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Failure analysis of fan mill in thermal power plant 68

Failure analysis of fan mill in thermal power plant

68th Society for Machinery Failure Prevention Technology Conference: Technology Solutions for Affordable Sustainment, MFPT 2014

作者： Liu, Chao Jiang, Dongxiang Chu, Fulei Department of Mechanical Engineering Tsinghua University Beijing100084 China State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Thermal Engineering Tsinghua University Beijing100084 China

Fan mill is an important device in thermal plants, which supply coal power to boiler. Crack failures recently occurred in pulverizing wheels of fan mills in a power plant in China. The cracks happens in quite a few pulverizing wheels and they affect the normal operation. To find out the root cause of the cracks, Finite Element Analysis (FEA) of the pulverizing wheel is carried out in this work. The assembly with real dimensions is modelled to calculate the concentrated stress and strain with centrifugal load, driving load, and operational temperature taken into account. Contact effects are included in the finite element model as well as nonlinear material property. Based on the analysis, the crack causes are determined: (i) the initial stress exceeds the yield limit in normal operational condition, resulting low safety coefficient;(ii) the stress increases significantly in the worn pulverizing wheel, where the risk of failure is greatly increased.

关键词： Cracks

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Design of grounding system for wind-photovoltaic-energy storage Hybrid power station 4

Design of grounding system for wind-photovoltaic-energy stor...

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2014 4th International Conference on High Voltage Engineering and Application, ICHVE 2014

作者： Lin, Cheng Sen, Wang Zhizhong, Li Jing, Wang Bo, Zhang Weidong, Shi Power Grid Grounding Engineering Laboratory of State Grid Corporation of China Xi'an Shaanxi710049 China State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing100084 China China Electric Power Research Institute Beijing100192 China

ISBN: (纸本)9781479966134

Based on the Chinese demonstration project of Zhangbei wind-photovoltaic-energy storage (W-PV-ES) hybrid generation, which is the world's biggest and Chinese first new energy utilization platform, the design of grounding system for W-PV-ES Hybrid power station was studied in this paper. Firstly according to the soil resistivity of that power station, measured by the Wenner four-electrode method, the soil constitution, that is three-level layer in summer and is four-level layer including an 1.5m high and 2000·m permafrost in winter, was got, and grounding grid models of W-PV-ES hybrid generation was studied. Then grounding system of that W-PV-ES station was designed, that was the single wind turbine uses concentric bicyclic earth electrode, whose radius are 7m and 10m, and the PV-ES power station uses one horizontal earth electrode every 10m in one direction, every 50m in another direction, and there are 2.5m long vertical grounding rods every 10m around the PV-ES station. For the substation, we adopt the horizontal grounding grid with a 10m interval between conductors and 0.8m burial depth. On the condition that earth current is 10KA, the earth's surface potential, contact potential, and step potential were simulated. After that safety of 35kV system and secondary system were analyzed, when there was short trouble. Finally influence on earth resistance by different grounding materials was studied, galvanized flat steel and copper material was presented as two kinds of selection schemes of grounding materials for considering economic considerations. © 2014 IEEE.

关键词： Energy storage

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A combined PWM algorithm to eliminate spikes of common mode voltages

A combined PWM algorithm to eliminate spikes of common mode ...

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IEEE Conference and Expo Transportation Electrification Asia-Pacific (ITEC Asia-Pacific)

作者： Fang Liu Zhengming Zhao Ting Lu Shusheng Wei Kai Li Sate Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China

Various pulse width modulation strategies have been proposed to reduce the common mode voltage (CMV) in the variable speed motor drive system. However, unexpected voltage spikes appear as a result of the dead time effect. This paper investigates the principles of those reduced CMV PWM (RCMV PWM) methods mathematically and analyzes the reasons for those voltage spikes theoretically and experimentally. Results suggest that three-dimension active zero state PWM and near state PWM can effectively eliminate the spikes even with the dead time effect taken into consideration. Then a combined algorithm using those two methods is proposed, and it covers the linearity modulation region as large as the conventional space vector PWM. The switchover between those two methods is smooth along with the variation of the modulation index. Experimental results show that no distortion is brought to the modulation wave and verify the validity and feasibility of the proposed combined algorithm.

