Test And Analysis For Sub-Synchronous Oscillation And Shaft Torsional Vibration

In the grid development structure of West Power to East,North Power to South,Global Energy Interconnection,and high voltage direct current transmission,long distance power transmission have become imperative.At the same time,traditional energy is becoming tighter,the sense of environment is enhanced,new energies have developed rapidly,the wind power is used more widely,power and electronic devices with high performance are widely used,and the application of rotary shaft step-less speed regulation equipment is increasing,which all bring the problem of sub-synchronous oscillation(SSO)and shaft torsional vibration to another historical stage with relative high-frequency occurrence.This thesis hits the point on the monitoring and analysis methods in the research of sub-synchronous oscillations and shaft torsional vibration,and then studied the torsional vibration problems relative with varied frequency speed regular induced draft fan.In this thesis,a torsional vibration test and analysis system based on single-ended instantaneous speed is developed,and an arbitrary torsional vibration signal simulator based on reverse demodulation of torsional vibration signal is developed to conveniently evaluate the analysis accuracy of torsional angle signal.The influence of pulse number,interpolation method,number of interpolation points and FFT window function on the accuracy of FFT analysis for torsional vibration test is evaluated.As FFT method can not be used to identify relative parameters of time-varying inter-harmonic torsional vibration and sub-synchronous oscillation signals with high accuracy and resolution,the analysis method for time-varying inter-harmonic has been studied.PRONY can identify signals with super-resolution.And,it is very sensitive to noise in low-lever PRONY identification.So,the improvement of the signal-to-noise ratio(SNR)of signals is helpful for the improvement of the accuracy of PRONY identification and reduction of the PRONY fitting order.Empirical modal decomposition methods(EMD,EEMD,CEEMD,CEEMDAN,ICEEMDAN and MCEEMD)are not restricted by the principle of signal uncertainty and can bring time-frequency analysis.However,there exists problems of modal aliasing and end-point effect,especially for signals in SSO.A denoising method based on combination of ICEEMDAN and permutation entropy is proposed.PRONY analysis after denoising can improve the accuracy.A wavelet threshold algorithm is proposed for denoising.Its denoising performance is slightly better than that of ICEEMDAN method,but the selection of wavelet basis function takes a lot of work.A united algorithm based on PRONY,ICEEMDAN,wavelet threshold denoising and Robust-ICA has been introduced for the time-frequency analysis of the signal.The signal is decomposed by ICEEMDAN,and the modal components decomposed are taken as the input parameter of Robust-ICA.Then,the independent components obtained are denoised by wavelet threshold.The denoised signal is then multiplied by the hybrid matrix of Robust-ICA,and the denoised signal will be obtained after the calculation of updated modal components.This method provides a possibility for a further improvement of the SNR on the basis of ICEEMDAN and wavelet threshold denoising.Then,PRONY is used to identify signals with high SNR for parameters with higher identification accuracy.In the measurement and analysis of torsional vibration and sub-synchronous vibration,not only the instantaneous velocity can be used to analyze,but also the other mechanical and electrical quantities can reflect the relevant characteristic information.The first bench mark of sub-synchronous oscillation(FBM)is studied.The torsional vibration modes are obtained by eigen-structure analysis method,and the related signals are obtained by transient time domain simulation.FFT and high-order PRONY analysis are carried out respectively.Among them,more modal information can be obtained from mechanical signals(rotational speed,torque,torsional vibration).Because of the existence of power frequency components,the mode components of sub-synchronous oscillation are relatively low,and they are presented in the form of complementary components of power frequency components.After PARK transformation,the symmetrical power frequency components will be converted into DC components,which can highlight the sub-synchronous oscillation components.In the analysis of active and reactive power information,more sub-synchronous oscillation information can be obtained than that obtained by voltage and current analysis.The problem of torsional vibration of induced draft fan shafting is the coupling of mechanical and electrical energy.It is difficult to solve the problem comprehensively by analyzing the reasons of mechanical structure or electrical control alone.The typical methods for the analysis of sub-synchronous oscillation,eigenvalue structure analysis(ESA)and time-domain transient simulation have been used for this problem.The transmission model of induced draft fan is obtained from the performance curve of the induced draft fan based on the step curve fitting,and then the transient simulation of ROBINCON high voltage converter is carried out in PSCAD.The unstable operation range of the induced draft fan shafting with running frequency can be obtained by ESA.However,the small-signal linear model adopted in the eigenvalue structure analysis is with certain errors,so this range is a relatively conservative.With the transient time-domain simulation analysis,the ideal frequency converter and ROBINCON high-voltage converter are simulated respectively.Then,the unstable operation frequency range of the system is obtained by scanning the frequency path by path.The electrical damping of ROBINCON high-voltage converter will change with the internal parameters of the high voltage converter.Besides,In the transient simulation,the influence of the shaft elastic parameters,damping parameters,voltage-frequency ratio,stator access reactance and resistance on the unstable operation range during the transient simulation have also been studied.With the wide application of variable frequency drive technology,more and more rotary shaft systems can adjust speed in a wide range.However,it is possible for them to run in the torsional resonance range for a long time.This torsional vibration problem is similar to the sub-synchronous oscillation problem in power system,which can take reference from the research on analysis and suppression of sub-synchronous vibration.It is suggested to deliver a similar simulation calculation at the beginning of the system design,and to note the resonance region of the system in the technical manual so to avoid the resonance range actively during operation.For the existing variable frequency drive system,it can carry out simulation tests according to the actual conditions,so to mark the resonance range in the system.During the speed regulation experiment,the influence of frequency change rate on resonance range should be considered.For systems with shaft torsional vibration,it can increase the self-damping of the system,or connect stator resistance serially or add torsional vibration monitoring during the variable frequency control for torsional vibration suppression control.