ngModelController doesn't currently support input type=file.
you can solve your issue with a custom directive.
app.directive('validFile',function(){
return {
require:'ngModel',
link:function(scope,el,attrs,ngModel){
el.bind('change',function(){
scope.$apply(function(){
ngModel.$setViewValue(el.val());
ngModel.$render();
});
});
}
}
});