Power system

Abstract

To provide a power system in which output of a power generator device is predicted and output power of the power generator device can be suppressed in advance.SOLUTION: A power system S1 includes a power generator device B1, a power load L1, and a target setting unit 11 that sets a system target value. The target setting unit 11 includes a supply prediction unit 111 that predicts a predicted supply value of the power generator device B1 after elapse of a prescribed time, a first processing unit 113 that calculates a required power value which is to be outputted from the power generator device B1 after elapse of the prescribed time, and a second processing unit 114 that calculates a predicted target value which is a system target value at a timing when the prescribed time elapses. The second processing unit 114 includes a determination unit 114a that determines whether the magnitude of power generated by the power generator device B1 is expected to be greater than a magnitude of power to be outputted from the power generator device B1 or not when the prescribed time elapses, and a calculation unit 114b that calculates the predicted target value in such a way that output power from the power generator device B1 when it is determined that the magnitude is expected to be greater is reduced compared to the output power when it is determined that the magnitude is expected not to be greater.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to power systems. [Background technology]

[0002] Power systems that manage a plurality of power generating devices connected to a power grid and control the reception of power from the power grid are becoming widespread. For example, Patent Document 1 discloses an example of a power system including a plurality of power control devices and a processing device. The processing device calculates an induction command value for controlling the power at a connection point with the power grid (connection point power) to a target power. Each power control device controls output power in a distributed manner using the induction command value calculated by the processing device. At this time, each power control device calculates a target value for output power based on an optimization problem using the induction command value. Then, the output power is controlled so that the output power becomes the target value. In this manner, energy management of the power system is performed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-150690 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a conventional power system, when the output power of a power generation device (power control device) is decreasing, the power that can be output from the power generation device may suddenly increase. For example, in a power generation device that generates solar power, the generated power varies with the change in the amount of solar radiation at the installation location of the solar cells, so that as the amount of solar radiation increases, the output power of the power generation device increases. However, in a power system in which reverse power flow is prohibited, if the increase in the output power of the power generation device exceeds the power consumption of the power load, reverse power flow may occur. Therefore, in a conventional power system, the output fluctuation of the power generation device may cause the output power of the power generation device to increase unnecessarily, and the connection point power may exceed the target value.

[0005] The present disclosure has been made in consideration of the above circumstances, and has a purpose to provide a power system that can predict the output of a power generation device and suppress the output power of the power generation device in advance. [Means for solving the problem]

[0006] The power system provided by the present disclosure is a power system that controls connection point power at a connection point with a power grid, and includes a power generation device capable of generating power using renewable energy, a power load to which power is supplied from at least one of the power grid or the power generation device, and a target setting unit that sets a system target value that is a target value of the connection point power, the target setting unit including a supply prediction unit that predicts a supply prediction value of power that can be output from the power generation device at a predetermined time ahead, a demand prediction unit that predicts a demand prediction value of power consumption of the power load at the predetermined time ahead, and a demand prediction unit that predicts the demand prediction value of power that can be output from the power generation device at the predetermined time ahead. The system includes a first processing unit that calculates a required power value to be output, and a second processing unit that calculates a predicted target value, which is a system target value for the specified time ahead, using the supply forecast value, the demand forecast value, and the required power value, and the second processing unit includes a judgment unit that judges whether the amount of generated power of the power generation device after the specified time has elapsed is expected to exceed the amount of power to be output from the power generation device or not, based on the supply forecast value and the required power value obtained at the current time, and a calculation unit that calculates the predicted target value so as to suppress the output power of the power generation device more when the amount of generated power is expected to exceed the amount of power to be output from the power generation device than when the amount of power is not expected to be exceeded.

[0007] In a preferred embodiment of the power system, the connection point power is a positive value when power is being supplied from the power grid, and the calculation unit sets a predetermined reference target value as the predicted target value when the expected value is not exceeded, and calculates a value greater than the reference target value as the predicted target value when the expected value is exceeded.

[0008] In a preferred embodiment of the power system, the first processing unit calculates, as the required power value, a value obtained by subtracting the reference target value from the demand forecast value.

[0009] In a preferred embodiment of the power system, the reference target value is 0, and the judgment unit judges that the supply forecast value predicted by the supply forecasting unit, during the period from before the specified time to the current time, changes from a small state to a large state relative to the required power value multiplied by a first margin coefficient, and when it is determined that the supply forecast value is exceeded, the calculation unit calculates the forecast target value by subtracting the value obtained by multiplying the minimum value of the supply forecast value during the period from before the specified time to the current time by a second margin coefficient from the demand forecast value.

[0010] In a preferred embodiment of the power system, the reference target value is 0, and the judgment unit judges that the supply forecast value predicted by the supply forecasting unit is smaller than the value obtained by multiplying the required power value by a first margin coefficient, and when it is determined that the supply forecast value is exceeded, the calculation unit calculates the forecast target value by subtracting the value obtained by multiplying the supply forecast value by a second margin coefficient from the demand forecast value. Effect of the Invention

[0011] In the power system of the present disclosure, the determination unit determines whether the magnitude of the power generated by the power generation device after a predetermined time has elapsed is expected to exceed the magnitude of the power to be output from the power generation device or not, based on the supply forecast value and required power value obtained at the present time, and the calculation unit calculates a forecast target value so as to suppress the output power of the power generation device more when the magnitude of the power generated by the power generation device is expected to exceed the magnitude of the power to be output from the power generation device after a predetermined time has elapsed than when the magnitude of the power generated by the power generation device is not expected to exceed the magnitude of the power to be output from the power generation device. With this configuration, when the magnitude of the power generated by the power generation device is predicted to exceed the magnitude of the power to be output from the power generation device after a predetermined time has elapsed, the forecast target value (predicted value of the system target value) is adjusted and the output power of the power generation device is suppressed. In other words, according to the power system of the present disclosure, the output of the power generation device is predicted, and the output power of the power generation device can be suppressed in advance when an excess is predicted. [Brief description of the drawings]

[0012] [Figure 1]1 is a block diagram showing a power system according to a first embodiment. [Diagram 2] 4 is a graph showing an example of calculation of a predicted target value of the power system according to the first embodiment. [Diagram 3] 6 is a simulation result showing a change in node power of the power system according to the first embodiment. [Figure 4] FIG. 11 is a block diagram showing a power system according to a second embodiment. [Diagram 5] 13 is a graph showing an example of calculation of a predicted target value of a power system according to the second embodiment. [Figure 6] 13 is a simulation result showing a change in node power of the power system according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the power system of the present disclosure will be described below with reference to the drawings. In the following, identical or similar components are designated by the same reference numerals and duplicated descriptions will be omitted.

