130W power transmitter for wireless power charging using magnetic resonance

In this paper, 130W power transmitter for wireless power charging using the magnetic resonance method is presented. The presented power transmitter is composed of a DDS(Direct Digital Synthesizer) for RF signal generation, a Class-F switching power amplifier for amplifying the RF signal up to 130W output power, a FSK module for communication to the receiver, AC to DC converter for supplying the DC power to components in the power transmitter and a MCU for controlling the output frequency and the output power level. The operating frequency range of the power transmitter is from 1.6MHz to 2.0MHz and the output power control range is from 1W to 130W with 2W step for adopting it to the 1.7MHz band wireless power charging system. To control the output power, the bias voltage of the power amplifier is controlled in the 30V~105V range. The optimal power transmission frequency searching and protection function is applied in the power transmitter using return loss measurement results. For implementing the return loss measurement, a bi-directional coupler and two power detection circuits are used. From the measurement results of the power transmitter the DC to RF power conversion efficiency is over 80% in the 50W~130W output power range. The wireless power charging system is implemented to apply the presented power transmitter. The system is designed to charge a 12V@20Ah LiFePO4 battery which is used for a walking-assistance vehicle. The output power control function is implemented by using the 424MHz FSK communications between the power transmitter and the receiver in order to maintain the power transmission efficiency. The average system DC to DC efficiency is about 50% during the wireless charging.