In order to solve the problem of Duffing oscillator’s limitations on signal detection

a new detection method for fundamental frequency based on extended Duffing oscillator is proposed. The critical chaotic amplitude of extended Duffing oscillator under discussion will not vary with the significant change of excitation frequency or sampling frequency

but almost remains constant for an arbitrary excitation frequency or sampling frequency. The proposed method is capable of effectively avoiding the limitation that traditional Duffing oscillators can only detect low-frequency signals. Its principle consists in using the periodic perturbation of a specific frequency to implement fundamental frequency detection based on extended Duffing oscillator’s resonance vibration. It is shown by research results that the extended Duffing oscillator has good noise immune property

and is capable of highly-accurate detection of power system fundamental frequency with a set of determined parameters. This work is supported by National Natural Science Foundation of China (No.61040049).