thanks for your contributions in advance.
i am building three level VSC back to back converter. It works perfectly without the power transformers at both ends. Now when I try to include the transformers of y/delta type there seem to be a correction factor for PLL of +/- (Pi/6). However, I tried to these phase shift corrections but it doesn't track the references.
i would appreciate if one can give a clear explanation about this problem and we can share models too for others to learn from our mistakes.