Improvements in Inductively Coupled Wireless Power Transfer Through Non-Sinusoidal Excitation and Closed-Loop Operation Using Optical Feedback

Abstract

In this research, two novel designs with low circuit complexity are proposed to improve the performance in inductively coupled wireless power transfer (WPT) systems. The first is non sinusoidal excitation technique. By analysing the characteristics of rectifier diodes, LR time constant, and circuit impedance for nonlinear signals, a triangular pulse input is designed to operate the rectifier diode at its high-conductance region. Compared with standard sinusoidal inputs, the output power and efficiency are both improved significantly by the designed waveform with a given input power. Since only modification of input waveforms is needed, this approach saves additional circuits that lead to an increased circuit complexity, so no extra hardware cost. The second technique is closed-loop operation with optical feedback. An infrared LED is introduced as both the rectifier and the signal source in the receiver in an inductively coupled WPT system. This LED is directly driven by the rectified current passing to the load. So, the intensity of the light emission is related to the time-dependent magnitude of the load current. A real-time information not subject to frequency or phase errors is then created and obtained by an optical receiver installed in the power transmitter side. This closed-loop operation can be further configured as a system in self-oscillation which allows the system to naturally operate at the best driving frequency and respond rapidly to any changes in the coupling parameters or charging conditions without external assistance. Despite the threshold voltage of the LED is higher than standard power diodes, the use of the LED still provides multiple benefits that outweigh its drawback. Lastly, mathematical equations with simplified circuit blocks are used to model the proposed system. Two key features, self-oscillation and real-time monitoring of load, are analysed. The design methodology provided by the model can then be used as a guideline for implementing closed-loop WPT systems in self-oscillation.