ON CANTOR SETS AND PACKING MEASURES

Chun Wei,Sheng-You Wen 대한수학회 2015 대한수학회보 Vol.52 No.5

For every doubling gauge g, we prove that there is a Cantor set of positive finite Hg-measure, Pg-measure, and Pg 0 -premeasure. Also, we show that every compact metric space of infinite Pg 0 -premeasure has a compact countable subset of infinite Pg 0 -premeasure. In addition, we obtain a class of uniform Cantor sets and prove that, for every set E in this class, there exists a countable set F, with F = E∪F, and a doubling gauge g such that E ∪ F has different positive finite Pg-measure and Pg 0 -premeasure.

Online Parameter Identification for State of Power Prediction of Lithiumion Batteries in Electric Vehicles Using Extremum Seeking

Chun Wei,Mouhacine Benosman,Taesic Kim 제어·로봇·시스템학회 2019 International Journal of Control, Automation, and Vol.17 No.11

Accurate state-of-power (SOP) estimation is critical for building battery systems with optimized performance and longer life in electric vehicles and hybrid electric vehicles. This paper proposes a novel parameter identification method and its implementation on SOP prediction for lithium-ion batteries. The extremum seeking algorithm is developed for identifying the parameters of batteries on the basis of an electrical circuit model incorporating hysteresis effect. A rigorous convergence proof of the estimation algorithm is provided. In addition, based on the electrical circuit model with the identified parameters, a battery SOP prediction algorithm is derived, which considers both the voltage and current limitations of the battery. Simulation results for lithium-ion batteries based on real test data from urban dynamometer driving schedule (UDDS) are provided to validate the proposed parameter identification and SOP prediction methods. The proposed method is suitable for real operation of embedded battery management system due to its low complexity and numerical stability.

Investigation of expanding-folding absorbers with functionally graded thickness under axial loading and optimization of crushing parameters

Chunwei Zhang,Limeng Zhu,Farayi Musharavati,Afrasyab Khan,Tamer A. Sebaey 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.6

In this study, a new type of energy absorbers with a functionally graded thickness is investigated, these type of absorbers absorb energy through expanding-folding processes. The expanding-folding absorbers are composed of two sections: a thin-walled aluminum matrix and a thin-walled steel mandrel. Previous studies have shown higher efficiency of the mentioned absorbers compared to the conventional ones. In this study, the effect of thickness which has been functionally-graded on the aluminum matrix (in which expansion occurs) was investigated. To this end, initial functions were considered for the matrix thickness, which was ascending/descending along the axis. The study was done experimentally and numerically. Comparing the experimental data with the numerical results showed high consistency between the numerical and experimental results. In the final section of this study, the best energy absorber functionally graded thickness was introduced by optimization using a thirdorder genetic algorithm. The optimization results showed that by choosing a minimum thickness of 1.6 mm and the exponential coefficient of 3.25, the most optimal condition can be obtained for descending thickness absorbers.

Three-Phase Four-Wire Inverter Topology with Neutral Point Voltage Stable Module for Unbalanced Load Inhibition

Chunwei Cai,Pufeng An,Yuxing Guo,Fangang Meng 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.5

A novel three-phase four-wire inverter topology is presented in this paper. This topology is equipped with a special capacitor balance grid without magnetic saturation. In response to unbalanced load and unequal split DC-link capacitors problems, a qusi-full-bridge DC/DC topology is applied in the balance grid. By using a high-frequency transformer, the energy transfer within the two split dc-link capacitors is realized. The novel topology makes the voltage across two split dc-link capacitors balanced so that the neutral point voltage ripple is inhibited. Under the condition of a stable neutral point voltage, the three-phase four-wire inverter can be equivalent to three independent single phase inverters. As a result, the three-phase inverter can produce symmetrical voltage waves with an unbalanced load. To avoid forward transformer magnetic saturation, the voltages of the primary and secondary windings are controlled to reverse once during each switching period. Furthermore, an improved mode chosen operating principle for this novel topology is designed and analyzed in detail. The simulated results verified the feasibility of this topology and an experimental inverter has been built to test the power quality produced by this topology. Finally, simulation results verify that the novel topology can effectively improve the inhibition of an inverter with a three-phase unbalanced load while decreasing the value of the split capacitor.

Design of a misalignment‑tolerant wireless charging system based on multidimensional cross‑coupling for autonomous underwater vehicles

Chunwei Cai,Qinyuan Cui,Xiangyao Meng,Shuai Wu,Wenping Chai 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.12

In this paper, a misalignment-tolerant wireless charging system based on multidimensional cross-coupling for autonomous underwater vehicles (AUVs) is proposed. The four transmitting coils of the proposed system magnetic coupler are divided evenly into two pairs as bipolar transmitting units. Subsequently, the uniform multi-dimensional horizontal magnetic flux can be obtained by two current vectors with a 90° phase difference exciting in the bipolar transmitting units. For the receiver, a couple of orthogonal coils are designed to form cross-coupling with the transmitter to pick up the maximum magnetic flux. Then, the proposed magnetic coupler combined with the proposed transmitter and receiver is designed through finite element analysis. Finally, a 900 W prototype is built and tested. Experimental results show that the system has stable output characteristics in the ranges of a − 20° to 20° rolling misalignment and a − 30 to 30 mm axial misalignment.

