Dynamic Stability Analysis for Helicopter Rotor/Fuselage Coupled Nonlinear Systems

In order to accurately predict the dynamic instabilities of a helicopterrotor/fuselage coupled system, nonlinear differential equations are derived and integrated in thetime domain to yield responses of rotor blade flapping, lead-lag and fuselage motions to simulatethe behavior of the system numerically. To obtain quantitative instabilities, Fast Fourier Transform(FFT) is conducted to estimate the modal frequencies, and Fourier series based moving-blockanalysis is employed in the predictions of the modal damping in terms of the response time history.Study on the helicopter ground resonance exhibits excellent correlation among the time-domain (TD)analytical results, eigenvalues and wind tunnel test data, thus validating the methodology of thepaper. With a large collective pitch set, the predictions of regressive lag modal damping from TDanalysis correlate with the experimental data better than from eigen analysis. TD analysis can beapplied in the dynamic stability analysis of helicopter rotor/fuselage coupled systems incorporatedwith nonlinear blade lag dampers.

Adaptive Control of Helicopter Ground Resonance with Magnetorheological Damper

The methodology for adaptive control of helicopter ground resonance with magnetorheological （MR） damper is presented. The adaptive inverse control method is used to control the output damping force of MR damper and the range of the damping force is given. Through the adaptive inverse control, the damping force of MR damper is fit to a desired damping force. With the background of applying MR damper to control of helicopter ground resonance, a model of loss force and an adaptive arithmetic for stabilization of the coupled rotor/fuselage system are presented. The simulation shows that the controller presented in this paper can stabilize the rotor/fuselage coupling system quickly and control the helicopter ground resonance effectively.

OPTIMIZATION DESIGN FOR SUPPRESSING "GROUND RESONANCE" OF THE HELICOPTER

The design problem for suppressing 'ground resonance' of the helicopter, with which few researchers have concerned so far, is studied in this paper. Based on the ideas of pole region placement in control theory and of optimization, the method for optimally designing the stiffness and damping parameters of the system with satisfying specified requirements is presented. The effective design criteria and procedures are presented according to the principle of 'ground resonance'.For illustrating the method presented in this paper three typical calculation modes are studied. The results are satisfactory.

A STUDY ON MECHANICAL MODEL OF THE HELICOPTER "GROUND RESONANCE

The key problem to the calculation and optimization design of the helicopter 'Ground Resonance' is to correctly build up a mechanical model. In the past, the literature was only concerned with the lag modes of the rotor blade and the flap modes were neglected. But such approaches should be reconsidered now. In order to study the influences of rotating multiblades rotor on the degrees of freedom and also the flap ''Ground Resonance' of a helicopter, it is necessary to consider not only the lag degrees of freedom but also the flap degrees of freedom. Using Lagrangian equation a dynamical equation of the space model for helicopter 'Ground Resonance'is deduced for the first time. Some computation results show that the mechanical model including both lag DOF and flap DOF is more reasonable.

Comparing High-resistance Grounding Method with Resonance Grounding Method for Large Generators

For large generators, the problem of high-resistance grounding method and the advantages of resonance, grounding method are discussed in detail, and an overall comparison is given in this paper. It is recommended that the latter should be adopted so as to increase the operation reliability of large generators and power systems.

Intermittent Arc Fault Detection Based on Machine Learning in Resonant Grounding Distribution Systems

In resonant grounding systems,most single-phaseto-ground faults evolve from IAFs(Intermittent Arc Faults).Earlier detection of IAFs can facilitate fault avoidance.This work proposes a novel method based on machine learning for detecting IAFs in three steps.First,the feature of zero-sequence current is automatically extracted and selected by a newlydesigned FINET(“For IAFs,Neuron Elaboration Net”),instead of traditional feature selection based on time-frequency decomposition.Moreover,data of the zero-sequence current divided by different time windows are successively input into the trained FINET.A proposed PSF(principal-subordinate factor)analyses the results obtained from FINET to improve anti-interference in the mentioned IAF detection algorithm.Experiments using PSCAD/EMTDC software simulation data show the proposed method is feasible and highly adaptable.In addition,the detection result of on-site recorded data demonstrates the effectiveness of the proposed method in practical resonant grounding systems.

Faulty Feeder Identification and Fault Area Localization in Resonant Grounding System Based on Wavelet Packet and Bayesian Classifier

Accurate fault area localization is a challenging problem in resonant grounding systems(RGSs).Accordingly,this paper proposes a novel two-stage localization method for single-phase earth faults in RGSs.Firstly,a faulty feeder identification algorithm based on a Bayesian classifier is proposed.Three characteristic parameters of the RGS(the energy ratio,impedance factor,and energy spectrum entropy)are calculated based on the zero-sequence current(ZSC)of each feeder using wavelet packet transformations.Then,the values of three parameters are sent to a pre-trained Bayesian classifier to recognize the exact fault mode.With this result,the faulty feeder can be finally identified.To find the exact fault area on the faulty feeder,a localization method based on the similarity comparison of dominant frequency-band waveforms is proposed in an RGS equipped with feeder terminal units(FTUs).The FTUs can provide the information on the ZSC at their locations.Through wavelet-packet transformation,ZSC dominant frequency-band waveforms can be obtained at all FTU points.Similarities of the waveforms of characteristics at all FTU points are calculated and compared.The neighboring FTU points with the maximum diversity are the faulty sections finally determined.The proposed method exhibits higher accuracy in both faulty feeder identification and fault area localization compared to the previous methods.Finally,the effectiveness of the proposed method is validated by comparing simulation and experimental results.

Fault Line Detection Using Waveform Fusion and One-dimensional Convolutional Neural Network in Resonant Grounding Distribution Systems

Effective features are essential for fault diagnosis.Due to the faint characteristics of a single line-to-ground(SLG)fault,fault line detection has become a challenge in resonant grounding distribution systems.This paper proposes a novel fault line detection method using waveform fusion and one-dimensional convolutional neural networks(1-D CNN).After an SLG fault occurs,the first-half waves of zero-sequence currents are collected and superimposed with each other to achieve waveform fusion.The compelling feature of fused waveforms is extracted by 1-D CNN to determine whether the fused waveform source contains the fault line.Then,the 1-D CNN output is used to update the value of the counter in order to identify the fault line.Given the lack of fault data in existing distribution systems,the proposed method only needs a small quantity of data for model training and fault line detection.In addition,the proposed method owns fault-tolerant performance.Even if a few samples are misjudged,the fault line can still be detected correctly based on the full output results of 1-D CNN.Experimental results verified that the proposed method can work effectively under various fault conditions.