General stability criterions for zero phase angle controlled loosely coupled inductive power transfer systems

Loosely coupled inductive power transfer (LCIPT) systems are designed to deliver power efficiently from a stationary primary source to one or more movable secondary loads over relatively large air-gaps, however this becomes more difficult as the complexity of the system grows. A general analysis of such LCIPT systems is essential for optimal system design. This analysis is undertaken for LCIPT systems that attempt to operate with zero phase angles between the primary input voltage and current in order to achieve minimum cost and maximum performance. The paper develops general boundary conditions that if followed ensures only one operating condition exists for any practical load thereby assuring stable operation and power transfer capability. This is verified by measuring a contact-less electric vehicle battery charging system