[0014] 1 shows a power system S1 according to the first embodiment. As shown in FIG. 1, the power system S1 includes a processing device A1, a plurality of power generation devices B1, a power load L1, and a power line 90.

[0015] The power system S1 is connected to the power system D via a connection point K. The power system S1 can receive power from the power system D via the connection point K. The power system S1 of this embodiment is a self-consumption type system, and reverse flow of outputting power to the power system D is prohibited. In the present disclosure, when power is being output from the power system S1 to the power system D (reverse flow state), the connection point power is assumed to be a negative value. On the other hand, when power is being output from the power system D to the power system S1 (power receiving state), the connection point power is assumed to be a positive value. The connection point power refers to the power at the connection point K between the power system S1 and the power system D.

[0016] In the power system S1, the processing device A1 and the multiple power generation devices B1 cooperate with each other to perform power control so that the connection point power becomes the system target value. The system target value is the target value of the connection point power. In the power control of the power system S1, the processing device A1 calculates an induction command value for controlling the connection point power to the system target value. Each power generation device B1 calculates a target value (individual target value) of the output power based on the induction command value calculated by the processing device A1. Then, each power generation device B1 controls the output power based on the calculated individual target value. In this way, the power system S1 controls the connection point power to the system target value by the multiple power generation devices B1 controlling the output power in a distributed manner. The induction command value is used by each power generation device B1 to calculate the individual target value, and is common to the multiple power generation devices B1.

[0017] The power load L1 is supplied with power from at least one of the power system D and the multiple power generation devices B1, and consumes the supplied power. The power load L1 includes, for example, general loads and important loads. The general loads include, for example, electrical equipment that is relatively less affected even if the power is cut off during a disaster. The important loads are important loads that require a continuous supply of power even during a disaster, and include, for example, emergency elevators, electrical equipment that requires continuous operation, and building lighting and air conditioning equipment. Note that the power load L1 may be either a general load or an important load. In this embodiment, the power system S1 includes one power load L1, but may also include multiple power loads L1.

[0018] The power lines 90 appropriately connect the power system D, the power load L1, and the multiple power generation devices B1. The power lines 90 construct a power network in the power system S1. In the example shown in Fig. 1, the power lines 90 include one that connects the power system D and a connection point K, one that connects the connection point K and the power load L1, and one that connects the connection point K and each power generation device B1.

[0019] Each of the multiple power generation devices B1 is connected to a connection point K. Each of the multiple power generation devices B1 is capable of generating power using renewable energy. In this embodiment, each of the multiple power generation devices B1 is capable of solar power generation using solar energy as renewable energy. Unlike this example, each of the power generation devices B1 may be capable of other power generation, such as wind power generation using wind energy and hydroelectric power generation using hydroelectric energy, instead of solar power generation. Each of the multiple power generation devices B1 controls the output power of its own device using an induction command value calculated by the processing device A1.

[0020] In this embodiment, since each power generation device B1 generates solar power, each of the multiple power generation devices B1 includes a solar cell 21. The solar cell 21 converts solar energy into electrical energy. In the illustrated example, each power generation device B1 includes one solar cell 21, but may include multiple solar cells 21. Furthermore, each of the multiple power generation devices B1 includes a power conversion unit 22 and a control unit 23 in addition to the solar cell 21. The power conversion unit 22 and the control unit 23 are, for example, a power conditioner (PCS: Power Conditioning System).

[0021] The power conversion unit 22 is connected between the solar cell 21 and the connection point K. The power conversion unit 22 converts the power generated by the solar cell 21 into power suitable for the power system D. The power generated by the solar cell 21 is DC power, and the power conversion unit 22 converts the DC power into AC power. The power conversion unit 22 is, for example, an inverter.

[0022] The control unit 23 controls the power conversion unit 22. The control unit 23 receives a guiding command value from the processing device A1. The control unit 23 calculates an individual target value based on an optimization problem using the received guiding command value. The guiding command value is a value for calculating the individual target value. This optimization problem includes an evaluation function and constraint conditions. The evaluation function is the same as that described in Patent Document 1, for example. For example, the control unit 23 performs the calculations of the following equations (1) and (2) derived from the evaluation function, as described in Patent Document 1. In the following equations (1) and (2), P ref is the individual target value of the power generating unit B1, pr is the induction command value, pr lmt is the induction command limit, and a1 to a4 are design parameters. lmt and design parameters a1 to a4 are the same as those described in Patent Document 1. As described in Patent Document 1, the calculation results are corrected by constraint conditions to calculate individual target values. However, in the power system S1, the connection point power is set to a negative value during reverse power flow, so the individual target value P ref is reversed between positive and negative. The constraint conditions are similar to the constraint conditions described in Patent Document 1 (constraint conditions set in the solar PCS). Alternatively, the control unit 23 may calculate the individual target value by solving the evaluation function under the constraint conditions. Then, the control unit 23 controls the power conversion unit 22 so that the magnitude of the output power of the power conversion unit 22 becomes the calculated individual target value.

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[0023] The processing device A1 can communicate with each of the power generating devices B1. The processing device A1 monitors the connection point power and calculates an induction command value for controlling the connection point power to a system target value. In this embodiment, the connection point power is controlled so that reverse power flow does not occur. The system target value is appropriately changed according to a predicted value of the power that can be output from the solar cell 21 of each power generating device B1. The system target value is usually (when the expected power is not exceeded as described later) a reference target value set in advance. In this embodiment, the reference target value is a value for avoiding the occurrence of reverse power flow and maximizing the use of the power generated by the solar cell, and is 0 kW. The connection point power uses a detection value of a detection unit 12 described later, but may be the following estimated value. It may be an estimated value calculated by having the processing device A1 acquire the value of each output power from each power generating device B1 and the value of power consumption from the power load L1, and using the acquired value of each output power and the acquired value of power consumption. The processing device A1 includes a target setting unit 11, a detection unit 12, and a command value calculation unit 13.

