Use the NewSubcase command to create a new subcase.
strCmdNewSubcase = "<NewSubcase Name="" "" ID="" "" AnalysisID="" "" IncludedLoads="" "" IncludedConstraints=""""/>"
For example:
strCmdNewSubcase = "<NewSubcase Name=""Subcase Test"" ID=""3"" AnalysisID=""1"" IncludedLoads=""1;2"" IncludedConstraints=""1""/>"