Power control device and power control method

Abstract

To provide a power control device avoiding destabilization due to a sudden change of renewable energy generation power.SOLUTION: A power control device can control a plurality of power conversion devices supplying power generated by using renewable energy to a power system, and has the power conversion device performing a first control using a part of the generated power for inertia supply and a second control not using the generated power for the inertia supply, a surplus inertia calculating unit obtaining surplus of inertia supplied to the power system, a control determination unit determining the first control and the second control based on the surplus of inertia obtained by the surplus inertia calculating unit per power conversion device, and a control transmission unit transmitting an operation control determined by the control determination unit to each power conversion device.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In order to achieve carbon neutrality by 2050, countries around the world are working to reduce greenhouse gas emissions. As a result, the introduction of solar power generation is progressing rapidly. If the number of solar power generation systems connected to the grid increases and the number of synchronous generators such as thermal power generation systems decreases, the inertia that maintains the grid frequency provided by the synchronous generators decreases, and when a power source trips, the grid frequency fluctuations become large, causing the grid to become unstable.

[0003] In order to maintain the inertia of the grid, the provision of inertia by a grid forming inverter (GFI), which is a power conversion device, is being considered. When the grid frequency fluctuates, the GFI inputs and outputs power to the grid to suppress the frequency fluctuation of the grid and provide inertia. The power that the grid forming inverter uses to supply inertia to the grid includes power from storage batteries, power from solar power generation equipped with small-capacity storage batteries, and power from solar power generation without storage batteries.

[0004] As the cost of storage batteries is high, there is a demand for a grid-forming inverter that uses electricity from photovoltaic power generation without the large number of storage batteries already installed.Patent Document 1 shows that in a GFI that uses electricity from photovoltaic power generation without a storage battery, in order to supply inertia to the grid, photovoltaic power generation does not generate electricity at the maximum power point, but generates electricity with a margin for increase. Regarding changes in inverter operation based on system inertia, Patent Document 2 shows a system that monitors the inertia of the system, judges the stability of the power system, decides whether or not to supply power based on the results of that judgment, and changes the setting value of the solar power generation inverter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-25394 A [Patent Document 2] JP 2019-201453 A Summary of the Invention [Problem to be solved by the invention]

[0006] In a grid-forming inverter that uses power from photovoltaic power generation without a storage battery, the photovoltaic power generation generates power with a guaranteed boost in order to supply inertia to the grid as described in Patent Document 1, so there is an issue that the amount of power generated is reduced compared to when power is generated at the maximum power point.

[0007] The system shown in Patent Document 2, which monitors the inertia of the system, determines the stability of the power system, and changes the setting value of the solar power generation inverter, changes the setting value when the system becomes unstable due to a system accident, etc., and does not solve the problem of a decrease in power generation due to the supply of inertia to the system when the system is stable.

[0008] In addition, because the grid-forming inverter performs AC voltage control, the grid-forming inverter using power from photovoltaic power generation and not equipped with a storage battery as shown in Patent Document 1 has the problem that when the amount of power generated by photovoltaic power generation suddenly changes, the voltage on the DC side becomes unstable, causing the control of the grid-forming inverter to become unstable. These problems are also the same for grid-forming inverters using power from wind power generation and not equipped with a storage battery.

[0009] The system in Patent Document 2 monitors the inertia of the power system, etc., to judge the stability of the power system, and based on the results of that judgment, decides whether or not to supply power, and changes the setting value of the solar power generation inverter. However, since the setting value is changed only when the system becomes unstable, the problem of system instability is not solved.

[0010] It is important to provide a power control device for a power conversion device that increases the power generation of renewable energy sources such as solar power generation and wind power generation that are controlled by a grid-forming inverter while ensuring the inertia required for the power grid, and prevents destabilization of the control of the grid-forming inverter due to sudden changes in the power generation of solar power generation, wind power generation, etc.