[0024] The target setting unit 11 sets a system target value at the present time. In this embodiment, the target setting unit 11 calculates a predicted value (predicted target value) of a system target value at a predetermined time ahead, and stores the predicted target value from the present time to the predetermined time ahead. Then, the target setting unit 11 sets the predicted target value calculated (stored) at a predetermined time before the present time as the system target value among the stored predicted target values. The target setting unit 11 includes a supply prediction unit 111, a demand prediction unit 112, a first processing unit 113, a second processing unit 114, a storage unit 115, and a reading unit 116. The supply prediction unit 111, the demand prediction unit 112, the first processing unit 113, the second processing unit 114, the storage unit 115, and the reading unit 116 can be configured by at least one CPU (Central Processing Unit) and at least one memory connected by bus communication (CAN: Controller Area Network), for example. It should be noted that the supply prediction unit 111, the demand prediction unit 112, the first processing unit 113, the second processing unit 114, the storage unit 115, and the reading unit 116 are not limited to those configured by a CPU and a memory.

[0025] The supply prediction unit 111 predicts the supply prediction value of the multiple power generation devices B1. The supply prediction value is the total value of the power that can be output by the multiple power generation devices B1 at a predetermined time ahead. In other words, the supply prediction unit 111 predicts the total value of the power that can be output from each power generation device B1 at a predetermined time ahead (the supply prediction value of the multiple power generation devices B1). The supply prediction unit 111 can communicate with, for example, a prediction system that predicts the amount of solar radiation at the installation location of each solar cell 21. The supply prediction unit 111 receives a solar radiation prediction at the installation location of each solar cell 21 from the prediction system, and estimates a predicted value of the amount of power generation of each solar cell 21 from the received solar radiation prediction. Then, the supply prediction value of the multiple power generation devices B1 is predicted by adding up the predicted values ​​of the amount of power generation of each solar cell 21. Note that the supply prediction unit 111 may not be configured to estimate the supply prediction value, but may be configured to acquire it from another system. In a configuration in which each power generation device B1 generates power from wind power, the supply prediction unit 111 predicts the amount of power generated by the wind turbine according to the wind power prediction at the installation site of the wind turbine. The supply prediction unit 111 stores the predicted supply prediction value in the storage unit 115.

[0026] The demand forecasting unit 112 forecasts a demand forecast value of the power load L1. The demand forecast value is a value of power (demand power) consumed by the power load L1 at a predetermined time ahead. In other words, the demand forecasting unit 112 forecasts a value of power consumption of the power load L1 (demand forecast value of the power load L1) at a predetermined time ahead. In addition, when the power system S1 includes a plurality of power loads L1, the demand forecast value is a total value of power consumed by each power load L1 at a predetermined time ahead. The demand forecasting unit 112 can communicate with, for example, a monitoring system that monitors the power load L1. The demand forecasting unit 112 receives a demand forecast of the power load L1 from the monitoring system. As a result, the demand forecasting unit 112 forecasts a demand forecast value of the power load L1. The demand forecasting unit 112 stores the forecasted demand forecast value in the storage unit 115.

[0027] The first processing unit 113 calculates the required power value by using the demand forecast value. The required power value is the total value of power to be output by the multiple power generation devices B1 at a predetermined time ahead. In other words, the first processing unit 113 uses the demand forecast value to calculate the total value (required power value) of power to be output from the multiple power generation devices B1 at a predetermined time ahead. The first processing unit 113 calculates the required power value by subtracting the standard target value from the demand forecast value. Therefore, the required power value is the difference between the demand forecast value and the standard target value. The first processing unit 113 stores the calculated required power value in the memory unit 115.

[0028] The second processing unit 114 calculates a predicted target value using the supply forecast value, the demand forecast value, and the required power value. The predicted target value is a target value (system target value) of the connection point power at a predetermined time ahead. In other words, the second processing unit 114 calculates a system target value (predicted target value) at a predetermined time ahead using the supply forecast value, the demand forecast value, and the required power value. The second processing unit 114 stores the calculated predicted target value in the storage unit 115. The second processing unit 114 includes a determination unit 114a and a calculation unit 114b.

[0029] The determination unit 114a determines whether the magnitude (total value) of the power generation of the multiple power generating devices B1 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed, or whether it is expected to not exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1. In a state in which the total value of the magnitude of the power generation of the multiple power generating devices B1 exceeds the total value of the power to be output from the multiple power generating devices B1, there is a high possibility that a reverse power flow will occur. In this embodiment, the determination unit 114a determines that the supply forecast value acquired by the supply forecasting unit 111 is expected to exceed the magnitude (total value) of the following comparison value during the period from a predetermined time ago to the present time. On the other hand, the determination unit 114a determines that the supply forecast value acquired by the supply forecasting unit 111 is expected to not exceed the magnitude (total value) of the following comparison value during the period from a predetermined time ago to the present time. The above comparison value is the required power value multiplied by the first margin coefficient, i.e. (demand forecast value-reference target value) x first margin coefficient. The first margin coefficient is a parameter that adjusts the rate at which it is judged to be an overrun, and is based on 1. The larger the first margin coefficient, the smaller the rate at which it is judged to be an overrun, and vice versa. Therefore, to increase the rate at which it is judged to be an overrun, it is sufficient to make the first margin coefficient smaller than 1.

