DC link back-to-back converters are widely used in industrial applications. This interest comes from their power factor unity capability on the utility grid and to maintain regulated output parameters, thanks to the decoupling between the grid and the load side. In this paper, a 150 KVA prototype of DC link back-to-back converter for electrical resistance seam welding applications is described. The focus of the paper is on the control strategy developed to absorb constant power from the three-phase utility grid. The key idea is to allow the voltage on the DC bus to vary in order to avoid the propagation at the input side of the pulsed power required by the load. An estimation procedure of the load parameters is presented too. The effectiveness of this control scheme has been proved by simulations and tests.