Research On Wideband Oscillation Analysis Method Of Wind Integrated Power System Based On Equivalent Modeling And Measurement Identification

With the increasing penetration of renewable energy and large-capacity power electronic equipment,the operating characteristics of modern power systems are greatly changing.The multi-timescale control interaction in the system has led to the frequent occurrence of wideband oscillation incidents,which seriously threatened the safe and stable operation of the system.As a renewable energy resource,wind power plays an important role in achieving goals of emission peak and carbon neutrality and has been developed rapidly in recent years.However,engineering practice and related research show that wideband oscillations may occur when wind farms are connected to AC systems with series compensation,weak AC systems and flexible DC transmission systems,which can be harmful to the power system.Therefore,it is necessary to analyze the wideband oscillation problem caused by the integrated wind power systems.This paper analysis the method of wideband oscillation caused by integrated wind power systems based on equivalent modeling and measurement identification.The main work is as follows:(1)An equivalent modeling method for grid-connected permanent magnetic synchronous generator wind turbine(PMSG-WT)is proposed.Based on the dynamic models of the electromechanical system and the control system of PMSG-WT,the relationships between the steady-state variables of PMSG-WT and wind speed are first deduced.Then,the wind speed-frequency two-variable admittance model can be established to represent the port characteristics of PMSG-WT under different operating conditions.Based on this,the equivalent modeling method of the grid-connected PMSG-WT is proposed,which realizes the dynamic equivalent modeling of PMSG-WT under various operating conditions.The accuracy and effectiveness of the proposed method are verified by time-domain simulations.The proposed method can effectively reduce the complexity of simulation modeling,speed up the simulationand can be applied to the analysis of wideband oscillation problems.(2)The influence of DC bus voltage dynamics in the modulation algorithm on the stability of the grid-connected PMSG-WT is analyzed.Firstly,two modulation algorithms of the converter are established according to whether the DC bus voltage dynamic is included.Secondly,the system state-space models and impedance models with two modulation algorithms are deduced respectively to analyze the influence of the two modulation algorithms on the system stability theoretically.Finally,the conclusions obtained by eigenvalue analysis and impedance analysis are verified by time-domain simulations.The conclusion clarifies the precondition of analyzing the grid-connected PMSG-WT by modeling the machine side as a current source with constant output power is that the DC bus voltage dynamic is considered in the modulation algorithm.(3)A stability analysis method of zeros identification based on frequency response characteristics of the determinant of the impedance matrix is proposed in this paper.Since it is difficult to build up an accurate impedance model analytically due to high complexity and unknown parameters,it is necessary to obtain the impedance model of the system by measurement and then analyze the system stability based on it.The proposed method firstly divides the concerned frequency band into several sub-bands.In each sub-band,a unified reduced-order frequency response model is then established,which retains the dominant oscillation mode and a simplified equivalent term of other modes.Therefore,the remaining parameters can be easily identified by the fitting algorithm.Finally,zeros of the reduced-order frequency response model in each sub-band can be solved to analyze the system stability.Both the eigenvalue analysis and time-domain simulations performed in three representative systems have validated the effectiveness and accuracy of the proposed procedure.This method does not need to obtain the zero-crossing frequency of the imaginary part of the impedance in advance and effectively reduces the difficulty of solving the zero-point of high-order impedance expressions.