Using Two Receiving Coils to Achieve Constant Output Power for Wireless Power Transfer

Magnetic coupling resonance wireless power transfer (MCR-WPT) technology has been in development for over a decade. The output power of the MCR-WPT system achieves the maximum value at two splitting frequencies and not at the natural resonant frequency because frequency splitting occurs in the over-coupled region. In order to achieve excellent transfer characteristics, optimization approaches have been used in many MCR-WPT projects. However, it remains a challenge to obtain a constant output power in a fixed-frequency mode. In this research, two receiving coils are used in the MCR-WPT system to achieve a uniform magnetic field. First, a circuit model of the MCR-WPT system is established, and transfer characteristics of the system are investigated by applying the circuit theory. Second, the use of two receiving coils to achieve a uniform magnetic field is investigated. Constant output power is then achieved in a fixed-frequency mode. Lastly, the experimental circuit of the MCR-WPT system is designed. The experimental results are consistent with the theoretical ones. The topology of using two receiving coils results in optimum transmission performance. Constant output power and high transfer efficiency are achieved in the higher frequency mode. If the distance between the two receiving coils is appropriate and the transmitting coil moves between the two receiving coils, the fluctuation of the output power of the MCR-WPT system is less than 10%.