Discussion on Operational Risk and Sustainability of Beijing-Tianjin Intercity HSR

Hongchang Li,Gaiping Zhang 한국환경경영학회 2010 한국환경경영학회 학술대회 Vol.2010 No.-

Current Self-Balancing Mechanism in ZVS Full-Bridge Converters

Hongchang Li,Michael A. de Rooij,Jingyang Fang,Haoxin Yang,Yi Tang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Full-bridge converters are widely used in isolated dc-dc conversion and wireless power transfer systems. A full-bridge converter can operate in zero-voltageswitching (ZVS) mode with the assistance of an inductive branch that connects the two switch nodes in parallel with the load. The inductive branch provides a ZVS current and has a very low resistance. A tiny volt-second imbalance between the switch nodes may cause a large current bias on the branch. However, it can be demonstrated experimentally that the current on the branch can be almost self-balanced without any dc blocking capacitor or balancing control. This paper quantitatively studies the current self-balancing mechanism and shows that the dead-time switch-node voltage can give a strong negative feedback effect that pushes the current bias toward zero. Experimental verification was carried out on a gallium-nitride device-based converter.

Silk Nonwoven: Recycling and Upcycling of Waste Silk into Bio-based Materials with High Value-Added Properties

Hongchang Wang,Liyao Cao,Yuling Li,Run Wen,Guangbiao Xu 한국섬유공학회 2023 Fibers and polymers Vol.24 No.10

With the increasing awareness of human environmental protection, the development of biodegradable bio-based materials has received more attention. As the off-cuts of silk, a natural protein fiber, waste silk still retains excellent properties such as biodegradability and biocompatibility, recycling and utilization of waste silk is currently very limited. To find a possible method to recycle low-cost waste silk and process it into high-value-added products, in this work, the waste silk from the silk spinning process was prepared into silk nonwoven (SN) with excellent air permeability, softness, water–oil amphiphilicity, biodegradability, and ultraviolet resistance by the wet laid process. The results showed that the uniform SN could be prepared when the alkali concentration was higher than 0.6%. The permeability of SN is higher than 80 mm/s, and the bending stiffness is lower than 0.085gf·cm2/cm. Notably, SN possesses entanglement at both fiber and fibril levels, enabling it to achieve a base strength of 0.58 MPa without additional reinforcement. The water contact angle and oil contact angle of SN were below 40° and 50°, respectively. The ultraviolet protection of SN-0.6 was classified as very good, with a degradation rate of 4.31% of SN-0.6 after 30 days of burial. The present research shows that silk nonwoven is a potential bio-based material with promising applications in the field of packaging and cleaning.

Three‑dimensional geometric optimization of WPT coils for coupling coefficient maximization

Weipeng Gao,Hongchang Li,Yi Tang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.5

High-power transfer capacity is a major design objective of wireless power transfer (WPT) systems. For magnetic couplingbased WPT systems, increasing the coupling coefficient of power transceiver coils is the key to improving the power transfer capacity under specified limits on resonant current and voltage stresses. An effective method to increase the coupling coefficient is to optimize the geometric distributions of the coil wire loops. The obstacle of the optimization is the high computational complexity caused by the high geometric degrees of freedom, especially for multiturn coils. This paper proposes a 3D optimization method to reduce the computational complexity and give the optimal wire loop distributions for the maximum coupling coefficient. Design examples show that the optimal wire loop distribution is nonuniform. The smallest loop-to-loop spacing occurs near the front outer circumferences of the coils. Compared with common spiral and helix coils, the optimization can achieve 20% increase in coupling coefficient. The increase in coupling coefficient and power transfer capacity is verified through experiments.

High-Speed Milling of Hardened Mold Steel P20 with Minimum Quantity Lubrication

Shixiong Wu,Hongchang Liao,Suyang Li,Jundong Bi,Zhiyang Li 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.5

Strong thermal–mechanical coupling and rapid tool failure easily occur in the milling process of hardened steel with solid end mills. This work investigates the effectiveness of minimum quantity lubrication (MQL) during high-speed milling of hardened mold steel. Three kinds of spraying modes were designed in the experiment. They are namely the spraying ways to the flank face (MQL-F), to the rake face (MQL-R) and to the rake and flank faces (MQL-FR). The cutting forces, tool wear, and chips when using the MQL modes and compressed air cooling mode (CAIR-F) were compared, and the wear mechanism and lubrication mechanism were further analyzed. The results showed that the tool wear values and milling forces of several MQL modes were significantly lower than those with CAIR-F. The milling force and tool wear values were successively reduced using MQL-R, MQL-F, and MQL-FR, with better lubrication of the rake face resulting in a smaller curvature radius for the chip. Abrasion wear, adhesion/attrition wear, and flaking/chipping were the main wear mechanisms. The MQL-FR method was the optimal method of the MQL modes. It could effectively reduce the cutting contact stress and unit cutting energy, and obviously reduced wear phenomena such as adhesion and chipping.

