Well UserControl and Form are two different things. UserControls are placed inside the Window. You have a Close method tied up with Window. If you want to force the Window.Close from inside of UserControl, definitely you can do so using the following.
Window parentwin = Window.GetWindow();
But if you want to close only the UserControl, why dont you deal with Visibility. You can make the UserControl.Visibility = Collapsed, or you can remove the UserControl from the Parent using
I dont know what you wanted from this.