How to check, that without the active damping the injected grid current is distorted & with activation of active damping, the injected grid current becomes sinusoidal ?

I have simulated the single phase grid connected inverter with LCL filter with active damping in MATLAB/Simulink R2021b. In the controller the everything else remains same, except that I have sensed the capacitor current , multiplied it with gain & subtracted with the original Vref, to get new Vref. This new Vref is then fed to the PWM switching block to get the required gate pulses. I have checked this simulation but the problem is that before the activation of active damping, the injected grid current is sinusoidal & after the activation of active damping, injected grid current is also sinusoidal. But it should not be like that. My question is, how to check, that without the active damping the injected grid current is distorted & with activation of active damping, the injected grid current becomes sinusoidal ? Can anybody atleast give me the suggestion.

Answer 1

[MULI]

Hi Siddharth,

• I understand that injected grid current remains sinusoidal before active damping. It might be due to the parameters of LCL filter and inverter. Make sure that the resonance effects of LCL filter would be noticeable without active damping by adjusting its parameters.
• I would suggest you to perform the Fast Fourier Transform(FFT) and Total harmonic distortion (THD) on the grid current before and after active damping. Comparision of these spectral analyses before and after implementing active damping control helps in analysing better.
• You can also try with different gain values for active damping control loop. It's possible that the gain was either too low to have unnoticeable effect or too high causing over damping.

Hope this clears your query!