Fully Self-Powered Inductor-Less Electromagnetic Vibration Energy Harvesting System Using Auxiliary Coils for Hysteresis Current MPPT Control

Abstract

Utilizing coil inductor of electromagnetic vibration energy harvester (EVEH) to form single stage ac–dc boost converter can make the self-powered milli-power system more compact. However, large output current harmonics of EVEH significantly degraded the output power in such system. This article proposes a new approach of adopting hysteresis current control to realize maximum power point tracking (MPPT) and reduce current harmonics in inductor-less converter by using auxiliary coils. The output characteristics and correlations between multiple coils are firstly studied to verify the feasibility of using auxiliary coil to represent the output of main coil. The optimal winding strategy for main coil and auxiliary coils is revealed for no degradation on maximum output power of main coil. Based upon these, a completely self-powered multicoil EVEH system is designed with auxiliary coils as reference for MPPT controller and as auxiliary power supply in cold-start. Experiments show that the designed prototype can obtain 9.54 mW output power at acceleration of 3 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with the overall efficiency of 77.6%. To charge a 10 mF supercapacitor from zero to 5 V, an average output power of 7.27 mW can be obtained with an average charging efficiency of 62.4%. In addition, the start-up method adopting auxiliary coil allows the system to cold-start when the output voltage is lower as 0.5 V. The proposed approach has been demonstrated to achieve high overall efficiency in milli-power self-powered EVEH system and also has significant advantages in cost and volume compared with using external devices to obtain reference.