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- 저자 : Zhao Sifeng (검색결과 2 건)
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Sifeng Zhao,Caiyong Ye,Shanming Wan 전력전자학회 2024 JOURNAL OF POWER ELECTRONICS Vol.24 No.2
For medium and high voltage drives, the three-level converter has better technical and economical performances than the two-level converter. Permanent magnetic brushless DC (BLDC) motors are widely used due to their simple control, lowresolution requirement of the position sensor, and high power density. The power switching devices in the non-conducting phase are blocked all the time when the two-phase conduction mode is used. Serious overvoltage of the inner power switching device occurs, which triggers the overvoltage alarm or causes system failure. In this paper, the overvoltage mechanism of the inner power switching device is analyzed in detail, and a mixed conduction mode containing a three-phase conduction mode in the first stage and a two-phase conduction mode in the second stage is proposed. The speed threshold for the switching of the two control modes is designed to suppress overvoltage in the starting stage and to reduce the loss of the converter at high speeds. The effectiveness of the overvoltage suppression and system safety of the proposed mixed conduction mode are verified by simulations and experiments.
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Influence of wheat-walnut intercropping on the Sitobion avenae and its predatory natural enemies
Gao Haifeng,Jia Shuangshuang,Liu Yongqiang,Shen Yuyang,Li Guangkuo,Zhao Sifeng,Ge Feng 한국응용곤충학회 2024 Journal of Asia-Pacific Entomology Vol.27 No.1
Intercropping is widely applied all over the world, and it often causes significant changes in the number of arthropod communities. Walnut-wheat intercropping systems are commonly applied in Southern Xinjiang of China. But it is still not clear how wheat-walnut intercropping influence pest and natural enemy populations, and their ratio in wheat fields. To clarify this question and provide guidance to pest management, field surveys were conducted in Xinjiang during 2017–2019. Three intercropping treatments were tested, which were wheat-walnut 10:6, 25:6, and monoculture wheat. Our results showed that the abundance of predators (mainly ladybeetles and lacewings) increased in wheat under wheat-walnut intercropping systems (especially in intercrop treatment 10:6). Compared with monoculture wheat, the ratio of predators to Sitobion avenae was not enhanced in wheatwalnut intercropping fields. S. avenae populations increased in the walnut intercropped wheat fields. The intercropping system was not beneficial to S. avenae control in wheat fields. Different measures should be taken to strengthen the control of S. avenae in walnut intercropped wheat fields.
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