create a Model reference and bind your entities like below,
var oSRVModel= new sap.ui.model.odata.ODataModel('XXXXX....XX/odata/sap/ZDEMO_PO_VR_SRV', true);
sap.ui.getCore().setModel(oSRVModel, 'oSRVModel');
Bind your fragment like,
oSRVModel>/EPoSet
oSRVModel>/PoDetailsSet
oSRVModel>/EPoiSet
