Analysis And Compensation Of Communication Delays And Packet Dropouts In Networked Control Systems

The networked control systems(NCSs)uses network to transmit the system signals.Compared with the traditional control system,it saves the wiring cost and has been widely used in various fields.However,due to the constraints of network hardware,the system signals will inevitably encounter network constraints such as time delays,packet dropouts and disorders.These network constraints will affect the control performance of the system.Networked predictive control(NPC)method as an active time-delay compensation method can compensate for the network constraints effectively.This paper based on the original NPC method,introduces the allowable time delay into the control rule,and proposes a variable gain control method.The main research contents are summarized as follows:1)To deal with the problem of time delays and packet dropouts in NCSs,the destination-based lumped delay(DBLD)is proposed to transform the packet dropout and disorder problem into time delay problem.Based on the previous research results,it is found that the general control system can tolerate a certain amount of time delay.This paper combines active time-delay control with traditional NPC to propose a new networked active time-delay compensation method.The event-trigger unit in the sensor reduces the number of data packets sent.The control law is designed in the controller to compensate for the impact of time delay on the system.The effectiveness of this method is proved by theoretical derivation and numerical simulation.2)To deal with the problems of time delays and packet dropouts in networked output tracking control system,the method proposed in chapter 2 is applied.By constructing an augmented system with tracking error,the output tracking problem is transformed into an asymptotic stability problem.The packet dropouts and disorders in forward and feedback channel are uniformly described as a round-trip time delay(RTTD).Based on the output of the system,the controller predicts the system state and adopts state feedback active time-delay control law to fully compensate for the time delay in the system.Finally,theoretical derivation and numerical simulation verify the effectiveness of the method.3)Based on the above research,this paper further propose an NPC method with time-varying gain control.The controller gain of traditional NCSs directly uses the controller gain of the local control system.When the system delay is too large or the lower bound of system delay is bigger than zero,it can not control the system well.The time-varying gain control method proposed in this paper adopts different controller gains according to different time delays,which can improve the adaptability of the system to time delays.Finally,the feasibility of this method is proved by numerical simulation.