In large pot over medium-high heat, heat oil; add onion, red pepper, green pepper, carrots, celery and garlic. Cook until onion has softened (5-6 minutes). Stir in tomatoes and their liquid, black beans, kidney beans, great Northern beans, corn, chili powder, salt, oregano and broth. Bring to a boil; reduce heat, simmer 20-30 mintues.