You could use qdbus, if available.
This command may be useful whenever the Kickstart/menu button in KDE doesn't work (you click on the menu button or hit Alt + F1 but the menu won't open), which means you're unable to log out or hibernate.
The following commands should work with KDE 5 (Plasma).
Hibernate via command line:
qdbus org.kde.Solid.PowerManagement /org/freedesktop/PowerManagement CanHibernate && qdbus org.kde.Solid.PowerManagement /org/freedesktop/PowerManagement Hibernate
Suspend via command line:
qdbus org.kde.Solid.PowerManagement /org/freedesktop/PowerManagement CanSuspend && qdbus org.kde.Solid.PowerManagement /org/freedesktop/PowerManagement Suspend
Show logout screen via command line:
qdbus org.kde.ksmserver /KSMServer logout 1 3 3