APPARATUS AND METHOD FOR CONTROLLING GAIN ACCORDING TO RATE OF CHANGE IN WATER LEVEL OF STEAM GENERATOR IN NUCLEAR POWER PLANTS

Provided is an apparatus for controlling a gain according to a water level change rate of a steam generator in nuclear power plants. The apparatus includes a water level variance detector detecting a water level variance of the steam generator, a change rate calculator calculating a water level change rate with respect to the detected water level variance, a compensation value calculator calculating a compensation gain value corresponding to the calculated water level change rate, a reactor power sensor sensing whether or not reactor power corresponds to certain power or less, and a gain compensation controller, when the reactor power corresponds to the certain power or less, outputting a control gain value obtained by combining a general gain value provided to control a proportional-integral (PI) controller with the compensation gain value to the PI controller

DETAILED DESCRIPTION

FIG. 4is a schematic view of a feedwater control system including an apparatus100for controlling a gain according to a water level change rate level of a steam generator of nuclear power plants, according to one or more embodiments of the present invention.

InFIG. 4, there are a steam flow1, a feed(water) flow2, a reactor power3, a steam generator level4, a steam-feedwater flow deviation5, zero6, a transfer logic7allowing a value provided from the zero6to be outputted when an input provided from a signal9for low reactor power control and allowing a value provided from the steam-feedwater flow deviation5to be outputted when the input is 0, a low reactor power control program8, the signal9for low reactor power control, a steam flow-feedwater flow deviation10, a steam generator level-steam flow-feedwater flow deviation11, a steam generator level setpoint12, a compensated steam generator level error13, a gain controller14, a control gain value15, a reset time constant program16, a reset time constant17, a proportional-integral (PI) controller18, a flow demand signal19, a main feedwater pump speed program20, a downcomer feedwater control valve position program21, an economizer feedwater control valve position program22, a low reactor power control program23, a signal24for low reactor power control, zero25, a transfer logic26allowing a value provided from the zero25to be outputted when an input provided from the signal24for low reactor power control is 1 and allowing a value provided from the economizer feedwater control valve position program22to be outputted when the input is 0. Since elements described above are identical to elements of a general feedwater control system for water level control logic, a description thereof in detail is omitted.

The apparatus100for controlling the gain according to the water level change rate level of the steam generator in the nuclear power plants is newly added to a general feedwater control system and will be described in detail with reference toFIG. 5.

FIG. 5is a block diagram of the apparatus100. The apparatus100includes a water level variance detector110, a change rate calculator120, a compensation value calculator130, a reactor power sensor140, and a gain compensation controller150.

The water level variance detector110detects a water level variance according to the steam generator level4and outputs a signal with respect to the detected water level variance to the change rate calculator120. The water level variance detector110calculates the water level variance by obtaining an absolute value from a variation value of the water level, for each execution interval of an algorithm.

The change rate calculator120calculates a water level change rate level with respect to the water level variance detected by the water level variation detector110and outputs a signal with respect to the calculated water level change rate level to the compensation value calculator130. The change rate calculator120obtains a differential value with respect to the water level variance, thereby calculating each water level change rate level with respect to the water level variance.

The compensation value calculator130calculates a compensation gain value corresponding to the water level change rate and outputs a signal with respect to the calculated compensation gain value to the gain compensation controller150. The compensation value calculator130includes information on a table with respect to compensation gain values corresponding to the water level change rates to calculate the compensation gain values. The compensation value calculator130calculates a compensation value to provide the PI controller with a smaller gain value as a value of the water level change rate increases.

On the other hand, the reactor power sensor140senses whether the reactor power3corresponds to certain power or less and outputs a sensed signal to the gain compensation controller150. Herein, the certain power is a reference value for determining whether or not the reactor power3is low, which may be a value arbitrarily determined corresponding to any value from about 10 to about 30% of a full reactor power. For example, when the certain power is determined as about 20%, the reactor power sensor140determines whether the reactor power3corresponds to about 20% or less of the full reactor power, based on the certain power.

The gain compensation controller150outputs a control gain value15obtained by combining a general gain value provided by the gain controller14with a compensation gain value to the PI controller18when a signal sensed by the reactor power sensor140is determined as corresponding to the certain power or less.

