Power stabilization device

Abstract

To provide a power stabilizing device capable of mitigating fluctuations in the synthetic power supplied even when the difference between the power from a fluctuating power source and the composite power becomes large.SOLUTION: The power stabilizing device includes a power storage unit for charging and discharging power, a power conversion unit for mutually converting input / output power generated by charging and discharging at the power storage unit between a power system and a power storage unit, and a control unit for setting at least one of a setting upper limit value and a setting lower limit value of the combined power of the power of a fluctuating power source connected to the power system and the power of the power storage unit to a value in accordance with a power restriction value either between the power storage unit and the power system or at the power storage unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power stabilizing device.

[0002] There is known a power stabilization device that combines a variable power source and a power storage unit to supply a composite power to a power grid, thereby mitigating fluctuations in the power supply (see, for example, Patent Documents 1, 2, and 3). In particular, the technology described in Patent Document 1 reduces the composite power in advance before a time period when power reduction is prohibited. This reduces the amount of power (kWh) that the power storage unit must discharge when the variable power source suddenly drops. [Prior art document] [Patent documents] [Patent Document 1] JP 2018-161041 A [Patent Document 2] JP 2019-115131 A [Patent Document 3] JP 2018-038132 A Summary of the Invention [Problem to be solved by the invention]

[0003] It is desirable to be able to mitigate fluctuations in the supplied combined power even when the difference between the output power of the variable power supplies and the combined power becomes large. [Means for solving the problem]

[0004] In order to solve the above problems, one aspect of the present invention provides a power stabilizing device. The power stabilizing device may include a power storage unit. The power storage unit may perform charging and discharging. The power stabilizing device may include a power conversion unit. The power conversion unit may convert input and output power resulting from charging and discharging in the power storage unit between the power grid and the power storage unit. The power stabilizing device may include a control unit. The control unit may set at least one of a set upper limit value and a set lower limit value of a combined power of the power of a variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value either between the power storage unit and the power grid or in the power storage unit.

[0005] The control unit may set the upper limit value to a value higher than the power limit value.

[0006] The control unit may include a first calculation unit. The first calculation unit may calculate a predicted value of the output power of the variable power source during a period from the current time to the end time of a designated time period for mitigating temporal fluctuations in the combined power. The control unit may include a second calculation unit. The second calculation unit may calculate at least one of a set upper limit value and a set lower limit value based on the predicted value and the power limit value.

[0007] The first calculation unit may calculate a predicted value based on a correlation between at least one of the output power of the variable power source, the outputtable power of the variable power source, and the combined power prior to the current time and the change in the at least one power over a predetermined time period.

[0008] The control unit may at least execute control to prohibit a decrease in the combined power during the designated time period. The first calculation unit may calculate, as one of the predicted values, a predicted lower limit value that is predicted to be possible as the output power of the variable power source during the period until the end of the designated time period. The second calculation unit may set the set upper limit value to a value equal to or less than a value obtained by adding the power limit value to the predicted lower limit value.

[0009] The control unit may at least execute control to prohibit an increase in the combined power during the designated time period. The first calculation unit may calculate, as one of the predicted values, a predicted upper limit value that is predicted to be the output power of the variable power source during the period until the end of the designated time period. The second calculation unit may set the set lower limit value to be equal to or greater than a value obtained by subtracting the power limit value from the predicted upper limit value.

[0010] The second calculation unit may change at least one of the set upper limit value and the set lower limit value within the designated time period, depending on the remaining time of the designated time period.

[0011] The first calculation unit may change the predicted lower limit value so that it becomes higher as the remaining time of the specified time period becomes shorter. The second calculation unit may change the set upper limit value so that it becomes higher as the remaining time of the specified time period becomes shorter.

[0012] The first calculation unit may change the predicted upper limit value so as to decrease as the remaining time of the specified time period decreases, and the second calculation unit may change the set lower limit value so as to decrease as the remaining time of the specified time period decreases.

[0013] The control unit may calculate a composite power reserve value according to the dischargeable energy amount of the power storage unit to enable control to prohibit a decrease in the composite power during the designated time period even when output from the variable power source is stopped. The second calculation unit may set the set upper limit value to a value equal to or lower than the smaller of the composite power reserve value and a value obtained by adding the power limit value to the predicted lower limit value.

[0014] The control unit may calculate a composite power reserve value according to the chargeable energy amount of the power storage unit to enable control to prohibit an increase in the composite power during the designated time period even when output from the variable power source is stopped. The second calculation unit may set the set lower limit value to be equal to or greater than the larger of the value obtained by subtracting the power limit value from the predicted upper limit value and the composite power reserve value.

[0015] The second calculation unit may calculate the target value of the combined power in the preparation time slot based on the remaining time in the preparation time slot before the designated time slot and a preset rate of change.

[0016] The power limit value may be the rated power value of the power conversion unit.

[0017] The power limit value may be a value of chargeable / dischargeable power of the power storage unit that changes depending on at least one of the ambient temperature of the power storage unit and the charge amount of the power storage unit.

