Control device and control method

Abstract

To provide a control device and a control method capable of contributing to maintenance of the frequency of an electric power system by having a good followability to AFC signals.SOLUTION: A control target of a control device is a thermal power plant including a turbine bypass valve for adjusting the amount of steam that bypasses a steam turbine driven by steam from a boiler. The control device controls the turbine bypass valve on the basis of a turbine bypass valve opening degree command value and controls the boiler on the basis of a boiler input command value. The turbine bypass valve opening degree command value is generated on the basis of an AFC signal in an AFC response mode of the thermal power plant. The boiler input command value is generated by adding a positive bias value to a base input value based on a load command value for the thermal power plant in the AFC response mode.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a control device and a control method. [Background technology]

[0002] There is known a thermal power plant that drives a steam turbine using steam generated in a boiler (steam generator). In this type of thermal power plant, a turbine bypass valve may be provided on a bypass line configured to bypass the steam turbine with respect to a line for supplying steam from the boiler to the steam turbine. The turbine bypass valve is typically used to contribute to shortening the start-up time by controlling the opening degree before the start-up of the steam turbine, or to suppress an increase in steam pressure by opening when the steam pressure in the steam turbine increases excessively.

[0003] By the way, electric power utilities who operate thermal power plants for generating electricity using the output of steam turbines are obligated under the Electricity Business Act to strive to maintain the voltage and frequency of the generated electricity at values ​​that are respectively specified in advance for the power grid to which the electricity is supplied.The electric power utilities have responded by controlling the boiler output based on load command values ​​provided by a central load dispatching center according to the supply and demand state in the power grid and AFC (Automatic Frequency Control) signals that correspond to relatively fast frequency fluctuations.

[0004] However, in thermal power plants using boilers with low response such as coal-fired boilers, it has been difficult to obtain good tracking of components corresponding to relatively fast frequency fluctuations such as AFC signals.To address this conventional problem, for example, Patent Document 1 proposes to improve tracking of the AFC signal by holding the above-mentioned turbine bypass valve in a fully closed state during normal operation, and generating a boiler input command value obtained by adding the AFC signal to a load command value when an AFC signal is received, and controlling the opening of the turbine bypass valve in proportion to the AFC signal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 59-145309 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above-mentioned Patent Document 1, when an AFC signal is received, the AFC signal is added to the load command value to generate a boiler input command value, so that a boiler input command larger than the load command value is obtained while the AFC signal is positive. On the other hand, when the AFC signal is negative, the boiler input signal is smaller than the load command value, and since there is little adjustment margin for controlling the opening degree of the turbine bypass valve corresponding to the AFC signal, it becomes difficult to respond to a large change in the AFC signal. In addition, in Patent Document 1, the boiler input signal is obtained by adding the AFC signal to the load command value, but as described above, there is a considerable time lag until the boiler input signal is reflected in the actual amount of steam from the boiler, and there is a risk that good coordination with the turbine bypass valve, the opening degree of which is controlled in proportion to the AFC signal, cannot be achieved.

[0007] At least one embodiment of the present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a control device and a control method that have good tracking ability for an AFC signal and can contribute to maintaining the frequency of a power system. [Means for solving the problem]

[0008] In order to solve the above problem, a control device according to at least one embodiment of the present invention includes: A control device for a thermal power plant including a boiler, a steam turbine driven by steam from the boiler, and a turbine bypass valve for adjusting an amount of steam bypassing the steam turbine, a turbine bypass valve position command value generating unit for generating a turbine bypass valve position command value of the turbine bypass valve based on an AFC signal in an AFC compatible mode of the thermal power plant; a turbine bypass valve control unit for controlling the turbine bypass valve based on the turbine bypass valve opening command value; a boiler input command value generating unit for generating a boiler input command value by adding a bias value of a positive sign to a base input value based on a load command value for the thermal power plant in the AFC compatible mode; a boiler control unit for controlling the boiler based on the boiler input command value; Equipped with.

[0009] In order to solve the above problem, a control method according to at least one embodiment of the present invention includes: A method for controlling a thermal power plant including a boiler, a steam turbine driven by steam from the boiler, and a turbine bypass valve for adjusting an amount of steam bypassing the steam turbine, comprising the steps of: generating a boiler input command value by adding a positive bias value to a base input value based on a load command value for the thermal power plant in an AFC-enabled mode of the thermal power plant; controlling the boiler based on the boiler input command value; generating a turbine bypass valve opening command value for the turbine bypass valve based on an AFC signal in the AFC compatible mode; controlling the turbine bypass valve based on the turbine bypass valve opening command value; Equipped with. Effect of the Invention

[0010] According to at least one embodiment of the present invention, it is possible to provide a control device and a control method that have good tracking ability for an AFC signal and thus can contribute to maintaining the frequency of a power system. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a thermal power plant according to an embodiment. [Diagram 2] 2 is a block diagram showing the internal configuration of the control device shown in FIG. 1. [Diagram 3] 3 is a control logic diagram of a turbine bypass valve opening command value generating unit in FIG. 2. [Figure 4] 4 is an example of a function included in the function calculator of FIG. 3. [Diagram 5] 3 is a control logic diagram of a boiler input command value generating unit in FIG. 2. [Figure 6] 6 is an example of a bias value calculated by the function calculator of FIG. 5. [Figure 7] FIG. 3 is a control logic diagram of a main steam valve position command value generating unit in FIG. 2. [Figure 8] 3 is a timing chart showing time variations of various signals in the control device of FIG. 2. [Figure 9] 1 is a graph showing an adjustment allowance of a plant in a load command value. [Figure 10] FIG. 11 is an overall configuration diagram of a thermal power plant according to another embodiment. [Figure 11] 11 is a part of a control logic diagram of a turbine bypass valve position command value generating unit included in the control device of FIG. 10. [Figure 12] 12 is a graph showing the relationship between the differential pressure and the gain in the function calculator of FIG. 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as the embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure. For example, expressions expressing relative or absolute configuration, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such a configuration, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions indicating that things are in an equal state, such as "identical," "equal," and "homogeneous," not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions describing shapes such as a rectangular shape or a cylindrical shape do not only refer to rectangular shapes, cylindrical shapes, etc. in the strict geometric sense, but also refer to shapes that include uneven portions, chamfered portions, etc., to the extent that the same effect is obtained. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions excluding the presence of other elements.

