Master’s Thesis Bandwidth and Quantization Constraints in Feedback Control

In classical feedback control problems the plant and the controller is assumed to communicate over a channel with full bandwidth, i.e. the channel has a infinite capacity. In this thesis the channel will instead be a digital channel with finite capacity and transport delay. Since different types of network are used in many different areas it is likely that control systems will also use these constrained control systems more and more. These control systems, where constraints in bandwidth may occur could be controllers sharing a common network connection to control each plant, e.g. can (Controller Area Network). Before any signal can be transmitted on the communication channel it has to be quantized before anything can be sent. In this quantizer, the number of bits can be altered. Changing the number of bits used, the performance of the system changes. But there are also other parameters that can affect the performance, for instance the saturation value in the quantizer. To control these quantized communication control systems, the control law is calculated using a model predictive control method. By evaluating cost functions the optimum number of bits to be used in the quantizer can be found, to get the best performance. Using between 2 to 8 of bits to quantize either the measurements of states or input to the plant gives good results on both stable and unstable systems. Simulations show that the controller to plant connection should get more bandwidth to get better performance. By looking at the different cost functions, it is clear that the measurement constrained system has better performance. Therefore the controller to plant connection should have more bandwidth.