JP7749999B2 - power stabilizer - Google Patents

Description

The present invention relates to a power stabilization device.

There is known a power stabilization device that combines a variable power source and a power storage unit to supply a combined 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 combined power in advance before a time period during which 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 documents]
[Patent Documents]
[Patent Document 1] JP 2018-161041 A [Patent Document 2] JP 2019-115131 A [Patent Document 3] JP 2018-038132 A

It is desirable to be able to mitigate fluctuations in the supplied composite power even when the difference between the output power of the variable power source and the composite power becomes large.

In order to solve the above problems, one aspect of the present invention provides a power stabilization device. The power stabilization device may include a power storage unit. The power storage unit may perform charging and discharging. The power stabilization 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 stabilization device may include a control unit. The control unit may set at least one of the set upper limit and set lower limit of the 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 the power limit value between the power storage unit and the power grid and in the power storage unit.

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

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.

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

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

The control unit may at least execute control to prohibit an increase in the combined power during the specified 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 up to the end of the specified time period. The second calculation unit may set the set lower limit value to a value equal to or greater than the predicted upper limit value minus the power limit value.

The second calculation unit may change at least one of the upper and lower limit settings within the specified time period depending on the remaining time in the specified time period.

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.

The first calculation unit may change the predicted upper limit value so that it decreases as the remaining time of the specified time period decreases. The second calculation unit may change the set lower limit value so that it decreases as the remaining time of the specified time period decreases.

The control unit may calculate a composite power reserve value based on the dischargeable energy amount of the power storage unit, which enables control to prohibit a decrease in composite power during a specified time period even if output from the variable power source is stopped. The second calculation unit may set the set upper limit value to be equal to or lower than the smaller of the value obtained by adding the power limit value to the predicted lower limit value and the composite power reserve value.

The control unit may calculate a composite power reserve value based on the amount of chargeable energy in the power storage unit, enabling control to prohibit an increase in composite power during a specified time period even if 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.

The second calculation unit may calculate the target value of the combined power during the preparation time period based on the remaining time during the preparation time period before the specified time period and a preset rate of change.

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

The power limit value may be the value of the chargeable and 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 level of the power storage unit.

Note that the above summary of the invention does not list all of the necessary features of the present invention. Subcombinations of these features may also constitute inventions.

1 is a conceptual diagram showing an example of the configuration of a power generation system according to an embodiment of the present invention. FIG. 4 is a diagram showing processing performed by a power stabilizing device in a first comparative example. FIG. 2 is a diagram showing the processing contents of the power stabilizing device according to the first embodiment of the present invention. FIG. 10 is a diagram showing processing performed by a power stabilizing device in a second comparative example. FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a second embodiment of the present invention. FIG. 11 is a diagram showing processing performed by a power stabilizing device in a third comparative example. FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a third embodiment of the present invention. FIG. 10 is a diagram showing the processing contents of a power stabilizing device according to a fourth embodiment of the present invention. 10 is another example of the processing contents performed by the power stabilizing device according to the first embodiment of the present invention. FIG. 10 is a scatter plot showing an example of power changes when the remaining time of the specified time is 10 minutes. FIG. 10 is a scatter plot showing an example of power changes when the remaining time of the specified time is 30 minutes. FIG. 10 is a diagram showing the cumulative frequency of power reductions for each remaining time of a specified time. 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. FIG. 13 is a diagram showing the processing contents of a power stabilizing device according to a fifth embodiment of the present invention. 10 is a diagram illustrating another example of processing performed by the power stabilizing device according to the second embodiment of the present invention. 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. 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.

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

Figure 1 is a conceptual diagram showing an example 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 Figure 1.

The power stabilization 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.

The power storage unit 12 charges and discharges. The power storage unit 12 is a power storage device such as a flywheel, secondary battery, or capacitor. The power conversion unit 13 converts input and output power P2 resulting from charging and discharging in the power storage unit 12 between the power grid 2 and the power storage unit 12 based on commands from the control unit 20 (here, the direction in which power is discharged from the power storage unit 12 is defined as "positive"). The power conversion unit 13 is sometimes referred to as a PCS (power conditioning system) or inverter.

If the power storage unit 12 is a flywheel, the power conversion unit 13 converts AC power on the flywheel side into AC power on the power grid 2 side in both directions. If the power storage unit 12 is a secondary battery or capacitor, the power conversion unit 13 converts DC power on the secondary battery or capacitor side into AC power on the power grid 2 side in both directions.

The power generation system 1 shown in FIG. 1 outputs composite power P3 (= P1 + P2), which is the composite of output power P1 from the variable power source 14 and power P2 from the power storage unit 12 (power P2 from the power conversion unit 13), to the interconnection point 3 of the power grid 2. The composite power P3 is the output (power plant output) of the entire power plant consisting of the variable power source 14 and the power storage unit 12. The power stabilization device 10 mitigates fluctuations in the composite power P3 by adjusting the input/output power P2 from the power storage unit 12.

