In this presentation, we describe electrical interfaces able to tune the resonant frequency of piezoelectric energy harvesters, thanks to the inverse piezoelectric effect. We propose an analysis of the influences of the electrical interface on the dynamics of the harvester, and show how these influences might be used to both optimize the harvested power and tune the resonant frequency of the system. Finally, we present a self-powered integrated circuit that makes use of this effect in order to harvest energy from a piezoelectric energy harvester while adjusting its dynamics in real-time. The total power consumption of our circuit lies around 1µW, its end-to-end efficiency is 94%, and it is able to adjust the resonant frequency of a highly coupled harvester from 49Hz to 60Hz. This makes our circuit a promising solution for extracting energy from piezoelectric energy harvesters while improving their robustness to aging and environmental changes thanks to its frequency tuning ability.