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[Introduction] The primary frequency modulation technology of thermal power units has been considered essential to ensure the power grid's safe and stable operation. [Method] The current primary frequency modulation technology, the auxiliary primary frequency modulation technology, the coupled frequency modulation control strategy, and the potential development direction of primary frequency modulation technology were reviewed. [Result] The results show that the primary frequency modulation technology for the unit mainly includes regulating valve pre-throttling, adjustable regenerative steam extraction frequency modulation, and condensate water throttling frequency modulation. Among them, the condensate water throttling frequency modulation technology should be the main mode. Auxiliary primary frequency modulation technology is mainly based on the fast-response rate characteristics of flywheel energy storage and battery to meet the unit input and output requirements. The focus and difficulty of coupled auxiliary frequency modulation technology are then analyzed. The system modeling and control strategy research based on frequency modulation technology can optimize the matching between unit parameters. [Conclusion] Thus, the application status of primary frequency modulation technology in recent years is compared, and it is considered that flywheel energy storage primary frequency modulation and sliding pressure operation optimization will be the key development direction.

• A power-control strategy for the CC-HTGR was developed. • Control method called integral mass flow control. • The bottoming cycle runs is adjusted by sliding pressure. • The topping cycle is controlled by the inventory. • CC-HTGR can operate efficiently in the load range of 100% to 30%. High-Temperature Gas-cooled Reactors (HTGRs) have excellent development prospects because of their inherent safety and multiple application areas, such as hydrogen production. The combined cycle coupled with HTGR is a type of cycle for cascade utilization of energy that can efficiently convert heat from HTGR. In this paper, an off-design control strategy, called integral mass flow control, is proposed. The calculation model is discussed, and the performance at partial load is analyzed. When the load changes, the topping cycle is controlled by the inventory, and the bottoming cycle is adjusted by sliding pressure (the temperature of the main steam remains unchanged, and the pressure changes with the load), while the mass flow of the topping cycle and that of bottoming cycle changes synchronously. With this control strategy, the combined cycle coupled with the HTGR can be operated safely and efficiently within a load range of 100% to 30%. [ABSTRACT FROM AUTHOR]

The 2×1000 MW ultra-supercritical steam turbine of Shanghai Waigaoqiao Phase III project, which uses grid frequency regulation and overload control through an overload valve, is manufactured by Shanghai Turbine Company using Siemens technology. Through optimization, the steam pressure is regarded as the criterion between constant pressure and sliding pressure operation. At high circulating water temperature, the turbine overload valve is kept closed when the unit load is lower than 1000 MW while at other circulating water temperatures the turbine can run in sliding pressure operation when the unit load is higher than 1000 MW and the pressure is lower than 27 MPa This increases the unit operation efficiency. The 3D bending technology in the critical piping helps to reduce the project investment and minimize the reheat system pressure drop which improves the unit operation efficiency and safety. By choosing lower circulating water design temperature and by setting the individual Boiler Feedwater Turbine condenser to reduce the exhaust steam flow and the heat load to the main condenser, the unit average back pressure and the terminal temperature difference are minimized. Therefore, the unit heat efficiency is increased. [ABSTRACT FROM AUTHOR]