Engineering nonlinearity characteristic compensation for commercial steam turbine control valve using linked MARS code and Matlab Simulink

Steam turbine control valves play a pivotal role in regulating the output power of the turbine in a commercial power plant. They thus have to be operated linearly to be run by an automatic control system. Unfortunately, the control valve has inherently nonlinearity characteristics. The flow increases more significantly near the closed end than near the open end of the stem travel given the valve position signal. The steam flow should nonetheless be proportional to the final desired quantity, output power, of the turbine to obtain a linear operation. This paper presents the valve engineering linked analysis (VELA) for nonlinearity characteristic compensation of the steam turbine control valve by using a linked two existing commercial software. The Multi-dimensional Analysis of Reactor Safety (MARS) code and Matlab Simulink have been selected for VELA to develop a steady state and transient analyzer of Ulchin Units 3&4 powered by the Optimized Power Reactor 1000 MWe (OPR1000). MARS is capable of modeling a wide range of systems from single pipes to full nuclear power plants. As one of standard nuclear power plant thermal hydraulic analysis software tools, MARS simulates the primary and secondary sides of the nuclear power plant. To simulate the electric power flow part, Matlab Simulink is chosen as the standard analysis software. Matlab Simulink having an interactive environment to model analyzes and simulates a wide variety of engineering dynamic systems including multimachine power systems. Based on the MARS code result, Matlab Simulink analyzes the power flow of the generator connected to an infinite bus for representing the grid connection. Three different scenarios are analyzed in VELA by considering the control valves opening sequence mechanism and the change rate of output power reference.