Similar to quick tiling to left / right, but places window in the middle of screen, width is changed to half of screen width if it was less.
1. install with systemsettings or download archive, unpack it and execute in created directory as regular user:
$ plasmapkg --type kwinscript -i .
2. create custom shortcut with this command:
qdbus org.kde.KWin /Scripting loadScript ~/.local/share/kwin/scripts/quickTileToCenter/contents/code/main.js; qdbus org.kde.KWin /Scripting start
Path to main.js can differ on your system, check it!
When you use shortcut, current active window will be tiled to center of screen.