[0018] The above summary of the invention does not list all of the necessary features of the present invention, and subcombinations of these features may also constitute inventions. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a conceptual diagram showing an example of the configuration of a power generation system according to an embodiment of the present invention. [Figure 2] FIG. 3 is a diagram showing processing performed by a power stabilizing device in a first comparative example. [Figure 3] FIG. 2 is a diagram showing the processing performed by the power stabilizing device according to the first embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing processing performed by a power stabilizing device in a second comparative example. [Figure 5] FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a second embodiment of the present invention. [Figure 6] FIG. 11 is a diagram showing processing performed by a power stabilizing device in a third comparative example. [Figure 7] FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a fourth embodiment of the present invention. [Figure 9] 6 is another example of processing performed by the power stabilizing device according to the first embodiment of the present invention. [Figure 10] FIG. 10 is a scatter plot showing an example of power changes when the remaining time of the specified time is 10 minutes. [Figure 11] FIG. 10 is a scatter plot showing an example of power changes when the remaining time of the specified time is 30 minutes. [Figure 12] FIG. 10 is a diagram showing the cumulative frequency of power reductions for each remaining time of a specified time. [Figure 13] FIG. 10 is a diagram illustrating an example of the correlation between the remaining time of a specified time and a decrease in power consumption. [Figure 14] FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a fifth embodiment of the present invention. [Figure 15] 10 is another example of processing performed by the power stabilizing device according to the second embodiment of the present invention. [Figure 16]FIG. 10 is a conceptual diagram showing an example of the configuration of a power generation system according to another embodiment of the present invention. [Figure 17] FIG. 10 is a conceptual diagram showing an example of the configuration of a power generation system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0021] FIG. 1 is a conceptual diagram showing an example of the configuration of a power generation system 1 according to one embodiment of the present invention. The power generation system 1 includes variable power sources 14-1 and 14-2 and a power stabilization device 10. The variable power sources 14-1 and 14-2 (sometimes collectively referred to as variable power sources 14) are power sources whose output fluctuates depending on the environment. The variable power source 14 may be a renewable energy power source such as a wind power generator or a solar power generator. The variable power source 14 may also be a distributed power source. However, the variable power source 14 is not limited to renewable energy. The variable power source 14 may be electrically connected to the power grid 2 via a transformer 4. The variable power source 14 may include load equipment that consumes energy supplied from the variable power source 14. In this embodiment, the variable power source 14-1 is a wind power generator, and the variable power source 14-2 is a solar power generator. However, the type and number of the variable power sources 14 are not limited to those shown in FIG. 1.

[0022] The power stabilizing device 10 has a power storage unit 12, a power conversion unit 13, and a control unit 20. The power storage unit 12 is connected to the power conversion unit 13. The power conversion unit 13 is connected to the interconnection point 3 via a transformer 6.

[0023] Power storage unit 12 performs charging and discharging. Power storage unit 12 is a power storage device such as a flywheel, a secondary battery, or a capacitor. Power conversion unit 13 converts input and output power P2 resulting from charging and discharging in power storage unit 12 between power grid 2 and power storage unit 12 based on a command from control unit 20 (here, the direction in which power is discharged from power storage unit 12 is defined as "positive"). Power conversion unit 13 may also be referred to as a PCS (power conditioning system) or an inverter.

[0024] When the power storage unit 12 is a flywheel, the power conversion unit 13 bidirectionally converts AC power on the flywheel side to AC power on the power grid 2 side. When the power storage unit 12 is a secondary battery or a capacitor, the power conversion unit 13 bidirectionally converts DC power on the secondary battery or capacitor side to AC power on the power grid 2 side.

[0025] The power generation system 1 shown in Fig. 1 outputs composite power P3 (=P1+P2) obtained by combining output power P1 from variable power source 14 and power P2 from power storage unit 12 (power P2 from power conversion unit 13) to interconnection point 3 of power grid 2. The composite power P3 is the output (power plant output) of the entire power plant made up of variable power source 14 and power storage unit 12. The power stabilization device 10 reduces fluctuations in the composite power P3 by adjusting the input / output power P2 from power storage unit 12.

[0026] The control unit 20 sets at least one of a set upper limit value Pupper and a set lower limit value Plower for a composite power P3, which is the output power P1 of the variable power source 14 connected to the power grid 2 and the power P2 of the power storage unit 12. The control unit 20 sets the set upper limit value Pupper and the set lower limit value Plower to values ​​corresponding to a power limit value Preg. The power limit value Preg may be a power limit value in the configuration between the power storage unit 12 and the power grid 2, or may be a power limit value of the power storage unit 12 itself. In this example, the power limit value Preg is the value of the rated power (W) (referred to as PCS rating) of the power conversion unit 13 (PCS) provided between the power storage unit 12 and the power grid 2.

[0027] 1 includes a first calculation unit 21, a second calculation unit 22, a storage unit 23, a power limit value limiter 24, a short-cycle fluctuation countermeasure limiter 25, a long-cycle fluctuation countermeasure limiter 26, a command value calculation unit 27, a power conversion unit control unit 28, and a measurement unit 16. However, the control unit 20 does not need to have all of these components, and the short-cycle fluctuation countermeasure limiter 25 may be omitted as appropriate.

[0028] In one example, the first calculation unit 21 calculates a predicted value that the output power P1 of the variable power source 14 can assume during the period up to the end of the specified time period in order to mitigate temporal fluctuations in the composite power P3. The predicted value may be a predicted upper limit value Pmax indicating the upper limit that can be assumed within the period with a predetermined probability, or a predicted lower limit value Pmin indicating the lower limit that can be assumed within the period with a predetermined probability. However, the predicted lower limit value Pmin for a specific period may be fixed to 0, and the predicted upper limit value Pmax may be fixed to the rated power (power plant rating) of the composite power P3.

[0029] The measurement unit 16 may measure the output power P1 of the variable power source 14. However, the measurement unit 16 may also measure the composite power P3 or the available output power of the variable power source 14. The available output power of the variable power source 14 is an estimate of the power that could be generated if output suppression were not performed in the variable power source 14. If the variable power source 14 is a wind power generator, the measurement unit 16 may estimate the available output power based on the wind speed measured by the anemometer 18. If the variable power source 14 is a solar power generator, the measurement unit 16 may estimate the available output power based on the amount of solar radiation or temperature measured by the pyranometer 17. However, if the available output power of the variable power source 14 is not used, the pyranometer 17 and the anemometer 18 can be omitted. Alternatively, the variable power source 14 may estimate its own available output power. The variable power source 14 may notify the control unit 20 of the estimated available output power. In this case, the pyranometer 17 and the anemometer 18 can also be omitted.

