Abstract
Parallel synchronized switch harvesting on inductor(P-SSHI) circuits have been proved to enhance piezoelectric vibration energy harvesting (PVEH), but the maximum conversion efficiency is obtained only when the voltage across the storage capacitor (VSC) equates to the optimal value. For bi-stable rotating PVEH with nonlinear magnetic force in engineering applications, however, the VSC will change greatly when powering real electric loads, thus it is impossible to maintain high conversion efficiency. In order to solve this problem, this paper presents an improved P-SSHI circuit with controllable optimal voltage (COV-PSSHI) by using a voltage control strategy between the storage capacitor and the electric load. The innovation is to control and maintain the VSC close to the optimal value. Firstly, the COV-PSSHI circuit is proposed and its theoretic model is built in detail. Then its average harvested power (AHP) is theoretically derived and AHP of the COV-PSSHI circuit is proved to be more than that of a classical P-SSHI circuit. In the end, experiments are performed to validate the performance of the COV-PSSHI circuit. It can be seen that the COV-PSSHI circuit can increase the AHP by factor 1.25 compared with classical P-SSHI circuits, which is enough to intermittently power the wireless sensor node. Also power consumption of the voltage control circuit has few effects on the COV-PSSHI circuit. In particular, it needs to optimize the envelop capacitor, the parallel inductor and two threshold voltages of the voltage controller in order to implement the COV-PSSHI circuit well in practice.