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Flexible unbalanced control with peak current limitation for virtual synchronous generator under voltage sags

Journal of Modern power systems and Clean Energy 2018年第1期6卷 61-72页

作者： Tianwen ZHENG Laijun CHEN Yan GUO Shengwei MEI State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Qinghai Key Lab of Efficient Utilization of Clean Energy New Energy Photovoltaic Industry Research Center Qinghai University

Virtual synchronous generator(VSG)is gridfriendly for integrating distributed generations(DGs)since it can emulate the operation mechanism of traditional synchronous generator(SG).However,the traditional VSG control strategy,which is mainly suitable for balanced voltage conditions,may lead to power oscillations,current unbalance and even overcurrent under unbalanced voltage *** overcome this difficulty,a flexible unbalanced control with peak current limitation for VSG under unbalanced operating conditions is *** on the basic VSG control algorithm,the control strategy integrates two novel control modules,which are current reference generator(CRG)and power reference generator(PRG).The proposed control strategy can flexibly meet different operation demands,which includes current balancing,constant active or reactive *** the injected currents are kept within safety values for a better utilization of the VSG power ***,the experimental platform is *** results demonstrate the validness and effectiveness of the proposed control strategy.

关键词： Virtual synchronous generator Unbalanced control Current reference generator power reference generator Voltage sags

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A predictive DC voltage control scheme for back-to-back converters based on energy balance modeling

A predictive DC voltage control scheme for back-to-back conv...

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2011 International Conference on Electrical Machines and systems, ICEMS 2011

作者： Yin, Lu Zhao, Zhengming Lu, Ting He, Fanbo Yuan, Liqiang State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9781457710445

This paper presents a predictive control scheme of DC-link voltage for back-to-back converters based on energy balance modeling. Since the variation of DC-link voltage is affected by the energy mismatch between rectifier and inverter, the energy distribution in a rectifier-inverter is analyzed. Moreover, in order to calculate the input and output energy in one control period accurately, the grid current is regulated by predictive control and the instantaneous active power consumed by the induction motor is estimated. Then, an equation based on energy balance in one control period is established, and the DC-link voltage can be controlled by solving it. Finally, simulation results show that with the proposed control scheme, the back-to-back converter exhibits both good dynamic and steady-state performances. © 2011 IEEE.

关键词： Energy balance

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control of parallel grid-connected photovoltaic inverters with common dc bus

Control of parallel grid-connected photovoltaic inverters wi...

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2nd IET Renewable power generation Conference, RPG 2013

作者： He, F. Zhao, Z. Yuan, L. Lu, T. State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9781849197588

This paper proposes a hierarchical control scheme for parallel grid-connected PV inverters with a common dc bus. Droop control and group coordination are implemented to achieve equal power sharing between inverters as well as zero steady-state error for dc voltage regulation. The implementation is specifically designed for distributed control to promote modularization and system reliability. Experimental results have verified that the proposed scheme is effective.

关键词： Electric power transmission networks

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Study on stress and strain for fatigue cumulation evaluation in turbine generator shafts due to torsional vibration

Study on stress and strain for fatigue cumulation evaluation...

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23rd International Congress on Condition Monitoring and Diagnostic Engineering Management, COMADEM 2010

作者： Jiang, Dongxiang Liu, Chao An, Xueli Chen, Jie State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Thermal Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9784883254194

The cracks emerged in a fossil-fired power plant in China in 2008 and several similar crack accidents had been detected in nuclear turbines in USA before. The possible causes of the cracks are analyzed in previous study while the torsional vibration is one of the most significant factors. The paper analyzes the impact of torsional vibration using the practical running data in some turbine generator unit. Based on the transient response analysis under emulational subsynchronous oscillation model simplified from the practical network, the torques acted on the coupling section are analyzed. Then the stress and strain field is calculated for local dangerous point search in Zone of Vulnerability (ZoV) and the fatigue damage criterion determination. Manson-Coffin equation is used to ascertain whether it is high-cycle fatigue or low-cycle fatigue and the fatigue data from standard test specimen is used. The method using local stress and strain analysis as well as fatigue damage cumulation study may establish a novel way to diagnose the crack in an early stage.

关键词： Transient analysis

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The analysis of stator MMF and the calculation of rotor losses in a 12-phase high speed asynchronous generator

The analysis of stator MMF and the calculation of rotor loss...

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ICEMS 2005: 8th International Conference on Electrical Machines and systems

作者： Cheng, Luo Xiangheng, Wang Puqi, Ning Department of Electrical Engineering State Key Laboratory of Control and Simulation of Power System and Generation Equipments Tsinghua University Beijing 100084 China

ISBN: (纸本)7506274078

To research the influence of multi-phase winding to generators and calculate the losses in solid rotors, the stator mint of a 12-phase asynchronous generator have been well analyzed and finite element method by ANSYS software has been applied to get the accurate losses in the rotor through both harmonic and transient 2-D analysis. The relationship between stator harmonic current and stator harmonic mint has been deduced and proved through ANSYS software to some extent, and rotor losses produced by both stator fundamental current and stator total current have also been obtained and compared. The results show that 12-phase stator winding with appropriate short pitch can effectively eliminate or reduce many mmf produced by stator fundamental and harmonic current and rotor losses are mainly produced by stator fundamental current.

关键词： Asynchronous generators

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Vibration characteristics on a wind turbine rotor using modal and harmonic analysis of FEM

Vibration characteristics on a wind turbine rotor using moda...

