Control-Free Inductive-Power-Transfer Transmitter With Misalignment Tolerance

Misalignment tolerance is a critical and challenging requirement for inductive power transfer (IPT) systems. To address this challenge, a transmitter (Tx) pad combining unipolar and bipolar coils is employed. This hybrid design enhances the magnetic flux, allowing a unipolar (or bipolar) receiver (Rx) pad to effectively capture it even in misaligned conditions. However, it is important to note that misalignment in positive and negative directions leads to a non-axially symmetric magnetic field distribution, resulting in a polarity reversal of the mutual inductance. This often requires complex detection and active control mechanisms to ensure misalignment tolerance, which can negatively impact system robustness. To overcome this challenge, this paper introduces a control-free and misalignment-tolerant IPT system. The proposed system utilizes a hybrid Tx pad consisting of rectangular and solenoidal coils, while the Rx pad is a rectangular coil. In order to eliminate the need for detection and control, a novel excitation method for the Tx coils is proposed, along with comprehensive schematics, modeling, and analysis. Additionally, the paper provides detailed parameter design considerations to minimize output fluctuation and achieve soft switching. Notably, the system maintains high power efficiency across the entire range of misalignment. To validate the effectiveness of the proposed control-free IPT system with misalignment tolerance, a 1-kW experimental prototype has been constructed. The experimental results show that the output voltage is 150 V with less than 4% fluctuation and the efficiency can be maintained at 90% with variation below 0.8% over a misalignment of 50% of the RSP length.