Steam generator level control system and method of preventing oscillation of steam generator level

A steam generator level control system configured to prevent oscillation of a steam generator level at a nuclear power plant, the steam generator level control system comprising:

• a comparator configured to compare a steam generator level with a predetermined level-set value;
• a proportional integral control output unit configured to generate a proportional integral control value by using an output from the comparator;
• a high-level priority control signal generator configured to output a signal instructing to enter a high-level priority control mode if the steam generator level is equal to or greater than first criteria, and output a signal deactivating the high-level priority control mode if the steam generator level is equal to or less than second criteria after the steam generator level is equal to first criteria;
• and
• a high-level priority control signal receiver configured to control a control signal using the proportional integral control value of the proportional integral control output unit to be transmitted to a main feedwater pump and a feedwater control valve in a normal mode, obstruct a control signal using a value of the proportional integral control output unit in the high-level priority control mode, and control a predetermined output value to be transmitted to the main feedwater pump and the feedwater control valve,
• wherein the proportional integral control output unit comprises:
• a proportional integral controller configured to generate a proportional integral control value by using an output from the comparator;
• and
• an output reducer configured to control the proportional integral controller to generate, for a certain time, the proportional integral control value lower than the proportional integral control value in the normal mode if a high-level priority control mode is deactivated according to a signal from the high-level priority control signal generator,
• wherein the output reducer reduces the proportional integral control value until the steam generator level is reduced to a value equal to or less than a predetermined value after the high-level priority control mode is deactivated.