[0030] The calculation unit 114b calculates a predicted target value based on the judgment result (expected to exceed or not expected to exceed) of the judgment unit 114a. When the judgment unit 114a judges that the expected power is not exceeded, the calculation unit 114b sets the above-mentioned reference target value as the predicted target value. When the judgment unit 114a judges that the expected power is exceeded, the calculation unit 114b calculates a value larger than the reference target value as the predicted target value so as to suppress the power value output from the multiple power generation devices B1 more than when the expected power is not exceeded. In the power system S1 in which the reference target value is 0 kW, when the judgment unit 114a judges that the expected power is exceeded, the calculation unit 114b calculates a predicted target value by subtracting the following value from the demand forecast value. The value is a value obtained by multiplying the minimum value of the supply forecast value during the period from a predetermined time ago to the present time by a second margin coefficient. If the predicted target value calculated when the expected power is exceeded is smaller than the reference target value, the calculation unit 114b corrects the predicted target value to a value equal to or larger than the reference target value (for example, sets the predicted target value to the reference target value). The second margin coefficient is a parameter that adjusts the degree to which the occurrence of reverse power flow is suppressed, and the smaller the second margin coefficient, the more reliably the occurrence of reverse power flow can be suppressed. The second margin coefficient is set to a value, for example, between 0 and 1. In this embodiment, the calculation unit 114b processes the following at the timing when the determination unit 114a changes from a not-exceeded expectation to an excess expectation. That is, the calculation unit 114b replaces the predicted target value calculated from a predetermined time before to the present time stored in the storage unit 115 with the predicted target value calculated at the timing when the not-exceeded expectation changed to an excess expectation. Note that the calculation method of the predicted target value when the expectation is exceeded is not limited to the above example.

[0031] The storage unit 115 stores the supply forecast value predicted by the supply forecast unit 111, the demand forecast value predicted by the demand forecast unit 112, the required power value calculated by the first processing unit 113, and the predicted target value calculated by the second processing unit 114 (calculation unit 114b). The supply forecast value, the demand forecast value, the required power value, and the predicted target value are values ​​predicted or calculated at least from a predetermined time ago to the present time, and are stored. Note that the predicted target value calculated at the present time is the system target value for a predetermined time ahead, as described above, and therefore the predicted target value stored in the storage unit 115 corresponds to the system target value from the present time to the predetermined time ahead.

[0032] The reading unit 116 reads out the predicted target value stored in the storage unit 115, which is a predicted target value stored a predetermined time ago, as a system target value. In this way, the target setting unit 11 sets the system target value. In this embodiment, since the predicted target value calculated at the present time is the system target value of the connection point power at a predetermined time ahead, the predicted target value calculated at the predetermined time ago corresponds to the system target value of the connection point power at the present time.

[0033] The detection unit 12 detects the connection point power. The detection unit 12 detects the power (connection point power) between the connection point K and the power system D. The detection unit 12 outputs the detection value of the connection point power to the command value calculation unit 13.

[0034] The command value calculation unit 13 calculates an induction command value using the system target value set by the target setting unit 11 and the connection point power detected by the detection unit 12. The calculation method of the induction command value is the same as that of the power system described in Patent Document 1. For example, the command value calculation unit 13 calculates an induction command value by solving state equations (simultaneous differential equations) shown in the following formulas (3) and (4). In the following formulas (3) and (4), P(t) is the connection point power, Pc(t) is the system target value, λ(t) is a state variable, pr(t) is the induction command value, and ε is a gradient coefficient. However, in the power system S1, since the connection point power is set to a negative value during reverse power flow, the connection point power P(t) and the system target value Pc(t) are reversed between positive and negative. This state equation is set in the command value calculation unit 13. The command value calculation unit 13 calculates the induction command value every predetermined time (for example, every 1 [sec]). The induction command value calculated by the command value calculation unit 13 is transmitted to each power generation device B1. Note that the command value calculation unit 13 may use a differential equation obtained by discretizing the state equations shown in the following formula (3) and the above formula (4) instead of the state equations. The differential equation is the same as that of the power system described in Patent Document 1.

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[0035] Next, a calculation example of the predicted target value performed by the target setting unit 11 will be described with reference to FIG. 2. FIG. 2 is a graph showing the calculation example, in which FIG. 2(a) shows the situation at time t1, FIG. 2(b) shows the situation at time t2 which is earlier than time t1, and FIG. 2(c) shows the situation at time t3 which is earlier than time t2. In FIG. 2(a) to (c), the horizontal axis shows time, and the vertical axis shows the magnitude of power. In addition, in FIG. 2(a) to (c), the predetermined time is set to 60 seconds. In this calculation example, the power generated by the solar cell 21 is assumed to change as shown by the two-dot chain line La1 due to changes in the amount of solar radiation. Therefore, the supply prediction value for a predetermined time ahead (60 seconds ahead) predicted by the supply prediction unit 111 changes as shown by the one-dot chain line La2. In addition, the required power value (demand prediction value-reference target value) calculated by the first processing unit 113 is assumed to change as shown by the one-dot chain line La3 (constant in the illustrated example). In the example shown in Fig. 2, the first margin coefficient is 1, and the second margin coefficient is 0.9. Therefore, the comparison value (required power value x first margin coefficient) coincides with the dashed dotted line La3. Also, the reference target value is set to 0 [kW].

[0036] At time t1 shown in FIG. 2(a), the supply prediction unit 111 predicts a supply prediction value Pt1. The supply prediction unit 111 stores the predicted supply prediction value in the storage unit 115 for a predetermined time (60 seconds), so that the supply prediction value shown by the solid line Lb2 from time t1-60 seconds to time t1 is stored in the storage unit 115. The first processing unit 113 also stores the calculated required power value in the storage unit 115 for a predetermined time (60 seconds), so that the required power value shown by the solid line Lb3 from time t1-60 seconds to time t1 is stored in the storage unit 115. At this time, as shown in FIG. 2(a), in the period from time t1-60 seconds to time t1, the supply prediction value shown by the solid line Lb2 is always smaller than the above-mentioned comparison value (required power value×first margin coefficient) corresponding to the solid line Lb3. Therefore, the judgment unit 114a of the second processing unit 114 judges that the supply prediction value is not expected to be exceeded. As a result, the calculation unit 114b of the second processing unit 114 calculates the reference target value (0 kW) as a predicted target value Pt3 for the predetermined time (60 seconds) ahead. Note that, since the target value is not expected to be exceeded before time t1, the memory unit 115 stores the predicted target value indicated by the solid line Lb4 from time t1 to time t1+60 seconds.

[0037] Next, at time t2 shown in FIG. 2(b), which is later than time t1, the supply prediction unit 111 predicts a supply prediction value Pt1. At time t2, the storage unit 115 stores the supply prediction value shown by the solid line Lb2 and the required power value shown by the solid line Lb3. At this time, in the period from time t2-60 seconds to time t2, the supply prediction value shown by the solid line Lb2 changes from a small state to a large state with respect to the above-mentioned comparison value (required power value x first margin coefficient) corresponding to the solid line Lb3, so the determination unit 114a of the second processing unit 114 determines that the supply prediction value is expected to be exceeded. As a result, the calculation unit 114b of the second processing unit 114 calculates a prediction target value Pt3 by subtracting a value obtained by multiplying the minimum value Pt2 of the supply prediction value during the period from time t2-60 seconds to time t2 by the second margin coefficient from the demand prediction value. It should be noted that ΔPx indicates the amount of change when the minimum value Pt2 is adjusted by the second margin coefficient.