[0013] In the following embodiment, a thermal power plant 1 will be described as an example of a thermal power plant that is a control target of a control device according to at least one embodiment of the present invention. Fig. 1 is a schematic configuration diagram of a thermal power plant 1 according to one embodiment.

[0014] The thermal power plant 1 includes a boiler 2, a steam turbine 4, and a condenser 12. In this embodiment, the thermal power plant 1 includes a high-pressure side turbine 4A and a low-pressure side turbine 4B as the steam turbine 4, but the thermal power plant 1 may include a single steam turbine 4 or may include three or more steam turbines 4.

[0015] The boiler 2 is a steam generator capable of generating superheated steam by exchanging heat generated by burning pulverized fuel with feed water or steam. The boiler 2 is, for example, a coal-fired (pulverized coal-fired) boiler that uses pulverized coal made by pulverizing coal (carbon-containing solid fuel) as pulverized fuel and burns this pulverized fuel with a burner.

[0016] In this embodiment, a coal-fired boiler is exemplified as the boiler 2, but the boiler 2 may use solid fuels such as biomass fuel, PC (Petroleum Coke) fuel generated during oil refining, and oil residue as fuel. The boiler 2 is not limited to using solid fuels as fuel, and may also use petroleum fuels such as heavy oil, light oil, and heavy oil, and liquid fuels such as industrial wastewater, and may also use gaseous fuels (natural gas, by-product gas, etc.) as fuel. The boiler 2 may also be a mixed-fuel boiler that uses a combination of these fuels.

[0017] Steam (superheated steam) generated in the boiler 2 is supplied to the steam turbine 4 via a main steam line 6. In this embodiment, the steam from the boiler 2 is first supplied to a high-pressure side turbine 4A provided upstream, thereby driving the high-pressure side turbine 4A. The main steam line 6 connects the boiler 2 and the high-pressure side turbine 4A. A main steam valve 8 is provided on the main steam line 6. The opening degree of the main steam valve 8 is controlled by a control device 100, so that the amount of steam supplied from the boiler 2 to the steam turbine 4 can be varied.

[0018] The steam that has completed its work in the high-pressure side turbine 4A is supplied to the low-pressure side turbine 4B provided downstream via a steam line 10, thereby driving the low-pressure side turbine 4B. The steam line 10 connects the high-pressure side turbine 4A and the low-pressure side turbine 4B. The steam that has completed its work in the low-pressure side turbine 4B is discharged to a condenser 12, whereby condensate is generated.

[0019] In addition, a bypass line 14 is provided which connects the main steam line 6 upstream of the main steam valve 8 with the condenser 12. A turbine bypass valve 16 is provided in the bypass line 14, and by adjusting the opening degree of the turbine bypass valve 16, a portion of the steam flowing through the main steam line 6 can be discharged to the condenser 12, bypassing the steam turbine 4.

[0020] The output shafts of the high pressure side turbine 4A and the low pressure side turbine 4B are each connected to a rotating shaft of a generator (not shown). The generator generates electricity by being driven by the power from these steam turbines 4. The electricity generated by the generator is supplied to an electric power system (e.g., a commercial power system) via a power transmission line (not shown).

[0021] Furthermore, the high-pressure side turbine 4A and the low-pressure side turbine 4B may have a common output shaft which is connected to a common generator, or the generators may include a first generator to which the output shaft of the high-pressure side turbine 4A is connected and a second generator to which the output shaft of the low-pressure side turbine 4B is connected.

[0022] The control device 100 is a control unit of the thermal power plant 1, and is composed of, for example, a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, for example, and the CPU reads the program into the RAM or the like and executes information processing and arithmetic processing to realize various functions. The program may be installed in a ROM or other storage medium in advance, may be provided in a state stored in a computer-readable storage medium, or may be distributed via a wired or wireless communication means. The computer-readable storage medium may be a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

[0023] Fig. 2 is a block diagram showing an internal configuration of the control device 100 of Fig. 1. The control device 100 includes a turbine bypass valve opening command value generating unit 110, a turbine bypass valve control unit 140, a boiler input command value generating unit 142, a boiler control unit 160, a main steam valve opening command value generating unit 162, and a main steam valve control unit 174. The turbine bypass valve opening command value generating unit 110 creates an opening command value Stb for the turbine bypass valve 16, and the turbine bypass valve control unit 140 controls the opening of the turbine bypass valve 16 based on the opening command value Stb. The boiler input command value generating unit 142 generates a boiler input command value BID, and the boiler control unit 160 controls the boiler 2 based on the boiler input command value BID. The main steam valve position command value generating unit 162 generates a main steam valve position command value Jd for controlling the opening of the main steam valve 8, and the main steam valve control unit 174 controls the main steam valve 8 based on the main steam valve position command value Jd.

[0024] Next, each component of the control device 100 shown in Fig. 2 will be described in detail. Fig. 3 is a control logic diagram of the turbine bypass valve opening command value generating unit 110 in Fig. 2. The turbine bypass valve opening command value generating unit 110 is a component for generating a turbine bypass valve opening command value Stb of the turbine bypass valve 16, and includes a first opening command value calculating unit 112, a second opening command value calculating unit 120, and a third opening command value calculating unit 130.

