A Novel Power Management Circuit Using a Super-Capacitor Array for Wireless Powered Capsule Robot

Wireless power transmission (WPT) based on near-field inductive coupling principle is a promising solution to the power supply issue of a freely moving capsule robot (CR) that employs dc motors as actuators. However, the limited inductive power can cause a voltage drop when dc motors start or stall, because short-time peak power is required. To handle the voltage drop issue, we propose the use of a novel power management circuit (PMC) that consists of four successively connected segments of a full-bridge rectifier for ac-dc conversion, a buck dc-dc converter for highly efficient voltage reduction, a power buffer for power storage and short-time power supply, and a low drop-out (LDO) regulator for voltage stabilization. The power buffer is implemented with a super-capacitor array (SCA) that employs the output voltage of the dc-dc converter as its charging voltage. To analyze and optimize the PMC containing the SCA (PMC-SCA), a model is built based on deducing the input resistance relations between each pair of adjacent segments, and its correctness is then validated experimentally. A comparison between the PMC-SCA and the traditional PMC (a rectifier + a regulator) is also conducted, and the former shows superiorities in both reducing voltage drop and improving safety related to temperature rise of onboard receiving coil (RC). Finally, a primary PMC-SCA prototype measuring Φ 13 mm × 4 mm is integrated to an inchworm-like CR for effectiveness validation; the CR working voltage is measured to be higher than 3 V at all times, which ensures the proper functioning of the CR.