A Mutual Inductance Measurement Method for the Wireless Power Transfer System

The characteristic of the Magnetic Resonance Wireless Power Transfer (MR-WPT) system is related on the coupling coefficients between coils, so it is very important to accurately measure mutual inductance. The method of measuring mutual inductance using the primary current and the secondary voltage, when the secondary circuit is opened, is commonly used and most reliable. However, a standard sine wave generator and a linear power amplifier are needed for measuring the mutual inductance. Due to the high frequency inverter of WPT system may be has distortion, it is not recommended to be as the sine wave generator for measuring the mutual inductance. The proposed method demonstrate that, although the output current waveform of the high frequency inverter and the voltage waveform on the secondary coil are highly distorted in PWM (Pulse Width Modulation) control mode, the base component's amplitudes of these waveforms are investigated by FFT (Fast Fourier Transform), and then, the mutual inductance is calculated by using these values. According to the above contents, the experimental platform is built, and then the experiments on the different duty cycle ratio and the different frequencies, that is, including the different quantities of its high-frequency harmonics, has been done. In addition, the same operation as above is repeated on the different distances, and the results are compared with the theoretical calculation values. Consequently, the results show that the method is very close to the theoretical value, and it is very stable in whole distance range. (paper)