Name the year for womens doubles being raina tzvetkova emilia dimitrova
CREATE TABLE "past_winners" (
  "year" real,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text,
  "mixed_doubles" text
);
SELECT "year" FROM "past_winners" WHERE "womens_doubles"='Raina Tzvetkova Emilia Dimitrova';