[0038] Also, at time ts shown in FIG. 2B between time t1 and time t2, the judgment result of the judgment unit 114a changes from a non-exceeded expectation to an excess expectation. The timing of the change from a non-exceeded expectation to an excess expectation is shown in FIG. 2B at the intersection of the supply forecast value shown by the solid line Lb2 and the above-mentioned comparison value corresponding to the solid line Lb3. At this time, the calculation unit 114b calculates the predicted target value Pt3'. Then, as described above, the calculation unit 114b replaces the predicted target value for the period from time ts to time ts+60 seconds with the predicted target value Pt3' at the timing of the change from a non-exceeded expectation to an excess expectation. As a result, the predicted target value for the period from time ts to time ts+60 seconds stored in the storage unit 115 is replaced with the predicted target value Pt3' instead of the predicted target value calculated before time ts (see the two-dot chain line Lc4).

[0039] Next, at time t3 shown in FIG. 2(c), which is later than time t2, the supply prediction unit 111 predicts a supply prediction value Pt1. At time t3, the storage unit 115 stores the supply prediction value shown by the solid line Lb2 and the required power value shown by the solid line Lb3. At this time, in the period from time t3-60 seconds to time t3, the supply prediction value shown by the solid line Lb2 is always greater than the above-mentioned comparison value (required power value x first margin coefficient) corresponding to the solid line Lb3. Therefore, the judgment unit 114a of the second processing unit 114 judges that the supply is not expected to be exceeded. As a result, the calculation unit 114b of the second processing unit 114 calculates the reference target value (0 kW) as the predicted target value Pt3 for a predetermined time (60 seconds) ahead.

[0040] 2(c), the judgment result of the judgment unit 114a changes from an expected exceedance to an expected not exceedance. At this time, the calculation unit 114b calculates a predicted target value Pt3'. This predicted target value Pt3' is the value when it is expected not to be exceeded, and is therefore the same as the reference target value (0 kW).

[0041] As described above, it can be seen from FIGS. 2(a) to (c) that in the processing device A1 of the power system S1, the system target value is changed in response to a change in the solar radiation prediction (supply prediction value).

[0042] FIG. 3 shows a simulation result of power control in the power system S1. FIG. 3(a) shows a change in the connection point power in the power system S1, FIG. 3(b) shows a change in the connection point power in the first comparative power system, and FIG. 3(c) shows a change in the connection point power in the second comparative power system. The first comparative power system is configured not to consider the solar radiation forecast (supply forecast value), and the system target value is fixed at a reference target value (0 kW). The second comparative power system is configured not to consider the solar radiation forecast (supply forecast value), and the system target value is fixed at a value larger than the reference target value (an offset is added to the system target value). In the simulation, the demand power of the power load L1 is 200 kW, the first margin coefficient is 1, and the second margin coefficient is 0.8. In each of FIG. 3(a) to (c), the solid line indicates the connection point power P(t), the dashed line indicates the system target value Pc(t), and the dashed line indicates the solar radiation amount SR.

[0043] As shown in FIG. 3(b), in the first power system to be compared, even if the amount of solar radiation changes, the system target value is fixed at 0 kW, which is the reference target value. As a result, for example, at the timing when the amount of solar radiation increases suddenly, the connection point power may become a negative value (reverse power flow may occur). In the first power system to be compared, in the power control, when the amount of solar radiation is low, the output power of each power generation device may not be the individual target value, and the connection point power may not match the system target value. In this case, in the first power system to be compared, an induced command value that increases the output power of each power generation device is continuously calculated, and the induced command value becomes saturated. In such a state, if the amount of solar radiation increases suddenly, the output power of each power generation device also increases suddenly, and a reverse power flow occurs. In contrast, in the power system S1, as shown in FIG. 3(a), the system target value is appropriately changed according to the amount of solar radiation. As a result, at the timing when the amount of solar radiation increases suddenly, the system target value is corrected upward, so that the induced command value does not become saturated, and the connection point power is controlled at a value of 0 kW or more. That is, in power system S1, the occurrence of reverse power flow is suppressed even in an environment where the amount of solar radiation changes.

[0044] Also, as shown in FIG. 3(c), in the second comparative power system, an offset is added to the system target value, so that the connection point power is controlled at a value of 0 kW or more. Therefore, as shown in FIG. 3(c), the occurrence of reverse power flow is also suppressed in the second comparative power system. However, as can be understood from a comparison between FIG. 3(a) and FIG. 3(c), in the second comparative power system, the value of the connection point power is relatively large compared to the power system S1. This is because, in the second comparative power system, an offset is added to the system target value, so that the power generated by each power generating device is suppressed even when the power generated by each power generating device can be utilized. In other words, in the second comparative power system, the power generated by each power generating device is unnecessarily suppressed. Therefore, it can be seen that the power system S1 can effectively utilize the power generated by each power generating device B1 while suppressing the occurrence of reverse power flow. For example, in the simulation performed by the inventor of the present application, the power system S1 utilized the power generated by each power generating device B1 by approximately 1.59 times as much as the power system S1 utilized the power generated by each power generating device B1 in the second comparative power system.

[0045] The functions and effects of the power system S1 according to the first embodiment are as follows.

