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Your search keyword '"Hao, Zhiguo"' showing total 109 results
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109 results on '"Hao, Zhiguo"'

16. CT Saturation Detection and Compensation: A Hybrid Physical Model- and Data-Driven Method.

Author

Yang, Songhao, Zhang, Yubo, Hao, Zhiguo, Lin, Zexuan, and Zhang, Baohui

Subjects
CURRENT transformers (Instrument transformer), SHORT-circuit currents, FAULT currents, DATA modeling, MAGNETIC flux
Abstract

Current transformer (CT) saturation is one of the dominant causes of relay protection devices’ malfunctions, which pose a threat to the safe operation of the power system. To address this problem, we propose a hybrid physical model- and data-driven method. The method firstly detects the CT saturation and then compensates it to reproduce the real waveform. Considering the multi-factor and strong nonlinearity of CT saturation, a data-driven model, namely the Fully Convolutional Network (FCN), is built to detect the operation status of CT. As for the compensation, a physical model of short-circuit current is used for its conciseness and universality. Through tactfully integrating the data model and the physical model, the proposed method is endowed with two major merits: the arduous adjustment of universal thresholds and parameters in existing methods is avoided, and the deficiency in generalization and interpretability of the data-driven method is assuaged. Simulation and experimental results verify the effectiveness of the proposed method. Furthermore, its application potential to future protection is explored. [ABSTRACT FROM AUTHOR]

Published
2022
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38. Holomorphic Embedding Power Flow for AC/DC Hybrid Power Systems Using Bauer's Eta Algorithm.

Author

Zhao, Yudi, Li, Chongtao, Ding, Tao, Hao, Zhiguo, and Li, Fangxing

Subjects
HYBRID power systems, HYBRID power, HIGH voltages
Abstract

In this paper, the holomorphic embedding power flow method (HELM) is designed to solve the AC/DC hybrid power flow equations. According to the power flow model of the high voltage direct current systems (HVDC), an appropriate embedding technique with three recursive algorithms is developed for three different control modes, which is compatible with existing achievements of HELM for AC systems. In this method, the advantages of HELM, such as non-iterative, deterministic and non-ambiguous, are fully retained. In addition, a new calculation strategy based on Bauer's Eta algorithm is designed for the implementation of Padé approximations and the recursive process to avoid redundant calculations without reducing accuracy. In order to verify the reliability and effectiveness of the proposed extended HELM, several power flow cases with different scale are studied by HELM and traditional iterative method. [ABSTRACT FROM AUTHOR]

Published
2021
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39. The research of sub synchronous oscillation in PMSG wind farm

Author

Zhang Baohui, He Qifei, Gao Feng, and Hao Zhiguo

Subjects
Engineering, Crowbar, Wind power, business.industry, Oscillation, 020209 energy, 020208 electrical & electronic engineering, 02 engineering and technology, Permanent magnet synchronous generator, AC power, Wind speed, Power (physics), Electric power system, Control theory, 0202 electrical engineering, electronic engineering, information engineering, business
Abstract

Under some certain conditions, the wind power farm which accesses to the power system may appears the phenomenon of sub synchronous oscillation (SSO). Doubly fed induction generator (DFIG) connected to power grid usually transports power energy by series compensated AC transmission or DC transmission, and the theory of SSO in DFIG wind farm is relatively clear and has been researched mostly. Permanent magnet synchronous generator (PMSG) wind farm connected to weak AC power grid also appears more SSO accidents, which causes multiple PMSG to take off the power grid and the damage of crowbar circuits. Because PMSG wind farm still appears sub synchronous oscillation accidents in the absence of series compensation or DC transmission when transmitted to the outside, SSO in PMSG wind farm is a new type of oscillation waiting to be researched. In order to investigate the mechanism of problem, the equivalent system model of D-PMSG connected with power grid was established in this paper. Through the transfer function, eigenvalue value analysis and electromagnetic transient simulation, the mechanism of sub synchronous oscillation was revealed. The influence on its characteristics from many factors was also analyzed, including delay time and the wind speed. The results show that the voltage delay link of controller feed forward in network side is the direct cause of sub synchronous oscillation. Finally, potential danger and its suppression measures of the SSO problem were discussed according to the characteristics of sub synchronous oscillation of D-PMSG wind farm.