[0030] The second calculation unit 22 calculates at least one of a set upper limit value (Pupper) and a set lower limit value (Plower) based on the predicted value (at least one of Pmin and Pmax) and the power limit value Preg. The storage unit 23 stores various data and parameters. In this example, the storage unit 23 may store data on the correlation between power (output power P1, the outputtable power of the variable power source 14, or the combined power P3) and a change in power over a predetermined time. The storage unit 23 may also store a power limit value in advance.

[0031] The power limit value limiter 24 may be a limiter circuit that controls the upper and lower limits of the composite power target value using at least one of the set upper limit value (Pupper) and set lower limit value (Plower) calculated by the second calculation unit 22. The short-cycle fluctuation countermeasure limiter 25 performs short-cycle fluctuation mitigation control to mitigate short-cycle fluctuations, which are power fluctuation components of the variable power source 14, that last for up to several tens of minutes. The long-cycle fluctuation countermeasure limiter 26 performs long-cycle fluctuation mitigation control to mitigate long-cycle fluctuations, which are power fluctuation components of the variable power source 14 that last for several tens of minutes to several hours. A composite power target value Pa, which is the target value of the composite power P3, may be input to the command value calculation unit 27 via the power limit value limiter 24, the short-cycle fluctuation countermeasure limiter 25, and the long-cycle fluctuation countermeasure limiter 26. Note that the controls by the long-cycle fluctuation countermeasure limiter 26 and the short-cycle fluctuation countermeasure limiter 25 may be prioritized over the control by the power limit value limiter 24.

[0032] The command value calculation unit 27 generates a command value based on the composite power target value Pa and the output power P1 of the variable power source 14. In this example, the command value calculation unit 27 generates the command value by subtracting the composite power target value Pa from the output power P1 of the variable power source 14. The power conversion unit control unit 28 controls the power conversion unit 13 based on the command value.

[0033] FIG. 2 is a diagram showing the processing performed by the power stabilizing device 10 in the first comparative example. FIG. 3 is a diagram showing the processing performed by the power stabilizing device 10 in the first embodiment of the present invention. As shown in FIGS. 2 and 3, the control unit 20 executes long-period fluctuation mitigation control to mitigate temporal fluctuations in the combined power P3 during a designated time period. In FIGS. 2 and 3, the control unit 20 executes at least control to prohibit a decrease in the combined power P3 during a designated time period from time T1 to T2. In FIGS. 2 and 3, short-period fluctuation mitigation control is not executed.

[0034] In the comparative example of FIG. 2, the set upper limit value Pupper is not set. Therefore, the maximum value of the combined power P3 is updated according to the output power P1 of the variable power source 14 during the specified time period. Even if the power P1 of the variable power source 14 decreases, the control unit 20 cannot reduce the value of the combined power P3. Therefore, the power P2 indicated by the difference (P3-P1) between the combined power P3 and the output power P1 of the variable power source 14 increases. As a result, the power P2 discharged from the power storage unit 12 may exceed the power limit value Preg (the rated power (W) of the power conversion unit 13 (PCS)). In this case, the power limit value Preg makes it difficult for the control unit 20 to perform long-period fluctuation mitigation control.

[0035] In the first embodiment shown in Figure 3, the first calculation unit 21 in Figure 1 calculates, as one of the predicted values, the predicted lower limit value Pmin that is predicted to be the output power P1 of the variable power source 14 within the period from the current time to the end time T2 of the specified time period (between T1 and T2) for mitigating the temporal fluctuation of the composite power P3.

[0036] The second calculation unit 22 calculates the set upper limit value Pupper based on the predicted lower limit value Pmin and the power limit value Preg. The second calculation unit 22 sets the set upper limit value Pupper to a value equal to or less than (Preg + Pmin) obtained by adding the power limit value Preg to the predicted lower limit value Pmin within the specified time period. Outside the specified time period, the set upper limit value Pupper may be set to the rated power value of the combined power P3. The control unit 20 sets the set upper limit value Pupper to a value higher than the power limit value Preg within the specified time period. The second calculation unit 22 may set the set upper limit value Pupper as the power limit value Preg within the specified time period (when the predicted lower limit value Pmin is fixed to 0). Note that, when the output power P1 of the variable power source 14 exceeds the set upper limit value Pupper, the power storage unit 12 may be charged with the difference obtained by subtracting the set upper limit value Pupper from the output power P1.

[0037] Fig. 4 is a diagram showing the processing performed by a power stabilizing device in a second comparative example. Fig. 5 is a diagram showing the processing performed by a power stabilizing device in a second embodiment of the present invention. In Figs. 4 and 5, the control unit 20 at least executes control to prohibit an increase in the combined power P3 during a specified time period from time T1 to T2. In Figs. 4 and 5, short-cycle fluctuation mitigation control is not executed.

[0038] In the second comparative example in FIG. 4, the set lower limit value Plower is not set. Therefore, the minimum value of the combined power P3 is updated according to the output power P1 of the variable power source 14 during the specified time period. Even if the output power P1 of the variable power source 14 increases, the control unit 20 cannot increase the value of the combined power P3. Therefore, the power P2 indicated by the difference (P1-P3) between the output power P1 of the variable power source 14 and the combined power P3 increases. As a result, the power P2 charged from the power storage unit 12 may exceed the power limit value Preg (the rated power (W) of the power conversion unit 13 (PCS)). In this case, the power limit value Preg makes it difficult for the control unit 20 to perform long-period fluctuation mitigation control.

