Three phase grid connected inverter-Capacitor in LCL filter

Hi all,

I am doing a simulation for three phase grid connected inverter for reactive power control. For LCL filter implementeation, I have made a model in which I am using converter side inductor Lf and grid side inductor Lg and ignoring the capacitor of LCL filter, the simulation is working fine. But when I add the capacitor the output waveforms are distrorted. The values of LCL filter are designed properly according to the LCL filter design criterea.

Is there any way to insert capacitor without resulting in distorted votlage,current and power waveforms. Somebody has recommended me to use doubly tuned harmonic filter instead of capacitor in the LCL filter, Is that a good solution? And will adding the harmonic filter is equivalent to adding the capacitor, will it effect the stability of the system.

Answer 1

[Pratyush]

Hi Javed,

Adding a capacitor to an LCL filter in a three-phase grid-connected inverter simulation and experiencing waveform distortions can be due to reasons like resonance, improper damping, parameter mismatch, or simulation settings. To address these issues:

1. Use active or passive damping methods to mitigate resonance effects.
2. Ensure the LCL filter design, including the capacitor value, is correct and avoids resonance near the switching frequency.
3. While a doubly tuned harmonic filter can reduce specific harmonics, it doesn't replace a capacitor's broad filtering role in an LCL filter. It might be used complementarily.
4. Check solver type and time step to accurately capture the filter dynamics.
5. Analyze the stability impact of any filter modifications, including adding damping or harmonic filters.

Hope this helps.