[0011] An object of the present invention is to provide a power control device that increases the power generated by renewable energy sources such as solar power generation and wind power generation by controlling a grid-forming inverter while ensuring the inertia required for the grid, and additionally to provide a power control device that avoids instability due to a sudden change in the power generated by renewable energy sources. [Means for solving the problem]

[0012] The object of the present invention is achieved by a power control device capable of controlling a plurality of power conversion devices that supply power generated using renewable energy to a power system, the power control device comprising: power conversion devices that perform a first control that uses a portion of the generated power for inertial supply and a second control that does not use the generated power for inertial supply; a surplus inertia calculation unit that calculates the surplus inertia to be supplied to the power system; a control decision unit that decides the first control and the second control for each power conversion device based on the surplus inertia calculated by the surplus inertia calculation unit; and a control transmission unit that transmits the operation control decided by the control decision unit to each power conversion device. Effect of the Invention

[0013] According to the present invention, it is possible to provide a power control device that avoids instability due to a sudden change in power generated from renewable energy. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a configuration of a plurality of GFIs connected to a grid and a power control device that controls the GFIs in an embodiment of the present invention. [Diagram 2] 4 is a flowchart showing a process of a power control device according to an embodiment of the present invention. [Figure 3(a)] 1 is a graph showing an example of a predicted power generation amount under MPPT control and a predicted power generation amount under GFI control of a solar power generator in an embodiment of the present invention. [Figure 3(b)] 1 is a graph showing an example of a predicted power generation amount under MPPT control and a predicted power generation amount under GFI control of a solar power generator in an embodiment of the present invention. [Figure 3(c)] 1 is a graph showing an example of a predicted power generation amount under MPPT control and a predicted power generation amount under GFI control of a solar power generator in an embodiment of the present invention. [Figure 4] 11 is a graph showing an example of a predicted result of the inertia of a synchronous generator, the inertia of a solar generator, and the excess inertia in an embodiment of the present invention. [Diagram 5] 1 is a graph showing an example of a power generation amount of a GFI control of a solar power generator, a power generation amount of a MPPT control, and a control plan of the solar power generator derived by a mixed integer linear programming method in an embodiment of the present invention. [Figure 6] 4 is a graph showing the amount of power generated by a solar power generator with and without excess inertia in an embodiment of the present invention. [Figure 7] 4 is a flowchart showing a process of a power control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a power control device for a power converter according to the present invention will be described in detail with reference to the drawings. EXAMPLES

[0016] A power control device for a power converter according to a first embodiment will be described with reference to FIGS. 1 to 6. FIG.

[0017] FIG. 1 is a block diagram showing the configuration of a plurality of GFIs connected to a power grid and a power control device that controls the GFIs in an embodiment of the present invention.

[0018] A plurality of power conversion devices (GFI) 103 are connected to a power system 102, and a photovoltaic power generator (PV) 104 is connected to each of the power conversion devices 103. A power control device 101 for the power conversion device, which controls the plurality of power conversion devices 103, is connected via a control signal line 108. The control unit of the power control device 101 for the power conversion device is made up of a surplus inertia calculation unit 105, a control decision unit 106, and a control transmission unit 107. The power conversion device 103 is a grid forming inverter that can supply inertia to the system.

[0019] The power control device 101 is realized by a computer equipped with a CPU (Central Processing Unit), a main memory device, an external memory device, and an input / output unit. In this embodiment, an example of realizing the power control device 101 by a stand-alone computer will be described, but the power control device 101 may be realized as a server on a cloud.

[0020] FIG. 2 is a flowchart showing the process of the power control device in the embodiment of the present invention.

[0021] In the first steps S1 to S4, the surplus inertia calculation unit 105 predicts the inertia of the system. In S1, a daily power generation plan of a synchronous generator such as a thermal power plant connected to the target system is acquired. The power generation plan is obtained from a system operator, an operator of the synchronous generator, or an organization such as the Organization for Cross-regional Coordination of Transmission Operators (OCCTO). Information obtained from the power generation plan is the presence or absence of power generation and the power generation capacity for each time period of the day.

