Abstract
It is difficult to model and determine the parameters of the steer-by-wire (SBW) system accurately, and the perturbation is variable with complex and changeable tire–road conditions. In order to improve the control performance of the vehicle SBW system, an adaptive fast super-twisting sliding mode control (AFST-SMC) scheme with time-delay estimation (TDE) is proposed. The proposed scheme uses TDE to acquire the lumped dynamics in a simple way and establishes a practical model-free structure. Then, a fractional order (FO) sliding mode surface and a fast super-twisting sliding mode control structure were designed on the basic super-twisting sliding mode to ensure fast convergence and high control accuracy. Since the uncertain boundary information of the actual system is unknown, a novel adaptive algorithm is proposed to regulate the control gain based on the control errors. Theoretical analysis concerning system stability is given based on the Lyapunov theory. Finally, the effectiveness of the method is verified through comparative experiments. The results show that the proposed TDE-AFST-FOSMC control scheme has the advantages of model-free, fast response and high accuracy.
Highlights
In recent years, the steer-by-wire (SBW) technology has been greatly developed and many research results have been achieved [1,2,3,4]
In order to carry out comparative research, the traditional adaptive sliding mode control (ASMC), the super-twisting sliding mode control based on time-delay estimation (TDE) (TDE-STSMC), the fast super-twisting fractional order sliding mode control based on TDE (TDE-FST-FOSMC) are selected as the controllers for comparative verification
Fractional order sliding mode surface s = λ1 e + λ2 D μ e is adopted in TDE-FST-FOSMC and TDE-AFST-FOSMC controllers, the parameter is selected as λ1 = 5, λ2 = 1, μ = 0.75, the parameter in super-twisting structure is selected as κ = 1
Summary
The steer-by-wire (SBW) technology has been greatly developed and many research results have been achieved [1,2,3,4]. The self-aligning torque is highly nonlinear and affected by many dynamic factors, which will greatly affect the steering tracking accuracy of SBW If these disturbance torques can be estimated and compensated in feedforward control, the performance of the SBW controller will be greatly improved. In the control design of actual systems, uncertain parameters, unknown dynamics, and unexpected disturbances may be encountered These unknown terms need to be estimated by appropriate methods. On the basis of existing research, combined with TDE and super-twisting sliding mode, an adaptive fast super-twisting sliding mode controller based on TDE is proposed In this controller, TDE is adopted to solve the estimation problem of lumped uncertainty including system parameters and disturbances. The proposed control scheme has the advantages of model-free, high tracking accuracy and strong robustness
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