[0025] In the first opening command value calculation unit 112, a subtractor 114 calculates a pressure difference ΔPs between a detection value Ps of the main steam pressure in the main steam line 6 and a target main steam pressure Pst, and a PI controller 116 determines a first opening command value Stb1 corresponding to the pressure difference ΔPs. The target main steam pressure Pst is calculated by adding a predetermined bias value Psb to a main steam pressure set value Pss, which is a reference value, in an adder 118. The bias value Psb is a parameter added to the main steam pressure set value Pss to be a threshold value for determining an abnormal rise in the main steam pressure Ps, and in this embodiment, the bias value Psb can be selectively switched between "0 MPa" and "1.0 MPa" by a switch SW1. The first opening command value Stb1 calculated in this manner functions as an opening command value for controlling the opening of the turbine bypass valve 16 when the main steam pressure Ps in the main steam line 6 rises abnormally.

[0026] The second opening command value calculation unit 120 is configured to calculate a second opening command value Stb2, which is an opening command value Stb for controlling the opening of the turbine bypass valve 16 at the time of startup. In the second opening command value calculation unit 120, a detection value Ps of the steam pressure (main steam pressure) in the main steam line 6 is input to a function calculator 122, whereby calculation is performed so that the opening control of the turbine bypass valve 16 suitable for the time of startup is performed.

[0027] The first opening command value calculation unit 112 and the second opening command value calculation unit 120 described above are connected via a switch SW2. The switch SW2 is switchable based on whether the operation mode is the startup mode or not. Specifically, when the operation mode is the startup mode, the switch SW2 selects the second opening command value calculation unit 120, and when the operation mode is not the startup mode, the switch SW2 selects the first opening command value calculation unit 112.

[0028] The third opening command value calculation unit 130 is configured to calculate the third opening command value Stb3, and includes a base opening calculation unit 132 and a bias opening calculation unit 134. The third opening command value Stb3 is obtained by an adder 136 adding the bias opening Stb3bias calculated by the bias opening calculation unit 134 to the base opening Stb3base calculated by the base opening calculation unit 132.

[0029] The base opening calculation unit 132 calculates a base opening Stb3base of the turbine bypass valve 16 based on a load command value L. The load command value L is provided, for example, from a central load dispatching center, and in the base opening calculation unit 132, a function calculator 138 converts it to a steam flow rate Qs. A subtractor 140 calculates a difference ΔQs between the steam flow rate Qs calculated by the function calculator 138 and a detected value Qsj of the steam flow rate at the outlet of the first bypass line. The difference ΔQs is input to a PI controller 142, whereby a corresponding base opening Stb3base is obtained. Note that a hold circuit 144 is provided on the output side of the PI controller 142, and is configured to hold a constant base opening Stb1 in the AFC compatible mode (while an AFC signal is being received).

[0030] The bias opening calculation unit 134 calculates the bias opening Stb3bias based on the AFC signal. In the bias opening calculation unit 134, the AFC signal is input to a function calculator 146, where it is converted into the bias opening Stb3bias. Fig. 4 shows an example of a function possessed by the function calculator 146 in Fig. 3. In Fig. 4, the function is defined so that the bias opening Stb3bias monotonically decreases as the AFC signal increases (note that the bias opening Stb3bias is defined to be constant within a range above an upper limit value and below a lower limit value of a preset AFC signal).

[0031] A switch SW3 is provided on the output side of the function calculator 146. The switch SW3 can switch between the calculation result of the function calculator 146 or a preset default value of "0%" as the bias opening Stb3bias based on whether or not the AFC compatible mode in which an AFC signal is input is in effect. That is, in the AFC compatible mode, the calculation result of the function calculator 146 is used as the bias opening Stb3bias, and in other operation modes, the bias opening Stb3bias is set to zero.

[0032] The base opening Stb3base and bias opening Stb3bias calculated in this manner are added together in an adder 136. A switch SW4 is provided on the output side of the adder 136, and is capable of switching between the calculation result of the adder 136 or a preset default value of "0%" as the third opening command value Stb3 based on whether or not the operation is in an AFC compatible mode in which an AFC signal is input. That is, in the AFC compatible mode, the calculation result of the adder 136 is used as the third opening command value Stb3, and in other operation modes, the third opening command value Stb3 is zero.

[0033] The turbine bypass valve position command value generating unit 110 is configured to select the larger of the outputs from the switches SW2 and SW4 as the position command value Stb by the high value selector HS. The position command value Stb is input to the turbine bypass valve control unit 140 (see FIG. 2) and is used for controlling the position of the turbine bypass valve 16.

[0034] The turbine bypass valve control unit 140 controls the turbine bypass valve 16 based on the turbine bypass valve position command value Stb calculated in this manner, thereby enabling a good response to the AFC signal in the AFC compatible mode while accurately avoiding a shortened start-up time and an abnormal rise in the main steam pressure during a series of operations of the thermal power plant 1. That is, at start-up, the second position command value Stb2 is output as the turbine bypass valve position command value Stb, thereby controlling the turbine bypass valve 16 in a manner suitable for start-up. Also, during normal times when the AFC signal is not received, the bias position Stb3bias based on the AFC signal is zero, so that the turbine bypass valve 16 is controlled based on the third position command value Stb3 which is the base position Stb3base. However, when the main steam pressure Ps becomes equal to or higher than the main steam pressure set value Pst and thus abnormally rises, the turbine bypass valve 16 is controlled based on the first position command value Stb1, thereby suppressing the abnormal rise in the main steam pressure Ps. In the AFC compatible mode in which the AFC signal is received, the turbine bypass valve 16 is controlled based on a third opening command value Stb3 obtained by adding a bias opening Stb3bias based on the AFC signal to the base opening Stb3base. As a result, even when there is a time lag until the boiler input signal is reflected in the steam volume, such as in the case of a coal-fired boiler as the boiler 2, good follow-up to the AFC signal can be obtained by controlling the opening of the turbine bypass valve 16 based on the AFC signal. Note that in the AFC compatible mode, an adjustment margin for the turbine bypass valve 16 can be obtained regardless of the magnitude of the load command value L by generating a boiler input command value BID as described later.