Published
2016

40. Inrush current discrimination in power transformer differential protection using wavelet packet transform based technique

Author

Liu Zhiyuan, Hao Zhiguo, Muhammad Farasat Abbas, and Zhang Guanjun

Subjects
Engineering, business.industry, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, Fault (power engineering), Inrush current, Wavelet packet decomposition, Wavelet, Software, Three-phase, Electronic engineering, Minimum description length, business, MATLAB, computer, computer.programming_language
Abstract

In this paper wavelet packet transform based technique is implemented to discriminate the inrush current from internal fault currents of three phase 240 MVA, 345/38.5 KV star delta connected power transformer. The Daubechies (db4) mother wavelet with two number of level of resolution is found to be optimal in providing information to discriminate the inrush currents from internal fault currents of power transformer. Minimum description length (MDL) criteria is used to select the optimal mother wavelet and number of level of resolution. In this paper a model of three phase star-delta connected power transformer is built using PSCAD software to get the samples of differential currents. Wavelet packet transform with multi resolution analysis is implemented using MATLAB wavelet tool box on these samples for discrimination purpose. The results show this technique is very useful over many traditional techniques for the discrimination of inrush currents.

Published
2016

41. An Accurate and Fast Start-Up Scheme for Power System Real-Time Emergency Control.

Author

Yang, Songhao, Hao, Zhiguo, Zhang, Baohui, and Hojo, Masahide

Subjects
*REAL-time control, *MEASUREMENT errors, *TEST systems
Abstract

With the development of PMUs in power systems, the response-based real-time emergency control becomes a promising way to prevent power outages when power systems are subjected to large disturbances. The first step in the emergency control is to start up accurately and fast when needed. To this end, this paper proposes a well-qualified start-up scheme for the power system real-time emergency control. Three key technologies are proposed to ensure the effectiveness of the scheme. They are, an instability index, a Critical Machines (CMs) identification algorithm, and a two-layer single machine infinite bus (SMIB) equivalence framework. The concave–convex-area-based instability index shows good accuracy and high reliability, which is used to identify the transient instability of the system. The CMs identification algorithm can track the changes of CMs and form the proper SMIB system at each moment. The new two-layer SMIB equivalence framework, compared with conventional ones, can significantly reduce the communication burden and improve the computation efficiency. The simulations in two test power systems show that the scheme can identify the transient instability accurately and fast to restore the system to stability after the emergency control. Besides, the proposed method is robust to measurement errors, which enhances its practicality. [ABSTRACT FROM AUTHOR]

Published
2019
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42. Study of the interaction between photovoltaic inverter and power quality harmonic and its suppression method

Author

Zhang Shifeng, Lei Da, Feng Lei, Hao Zhiguo, Yang Yunlei, and Chang Xiao

Subjects
Engineering, business.industry, 020209 energy, Impedance matching, Impedance bridging, Quarter-wave impedance transformer, 02 engineering and technology, Input impedance, Equivalent impedance transforms, Control theory, 0202 electrical engineering, electronic engineering, information engineering, Harmonic, Damping factor, Output impedance, business
Abstract

In the process of photovoltaic (PV) generator was connected to the grid, in order not to affect the power quality of grid, the current harmonic component from PV inverter needs to meet the relevant interconnection standards. This topic put-forwards a method based on impedance analysis, which analyses the harmonic interaction between the photovoltaic (PV) grid-connected inverter and power grid containing background harmonic. The basic reason of harmonic resonance problem caused by grid-connected PV system is duo to the existence of impedance intersection at the point of common connection (PoC), which is determined by the equivalent output impedance of the inverter and the equivalent impedance of the grid. At that intersection point, the sum of the impedance reduced to the minimum value and the current amplitude significantly increased, which leads to the harmonic resonance phenomenon. To analyze this problem, this paper established the NORTON equivalent model of the inverter, developed the expression for the equivalent output impedance of the inverter, and analyzed the reasonable range of the equivalent inverter output impedance based on the maximum limit of photovoltaic (PV) grid harmonic voltage, current and harmonic resonance conditions. On this basis, the PI control and the quasi PR control methods were used respectively to adjust the equivalent output impedance of inverter. Based on the simulation experiment, the equivalent output impedance was effectively suppressed, and the harmonic resonance phenomenon was avoided.

