Annual election of board members if there are 3 positions open and the same 3 members run for the Board is the election necessary?

Yes, and here's why.

Your membership may only be allowed to vote for board members and to vote regarding the annual budget -- read your governing documents to confirm this. (And your membership confirms its faith in board members by voting for them.)

Because your board leads a legal corporation, and the governing documents for your private democracy state that board member terms are limited to some number of years, board members must be re-elected in order to conform to the law.

If a member -- unit owner -- challenges a decision or action of the board, the board members may be asked to prove their right to decide or act. If not properly elected, the action or decision could be in jeopardy. This is not a situation in which a corporation wants to find itself, legally.