Analysis And Control Research On Low Frequency Oscillation Of Large-scale Wind Power Grid In Power System

Large area interconnected power system gets fast development in recent years.The phenomenon of low frequency oscillation is inherent in interconnected power system.The oscillation stability is a prerequisite to guarantee the safe operation of the system,so get great attention.At the same time,the wind as the most development potential of renewable energy in the power grid,wind power penetration permeability increases year by year in recent years.When a large-scale wind farm interconnected,the installed wind power reaching a certain level,the inter-area and intra-area low frequency oscillations become bottlenecks that restrict the tie line transmission and wind power given capacity.Large-scale wind power connected to the power system,which may produce adverse effect to inter-area and intra-area negative damping or weak damping problem.Therefore,the low frequency oscillation with large-scale wind power connected system has become an important subject to study.There are three methods to the low frequency oscillation characteristics with wind power interconnected power system,which are modal analysis method,the measurement signal analysis method and low-frequency oscillation probabilistic small signal stability analysis method.Three analysis methods results consistently show that,the connection of a large scale wind power and power system produce certain effect on low frequency oscillations.In order to prevent the low frequency oscillation of power system connected the large-scale wind power,this paper puts forward two improvements on the control strategy of doubly-fed wind power generator,increasing the additional damping control,the additional control parameters is determined by using the modal control theory and cultural differential evolution algorithm based on neighborhood topology.The simulation results show that the two additional damping controls effectively restrain the interconnected power system low frequency oscillation,and increase the small signal stability of the system.The main research results are as follows:(1)Research low frequency oscillation analysis method based on the measured signal.According to the low-frequency oscillation characteristics of the measured signal,puts forward two kinds of low frequency oscillation analysis method based on the measured signal.The first kind of analysis method is the application of the existing stochastic subspace identification method in the low frequency oscillation analysis;the second is put forward the phase space reconstruction combined with the improvement wavelet analysis theory.Based on the data reduction and the frequency band wavelet fusion algorithm,the high dimension matrix after the phase space reconstruction is as input,lifting wavelet recognition of high dimension problems.Application of these two methods to recognize the pattern of the added noise signal,tests show that this method has high validity and accuracy of pattern identification results.(2)Study on the low frequency oscillation probabilistic small disturbance stability analysis methods,and put forward the application of credibility theory on low-frequency oscillation for probabilistic small signal stability analysis of large-scale wind farm interconnected power system.Low frequency oscillation probability reliability index is presented in this paper,and the fuzzy simulation algorithm is applied for calculating the expectations and variances of damping ratio and frequency of oscillation mode and low frequency oscillation probability reliability index.It is verified that credibility theory is feasible for low frequency oscillation probabilistic stability considering wind speed correlation in comparison with monte carlo method and two-point analysis method,and this method has the characteristics of high precision and fast solving;this method only needs to be according to the actual situation to determine the membership function of the uncertain parameters type and range,mathematical model is simple and easy to implement.(3)Put forward to improve the control strategy of doubly-fed wind power generator,the active power fluctuations of wind generator is as the identification signal,the additional damping PID control is added,damping control current is produced,access to the d-axis current component control inner ring of grid-side converter control of the doubly-fed wind power generator.The closed-loop mathematic models of wind power interconnected is established,the modal control theory is applied to determinate control parameters.With large-scale wind farms connected two-area four-machine system as an example,the system failure of and wind speed disturbance two running situation has carried on the simulation analysis,compared with the without considering additional damping control.The simulation results show that the proposed method can effectively restrain on low frequency oscillation,and damping control is stable.(4)In order to the tie line power oscillations with large wind farm interconnected power system,put forward a additional active damping control in the doubly-fed wind power generator control.First,the tie line active power is as control identification signal too,additional PID control links are added,access to the q-axis current component inner ring of rotor-side converter control of doubly-fed wind power generator.Then,the control parameters are identified.Probabilistic small signal stability analysis is conducted,get the optimization goal,the optimal control parameters are gotten with the application of cultural differential evolution algorithm based on neighborhood topology.Finally,the proposed new control simulation analysis is conducted,the results show that the improved control can effectively damp inter-area active power oscillation,improve the damping characteristics of large-scale wind power grid.