Smart Wireless-powered LED Driver Prototype with Red Pitaya
Wireless inductive links have been successfully implemented in many applications, for instances, biomedical implants, battery chargers, transportation, and induction heating. A wireless inductive link consists of an excitation source, input matching circuit, transmitting and receiving coils, output matching and rectifying circuit and load (end-use device). The centers of the transmitting and receiving coils are typically placed in coaxially aligned position and the electric energy is delivered from the transmitting coil to the receiving coil through alternating magnetic fields. The system is optimized towards the maximum power transfer efficiency.
The key characteristic of the wireless inductive link is that the transmitter and receiver have no physical contact but are coupled by magnetic field. In principle, the receiver has spatial freedom to be displayed freely from the transmitter. However, the power transfer efficiency and the transmitted power are significantly affected by the strength of the magnetic coupling and the spatial displacement between the coils. In practice, inevitable spatial misalignment between the two coils leads to the variation of the strength of the magnetic coupling. In order to regulate the receiver-side power, on-the-spot measurement of the electrical quantities and establishment of communication link between the transmitter and receiver are sometimes applied. The load modulation scheme is often applied to perform both power and signal transfer in the wireless inductive link.
Another perspective of determining the mutual inductance between the two coils, the receiver-side electrical information, and the load power, obtained by sensing the transmitter-side input voltage and input current is given. The nonlinear input voltage-current characteristics of the receiver-side rectifying circuit, which causes current distortions in the system, are taken into consideration in the time-domain analysis. The online mutual inductance estimation technique is firstly verified by simulation on PSIM.
Then, the proposed technique is implemented on a 4W wireless-powered LED driver to regulate the receiver-side power and determine the real-time parameters of the inductive link. The driver prototype is given in above figures. Experimental results reveal that the LED power can be regulated over ±25% spatial misalignment over the operating zone and the estimated mutual inductance has found to be in close agreement with the theoretical predictions.
More details information and demonstration video can be download from IEEE Xplore.
(b) Top View of the Transmitter.
Author: Jeff Po-Wa CHOW, Henry Shu-Hung CHUNG, and Chun-Sing CHENG
The authors would like to acknowledge the support of RS Components for the Red Pitaya and required equipment in this project.