This year, Tisha B’av begins on Mos’ae Shabbat. In such a case, a conventional Havdala is not recited. There is no wine because it is a fast, and there are no Besamim (spices), because enjoying the fragrant aromas on a day of mourning is not appropriate. We do recite the Beracha "Boreh Meoreh HaEsh" on the fire, because that was instituted specifically for Mosa’eh Shabbat.
On Sunday Night, at the conclusion of the fast, we make Havdala consisting of two Berachot: "Boreh Pri Hagefen" on the wine and "Hamavdil Ben Kodesh L’chol." The Beracha on the Besamim is not recited on Sunday night, because it is no longer appropriate. The whole point of smelling the spices is to invigorate the body on Mosa’eh Shabbat as the extra Neshama of Shabbat departs. According to the Tosafot, this is why the Beracha of Besamim is not recited on Mosa’eh Shabbat that falls on Yom Tob. Since the holiday also brings an extra Neshama, there is no vacuum to fill. Others explain that the reason is that the festive Yom Tov Seudah fills the place of the Besamim.
It should be pointed out that we do not begin the Havdala with the conventional Pesukim of Beracha: "Rishon Lesion etc." Those Pesukim were instituted to arouse joy and good fortune as the new week begins. Since in this case, the Havdala is recited on Sunday nIght, after the new week has begun, the Pesukim are omitted. The Havdala begins with "Kos Yeshuot Essa," and then the two Berachot.
If a person must eat on Tisha B’av, for Halachically approved medical reasons, they must first recite Havdala. According to Hacham Ovadia, this is done immediately on Mosa’eh Shabbat, even if they don’t need to eat until the morning. When making Havdala, they also omit the introductory Pesukim and the Beracha on Besamim, because it is still a day of mourning.
SUMMARY
On Mosa’eh Shabbat, the beginning of Tisha B’av, the Beracha on the flame is the only part of Havdala recited. On Sunday night, at the conclusion of the fast, the Beracha on the wine and "Hamavdil" is recited, with no introductory Pesukim, and without the Beracha on the Besamim.
One who is allowed to eat on Tisha B’av must recite Havdala, without the Pesukim and spices, on Mosa’eh Shabbat.