[0035] Next, FIG. 5 is a control logic diagram of the boiler input command value generating unit 142 in FIG. 2. In the boiler input command value generating unit 142, the load command value L is first input to a change rate limiter 144. In the change rate limiter 144, the change rate of the load command value L, which changes from moment to moment, is limited to a predetermined value or less, and output as a first command value D1. A frequency control signal Df is added to the first command value D1 by an adder 146 to obtain a second command value D2 (MWD). The frequency control signal Df contributes to stabilization of the power system by adding a load component corresponding to the fluctuation of the system frequency to the first command value D1 (generator output command). In FIG. 5, the system frequency is input to a function calculator 147, a load component corresponding to the system frequency is calculated, and the result of limiting the change rate by inputting the output to a change rate limiter 149 is added to the first command value D1 as a frequency control signal Df.

[0036] 5 is configured to add the frequency control signal Df to the first command value D1, but not to add the AFC signal. This is because the turbine bypass valve 16 is kept at an appropriate opening so as to respond to increases and decreases in the turbine intake flow rate by increasing the boiler input command value BID by adding a bias value Dbias (described later), and therefore there is no need to increase or decrease the boiler input command value BID by adding an AFC signal.

[0037] Subsequently, the second command value D2 output from the adder 146 is further added with the main steam pressure control signal Ds in an adder 148 to become a third command value D3. The main steam pressure control signal Ds is obtained by calculating in a subtractor 150 a pressure difference ΔPs between the target main steam pressure Pst, which is calculated by inputting the second command value D2 to a function calculator 152, and the detected value Ps of the main steam pressure in the main steam line 6, and inputting the pressure difference ΔPs to a PI controller 154.

[0038] Furthermore, in an adder 156, a bias value Dbias is added to a third command value D3, which is a base value based on a load command value L for the thermal power plant 1, to generate a boiler input command value BID. The bias value Dbias can be switched by a switch SW6, and in the AFC compatible mode, a positive value calculated by a function calculator 158 is selected, and in other operation modes, "0%" is selected.

[0039] FIG. 6 shows an example of the bias value Dbias calculated by the function calculator 158 in FIG. 5. In the example of FIG. 6, the bias value Dbias is set to be substantially constant and independent of the load command value L when the load command value L (second command value D2) input to the boiler input command value generator 142 is equal to or less than a predetermined value. For example, the value is set corresponding to the maximum decrease value with respect to the reference value of the AFC signal. As a result, in the AFC compatible mode, even when the load command value L changes, the constant bypass value does not change, so that the adjustment margin of the turbine bypass valve 16 can be secured in a wide load range. That is, even when the AFC signal is negative in the AFC compatible mode, a boiler output larger than the load command value L can be secured regardless of whether the AFC signal is positive or negative by adding the bias value Dbias, which is a constant value having a positive sign, to generate the boiler input command value BID, and the tracking ability can be improved by controlling the opening degree of the turbine bypass valve 16 in response to the AFC signal.

[0040] In addition, in a range where the load command value L is greater than a predetermined value, the bias value Dbias is set to decrease as the load command value L approaches the upper limit value (100%). In the example shown in Fig. 6, in a range where the load command value L is from 95% to the upper limit value (100%), the bias value Dias is set to decrease monotonically as the load command value L increases.

[0041] The boiler input command value BID calculated in this manner is input to the boiler control unit 160 (see FIG. 2). The boiler control unit 160 controls the boiler 2 based on the boiler input command value BID.

[0042] 7 is a control logic diagram of the main steam valve position command value generating unit 162 in FIG. 2. In the main steam valve position command value generating unit 162, the AFC signal is converted to a fourth command value D4 by a function calculator 164. The switch SW7 selects the fourth command value D4 in the AFC compatible mode to input it to a change rate limiter 166, and the result is added to the above-mentioned first command value D1 (see FIG. 5) by an adder 168 to obtain a fifth command value D5. By adding the output signal from the change rate limiter 166 to the first command value D1 in this way, the fluctuation range of the main steam pressure during the operation of the turbine bypass valve 16 can be reduced, and the responsiveness of the generator output to the AFC signal can be improved. The deviation ΔP of the fifth command value D5 from the output detection value P of the generator (not shown) connected to the steam turbine 4 is calculated by a subtractor 170, and a main steam valve position command value Jd corresponding to the deviation ΔP is generated by a PI controller 172. In other operation modes, the switch SW7 selects the default value "0%", and the fifth command value D5 becomes the first command value D1 itself.

[0043] The main steam valve position command value Jd generated in this manner by the main steam valve position command value generating unit 162 is provided to a main steam valve control unit 174. The main steam valve control unit 174 performs opening control of the main steam valve 8 based on the main steam valve position command value Jd. As a result, the opening of the main steam valve 8 is controlled in coordination with the opening of the turbine bypass valve 16, which also takes into account the AFC signal, based on the main steam valve position command value Jd taking into account the AFC signal, thereby improving the follow-up to the AFC signal.

[0044] Next, the control of the thermal power plant 1 by the control device 100 having the above configuration will be described. Fig. 8 is a timing chart showing time changes of various signals in the control device 100 of Fig. 2. Fig. 8 shows time changes of (a) the AFC signal, (b) the load command value L, (c) the fifth command value D5, (d) the second command value D2, (e) the third command value D3, (f) the boiler input command value BID, (g) the main steam valve position command value Jd, (h) the turbine bypass valve position command value Stb, (i) the generator output P, ​​and (j) the main steam pressure deviation ΔPs (=detected value Ps of the main steam pressure-target main steam pressure Pst) in the case where the control device 100 transitions to the AFC compatible mode by receiving an AFC signal after time t0 in an initial state in which the control device 100 controls the thermal power plant 1 in the normal mode.