Published
2016

43. Analysis of photovoltaic power generation system low voltage ride through control during asymmetric fault

Author

Wang Jin, Zhang Jinhua, and Hao Zhiguo

Subjects
Operating point, Engineering, 021103 operations research, business.industry, 020208 electrical & electronic engineering, 0211 other engineering and technologies, Hardware_PERFORMANCEANDRELIABILITY, 02 engineering and technology, Voltage optimisation, Fault (power engineering), Maximum power point tracking, Power (physics), Control theory, 0202 electrical engineering, electronic engineering, information engineering, Transient (oscillation), Low voltage ride through, business, Power control
Abstract

The electromagnetic transient model of photovoltaic power generation system is established based on PSCAD/EMTDC platform. The mechanism that 100Hz fluctuations appearing of PV output power and PV array operating point during asymmetric fault are simulated and theoretical analyzed. The paper proposes a positive and negative sequence separation control strategy, to filter the negative sequence current, making PV output current do not contain negative sequence component and outputting standard sinusoidal current waveform during asymmetric fault. The paper also proposes a DC voltage fluctuation suppression control strategy, to eliminate the DC voltage fluctuations and make the PV array operating point stable. Finally, simulation verification is made on PSCAD/EMTDC platform.

Published
2016

44. Research of VFTO in 110kV minimized GIS

Author

He Qifei, Hao Zhiguo, and Guo Jie

Subjects
Engineering, Emtp, Ground, business.industry, Electrical engineering, Disconnector, Fault (power engineering), law.invention, Overvoltage, law, Electrical equipment, Electronic engineering, business, Transformer, Circuit breaker
Abstract

110kV minimized gas insulated substation (GIS) has been widely used in China, due to its great electrical properties. The closing or opening operation of disconnector switches (DS) and circuit breaker (CB), and single-phase ground fault are all probable to cause the very fast transient overvoltage (VFTO), which is a threat to the power system. Compared to the structure of higher voltage GIS, three-phase electrical equipment in 110kV minimized GIS is placed in the same box. So we must establish the three-phase model of GIS and then calculate its VFTO. This paper referred to 110 kV minimized GIS power system. Using the Electro-magnetic Transient Program (EMTP), numerical simulation and analysis of VFTO in different DS, CB operation modes and single-phase grounding fault were carried out. And the data of VETO under different operation modes, including the frequency, amplitude, steepness and waveform were obtained. Then it calculated and analyzed the influence on VFTO of length of branch bus and transformer entrance capacitance, in order to provide reference basis to the structure design of GIS and analysis of VFTO.

Published
2015

50. Optimal storage sizing for composite energy storage and wind in Micro grid

Author

Wang Xiao-li, Baohui Zhang, Chao Guang, Hao Zhiguo, Zhang Shifeng, and Ye Zhigang

Subjects
Pumped-storage hydroelectricity, Battery (electricity), Engineering, Wind power, Power station, business.industry, Computer data storage, Control engineering, Grid energy storage, business, Energy storage, Sizing, Automotive engineering
Abstract

Energy storage system is necessary to maintain steady operation of the micro-grid and decrease its influence on the distribution grid. In this paper, some research has been carried on in optimal storage sizing in composite energy storage system in wind micro grid. The energy storage system is composed of battery and fly-wheel, which combines advantages of both sides. Cost function is used as the objective function and the loss of load and the generation spilled are considered during the calculation. We considered the constraint functions from the power, energy aspects and set rules for composite storage system. The optimization for a one-week example has been studied in this paper. After summary and comparison, some conclusions are obtained.

Published
2014

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