[0039] In the second embodiment shown in Figure 5, the first calculation unit 21 in Figure 1 calculates, as one of the predicted values, a predicted upper limit value Pmax that is predicted to be possible for the output power P1 of the variable power source 14 within the period from the current time to the end time T2 of a specified time period (between T1 and T2) for mitigating the temporal fluctuation of the composite power P3.

[0040] The second calculation unit 22 calculates the set lower limit value Plower for the designated time period based on the predicted upper limit value Pmax and the power limit value Preg. The second calculation unit 22 sets the set lower limit value Plower for the designated time period to a value equal to or greater than the value (Pmax - Preg) obtained by subtracting the power limit value Preg from the predicted upper limit value Pmax. The second calculation unit 22 may set the set lower limit value Plower to 0 for periods other than the designated time period. The control unit 20 sets the set lower limit value Plower for the designated time period to a value smaller than the value obtained by subtracting the power limit value Preg from the rated power of the composite power P3. The second calculation unit 22 may set the set lower limit value Plower for the designated time period to a value obtained by subtracting the power limit value Preg from the rated power of the composite power P3 (when the predicted upper limit value Pmax is fixed to the rated power of P3).

[0041] According to the configurations shown in Figures 3 and 5, it is possible to prevent the absolute value of power P2 from exceeding the power limit value in the configuration between the power storage unit 12 and the power system 2 and the power limit value of the power storage unit 12 itself.

[0042] In particular, the first calculation unit 21 and the second calculation unit 22 calculate at least one of the set upper limit value Pupper and the set lower limit value Plower based on the predicted values ​​(Pmax, Pmin) that the output power P1 of the variable power source 14 can assume during the period from the current time to the end time T2 of the specified time period (T1 to T2) and the power limit value Preg. Therefore, the set upper limit value Pupper and the set lower limit value Plower can be set with high accuracy. By setting the set upper limit value Pupper to be greater than the power limit value Preg, the amount of charge that must be stored in the power storage unit 12 can be reduced. Therefore, the power storage unit 12 can be made smaller.

[0043] Next, a case where the control unit 20 executes the short-cycle fluctuation mitigation control and the long-cycle fluctuation mitigation control will be described.

[0044] FIG. 6 is a diagram illustrating the processing performed by a power stabilizing device in a third comparative example. FIG. 7 is a diagram illustrating the processing performed by a power stabilizing device in a third embodiment of the present invention. In FIGS. 6 and 7, long-period fluctuation mitigation control is performed during a specified time period (from T1 to T2). Short-period fluctuation mitigation control is performed throughout the entire time period. As shown in FIG. 6, the composite power P3 smoothed by the short-period fluctuation mitigation control reaches its highest value during the specified time period. Even if the power P1 of the variable power source 14 decreases, the control unit 20 cannot reduce the value of the composite power P3. Therefore, the power P2, which is the difference (P3 - P1) between the composite power P3 and the output power P1 of the variable power source 14, increases. As a result, the power P2 discharged from the power storage unit 12 may exceed the power limit value Preg (the rated power (W) of the power conversion unit 13 (PCS)). In this case, the control unit 20 has difficulty performing the long-period fluctuation mitigation control due to the power limit value Preg.

[0045] As shown in FIG. 3, the control unit 20 may set the set upper limit value Pupper to the rated value of the composite power P3 outside the designated time period and change the set upper limit value Pupper to, for example, a power limit value Preg at the start time T1 of the designated time period. However, when the control shown in FIG. 3 is applied, the fluctuation rate may exceed the allowable short-cycle fluctuation. Therefore, as shown in FIG. 7, the second calculation unit 22 calculates the set upper limit value Pupper for the preparation time period based on the remaining time in the preparation time period (before T1) before the designated time period and a preset rate of change. In other words, the second calculation unit 22 calculates the composite power target value for the preparation time based on the remaining time in the preparation time period (before T1) before the designated time period and a preset rate of power change in the short-cycle fluctuation mitigation control.

[0046] According to the control shown in FIG. 7 , the composite power P3 is controlled within a range from 0% to 100% of the power plant rating (P3 rating). The control unit 20 executes control to prohibit a decrease in the composite power P3 during the designated time period. During a preparation stage before the start of the designated time period (between times Ts and T1 in this example), the second calculation unit 22 may calculate the set upper limit value Pupper of the composite power P3 so as to satisfy the following equation: "Pupper = Preg (in one example, PCS rating) + time until the start of the designated time period × power change rate in short-cycle fluctuation mitigation control." Alternatively, during a preparation stage before the start of the designated time period, the second calculation unit 22 may calculate the set upper limit value Pupper of the composite power P3 so as to satisfy the following equation: "Pupper = (Preg (in one example, PCS rating) + Pmin) + time until the start of the designated time period × power change rate in short-cycle fluctuation mitigation control." The output change rate in short-period fluctuation mitigation control may be a value specified by the transmission and distribution company (for example, 1% / minute), or may be a value specified by the transmission and distribution company with a margin (for example, 0.9% / minute).

[0047] As shown in FIG. 7, the second calculation unit 22 decreases the set upper limit value Pupper from the rated value of the combined power P3 to Preg (or Preg+Pmin) at a predetermined rate of change as the remaining time of the preparation time period decreases.

[0048] As for the composite power target value P3a during the preparation time period, in the interval (the interval from Ts to Tc) where the composite power P3 smoothed by the short-cycle fluctuation mitigation control is less than the set upper limit value Pupper, the smoothed composite power P3 is output. On the other hand, when the smoothed composite power P3 becomes equal to or greater than the set upper limit value Pupper, the composite power P3 is output so as to follow the composite power target value P3a limited by the set upper limit value Pupper.

