How to close a Global Quick Action Lightning Component popup?

Use $A.get("e.force:closeQuickAction").fire();inside your component controller at the necessary place. This line will close the modal box automatically.

The code I used was fine. I found following Known Issue existing for this same issue and it has been Fixed already in the platform now, and the Close behavior is not consistent with this Event firing from any context.

https://success.salesforce.com/issues_view?id=a1p3A0000001CcxQAE&title=lightning-component-which-uses-force-closequickaction-is-working-when-added-as-object-action-but-not-as-global-action