This paper presents a review and a comparative analysis between mathematical models for the efficiency of power converters. Two different types of models are considered, being one for converters subject solely for output power variations, and a second one also considering input voltage variations. Both cases are particularly important for systems fed by renewable sources as photovoltaic panels or wind turbines. Knowledge of the appropriate models is of interest in the development of high-performance systems, allowing one to optimize the global efficiency of the converter system. Experimental results concludes the comparison between the investigated models and a discussion of pros and cons of each model are presented, providing to authors a better choice for modeling the efficiency behavior of power converters.