What I want is:
Thus the logs folder never grows
The TimeBasedTriggeringPolicy works based of the filePattern. Basically, the smallest unit of time in the file pattern (%d) is the triggering time interval. In your case the value is 'dd' hence the policy is triggered every day.
The presence of %i in your filePattern keeps multiple log files for a day.
I would recommend trying without the %i in the filePattern.