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302 results on '"Zhang, Hengxu"'

190. Wide-area Frequency Based Event Location Estimation

Author

Xia, Tao, primary, Zhang, Hengxu, additional, Gardner, Robert, additional, Bank, Jason, additional, Dong, Jingyuan, additional, Zuo, Jian, additional, Liu, Yilu, additional, Beard, Lisa, additional, Hirsch, Peter, additional, Zhang, Guorui, additional, and Dong, Rick, additional

Published
2007
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194. Quantitative frequency security assessment method considering cumulative effect and its applications in frequency control.

Author

Zhang, Hengxu, Li, Changgang, and Liu, Yutian

Subjects
*WIND power, *SOLAR energy, *ELECTRIC power systems, *SYSTEMS design, *STOCHASTIC convergence
Abstract

Rising wind and solar generation penetrations change power system frequency behaviors significantly. Large disturbances may cause serious frequency deviations and lead to stability problems. It is important to provide a comprehensive and quantitative frequency security assessment (FSA) method for situation awareness and control decision-making in power systems. In this paper, a new FSA approach considering cumulative effect of frequency deviations on power equipment is proposed to quantitatively assess the impact of power system frequency deviations. It provides a unified expression of frequency security index (FSI) and has advantages of linearity, smoothness and monotonicity over existing methods. The FSI is calculated based on frequency trajectory obtained from wide-area measurement system (WAMS) or numerical simulations by which wind and solar generation can be taken into account. With sensitivity analysis of frequency security margin, the proposed FSA method has been applied to critical disturbance and critical control amount searching with frequency security constraints. The searching procedure is easy to implement, and computationally efficient with good convergence. The feasibility of the proposed FSA method and its applications are demonstrated on the 10-machine 39-bus New England test system. [ABSTRACT FROM AUTHOR]

Published
2015
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196. Fast analysis of active power-frequency dynamics considering network influence.

Author

Li, Changgang, Liu, Yutian, and Zhang, Hengxu

Abstract

Analysis of frequency dynamics due to large active power imbalance is an important but time-consuming task of power system operation. Ignoring influence of reactive power and voltage on active power-frequency dynamics, a new direct current loadflow based frequency response model (DFR) is proposed in this paper. It is developed with “flat voltage” assumption to simplify generating unit and load models. Unlike average system frequency model (ASF) and system frequency response model (SFR), network is preserved in DFR model with direct current network equations. Accuracy and efficiency of DFR model are verified test systems. DFR model finds a balance point between full-time domain simulation and ASF model. It is a promising method for on-line evaluations. [ABSTRACT FROM PUBLISHER]

Published
2012
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197. Optimal transmission planning based on quantitative security risk in uncertain environment.

Author

Ma, Changhui, Zhang, Pengfei, Zhang, Lei, and Zhang, Hengxu

Abstract

The present status of transmission planning is reviewed from various viewpoints and the new requirements of transmission planning resulting from development of electricity markets are discussed. In the deregulated electricity market, there is no longer centrally coordinated planning of new generation or closure of existing generation, which are basically at the generation companies' own discretion, and price bidding of electricity market results in more uncertain injection power. Transmission system planning in the electricity market environment has to be confronted with much more uncertain factors. In order to ensure a flexible transmission system, this paper extends the transmission planning model, which considers both static security risk and dynamic security risk, to deal with uncertain injection power at the buses. A global optimization framework is developed to resolve the problems caused by the multi-object mathematical model and uncertain power injections. A numerical example is presented to illustrate the validity of the method. [ABSTRACT FROM PUBLISHER]

Published
2012
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198. Mid-infrared free space wavelength beam splitter based on dual frequency reflective metalens

Author

Wu, Boqi, Chi, Yaodan, Zhang, Hengxu, Zhao, Chunlei, Zhao, Yang, Lv, Sa, and Yang, Jia

Abstract

We present a reflective metalens with a hybrid antenna structure, which can realize the beam splitting function of two wavelengths in free space. A key feature of our design is the presence of phase-independent regulation at two different wavelengths in each nanoresonator, which can generate a specific phase or a continuous sweep in the range of 0° to more than 300°. To demonstrate the wavefront manipulation ability of the array, we simulated the characteristics of wavelength beam splitting, especially the free space wavelength beam splitter with a focal length of 300 μm and a relative focal position of 100 μm.

Published
2022
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199. Evaluation of DFIGs' Primary Frequency Regulation Capability for Power Systems with High Penetration of Wind Power.

Author

Li, Changgang, Hang, Zhi, Zhang, Hengxu, Guo, Qi, Zhu, Yihua, and Terzija, Vladimir

Subjects
WIND power, INDUCTION generators, TURBINE generators, ELECTRIC power distribution grids, WIND turbines
Abstract

Accompanying the continuous increase in wind power penetration, the power system inertia is reduced, and the system frequency regulation performance deteriorates. Wind turbine generators are required to participate in primary frequency regulation (PFR) to support system frequency. Here, the PFR capability of the widely-used doubly-fed induction generator (DFIG) is evaluated to estimate the participation of the DFIG in system frequency control. The frequency regulation model of the DFIG is established and briefly discussed. The equivalent PFR droop coefficient is then deduced from the model using a small signal increment method to evaluate the DFIG's PFR capability. Key factors affecting the equivalent droop coefficient are studied, and the droop control is optimized to keep the equivalent droop coefficient in the desired range. The proposed method is verified utilizing a provincial power grid model of China. [ABSTRACT FROM AUTHOR]

Published
2020
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200. STEPS: A Portable Dynamic Simulation Toolkit for Electrical Power System Studies.

Author

Li, Changgang, Wu, Yue, Zhang, Hengxu, Ye, Hua, Liu, Yutian, and Liu, Yilu

Subjects
*DYNAMIC simulation, *APPLICATION program interfaces, *HYBRID systems, *SYSTEM analysis, *PYTHON programming language, *OPEN source software
Abstract

Numerical simulation is the key technique for large-scale power system analysis. Redistribution of global renewable power via international interconnections requires new simulation tools to study the interconnected systems with different nominal frequencies as a whole. This paper introduces an open-source simulation toolkit for electrical power systems (STEPS) hosted at Github. Its kernel is coded in C++ with major functions of power flow and electro-mechanical dynamic simulation. Flexible options are provided and configurable to improve power flow solution and dynamic simulation. Common devices and models are supported in STEPS for AC/DC hybrid system studies. The study of interconnected systems with different nominal frequencies is supported in STEPS for research of international interconnection. Application program interfaces are provided and wrapped with Python to enable high-level interfaces for general applications. STEPS is thread-safe, and parallel computation is supported in both kernel-level and task-level parallelization to accelerate simulation. It is portable and works on Windows and GNU/Linux platforms. Cases from small to large-scale systems are thoroughly tested to validate the toolkit with commercial packages as benchmarks. [ABSTRACT FROM AUTHOR]

Published
2021
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