In this paper, an equivalent electric model for railway vehicle suspension harvester is proposed. With reference to the maximization of the extracted power, the open issues for such kinds of systems are reviewed. In particular, it is evidenced that the use of passive diode bridge rectifiers unavoidably leads to a reduction of power with respect to both the resistive load case and the theoretical optimal load case. Therefore, suitable average power maximization techniques and power electronics architectures are needed. In this paper, two techniques are proposed. The first technique is based on the adoption of additional passive components and, in the considered test cases, it allows the increase of the power output up to 45%. The second technique is based on the adoption of a properly controlled active power electronic interface and it is much more efficient since, in the considered test cases, it allows the increase of the power output up to 135%.