This is the final article in a series of articles covering multi-loop control systems. The previous articles discussed the main function of the instrumentation and control systems (I&C systems) of power plant units - namely, controlling the network frequency in accordance with current requirements. In this article, solutions to facilitate the implementation of algorithms developed by Intermatic AG specialists for controlling the frequency and power of large power plant units are considered. These solutions pertain to the main closed-loop control systems of a power plant unit comprising a high-power once-through boiler and the power plant unit as a whole. The key methods for ensuring the compliance of power plant unit characteristics with norms of participation in the primary frequency control (PFC) and load control (LC) are discussed in this article. These methods use the following: the “combined load control system (CLCS)” instead of the existing load and power control systems known as LCS1 (“the turbine follows the boiler”) and LCS2 (“the boiler follows the turbine”); various types of “forcing”; a differentiator for steam pressure upstream of the turbine, being added to the LCS control deviation. Typical problems encountered by Intermatic AG specialists at 300 and 800 MW power plant units during the commissioning and final test (considering the tests at coal-fired power plant units of Reftinskaya thermal power plant (TPP), Berezovskaya TPP, and gas-fired power plant units of Perm TPP) as well as methods for solving these problems are described in this article. Specifically, this article considers a comprehensive approach to the frequency and power closed-loop control (FPC) system engineering and commissioning. Such an approach assumes that, in addition to the main coordinated control system (CS) of power and steam pressure upstream of the turbine, the I&C system of a power plant unit should also include up-to-date CSs for supplying the boiler with feed water and fuel; additionally, this I&C system should also include temperature controllers for ensuring efficient boiler operation; thus, this approach unites the unit power control with the unit participation in grid frequency control, thus solving the problem of power and frequency control of power plant units. An important condition to ensure the successful resolution of grid frequency control problems at power plants is ensuring temperature control during boiler operation. The presentation of methods is accompanied by examples of temperature CS during the final test or compliance with norms of the power plant unit participation in the PFC that was successfully performed at the Berezovskaya TPP 800 MW coal-fired power plant units for the first time in the Russian power grid.
This work reflects many years of experience in the development and implementation of an automated process control system at traditional power units with a capacity of 300 to 800 MW. It is part of a series of articles devoted to multiply connected automatic control systems, their development in accordance with modern requirements for maintaining the frequency and power of the power system. The interrelations of the main circuits of automatic control of power units and ways to neutralize the negative interrelations between them are described in detail. The problems of regulating the frequency and power of power units and solving power system problems are considered. A simplified matrix of the power unit control object is presented. Three types of autonomy (autonomy I, II, and III) and the relationship between the main leading and driven operating parameters of the power unit are considered. The advantages of the combined variant of the implementation of the Standard unit load control systems (LCS) are shown, which makes it possible to use each technological solution regardless of the current mode of operation of the power unit. A method for neutralizing the interconnections between local automatic control systems (LACS) both in the LCS-1 structure and in the combined LCS is described in detail by switching on compensation devices with the implementation of the invariance of the main controlled variables during disturbances in the boiler’s operation. Methods have been developed and improved to improve the dynamics of regulation of important technological parameters. The developed structural solutions for equipment automation are widely used in the implementation of distributed automated control systems. The schemes of the main channels of automatic control of the power units considered in the article are given, in the process of adjusting the process control systems of which positive results were obtained. The implementation of the optimal settings for the main control loops ensures an increase in the quality of the control processes of the power unit as a whole.
The first decade of the new century, from 2000 to 2010, was marked by widescale use in the Russian power industry of modern microprocessor equipment and a fundamentally new level of power unit automation implemented on the basis of this equipment, with which it becomes possible to comply with the modern power grid requirements relating to unit load control (LC) and primary frequency control (PFC). The new control systems are used in two types of power units: classic steam power units (SPUs) and combined cycle power units (CCPUs), which are new ones for the Russian power industry. The discussion in this article is limited to SPUs only. A list of 29 accomplished projects is given, the LC and PFC requirements posed to different equipment types are presented, and the technical solutions developed by Intermatic AG specialists for improving the dynamic characteristics of once-through boiler units for fulfilling the LC and PFC requirements are considered in detail. Unlike the conventional solutions involving separate consideration of the power unit’s main automatic control loops, a unified general structure of the automatic frequency and power control system (AFPCS) is proposed, which includes five main process groups: automatic frequency and power control proper, control of water and fuel flowrates, maintaining of the boiler temperature operation mode, the automatic control system (ACS) of coal-pulverization systems for coal-fired power units or fuel controllers for gas-and-oil-fired power units, and the boiler gas–air path ACS. The suggested version of presenting information for online indication of the automated power unit’s current operation mode is recommended.
