An Inductive Power Transfer System Supplied by a Multiphase Parallel Inverter

The output power of a single-phase inverter is insufficient for high-power applications, such as fast wireless chargers for electrical vehicles. A higher power level can be obtained via a multiphase parallel resonant inverter, which comes with a possible cost of the unbalance current problem. Coupled inductors with a cyclic cascade connection instead of a complex controller are employed to alleviate this problem. A blocking capacitor is introduced to stop the dc component of the circulating current. Equations for suppressing ability of circulating currents under the proposed topology with various numbers of parallel phases are derived. Main power loss components are analyzed and the reason why multiphase systems with a high output current have a higher efficiency is theoretically explained. A prototype of an inverter with six-phase half-bridge parallel topology is developed and built to verify the theoretical analysis. The prototype is used to supply an inductive power transfer system, which delivers power at a distance of 20 cm. When the receiving power of the 6.87 load in the rectifier is 20 kW, one obtains a 95.6% efficiency measured as the power of the dc-load divided by that of dc-input at the inverter.