Direct energy balance based active disturbance rejection control for coal-fired power plant

The conventional direct energy balance (DEB) based PI control can fulfill the fundamental tracking requirements of the coal-fired power plant. However, it is challenging to deal with the cases when the coal quality variation is present. To this end, this paper introduces the active disturbance rejection control (ADRC) to the DEB structure, where the coal quality variation is deemed as a kind of unknown disturbance that can be estimated and mitigated promptly. Firstly, the nonlinearity of a recent power plant model is analyzed based on the gap metric, which provides guidance on how to set the pressure set-point in line with the power demand. Secondly, the approximate decoupling effect of the DEB structure is analyzed based on the relative gain analysis in frequency domain. Finally, the synthesis of the DEB based ADRC control system is carried out based on multi-objective optimization. The optimized ADRC results show that the integrated absolute error (IAE) indices of the tracking performances in both loops can be simultaneously improved, in comparison with the DEB based PI control and H∞ control system. The regulation performance in the presence of the coal quality variation is significantly improved under the ADRC control scheme. Moreover, the robustness of the proposed strategy is shown comparable with the H∞ control. •The decoupling ability of the direct energy balance strategy is analyzed in both time-domain and frequency domain.•The control objective in terms of the coal quality variation is put forward and studied from an academic point of view.•The nonlinearity of the boiler-turbine unit is analyzed via gap metric and tackled based on active disturbance rejection control (ADRC).•Multi-objective optimization is used for tuning the parameters of ADRC.•The proposed strategy fulfills the objectives of tracking, disturbance rejection and robustness by slightly modifying the currently-using control structure.