[0049] 4 and 5, when the control unit 20 executes control to prohibit an increase in the composite power P3 during a designated time period, in the preparation stage before the start of the designated time period (between times Ts and T1 in this example), the second calculation unit 22 may calculate the set lower limit value Plower of the composite power P3 so as to satisfy the following equation: "Set lower limit value Plower of the composite power P3 = (Pmax - Preg) - Length of time until the start of the designated time period x Power change rate in the short-cycle fluctuation mitigation control." Alternatively, the second calculation unit 22 may calculate the set lower limit value Plower of the composite power P3 so as to satisfy the following equation: "Set lower limit value Plower of the composite power P3 = (Rated composite power P3 (rated power plant) - Preg) - Length of time until the start of the designated time period x Power change rate in the short-cycle fluctuation mitigation control."

[0050] According to the control shown in FIG. 7, it is possible to keep the combined power within an appropriate range in a designated time period while constantly executing short-cycle fluctuation mitigation control.

[0051] Fig. 8 is a diagram showing the processing performed by a power stabilizing device according to a fourth embodiment of the present invention. Fig. 9 is another example of the processing performed by a power stabilizing device according to the first embodiment of the present invention. In the first embodiment described in Fig. 3, if the output power P1 of the variable power source 14 does not fall below the power limit value Preg as shown in Fig. 9, the amount of power hatched with diagonal lines in Fig. 9 will be surplus. In this way, if the combined power P3 is limited to a value equal to or lower than the PCS rating, for example, even though the potential output level of the output power P1 of the variable power source 14 is high, surplus power will be generated.

[0052] If the storage capacity (kWh) of the power storage unit 12 is greater than the amount of surplus power (kWh), the surplus power can be charged. However, due to demands for miniaturization and cost reduction of the power stabilization device 10, it is necessary to reduce the storage capacity. Therefore, the surplus power may have to be discarded by the output suppression function of the variable power source 14.

[0053] The fourth example of FIG. 8 reduces the amount of surplus power compared to the example shown in FIG. 9. The second calculation unit 22 changes at least one of the set upper limit value Pupper and the set lower limit value Plower within the specified time period (the time from T1 to T2) according to the remaining time of the specified time period. In the example shown in FIG. 8, the second calculation unit 22 changes the set upper limit value Pupper (shown by a dashed line) within the specified time period (the time from T1 to T2) according to the remaining time of the specified time period. More specifically, the first calculation unit 21 changes the predicted lower limit value Pmin so that it increases as the remaining time of the specified time period decreases, as shown by the two-dot chain line. Note that if the output power P1 of the variable power source 14 fluctuates periodically, the first calculation unit 21 may control the predicted lower limit value Pmin so that the average value of the predicted lower limit value Pmin increases as the remaining time of the specified time period decreases, while also fluctuating periodically. The second calculation unit 22 may change the set upper limit value Pupper so that it increases as the remaining time of the specified time period decreases, as shown by the dashed dotted line. The second calculation unit 22 may control the set upper limit value Pupper so that the average value of the set upper limit value Pupper increases as the remaining time of the specified time period decreases, while the set upper limit value Pupper fluctuates periodically.

[0054] In one example, the first calculation unit 21 acquires the output power P1 (renewable energy output power) of the variable power source 14 before the current time and stores it in the storage unit 23. The first calculation unit 21 may use the output power P1 of the variable power source 14 before the current time as input, and calculate the current output power P1 of the variable power source 14 using a moving average, an LPF (low pass filter), a maximum value calculation, a minimum value calculation, a median value calculation, or a combination thereof. The maximum value calculation is a process of acquiring the maximum value in a predetermined period before the current time, the minimum value calculation is a process of acquiring the minimum value in a predetermined period before the current time, and the median value calculation is a process of acquiring the median value in a predetermined period before the current time.

[0055] 8, when the control unit 20 at least executes control to prohibit a decrease in the composite power P3 during the designated time period, the first calculation unit 21 estimates a power change (power decrease) during the designated time period. The power decrease may be an estimate of the value to which the current output power P1 will decrease. As the remaining time during the designated time period decreases, the likelihood that the power P1 will decrease decreases, and therefore the estimated power decrease decreases.

[0056] FIG. 10 is a scatter plot showing an example of power changes when the remaining time in the specified time slot is 10 minutes. FIG. 11 is a scatter plot showing an example of power changes when the remaining time in the specified time slot is 30 minutes. In FIGS. 10 and 11, the horizontal axis represents the output power P1 of the variable power source 14 at the current time, and the vertical axis represents the minimum value of the variable power source 14 during the remaining time in the specified time slot. The power reduction in the output power P1 varies depending on the length of time remaining in the specified time slot. When the remaining time (time window) in the specified time slot is 30 minutes, there is greater variation than when the remaining time (time window) in the specified time slot is 10 minutes. Therefore, the power reduction (reduced power value), which is the difference between the current output power P1 and the minimum value of the power P1 within the remaining time, becomes larger.

[0057] Fig. 12 is a diagram showing the cumulative frequency of power reduction according to the remaining time of the specified time. In Fig. 12, when the power reduction is guaranteed at a cumulative frequency of 99.7% or more, the power reduction becomes larger as the time becomes longer, as shown in Fig. 12.

