modelName = 'archModel';
arch = systemcomposer.createModel(modelName); % Create model
rootArch = get(arch,'Architecture'); % Get architecture

newComponent = addComponent(rootArch,'Component1'); % Add component
inPortComp = addPort(newComponent.Architecture,...
'testSig','in'); % Create in-port on component
inPortArch = addPort(rootArch,'testSig','in'); % Create in-port on architecture
compDestPort = getPort(newComponent,'testSig'); % Extract component port object
archSrcPort = getPort(rootArch,'testSig'); % Extract architecture port object

interface = arch.InterfaceDictionary.addInterface('interface'); % Add interface
interface.addElement('x'); % Create interface element
archSrcPort.setInterface(interface); % Set interface on architecture port

conns = connect(archSrcPort,compDestPort,'SourceElement','x'); % Connect ports
elem = getSourceElement(conns)