H_∞Performance Analysis And Controller Design Of Networked Control Systems

With the development of computer, network and communication technologies, net-worked control systems have been widely applied in many industrial control filed. By us-ing communication channels to connect several systems with different geographical posi-tion and independent functions, one can establish networked systems. The establishment of networked control systems is based on the communication channels, and networked control systems show high research values and application values.Such closed-loop systems whose sensors, controllers and actuators are connected via a network medium, are called networked control systems (NCSs). Considerable at-tentions have been paid to NCSs for their advantages such as resource sharing, low cost in installation and maintenance, good fault-tolerant and fault detection ability, high reli-ability, etc. However, the insertion of communication networks into control systems will inevitably lead to packet dropouts, network-induced delays, communication constraints, multiple packet transmissions, packet disordering, etc. Such challenges will degrade the performance of the control systems. At the same time, the sampled plant states and con-trol inputs are transmitted through communication network, and external disturbances are unavoidable. Then it is important to reduce the negative influences of disturbances. HI performance analysis is a good choice for reducing the negative influences of dis-turbances, and the problem of H1performance analysis for NCSs has been paid much attention in the literature. In the case of considering such network-induced characteris-tics, it is significant to optimize the H∞performance of NCSs with external disturbance by designing the controllers appropriately.Based on previous works derived in the literature, and by taking network-induced delays and packet dropouts into account, this thesis proposes a controller design crite-rion for discrete-time networked control systems with packet dropouts and non-uniformly distributed network-induced delays. Considering the case that the length of sampled data may surpass the the maximum admissible length of the network packets, this thesis presents the controller design criteria for multiple packet transmission-based NCSs with non-uniformly distributed network-induced delays and packet dropouts. The communica-tion channels in NCSs are usually shareable. A new model for communication channels sharing-based continuous-time NCSs is established, and a new controller design method is proposed to compensate the negative influences of network-induced delays and packet dropouts. For dynamic output feedback NCSs considering network-induced delays and packet dropouts in sensor-to-controller channel and network-induced delays in controller-to-actuator channel, a new closed-loop model is established. For continuous-time NCSs considering network-induced delays and packet dropouts in sensor-to-controller chan-nel and network-induced delays in controller-to-actuator channel, an observer-based con-troller design method was proposed.The main contributions of this paper are summarized as follows:The controller design problem of discrete-time NCSs with packet dropouts and non-uniformly distributed network-induced delays is investigated. By establishing a new model for the considered discrete-time NCSs, and defining a new Lyapunov functions and using linear matrix inequality method, a new controller design method is proposed. Different from the existing methods which choose the midpoint as the demarcation point of non-uniformly distributed network-induced delays, a new algorithm which is used to choose the dividing point is proposed to optimize the systems performance.By considering the non-uniform distribution characteristic of network-induced de-lays and packet dropouts in sensor-to-controller channel and controller-to-actuator chan-nel, two new models for multiple-packet transmission-based continuous-time NCSs are established. Then, based on the established models, a new Lyapunov functional and continuous-time Jensen inequality, the stabilizing controller design methods for multiple packet transmission-based NCSs are presented.The problem of dual communication channels sharing-based network-induced delay and packet dropout compensation for continuous-time NCSs is studied. By introducing a dual communication channel sharing-based network-induced delays and packet dropouts compensation method, a new model for NCSs which can receive more than one control input during a system control input updating time interval was presented. Based on the established model, an effective controller design criterion was proposed. Even for the NCSs without considering network-induced delays and packet dropouts compensation, the proposed controller design method is still applicable.Dynamic output feedback controller design for linear continuous-time NCSs is ad-dressed. By taking network-induced delays and packet dropouts in sensor-to-controller channel and network-induced delays in controller-to-actuator channel into account, an augmented close-loop model for the considered dynamic output feedback NCSs was es-tablished. A linear estimation-based method is proposed to estimate the measurement output, and the non-uniform distribution characteristic of the measurement output arrival instant is taken into full consideration to design an effective dynamic output feedback controller.The problem of control design for observer-based linear continuous-time NCSs was studied. For the NCSs considering network-induced delays and packet dropouts in sensor-to-controller channel and network-induced delays in controller-to-actuator channel, by taking the non-uniform distribution characteristic of measurement output arrival instant into full account, an observer-based augmented close-loop NCSs model was established. To reduce the conservatism induced by measurement output waiting, a linear estimation-based method was introduced to estimate the measurement output. By defining a new Lyapunov functional, the observer-based controller design method was proposed.