[0058] FIG. 13 is a diagram showing an example of the correlation between the remaining time of a specified time period and power reduction. In FIG. 13, the horizontal axis represents the remaining time T of the specified time period, and the vertical axis represents the power reduction Pd (%). As indicated by the dotted line, the probability of power reduction Pd increases as the remaining time increases. Note that a function F(T) indicating the correlation between the current output power P1 of the variable power source 14 and the power reduction Pd may be set based on actual data (dotted line). In this case, the function F may be designed so that the function F is always larger at any given time than the curve (dotted line) of the power reduction to be compensated for based on the actual data. The function F may be composed of a linear function and a portion that saturates at a power reduction of 100%.

[0059] The first calculation unit 21 can calculate the predicted lower limit value Pmin for each remaining time period in the specified time slot by subtracting the power reduction Pd from the current output power P1 of the variable power source 14. In other words, the first calculation unit 21 may calculate the predicted lower limit value Pmin as a predicted value based on the correlation between the output power P1 of the variable power source 14 before the current time and the change in the output power P1 over a predetermined time period, as described with reference to Figures 10 to 13.

[0060] The second calculation unit 21 calculates the set upper limit value Pupper of the composite power P3. As shown in Fig. 8, when the control unit 20 at least executes control to prohibit a decrease in the composite power P3 during a specified time period, the second calculation unit 21 may set the set upper limit value Pupper of the composite power P3 to max(0, Pmin) + Preg (PCS rating). The predicted lower limit value Pmin may be calculated as the output power P1 of the variable power source 14 minus the power reduction Pd.

[0061] As the remaining time of the specified time period becomes shorter, the power drop Pd becomes smaller. Therefore, as the remaining time of the specified time period becomes shorter, the predicted lower limit value Pmin (output power P1 of variable power source 14 - power drop Pd) increases. At the timing when the predicted lower limit value Pmin (output power P1 of variable power source 14 - power drop Pd) becomes greater than 0, the set upper limit value Pupper of the composite power P3 exceeds Preg (PCS rating), and the composite power P3 increases. As the composite power P3 increases, the amount of surplus power (the hatched portion in FIG. 8) decreases, particularly in the latter half of the specified time period compared to the middle point. As a result, the amount of power that cannot be fully charged in the power storage unit 12 decreases, and power generation loss can be reduced.

[0062] Note that when at least control to prohibit a decrease in the composite power P3 is executed during the specified time period, even if the output power P1 of the variable power source 14 decreases during the specified time period and the set upper limit value Pupper of the composite power P3 temporarily decreases, the composite power P3 cannot be decreased. Because the predicted lower limit value Pmin for the time window (remaining time) is taken into consideration, the set upper limit value Pupper may fall below the composite power P3. However, the set upper limit value Pupper means that the composite power P3 may be increased up to this value. Meanwhile, the long-period fluctuation countermeasure limiter 26 in FIG. 1 executes control to prohibit a decrease in the composite power P3. In the control unit 20, the long-period fluctuation countermeasure limiter 26 is applied with priority over the power limit value limiter 24, which has the set upper limit value Pupper as its upper limit. This gives priority to the control to prohibit a decrease in the composite power P3.

[0063] The first calculation unit 21 may predict the predicted lower limit value Pmin based on the correlation between the output power P1 of the variable power source 14 and changes in the output power P1. However, the first calculation unit 21 may also predict the predicted lower limit value Pmin based on the correlation between the available output power of the variable power source 14 and changes in the available output power of the variable power source 14 within each time period. The first calculation unit 21 may also predict the predicted lower limit value Pmin based on the correlation between the composite power P3 and changes in the composite power P3 within each time period.

[0064] FIG. 14 is a diagram showing the processing performed by a power stabilizing device according to a fifth embodiment of the present invention. FIG. 15 is another example of the processing performed by a power stabilizing device according to a second embodiment of the present invention. In the second embodiment described in FIG. 5, as shown in FIG. 15, if the output power P1 of the variable power source 14 does not increase beyond "total power P3 rating (power plant rating) - power limit value Preg," the power storage unit 12 must discharge the amount of power indicated by the diagonally hatched portion in FIG. 15. In this way, if the set lower limit value Plower of the combined power P3 is set high even though the output power P1 of the variable power source 14 does not increase, the amount of discharge from the power storage unit 12 increases.

[0065] The fifth example of FIG. 14 reduces the amount of discharge from the power storage unit 12 compared to the example shown in FIG. 15 . The second calculation unit 22 changes the set lower limit value Plower within the designated time period (the time from T1 to T2) depending on the remaining time of the designated time period. More specifically, the first calculation unit 21 changes the predicted upper limit value Pmax so that it decreases as the remaining time of the designated time period decreases, as indicated by the two-dot chain line. Note that, if the output power P1 of the variable power source 14 fluctuates periodically, the first calculation unit 21 may control the predicted upper limit value Pmax so that it also fluctuates periodically, and the average value of the predicted lower limit value Pmax decreases as the remaining time of the designated time period decreases. The second calculation unit 22 may change the set lower limit value Plower so that it decreases as indicated by the one-dot chain line as the remaining time of the designated time period decreases. The second calculation unit 22 may perform control such that the set lower limit value Plower varies periodically and the average value of the set lower limit value Plower decreases as the remaining time of the designated time period decreases.

[0066] In one example, the first calculation unit 21 acquires the output power P1 (renewable energy output power) of the variable power source 14 before the current time and stores it in the storage unit 23. The first calculation unit 21 may use the output power P1 of the variable power source 14 before the current time as input, and calculate the current output power P1 of the variable power source 14 using a moving average, an LPF (low pass filter), a maximum value calculation, a minimum value calculation, a median value calculation, or a combination thereof. The maximum value calculation is a process of acquiring the maximum value in a predetermined period before the current time, the minimum value calculation is a process of acquiring the minimum value in a predetermined period before the current time, and the median value calculation is a process of acquiring the median value in a predetermined period before the current time.

