Study On Parameter Configuration And Application For Extended State Observer Based On Frequency-domain Indices

Active disturbance rejection control(ADRC) is a kind of control method which is independent on the accurate mathematical model of controlled object. The key strategy of ADRC is to apply extended state observer(ESO) to observe and compensate the total disturbance outside of the series of pure integrals to improve the robustness of system. In order to achieve such purpose, it is necessary for engineer to design effectively the parameters of ESO. But due to the employment of special nonlinear functions, the relationship between the parameters and performance of ESO is not intuitive, and consequently, the configuration of these parameters is an intractable task. Aiming to improve the performance of ESO in a different way, this paper investigates the parameter configuration deeply from frequency-domain perspective.Firstly, the transfer function from the total disturbance to the output of traditional three-order ESO is derived and the general frequency-domain index is stated. Based on the analysis on monotonicity of amplitude-frequency characteristic and phase-frequency characteristic of the derived transfer function, the sufficient conditions satisfying the frequency-domain index are obtained for three situations. Furthermore, with frozen coefficient method, the parameter configuration method for general three-order nonlinear ESO is proposed. The simulations validate the effectiveness.Secondly, with the purpose of reducing the compensation amount of ESO and improving the performance of system, a modified ESO is designed for the general two-order system under the condition that the normal modal of controlled object is available. Furthermore, using transfer functions transform, the parameter configuration method based on frequency-domain index for the modified ESO is gained. And the simulations and analysis are conducted to test the effectiveness of the modified ESO and its parameter configuration method by comparison with the traditional ESO.Finally, considering limitation on frequency band expansion of nonlinear PD controller employed by ADRC, a novel control strategy by combine the modified ESO, series correction controller and feed-forward control is proposed, where the modified ESO is able to enhance the robustness, the series correction link is able to improve the feedback characteristics and the feed-forward control is able to benefit the response characteristics. Then, this control strategy is applied in some simulation turntable, and its effectiveness is proved by experiment results.