Is there a way to model self inductance and mutual inductance of a transfomer?

Hi everyone, I need to design a transformer as a part of the full bridge dc-dc converter model. The transformer is the typical galvanically isolated central tap transformer that steps down the voltgage before we pass it int the final recitifier.However i face a problem with designing the transformer. if i use a two normal mutual inductances , i get the following MATLAB warning: Warning: Matrix is close to singular or badly scaled. RCOND= xxxxxxx. In ..\MATLAB\R2011b\toolbox\physmod\powersys\powersys\private\etass.p>etass at 239

However , while using a linear transformer block, i cannot input the mutual inductance value and my model with a linear transformer and with the mutual inductance gives two very different results. Is there any way to model a centre tapped tranformer in MATLAB, where i can input the mutual inducntance values?