CN-119315569-B - Grid-connected inverter low-frequency-band oscillation suppression implementation method based on voltage feedforward

CN119315569BCN 119315569 BCN119315569 BCN 119315569BCN-119315569-B

Abstract

The invention provides a method for realizing low-frequency oscillation suppression of a grid-connected inverter based on voltage feedforward, which relates to the technical field of power electronic technology power converter performance, the method is realized by the steps of selecting a voltage feedforward module, establishing a mathematical model of the voltage feedforward module, designing parameters of the mathematical model of the voltage feedforward module, connecting the established mathematical model and the voltage feedforward module with the completed parameter design to the output end of the grid-connected inverter, enabling the output end of the grid-connected inverter to be connected with a virtual impedance in parallel, and the like. According to the invention, the virtual impedance is connected in parallel at the output end of the grid-connected inverter through voltage feedforward, so that the intersection frequency of the impedance of the grid-connected inverter and the impedance of the power grid is changed, the phase margin is improved, the stability of the low frequency band of the system is enhanced, and the oscillation phenomenon of the low frequency band of the system is inhibited.

Inventors

HUANG SONGTAO
HUANG YUKAI
REN ZIAO
YE JIE
XU JINBANG
SHEN ANWEN

Assignees

华中科技大学

Dates

Publication Date: 20260512
Application Date: 20240716

Claims (5)

1. The method for realizing the low-frequency oscillation suppression of the grid-connected inverter based on voltage feedforward is characterized by comprising the following steps of: s100, selecting a voltage feedforward module, wherein the voltage feedforward module adopts a band-pass filter; S200, establishing a mathematical model of a voltage feedforward module, wherein the mathematical model of the voltage feedforward module has the expression: Wherein omega dh 、ω dl is the upper and lower limits of the angular frequency of the band-pass filter, k d is the impedance shaping coefficient, s represents the complex variable on the complex plane, is the complex frequency variable in the Laplace transformation domain, which is a method for describing a linear time-invariant system, which converts the function of the time domain into the function on the complex plane, wherein s is a complex number written s=σ+jω, wherein σ is the real part, j is the imaginary unit, ω is the angular frequency; S300, designing mathematical model parameters of a voltage feedforward module, wherein the mathematical model parameters comprise impedance shaping coefficient k d , upper and lower limit omega dh and omega dl of the angular frequency of the band-pass filter are selected to improve the impedance characteristic of a low frequency band; S400, connecting a voltage feedforward module with an established mathematical model and a completed parameter design to the output end of the grid-connected inverter so as to connect a virtual impedance in parallel to the output end of the grid-connected inverter; The impedance shaping coefficient k d is selected by drawing a Nyquist curve of the grid-connected inverter impedance after the introduction of the band-pass filter, observing the change of the Nyquist curve along with the impedance shaping coefficient k d , and finding the impedance shaping coefficient k d which enables the system stability margin to be maximum in the Nyquist curve.
2. The method for suppressing low-frequency oscillation of a grid-connected inverter based on voltage feedforward according to claim 1, wherein the band-pass filter is a low-frequency band-pass filter.
3. The method for suppressing low-frequency oscillation of a grid-connected inverter based on voltage feedforward according to claim 1, wherein two band-pass filters are provided, and the PCC grid-connected voltage v d 、v q is respectively input into the two band-pass filters.
4. The method for suppressing low-frequency oscillation of a grid-connected inverter based on voltage feedforward as recited in claim 1, wherein the upper and lower limits ω dh and ω dl of the angular frequency of the band-pass filter are set to 200Hz and 50Hz.
5. The method for suppressing low-frequency oscillation of a grid-connected inverter based on voltage feedforward as recited in claim 1, wherein the selecting of the impedance shaping coefficient k d further comprises finding an impedance shaping coefficient k d that maximizes a system stability margin in a Nyquist curve and controlling the magnitude of the impedance amplitude.

Description

Grid-connected inverter low-frequency-band oscillation suppression implementation method based on voltage feedforward Technical Field The invention relates to the technical field of power electronic technology power converter performance, in particular to a grid-connected inverter low-frequency-band oscillation suppression implementation method based on voltage feedforward. Background With the continuous improvement of the permeability of new energy, the broadband oscillation risk and the potential influence area of the grid-connected inverter also show an expanding trend. The broadband oscillation phenomenon which is caused by the interaction of the grid-connected inverter and the power grid becomes a great hidden trouble for maintaining safe operation of the new energy power system. The power electronic equipment can be damaged under the slight condition, and the large-area off-grid fault of the new energy power generation unit, the whole operation of the system and even part of the power grid area are forced to be disconnected under the serious condition. Analysis and research on the stability of the interaction of the grid-connected inverter and the power grid and the oscillation suppression strategy are facilitated, safety and stability of grid connection of the inverter are ensured, and development of a new energy power generation system is promoted. The power grid impedance is not negligible in the following situations that 1, the long-distance power transmission line increases the resistance and inductance of the power grid, resulting in higher power grid impedance. 2. Weak grid, smaller grid capacity or larger load near grid connection point, resulting in higher local grid impedance. 3. Distributed power generation, i.e. remote access points of distributed power sources such as wind power and photovoltaic, can lead to non-negligible impedance of the power grid. When the impedance of the power grid is not negligible, the disturbance deviation of the output phase angle of the phase-locked loop can influence the current control system, so that the output modulation of the current loop and the output current of the grid-connected inverter are influenced. The frequency domain characteristic of the phase-locked loop can influence the low-frequency-band impedance characteristic of the grid-connected inverter, and the stability margin at the intersection frequency is reduced to generate a low-frequency-band oscillation phenomenon due to the increase of the control bandwidth of the phase-locked loop or the impedance of the grid. Among them, a Phase Locked Loop (PLL) is a control system for synchronizing phases of a system. In grid-tied inverters, PLLs are used to detect and track the phase of the grid voltage, ensuring that the inverter output is synchronized with the grid. Phase angle disturbance deviation refers to the phase-locked loop output deviation of phase angle from grid phase angle. Such deviations may be due to grid fluctuations or noise. The current loop is a closed loop control link in the current control system, and stable output is realized by controlling current through feedback. The crossover frequency is the crossover of the open loop gain curve with the 0dB line. It reflects the frequency response characteristics of the system at which the phase margin of the system is minimal. The increase in the grid impedance affects the frequency domain characteristics of the phase locked loop and thus the stability of its output phase angle. The phase-locked loop output phase angle disturbance deviation can cause errors of a current control system, and the adjustment precision of the current loop is affected. An increase in the control bandwidth of the phase-locked loop or an increase in the grid impedance reduces the stability margin at the crossover point frequency, resulting in low-band oscillations. And the output current of the grid-connected inverter is unstable due to low-frequency oscillation, the harmonic distortion of a power system is increased, and the reliability of the whole system is reduced. In short, when there is a large impedance in the power system, the control system is susceptible to disturbances, resulting in instability and oscillations of the system. Such oscillations can affect the stability and efficiency of the power system. In order to solve the problem of low-frequency oscillation, in the prior art, additional damping is introduced into the low-frequency band by introducing virtual impedance to reshape the impedance characteristic of the low-frequency band of the system, which mainly comprises the following types: 1. Virtual impedance is introduced directly into the phase-locked loop to suppress the negative damping effect of the phase-locked loop. However, this approach suffers from the disadvantages of (1) increased complexity, introducing virtual impedance, and increased complexity of the control system, especially if precise adjustment of the virtual impedance parame