Flexible Electric Power Control for Coal-Fired Units by Incorporating Feedwater Bypass

The improvement of the operating flexibility of a thermal power unit has always been an essential issue due to its substantial support to power system stability. In addition, this issue has become increasingly important for the large-scale integration of fluctuant wind energy. The feedwater bypass (FWB) is an effective method for raising the load-following capability of a power unit by quickly activating its thermal storage system. However, understanding the dynamic characteristics of the FWB and designing appropriate control strategies for this method remain as challenges. In this paper, mathematical models that describe the static and dynamic characteristics of the FWB in unit power output are presented and discussed. Then, an optimized control strategy for improving a power unit's load-following capability is developed by combining FWB and the traditional coordinated control strategy (CCS). Last, field tests on a 300-MW power unit show that the unit ramp rate can be raised to twice that in traditional CCS using the improved strategy. Moreover, the strategy can be extensively used in coal-fired units for the flexible power regulation and the primary frequency control of power grids.