[0046] In the power system S1, the second processing unit 114 calculates a predicted target value using a supply forecast value, a demand forecast value, and a required power value. Specifically, the second processing unit 114 includes a determination unit 114a and a calculation unit 114b. The determination unit 114a determines whether the magnitude (total value) of the power generated by the multiple power generating devices B1 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed based on the supply forecast value and the required power value obtained at the present time, and the calculation unit 114b calculates a predicted target value so as to suppress the output power of each power generating device B1 when the magnitude (total value) of the power generated by the multiple power generating devices B1 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed .... According to this configuration, when it is predicted that the magnitude (total value) of the power generated by the multiple power generating devices B1 will exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed, the predicted target value (predicted value of the system target value) is adjusted, and the output power of each power generating device B1 is suppressed. Therefore, the power system S1 can perform power control so that the total value of the output power of the power generating devices B1 does not exceed the power consumption of the power load L1 by adjusting the predicted target value (predicted value of the system target value) using the supply prediction value (predicted value of the power that can be output) of each power generating device B1. That is, the power system S1 can predict the output of each power generating device B1 and suppress the output power of each power generating device B1 in advance when the output power is expected to exceed the power consumption of the power load L1. For example, the power system S1 is a system in which reverse power flow is prohibited, and when the total value of the output power of the power generating devices B1 exceeds the power consumption of the power load L1, reverse power flow occurs. Therefore, when reverse power flow is predicted to occur (when it is determined that the output power is expected to exceed the power consumption), the power system S1 suppresses the output power of each power generating device B1 by adjusting the predicted target value (predicted value of the system target value). As a result, the power system S1 suppresses the occurrence of reverse power flow by preventing the total value of the output power of the power generating devices B1 from exceeding the power consumption of the power load L1. That is, the power system S1 can suppress the occurrence of reverse power flow by adjusting the system target value for a predetermined time ahead according to the predicted value (supply predicted value) of the power that can be output from the multiple power generation units B1.

[0047] In the power system S1, the calculation unit 114b sets the predicted target value when the expected power is not exceeded to a reference target value (e.g., 0 kW), and calculates a value larger than the reference target value (e.g., 0 kW) as the predicted target value when the expected power is exceeded. In a configuration in which the connection point power is a positive value when power is supplied from the power grid D to the power system S1 (when receiving power), if the power consumption of the power load L1 is fixed, the output power of each power generating device B1 is suppressed as the system target value increases. Therefore, when the expected power is exceeded, the predicted target value is larger than the reference target value, so that the output power of each power generating device B1 is suppressed compared to when the expected power is not exceeded. In other words, the power system S1 can suppress the output power of each power generating device B1 when the expected power is exceeded more than when the expected power is not exceeded.

[0048] The power system S1 is a system in which reverse power flow is prohibited. In this configuration, if the connection point power is assumed to be a positive value when power is supplied from the power grid D to the power system S1 (when receiving power), the power system S1 performs power control so that the connection point power does not become a negative value (so as to maintain 0 or a positive value). In this power control, the calculation unit 114b sets the predicted target value when no excess is expected to be a reference target value of 0 kW, and calculates a value larger than the reference target value (0 kW) as the predicted target value when an excess is expected to be exceeded. As a result, when a reverse power flow is predicted to occur (when an excess is expected), the predicted target value (i.e., the system target value) becomes larger than the reference target value, so that the output power of each power generating device B1 is suppressed so that the connection point power does not become a negative value, and the occurrence of a reverse power flow is suppressed. On the other hand, when a reverse power flow is predicted not to occur (when no excess is expected), the predicted target value becomes the reference target value of 0 kW, so that the generated power of each power generating device B1 can be effectively utilized, as can be understood from the comparison result with the second power system to be compared described above. In other words, the power system S1 can effectively utilize the power generated by each power generation device B1 while suppressing the occurrence of reverse power flow.

[0049] In the power system S1, the reference target value is 0 kW, and the determination unit 114a determines that the supply forecast value acquired by the supply forecasting unit 111 is an excess expected value when the supply forecast value acquired by the supply forecasting unit 111 during the period from a predetermined time ago to the present time changes from a smaller state to a larger state relative to the value obtained by multiplying the required power value (demand power value-reference target value) by a first margin coefficient. When it is determined that the supply forecast value is an excess expected value, the calculation unit 114b calculates the forecast target value by subtracting the value obtained by multiplying the minimum value of the supply forecast value during the period from a predetermined time ago to the present time by a second margin coefficient from the demand forecast value. With this configuration, when it is determined that the supply forecast value is an excess expected value, the forecast target value can be made larger than the reference target value, so that the output power of each power generating unit B1 can be suppressed.

[0050] FIG. 4 shows a power system S2 according to the second embodiment. The power system S2 is different from the power system S1 in the following respects. The processing device A1 of the power system S2 includes a second processing device 117 instead of the second processing device 114. Note that FIG. 4 shows only the processing device A1 of the power system S2. The configuration other than the processing device A1 is the same as that of the power system S1.

[0051] The second processing unit 117 calculates a system target value (predicted target value) of the connection point power at a predetermined time ahead by using the supply forecast value, the demand forecast value, and the required power value, similarly to the second processing unit 114. The second processing unit 117 includes a determination unit 117a and a calculation unit 117b.

[0052] The determination unit 117a, like the determination unit 114a, determines whether the magnitude (total value) of the power generation of the multiple power generating devices B1 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed based on the supply prediction value and the required power value obtained at the present time, or is expected to not exceed the magnitude (total value). However, the determination criterion is different from that of the determination unit 114a. Specifically, the determination unit 117a determines that the supply prediction value predicted by the supply prediction unit 111 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 when the supply prediction value is smaller than the comparison value (required power value x first margin coefficient). For example, if the supply prediction value is smaller than the comparison value (required power value x first margin coefficient), there is a risk that the magnitude (total value) of the power generation of the multiple power generating devices B1 will exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 if the current situation remains the same when the amount of solar radiation on the power generating device B1 increases in the future. In other words, as the amount of solar radiation on the power generation device B1 increases, there is a possibility that the power generation device B1 will output more power than necessary, so it can be determined that the power generation amount is overestimated. On the other hand, when the supply forecast value predicted by the supply forecasting unit 111 is equal to or greater than the comparison value, the determination unit 114a determines that the power generation amount is not overestimated.