关键词： Pulse width modulation Vectors Switches Inverters Integrated circuits Induction motors

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Direct heuristic dynamic programming method for power system stability enhancement

Direct heuristic dynamic programming method for power system...

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2014 American control Conference, ACC 2014

作者： Yu, Miao Lu, Chao Liu, Yongjun School of Mechanical-electronic and Automobile Engineering Beijing University of Civil Engineering and Architecture Beijing 100044 China State Key Laboratory for Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing 100084 China Technology Research Centre of China Southern Power Grid Guangzhou 510623 China

ISBN: (纸本)9781479932726

In this paper a neural network-based approximate dynamic programming method, namely direct heuristic dynamic programming (direct HDP), is applied to power system stability control. Direct HDP is a learning and approximation based approach to address nonlinear system control under uncertainty. In the present paper, real-time system responses provided by wide area measurement system (WAMS) are used to construct such controllers which are uniquely tailored for the problems under consideration. In addition, the controller learning objective is formulated as a reward function that reflects global characteristics of the power system low frequency oscillation under the consideration of coupling effect among system components. The contribution of the paper includes a convergence proof of the direct HDP algorithm using an LQR framework, as well as case study to illustrate the proposed learning control algorithm. The case study aims at providing a new solution to a difficult large scale system coordination problem where the China Southern power Grid is used for. © 2014 American Automatic control Council.

关键词： controllers

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Reducing the Impact of Source Internal Resistance by Source Coil in Resonant Wireless power Transfer

Reducing the Impact of Source Internal Resistance by Source ...

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IEEE Energy Conversion Congress and Exposition

作者： Yiming Zhang Ting Lu Zhengming Zhao State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing China

ISBN: (纸本)9781479957774

Wireless power transfer (WPT) is the state-of-the-art research interest. In the WPT system efficiency is an important figure of merit. In order to reduce the impact of the source internal resistance and improve the system efficiency of the conventional two-coil structure, a source coil is added to the two-coil structure, forming a three-coil structure. Both the two-coil structure and the three-coil structure are modeled and analyzed with the circuit theory. The system efficiencies of both structures with optimal loads and a fixed load are deduced. The system efficiency of the three-coil structure is proved to be higher than that of the two-coil structure. An experimental apparatus is implemented and the experimental results match well with the theoretical calculations. The larger the source internal resistance, the more significantly the addition of the source coil improves the system efficiency.

关键词： Coils Wireless communication Resistance Magnetic resonance Integrated circuit modeling Equivalent circuits

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RF energy harvesting with broadband antenna

RF energy harvesting with broadband antenna

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IEEE Conference and Expo Transportation Electrification Asia-Pacific (ITEC Asia-Pacific)

作者： Xudong Wang Zhengming Zhao Guanhua Chen Fanbo He State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing P. R. China

A broadband RF energy harvesting system over a frequency range of 900MHz-3GHz has been designed and tested. Some detailed issues of RF design have been studied and tested to improve the efficiency of the rectifier. Test results show that as low as -20dBm RF power can be harvested by this system. The series and parallel connections of two RF energy harvesting systems have also been studied, compared with the single system.

关键词： Radio frequency Broadband antennas Rectifiers Energy harvesting Broadband communication Antenna measurements

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Research on HVIGBT transient mixture model and parameter extraction method

Research on HVIGBT transient mixture model and parameter ext...

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IEEE Conference and Expo Transportation Electrification Asia-Pacific (ITEC Asia-Pacific)

作者： Gaohui Feng Zhengming Zhao Liqiang Yuan Shiqi Ji Jincheng Zhao Mechanical Engineering College Shijiazhuang China State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China

This paper presents a kind of HVIGBT transient mixture model and corresponding parameter extraction method. The HVIGBT model can divide into MOSFET and BJT two parts. The two models are formed respectively according to HVIGBT work principle, in addition, the carrier transport equations have been simplified for avoiding Kirk effect in BJT model. The transient model is realized in PSIM software in the paper. Extraction methods, which include estimation by empirical values, calculation by testing waveforms and comparison with same type models, are adopted in extracting model parameters. Through comparing testing and simulation waveforms, the model's simulation accuracy is proved.

