is increased. Thus, load shedding caused by insufficient availability of seconds reserve can be avoided. A case study on typical island systems with a large number of different units is demonstrated using the proposed procedure. Results from the study validated robust performance of the proposed procedure that minimizes fuel costs while maintaining frequency security condition.     

Application of Sequential Learning Neural Networks to Civil Engineering Modeling Problems

A sequential orthogonal approach to the building and training of a single hidden layer neural network is presented in this paper. The Sequential Learning Neural Network (SLNN) model proposed by Zhang and Morris [1]is used in this paper to tackle the common problem encountered by the conventional Feed Forward Neural Network (FFNN) in determining the network structure in the number of hidden layers and the number of hidden neurons in each layer. The procedure starts with a single hidden neuron and sequentially increases in the number of hidden neurons until the model error is sufficiently small. The classical Gram–Schmidt orthogonalization method is used at each step to form a set of orthogonal bases for the space spanned by output vectors of the hidden neurons. In this approach it is possible to determine the necessary number of hidden neurons required. However, for the problems investigated in this paper, one hidden neuron itself is sufficient to achieve the desired accuracy. The neural network architecture has been trained and tested on two practical civil engineering problems – soil classification, and the prediction o strength and workability of high performance concrete.