As per the MSDN article http://technet.microsoft.com/en-us/library/jj219802(v=office.15).aspx
A continuous crawl does not process or retry items that return errors more than three times. A "clean-up" incremental crawl automatically runs every four hours for content sources that have continuous crawl enabled to re-crawl any items that repeatedly return errors. This incremental crawl will try to crawl the item again and then will postpone retries if the error persists.
But can I schedule the incremental crawl to run every 30 minutes apart from running the continues crawl? In the SharePoint admin screen, I can either either schedule the incremental or continues crawl but not both.
Can I do this using a PowerShell script?