Research On Advanced Control Theory And Application Of AC Servo System

In recently,AC servo drive has been widely used in Computer Numerical Con-trol machine,medical equipment,automobile industry and industrial robots,etc.As the rapid development of modern industry,people have higher requirement for the per-formance index of servo drive,such as dynamic response,steady state error,tracking precision of position and the disturbance rejection ability.However,since the system is coupled,nonlinear and multiple-variable,traditional linear control methods can not satisfy the requirement of high performance.Researching for advanced and intelligent algorithm has become a hot topic.First,in this paper,the research background of AC servo system is introduced,and major AC servo control algorithms are discussed in brief.Then,the mathematical model of AC servo system,vector control and direct torque control are described.The main works are summarized as follows:1.Basing on direct torque control of induction motor and considering the prob-lem of disturbances in servo system,we propose a composite control scheme based on extended state observer(ESO)and continuous finite time control(FTC)to improve the disturbance rejection property of system.The main contents of this part include:(1)An extended state observer is introduced to estimate the disturbances of system.The estimated value is used in the feed-forward compensation design.(2)A continuous feedback-based finite-time control technique is applied in the feedback design.(3)The stability of the controller is analyzed.(4)Simulation and experimental comparisons with other two control methods,traditional PI and P+ESO,are given to verify the effectiveness of the proposed method.2.Relative differences of permanent magnet synchronous motor(PMSM)in con-trol periods between the speed loop and current loops are becoming smaller or even vanishing.Therefore cascade control scheme seems to be unnecessary.Non-cascade structure can be seen as an alternative.Under the structure of single-loop,focusing on how to effectively deal with disturbances,we propose a composite controller,which merges speed loop and q-axis current loop into one single loop.The main contents of this part include:(1)An third order extended state observer is employed to estimate the disturbance.The estimated value is used in the feed-forward compensation design to improve the capability of system anti-disturbance.(2)A feedback-based proportional derivative(PD)is applied in the feedback design.(3)The stability of the controller is analyzed.(4)Several groups of simulations and experiments are carried out and the results demonstrate the effectiveness of the proposed scheme.3.In some applications with variations of load inertia,e.g.recoiling machine,carrying robot and welding robot,it is difficult to achieve the desired performances.If the inertia of system is increased to more than several times of the original inertia,the control performances can not be guaranteed.Motivated by this issue,we propose an online inertia identification method.The main contents of this part include:(1)The common methods of inertia identification are introduced,such as least square(LS)and model reference adaptive(MRA).(2)The inertia identification method of harmonic injection is described in details.(3)Considering the performance degradation caused by-inertia change,an adaptive control scheme is developed.By using inertia identification technology,the feedforward compensation gain can be tuned automatically according to the identification value.(4)Several groups of simulations and experiments are carried out and the results demonstrate the effectiveness of the proposed scheme.4.Under the non-cascade structure,permanent magnet synchronous motor(PMSM)regulates the speed and current in one loop.Conventional control methods of AC servo system usually balance current constraint requirement and dynamic performance.In order to solve this drawback,a novel current-constrained controller is developed.The main contents of this part include:(1)The conflict between fast response of system and current constraint is discussed in detail.(2)The defects of existing methods of current constraint are researched and analyzed.(3)An improved current constrained controller is proposed to keep the q-axis current in a safety zone.(4)The stability of the con-troller is analyzed.(5)Compaxative experimental results between the classic PID and the current-constrained controller on PMSM servo system verify the effectiveness of the presented control scheme.5.Aiming at the issue proposed in last chapter,and considering the effect of disturbance in the system,we propose a composite current constrained controller which combines GPI observer with finite time current constrained controller together.The main contents of this part include:(1)A finite time current constrained controller is proposed to keep the q-axis current in a safety zone.(2)Generalized proportional integral observer(GPIO)is designed to estimate the disturbances of system.(3)The stability of the controller is analyzed.(4)Both simulations and experiments are carried out and the results demonstrate the effectiveness of the proposed control scheme.