[0022] In S2, the inertia to be supplied to the system for each synchronous generator per day is predicted based on the power generation plan of the synchronous generator imported in S1. The inertia is calculated by multiplying the inertia constant, which is calculated from the mass, size, rotation speed, etc. of the turbine rotor of each synchronous generator, by the power generation capacity. The inertia constant is a value calculated in advance for each synchronous generator, and the power generation capacity is taken from the power generation plan.

[0023] In addition to the synchronous generators and grid forming inverters, there are devices that supply inertia to the grid. If the inertia is large enough to not be negligible, the plans for the devices and inertia predictions are also performed in S1 and S2.

[0024] In S3, the predicted amount of solar radiation at the location where the solar power generator is installed is imported. For example, the solar radiation prediction is provided as a solar radiation prediction service for solar power generation. Instead of the predicted amount of solar radiation, the predicted amount of power generation may be provided.

[0025] If the generator is a wind turbine, the forecast is for the wind power at the location where the wind turbine is installed, and it is necessary to use predicted weather information depending on the type of renewable energy used for power generation.

[0026] In S4, the surplus inertia calculation unit 105 uses the predicted solar radiation at the location where the solar power generator is installed, which was acquired in S3, to calculate the predicted power generation amount of the solar power generation. Specifically, the predicted power generation amount is calculated by multiplying the predicted solar radiation amount by the system capacity of the solar power generator and the system output coefficient (corresponding to the loss coefficient that indicates the loss of the power generation amount).

[0027] Alternatively, the predicted power generation amount may be calculated from the predicted amount of solar radiation using the past relationship between the amount of solar radiation and the amount of power generation by the solar power generator.

[0028] The predicted power generation amount calculated here is the amount of power generation when solar power generation is performed under control at the maximum power point (MPPT (Maximum Power Point Tracking) control).

[0029] Furthermore, in addition to the amount of power generated under MPPT control, the inertia provided to the grid and the amount of power generated by solar power are also predicted when control that provides inertia to the grid (GFI control) is performed using the power generated by the predicted MPPT control.

[0030] This prediction uses the relationship between the power generation amount under MPPT control set for each power conversion device and the grid supply inertia and power generation amount under GFI control. Here, S3 may be provided with data on predicted power generation amount instead of data on predicted solar radiation amount. In that case, S4 predicts the inertia and power generation amount to be provided to the grid under GFI control using the predicted data on power generation amount taken in S3.

[0031] Figure 3 shows an example of the predicted power generation amount of the photovoltaic generator under MPPT control and GFI control calculated in S3 and S4. The horizontal axis is time, the vertical axis is the predicted power generation amount, the thick line of the graph is the predicted power generation amount under MPPT control, and the thin line is the predicted power generation amount under GFI control.

[0032] Here, the predicted power generation amount for one day from midnight to midnight is calculated at one-minute intervals, but the period can be one hour instead of one day, and the time interval can be every 30 minutes instead of every minute. A shorter period allows for higher prediction accuracy, while a longer period allows for an increase in power generation amount using data from a longer period.

[0033] Also, a shorter time interval makes predictions more difficult, but allows more data to be used to generate more electricity.

[0034] Figures 3(a) to (c) show examples of different weather conditions at the location where the solar power generator is installed: (a) is clear, (b) is cloudy, and (c) is sunny with occasional clouds.

[0035] The amount of power generated under MPPT control on a clear day (a) is simply a stable amount of power generated; as the sun rises towards midday, the amount of solar radiation increases and the amount of power generated increases, and as the sun sets, the amount of solar radiation decreases and the amount of power generated decreases.

[0036] The amount of power generated by GFI control is less than that by MPPT control because there is a need to secure a margin for increasing the amount of power generated to supply inertia to the grid.