[0053] The calculation unit 117b calculates a predicted target value based on the judgment result (expected to be exceeded or not expected to be exceeded) of the judgment unit 117a. When the judgment unit 117a judges that the demand is not expected to be exceeded, the calculation unit 117b sets the set reference target value as the predicted target value, and when the judgment unit 117a judges that the demand is expected to be exceeded, the calculation unit 117b calculates a value larger than the reference target value as the predicted target value. In the power system S2 in which the reference target value is 0 kW, when the judgment unit 117a judges that the demand is expected to be exceeded, the calculation unit 117b calculates a predicted target value by subtracting the following value from the demand forecast value. The value is a value obtained by multiplying the supply forecast value by the second margin coefficient (supply forecast value x second margin coefficient). Thus, the calculation unit 117b has a different calculation method for the predicted target value in the case of expected to be exceeded, compared to the calculation unit 114b. If the predicted target value calculated at the time of expected excess is smaller than the reference target value, the calculation unit 117b corrects the predicted target value to a value equal to or greater than the reference target value (for example, sets it to the reference target value), similar to the calculation unit 114b.

[0054] Next, a calculation example of the predicted target value performed by the target setting unit 11 in the power system S2 will be described with reference to FIG. 5. FIG. 5 is a graph showing the calculation example, in which FIG. 5(a) shows the situation at time t1, and FIG. 5(b) shows the situation at time t2, which is earlier than time t1. In FIGS. 5(a) and (b), the horizontal axis shows time, and the vertical axis shows the magnitude of power. In addition, in FIGS. 5(a) and (b), the above-mentioned predetermined time is set to 60 seconds. In this calculation example, the power generated by the solar cell 21 is assumed to change as shown by the two-dot chain line La1 due to changes in the amount of solar radiation. Therefore, the supply prediction value for a predetermined time ahead (60 seconds ahead) predicted by the supply prediction unit 111 changes as shown by the one-dot chain line La2. In addition, the required power value (demand prediction value-reference target value) calculated by the first processing unit 113 is assumed to change as shown by the one-dot chain line La3 (constant in the illustrated example). In the example shown in Fig. 5, the first margin coefficient is 1, and the second margin coefficient is 0.9. Therefore, the comparison value (required power value x first margin coefficient) coincides with the dashed dotted line La3. Also, the reference target value is set to 0 [kW].

[0055] At time t1 shown in FIG. 5(a), the supply prediction unit 111 predicts a supply prediction value Pt1. At this time, as shown in FIG. 5(a), the supply prediction value Pt1 is smaller than the above-mentioned comparison value (required power value×first margin coefficient) corresponding to the required power value Pt4. Therefore, the judgment unit 117a of the second processing unit 117 judges that the demand is expected to be exceeded. As a result, the calculation unit 117b of the second processing unit 117 calculates a predicted target value Pt3 by subtracting a value obtained by multiplying the supply prediction value Pt1 by the second margin coefficient from the demand prediction value. Note that ΔPx indicates the amount of change when the supply prediction value Pt1 is adjusted by the second margin coefficient.

[0056] Next, at time t2 shown in FIG. 5(b), which is later than time t1, the supply prediction unit 111 predicts a supply prediction value Pt1. At this time, as shown in FIG. 5(b), the supply prediction value Pt1 is equal to or greater than the above comparison value (required power value×first margin coefficient) corresponding to the required power value Pt4. Therefore, the judgment unit 117a of the second processing unit 117 judges that the required power value is not expected to be exceeded. As a result, the calculation unit 117b of the second processing unit 117 calculates the reference target value (0 kW) as a predicted target value Pt3 for a predetermined time (60 seconds) ahead.

[0057] 5B, between time t1 and time t2, the judgment result of the judgment unit 117a changes from expected to be exceeded to expected not to be exceeded. At this time, the calculation unit 117b calculates the predicted target value Pt3'. This predicted target value Pt3' is the value when expected not to be exceeded, and is therefore the same value as the reference target value (0 kW).

[0058] As described above, it can be seen from FIGS. 5(a) and (b) that in the processing device A1 of the power system S2, similarly to the power system S1, the system target value is changed in response to changes in the solar radiation forecast (supply forecast value).

[0059] FIG. 6 shows the results of a simulation showing power control in power system S2. The simulation in FIG. 6 was performed under the same conditions as the simulation in FIG. 3. FIG. 6(a) shows the change in node power in power system S2. For ease of understanding, FIGS. 6(b) and 6(c) respectively show the results of a simulation in the first comparative power system shown in FIG. 3(b) and the results of a simulation in the second comparative power system shown in FIG. 3(c). In each of FIGS. 6(a) to 6(c), the solid line shows the node power P(t), the dashed line shows the system target value Pc(t), and the dashed-dotted line shows the solar radiation SR.

[0060] As shown in FIG. 6(a), in the power system S2, the system target value changes according to the amount of solar radiation, similar to the power system S1. As a result, when the amount of solar radiation rises sharply, the system target value is revised upward, and the induction command value does not become saturated, so that the connection point power is controlled at a value of 0 kW or more. That is, in the power system S2, similar to the power system S1, the occurrence of reverse power flow is suppressed even in an environment where the amount of solar radiation changes. Also, as can be understood from a comparison between FIG. 6(a) and FIG. 6(c), in the power system S2, similar to the power system S1, it can be seen that the power generated by each power generating device B1 can be utilized more effectively than the second comparative power system. For example, in the simulation performed by the inventor of the present application, the power system S2 utilized the power generated by each power generating device B1 by approximately 1.59 times as much as the second comparative power system.

[0061] The functions and effects of the power system S2 according to the second embodiment are as follows.

[0062] In the power system S2, the second processing unit 117 includes a judgment unit 117a and a calculation unit 117b. The judgment unit 117a judges whether the magnitude (total value) of the power generated by the multiple power generating devices B1 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed based on the supply prediction value and the required power value obtained at the present time, and the calculation unit 117b calculates a prediction target value so as to suppress the output power of each power generating device B1 when the magnitude (total value) of the power generated by the multiple power generating devices B1 is expected to exceed the magnitude (total value) of the power to be output from the multiple power generating devices B1 after a predetermined time has elapsed, more than when the magnitude (total value) of the power generated by the multiple power generating devices B1 is expected to not exceed the magnitude (total value). Therefore, like the power system S1, the power system S2 predicts the output of each power generating device B1 and can suppress the output power of each power generating device B1 in advance when the magnitude is expected to exceed the magnitude (total value) of the power generated by the multiple power generating devices B1. Also, like the power system S1, the power system S2 is a system in which reverse power flow is prohibited, and when reverse power flow is predicted to occur (when it is determined that the magnitude is expected to exceed the magnitude), the output power of each power generating device B1 is suppressed by adjusting the prediction target value (prediction value of the system target value) to suppress the occurrence of reverse power flow. That is, like the power system S1, the power system S2 can suppress the occurrence of reverse power flow by adjusting the system target value for a predetermined time ahead according to the predicted value (supply predicted value) of the power that can be output from the multiple power generation devices B1. In addition, the power system S2 has the same configuration as the power system S1 and thus achieves the same effects as the power system S1.

