Dear All,
I am working on the grid connected 3 level inverter using space vector modulation. I am using cascaded voltage oriented controller to control the grid current. But the wave shape of reference and actual value of active and reactive component look like as in the attached file.
My question:
(1) Do I need to normalise the voltages before making the space vector modulation signal?
(2) What is the step size for nonlinear current controller?
Could anyone please help me by giving the answers.
Tamanna Alam
Can you post your system and/or control architecture, so that the specifics could be understood better?
from what i am seeing in the id and iq , there are harmonics in both of them, do a THD analysis using power GUI (assuming you are using Matlab )@@, you will see what are harmonic components in the waveform and check if they should even be present in the system or not.
as far as normalization goes, yeah it is required in general, as per my experience.
I have attached here the schematic of current controller and the output of PLL.
In space vector modulation, normalisation is done while dwell time calculation.
Do I need to normalise twice that means normalise the output of current controller and again normalise in dwell time calculation?
Tamanna Alam
The SVPWM is readily available in Matlab , there u would need to convert all modulation signals (of a , b ,c phase ) in space vector which will have a magnitude between 0 to 1 ( use of saturation block is advised) , in total u just need to divide the o/p of current controller by Vdc/2, since it is not done internally within the block . In the Matlab picture, the PWM block is not visible.
Your Id reference is very high , I would suggest you recheck the power you are pushing into the system and change the Dc bus voltage so that you don't have to push such high current at all.
PWM block is constructed at the final stage of space vector modulation. Output is also divided by VDC/2 during dwell time calculation. I am attaching here the PWM signal.
The same controller, same values, I have used to make the grid connected inverter using sinusoidal PWM and it is functioning properly.
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