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A New Definition of Short-circuit Ratio for Multi-converter HVDC Systems
Dengfeng Liu,Dongyuan Shi,Yinhong Li 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.5
In this paper, a new definition of short-circuit ratio concept for multi-converter HVDC systems is proposed. Analysis results of voltage interaction between converters show that the reactive power-voltage characteristic of a converter has a dominant effect on voltage interaction level compared with its active power-voltage characteristic. Such a relation between converter reactive power and voltage interaction level supports taking the former into account in the definition of short-circuit ratio concept for multi-converter systems. The proposed definition is verified by the method of maximum power curve for various system configurations. Furthermore, a formula to calculate transient overvoltage for multi-converter systems is derived based on the proposed definition, and the efficiency of the derived formula is verified.
A New Definition of Short-circuit Ratio for Multi-converter HVDC Systems
Liu, Dengfeng,Shi, Dongyuan,Li, Yinhong The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.5
In this paper, a new definition of short-circuit ratio concept for multi-converter HVDC systems is proposed. Analysis results of voltage interaction between converters show that the reactive power-voltage characteristic of a converter has a dominant effect on voltage interaction level compared with its active power-voltage characteristic. Such a relation between converter reactive power and voltage interaction level supports taking the former into account in the definition of short-circuit ratio concept for multi-converter systems. The proposed definition is verified by the method of maximum power curve for various system configurations. Furthermore, a formula to calculate transient overvoltage for multi-converter systems is derived based on the proposed definition, and the efficiency of the derived formula is verified.
Dengfeng Yang,Li’ang Cao,Yang Liu,Zhilian Zhang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10
Based on the analysis of the plateau performance for a 6 cylinder 8.6 L turbocharged diesel engine, a novel gas turbocharging system (GTS) is proposed to recover the engine power at high altitudes. Besides, a rolling-reflux combustor is designed to meet the structural requirements of GTS as well as to reduce the flow loss. Both the structure of the rolling-reflux combustor and the cycle thermal calculation of the GTS were described in detail in present work. The performance changes and the fuel consumption rate with engine speed at different altitudes of the GTS are compared to the original engine. Results show that when the altitude changes from 3 km to 5 km, the torque and power of the diesel engine with GTS can be recovered to that at sea level. Then, the particle image velocimetry (PIV) test is performed to study the cold flow field at the cylinder head of the rolling-reflux combustor, and the flow conditions are analyzed in detail. Finally, the flow bench is built and the aerodynamic experiment is carried out to verify the effectiveness of GTS.
An Integral Function Approach to the Exponential Stability of Linear Time-Varying Systems
Yu Yao,Kai Liu,Jian Guo,Dengfeng Sun,Venkataramanan Balakrishnan 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.6
This paper studies the exponential stability of linear time-varying (LTV) systems using the recent pro-posed integral function. By showing the properties of the integral function and applying the Bellman-Gronwall Lemma, a sufficient and necessary condition for the exponential stability of LTV systems is derived. Furthermore, the exponential decay rate of the system trajectories can be obtained by computing the radii of convergence of integral function. The algorithm for computing the integral function is also developed and two classical examples are given to illustrate the proposed approach.
Xinfa Sun,Yucheng Zhao,Weiming Yang,Wenyu Li,Dengfeng Yang,Haishun Liu 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.12
The additive manufacturing of titanium alloy parts has important scientific significance and practical value. Controllingthe distribution of residual stress caused by the high cooling rate and temperature gradient is the key to regulating the performanceof devices obtained from additive manufacturing. In this work, the effects of the interlayer scanning angle on theresidual stress in Ti–6Al–4V parts manufactured by selective laser melting were investigated by finite element simulations. We studied how changing the interlayer deflection angle alleviated residual stress under different energy inputs. The resultsshowed that the residual stress in the z-direction was reduced by the deflection angle of 67° and 90°, and the non-uniformdistribution of residual stress was reduced by a deflection angle of 67°. The combination of a chessboard pattern and interlayerdeflection angle greatly alleviated the generation of residual stress. This work has important guiding significance forthe additive manufacturing design of high-quality and high-performance titanium alloy devices.