The Application of a New PID Autotuning Method for the Steam/Water Loop in Large Scale Ships

Shiquan Zhao,Clara-Mihaela Ionescu,Robain De Keyser,Sheng Liu

doi:10.3390/pr8020196

Abstract

In large scale ships, the most used controllers for the steam/water loop are still the proportional-integral-derivative (PID) controllers. However, the tuning rules for the PID parameters are based on empirical knowledge and the performance for the loops is not satisfying. In order to improve the control performance of the steam/water loop, the application of a recently developed PID autotuning method is studied. Firstly, a ‘forbidden region’ on the Nyquist plane can be obtained based on user-defined performance requirements such as robustness or gain margin and phase margin. Secondly, the dynamic of the system can be obtained with a sine test around the operation point. Finally, the PID controller’s parameters can be obtained by locating the frequency response of the controlled system at the edge of the ‘forbidden region’. To verify the effectiveness of the new PID autotuning method, comparisons are presented with other PID autotuning methods, as well as the model predictive control. The results show the superiority of the new PID autotuning method.

Highlights

The steam/water loop in a steam power plant is the process that provides water for the boiler and recycles the waste steam from the turbine [1]
The test on a simple single input single output (SISO) system example is provided to verify the effectiveness of the KC PID autotuning method
In the KC method, the performance requirements, such as robustness or phase margin and gain margin, are obtained by locating the frequency response of the process to be tangential to the boundary of the ‘forbidden region’

Summary

Introduction

The steam/water loop in a steam power plant is the process that provides water for the boiler and recycles the waste steam from the turbine [1]. The steam/water loop is a system with multiple variables and strong interactions. For the coupling issue between the water level control loops in deaerator and condenser, a fuzzy. A generic model was used for the controller design [23] In this method, the exhaust gas flow was estimated with an observer, which comes from the loops with high pressure or low pressure. A PID autotuner—named the KC autotuning method—is applied to the steam/water loop in large scale ships. The unit for input rates is measured in opening degree per second

Detailed Theory of KC Autotuning Method

Slope of the ‘Forbidden Region’

Application to Mimo System

A Brief Introduction of Other PID Autotuners

A Simple Single Input Single Output System Example

Conclusions