Power Stability Enhancement in Inductive Wireless Power Transfer Systems: A Review

Inductive Wireless Power Transfer (IWPT) using magnetic induction has seen remarkable progress over the past few decades. Despite their growing popularity, IWPT systems suffer from output power instability due to variations in system parameters. This paper provides a comprehensive review of the strategies for maintaining stable output power under system parameters that deviate from the original design specifications. First, the root cause of power instability and the state-of-the-art techniques for avoiding the output power decrease are carefully examined. In addition, by comparing these methods, this paper clarifies their respective application scenarios and offers insights into their practical benefits. Furthermore, this paper outlines potential future advancements in improving the robustness and reliability of IWPT systems. As presented, the output power instability is induced by frequency mismatch and coupling coefficient variation. Resonant frequency regulation, operation frequency regulation, and coupling optimization are targeted techniques for the issues. Based on the comparison, respective application scenarios are clarified. Moreover, the trade-offs should be carefully weighed in terms of their impact, complexity, and cost. Future research directions on variable devices, closed-loop control, and new mechanisms for power stability enhancement are highlighted, thereby facilitating the pervasive application of IWPT systems.