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2010 2nd World Non-Grid-Connected Wind power and Energy Conference, WNWEC 2010

作者： Liu, Chao Jiang, Dongxiang Chen, Jie State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Thermal Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9781424489213

A wind turbine rotor system containing blades has its own characteristics. The vibration characteristics of blades with special airfoil can influence the vibration characteristics of the rotor system. This paper analyzed the vibration characteristics of a wind turbine rotor including blades with two-dimensional airfoil. The Finite Element Method (FEM) is applied to establish the rotor model, with the purpose that the FEM can adjust complex blades airfoils and acquire the details of the blades vibration characteristics. The modal characteristics are extracted based on the wind turbine model established in the laboratory. Using harmonic analysis of FEM, the excitation forces on the blades caused by the stochastic wind load are imposed on the rotor model and the stable response of the rotor system is calculated using ANSYS. Then the vibration characteristics are analyzed and the characteristics of the harmonic response are studied under different phases of the circumferential and axial forces. © 2010 IEEE.

关键词： Harmonic analysis

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Design, simulation and analysis of the low stray inductance bus bar for voltage source inverters

Design, simulation and analysis of the low stray inductance ...

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2011 International Conference on Electrical Machines and systems, ICEMS 2011

作者： Yuan, Liqiang Yu, Hualong Wang, Xuesong Zhao, Zhengming State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9781457710445

Hard-switching technique under the high voltage and high current is one of main trends of high power inverters. Under this switching mode, the stray parameters of the commutating loops, especially the stray inductance of the DC bus bar, have significant influence on the switching process, electromagnetic interference and component stress of the semiconductor switches. It becomes one of the key points for the safe operation of inverters. Based on an actual 55kW inverter, the design, simulation and analysis for its bus bar is described in this paper. The bus bar model is built with the method of Partial Element Equivalent Circuit (PEEC), and the stray parameters are extracted from PEEC model and applied in the circuit simulation. Compared with the experimental results, the modeling validity is proved, and the simplified modeling process and design principles for complex physical bus bar are presented. © 2011 IEEE.

关键词： Circuit simulation

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A systematic and qualitative assessment method and software design for energy efficiency of typical electric machine systems with pumps and fans

A systematic and qualitative assessment method and software ...

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11th International Conference on Electrical Machines and systems, ICEMS 2008

作者： Yi, Lei Zhengming, Zhao Jing, Xue State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9787506292214

Three-phase induction motors as well as power converters are intrinsically efficient machines and devices. However, due to the common misapplication of them with loads like pumps and fans, these electric machine systems are considered a great potential of energy conservation in industries. As to assessing methods of energy conservation, neither the study of induction machine efficiency nor the analysis of pumps and fans performance is new. However, the systematic and qualitative analysis and assessment of the energy efficiency of induction machines, loads and control devices acting as a whole system are still complicated yet indispensable for electric machine system energy conservation program in China. In this paper, a systematic and qualitative assessment method for energy application efficiency of electric machine system is raised. Based on this method, an assessing computer program is designed to provide referencing information for making investment decisions regarding energy efficiency measures at manufacturing plants. An expert system is also designed to choose equipments that match each other.

关键词： Investments

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Finite element analysis on damping characteristics for vibro-impact of integral shroud blade

Finite element analysis on damping characteristics for vibro...

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Joint Conference on Society for Machinery Failure Prevention Technology Conference, MFPT 2015 and ISA's 61st International Instrumentation Symposium, IIS 2015 - Technology Evolution: Sensors to systems for Failure Prevention

作者： Wang, Nan-Fei Jiang, Dong-Xiang Chen, Jing-Ming State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Thermal Engineering Tsinghua University Beijing100084 China

By using theoretical and experimental methods, dynamic characteristics of turbine blades with integral shrouds are studied, and the mechanism of vibro-impact and the effective factors of integrally shrouded blades are mainly presented. By means of finite element calculation, the dynamic frequencies and vibration mode shapes of single shrouded blade are explored under different rotating speeds. The three-dimensional entity unit integral dynamics equation of blades with vibro-impact are established by using nonlinear damping model in this paper. With the help of 3D software Solidworks, the solid model of blade is built. With the aid of FEA software ANSYS, the dynamics and static characteristics of single blade are obtained. Meanwhile, by building the model to set different shroud clearance and exciting force amplitude, the relationships between displacement of blade tip and influence of such as blade shroud clearance and exciting force amplitude are demonstrated. The results of the analysis indicate that the collision structural is an ideal damping structure. As the clearance between blade shrouds is smaller, the damping effect is better. Moreover, results show that blades adopting collision damping mechanism can achieve good damping effect when the blades are subjected to greater exciting force.

关键词： Finite element method

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Feature extraction in machine degradation with variational mode decomposition

Feature extraction in machine degradation with variational m...

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

The measured parameters change with the machine degradation, where the trends of the parameters can be applied in condition prediction. The deterioration of the parameters usually present characteristics in a monotonic or low-frequency way. As the measure signal are merged with instant signals, noise and measurement error in different frequency bands, model decomposition approaches are widely applied to separate the different bands for feature extraction. Among the model decomposition methods, Variational model decomposition is recently proposed by K. Dragomiretskiy and D. Zosso as a non-recursive model which can extract modes concurrently. This work will analyze its effectiveness in degradation feature extraction and application in condition prediction in prognosis. Firstly, variational model decomposition is analyzed, where the characteristics of variational model decomposition are compared with another mode decomposition method ensemble empirical mode decomposition. simulation data is applied to test the effectiveness of the mode decomposition methods. Secondly, field data with component degradation is collected, and the degradation feature extraction is applied with the three methods mentioned above.

关键词： Empirical mode decomposition

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