Ultra-supercritical (USC) coal fired units are required to improve operational flexibility, in order to absorb more renewable energy generation into power grid. However, strong nonlinearity and various disturbances deteriorate the control performance of coordinated control system (CCS) severely. To this end, this work proposes a computationally efficient nonlinear model predictive control (NMPC) method with integral action. Firstly, successive linearization (SL) is used to obtain linear predictive model at each sampling interval, and control action can be calculated online in an explicit form to promote the calculational efficiency. Then integral action is combined with the NMPC to reject various disturbances containing real measure noises, and the detailed procedure for parameter tuning is presented to meet different requirements on tracking performance and variation rate of control action. Lastly, stability analysis and simulation tests are performed to validate its effectiveness. Simulation results reveal that the proposed method has excellent computational efficiency, load tracking and anti-disturbance performances under wide load range from 30% to 100% rated load compared with the NMPC-SL method, constant MPC, conventional proportional-integral-derivative control and neural network generalized predictive control. Its computational efficiency increases by 87% compared with NMPC methods using quadratic programming. Besides, the designed CCS owns the satisfactory root mean square errors, namely, 0.453 MPa, 4.223 kJ/kg and 0.725 MW, and the mean absolute relative error of unit load decreases by at least 80% compared with other control strategies. Therefore, the proposed method can provide reference for improving operational flexibility and anti-disturbance performances of USC units.
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