I have designed a controller using predictive control for NPC VSI 3 level . the out put result shows that there is shift in one phase of the three phases what could be the possible errors
Vishal,
You have not given any detail of the predictive control. This could have different forms. For the moment I am assuming that the control:
If this interpretation is correct, then one or more of the following could be the problem:
- The R-phase neutral is not clamped properly (notice a negative DC shift in the waveform) !
- One of the Y-B or B-Y switchings (most likely Y-B) is not occurring when it should ! This may or may not be due to the bad clamp of R-phase.
- One of the Y or B phase devices is failing to switch at the pint where you observe a sudden simultaneous discontinuity in those two waveforms.
- You have not mentioned anything about the load ! There could be a goof in the load unbalance that could lead to a similar effect.
- I am assuming that the desired current at each instant and measured current are assuming correct values. If for example, one of the measurements is not proper, then that may show up as an unbalance. (Least likely !)
Will it be possible for you to post the output voltage switching waveforms as well ? That may give everyone a better lead !!
Cheers !
-Sanjay
I think Rdc is causing the problem which connected in series with a voltage source, Is the any method for the calculation of Rdc and RL values for load
Hi Vishal,
Frankly, I am rather surprised at your observation !
I can not think of any reason as to why the resistance on source side may lead to a change in unbalance unless there is an issue of neutral grounding (eg. the ground you have used for diode clamps is not at the same potential as the ground on the DC side, or something as erroneous and weird as that !!).
Anyway, I will avoid "guessing" further unless you may show us the circuit configuration. I hope it will not be difficult for you to post it ?
Regarding the values of Rdc and RL that you have now posed:
- The DC side resistance depends on the nature of the DC source (eg. a battery and a PV panel will have different characteristic values of Rdc - you should not tamper with them arbitrarily !)
- The load side resistance (star or delta connected) can be chosen by you depending on the three phase current you want the load side to draw, and on any load side voltages (eg., network bus voltage, or motor load back emf, if any) that may be included.
Hope all that helped !
-Sanjay
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