Dual-tuning IPT Systems for Low Bandwidth Communications

This paper presents the design, implementation and performance of a low bandwidth physical communications channel for both new and existing inductive (contact-less) power transfer (IPT) applications, wherein power is transferred in the frequency range of 10 kHz to 50 kHz. The designed communications system operates at around 500 kHz without limiting power transfer, thereby maintaining the advantageous characteristics of IPT systems. The properties of the communications channel can be determined using the same magnetic coupling theory as applied for the power transfer. Its bandwidth is designed for control applications and is capable of up to 19.2 kbps. The channel was installed and evaluated on an existing electronic factory automation IPT system. Mathematical analysis of the channel resulted in a calculated path attenuation of 37 dB which compares favorably with practical measurements of typically 34 dB. When a real IPT power supply is present, harmonics of the power transfer frequency exist at the communications frequency and as such the communications channel utilizes a number of passive parallel and series tuned filters to maintain a signal to noise ratio of at least 10 dB.