Search

For a HVDC converter station, the commonly used power loss determination methods are difficult to accurately reflect the changes of power loss of the converter in real time, given that the operating parameters of the converter station are dynamically changing when the converter station is running normally. Therefore, this paper proposes a method for predicting power loss of HVDC converters based on support vector regression. According to this method, firstly, the power loss data of a converter is analyzed. Then the appropriate feature in the power loss data is selected and thus a dataset of power loss samples can be obtained for further work. By applying the support vector regression algorithm to the dataset collected before, it is possible to predict the power loss of a converter for various operating parameters of the HVDC converter station. Finally, the cross-validation method was used to validate the stability of the prediction method. The result of the validation shows that the proposed method is able to accurately and stably predict the power loss of a converter of the HVDC converter station in real time.

Significance Understanding the relation between crystal structure and electronic properties is crucial for designing new quantum materials with desired functionality. So far, controlling a chemical bond is less considered as an effective way to manipulate the topological electrons. In this paper, we show that the V–Al bond acts as a shield for protecting the topological electrons in Dirac semimetal VAl3. The Dirac electrons remain intact in the V1−xTixAl3 solid solutions, even after a substantial part of V atoms have been replaced. A Lifshitz transition from Dirac semimetal to trivial metal occurs as long as the V–Al bond is completely broken. Our finding highlights a rational approach for designing new quantum materials via controlling their chemical bond., Topological electrons in semimetals are usually vulnerable to chemical doping and environment change, which restricts their potential application in future electronic devices. In this paper, we report that the type-II Dirac semimetal VAl3 hosts exceptional, robust topological electrons which can tolerate extreme change of chemical composition. The Dirac electrons remain intact, even after a substantial part of V atoms have been replaced in the V1−xTixAl3 solid solutions. This Dirac semimetal state ends at x=0.35, where a Lifshitz transition to p-type trivial metal occurs. The V–Al bond is completely broken in this transition as long as the bonding orbitals are fully depopulated by the holes donated from Ti substitution. In other words, the Dirac electrons in VAl3 are protected by the V–Al bond, whose molecular orbital is their bonding gravity center. Our understanding on the interrelations among electron count, chemical bond, and electronic properties in topological semimetals suggests a rational approach to search robust, chemical-bond-protected topological materials.

Aim To study the chemical constituents of Cupressus gigantea . Methods The chemical constituents were isolated by various chromatographic methods, and the chemical structures were elucidated on the basis of spectral analysis (NMR, MS). Results A new labdane-type diterpenoid, fourteen known diterpenoids, and two known sesquiterpenoids were isolated from the stems and leaves of Cupressus gigantea . The structure of the new compound ( 1 ) was elucidated on the basis of the analysis of spectroscopic data. Conclusion Compound 1 is a new sesquiterpenoid, compounds 1–17 were isolated from this plant for the first time.