I am simulating three phase grid ties inverter and the filter capacitors are connected in star connection. The neutral point of filter cap is connected to the the mid point of split cap. My simulation causes imbalance in voltage at mid point of split which leads my current controller into saturation region.How can I eliminate this error?
Try adding in high value resistors in parallel with split cap as a voltage divider. Should be good enough for simulation
I have already tried by taking higher value of resistor in range of Mega ohm but it doesn't work.I am simulating grid tied inverter and DC voltages are 900 volt. The circulating current cause imbalance in split cap voltages and it shows 400 v and -500 v and with 20 v pk-pk ripple.
try this
http://www.ee.iisc.ernet.in/new/people/faculty/vjohn/PaperPdf/2011_NPEC_Anirban.pdf
Try to view the power transfer and power adaptation conditions between source and load via inverter; and evaluate the loss charge that causes imbalance;
Well, you have to determine where the imbalance is coming from in your circuit and take measures to correct it. Without seeing your schematic or block diagram, I can't be of much help. For example, it's not clear to me why you have split capacitors in the first place. Is the input to your inverter 1-Phase AC, 3-Phase AC, or DC? One way to fix it, is to put ballasting resistors across each of the two series caps. This is done in real life to minimize imbalances due to unequal capacitor leakage current. In a simulation, you have no leakage current unless you added it to your model, and even so, why would it be unbalanced? The value of the resistors depends on how much current imbalance there is in your circuit and you need to return to your simulation to know that. I'm designing a real 90 kVA 3-Phase, 400 Hz, sine wave inverter that runs form 3-Phase 60 Hz AC at 480 VAC. So I've had to deal with all these sorts of problems.
Try this
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=4758468&queryText=miranda%20homeroi&newsearch=true
Of course by adding resistors in parallel with the capacitors , the difference between capacitors voltage reduce BUT the resistors reduce the efficiency too. So its a better way to use a active balancing circuit by using IGBT and inductor (in this case 2 IGBT and 1 inductor) . then you can balance the capacitors voltage. its so fast and so efficient.
trust me , I use it before.
Active cap voltage balancing also suffers from the same loses as resistor balancing, perhaps at a slightly lower lever, so it's not a big advantage for the extra complexity usually.