Automatic Time-Division Multiplexing for Inductive Power Transfer to Multiple Stainless-Steel-Enclosed Receivers

Linear actuators employed in the food-processing or pharmaceutical industry must be enclosed in stainless steel (SS) for hygienic reasons. Therefore, cables and cable carriers should be avoided and wireless, i.e., inductive power transfer (IPT) should be employed. To achieve high efficiencies, the magnetic field components of the IPT system should be oriented parallel to the SS enclosures, which can be achieved with a coaxial arrangement of closed magnetic cores mounted on the moving part / slider and a stationary primary winding. As an alternative to the typically employed current-impressed operating modes of IPT systems with a constant primary-winding current that limits part-load efficiency, the high magnetic coupling of this arrangement facilitates operation as an isolated constant-voltage-transfer-ratio series-resonant dc-dc converter, i.e., a dc transformer (DCX). However, then, only a single receiver can receive power at any given time, and a time-division multiplexing (TDM) method is needed to supply multiple receivers with power in a cyclic manner. This paper proposes a novel automatic TDM (A-TDM) method that, unlike previous TDM methods, does not require any communication link nor a central controller. The new method is verified during startup, steady-state operation, and under load transients using an exemplary SS-enclosed IPT system with two 100W receivers.