Research On Model-free Sliding Mode Control Strategy For Permanent Magnet Linear Synchronous Motor

Permanent magnet linear synchronous motor(PMLSM)is the key component of a direct drive servo system.It can move in a straight line without intermediate mechanical transmission.PMLSM has the advantages of large acceleration,high precision,good retention,high efficiency,flexible combination,and has been widely used in precision machining,urban rail transit,aerospace,and other fields.When PMLSM runs under complex working conditions,it is susceptible to uncertain factors such as changes in motor parameters,thrust fluctuations,friction force,and load force.These uncertain disturbances will directly act on the motor body and cannot be weakened through the intermediate transmission device,which will ultimately adversely affect the stability and dynamic characteristics of PMLSM.Therefore,an advanced control strategy plays an important role in the high-precision operation of PMLSM.Oriented to the field of precision motion control,this paper takes PMLSM as the research object and carries out a series of related research on the design of its speed-tracking control strategy.The main research contents are as follows:Firstly,the research status and application of linear motors at home and abroad are briefly introduced,and the research results of linear motor control strategy in the current literature are summarized.Then,the basic structure and working principle of PMLSM are explained,and the dynamics model of PMLSM in a synchronous rotation coordinate system is deduced by combining with coordinate transformation.Then,the basic PMLSM drive control system is built according to vector control and PI control.At present,many control strategies of PMLSM are designed based on mathematical models,which makes the performance of the controller easy to be affected by the change of system parameters and lumped disturbance.Therefore,in this paper,a new model-free control strategy is adopted and the ultra-local model of PMLSM is established,which effectively reduces the dependence of the controller on the precise mathematical model of the system.Secondly,a prescribed performance based model-free fractional order sliding mode control strategy is proposed to prevent PMLSM from being affected by lumped disturbance,the flux of permanent magnet,and friction coefficient.To ensure that the speed tracking error is confined within the prescribed range and improve the dynamic characteristics of the system,a prescribed performance control is used.Then the ultra-local model is established according to the input and output signals of the speed loop of the PMLSM feed system.Then an extended state observer is designed to estimate the unknown total disturbance online in the ultra-local model and feed-forward to the velocity loop controller.Finally,the feedback controller of the velocity loop controller is designed as a fractional sliding mode controller,which makes the system state converge to the equilibrium point in a very short time,and effectively strengthens the robustness of the PMLSM feed system.Finally,the effectiveness of the controller is verified by MATLAB/Simulink simulation.Then,an observer-based model-free fractional order nonsingular fast terminal sliding mode control strategy is proposed,which further improves the ability of PMLSM to suppress matching and mismatching disturbances.Firstly,an ultra-local model is established according to the input and output signals of the external speed loop and the internal current loop of the PMLSM servo system.Then,two finite-time disturbance observers are designed to estimate the matched and unmatched disturbances in the ultra-local model quickly and accurately.Then,a fractional order nonsingular fast terminal sliding mode control strategy is designed to effectively achieve the finite-time convergence of the system states and improve the dynamic responsiveness and robustness of the system.In addition,the proposed controller belongs to non-cascade control,which simplifies the structure of the controller effectively.Finally,MATLAB/Simulink simulation verifies the superiority and feasibility of the proposed control strategy.Finally,to verify the control effect of the proposed control strategy in practice,a semi-physical simulation platform of the PMLSM driving system is built based on d SPACE DS1104,and the proposed control strategy is compared with PI control,traditional model-free control,nonsingular terminal sliding mode control and other methods to further prove the effectiveness of the proposed control strategies.