Abstract
To reduce calculation errors of FFT based Nyquist plots in fuel cells under electrically noisy environments, a space-average noise reduction algorithm was applied instead of traditional time-average noise reduction algorithm. With an appropriate M-sequence input signal conditions and data sampling frequency, Nyquist plots of frequency ranging from about 0.38 Hz to 10 kHz were obtained about every 3 seconds including calculation time, etc. Maximum impedance percentage difference between the space-average FFT methods and comparable FRA method was less than 6%. By using the space-average FFT methods, Nyquist plots in transient states such as step responses and ramp responses were obtained. Also, Nyquist plots during US06 drive cycles were obtained about every 3 seconds.
