An Efficient Robust Predictive Control of Main Steam Temperature of Coal-Fired Power Plant

Di Wang,Xiao Wu,Jiong Shen

doi:10.3390/en13153775

Abstract

Regulating performance of the main steam temperature (MST) system concerns the economy and safety of the coal-fired power plant (CFPP). This paper develops an offset-free offline robust model predictive control (RMPC) strategy for the MST system of CFPP. Zonotope-type uncertain model is utilized as the prediction model in the proposed RMPC design owing to its features of higher accuracy, compactness of representation and less complexity. An offline RMPC aiming at the system robustness and computational efficiency is then developed to maintain the desired steam temperature in case of wide operating condition change. The proposed RMPC is realized by two stages: in the first stage, the RMPC law set, which is the piecewise affine (PWA) of the MST system state is designed offline; then in the second stage, the explicit control law is selected online according to the current state. To achieve an offset-free tracking performance, a manipulated variable target observer is employed to update the chosen RMPC law. The control simulations using on-site operating data of a 1000 MW ultra-supercritical power plant show that the proposed approach can achieve satisfactory control performance and online computation efficiency even under complicated operating conditions.

Highlights

With the rapidly developing of human society and economy, the environmental deterioration arising from fossil fuels firing becomes extremely urgent
Great concern has been paid on the control of main steam temperature (MST), which plays a critical role for the operation of coal-fired power plant (CFPP)
The proposed offline robust model predictive control (RMPC) approach for MST system is tested by control simulations

Summary

Introduction

With the rapidly developing of human society and economy, the environmental deterioration arising from fossil fuels firing becomes extremely urgent. Great concern has been paid on the control of main steam temperature (MST), which plays a critical role for the operation of coal-fired power plant (CFPP). The MST must be maintained within an expected range without frequent variation for the economy and safety reasons [2]: The excessively high MST results in serious damage of the superheater and inlet pipe of turbine; The excessively low MST decreases the net efficiency of power plant, and the steam in the last stage of the low pressure turbine may become wet under low MST condition, which endangers the turbine blades; The frequent temperature fluctuation worsens the heat exchanging in superheater and increases thermal stress of the superheater and turbine cylinder, which will bring material damage to the plant. Conventional PID-based controllers [3,4], which are robust to deal with the model-mismatches and unpredictable disturbances, can effectively maintain the MST when the CFPP is operated in a given working condition; for a load increase from

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