scholarly journals Inside-wind-farm/Wind-farm-grid sub-synchronous oscillation characteristics analysis in grid-connected system of multiple DFIGs

2021 ◽  
Vol 2076 (1) ◽  
pp. 012116
Author(s):  
Mengxue Sun ◽  
Ruixin Gao ◽  
Yuhui Ji ◽  
Xin Long ◽  
Changzhi Yao ◽  
...  
Keyword(s):  
Oscillation Frequency ◽  
Wind Farm ◽  
Oscillation Mode ◽  
Time Domain Simulation ◽  
Synchronous Oscillation ◽  
Machine Model ◽  
Oscillation Modes ◽  
Characteristics Analysis ◽  
The Stability ◽  
Oscillation Characteristics

Abstract Aiming at the sub-synchronous oscillation (SSO) problem of the grid-connected system of multiple DFIGs, most of the existing theoretical studies take the entire wind farm as a single-machine model, the stand-alone model cannot reflect the inside-wind-farm oscillation mode produced by the interactions among DFIGs in the wind farm. Therefore, this paper takes the equivalent value of DFIG-based wind farm to three DFIGs, establishes a mathematical model of the grid-connected system of three DFIGs, and studies the sub-synchronous oscillation modes existing in the system through eigenvalue analysis and participation factor analysis. The results show: When the length of transmission line increases, the oscillation frequency of the inside-wind-farm/wind-farm-grid sub-synchronous oscillation mode increases, the damping decreases and the stability weakens; when the number of grid-connected DFIGs increases, the oscillation frequency of the inside-wind-farm/wind-farm-grid sub-synchronous oscillation mode decreases, the damping increases and the stability enhances. Finally, a time-domain simulation model of the grid-connected system of multiple DFIGs was built in PSCAD/EMTDC to verify the correctness of the theoretical analysis results.

Three-dimensional oscillation characteristics of electrostatically deformed drops

1991 ◽  
Vol 227 ◽  
pp. 429-447 ◽  
Author(s):  
James Q. Feng ◽  
Kenneth V. Beard
Keyword(s):  
Electric Field ◽  
Three Dimensional ◽  
Normal Modes ◽  
Oscillation Mode ◽  
Mode Shapes ◽  
Physical Factors ◽  
Mathematical Framework ◽  
Drop Shape ◽  
Oscillation Modes ◽  
Oscillation Characteristics

A three-dimensional asymptotic analysis of the oscillations of electrically charged drops in an external electric field is carried out by means of the multiple-parameter perturbation method. The mathematical framework allows separate treatments of the quiescent deformation due to the electric field and the oscillatory motions caused by other physical factors. Without oscillations, the solution for the quiescent drop shape exhibits a prolate deformation with a slight asymmetry about the drop's equatorial plane. This axisymmetric quiescent deformation of the equilibrium drop shape is shown to modify the oscillation characteristics of axisymmetric as well as asymmetric modes. The expression of the characteristic frequency modification is derived for the oscillation modes, manifesting fine structure in the frequency spectrum so the degeneracy of Rayleigh's normal modes for charged drops is removed in the presence of an electric field. Physical reasoning indicates that the degeneracy of the oscillation modes is associated with the spherical symmetry of the system, so the removal of the degeneracy may be regarded as a consequence of the symmetry breaking caused by the electric field. In addition, the small-amplitude oscillation mode shapes are also modified as a result of the coupling between the oscillatory motions and the electric field as well as the quiescent deformation.

Static and Dynamic Characteristics Analysis of Precise Composite CNC Grinding Machine

2011 ◽  
Vol 411 ◽  
pp. 88-93
Author(s):  
Hong Lin Zhao ◽  
Yun Fei Sun ◽  
Rui Chen ◽  
Yu Mei Huang ◽  
Guang Peng Zhang ◽  
...  
Keyword(s):  
Finite Element ◽  
Dynamic Characteristics ◽  
Element Model ◽  
Machine Model ◽  
Static And Dynamic Characteristics ◽  
Cnc Grinding ◽  
Characteristics Analysis ◽  
The Subject ◽  
Grinding Machine ◽  
Cnc Grinding Machine

The parameters of joint parts must be included in the finite element model of a whole grinding machine. The subject investigated in this paper is B2-K3000 high-precision composite flexible grinding machine. Through finite element modeling, the joint part parameters are integrated into the whole grinding machine model to establish a dynamic model and then analyze its static and dynamic characteristics. The result shows that the whole grinding machine possesses good features, but it still needs to be improved. This paper gives suggestions for its structure development and application.

scholarly journals Torsional vibration characteristics analysis of DFIG-based wind farm and its equivalent model

2017 ◽  
Vol 12 (5) ◽  
pp. 646-656
Author(s):  
Da Xie ◽  
Junbo Sun ◽  
Yupu Lu ◽  
Yucheng Lou ◽  
Chenghong Gu ◽  
...  
Keyword(s):  
Torsional Vibration ◽  
Wind Farm ◽  
Vibration Characteristics ◽  
Equivalent Model ◽  
Characteristics Analysis

scholarly journals Research on the Unstable Branch Screening Method for Power System With High-Proportion Wind Power

2022 ◽  
Vol 9 ◽  
Author(s):  
Fei Tang ◽  
Xiaoqing Wei ◽  
Yuhan Guo ◽  
Junfeng Qi ◽  
Jiarui Xie ◽  
...  
Keyword(s):  
Power System ◽  
Wind Power ◽  
Wind Farm ◽  
Simulation Analysis ◽  
Screening Method ◽  
Prediction Method ◽  
Stability Margin ◽  
Screening Methods ◽  
Unstable Branch ◽  
Oscillation Characteristics