Synthesis and Curing of AUT-PNIMMO with Three Functional Groups

Xiaochuan Wang,Ping Li,Xianming Lu,Hongchang Mo,Minghui Xu,Ning Liu,Yuanjie Shu 한국고분자학회 2019 폴리머 Vol.43 No.4

T-PNIMMO with three functional groups was synthesized by cationic ring opening polymerization of NIMMO (3-nitratomethyl-3-methyloxetane) in the presence of TMP (trimethylolpropane) catalyzed by BF3·OEt2. Then AUTPNIMMO was synthesized by T-PNIMMO and allyl isocyanate. The polymers were characterized by FTIR, 1H NMR, 13C NMR, and their thermal stability was estimated by DSC. Moreover, tensile testing was used to evaluate the mechanical properties of polyurethane elastomer based on T-PNIMMO and toluene-2,4-diisocyanate (TDI), and isoxazoline elastomer based on AUT-PNIMMO and tetramethyl-terephthalobisnitrile oxide (TTNO). This showed an increase of tensile strength from 2.0 to 4.0 MPa and elongation at break from 150% to 500%, respectively. These results indicated that AUTPNIMMO exhibited a good thermal stability, had satisfactory mechanical properties and was expected to be used in the composite solid propellant and polymer bonded explosives.

Sensorless Control Strategy of Permanent Magnet Synchronous Motor Based on Fuzzy Sliding Mode Controller and Fuzzy Sliding Mode Observer

Zou Xinhong,Ding Hongchang,Li Jinhong 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3

This paper proposes a permanent magnet synchronous motor sensorless control strategy based on fuzzy sliding mode controller and fuzzy sliding mode observer. In order to improve the response speed of the system and the anti-interference ability of the system, a sliding mode controller (SMC) is used to replace the PI regulator in the speed loop. In order to suppress the chattering caused by sliding mode variable structure control and reduce the error caused by chattering, the SMC and sliding mode observer (SMO) are improved. An integral sliding mode surface is used in the SMC, and a continuous saturation function is used instead of a discontinuous sign function. The square of the speed error is introduced in the switch term of the exponential approaching law to improve the dynamic quality of approaching motion. The switching function in the SMO also uses a saturation function to suppress chattering caused by switching. Fuzzy rules are established to adaptively adjust the switching gain of the SMO and the parameters in the SMC’s reaching law, which further improves the performance of the control system. Simulations and experiments prove that the proposed control strategy has the characteristics of small chattering, fast response speed, and strong robustness.

Operating area analysis and design of WPT systems with MEPT control

Weipeng Gao,Yanfang Fan,Chengxuan Wang,Kangping Wang,Hongchang Li 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.4

Coupled resonant tanks are key parts of wireless power transfer (WPT) systems with magnetic resonant coupling. Researchers have proposed different resonant tank design methods to improve power transfer efficiency, increase power density, reduce magnetic flux leakage, or lower VA ratings. Practical WPT systems require a closed-loop control to cope with the variations of operation conditions, but only a few studies have considered the safe operating area (SOA) of systems under closed-loop control in resonant tanks designs. In this work, we analyze closed-loop voltage and current stress characteristics from the aspect of maximum efficiency point tracking control and derive the SOA with a given set of stress limits. Then, we propose a resonant parameter design method of allowing the system to safely operate with any specified range of coupling coefficient and output power. The current stress was minimized in the design to reduce the conductive loss. As for the verification, an experimental prototype was built according to the design method.

Hierarchical Model Predictive Control of Modular Multilevel Matrix Converter for Low Frequency AC Transmission

Lang Huang,Xu Yang,Bin Zhang,Liang Qiao,Hongchang Li,Mofan Tian 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The modular multilevel matrix converter (M3C) applied to a low frequency alternating current (LFAC) transmission system is investigated. Due to the complexity and tight coupling of the converter, a novel hierarchical model predictive control (MPC) scheme with a cascaded structure of power control, capacitor voltage averaging and balancing control for M3C is proposed. The terminal behavioral model of M3C is derived out and the fast separated space-vectors approximation method is realized. The proposed scheme clearly achieves the system-level multi-objective control without the empirical procedure of the weighting factor design and significantly reduces the computational cost. This is the first time to apply the MPC to a converter in a hierarchical structure. Simulation results of a 7-level M3C are provided to illustrate the system’s performance.