Power Extracted from Piezoelectric Harvesters with Passive and Active AC/DC Stages

In Resonant Piezoelectric Vibration Energy Harvesters (RPVEHs) applications the maximization of the extraction of power represents one of the most important aspects. Typically, in practical applications an RPVEH is used for supplying DC loads and, for this reason, a power electronics AC/DC interface is placed between the RPVEH and the DC load. Two architectures are the most exploited ones for the AC/DC conversion in RPVEH applications. The first one is based on the use of a passive AC/DC diode bridge rectifier. Such type of architecture needs a monodimensional Maximum Power Point Tracking (MPPT) algorithm for maximizing the extraction of power. The second possibility is represented by a single active AC/DC stage based on a bidirectional active bridge rectifier. In this case, for the maximum power extraction, a multidimensional MPPT algorithm is needed with a not negligible increase in the overall system complexity. On the basis of the above considerations, from the designer point of view, the correct choice of the most suitable AC/DC interface is of utmost importance. Such a choice must take into account the system complexity (that is strictly linked to both power stage and control circuitry losses) and requires a correct quantification of the increase of power obtainable with an active AC/DC interface with respect to a passive one. This paper is focused just on such an aspect. In particular, the increase of power that can be obtained by using an active AC/DC converter is theoretically demonstrated and quantified as a function of the main RPVEH characteristics. Moreover, such a theoretical analysis is also experimentally validated.