Dynamic coil switching strategies for significant efficiency increases in electromagnetic energy generators

Abstract

The development of self-powering systems has been recognized as critical such that innovative stand-alone emerging technologies can operate sustainably from scavenged ambient energy. Electromagnetic generators (EMGs) using magnetic levitation architectures for mechanical vibration energy harvesting are a promising technology that can be tailored to specific needs and provide low-cost electric powering for both small-scale and large-scale devices. They also present non-complex design, with low maintenance requirements and can operate with stable performance for long periods of time. Despite these prominent features, their complex non-linear and hysteresis-based resonant characteristics makes performance optimization hard to achieve and still needs to be addressed as a function of the input excitation. Numerical and experimental results are here provided to demonstrate the effectiveness of a new concept of EMG that aims to dynamically adapt the coil-array architecture throughout its operation to ensure maximum harvested power and to optimize the transduction mechanism efficiency. The self-adaptive motion-driven levitation-based autonomously rearranges each coil independently as a function of the instantaneous time-varying characteristics of the levitating magnet (LM) position. The mechanism features two dynamic coil switching strategies: (i) on/off switching, by short circuiting, with transmission gate switches, the coils without influence on the electromotive force; and (ii) reversing polarity switching, to avoid the sum of electromotive forces cancels each other. Average output powers of 635 mW (up to ∼4.1 W of peak power) were obtained with only the 4-centre (out of 14) permanently active coils, while only 292 mW (up to 833 mW of peak power) were achieved with the 14-coils permanently connected under optimal load conditions and harmonic translational input excitations with 15 Hz frequency and 20 mm amplitude. However, the adaptive generator was able to provide an impressive average power output of 3 W under the same conditions. Up to 14-fold larger output average power and 5.5-fold larger electric efficiency demonstrate the potential of the proposed coil switching self-adaptation system for enhancing the total energy conversion from general widespread mechanical vibrations.