On-line Measurement And Analysis Of Stability And Impedance Of Grid-connected Inverter Based On PLL

As more and more grid-connected inverters are connected to the grid,in the past decade,power system resonance,instability analysis,and online measurement of system impedance have become increasingly practical.Due to changes in grid impedance,grid-connected inverters may experience unexpected resonance and instability problems.The voltage source converter(VSC)is one of the basic components of the power system.It is widely used in the integration of renewable energy and energy storage grids,high-voltage DC transmission,and flexible AC transmission systems.High frequency pulse modulation control is the key to the application of VSCs.It makes VSCs more advantageous than traditional line commutation converters in volume,cost,response speed and operational flexibility.On the other hand,high-frequency control also creates new system stability and grid resonance problems,which are not common in traditional power systems.This paper proposes a three-phase grid-connected VSC impedance modeling,stability analysis and grid impedance online measurement method,through a phase-locked loop(PLL)and grid voltage synchronization inverter to solve the system high frequency Control instability and resonance problems.The application proposed in this paper is to integrate wind energy into the power grid,and use the harmonic linearization method to model the positive and negative sequence impedance of the three-phase inverter.The model can also be used to analyze the resonance and The stability of the system is controlled,and the phase-locked loop design is optimized to minimize such resonance problems.This paper also introduces the method of measuring grid impedance using grid-connected inverter as the measuring device,and explains the implementation of online grid impedance measurement algorithm in grid-connected inverter in DSP.Power grid disturbances are generated by grid-connected inverters.The measured voltage and current responses are transferred through an online DFT algorithm,which helps extract sequence components in the frequency domain,and also enables online calculation of the grid impedance based on the measured voltage and current sequence components.Finally,the stability of the impedance model and the feasibility of the online measurement algorithm are verified by simulation.