[0067] 14, when the control unit 20 at least executes control to prohibit an increase in the composite power P3 during the designated time period, the first calculation unit 21 estimates a power change (power increase) during the designated time period. The power increase may be an estimate of the amount by which the current output power P1 will increase. As the remaining time during the designated time period decreases, the likelihood that the power P1 will increase decreases, and therefore the estimated power increase decreases.

[0068] The first calculation unit 21 can calculate the predicted upper limit value Pmax for each remaining time period in the specified time slot by adding the power increase Pi to the current output power P1 of the variable power source 14. In other words, the first calculation unit 21 may calculate the predicted upper limit value Pmax as a predicted value based on the correlation between the output power P1 of the variable power source 14 before the current time and the change in the output power P1 over a predetermined time period, as described with reference to Figures 10 to 13.

[0069] The second calculation unit 21 calculates the set lower limit value Plower of the composite power P3. As shown in Fig. 14, when the control unit 20 at least executes control to prohibit an increase in the composite power P3 during a specified time period, the second calculation unit 21 may set the set lower limit value Plower of the composite power P3 as min (rated power of the composite power P3, Pmax) - Preg (PCS rating). Note that the predicted upper limit value Pmax may be calculated as the output power P1 of the variable power source 14 + the power increase Pi.

[0070] As the remaining time of the specified time slot becomes shorter, the power increase Pi becomes smaller. Therefore, as the remaining time of the specified time slot becomes shorter, the predicted upper limit value Pmax (output power P1 of the variable power source 14 + power increase Pi) decreases. When the predicted upper limit value Pmax (output power P1 of the variable power source 14 + power increase Pi) becomes smaller than the composite power P3 rating (power plant rating), the set lower limit value Plower of the composite power P3 falls below "P3 rating (power plant rating) - Preg (PCS rating)", and the composite power P3 decreases. Because the composite power P3 decreases, the amount of discharged power from the power storage unit 12 (the hatched portion in FIG. 14 ) decreases, particularly in the latter half of the specified time slot rather than the middle. As a result, it is possible to mitigate a decrease in the charge rate of the power storage unit 12.

[0071] Note that, when at least control to prohibit an increase in the composite power P3 is executed during the specified time period, even if the output power P1 of the variable power source 14 increases during the specified time period and the set lower limit value Plower of the composite power P3 temporarily increases, the composite power P3 cannot be increased. Because the predicted upper limit value Pmax for the time window (remaining time) is taken into consideration, the set lower limit value Plower may exceed the composite power P3. However, the set lower limit value Plower means that the composite power P3 may be lowered up to this value. Meanwhile, the long-period fluctuation countermeasure limiter 26 in FIG. 1 executes control to prohibit an increase in the composite power P3. In the control unit 20, the long-period fluctuation countermeasure limiter 26 is applied with priority over the power limit value limiter 24, which has the set lower limit value Plower as its lower limit. This gives priority to the control to prohibit an increase in the composite power P3.

[0072] The first calculation unit 21 may calculate the predicted upper limit value Pmax based on the correlation between the output power P1 of the variable power source 14 and changes in the output power P1. However, the first calculation unit 21 may also calculate the predicted upper limit value Pmax based on the correlation between the available output power of the variable power source 14 and changes in the available output power of the variable power source 14 within each hour. The first calculation unit 21 may also calculate the predicted lower limit value Pmax based on the correlation between the composite power P3 and changes in the composite power P3 within each hour.

[0073] FIG. 16 is a conceptual diagram showing a configuration example of a power generation system 1 according to another embodiment of the present invention. In the power stabilization device 10 described with reference to FIGS. 1 to 15, the power limit value Preg is the power limit value in the configuration between the power storage unit 12 and the power grid 2 and the power limit value of the power storage unit 12 itself. In particular, the power limit value Preg is the rated power (PCS rating) of the power conversion unit. However, in the configuration shown in FIG. 16, the power limit value Preg is the value of the chargeable / dischargeable power of the power storage unit 12, which varies depending on at least one of the ambient temperature of the power storage unit 12 and the charge amount of the power storage unit 12. The second calculation unit 22 may calculate at least one of the set upper limit value Puppoer and the set lower limit value Plower using the value of the chargeable / dischargeable power of the power storage unit 12 as the power limit value Preg. The other configurations are the same as those described with reference to FIGS. 1 to 15, and therefore, repeated description will be omitted.

[0074] Fig. 17 is a conceptual diagram showing an example of the configuration of a power generation system 1 according to another embodiment of the present invention. The technologies described in Japanese Patent Application Laid-Open Nos. 2018-161041, 2019-115131, and 2018-038132, which are cited as prior art, may be used together with the technologies described in Figs. 1 to 16.

[0075] 17 includes a composite power reserve value calculation unit 29. The composite power reserve value calculation unit 29 in the control unit 20 calculates a composite power reserve value that enables control to prohibit a decrease in composite power P3 during a designated time period even when output from the variable power source 14 is stopped, according to the amount of dischargeable power of the power storage unit 12. The second calculation unit 22 may set the set upper limit value Pupper to a value (Preg+Pmin) obtained by adding the power limit value Preg to the predicted lower limit value Pmin, or the composite power reserve value, whichever is smaller.

[0076] The control unit 20 may calculate a composite power reserve value according to the chargeable energy of the power storage unit 12, so as to enable control to prohibit an increase in the composite power P3 during a specified time period even when output from the variable power source 14 is stopped. The second calculation unit 22 may set the set lower limit value Plower to be equal to or greater than the larger of the value obtained by subtracting the power limit value Preg from the predicted upper limit value Pmax and the composite power reserve value.

