Omnidirectional Wireless Power Transfer Based on Constant Coupling Polarity Concept

With the rapid development of industrial and service robots, the cross-joint dynamic wireless power transfer (WPT) technology has attracted more and more attention. Unfortunately, the current range of motion angles that can achieve WPT coverage is limited, with the maximum coverage spanning from an axial angle ${\bm{\theta }}$ ranging from 0° to 75° and a circumferential angle ${\bm{\varphi }}$ of 360°. Currently, the realization of an omnidirectional WPT (omni-WPT) system remains elusive. This article pioneers in highlighting that maintaining constant coupling polarity (CCP) between the transmitting (Tx) and receiving (Rx) coils throughout the entire relative motion range is a fundamental requirement for achieving omni-WPT. Leveraging this insight, the cross-joint WPT with an omnidirectional operating angle is achieved for the first time. Subsequently, guidelines for designing a coupler based on CCP are provided, balancing the need for high transfer efficiency and low coupling fluctuation. To validate the effectiveness, a 13.56 MHz cross-joint omni-WPT system with ${\bm{\theta }}$ ε [0°, 180°], ${\bm{\varphi }}$ ε [0°, 360°] is designed, constructed and tested. The experimental results show that high efficiencies of more than 90% are achieved with low efficiency fluctuation of 1.73%. Meanwhile the output power fluctuation on the load is only 4.89%.