The sooner the system instability is predicted and the unstable branches are screened, the timelier emergency control can be implemented for a wind power system. In this paper, aiming at the problem that the existing unstable branch screening methods are lack prejudgment, an unstable branch screening method for power system with high-proportion wind power is proposed. Firstly, the equivalent external characteristics model of the wind farm was deduced. And based on this, the out-of-step oscillation characteristics of the power system with high proportion wind power was analyzed. Secondly, based on the oscillation characteristics, line weak-connection index (LWcI) was proposed to quantify the stability margin of a branch. Then an instability prediction method and an unstable branch screening method were proposed based on LWcI and voltage phase angle difference. Finally, the rapidity and effectiveness of the proposed method are verified through the simulation analysis of IEEE-118 system.

scholarly journals MECHANICAL CHARACTERISTICS ANALYSIS OF A BIONIC MUSCLE CABLE-DRIVEN LOWER LIMB REHABILITATION ROBOT

2020 ◽  
Vol 20 (10) ◽  
pp. 2040037
Author(s):  
YAN-LIN WANG ◽  
KE-YI WANG ◽  
ZI-XING ZHANG ◽  
LIANG-LIANG CHEN ◽  
ZONG-JUN MO
Keyword(s):  
Lower Limb ◽  
Mechanical Characteristics ◽  
Safety Evaluation ◽  
Parallel Robots ◽  
Rehabilitation Robot ◽  
Machine Model ◽  
Characteristics Analysis ◽  
Limb Rehabilitation ◽  
And Control ◽  
Lower Limb Rehabilitation

Cable-driven parallel robots (CDPR) have been well used in the rehabilitation field. However, the cables can provide the tension in a single direction, there is a pseudo-drag phenomenon of the cables in the CDPR, which will have a great impact on the safety of patients. Therefore, the novelty of this work is that a bionic muscle cable is used to replace the ordinary cable in the CDPR, which can solve the pseudo-drag phenomenon of the cables in the CDPR and improve the safety performance of the rehabilitation robot. The cable-driven lower limb rehabilitation robot with bionic muscle cables is called as the bionic muscle cable-driven lower limb rehabilitation robot (BMCDLR). The motion planning of the rigid branch chain of the BMCDLR is studied, and the dynamics and system stiffness of the BMCDLR are analyzed based on the man–machine model in this paper. The influence of the parameters of the elastic elements in the bionic muscle cables on the mechanical characteristics of the BMCDLR system was analyzed by using simulation experiments. The research results can provide a reference basis for research on the safety evaluation and control methods of the BMCDLR system.

scholarly journals Dynamic simulation of the oscillation characteristics of supercritical carbon dioxide impacting jets

2018 ◽  
Vol 25 (1) ◽  
pp. 61-71 ◽  
Author(s):  
Xinwei Zhang ◽  
Yiyu Lu ◽  
Jiren Tang ◽  
Zhe Zhou ◽  
Qian Li
Keyword(s):  
Carbon Dioxide ◽  
Numerical Model ◽  
Supercritical Carbon Dioxide ◽  
Oscillation Frequency ◽  
High Speed ◽  
Rock Breaking ◽  
Target Distance ◽  
Inlet Pressure ◽  
Oscillation Characteristics ◽  
Supercritical Carbon

A numerical model was established to investigate the dynamic oscillation characteristics of supercritical carbon dioxide (sc-CO2) impacting jets. The jet hydrodynamics, heat transfer, and physical properties of sc-CO2 fluid were incorporated into the model. The coupling of multiple fields with large velocity and pressure gradients was achieved using a modified SIMPLE segmentation algorithm. Laboratory experiments validated the reliability of the numerical model by detecting dynamic changes in the pressure on the centerline of the sc-CO2 impacting jet. Analysis of the flow field showed single or double high-speed sc-CO2 mass structures for the sc-CO2 impacting jet, revealing the generation mechanism of the impacting oscillation frequency and the mechanism of improved rock-breaking efficiency by sc-CO2 jet. The oscillation frequency equation was obtained through a quantitative treatment of the velocity and motion area of the sc-CO2 mass. Finally, the equation and simulation results were used to analyze the influences of the target distance, inlet pressure and temperature on the sc-CO2 jet oscillation characteristics. The results showed that the oscillation frequency and amplitude first increased and then decreased with increases in the target distance. The oscillation frequency and amplitude both increased with increasing inlet pressure; the oscillation frequency increased slowly with increasing temperature.

scholarly journals Impedance Aggregation Method of Multiple Wind Turbines and Accuracy Analysis

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2035 ◽  
Author(s):  
Liang Chen ◽  
Heng Nian ◽  
Yunyang Xu
Keyword(s):  
Stability Analysis ◽  
Reference Frame ◽  
Wind Turbines ◽  
Power Distribution ◽  
Wind Farm ◽  
System Level ◽  
Small Signal ◽  
Impedance Model ◽  
The Stability ◽  
The Impact

The sequence domain impedance modeling of wind turbines (WTs) has been widely used in the stability analysis between WTs and weak grids with high line impedance. An aggregated impedance model of the wind farm is required in the system-level analysis. However, directly aggregating WT small-signal impedance models will lead to an inaccurate aggregated impedance model due to the mismatch of reference frame definitions among different WT subsystems, which may lead to inaccuracy in the stability analysis. In this paper, we analyze the impacts of the reference frame mismatch between a local small-signal impedance model and a global one on the accuracy of aggregated impedance and the accuracy of impedance-based stability analysis. The results revealed that the impact is related to the power distribution of the studied network. It was found that that the influence of mismatch on stability analysis became subtle when subsystems were balanced loaded. Considering that balanced loading is a common configuration of the practical application, direct impedance aggregation by local small-signal models can be applied due to its acceptable accuracy.

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