The control unit 20 sets at least one of the set upper limit value Pupper and the set lower limit value Plower for the combined 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 the power limit value Preg. The power limit value Preg may be the power limit value in the configuration between the power storage unit 12 and the power grid 2, or may be the power limit value of the power storage unit 12 itself. In this example, the power limit value Preg is the rated power (W) (referred to as the PCS rating) of the power conversion unit 13 (PCS) provided between the power storage unit 12 and the power grid 2.

The control unit 20 shown in FIG. 1 includes a first calculation unit 21, a second calculation unit 22, a memory 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.

In one example, the first calculation unit 21 calculates a predicted value that the output power P1 of the variable power source 14 can take during the period until 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 that indicates the upper limit that can be taken with a predetermined probability within the period, or a predicted lower limit value Pmin that indicates the lower limit that can be taken with a predetermined probability within the period. 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.

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 from 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 actinometer 17. However, if the available output power of the variable power source 14 is not used, the actinometer 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 actinometer 17 and the anemometer 18 can also be omitted.

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 memory unit 23 stores various data and parameters. In this example, the memory unit 23 may store data on the correlation between power (output power P1, the available output power of the variable power source 14, or composite power P3) and changes in power over a predetermined time period. The memory unit 23 may also store a power limit value in advance.

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. The 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, short-cycle fluctuation countermeasure limiter 25, and long-cycle fluctuation countermeasure limiter 26. Note that control by the long-cycle fluctuation countermeasure limiter 26 and short-cycle fluctuation countermeasure limiter 25 may take priority over control by the power limit value limiter 24.

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.

Figure 2 is a diagram showing the processing performed by the power stabilization device 10 in the first comparative example. Figure 3 is a diagram showing the processing performed by the power stabilization device 10 in the first embodiment of the present invention. As shown in Figures 2 and 3, the control unit 20 performs long-term fluctuation mitigation control to mitigate temporal fluctuations in the composite power P3 during a specified time period. In Figures 2 and 3, the control unit 20 at least performs control to prohibit a decrease in the composite power P3 during a specified time period from time T1 to T2. In Figures 2 and 3, short-term fluctuation mitigation control is not performed.

In the comparative example in Figure 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 lower the value of the combined power P3. Therefore, the power P2, which is the difference between the combined power P3 and the output power P1 of the variable power source 14 (P3 - P1), becomes large. 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.

In the first example 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 possible output power P1 of the variable power source 14 during the period from the current time to the end time T2 of the specified time period (between T1 and T2) for mitigating temporal fluctuations in the composite power P3.

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 within the specified time period to a value equal to or less than the value (Preg + Pmin) obtained by adding the power limit value Preg to the predicted lower limit value Pmin. Outside the specified time period, the set upper limit value Pupper may be set to the rated power value of the composite 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 Puper, the difference in power obtained by subtracting the set upper limit value Puper from the output power P1 may be charged to the power storage unit 12.

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

In the second comparative example in Figure 4, the set lower limit value Plower is not set. Therefore, the minimum value of the composite 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 composite power P3. Therefore, the power P2, which is the difference between the output power P1 of the variable power source 14 and the composite power P3 (P1 - 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.

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

The second calculation unit 22 calculates the set lower limit value Plow for the specified 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 Plow for the specified 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 Plow for periods other than the specified time period to 0. The control unit 20 sets the set lower limit value Plow for the specified 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 Plow for the specified 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).

The configurations shown in Figures 3 and 5 can 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 grid 2 and the power limit value of the power storage unit 12 itself.

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.

Next, we will explain when the control unit 20 performs short-term fluctuation mitigation control and long-term fluctuation mitigation control.

Figure 6 is a diagram showing the processing performed by the power stabilization device in the third comparative example. Figure 7 is a diagram showing the processing performed by the power stabilization device in the third embodiment of the present invention. In Figures 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 at all times. As shown in Figure 6, the composite power P3 smoothed by 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 between the composite power P3 and the output power P1 of the variable power source 14 (P3 - P1), 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 long-period fluctuation mitigation control due to the power limit value Preg.

As shown in FIG. 3, the control unit 20 sets the set upper limit value Pupper to the rated composite power P3 outside the designated time period, and can change the set upper limit value Pupper to, for example, the power limit value Preg at the start time T1 of the designated time period. However, when applying the control shown in FIG. 3, 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 value 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.