[0045] Although the (a) AFC signal generally has a complex waveform centered around a reference value (0%), in this embodiment, for ease of explanation, an AFC signal that varies stepwise over time is exemplified (specifically, the (a) AFC signal varies stepwise from "+3%" at time t0 to t1, from "+5%" at time t1 to t2, and from "+1%" at time t2 to t3). In addition, in order to easily explain the responsiveness to the (a) AFC signal, the (b) load command value L that the control device 100 receives from the central load dispatching center is assumed to be constant (50%).

[0046] In the AFC compatible mode, the switch SW7 selects the function calculator 164 side, and the adder 168 adds the first command value D1 to a calculated value obtained by inputting the fourth command value D4 based on the AFC signal to the change rate limiter 166, thereby obtaining the fifth command value D5. As a result, the fifth command value D5 has a waveform in which the AFC signal (a), which changes over time, is added to the load command value L (b), which is constant (50%).

[0047] The (d) second command value D2 is obtained by adding a frequency control signal Df in an adder 146 to the (b) load command value L, the rate of change of which has been limited by the rate of change limiter 144. In this embodiment, the frequency control signal Df is set to zero, and the second command value D2 having a constant value (50%) like the (b) load command value L is shown.

[0048] (e) The third command value D3 is obtained by adding the main steam pressure control signal Ds to the (d) second command value D2 in adder 148, and exhibits a behavior that fluctuates around the second command value D2 due to the time-varying main steam pressure control signal Ds being added to the (d) second command value D2, which has a constant value (50%).

[0049] The boiler input command value BID (f) is obtained by adding the bias value Dbias to the third command value D3 (e) in the adder 156. In the AFC compatible mode, a constant value (5%) set by the function calculator 158 is added as the bias value Dbias. The constant value is added to the boiler input command value BID at the timing when the AFC mode is set (before the time t0 when the AFC signal is input). After the boiler load has increased to the constant value, the AFC signal is input. As a result, the boiler input command value BID (f) exhibits a behavior that fluctuates around a value obtained by adding the bias value Dbias (5%) to the second command value D2 (50%). Here, the AFC mode may be set by the operator or automatically at a predetermined time.

[0050] (g) The main steam valve opening command value Jd is calculated in the PI controller 172 based on the deviation ΔP between (c) the fifth command value D5 and (i) the generator output P, ​​and a time change reflecting the trend of the first command value D1 is shown for the waveform corresponding to the boiler input command value BID.

[0051] (h) The turbine bypass valve opening command value Stb is calculated by adding the bias opening Stb3bias based on the (a) AFC signal to the constant base opening Stb3base after time t0 when the AFC signal is input, and therefore shows a gradual change over time corresponding to the (a) AFC signal.

[0052] (i) The generator output P, ​​while fluctuating over time, shows an increase / decrease trend corresponding to (a) the AFC signal. This shows that the power generation control of the thermal power plant 1 is performed in response to the AFC signal, and good tracking to the AFC signal is obtained.

[0053] (j) The main steam pressure deviation ΔPs is the differential pressure between the steam pressure Ps in the main steam line 6 and the target main steam pressure Pst, as described above, and varies over time in response to the load on the high-pressure side turbine 4A. The main steam pressure deviation ΔPs increases and decreases in response to the AFC signal while varying over time.

[0054] FIG. 9 is a graph showing the load adjustment allowance of the plant with respect to the load command value L. In FIG. 9, in order to easily compare the effect of the bias value Dbias, the load adjustment allowance of the boiler input command value BID when the bias value Dbias is fixed to 0% is shown by a broken line as a comparative example. According to this comparative example, the boiler input command value BID with the bias value Dbias set to 0% has only an adjustment allowance according to the load command value L as described above with reference to FIG. 5, so that the load adjustment allowance decreases as the load command value L decreases. In contrast, in this embodiment, a constant value having a positive sign is added as the bias value Dbias to obtain the boiler input command value BID, so that a constant load adjustment allowance can be obtained up to the low load side by using the turbine bypass valve 16 in combination, regardless of the magnitude of the load command value L, as shown by a solid line in FIG. 9.

[0055] In the above comparative example, the turbine bypass valve 16 is not opened or closed, and the load is adjusted by increasing or decreasing the boiler input command value BID. As shown by the dashed line in FIG. 9, the load adjustment margin in the low load range is narrower than that in the high load range. In contrast, in this embodiment, the bias value Dbias is added to the boiler input command value BID to fix it, and then the turbine bypass valve 16 is opened or closed, so that the load adjustment margin can be maintained at the same level as that in the high load range up to the low load range. That is, compared to the comparative example, the load adjustment margin in the low load range can be expanded. This is achieved by increasing the boiler input command value BID by the amount of the bias value Dbias added, increasing the evaporation amount in advance, and using the evaporation amount as a buffer for the load adjustment margin. In other words, it can be said that the operation control is "load adjustment margin priority". With such control, even when the boiler 2 is operated in a load range lower than 100% load, it is possible to address the issue of ensuring load adjustment capability accompanying an increase in renewable energy, etc.

[0056] Next, a control device 100' for controlling a thermal power plant 1' according to another embodiment will be described. FIG. 10 is an overall configuration diagram of a thermal power plant 1' according to another embodiment. In this embodiment, in addition to a first bypass line 14 corresponding to the bypass line 14 in the embodiment shown in FIG. 1, a second bypass line 15 is provided. The first bypass line 14 communicates the upstream side and the downstream side of the main steam line 6, and a first turbine bypass valve 16 is provided in the first bypass line 14. The opening degree of the first turbine bypass valve 16 can be controlled by the control device 100', and depending on the opening degree, a part of the steam flowing through the main steam line 6 can be supplied to the steam line 10 via the first bypass line 14, bypassing the high-pressure side turbine 4A.

