Direct calculation of source impedance to adaptive maximum power point tracking for broadband vibration energy harvesting

This article presents an adaptive maximum power point tracking technique for broadband vibration energy harvesting. The presented technique employs a discontinuous conduction mode buck–boost converter to emulate a matched resistor for a vibration energy harvester. Instead of traversal search, the optimal duty cycle can be tuned in one step based on direct calculation of source impedance, which is realized by active pulse width modulation perturbation strategy; based on it, the circuit can work well in impedance match adaptively without any prior knowledge of a harvester. The prototype circuit is implemented by an ultra-low-power consumption MSP430 microcontroller with a stable external power supply. It produces 1.32 mW (0.4 g and 88.2 Hz acceleration) from a piezoelectric vibration energy harvester and 1.16 mW (0.12 g and 19.3 Hz acceleration) from an electromagnetic vibration energy harvester. According to the definition of power–bandwidth product, the experimental results achieve 75.2% and 39.9% of the theoretical optimal capacity of the piezoelectric vibration energy harvester and electromagnetic vibration energy harvester, respectively. The detailed experimental data indicate that the proposed approach achieves a large improvement than employing a fixed load resistance in a wide frequency band. Furthermore, the possibility of self-powered is confirmed based on a brief estimation of power losses on the proposed circuit.