Analysis of the possibilities for control-free voltage and current source operation of “wireless power transfer - wpt” systems

Recently Wireless Power Transfer (WPT) is widely studied in order to efficiently feed many different kinds of loads through a large air gap and loosely coupled transformer. The transformer presents large leakage inductances, resulting in poor voltage regulation against load variation. Moreover, the low magnetizing inductance, results in high magnetizing currents, reducing the overall efficiency. In order to improve the WPT performance, capacitive compensation techniques are applied in both sides of the transformer. Series compensation is commonly used at the primary side of the WPT transformer while Series or Parallel compensation is eligible to the secondary side. This paper compares the two compensation strategies based on a simple approach, comprehensively highlighting the pro and cons of each one. Also the open loop operation in voltage source and current source modes, and the effect of the gap length for both compensation strategies are discussed. Experimental results validate the simplified WPT model, the operation at constant voltage and constant current, and highlights the effect of the parameters mismatch (components tolerance, parasitic elements, etc.) on the expected behavior.