A Current-Driven SSHI for Piezoelectric Vibration Energy Harvesters

An SSHI-based interface circuit for piezoelectric vibration energy harvesters is presented and experimentally validated. The developed solution relies on current-driven regulation of the rectifier output voltage downstream of a parallel SSHI stage. By measuring only the rectifier output current, the proposed Current-Driven SSHI (CD-SSHI) interface directly and continuously sets the rectified DC voltage to its optimal value under time-varying vibration conditions, without resorting to the perturbative approaches of classical Maximum Power Point Tracking (MPPT) techniques. The CD-SSHI reaches and tracks the Maximum Power Point (MPP) without the steady-state oscillations typical of perturb and observe MPPT, and without the power interruptions characteristic of the fractional open circuit voltage MPPT. Moreover, the proposed CD-SSHI interface significantly increases dynamic performance compared to an SSHI coupled with a conventional implementation of the P&O MPPT control. A theoretical analysis based on a general equivalent circuit model is developed to support the proposed circuit. Experimental results obtained from a prototype implementation demonstrate the effectiveness of the CD-SSHI interface in terms of both steady-state efficiency and dynamic response.