A300 Captain reported a failure of the pitch trim system and autopilot during climb to cruise altitude. The Captain returned to the departure airport and landed safely.

Narrative

Aircraft had #1 Pitch Trim and #1 Yaw Damper MEL'd prior to departure. On climb out passing 17;000 ft. #2 Pitch Trim and #2 Auto Pilot disengaged. I coordinated with ZZZ Center for a level off at FL200 to troubleshoot. Ran ECAM and QRH procedures but pitch trim would only stay engaged for 20-30 seconds before tripping off again. Considering the options; the FO (First Officer) and I agreed that it would be safer to return to ZZZ than continue the four hour flight to ZZZ1 with no autopilot; manual only pitch trim and non-RVSM. I Sent an ACARS to operations with our situation and intentions. Operations acknowledged and asked if we were [requesting priority handling]; which we were not. I then coordinated with ZZZ center for a return to the airport. Passing 10;000 ft. I took Pilot Flying duties and we requested vectors for a long final in order to get a better feel for the manual trim in landing configuration. We received vectors for a 14 mile final for runway XX; slowed and configured early for an uneventful landing and taxi back. After shutdown I was called by the duty officer to fill him in and then called Dispatch to see if there were any unanswered questions.Pitch trim system failure.No suggestions for the root cause; system failures are part of flying.