Aim of this work is to determine the losses of power converters by calculation and simulation and to compare these results with measurements on real converters. The comparisons concern the following circuits: a conventional matrix converter, a very sparse matrix converter and a back-to-back converter. Simulations have been done with PSpice, including the complete semiconductor models. The results are compared with the values obtained by analytical methods and with the measurements made on two prototypes. The results presented in the paper can be regarded as preliminary. Indeed, the differences between them are rather large and require additional work to be explained more completely.