[0057] Further, a second bypass line 15 is provided in the steam line 10 between the upstream side of the low-pressure side turbine 4B and the condenser 12. A second turbine bypass valve 17 is provided in the second bypass line 15. The opening degree of the second turbine bypass valve 17 can be controlled by the control device 100, and depending on the opening degree, a portion of the steam flowing through the steam line 10 can be supplied to the condenser 12 via the second bypass line 15, bypassing the low-pressure side turbine 4B.

[0058] The control device 100′ has a common configuration with the control device 100 according to the above-described embodiment (see FIG. 2). A turbine bypass valve opening command value generating unit 110 in the control device 100′ generates a turbine bypass valve opening command value Stb corresponding to the first turbine bypass valve 16. The opening degree of the second turbine bypass valve 17 is appropriately controlled to adjust the reheat steam pressure (the inlet pressure of the low-pressure side turbine 4B) to a specified value during startup and normal operation of the thermal power plant 1'. The target opening value of the second turbine bypass valve 17 typically differs between startup and normal operation of the thermal power plant 1' and is appropriately set for each.

[0059] Fig. 11 is a part of a control logic diagram of a turbine bypass valve position command value generating unit 110' provided in the control device 100' in Fig. 10. The turbine bypass valve position command value generating unit 110' basically has a common control logic with Fig. 3, but Fig. 11 shows only a bias position calculation unit 134' and a bias position correction unit 200 of the turbine bypass valve position command value generating unit 110' (note that other configurations of the turbine bypass valve position command value generating unit 110' are omitted in Fig. 11 because they are similar to those of the turbine bypass valve position command value generating unit 110 shown in Fig. 3).

[0060] The bias opening correction unit 200 corrects the bias opening Stb3bias based on the load of the high-pressure side turbine 4 A. In this embodiment, the bias opening correction unit 200 calculates a differential pressure ΔP′ between the main steam pressure Ps in the main steam line 6 and the steam pressure Pse in the steam line 10 by a subtractor 202 as a parameter for evaluating the load of the high-pressure side turbine 4 A, and inputs the differential pressure ΔP′ to a function calculator 204 to calculate a gain G for correcting the bias opening Stb3bias.

[0061] Fig. 12 is a graph showing the relationship between the differential pressure ΔP' and the gain G in the function calculator 204 in Fig. 11. In this example, the gain G is specified to monotonically decrease as the differential pressure ΔP' for evaluating the load on the high-pressure side turbine 4A increases. The gain G calculated in this manner is multiplied by the output of the function calculator 146 based on the AFC signal in the correction unit 206, and is used to correct the bias opening Stb3bias.

[0062] Although the influence of the bias value Stb3bias on the third opening command value Stb3 becomes smaller on the lower load side, in this embodiment, a gain G that increases as the load on the high-pressure side turbine 4A becomes smaller is set for the bias opening Stb3bias included in the third opening command value Stb3 in this way. This makes it possible to effectively obtain the effect of the bias value Stb3bias in the third opening command value Stb3 even on the low load side, and to obtain good tracking ability to the AFC signal over a wide load range.

[0063] As described above, according to the above embodiment, it is possible to provide a control device and a control method capable of maintaining a power generation frequency with good tracking ability to an AFC signal.

[0064] The contents described in each of the above embodiments can be understood, for example, as follows.

[0065] (1) A control device according to one aspect includes: A control device (e.g., the control device 100, 100') of a thermal power plant (e.g., the thermal power plant 1, 1' of the above embodiments) including a boiler (e.g., the boiler 2 of the above embodiments), a steam turbine (e.g., the steam turbine 4 of the above embodiments) driven by steam from the boiler, and a turbine bypass valve (e.g., the turbine bypass valve 16 of the above embodiments) for adjusting an amount of steam bypassing the steam turbine, a turbine bypass valve position command value generating unit (e.g., the turbine bypass valve position command value generating unit 110 in the above embodiment) for generating a turbine bypass valve position command value (e.g., the turbine bypass valve position command value Stb in the above embodiment) of the turbine bypass valve based on an AFC signal in an AFC compatible mode of the thermal power plant; a turbine bypass valve control unit (for example, the turbine bypass valve control unit 140 in the above embodiment) for controlling the turbine bypass valve based on the turbine bypass valve opening command value; a boiler input command value generating unit (e.g., the boiler input command value generating unit 142 in the above embodiment) for generating a boiler input command value (e.g., the boiler input command value BID in the above embodiment) by adding a bias value of a positive sign (e.g., the bias value Dbias in the above embodiment) to a base input value (e.g., the second command value D2 in the above embodiment) based on a load command value (e.g., the load command value L in the above embodiment) for the thermal power plant in the AFC compatible mode; A boiler control unit (for example, the boiler control unit 160 in the above embodiment) for controlling the boiler based on the boiler input command value; Equipped with.

[0066] According to the above aspect (1), in the AFC compatible mode, the opening of the turbine bypass valve is controlled based on the opening command value generated based on the AFC signal, thereby obtaining good tracking to the AFC signal. Meanwhile, the boiler input command value is generated by adding a bias value with a positive sign to a base input value based on a load command value. As a result, when the turbine bypass valve is controlled by the opening command value based on the AFC signal, it is possible to ensure an opening adjustment margin for the turbine bypass valve, regardless of the positive or negative sign of the AFC signal.

[0067] (2) In another embodiment, in the above embodiment (1), The bias value is constant regardless of the load command value as long as the load command value is within a range equal to or less than a predetermined value.

