Research on resonance suppression strategy of LCL grid-connected inverter
Zhang, Shuyue (2026)
Kandidaatintyö
2026
School of Energy Systems, Sähkötekniikka
Kaikki oikeudet pidätetään.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2026051041921
https://urn.fi/URN:NBN:fi-fe2026051041921
Tiivistelmä
This thesis focuses on the inductor-capacitor-inductor (LCL) grid-connected inverter, to address resonances problems and improve grid current quality. Because of the introduction of LCL filter, this system shows inherent resonance characteristics. And the grid current quality lower down because of grid harmonics and impedance change.
To solve above problems, a system mathematics model established for analysing the resonance characteristics of the LCL system, providing a theoretical basis for subsequent control strategy design. And then, a dual closed-loop current control structure introduced to analyse without damping and active damping method respectively. What’s more, using grid voltage feedforward strategy to improve control method, at the same time, designing Proportional-Integral (PI) controller parameters and damping coefficient. Finaly, MATLAB/Simulink modelling and simulation were used to verify the design rationality under the different working condition.
As the simulation result depicts, the proposed control strategy can effectively suppress system resonance, reduce the total harmonic distortion (THD) of the grid-connected current, and improve system stability and current tracking performance. Specifically, under 5th harmonic injection, the THD is reduced from 3.18% to 0.33%; for 5th–13th harmonic conditions, the THD decreases from 2.25% to 1.11%; in high-frequency harmonic conditions (34th), the THD is reduced from 3.41% to 1.20%, indicating an improvement of approximately 64.8%. Under voltage sag conditions, a slight reduction in THD from 2.94% to 2.74% is also observed. These results demonstrate that the proposed feedforward strategies exhibit good control performance under different frequency conditions.
To solve above problems, a system mathematics model established for analysing the resonance characteristics of the LCL system, providing a theoretical basis for subsequent control strategy design. And then, a dual closed-loop current control structure introduced to analyse without damping and active damping method respectively. What’s more, using grid voltage feedforward strategy to improve control method, at the same time, designing Proportional-Integral (PI) controller parameters and damping coefficient. Finaly, MATLAB/Simulink modelling and simulation were used to verify the design rationality under the different working condition.
As the simulation result depicts, the proposed control strategy can effectively suppress system resonance, reduce the total harmonic distortion (THD) of the grid-connected current, and improve system stability and current tracking performance. Specifically, under 5th harmonic injection, the THD is reduced from 3.18% to 0.33%; for 5th–13th harmonic conditions, the THD decreases from 2.25% to 1.11%; in high-frequency harmonic conditions (34th), the THD is reduced from 3.41% to 1.20%, indicating an improvement of approximately 64.8%. Under voltage sag conditions, a slight reduction in THD from 2.94% to 2.74% is also observed. These results demonstrate that the proposed feedforward strategies exhibit good control performance under different frequency conditions.