This paper proposes an analytical methodology to evaluate the power processed by dc-dc converters operating as series voltage regulators, which provide an alternative to increase efficiency in photovoltaic systems. Via the analysis of both active and nonactive power processing, the proposed methodology allows to clearly distinguish among circuit topologies as truly partial-power processing (PPP) or just partial active power processing topologies. When an isolated dc-dc topology is connected in series as a voltage regulator, the overall processed power can be reduced, which reduces power losses and improves efficiency. Conversely, this paper also demonstrates that some series-regulator topologies may not actually reduce the proportion of nonactive processed power. To demonstrate the applications of the proposed methodology and to emphasize its significance, two well-known series-connected voltage regulators (flyback and full-bridge phase shift) and a full-power regulator (boost) were evaluated. The results indicate that the full-bridge series regulator can perform a true PPP, whereas the flyback series-regulator processes the same amount of power as that processed by conventional nonisolated boost converters and cannot be considered a partial-power topology. This study finding contradicts assertions in the literature that this topology achieves high-efficiency dc-dc conversion through PPP. To confirm the theoretical analysis, experimental results from three 750-W prototypes are presented alongside its simulations. EVALUATION OF POWER PROCESSING IN SERIES-CONNECTED PARTIAL-POWER CONVERTERS