The gain compensation controller150controls the control gain value15to be outputted in inverse proportion to the water level change rate when the reactor power3corresponds to the certain power or less. For example, in a case, in which the certain power is determined as about 20%, when the reactor power corresponds to about 20% or less, the gain compensation controller150allows an output of the PI controller18to be gradually changed by decreasing a gain of the PI controller18when a change of the steam generator level is great in a low power operation section with reactor power of 20% or less. Also, when the change of the steam generator level is small, the output of the PI controller18is allowed to have a normal change rate by increasing the gain, thereby corresponding to the nonlinearity of controlling the steam generator level, caused by feedwater at a low temperature.

On the other hand, the gain compensation controller150controls the control gain value15excluding the compensation gain value to be outputted to the PI controller18when the reactor power3is more than the certain power. For example, in a case, in which the certain power is determined as about 20%, in a high power section, in which the reactor power3corresponds to 20% or more, the gain compensation controller150only outputs the general gain value provided by the gain controller14to the PI controller18while excluding the compensation gain value provided by the compensation value calculator130.

FIG. 6is a graph illustrating a result of comparing water levels of the steam generator when power of a low power reactor is increased/cut back. {circle around (1)} is a result of comparing the steam generator levels in a general manner while a load of nuclear power plants is changed, that is, the reactor power is changed in a low power operation section. {circle around (2)} is a result of comparing the steam generator levels according to an embodiment of the present invention while a load of nuclear power plants is changed in the low power operation section. According to one or more embodiments of the present invention, rather than the general manner, a range of fluctuation in the steam generator level caused by the reactor power may be drastically mitigated in the low power operation section.

Hereinafter, a method of controlling a gain, according to embodiments of the present invention, will be described with reference to the attached drawings.

FIG. 7is a flowchart of a method of controlling a gain according to a water level change rate of a steam generator in nuclear power plants, according to one or more embodiments of the present invention.

A water level variance of the steam generator is detected (200). The water level variance is calculated by obtaining an absolute value from a variance value of the water level, for each execution interval of an algorithm.

After operation200, a water level change rate with respect to the detected water level variance is calculated (202). Each water level change rate with respect to the water level variance is calculated by obtaining a differential value with respect to the detected water level variance.

After operation202, a compensation gain value corresponding to the calculated water level change rate is calculated (204). Systematically, information on a table with respect to compensation gain values corresponding to the water level change rates, respectively, is provided. A compensation value is calculated to allow a value of the water level change rate to increase when a smaller control gain value is to be provided to a PI controller.

After operation204, it is determined whether or not reactor power corresponds to certain power or less(206). The certain power is a reference value for determining whether or not the reactor power is low and may be determined as any value from about 10 to about 30% of the full reactor power. For example, when the certain power is set as about 20%, based thereon, it is determined whether the reactor power corresponds to 20% or less or not.

After operation206, if the reactor power corresponds to the certain power or less, a control gain value obtained by combining a general gain value provided by the gain controller14with the compensation gain value is outputted to the PI controller (208). The operation of outputting the control gain value to the PI controller includes, if the reactor power corresponds to the certain power or less, outputting the control gain value in inverse proportion to the water level change rate to the PI controller. For example, when the certain power is set as 20%, in an operation section with the reactor power of 20% or less, which is a low power section, when a change in a steam generator level is great, a gain of the PI controller is reduced to allow an output of the PI controller to be gradually changed. Also, when the change is small, the gain is increased to allow the output of the PI controller to have a normal change rate, thereby corresponding to the nonlinearity of controlling the steam generator level, caused by feedwater at a low temperature.

In operation206, if the reactor power is more than the certain power, the control gain value excluding the compensation gain value is outputted to the PI controller (210). For example, when the certain power is set as 20%, in a high power section, in which the reactor power corresponds to more than 20%, excluding a compensation gain value, only a general gain value provided by the gain controller14is outputted to the PI controller.

As described above, according to the one or more of the above embodiments of the present invention, there is provided an effect of notably easing an excessive water level phenomenon of a steam generator by effectively controlling a contraction/expansion effect of a water level of the steam generator, caused by feedwater at a low temperature in a low power operation section.

Through this, a possibility of shutdown of a reactor, caused by an excessive fluctuation in a water level of a steam generator while reactor power is increased/cut back in a low power section, may be reduced, thereby drastically reducing a load on an operator and contributing to increasing a coefficient of utilization and economic feasibility of nuclear power plants

On the other hand, the method described above may be embodied as codes/instructions/programs that can be computer readable. For example, the method can be implemented in general-use digital computers that execute the codes/instructions/programs using a computer-readable recording medium. Examples of the computer-readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, magnetic tapes, etc.) and optical recording media (e.g., CD-RMOs or DVDs).