Switching Delay Effects on Nonlinear Piezoelectric Energy Harvesting Techniques

Energy harvesting using piezoelectric elements received much attention as vibrations are widely available and as piezoelectric transducers feature high-power densities and promising integration potentials. It has also been shown that applying a nonlinear treatment on the output voltage of the piezoelectric material can significantly enhance the performance of the device. This process consists of inverting the piezoelectric voltage when the displacement is maximum, which therefore requires a way of synchronization. In practical applications, however, a delay may happen between the inversion and the actual occurrence of an extremum. The purpose of this paper is to investigate the effect of such a delay on the microgenerator performance and therefore to predict the power output that can be expected under real circumstances. Theoretical analysis validated through experimental measurements shows that the effect may not be the same for positive or negative delays. It is also demonstrated that the effect is not significant as long as the delay is small. The acceptable delay range also increases as the electromechanical system becomes more coupled and/or less damped. Under such configuration, the output power can even be slightly increased as the delay permits controlling the tradeoff between energy extraction and damping effect.