In this paper, a new continual self-tuning control scheme based on an
unknown process response under load disturbance is proposed. It can re
-estimate the possibly changed process frequency response using the be
nign process transients under an unknown step or impulse, like load di
sturbance. According to the disturbance response pattern, the unknown
step/impulse like load disturbance is assumed to be generated by passi
ng a step or an impulse through unknown rational function dynamics. Wi
th process input and output frequency response computed by FFT, the be
st estimation of the process frequency response is obtained using the
least squares method. Based on the re-estimated process frequency resp
onse, a PID controller is re-tuned to adapt to the possible changes in
the process. The effectiveness of the method is demonstrated through
simulation examples and real-time tests.