Foreign object detection circuit and foreign object detection method

A foreign object detection circuit arranged in a receiver of a wireless power transmission system, wherein the foreign object detection circuit comprises an excitation injection module and a foreign object detection module, as well as a resonance circuit coupled to the receiver in the wireless power transmission system, the resonance circuit comprising a receiving coil and a resonant capacitor connected in series, and wherein:

• the excitation injection module is configured to apply an excitation with a voltage step to the resonance circuit, and enable the resonance circuit to generate a self-excited oscillation;
• and
• the foreign object detection module is configured to measure a quality factor of a receiver terminal based on the self-excited oscillation of the resonance circuit, and determine whether a foreign object exists in the wireless power transmission system or not based on the quality factor, and wherein measuring the quality factor of the receiver terminal comprises:
• applying an excitation with a voltage step to a resonance circuit formed by a receiving coil and a resonant capacitor in the receiver, and enabling the resonance circuit to generate a self-excited oscillation;
• sampling a capacitor voltage in the resonance circuit to obtain a sampling voltage signal;
• performing a peak holding on the sampling voltage signal so as to output a peak voltage signal, and converting the sampling voltage signal into a square signal synchronously;
• performing an analog-to-digital conversion and sampling synchronously on the peak voltage signal and the square signal to obtain a peak voltage of each wave crest and a corresponding cycle number thereof;
• and
• calculating the quality factor according to the peak voltage of each wave crest and the corresponding cycle number thereof.

A foreign object detection method applied to a wireless power transmission system, comprising:

• step a) establishing a communication link between a transmitter and a receiver in the wireless power transmission system;
• step b) performing, by the transmitter and the receiver, a wireless power transmission based on a magnetic coupling;
• and
• step c) measuring a quality factor of a receiver terminal, and determining whether a foreign object exists in the wireless power transmission system or not based on the quality factor, wherein measuring the quality factor of the receiver terminal comprises:
• applying an excitation with a voltage step to a resonance circuit formed by a receiving coil and a resonant capacitor in the receiver, and enabling the resonance circuit to generate a self-excited oscillation so as to obtain a damped sinusoidal waveform with a resonance attenuation envelope;
• comparing the damped sinusoidal waveform with a threshold voltage, and detecting a last moment at which a value of the damped sinusoidal waveform is equal to the threshold voltage;
• determining a moment corresponding to a peak value of the damped sinusoidal waveform according to the last moment, wherein the moment corresponding to the peak value and the last moment are located in a same cycle of the damped sinusoidal waveform;
• determining the peak value of the damped sinusoidal waveform according to the last moment, the moment corresponding to the peak value and the threshold voltage;
• and
• calculating the quality factor according to the moment corresponding to the peak value and a ratio of a voltage value of the voltage step to the peak value.