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 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 upper limit value Pupper of the composite power P3 so that it satisfies the following equation: "Set upper limit value Pupper of the composite power P3 = Preg (in one example, PCS rating) + length of time until the start of the designated time period × power change rate in short-cycle fluctuation mitigation control." Alternatively, during the preparation stage before the start of the designated time period, the second calculation unit 22 may calculate the set upper limit value Pupper so that it satisfies the following equation: "Set upper limit value Pupper of the composite power P3 = (Preg (in one example, PCS rating) + Pmin) + length of time until the start of the designated time period × power change rate in short-cycle fluctuation mitigation control." The output change rate in short-cycle 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).

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

During the preparation period, the smoothed composite power target value P3a is output in the interval (the interval from Ts to Tc) where the composite power P3 smoothed by short-cycle fluctuation mitigation control is less than the set upper limit value Pupper. On the other hand, when the smoothed composite power P3 exceeds 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.

As shown in Figures 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 that it satisfies the following equation: "Plower: Set lower limit value of composite power P3 = (Pmax - Preg) - Length of time until the start of the designated time period x Power change rate in short-cycle fluctuation mitigation control." Alternatively, in the preparation stage before the start of the designated time period, the second calculation unit 22 may calculate the set lower limit value Plower so that it satisfies the following equation: "Plower: Set lower limit value of 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 short-cycle fluctuation mitigation control."

The control shown in Figure 7 allows short-term fluctuation mitigation control to be constantly performed while keeping the combined power within an appropriate range during the specified time period.

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

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 also 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.

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) depending on 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 the dashed line) within the specified time period (the time from T1 to T2) depending on 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 dashed 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 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 indicated by the dashed dotted line. The second calculation unit 22 may control the set upper limit value Pupper so that it periodically fluctuates and the average value of the set upper limit value Pupper increases as the remaining time of the specified time period decreases.

In one example, the first calculation unit 21 acquires the output power P1 (renewable energy output power) of the variable power source 14 prior to the current time and stores it in the memory unit 23. The first calculation unit 21 may input the output power P1 of the variable power source 14 prior to the current time 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 during a predetermined period prior to the current time, the minimum value calculation is a process of acquiring the minimum value during a predetermined period prior to the current time, and the median value calculation is a process of acquiring the median value during a predetermined period prior to the current time.

As shown in FIG. 8, when the control unit 20 at least executes control to prohibit a decrease in the composite power P3 during the specified time period, the first calculation unit 21 estimates a power change (power decrease) during the specified 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 specified time period decreases, the likelihood that the power P1 will decrease decreases, and therefore the estimated power decrease becomes smaller.

Figure 10 is a scatter plot showing an example of power changes when the remaining time in the specified time period is 10 minutes. Figure 11 is a scatter plot showing an example of power changes when the remaining time in the specified time period is 30 minutes. In Figures 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 for the remaining time in the specified time period. The power reduction in output power P1 varies depending on the length of time remaining in the specified time period. When the remaining time (time window) in the specified time period is 30 minutes, there is greater variation than when the remaining time (time window) in the specified time period 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 power P1 within the remaining time, is greater.

Figure 12 shows the cumulative frequency of power reductions based on the remaining time of the specified time. In Figure 12, if power reduction is guaranteed at a cumulative frequency of 99.7% or more, as shown in Figure 12, the power reduction increases as the time increases.

Figure 13 is a diagram showing an example of the correlation between the remaining time of a specified time period and power reduction. In Figure 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 longer the remaining time, the higher the probability of power reduction Pd. Note that a function F(T) showing the correlation between the current output power P1 of the variable power source 14 and power reduction Pd may be set based on actual data (dotted line). In this case, function F may be designed so that it is always larger at any given time than the curve (dotted line) of the power reduction to be compensated for based on actual data. Function F may be composed of a linear function and a portion that saturates at a power reduction of 100%.

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, as described in Figures 10 to 13, 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 prior to the current time and the change in the output power P1 over a predetermined time period.

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.

As the remaining time of the specified time period shortens, the power drop Pd decreases. Therefore, as the remaining time of the specified time period shortens, the predicted lower limit Pmin (output power P1 of the variable power source 14 - power drop Pd) increases. When the predicted lower limit Pmin (output power P1 of the 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 area in Figure 8) decreases, particularly in the latter half of the specified time period rather than the middle. As a result, the amount of power that cannot be fully charged in the power storage unit 12 decreases, reducing power generation losses.

When control prohibiting a decrease in composite power P3 during a specified time period is at least executed, even if the output power P1 of the variable power source 14 decreases during the specified time period and the set upper limit value Puper 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 Puper may fall below the composite power P3. However, the set upper limit value Puper means that the composite power P3 may be increased up to this value. Meanwhile, the long-period fluctuation countermeasure limiter 26 in Figure 1 executes control prohibiting a decrease in 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 Puper as its upper limit. This gives priority to control prohibiting a decrease in composite power P3.

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.

