Study And Application Of The Event-driven Control

In industrial process control systems, every process unit always serves a plurality of control loops and copes with several tasks at same time. The operation load rate of the process unit and the communication load of the different units represent an important index of industrial control systems. Event-driven control is a method to reduce the computing and communication load under the premise of ensuring effective control quality. Moreover, it can effectively prolong the service life of the actuator by reducing the frequency action of it due to the feature of curbing the change frequency of control value.In this work, a general design process of an event-driven controller is presented independent from the control algorithm. Analyzing the time response of output and the characteristic of control actions of event-driven systems under disturbance, event-driven systems is concluded to be modeled as sample and hold systems. On this basis, the stability criteria is given with small gain theorem as well as the tuning rules of the control parameters.On the basis of the theory deduction, the water level control in nuclear steam generator is selected as a representative of industrial process to apply the event-driven control design method. With the structure of the event-driven control method, a two-degree-of-freedom Internal Model Control (IMC) is used as the feedback controller and a dynamic element driven by steam flow rate is utilized as feedforward controller. Both controllers consist the control diagram of the steam generator water level hybrid control system. In addition, the gain-scheduling method is applied to combine the feedback and feedforward controllers designed with five typical conditions together in order to achieve good global control performance. Moreover, parameter tuning rules of the control system are summarized based on the deep analysis of the control system and are given from the practice point of view. Simulation results show that the proposed method has good control performance at all power levels and meanwhile the number of event and the CPU utilization in the applied event-driven controller are considerably reduced.