Maximum Efficiency Formulation for Multiple-Input Multiple-Output Inductive Power Transfer Systems

Efficiency maximization based on load optimization has been thoroughly investigated for the conventional single-input single-output (SISO) inductive power transfer (IPT) system. This paper further extends the problem for multiple-input multiple-output (MIMO) IPT system operating at a single frequency. For the MIMO IPT system, efficiency maximization requires a joint optimization of loads-at the receivers-and input currents-in the transmitters. The optimal complex values of input currents and loads are derived by applying the first-order necessary condition, followed by the second partial derivative test. The derived maximum efficiency expression enables performance evaluation for any coil configuration, under any coil arrangement and at any frequency. Effectiveness and feasibility of the derived formulas are evaluated by electromagnetic simulations. Our work generalizes a theory on efficiency maximization for SISO, single-input multiple-output, multiple-input single-output, and MIMO systems.