Alternating Resistive Impedance Matching for an Impact-Type Microwind Piezoelectric Energy Harvester

This paper proposes alternating resistive impedance matching for an impact-type microwind piezoelectric energy harvester (PEH). The proposed PEH is composed of a piezoelectric cantilever and a small wind turbine, which strikes the free end of the cantilever to generate vibrations. The motion of the cantilever is divided into two action periods, impact and vibration, whose optimal resistive loads are different. The impact period detector, in collaboration with a wake-up circuit, identifies the current period and sets the frequency and duty cycle of the oscillator to provide the optimal load for each period. When the cantilever generates energy, the wake-up circuit activates the converter to charge the battery. Otherwise, the circuit goes into sleep mode to save power. The proposed circuit is able to cold start even if the battery is completely drained. Experimental results indicate that the efficiency of the proposed circuit is 70.3% for a wind speed of 1.3 m/s, which is 6.3% higher than that of an existing resistive matching circuit with sleep mode and 7.7% higher than that of a circuit without sleep mode. The proposed circuit is intended for low-speed winds, but it also achieves high efficiency for higher wind speeds.