A Novel Zero-Voltage-Switching Push-Pull Forward Converter with a Parallel Resonant Network

Chunwei Cai,Chunyu Shi,Yuxing Guo,Zi Yang,Fangang Meng 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.1

A novel zero-voltage-switching (ZVS) push-pull forward converter with a parallel resonant network is presented in this paper. The novel topology can provide a releasing loop for the energy storage in a leakage inductor for the duration of the power switching by the resonant capacitors paralleled with the primary windings of the transformer. Then the transformer leakage inductor is utilized to be resonant with the parallel capacitor, and the ZVS operation is achieved. This converter exhibits many advantages such as lower duty-cycle losses, limited peak voltage across the rectifier diodes and a higher efficiency. Furthermore, the operating principles and key problems of the converter design are analyzed in detail, and the ZVS conditions are derived. A 500W experimental converter prototype has been built to verify the effectiveness of the proposed converter, and its maximum efficiency reaches 94.8%.

Effects of Cloud Microphysical Latent Heat on a Heavy Rainstorm in Beijing

Chunwei Guo,Hui Xiao,Huiling Yang,Liang Zhai,Xiangchen Kong 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.3

The latent heat produced by cloud microphysical processes can greatly affect the thermal and dynamic structure of the atmosphere, as well as the development and evolution of clouds and precipitation. In this study, to examine the consequences of different kinds of latent heat produced by microphysical processes, four sensitivity tests were conducted based on the control simulation results of a heavy rainstorm occurred in Beijing on 21 July 2012 using theWeather Research and Forecasting Model (WRF).Without the latent heat absorption of evaporation, the convective cloud system developed stronger, and the accumulated precipitation amount increased.Without the latent heat release of deposition, the transit time of the surface front was delayed; in addition, the convective cloud system developed weakly. The accumulated conversion amounts of microphysical processes and the accumulated rainfall amount in the deposition adiabatic test were far less than those in the other tests.Without the latent heat of melting and freezing, the convective cloud system did not change substantially, and there was only a minor effect on precipitation. Hydrometeor production exhibited some changes related to precipitation in the five tests. The latent heat produced by the convective system varied substantially in the five tests with a change in the latent heat budget.

Application of Lagrangian approach to generate P-I diagrams for RC columns exposed to extreme dynamic loading

Zhang, Chunwei,Abedini, Masoud Techno-Press 2022 Advances in concrete construction Vol.14 No.3

The interaction between blast load and structures, as well as the interaction among structural members may well affect the structural response and damages. Therefore, it is necessary to analyse more realistic reinforced concrete structures in order to gain an extensive knowledge on the possible structural response under blast load effect. Among all the civilian structures, columns are considered to be the most vulnerable to terrorist threat and hence detailed investigation in the dynamic response of these structures is essential. Therefore, current research examines the effect of blast loads on the reinforced concrete columns via development of Pressure- Impulse (P-I) diagrams. In the finite element analysis, the level of damage on each of the aforementioned RC column will be assessed and the response of the RC columns when subjected to explosive loads will also be identified. Numerical models carried out using LS-DYNA were compared with experimental results. It was shown that the model yields a reliable prediction of damage on all RC columns. Validation study is conducted based on the experimental test to investigate the accuracy of finite element models to represent the behaviour of the models. The blast load application in the current research is determined based on the Lagrangian approach. To develop the designated P-I curves, damage assessment criteria are used based on the residual capacity of column. Intensive investigations are implemented to assess the effect of column dimension, concrete and steel properties and reinforcement ratio on the P-I diagram of RC columns. The produced P-I models can be applied by designers to predict the damage of new columns and to assess existing columns subjected to different blast load conditions.

Three-Phase Four-Wire Inverter Topology with Neutral Point Voltage Stable Module for Unbalanced Load Inhibition

Cai, Chunwei,An, Pufeng,Guo, Yuxing,Meng, Fangang The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.5

A novel three-phase four-wire inverter topology is presented in this paper. This topology is equipped with a special capacitor balance grid without magnetic saturation. In response to unbalanced load and unequal split DC-link capacitors problems, a qusi-full-bridge DC/DC topology is applied in the balance grid. By using a high-frequency transformer, the energy transfer within the two split dc-link capacitors is realized. The novel topology makes the voltage across two split dc-link capacitors balanced so that the neutral point voltage ripple is inhibited. Under the condition of a stable neutral point voltage, the three-phase four-wire inverter can be equivalent to three independent single phase inverters. As a result, the three-phase inverter can produce symmetrical voltage waves with an unbalanced load. To avoid forward transformer magnetic saturation, the voltages of the primary and secondary windings are controlled to reverse once during each switching period. Furthermore, an improved mode chosen operating principle for this novel topology is designed and analyzed in detail. The simulated results verified the feasibility of this topology and an experimental inverter has been built to test the power quality produced by this topology. Finally, simulation results verify that the novel topology can effectively improve the inhibition of an inverter with a three-phase unbalanced load while decreasing the value of the split capacitor.

A Novel Zero-Voltage-Switching Push-Pull Forward Converter with a Parallel Resonant Network

Cai, Chunwei,Shi, Chunyu,Guo, Yuxing,Yang, Zi,Meng, Fangang The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.1

A novel zero-voltage-switching (ZVS) push-pull forward converter with a parallel resonant network is presented in this paper. The novel topology can provide a releasing loop for the energy storage in a leakage inductor for the duration of the power switching by the resonant capacitors paralleled with the primary windings of the transformer. Then the transformer leakage inductor is utilized to be resonant with the parallel capacitor, and the ZVS operation is achieved. This converter exhibits many advantages such as lower duty-cycle losses, limited peak voltage across the rectifier diodes and a higher efficiency. Furthermore, the operating principles and key problems of the converter design are analyzed in detail, and the ZVS conditions are derived. A 500W experimental converter prototype has been built to verify the effectiveness of the proposed converter, and its maximum efficiency reaches 94.8%.