Research On Synthetic Methods Of Control System With Limited Communication

With the rapid development of computer networks and communication technology, a new kind of feedback control systems has been receiving more and more attentions in recent years, whose control loops are closed via digital communication networks. Compared with the traditional point-to-point case, the insertion of communication networks changes the way of data transmission and has wider application. Meanwhile, some detrimental phenomena are inevitably yielded, e.g., signal transmission delay, data packet losses, quantization error, etc., which may deteriorate the performance or even de-stabilize the systems. Hence, it is a quite important practical problem on how to guarantee the desired dynamic performance of the controlled systems under the limited communication.By analyzing the features and limitations of some existing works and control methods, this thesis has proposed some novel designing methods by means of some advanced control theory and methods including sliding mode control and predictive control. The effectiveness of these proposed methods has been validated from theorical proof and numerical simulation.The main contribution in this thesis is as follows:(1) Considering the problem of sliding mode control for stochastic sytems subject to packet dropout. An estimation method is introduced to compensate the lost data, and then, both the sliding function and sliding mode controller are designed, respectively, dependent on dropout probability. By means of Lyapunov function, the analysis on both the reachabiltiy and the stability of system states are made, simultaneously. Moreover, sufficient conditions are derived to ensure the stochastic stability, and the reachability of specified sliding surface is also proven.(2) Considering the H∞control problem for linear discrete systems subject to multiple packet dropouts. For the two cases that system state is available and unavailable, the accordingly estimation methodd are proposed to compensate the lost signals, respectively. The H∞controllers are designed, respectively, based on state-feedback and output-feedback, and sufficient conditions are derived to ensure that the closed-loop systems are exponentially mean-square stable with prescribed H∞disturbance attenuation level. (3) Considering the output-feedback control problem for linear systems subject to signal quantization and packet dropout. An estimation method is firstly utilized to cope with the effect of random packet loss. The sector bound method is proposed to treat the quantized error as sector-bounded uncertainty. And then, the dynamic output-feedback controller is designed such that the closed-loop system is ensured to be exponentially mean-square stable, despite the effect of both packet loss and signal quantization.(4) The stabilizing predictive control is investigated for constrained systems with quantization and communication delays. Based on the quantization matrix, the input-saturated control systems with logarithmic quantizers are described as constrained control systems with structured norm-bounded uncertainties. A quantized and networked predictive control algorithm is presented by using a multirate delay compensation strategy. The proposed predictive controller not only efficiently reduces the negative effects of the quantization and communication delays but also guarantees the closed-loop stability and constraints satisfaction.(5) It is investigated how the existing conventional control laws can still attain the desired dynamic performance when there exist quantized errors. By designing a quantizer with adaptive parameters, a new H∞controller with the adaptive updating scheme is proposed. This proposed scheme may ensure that the systems states with quantized signals attain the same H∞disturbance attenuation level as the one without quantization. It is shown that the updating of quantizer's parameters is adaptively dependent on the system state, which is directly affected by the probability of packet dropout.