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.     

Maximum Cardinality Search for Computing Minimal Triangulations of Graphs

We present a new algorithm, called MCS-M, for computing minimal triangulations of graphs. Lex-BFS, a seminal algorithm for recognizing chordal graphs, was the genesis for two other classical algorithms: LEX M and MCS. LEX M extends the fundamental concept used in Lex-BFS, resulting in an algorithm that not only recognizes chordality, but also computes a minimal triangulation of an arbitrary graph. MCS simplifies the fundamental concept used in Lex-BFS, resulting in a simpler algorithm for recognizing chordal graphs. The new algorithm MCS-M combines the extension of LEX M with the simplification of MCS, achieving all the results of LEX M in the same time complexity.     

Comparison of activities in selective catalytic reduction of NOx by C3H8 over Co/MFI, Fe/MFI, and H/MFI zeolite catalysts

The Co/MFI(SiO₂/Al₂O₃ = 30) were prepared by a precipitation method with NaOCl in alkali solutions exhibited high activities to N₂ at 250 °C for the selective catalytic reduction (SCR) of NO_x. These catalysts showed two UV–vis bands at 700 and 400 nm, indicating the presence of octahedral Co(III) as well as tetrahedral Co(II). The high SCR activity over such Co(III, II)/MFI(30) seems to come from Co(III)---O moieties. The Co(II)MFI(30) catalysts prepared from Co(II)Cl₂ exhibited low SCR activities due to the presence of tetrahedral Co(II) ions in MFI. Less CO formation occurred over Co/MFI catalysts. The Fe/MFI(30) catalyst exhibited high activity due to the presence of some Fe---O species in MFI but more amount of CO were produced during SCR. H/MFI(30) catalyst exhibited a good SCR activity. However, more amount of carbonaceous deposits were produced on it. The correlation between acid concentration and SCR activity was discussed over H/MFIs.     

Multiple object semilinear motion planning

We present a method based on extended linear real quantifier elimination for multiple object semilinear motion planning, i.e. finding collision-free trajectories for several robots in a time dependent environment. For practical applicability the method is limited to polygonal objects and linear trajectories. It can, however, deal with situations involving even non-convex objects.     

Deactivation of V2O5-WO3-TiO2 SCR catalyst at a biomass-fired combined heat and power plant

The deactivation of a commercial type V₂O₅-WO₃-TiO₂ monolith catalyst under biomass combustion was studied at a full-scale grate-fired power plant burning straw/wood using a slip stream pilot scale reactor. The aerosols in the flue gas consisted of a mixture of potassium chloride and sulphate. Three catalyst elements were exposed at 350 °C, and one element was exposed at 250 °C for comparison. The catalyst activity was measured in the reactor at the exposure temperature by addition of NH₃ and extra NO. The activity, in terms of a first-order rate constant, dropped by 52% after about 1140 h indicating a very fast deactivation compared to coal firing. It was also found that the reactor temperature was not of importance for the deactivation rate. SEM-EDX analysis showed that particle deposition and pore blocking contributed to the deactivation by decreasing the diffusion rate of NO and NH₃ into the catalyst. However, potassium also penetrated into the catalyst wall and the resulting average K/V ratio in the catalyst structure was high enough (about 0.3–0.5) for a significant chemical deactivation. Chemisorption studies carried out in situ showed that the amount of chemisorbed NH₃ on the catalyst decreased as a function of exposure time, which reveals that Brøndsted acid sites had reacted with potassium compounds and thereby rendered inactive. When washed by 0.5 M H₂SO₄ the regenerated catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C, but even though reactivation is possible, the deactivation rate appears too high for practical use of the SCR process in straw combustion.     

Compile-time copy elimination

Single-assignment and functional languages have value semantics that do not permit side-effects. This lack of side-effects makes automatic detection of parallelism and optimization for data locality in programs much easier. However, the same property poses a challenge in implementing these languages efficiently. This paper describes an optimizing compiler system that solves the key problem of aggregate copy elimination. The methods developed rely exclusively on compile-time algorithms, including interprocedural analysis, that are applied to an intermediate data flow representation. By dividing the problem into update-in-place and build-in-place analysis, a small set of relatively simple techniques—edge substitution, graph pattern matching, substructure sharing and substructure targeting—was found to be very powerful. If combined properly and implemented carefully, the algorithms eliminate unnecessary copy operations to a very high degree. No run-time overhead is imposed on the compiled programs.     

基于MATLAB仿真的无功补偿电容器投切控制研究

对目前常用的无功补偿电容器投切控制方案所存在的不足进行了详细的分析,给出了补偿电容器投切的优化控制方案,并在MATLAB电力仿真环境下进行了仿真试验。结果表明,所提出的优化方案达到较理想的效果。     

低温吸附法脱除一氧化碳中甲烷的实验研究

在液氮温度下,采用吸附剂CNA X进行低温脱甲烷动态吸附实验,结果表明CNA X在液氮温度下可以将一氧化碳中0 1%左右的甲烷脱除到10×10-6。     

Obtaining shorter regular expressions from finite-state automata

We consider the use of state elimination to construct shorter regular expressions from finite-state automata (FAs). Although state elimination is an intuitive method for computing regular expressions from FAs, the resulting regular expressions are often very long and complicated. We examine the minimization of FAs to obtain shorter expressions first. Then, we introduce vertical chopping based on bridge states and horizontal chopping based on the structural properties of given FAs. We prove that we should not eliminate bridge states until we eliminate all non-bridge states to obtain shorter regular expressions. In addition, we suggest heuristics for state elimination that leads to shorter regular expressions based on vertical chopping and horizontal chopping.     

瞬时吸收率检测与高频噪声的剔除

在高分辨率处理过程中，由于地震数据记录中存在着一类并不被人们十分注意的，但影响却十分严重的高频噪声，使得高分辨率处理结果陷入一种“混沌”状态。为此，本文仔细分析和研究了这类噪声产生的物理机制和原因，并提出瞬时吸收率检测与高频噪声剔除的方法。