Figure 14 is a diagram showing the processing performed by a power stabilization device according to a fifth embodiment of the present invention. Figure 15 is another example of the processing performed by a power stabilization device according to a second embodiment of the present invention. In the second embodiment described in Figure 5, as shown in Figure 15, if the output power P1 of the variable power source 14 does not increase beyond "total power P3 rated (power plant rated) - power limit value Preg," the power storage unit 12 must discharge the amount of power indicated by the diagonally hatched portion in Figure 15. In this way, if the set lower limit value Plower for 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 power discharged from the power storage unit 12 will increase.

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 specified time period (the time from T1 to T2) depending on the remaining time of the specified time period. More specifically, the first calculation unit 21 changes the predicted upper limit value Pmax to decrease 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 upper limit value Pmax to also fluctuate periodically, while controlling the average value of the predicted lower limit value Pmax to decrease as the remaining time of the specified time period decreases. The second calculation unit 22 may change the set lower limit value Plower to decrease as the remaining time of the specified time period decreases, as shown by the one-dot chain line. The second calculation unit 22 may control the set lower limit value Plower so that the average value of the set lower limit value Plower decreases as the remaining time of the specified time period decreases while the set lower limit value Plower fluctuates periodically.

In one example, the first calculation unit 21 acquires the output power P1 (renewable energy output power) of the variable power source 14 prior to the current time and stores it in the memory unit 23. The first calculation unit 21 may input the output power P1 of the variable power source 14 prior to the current time 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 during a predetermined period prior to the current time, the minimum value calculation is a process of acquiring the minimum value during a predetermined period prior to the current time, and the median value calculation is a process of acquiring the median value during a predetermined period prior to the current time.

As shown in FIG. 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 the 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 of an increase in power P1 decreases, and therefore the estimated power increase decreases.

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 prior to the current time and the change in the output power P1 over a predetermined time period, as described in Figures 10 to 13.

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 (the 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.

As the remaining time of the specified time period shortens, the power increase Pi decreases. Therefore, as the remaining time of the specified time period shortens, 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 less 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 area in Figure 14) decreases, particularly from the middle to the latter half of the specified time period. As a result, the decrease in the charge rate of the power storage unit 12 can be mitigated.

Note that, at least when control prohibiting an increase in the composite power P3 during a specified time period is executed, even if the output power P1 of the variable power source 14 increases during the specified time period and the set lower limit value Plow 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 Plow may exceed the composite power P3. However, the set lower limit value Plow means that the composite power P3 may be lowered up to this value. Meanwhile, the long-period fluctuation countermeasure limiter 26 in Figure 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 Plow as its lower limit. This gives priority to control prohibiting an increase in the composite power P3.

The first calculation unit 21 may predict 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 predict 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 time period. The first calculation unit 21 may also predict the predicted lower limit value Pmax based on the correlation between the composite power P3 and changes in the composite power P3 within each time period.

Figure 16 is a conceptual diagram showing an example configuration of a power generation system 1 according to another embodiment of the present invention. In the power stabilization device 10 described in Figures 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 Figure 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 Puppor 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 configuration is the same as that described in Figures 1 to 15, and therefore will not be described again.

Figure 17 is a conceptual diagram showing an example configuration of a power generation system 1, which is another embodiment of the present invention. The technologies described in JP 2018-161041 A, JP 2019-115131 A, and JP 2018-038132 A, which are cited as prior art, may be used together with the technologies described in Figures 1 to 16.

The power stabilization device 10 shown in FIG. 17 includes a composite power reserve value calculation unit 29. The composite power reserve value calculation unit 29 in the control unit 20 calculates the composite power reserve value based on the dischargeable energy of the power storage unit 12, enabling control to prohibit a decrease 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 upper limit value Pupper to the smaller of the composite power reserve value or the value (Preg + Pmin) obtained by adding the power limit value Preg to the predicted lower limit value Pmin.

The control unit 20 may calculate a composite power reserve value based on the amount of chargeable energy in the power storage unit 12, enabling control to prohibit an increase in the composite power P3 during a specified time period even if 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.

The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be clear 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.

1... Power generation system, 2... Power grid, 3... Interconnection point, 4... Transformer, 6... Transformer, 10... Power stabilization device, 12... Power 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-term fluctuation countermeasure limiter, 26... Long-term fluctuation countermeasure limiter, 27... Command value calculation unit, 28... Power conversion unit control unit, 29... Composite power reserve value calculation unit

Claims (14)

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 according to a power limit value between the power storage unit and the power grid and in either the power storage unit. The power stabilizing device according to claim 1 , wherein the control unit sets the lower limit value so that the set lower limit value decreases as the power limit value increases. 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 . 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 . 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. 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. 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. 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. 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. 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. 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. 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 . 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 . The power stabilization device described in any one of claims 1 to 12, wherein the power limit value is a value of the chargeable and dischargeable power of the power storage unit that varies depending on at least one of the ambient temperature of the power storage unit and the charge amount of the power storage unit.