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Bihua Hu,Zhaohong Tang,Zhi Zhang,Jinqing Linghu,Jihong Qian,Xiangyun Qin,Bumin Meng,Rong Han 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.12
Currently, Z-source networks are widely employed to extend the output-voltage range of inverters operating at a low voltage DC source. However, these inverters are troubled by low power-conversion efficiency and an obvious current distortion due to the copper losses and core losses of the inductors. In addition, they have limited voltage levels. In this paper, a novel boost network composed of two power switches, two capacitors, and two diodes is proposed to overcome these shortcomings. Meanwhile, a corresponding modulation strategy is also set forth to achieve capacitor voltage self-balancing and to regulate the output AC voltage. Moreover, by adding more switched-capacitor cells, the range of the output voltage can be further improved, and the max DC/AC-voltage conversion ratio of the inverter with n cells is √3( n + 1)/3. At last, an inverter prototype with a 1 kW power rating is built, and the obtained results demonstrate that this inverter possesses the following superiorities: a wider range of output voltage, automatic balancing of the capacitor voltage, less current distortion, and high-efficiency power conversion.
Qingyu Wu,Qiushneg Li,Xiangyun Hu,Zhanwu Lu,Wenhui Li,Xiaoran Wang 한국지질과학협의회 2023 Geosciences Journal Vol.27 No.2
Internal structure imaging of the Earth, along with determining basin structure, can aid in evaluating potential seismic hazards. However, the high operating cost limits the current geophysical exploration methods; moreover, it is difficult to apply these techniques over a large area, which limits our understanding of the Quaternary structure and the development of earthquake prevention science. A combination of dense array observation technology and ambient noise surface wave tomography is being rapidly developed as a high-resolution urban detection method. Here, we report the ambient noise imaging results of a high-density array experiment. In the ambient noise surface wave tomography method (e.g., surface wave tomography; Eikonal tomography), the signal is assumed to be a single mode. However, several multimode signals were detected in this dataset. With the use of traditional methods to measure the dispersion, mode confusion occurs and the extracted dispersion curve jumps. To solve this problem, by combining the advantages of phase-matched filtering and dispersion compensation, we realized the automatic pickup of fundamental group velocity using reference phase velocity. From this, a Rayleigh wave group velocity map was obtained. The regional average phase velocity information was included in the inversion steps to reduce the uncertainty in the inversion of shear wave velocity. Finally, an S-wave velocity structure model was obtained within a depth of 500 m. The velocity structure was roughly layered and grew with depth. In the depth range of 240–320 m, obvious decreases in the S-wave velocity were observed. Compared with geothermal drilling data, this was speculated to be the reflection of a water-rich (confined water) sand layer. This study provides a technical approach for and a processing example of a high-density array, and its velocity model can be used as a reference for urban subsurface structure, underground space utilization, and earthquake disaster prevention and control.