Highly Misalignment-Tolerant Series-Series IPT System with Overcurrent and Overpower Protection for Underwater Manta Ray Robots

Inductive power transfer (IPT) technology is becoming a convenient and promising charging solution for underwater vehicles and robots. The conventional resonant SS IPT system potentially has overcurrent and overpower issues at weak magnetic coupling conditions. This paper proposed an SS IPT system with a detuned transmitter circuit, which limits the transmitting current and system power at weak and even zero coupling conditions and achieves a high misalignment tolerance with stable output power. A detuned SS IPT prototype is implemented with a switching frequency of 250kHz and a primary resonant frequency of 200kHz. The system performance is tested in both air and saltwater with an input dc voltage of 150V and a 14.8V lithium battery load. Experimental results show that the maximum transmitting current only achieves 2.48A with a low power loss of 10.1W at zero coupling condition and the maximum achievable system power is limited at 190W. With a transfer distance of 50mm and a horizontal misalignment range of [-60mm 60mm], the output power has a small fluctuation of 31.25% and 26.3% in air and saltwater, respectively. In the aligned condition, the maximum system efficiency achieves 91.37% with 129.6W in air and 87.79% with 128.4W in saltwater.