Virtual admittance method for improving stability of grid-tied inverter in weak grid

Abstract

The invention provides a virtual admittance method for improving the stability of a grid-tied inverter under a weak grid. The virtual admittance method comprises the steps of S1, determining, according to a d-q admittance model of a grid-tied inverter, an interaction relationship between an inverter and a weak grid, the interaction relationship being that when the impedance of the weak grid is not greater than a first grid impedance value Zg0, a grid-tied system can maintain stability and when the impedance of the weak grid changes to a second grid impedance value Zg, the grid-tied system becomes unstable, where Zg=Zg0+Z'g, Z'g being the change value of the impedance of the weak grid and the change being greater than 0; and S2, measuring the change value Z'g of the impedance of the weak grid online, and connecting a virtual admittance Yp in a control loop of the grid-tied inverter and adaptively adjusting the grid impedance change with the virtual admittance Yp, so that a Nyquist curve of the impedance ratio (Zg0+Z'g) (Yout_cl+Yp) of the grid-tied system is enabled to be the same as Zg0 Yout_cl, Yout_cl being the output admittance of the inverter, the stability of the grid-tied system can be maintained and the stability of the grid-tied inverter under the weak grid is improved. Further, the realized order of the virtual admittance in the control loop can be reduced and the practicality is improved.

Description

technical field [0001] The invention relates to the technical fields of new energy grid connection and power electronics in a power system, and in particular relates to an adaptive virtual d-q admittance method for improving the stability of a grid-connected inverter under a weak power grid. Background technique [0002] Almost all distributed power sources are connected to the AC distribution network through grid-connected inverters. At this time, a dynamic interconnection system is formed between the grid-connected inverters and the distribution network. There may be an interaction between the two impedances, resulting in resonance problems. [0003] At present, most studies on the interaction between power electronic devices and the grid in distributed generation systems use the analysis method of impedance modeling. The essence of the analysis method based on impedance stability is to divide the system into two subsystems of power supply and load, establish the impedanc...

AI Technical Summary

Problems solved by technology

The d-q impedance model of the three-phase grid-connected inverter is proposed, and the stability analysis of the grid-connected system is carried out using the d-q impedance ratio matrix, but no study is made on how to use the corresponding d-q impedance model to design virtual admittance to improve the weak grid System stability under

Images