SYSTEM IDENTIFICATION
The block diagram of the active suspension system is presented in the figure at right. Two models for the system will be identified, corresponding to the primary and secondary path. Here up denotes the input of the primary path (excitation of the shaker), u is the input of the secondary path (proportional to the piston position) and y is the system output (residual force). The sampling frequency for data acquisition is chosen to be Fs = 800 Hz.
Discrete-time model
Primary path model: To identify the primary path model the shaker is excited by a PRBS using a 10-bit shift register with a clock frequency of Fs/2 and the input-output data have been saved in data_prim2.mat. The adopted number of parameters of the polynomials C(z^{-1}) and D(z^{-1}) are nc = 8 and nd = 12, respectively. The parameters of the model are available in the form of the MAT file: primary_model.mat
A non parametric model of the primary path can be idenfied by the spectral analysis method. This analysis shows that the model contains a high-resonant mode at frequency about 31,5 Hz. The magnitude of the model frequency characteristic is given in the figure bellow:
The magnitude of the model frequency characteristic has been calculated with the following M file: mag_cal.m
Secondary path model: To identify the secondary path model the input u is excited by the same PRBS with a clock frequency of Fs/4. The input-output data have been saved in data_sec4.mat. The adopted number of parameters of the polynomials A(z^{-1}) and B(z^{-1}) are na =14 and nb = 16, respectively. Note the existence of a double derivator in the model. The parameters of the model are available in the form of the MAT file:
Continuous-time model
The continuous-time models of the plant have been obtained by conversion of discrete-time models using the zero-order hold method.
Primary path continuous model: The parameters of the model are available in the form of the MAT file: primary_con.mat
Secondary path continuous model: The parameters of the model are available in the form of the MAT file: secondary_con.mat
The real-time data acquired on the system are available in the data acquisition section.
Note: The files may be downloaded by clicking on “file_name” with the right button of your mouse and choosing “save link as (Netscape)/download link to disk (Internet Explorer)” option. A compressed version of all files is available in the file: data.zip.