Study On Active Compensation Method For Long Time Delay And Data Loss Of Networked Control System

Networked control system(NCS)has a feedback loop through network.It has been the research hotspot and trends in control field that introducing network to local control to form a remote control system.Compared with traditional point-to-point system,NCS has many advantages,such as low cost,light weight,easy installation and maintenance,high reliability and flexibility,etc.But network makes some inevitable problems in data transmission process,such as network induced delay,data packet loss and disorder,quantitative and communications limited,etc.The main effects are the network induced delay and data packet loss that will degrade system performance,sometimes cause system instability.Due to the network,traditional control theory for local control system is no longer adaptive for NCS.Therefore,there have important theoretical value and broad application prospect to model system,present advanced control strategy,analyze the stability of NCS.In this paper,the active compensation control method is studied which can compensate the impact of network delay and data packet loss on the premise of ensuring the closed-loop system stability.The main research work of this paper can be summarized as follows:(1)This paper studies on an active compensation method based on model predictive control,which can compensate the impact of network induced delay,data packet loss and misorder.The controller gain is not a fixed value,but a variable value which depends on the time delay of feedback channel.So the compensation effect is better.For data packet loss,the common ZOH method is not employed in this paper.A delay compenstor is set up on actor side to compensate datapacket loss dynamicaly.The rule of selecting control input is established for the case that both time delay and data packet loss exist in network.The model of closed-loop system is studied and the Lyapunov function is used to analyze the stability of closed-loop system.(2)Combining state feedback predictive control with event-trigger scheme,this paper presents a predictive triggered control method for NCS.This method can effectively reduce network traffic under the premise of ensuring system stability.The same event trigger mechanismes are set up on controlled object and controller side.The controller does not output control signal in each sample period.In view of the coupling between system state and event trigger scheme,the controller is designed to predict system state on trigger time and calculate the multi-step predictive control signal.This method can better compensate time delay and packt loss because the controller gain is not a fixed value,but a variable depend on the trigger interval.A new packet form is designed to pack the multi-step control input and its corresponding acting time into one packet with timestamp.The closed-loop system is modeled as a switching system,and the stability is analyzed by means of a switched Lyapunov fuction.(3)This paper proposes an active compensation method in the case that the controlled object is described by AR model.The feedback channel time delay is compensated by GPC algorithm.To compensate unknown time delay of forward channel,the compensation block is designed on controller side to amend the control signal by calculating the deviation between the actual control input and the control signal output by controller.The closed-loop system is modeled and its stability is analyzed.This method is simple,easy to achieve in practical engineering.Combining the predictive control with PID feedback structure,this paper presents a self-tuning PID control method.The equation is builded about the relationship between the control increment and future output error.The GPC objective function with the characteristic of PID structure is constructed to derive multi-step control input based on rolling optimization strategy in finite time.The PID parameters can be adjusted according to the predictive output error.So it has strong robustness.According to the system feature,the model of closed-loop system and its stability are analyzed.(4)In the case that the NCS model is uncertain or difficult to model,this paper proposes an compensation strategy based on closed-loop subspace method.In orther articles the open-loop subspace method usually used to identify system parameters.However,the bias of estimation causes the fail to meet the requirement of system performance.To overcome this shortcoming,this paper constructs the extended input state with the input and output error sequences to estimate the system matrixes.The consistency of the identification method is analyzed.In order to compensate network time delay,predictive control algorithm based on closed-loop subspace is designed.To realize the recursive calculation online,a simple method of updating parameter is designed to replace the complex matrix LQ decomposition.The optimal multi-step control input sequence is calculated to active compensate network time delay.