[0068] According to the above aspect (2), the bias value added to the base input value when generating the boiler input command value is set to a constant value regardless of the load command value. This ensures that the bypass value does not change even when the load command value changes, and therefore the adjustment margin for the turbine bypass valve can be secured over a wide load range.

[0069] (3) In another embodiment, in the above embodiment (2), The bias value is set corresponding to the maximum decrease value of the AFC signal with respect to the reference value.

[0070] According to the above aspect (3), a constant bias value is set corresponding to the maximum decrease value of the AFC signal from the reference value regardless of the load command value, which makes it possible to always secure an adjustment margin for the turbine bypass valve in response to the AFC signal that changes from moment to moment, and obtains good tracking of the AFC signal.

[0071] (4) In another embodiment, in any one of the above (1) to (3), The opening command value generating unit is configured to generate the opening command value by adding a bias opening based on the AFC signal (e.g., the bias opening Stb3bias in the above embodiment) to a base opening of the turbine bias valve at the time of transition to the AFC compatible mode (e.g., the base opening Stb3base in the above embodiment).

[0072] According to the above aspect (4), the turbine bias valve opening control value is generated by adding the bias opening to the base opening. The base opening is the opening of the turbine bias valve when the thermal power plant transitions from the normal mode to the AFC signal compatible mode, and is generated by adding the bias value based on the AFC signal, which changes from moment to moment, to the base opening. By controlling the turbine bypass valve opening based on such an opening control value, good tracking ability to the AFC signal can be obtained.

[0073] (5) In another embodiment, in the above embodiment (4), The base opening degree is an intermediate opening degree between a fully open state and a fully closed state.

[0074] According to the above aspect (5), in the AFC compatible mode, the base opening, which is the reference for controlling the opening of the turbine bypass valve, is set to an intermediate opening. As a result, when the opening of the turbine bypass valve is changed based on the AFC signal, an adjustment margin for the turbine bypass valve is ensured regardless of the sign of the AFC signal, and good follow-up to the AFC signal can be obtained.

[0075] (6) In another embodiment, in any one of the above (1) to (5), The thermal power plant further includes a main steam valve (for example, the main steam valve 8 in the above embodiment) for adjusting an amount of main steam supplied from the boiler to the steam turbine, The control device includes: a steam valve position command value generating unit (for example, the main steam valve position command value generating unit 162 in the above embodiment) for generating a steam valve position command value (for example, the main steam valve position command value Jd in the above embodiment) based on the AFC signal; a main steam valve control unit (for example, the main steam valve control unit 174 in the above embodiment) for controlling the main steam valve based on the steam valve position command value; It further comprises:

[0076] According to the above aspect (6), the opening of the main steam valve is controlled based on the main steam valve position command value generated based on the AFC signal. As a result, the main steam valve operates in coordination with the turbine bypass valve, the opening of which is similarly controlled based on the AFC signal, thereby improving the tracking ability to the AFC signal.

[0077] (7) In another embodiment, in any one of the above (1) to (6), The steam turbine further includes a bias opening correction unit (for example, the bias opening correction unit 200 in the above embodiment) for correcting the bias opening based on the load of the steam turbine.

[0078] According to the above aspect (7), by correcting the bias opening based on the load of the steam turbine, it is possible to improve the ability of the bias opening to follow the AFC signal over a wide load range of the steam turbine.

[0079] (8) In another embodiment, in the above embodiment (7), The bias opening correction unit corrects the bias opening so that the amount of correction increases as the load decreases.

[0080] According to the above aspect (8), the correction amount of the bias opening is set to increase as the load of the steam turbine decreases. This makes it possible to effectively improve the tracking of the AFC signal by the bias opening even on the low load side where the effect of the bias opening is relatively small.

[0081] (9) In another embodiment, in the above embodiment (7) or (8), The bias opening correction unit calculates the load based on the pressure difference (e.g., the pressure difference ΔP' in the above embodiment) between the supply steam pressure (e.g., the main steam pressure Ps in the above embodiment) and the exhaust steam pressure (e.g., the turbine exhaust pressure Pse in the above embodiment) of the steam turbine.

[0082] According to the above aspect (9), the load of the steam turbine can be appropriately evaluated based on the differential pressure between the steam pressure supplied to the steam turbine and the steam pressure discharged from the steam turbine, without adding a new sensor or the like.

[0083] (10) In another embodiment, in any one of the above (1) to (9), The turbine bypass valve is provided in a bypass line that communicates between the upstream side and the downstream side of the steam turbine.

[0084] According to the above aspect (10), by providing a turbine bypass valve in a bypass line connecting the upstream and downstream sides of a steam turbine, for example, by adjusting the opening degree at the time of startup of a thermal power plant, steam can be supplied to the downstream side of the steam turbine, and various components (such as a reheater) downstream of the steam turbine can be suitably protected.

[0085] (11) In another embodiment, in any one of the above (1) to (9), The turbine bypass valve is provided in a bypass line that communicates between the upstream side of the steam turbine and a condenser provided downstream of the steam turbine.

[0086] According to the aspect of (11) above, when the turbine bypass valve is controlled by an opening command value based on an AFC signal, it is possible to ensure an opening adjustment allowance for the turbine bypass valve by simpler control, regardless of the positive or negative sign of the AFC signal (for example, it is possible to eliminate the need for the bias opening correction unit in (9) above).

