Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Electrical and Computer Engineering

Supervisor(s)

Dr. Jin Jiang

Abstract

In modern Distributed Control Systems (DCS), an industrial computer network protocol known as fieldbus is used in chemical, petro-chemical and other process industries for real-time communication between digital controllers, sensors, actuators and other smart devices. In a closed-loop digital control system, data is transferred from sensor to controller and controller to actuator cyclically in a timely but discontinuous fashion at a specific rate known as sampling-rate or macrocycle through fieldbus. According to the current trend of fieldbus technology, in most industrial control systems, the sampling-rate or macrocycle is fixed at the time of system configuration. This fixed sampling-rate makes it impossible to use a multi-rate controller that can automatically switch between multiple sampling-rates at run time to gain some advantages, such as network bandwidth conservation, energy conservation and reduction of mechanical wear in actuators.

This thesis is concerned about design and implementation of a dual-rate controller which automatically switches between the two sampling-rates depending on system’s dynamic state. To be more precise, the controller uses faster sampling-rate when the process goes through transient states and slower sampling-rate when the process is at steady-state operation. The controller is based on a Model Predictive Control (MPC) algorithm and a Kalman filter based observer.

This thesis starts with theoretical development of the dual-rate controller design. Subsequently, the developed controller is implemented on a Siemens PCS 7 system for controlling a physical process. The investigation has concluded that this control strategy can indeed lead to conservation of network bandwidth, energy savings in field devices and reduction of wear in mechanical actuators in fieldbus based distributed control systems.


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