1. A feedback control system for automatic on-line training of a controller for a plant, comprising: a reinforcement learning agent connected in parallel with the controller; the learning agent comprising an actor network and a critic network operatively arranged to carry out at least one sequence of a stability phase followed by a learning phase; and wherein said stability phase comprises determining a multi-dimensional boundary of values, and said learning phase comprises generation of a plurality of updated weight values in connection with the on-line training, if and until one of said updated weight values reaches said boundary, at which time a next sequence is carried out comprising determining a next multi-dimensional boundary of values followed by a next learning phase.