[0087] (12) A control method according to one aspect includes the steps of: A control method for a thermal power plant (e.g., the thermal power plant 1, 1' in the above embodiment) including a boiler (e.g., the boiler 2 in the above embodiment), a steam turbine (e.g., the steam turbine 4 in the above embodiment) driven by steam from the boiler, and a turbine bypass valve (e.g., the turbine bypass valve 16 in the above embodiment) for adjusting an amount of steam bypassing the steam turbine, comprising: generating a boiler input command value (e.g., the boiler input command value BID in the above embodiment) by adding a positive bias value (e.g., the bias value Dbias in the above embodiment) to a base input value (e.g., the second command value D2 in the above embodiment) based on a load command value (e.g., the load command value L in the above embodiment) for the thermal power plant in an AFC compatible mode of the thermal power plant; controlling the boiler based on the boiler input command value; generating a turbine bypass valve opening command value (for example, the turbine bypass valve opening command value Stb in the above embodiment) for the turbine bypass valve based on an AFC signal in the AFC compatible mode; controlling the turbine bypass valve based on the turbine bypass valve opening command value; Equipped with.

[0088] According to the above aspect (12), in the AFC compatible mode, the opening of the turbine bypass valve is controlled based on the opening command value generated based on the AFC signal, thereby obtaining good tracking to the AFC signal. Meanwhile, the boiler input command value is generated by adding a bias value with a positive sign to a base input value based on a load command value. As a result, when the turbine bypass valve is controlled by the opening command value based on the AFC signal, it is possible to ensure an opening adjustment margin for the turbine bypass valve, regardless of the positive or negative sign of the AFC signal.

[0089] (13) In another embodiment, in the above embodiment (12), After the boiler is controlled by the boiler input command value so that the load of the boiler increases above the load command value, the turbine bypass valve is controlled based on the opening command value.

[0090] According to the above aspect (13), the load of the boiler increases beyond the load command value, and then the turbine bypass valve opening adjustment margin is secured, and then the turbine bypass valve opening control is performed. As a result, when the turbine bypass valve opening control is performed based on the AFC signal, the opening adjustment can be performed in response to the AFC signal regardless of whether the AFC signal is positive or negative, and good tracking ability to the AFC signal can be obtained. [Explanation of symbols]

[0091] 1. Thermal power plants 2. Boiler 4. Steam turbine 4A High pressure turbine 4B Low pressure turbine 6 Main Steam Line 8 Main Steam Valve 10 Steam Line 12 Condenser 14 Bypass Line (First Bypass Line) 15 Second Bypass Line 16 Turbine bypass valve (first turbine bypass valve) 17 Second turbine bypass valve 100 Control device 110 Turbine bypass valve opening command value generation unit 112 First opening command value calculation unit 120 Second opening command value calculation unit 130 Third opening command value calculation unit 132 Base opening calculation unit 134 Bias opening calculation unit 140 Turbine bypass valve control section 142 Boiler input command value generation unit 144 Hold Circuit 160 Boiler control unit 162 Main steam valve opening command value generation unit 174 Main steam valve control section 200 Bias opening correction unit 206 Correction section

Claims

1. A control device for a thermal power plant including a boiler, a steam turbine driven by steam from the boiler, and a turbine bypass valve for adjusting an amount of steam bypassing the steam turbine, a turbine bypass valve position command value generating unit for generating a turbine bypass valve position command value of the turbine bypass valve based on an AFC signal in an AFC compatible mode of the thermal power plant; a turbine bypass valve control unit for controlling the turbine bypass valve based on the turbine bypass valve opening command value; a boiler input command value generating unit for generating a boiler input command value by adding a positive bias value to a base input value based on a load command value for the thermal power plant without adding the AFC signal in the AFC compatible mode; a boiler control unit for controlling the boiler based on the boiler input command value; A control device comprising:

2. 2. The control device according to claim 1, wherein the bias value is constant regardless of the load command value in a range in which the load command value is equal to or less than a predetermined value.

3. 3. The control device according to claim 2, wherein the bias value is set corresponding to a maximum decrease value of the AFC signal with respect to a reference value.

4. 4. The control device according to claim 1, wherein the turbine bypass valve position command value generation unit is configured to generate the turbine bypass valve position command value by adding a bias opening based on the AFC signal to a base opening of the turbine bypass valve at the time of transition to the AFC compatible mode.

5. The control device according to claim 4 , wherein the base opening degree is an intermediate opening degree between a fully open state and a fully closed state.

6. The thermal power plant further includes a main steam valve for adjusting an amount of main steam supplied from the boiler to the steam turbine, The control device includes: a main steam valve position command value generating unit for generating a main steam valve position command value based on the AFC signal; a main steam valve control unit for controlling the main steam valve based on the main steam valve position command value; The control device according to claim 1 , further comprising:

7. The control device according to claim 4 , further comprising a bias opening correction unit for correcting the bias opening based on a load of the steam turbine.

8. The control device according to claim 7 , wherein the bias opening correction unit corrects the bias opening such that a correction amount increases as the load decreases.

9. The control device according to claim 7 or 8, wherein the bias opening correction unit determines the load based on a pressure difference between a supply steam pressure and an exhaust steam pressure of the steam turbine.

10. The control device according to claim 1 , wherein the turbine bypass valve is provided in a bypass line that communicates between an upstream side and a downstream side of the steam turbine.

11. 10. The control device according to claim 1, wherein the turbine bypass valve is provided in a bypass line that communicates between an upstream side of the steam turbine and a condenser provided downstream of the steam turbine.

12. A method for controlling a thermal power plant including a boiler, a steam turbine driven by steam from the boiler, and a turbine bypass valve for adjusting an amount of steam bypassing the steam turbine, comprising the steps of: generating a boiler input command value by adding a positive bias value to a base input value based on a load command value for the thermal power plant without adding an AFC signal in an AFC-enabled mode of the thermal power plant; controlling the boiler based on the boiler input command value; generating a turbine bypass valve opening command value for the turbine bypass valve based on the AFC signal in the AFC compatible mode; controlling the turbine bypass valve based on the turbine bypass valve opening command value; A control method comprising:

13. 13. The control method according to claim 12, wherein after the boiler is controlled by the boiler input command value so that a load of the boiler increases above the load command value, the turbine bypass valve is controlled based on the turbine bypass valve position command value.

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