A319 Captain experienced uncommanded go-around during visual approach with autopilot and autothrottle engaged. Flaps were oversped and thrust could not be reduced until reaching 2500 FT. A second approach attempt produced the same result. The third attempt with autopilot and autothrottle off was successful.

Narrative

Due to ATIS at ZZZ and direction of flight; we set up to arrive on XXR. Once handed off to Approach we were told to expect Runway XXL and revised FMS; re-briefed; and repeated Descent / Approach Check. Upon handing us off to tower; the tower advised us clear for visual on 'XXR'. When questioned he apologized and continued with vector for XXL. We had made no changes to FMS for clearance in error. We were vectored to descent outside the FAF. The First Officer was pilot flying and had autopilot 2 engaged. All indications and procedures were normal until inside the FAF at approximately 1700 MSL at which time the aircraft executed an UNCOMMANDED go-around. Initially this was indicated by speed bug rising rapidly and disappearing off-scale along with significant power increase. First Officer attempted to disconnect autopilot and autothrottles using any acceptable means possible with no effect. I as pilot monitoring also attempted disconnect with no effect. Due to the nature and rapidity with which this event occurred; we were only able to get gear up before we rapidly exceeded 40-50 KT overspeed of flaps even though they were in early stage of retraction. At approximately 3000 MSL we regained control of aircraft although not entirely sure how other than repeated disconnect attempts. We were at 250 KTS. We advised ATC that we had gone around and were able to return; so they vectored for another attempt. This time with vectors arriving from East side of airport the SAME SCENARIO REPEATED in its entirety! We had aircraft set up with First Officer flying and autopilot 2 engaged; because we had no reason to believe there was a problem with that configuration; although we weren't sure why it had happened. After the SECOND UNCOMMANDED go-around we manually flew the aircraft to uneventful landing on XXL. During the second go-around ATC queried what the problem was and I advised them we had an Auto-Throttle Problem and would return to land without system active and expected no further issues. 'Emergency' WAS NOT declared. As pilots we naturally question ourselves repeatedly as to whether we may have done something wrong but could come up with nothing. It is our understanding; however; that this is not the first occurrence of this type and AIRBUS is aware of it.