Improving the Concept of High Power Unit Closed-Loop Control for Conventional Thermal Power Plants to Comply with Unit Load Control and Primary Frequency Control Requirements

— 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: conventional thermal power plant (TPP) units and combined cycle power plant (CCPP) units, which are new ones for the Russian power industry. The discussion in this article is limited to conventional TPP units 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 Interautomatika AG 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 frequency and power closed-loop control (FPC) is proposed, which includes five main process groups: frequency and power control proper, control of water and fuel flowrates, maintaining of the boiler temperature operation mode, the closed-loop control (CLC) system of coal-pulverization systems for coal-fired power units or fuel closed-loop controllers for gas-and-oil-fired power units, and the boiler gas–air path CLC system. The suggested version of presenting information for the operator monitoring of the automated power unit’s current operation mode is recommended.