[0077] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention. [Explanation of symbols]

[0078] 1 Power generation system, 2 Power system, 3 Interconnection point, 4 Transformer, 6 Transformer, 10 Power stabilization device, 12 Energy storage unit, 13 Power conversion unit, 14 Variable power source, 16 Measurement unit, 17 Pyranometer, 18 Anemometer, 20 Control unit, 21 First calculation unit, 22 Second calculation unit, 23 Memory unit, 24 Power limit value limiter, 25 Short-period fluctuation countermeasure limiter, 26 Long-period fluctuation countermeasure limiter, 27 Command value calculation unit, 28 Power conversion unit control unit, 29 Combined power reserve value calculation unit

Claims

1. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets a set lower limit value of a combined power of the power of a variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit.

2. A power stabilizing device as described in claim 1, wherein the control unit sets the set lower limit value to be smaller as the power limit value is larger.

3. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets at least one of a set upper limit value and a set lower limit value of a combined power of the power of the variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit; The control unit sets the set upper limit value to a value higher than the power limit value.

4. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets at least one of a set upper limit value and a set lower limit value of a combined power of the power of the variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit; The control unit a first calculation unit that calculates a predicted value that the output power of the variable power source can take during a period from a current time to an end time of a designated time period for mitigating temporal fluctuations in the combined power; a second calculation unit that calculates at least one of the set upper limit value and the set lower limit value based on the predicted value and the power limit value, the control unit at least executes control to prohibit a reduction in the combined power during the designated time period; the first calculation unit calculates, as one of the predicted values, a predicted lower limit value that is predicted to be possible as output power of the variable power source within the period until an end time of the specified time period; The second calculation unit sets the set upper limit value to a value equal to or less than a value obtained by adding the power limit value to the predicted lower limit value.

5. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets at least one of a set upper limit value and a set lower limit value of a combined power of the power of the variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit; The control unit a first calculation unit that calculates a predicted value that the output power of the variable power source can take during a period from a current time to an end time of a designated time period for mitigating temporal fluctuations in the combined power; a second calculation unit that calculates at least one of the set upper limit value and the set lower limit value based on the predicted value and the power limit value, the control unit at least executes control to prohibit an increase in the combined power during the designated time period; the first calculation unit calculates, as one of the predicted values, a predicted upper limit value that is predicted to be possible as output power of the variable power source within the period until an end time of the specified time period; The second calculation unit sets the set lower limit value to a value equal to or greater than the predicted upper limit value minus the power limit value.

6. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets at least one of a set upper limit value and a set lower limit value of a combined power of the power of the variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit; The control unit a first calculation unit that calculates a predicted value that the output power of the variable power source can take during a period from a current time to an end time of a designated time period for mitigating temporal fluctuations in the combined power; a second calculation unit that calculates at least one of the set upper limit value and the set lower limit value based on the predicted value and the power limit value, The second calculation unit changes at least one of the set upper limit value and the set lower limit value within the designated time period according to the remaining time of the designated time period.

7. 7. The power stabilization device according to claim 4, wherein the first calculation unit calculates the predicted value based on a correlation between at least one of the output power of the variable power source, the outputtable power of the variable power source, and the combined power prior to the current time and a change in the at least one power over a predetermined time.

8. the first calculation unit changes the prediction lower limit value so as to increase as the remaining time of the specified time period decreases, The power stabilizing device according to claim 4 , wherein the second calculation unit changes the set upper limit value so as to increase as the remaining time of the specified time period decreases.

9. the first calculation unit changes the predicted upper limit value so as to decrease as the remaining time of the specified time period decreases, The power stabilizing device according to claim 5 , wherein the second calculation unit changes the set lower limit value so as to decrease as the remaining time of the specified time period decreases.

10. the control unit calculates a composite power reserve value according to a dischargeable amount of power of the power storage unit, the composite power reserve value being used to enable control to prohibit a decrease in the composite power during the designated time period even when output from the variable power source is stopped; 5. The power stabilizing device according to claim 4, wherein the second calculation unit sets the set upper limit value to a smaller value of the combined power reserve value and a value obtained by adding the power limit value to the predicted lower limit value.

11. the control unit calculates a composite power reserve value according to the chargeable energy amount of the power storage unit, the composite power reserve value being used to enable control to prohibit an increase in the composite power during the designated time period even when output from the variable power source is stopped; The power stabilizing device according to claim 5 , wherein the second calculation unit sets the set lower limit value to a value equal to or greater than the larger of the value obtained by subtracting the power limit value from the predicted upper limit value and the composite power reserve value.

12. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets at least one of a set upper limit value and a set lower limit value of a combined power of the power of the variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit; The control unit a first calculation unit that calculates a predicted value that the output power of the variable power source can take during a period from a current time to an end time of a designated time period for mitigating temporal fluctuations in the combined power; a second calculation unit that calculates at least one of the set upper limit value and the set lower limit value based on the predicted value and the power limit value, The second calculation unit calculates a target value of combined power during a preparation time period before the designated time period based on a remaining time during the preparation time period and a preset rate of change.

13. a power storage unit that charges and discharges; a power conversion unit that converts input and output power resulting from the charging and discharging of the power storage unit between a power grid and the power storage unit; a control unit that sets at least one of a set upper limit value and a set lower limit value of a combined power of the power of the variable power source connected to the power grid and the power of the power storage unit to a value corresponding to a power limit value between the power storage unit and the power grid and in the power storage unit; A power stabilization device, wherein the power limit value is a value of the rated power of the power conversion unit.

14. 13. The power stabilization device according to claim 1, wherein the power limit value is a value of chargeable and dischargeable power of the power storage unit that varies depending on at least one of an ambient temperature of the power storage unit and a charge amount of the power storage unit.

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