PID Controllers Parameters Self-Tuning Algorithm Based on Frequency Characteristic

According to the problems in getting the vibrate period-Tc and amplitude-Kc with the critical scaling limited method and relay-tuning method, based on step response and FFT, proposed a new method to obtain the frequency characteristics of the controlled object, then to obtain the TC, KC and PID parameters. In the step response, the initial steady-state value is usually not zero, which doesn´t meet the definition conditions of the transfer function; And the terminal steady-state value is not zero, which makes Fourier integral non-integrable in the infinite range. While directly to process FFT on the step response data can not get the frequency characteristic which meet the design requirements of controller. In this paper, firstly uses high-pass filter to do pre-processing to the step response data, And then do FFT, to obtain the frequency characteristics with high precision, especially for the middle and low frequency band for the controller design and self-tuning, the precision of the amplitude-frequency characteristic and phase-frequency characteristics can satisfy the application requirements completely. In a first-order inertia link plus time delay system, this algorithm is effective which has been comprehensively verified in the semi-physical, real-time, closed-loop simulation.