ComponentA is your component on the page and
ComponentB is the component used as a Global Action.
Are you saying you want ComponentA to open ComponentB as a global action just so that ComponentB displays as a modal in the middle of the screen? If that's the case, I would not recommend that approach. Take a look at the Modal component in SLDS: https://www.lightningdesignsystem.com/components/modals/
You can have a Lightning Component open a modal in the middle of the screen. Check out the PropertyMap and PictureGallery components in the DreamHouse sample app for an example.
However, if your use case is that the component on the page and the component used as a global action need to reuse shared functionality, then I would encapsulate the shared functionality in a separate component (ComponentC), and have both ComponentA and ComponentB use ComponentC as needed. ComponentA would instantiate it in a modal as described above (and as as illustrated in the PropertyMap and PictureGallery components in DreamHouse)