Self tuning pick-ups for inductive power transfer

Inductive power transfer systems are now commonly used in ultra clean or dirty industrial applications to deliver power to both moving and stationary loads without contact. Each load requires a power pick-up and regulator that is coupled to a track, which carries a resonant current at VLF frequencies (typically 10-50 kHz). Modern pick-ups are tuned for resonance at the track frequency and their power delivery increasingly depends on accurate tuning of the resonant circuit. In this paper a new self tuning power regulator for inductive power transfer systems is proposed and a control strategy described. The system uses a binary weighted series of capacitors that can be switched via simple relays across a parallel resonant pick-up circuit. There are no additional switching losses during tuning, detection and operation so that the technique is applicable to high power pick-ups. The tuning circuit is evaluated under simulation and then made to operate on a practical 500 W pick-up regulator used in materials handling applications. In both simulation and experiment it is shown to successfully detect the tuning state of the system and correct for it during operation.