In a skillet, heat oil over medium heat. Add the onions, celery and carrots, and cook, stirring often, until softened. About 5 - 7 minutes.Add the garlic, caraway seeds, salt and peppercorns and cook for about 1 minute.Transfer the carrot/onion/celery mixture to a food processor, add ½ of the tomatoes & juice, then process until smooth.Transfer to a slow cooker.Add the remaining tomatoes, sugar, beets and potato.Add the stock. Stir.Cover and cook on low for 6 hours, or on high for 3 hours, or until the vegetables are tender.After this time add the vinegar, and cabbage, mix well and cook on high for 20 - 30 minutes more.Instead of pureeing the vegetables before the soup has cooked, use an immersion blender and puree the soup after it has cooked (at the step just before you add the vinegar and cabbage).