Self-adaptive method for improving system stability of lcl type grid-connected inverter under weak grid conditions

Abstract

A method for adaptively improving the stability of an LCL grid-connected inserter system under the condition of a weak grid comprises the following steps: adding a lead correction link to the LCL grid-connected inserter system, and pre-configuring the parameters of the lead correction link; measuring the inductive impedance (Lg) of the grid through a small signal injection method; judging whether there is a need to set the parameters of the lead correction link; if there is no need to set the parameters of the lead correction link, ending the process; and if there is a need to set the parameters of the lead correction link, setting the indexing coefficient (a) and the time constant (T) of a lead network in the lead correction link, and setting the adjustment coefficient (ka) of the lead correction link. According to the invention, the lead correction link is added to the LCL grid-connected inserter system, the impedance of the grid is measured through the small signal injection method, and the parameters of the lead correction link are set to make compensation for the system phase when the phase angle margin of the system is insufficient. By adaptively adjusting the parameters of the lead correction link to make compensation for the phase margin of the system according to the result of grid impedance measurement, enough stable margin can be kept for the system, and safe and stable operation of the system can be ensured.

Description

technical field [0001] The invention relates to a method for stabilizing an LCL type grid-connected inverter. In particular, it relates to a method for self-adaptively improving the stability of an LCL type grid-connected inverter system under weak grid conditions based on phase margin compensation. Background technique [0002] The proportion of distributed power generation systems represented by renewable energy such as solar energy and wind energy in power systems is increasing day by day. The grid-connected inverter is the interface unit between distributed energy and the grid, so how to improve the stability of the grid-connected inverter is very important. Compared with the single L filter, the LCL filter presents high impedance to high-order harmonics due to the increase of the capacitor branch, and has better high-order harmonic attenuation capability. The LCL filter can achieve the same filtering effect when the total inductance value is much smaller than that of ...

AI Technical Summary

Problems solved by technology

Long cables and a large number of transformer devices make the impedance at the common coupling point of the grid larger. At this time, the grid cannot be equivalent to an ideal voltage source. This type of grid is called a weak grid, and the impedance is mainly inductive.

The existence of grid impedance has a significant impact on the stability of grid-connected inverters

[0004] The change of grid impedance will not make the active damping of the system invalid and cause resonance problems, but it will reduce the stability margin of the grid-connected system

When the stability margin of the grid-connected system decreases to zero, the grid-connected system will appear unstable, which will affect the safe and stable operation of the LCL grid-connected inverter

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