This paper studies and develops general analytical expressions to obtain three-phase current symmetrization under unbalanced voltage conditions. It proposes two procedures for this symmetrization: the application of the traditional expressions assuming symmetry conditions and the use of optimization methods based in the general analytical equations. Specifically, the paper applies and evaluates these methods to analyze the Steinmetz system design. Several graphics evaluating the error introduced by assumption of balanced voltage in the design are plotted and an example is studied to compare both procedures. In the example the necessity to apply the optimization techniques in highly unbalanced conditions is demonstrated.