Incremental backup in postgresql in windows
Yes, it is right that the incremental backups are not possible in postgresql. 

I don't know if there is an alternative for pg_rman in windows but you can achieve the incremental backup in postgres with the continuous archiving. Which can be later restored with PITR (point in time recovery)

Details on:
https://www.postgresql.org/docs/current/static/continuous-archiving.html