make online model according to the lattice.Lattice instance
            :param lattice_instance: lattice.Lattice instance, created from lte/json file
            :param use_bl: selected beamline name
            :param simu: online modeling type, 'simu': simulation,
                         'online': online (incorporate control fields)

def _create_online_model(self, lattice_instance, use_bl, mode='simu'):
        """ make online model according to the lattice.Lattice instance
            :param lattice_instance: lattice.Lattice instance, created from lte/json file
            :param use_bl: selected beamline name
            :param simu: online modeling type, 'simu': simulation,
                         'online': online (incorporate control fields)
        """
        new_model = models.Models(name=use_bl, mode=mode)
        ele_name_list = lattice_instance.getElementList(use_bl)
        ele_eobj_list = []
        for ele in ele_name_list:
            ele_eobj_list.append(lattice_instance.makeElement(ele))
        new_model.addElement(*ele_eobj_list)

        return new_model