[0063] In power system S2, the reference target value is 0 kW, and the determination unit 117a determines that the supply forecast value acquired by the supply prediction unit 111 is an excess expected value when it is smaller than the value obtained by multiplying the required power value (demand power value-reference target value) by the first margin coefficient. Then, when it is determined that the supply forecast value is an excess expected value, the calculation unit 117b calculates the forecast target value by subtracting the value obtained by multiplying the supply forecast value by the second margin coefficient from the demand forecast value. With this configuration, when it is determined that the supply forecast value is an excess expected value, the forecast target value can be made larger than the reference target value, so that the output power of each power generation unit B1 can be suppressed.

[0064] In each of the power systems S1 and S2 according to the first and second embodiments, an example has been shown in which the processing device A1 calculates an induction command value from a system target value and transmits the induction command value to each power generating device B1. Unlike this example, in the power system of the present disclosure, the processing device A1 may calculate an individual target value for each power generating device B1 from the system target value and transmit the calculated individual target value to the corresponding power generating device B1. However, in a configuration in which the processing device A1 calculates the individual target value for each power generating device B1, the calculation load is concentrated on the processing device A1, so in order to reduce the calculation load of the processing device A1, it is preferable to calculate the induction command value from the system target value.

[0065] In each of the power systems S1 and S2 according to the first and second embodiments, an example is shown in which a plurality of power generation units B1 are provided. Unlike this example, the power system of the present disclosure may be configured to include one power generation unit B1. In this modification, the target setting unit 11 may be provided in the power generation unit B1, and the power generation unit B1 may control the output power so as to achieve a predicted (calculated) system target value.

[0066] In each of the power systems S1 and S2 according to the first and second embodiments, an example has been shown in which reverse power flow is prohibited and power control is performed so that the connection point power does not become smaller than 0 kW (the reference target value is set to 0 kW). Unlike this example, the power system of the present disclosure may be configured to perform power control so that the connection point power does not become smaller than a predetermined value. In this example, the above-mentioned predetermined value is set as the reference target value. Then, in the calculation unit 114b of the power system S1, the predicted target value may be calculated by subtracting the next value from a value obtained by subtracting the reference target value from the demand forecast value (i.e., the required power value). The value is a value obtained by multiplying the value obtained by subtracting the reference target value from the minimum value of the supply forecast value within the period from a predetermined time ago to the present time by the second margin coefficient. Also, in the calculation unit 117b of the power system S2, the predicted target value may be calculated by subtracting the next value from a value obtained by subtracting the reference target value from the demand forecast value (i.e., the required power value). The value is a value obtained by multiplying the value obtained by subtracting the reference target value from the supply forecast value by the second margin coefficient. The method of calculating the predicted target value is not limited to the above example.

[0067] The power system according to the present disclosure is not limited to the above-described embodiment. The specific configuration of each part of the power system according to the present disclosure can be freely designed in various ways. [Explanation of symbols]

[0068] S1, S2: power system, A1: processing device, B1: power generation device, D: power system, K: connection point, L1: power load, 11: target setting unit, 111: supply forecasting unit, 112: demand forecasting unit, 113: first processing unit, 114, 117: second processing unit, 114a, 117a: judgment unit, 114b, 117b: calculation unit, 12: detection unit, 13: command value calculation unit, 21: solar cell, 22: power conversion unit, 23: control unit

Claims

1. A power system that controls a connection point power at a connection point with a power grid, A power generation device capable of generating power using renewable energy; a power load to which power is supplied from at least one of the power grid and the power generation device; a target setting unit that sets a system target value that is a target value of the connection point power, The goal setting unit, a supply prediction unit that predicts a supply prediction value of power that can be output from the power generation device at a predetermined time ahead; a demand prediction unit that predicts a demand prediction value of power consumption of the power load at the predetermined time ahead; a first processing unit that calculates a required power value to be output from the power generation device at the predetermined time ahead using the demand forecast value; a second processing unit that calculates a predicted target value that is a system target value for the predetermined time ahead by using the supply forecast value, the demand forecast value, and the required power value, The second processing unit includes a judgment unit that judges whether the amount of generated power of the power generation device after the specified time has elapsed is expected to exceed the amount of power to be output from the power generation device or not, based on the supply forecast value and the required power value obtained at this time, and a calculation unit that calculates the predicted target value so as to suppress the output power of the power generation device more when the amount of generated power is expected to exceed the amount of power to be output from the power generation device than when the amount of required power is not expected to exceed the amount of power.

2. The node power is a positive value when power is supplied from the power grid; The power system of claim 1 , wherein the calculation unit sets a predetermined standard target value as the predicted target value when the expected condition is not exceeded, and calculates a value greater than the standard target value as the predicted target value when the expected condition is exceeded.

3. The power system according to claim 2 , wherein the first processing unit calculates, as the required power value, a value obtained by subtracting the reference target value from the demand forecast value.

4. The reference target value is 0, the determination unit determines that the supply forecast value predicted by the supply forecast unit during the period from the predetermined time before to the current time has changed from a state smaller than a value obtained by multiplying the required power value by a first margin coefficient to a state larger than the required power value, The power system of claim 2 or claim 3, wherein when it is determined that the demand is exceeded, the calculation unit calculates the forecast target value by subtracting from the demand forecast value a value obtained by multiplying the minimum value of the supply forecast value within the period from the specified time before to the present time by a second margin coefficient.

5. The reference target value is 0, The determination unit determines that the supply forecast value predicted by the supply forecasting unit is an excess expectation when the supply forecast value is smaller than a value obtained by multiplying the required power value by a first margin coefficient, The power system according to claim 2 or claim 3, wherein when it is determined that the demand is expected to be exceeded, the calculation unit calculates the forecast target value by subtracting a value obtained by multiplying the supply forecast value by a second margin coefficient from the demand forecast value.

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