Characteristic Analysis And Parameter Optimization Of Impedance Port Of Three-phase Power Grid Simulator

With the development and growth of the energy industry,in terms of power applications,renewable new energy sources continue to penetrate through distributed power generation.While distributed power generation and micro grids have become a development trend,the interaction between grid-connected inverters and the grid,and between inverters and inverters is also increasing.The grid simulation system,as a test system for grid-connected inverters,plays an important role in the stable development of the power system.However,the oscillation generated by the coupling between the grid simulator and the grid-connected inverter is inconsistent with the principle of the interaction between the grid-connected inverters.The former is the interactive oscillation of multiple inverters,and the latter is the coupling between the grid impedance and the inverter impedance.The interaction between the impedance of the grid simulator and the inverter will reduce the accuracy and reliability of the grid-connected test.Therefore,while ensuring that the grid simulation system effectively simulates the grid operation waveform and fault waveform,how to avoid the coupling oscillation between the grid simulator and the grid-connected inverter is of great significance to the reliability of the grid-connected test.This article will take the three-phase power grid simulator as the research object,and analyze the impedance port characteristics of the power grid simulator.Aiming to avoid coupling oscillations to improve the accuracy and reliability of power grid simulation system testing,the following studies have been made:First of all,the different functional requirements of the grid simulator are determined through grid connection test standards and grid operating conditions.According to the functional requirements,the topology structure of the power grid simulator is given.The inverter unit adopts a three-phase three-wire inverter and an LC filter structure.On this basis,the mathematical models in different coordinate systems are deduced and compared to lay the foundation for the establishment of the impedance model of the power grid simulator.The voltage source impedance model of the inverter link of the power grid simulation system is established.Secondly,the controller structure of the power grid simulation system is designed,and the double closed-loop control structure of voltage feedback outer loop and current feedback inner loop is adopted.Analyze the control principle of proportional resonance(PR)control in the voltage control link,and determine the dual-loop control parameters of the power grid simulator based on the main circuit parameters of the power grid simulation system.The failure mechanism of the power grid simulator based on the impedance model is analyzed,and the coupling effect between the power grid simulator and the grid-connected inverter is analyzed through the impedance frequency domain characteristics.In order to verify the stable operation and failure state of the system,a simulation experiment was performed on the power grid simulator to verify the oscillation problem caused by the interaction between the power grid simulator and the grid-connected inverter.Finally,according to the characteristics of the impedance port,a new optimization idea of ??transforming the closed-loop control into an open-loop tracking function in the high frequency band to achieve impedance passivity is proposed for reshaping the impedance.Increase the notch filter to ensure that the low frequency band can have enough gain to solve the influence of the high frequency open loop on the gain of the low frequency state.Finally,the passive performance of the power grid simulator in the high frequency band is guaranteed in the high frequency band,and at the same time,it can achieve effective and accurate tracking in the whole frequency band.Based on this optimization method,the passive range of the power grid simulator is finally expanded,and the range of testable inverters of the power grid simulator is enlarged,and the accuracy of the power grid simulator test is improved.