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LLCL grid-connected inverter resonance suppression method adapting to power grid impedance change

A technology of resonance suppression and grid impedance, applied in AC networks to reduce harmonics/ripples, electrical components, circuit devices, etc., can solve problems affecting system stability, etc., to improve the quality of grid-connected current and enhance anti-interference , the effect of enhancing stability

Pending Publication Date: 2020-01-21
LANZHOU UNIVERSITY OF TECHNOLOGY
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  • Abstract
  • Description
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  • Application Information

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Problems solved by technology

Although the grid-connected current quality can be improved to a certain extent, in the case of a weak grid, the grid impedance that changes with the grid operation mode changes at all times is the main factor affecting the system stability.

Method used

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  • LLCL grid-connected inverter resonance suppression method adapting to power grid impedance change
  • LLCL grid-connected inverter resonance suppression method adapting to power grid impedance change
  • LLCL grid-connected inverter resonance suppression method adapting to power grid impedance change

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Embodiment 1

[0046] figure 2 is the mathematical model of the LLCL filter, and the output current i of the inverter is obtained from the figure 1 and grid current i 2 Respectively relative to the inverter output voltage U inv The transfer function G 1 (s) and G 2 (s) are:

[0047]

[0048] by the transfer function G 2 (s) The Bode diagram of its frequency characteristics can be obtained, such as image 3 shown. The LLCL filter system is a third-order system, which has a good attenuation capability in the high frequency band, but resonance peaks are prone to occur at the resonance frequency, and the gain is above 0dB, which affects the output current and the normal operation of the system . In a set grid impedance L g Under changing conditions, the influence of grid impedance on system stability is analyzed, and the transfer function G is obtained by simulation 2 (s) Bode diagram of frequency characteristics Figure 4 shown. From Figure 4 It can be seen that as the grid im...

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Abstract

The invention relates to the technical field of grid-connected inverter harmonic resonance control methods, and aims to provide an LLCL grid-connected inverter resonance suppression method adapting topower grid impedance change. The method mainly comprises a third-order LLCL filter, a power grid voltage feedforward control strategy and a capacitance current feedback control strategy. According tothe power grid voltage feedforward control strategy, a voltage feedforward channel is added on the basis of a weighted current control strategy; the interference of power grid voltage is effectivelysuppressed by adopting a power grid voltage feedforward strategy, thereby effectively suppressing resonance peaks, reducing a grid-connected harmonic content, and introducing the capacitive current feedback on the basis of a power grid voltage feedforward control strategy. The invention has the beneficial effects that a traditional power grid voltage feedforward control method is reserved, so theinfluence of power grid voltage distortion on the grid-connected current is eliminated, the harmonic peak of the system at the resonant frequency is effectively restrained by introducing capacitive current feedback, the harmonic content of the grid-connected current is reduced, and the grid-connected quality of the grid-connected current is improved.

Description

technical field [0001] The invention relates to the technical field of harmonic resonance control methods for grid-connected inverters, in particular to a method for suppressing resonance of LLCL grid-connected inverters that adapts to grid impedance changes. Background technique [0002] As a power conversion device, the grid-connected inverter plays a vital role in the process of connecting distributed power sources such as wind power generation and photovoltaic power generation with the AC power grid. Due to the particularity of the geographical location of the distributed power generation, the electric energy needs to be connected to the grid through long transmission lines and transformers. There is a non-negligible and variable impedance at the point of common coupling (PCC) of the power grid, which makes the power grid appear Weak grid characteristics of high impedance. In the case of a weak grid, changes in grid impedance can easily lead to a decrease in the bandwid...

Claims

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Application Information

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IPC IPC(8): H02J3/38H02J3/01
CPCH02J3/381H02J3/01Y02E40/40
Inventor 吴丽珍安利锋郝晓弘陈伟杨新华张永年丁安邦王刚
Owner LANZHOU UNIVERSITY OF TECHNOLOGY
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