关键词： Mathematical model Testing Semiconductor device modeling Transient analysis Insulated gate bipolar transistors Integrated circuit modeling Capacitance

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An adaptive wind power smoothing method with energy storage system

An adaptive wind power smoothing method with energy storage ...

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IEEE General Meeting power& Energy Society

作者： Hanchen Xu Can Wang Chao Lu Zhigang Lu State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China Electric Power Research Institute of China Southern Power Grid Guangzhou China

The random and intermittent nature of wind power (WP) makes the integration of large-scale wind farms into power system problematic. The energy storage system (ESS) is an effective means to smooth the WP. This paper presents a novel Kalman filter (KF) based adaptive wind power smoothing method to determine the power output of an ESS. ESS capacity can be significantly reduced by adjusting the parameters of KF adaptively according to the WP fluctuation. Meanwhile, a fuzzy logic controller is introduced to manage the remained energy level (REL) of the ESS. By considering the current WP fluctuation, the REL and the power output of the ESS together in the controller, the REL can be successfully managed to a reasonable range without deteriorating the WP fluctuation. A test case based on data from an actual wind farm validated the effectiveness of the proposed method.

关键词： Fluctuations Wind power generation Energy storage Wind farms Kalman filters Fuzzy logic Smoothing methods

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Simplified equivalent models of large-scale wind power and their application on small-signal stability

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Journal of modern power systems and Clean Energy 2013年第1期1卷 58-64页

作者： Nan DING Zongxiang LU Ying QIAO Yong MIN State Key Laboratory of Control and Simulation of Power System and Generation Equipments Tsinghua UniversityBeijing 100084China

With the rapid growth of grid-connected wind power penetration level,it is necessary to study the impacts of wind power on power system *** small-signal stability of power systems with large-scale wind power is explored using the eigenvalue analysis method.A prototype sample system,the two-synchronous-generator system with a wind farm,is proposed for theoretical ***,simplified models of wind turbines(WTs)and the corresponding equivalent models of wind farms are *** kinds of typical WT models,i.e.,squirrel cage induction generator,doubly-fed induction generator,and permanent magnet synchronous generator are ***,based on the simplified equivalent models,effects of large-scale wind farms on the electromechanical oscillation modes(EOMs)of synchronous systems are *** results indicate that wind farms of the three kinds of WTs have positive effects on ***,long transmission lines connecting wind farmto the systemmay produce negative effects on the small-signal stability of the system.

关键词： Wind turbine(WT) Small-signal stability Electromechanical oscillation mode(EOM) Simplified model Equivalent model

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Phase-Shift control of Isolated Bidirectional DC-DC Converters for Unidirectional power Flow

Phase-Shift Control of Isolated Bidirectional DC-DC Converte...

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IEEE Energy Conversion Congress and Exposition

作者： Junjie Ge Zhengming Zhao Junchao Ma Fanbo He Liqiang Yuan Ting Lu State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University 100084 Beijing P. R. China

ISBN: (纸本)9781479957774

In the conventional phase-shift control of isolated bidirectional DC-DC converters, the phenomenon of power backflow is quite obvious. General improved phase-shift control methods can reduce the power backflow of the input. However, they do not take the power backflow of the output into consideration. In this paper, a novel phase-shift control of isolated bidirectional DC-DC converters for unidirectional power flow is proposed. It can eliminate the power backflows of both the input and the output at the same time. Furthermore, the converters in the proposed phase-shift control can achieve the zero-current switching in the whole power rang. Experimental results from a prototype verify the feasibility and validity of the proposed control method, and show superior performance.

关键词： DC-DC power converters Voltage control Load flow control systems Educational institutions Prototypes

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