Research on inertia characteristics and lifting strategy of grid-connected inverter
Objectives To address the problem of low inertia operation in the power system caused by the in-tegration of a large-scale new energy source,Methods the inertia characteristics of grid-connected inverters were analyzed and methods of improving their inertia level were studied.Firstly,the essence of inertia in the power system was analyzed,and the relationship between the inertia level of grid-connected inverters and their device parameters was derived.The root locus method was used to plot the root locus of the DC-side voltage control loop with the DC-side capacitance as a variable.The value of the DC-side capacitance was optimized based on the root locus and the requirements for inverter inertia level under different grid conditions.Then,a frequency feedback loop was introduced into the DC-side voltage control loop of the grid-connected inverter,and an improved control strategy for the DC-side voltage and modulation strategy for the inverter were proposed to enhance the instantaneous inertia level of the grid-connected inverter.This allowed the DC-side capacitance to charge and discharge according to the fluctuation of the grid frequency,suppressing the instantaneous rate of change of the grid frequency.Results The proposed inertia enhance-ment strategy was validated using MATLAB/Simulink simulation platform.It was found that compared with the proposed strategy not used,when the DC-side capacitance was set to 0.4 F and the virtual inertia time constant was 5 s,the maximum deviation of the system frequency drop was reduced by 0.11 Hz,and the average drop rate was reduced by 0.035 Hz/s.Conclusions The proposed strategy could effectively improve the inertia level of grid-connected inverters and suppress the instantaneous variation of the grid frequency.
power systeminverterfrequency stabilizationinertiacapacitor voltagevoltage control
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