A novel online model identification method based on frequency domain analysis has been proposed

which has simple algorithm and is easy to realize.Moreover

this method has good noise immunity and identification precision.Input and output signal of the PID regulator both contain spectrum composition which is the same as the identification spectrum signal.The change of amplitude characteristic and phase property of spectrum is related to the properties of PID regulator

control object and the closed loop control systems.The control model can be identified through amplitude and phase comparison for spectrum of input and output signals.The simulation and application results verified the effectiveness of this method.When the Gauss interference signal with 80 Hz bandwidth and whose average amplitude is 100% of square wave identification signal was added to the input of reference filter module group

the simulation accuracy of phase-frequency characteristics of second order inertia link identification was higher than 0.64°

and the simulation accuracy of amplitude-frequency characteristics of that was better than 1.1%.