Research On Sequential Impedance Modeling And Impedance Measurement Of New Energy Grid-connected Inverter

With the large-scale integration of new energy systems into the grid,the grid-connected system composed of inverter-based power electronic devices widely exists at the end of the system,and the coupling mechanism of various parts within the system is complex,which poses new challenges and more complex issues to the stability of modern power grids.In view of the stability analysis based on impedance,the impedance modeling,measurement methods,and measurement processes of inverters and power plants have been thoroughly discussed and studied by researchers.Research and proposed schemes in this paper are based on rich supplements and innovations based on previous studies on inverter,power plant impedance modeling and impedance measurement.1)In this paper,a sequential impedance modeling method based on harmonic linearization is used to establish a sequential impedance model containing a phase-locked loop.The influence of the phase-locked loop bandwidth,current loop bandwidth,filter parameter structure and other factors on the sequence impedance and the effective frequency are qualitatively and quantitatively analyzed.On this basis,using the idea of multi-harmonic linearization and disturbance superposition,a sequence impedance model considering frequency coupling and dynamic process on the DC side was established,and the coupling generation mechanism and frequency characteristics were analyzed.Finally,the impedance model of the power plant cluster considering frequency coupling and line impedance is established.Based on the analysis of the established impedance model,simplified conditions and suggestions for impedance models at different analytical frequency bands are given.2)In order to verify the accuracy of the above impedance model,an impedance measurement platform based on Simulink,controller hardware-in-the-loop,and power hardware-in-the-loop was established.Aiming at the stability problem of power hardware-in-the-loop simulation,a digital-analog hybrid model of the power hardwarein-the-loop simulation system is established to analyze the system stability.In order to improve the measurement efficiency,a continuous disturbance injection method with independent control of disturbance frequency and amplitude is proposed,which can continuously inject disturbance signals with different frequencies and amplitudes.Finally,the accuracy of the impedance model established in this paper is verified on the loop impedance measurement platform of the controller hardware in the loop based on the RTLAB simulator3)In response to the problem of sampling range,static working point stability and power grid impedance during online impedance measurement,the online impedance measurement range is often limited.The relationship between the grid impedance,sensor measurement sampling range,static working point stable's harmonic upper limit and the impedance measurement range is established during the online measurement of gridconnected equipment impedance.The expression of the impedance online measurement range is derived,and the influence of various factors on the online impedance measurement range is quantitatively analyzed.The proposed analysis method can accurately obtain the online impedance measurement range.It provides a basis for the method of injecting disturbance,amplitude design and equipment protection in online impedance measurement.Aiming at the limited measurement range,a method of hybrid disturbance injection to expand the impedance measurement range is proposed.Finally,analysis of the proposed impedance measurement range and the proposed method of extending the impedance range are verified by simulation.