Automatic Phase Current Sharing for a Multiphase Wireless Power Transfer System Based on Positively and Negatively Coupled LC Resonant Loop

Paralleling multiple phases of a high-frequency inverter can improve its current rating. Passive paralleling is normally adopted due to its simplicity and effectiveness to balance the phase output currents. This paper proposed a novel automatic current sharing method for a multiphase inverter. An external LC resonant loop is positively and negatively coupled with two adjacent phases, respectively. In this way, no extra impedance is introduced for the power flow path. However, an extremely large impedance is introduced for the circulating path of imbalanced currents so as to suppress them. Furthermore, the self-inductance of the LC resonant loop can be small to reduce the cost and volume. The coupled inductors for each phase can be designed individually, allowing for modularity and expansibility for any phases. The mathematical model and the current sharing principle of the proposed method are analyzed in detail. The inductor-capacitor-capacitor series compensated wireless power transfer (WPT) system for electric vehicles is adopted as the application scenario. A 2.2-kW WPT experimental prototype with a three-phase inverter verifies the effectiveness of the proposed current sharing method.