[0037] On a cloudy day (b), the amount of solar radiation reaching the solar generator is low, and the amount of power generated by MPPT control is less. As with (a), the amount of power generated by GFI control is less than that by MPPT control because a boost is required to supply inertia to the grid. If the amount of power generated is low and the boost cannot be secured, the inertia that can be supplied to the grid will be reduced.

[0038] (c) In the case of sunny with occasional clouds, the amount of electricity generated decreases as the clouds pass over the solar panel, and then increases once the clouds have finished passing over the panel, resulting in a sudden change in the amount of electricity generated.

[0039] It is not easy to predict the time when power generation will suddenly change down to the minute, but it is possible to predict when sudden changes in power generation will occur due to the passage of clouds.

[0040] When the amount of power generated changes suddenly, the power used by the GFI control changes suddenly, which can cause the GFI control to become unstable. Also, when the GFI control follows a sudden change in the amount of power generated, the amount of power generated by the GFI control may decrease by more than the allowance secured during steady state. Therefore, it is desirable to determine the amount of power generated by the GFI control by taking into account the characteristics of the GFI control.

[0041] Returning to Fig. 2, in S5, the surplus inertia calculation unit 105 calculates the surplus inertia of the grid. The surplus inertia is calculated by subtracting the required inertia of the grid from the total inertia of the grid. The total inertia of the grid is calculated as the sum of the inertia of the synchronous generators calculated in S2 and the sum of the inertia supplied to the grid when the power conversion device of the photovoltaic generator performs GFI control calculated in S4.

[0042] If there is any device that supplies inertia to the grid other than the synchronous generator and the grid forming inverter, the inertia supplied by this device is also added to the total inertia.

[0043] The required inertia is the inertia required for the system frequency to fall within an allowable range (for example, 50 Hz ± 0.2 Hz) when an accident such as a hypothetical power supply failure occurs, and is determined in advance by system analysis, etc.

[0044] Figure 4 shows an example of the predicted results of inertia and excess inertia obtained in S1 to S5 in Figure 2. The horizontal axis represents the time of day from midnight to midnight, and the vertical axis represents the inertia of the system. The inertia of the synchronous generators indicated by the diagonal lines in the figure is the sum of the inertia of the synchronous generators obtained in S2, and the inertia of the photovoltaic generators added on top of the inertia of the synchronous generators from 6:00 to 18:00 in the figure is the inertia of the photovoltaic generators, which is the sum of the inertia of the GFI control of photovoltaic power generation obtained in S4.

[0045] In the figure, the inertia supplied by the storage battery is added to the inertia of the synchronous generator from 0:00 to 6:00 and from 18:00 to 24:00.

[0046] The required inertia used in S5 is shown by the dotted line in the figure. The sum of the inertia of the synchronous generators and the inertia of the GFI control of the solar power generation exceeds the required inertia, which becomes the surplus inertia. This surplus inertia is used to increase the amount of power generated by the solar power generation.

[0047] In addition, if the sum of the inertia of the synchronous generators and the inertia of the solar power generation falls below the required inertia, the total inertia of the system will meet the required inertia using the inertia provided by the grid-forming inverter of the storage battery.

[0048] Returning to FIG. 2 again, in S6, the control decision unit 106 judges whether there is excess inertia. In other words, it judges whether the excess inertia found in S5 is positive. If there is excess inertia, the control decision unit 106 formulates a plan for control of the power conversion device 103 in S7. Here, it is determined whether the control of each of the multiple power conversion devices 103 connected to the grid should be GFI control or MPPT control, so that the total amount of power generated by the photovoltaic generators increases within a range in which the excess inertia does not become negative. In S8, in accordance with the formulated plan, the control transmission unit 107 sends a control change command to the power conversion device 103 that will perform the control change.

[0049] In the case of a system in which many photovoltaic power converters 103 are connected, it is advisable to formulate a plan to maximize the total amount of power generated by the photovoltaic power generators using mixed integer linear programming. Mixed integer linear programming is an optimization method for finding setting variables that maximize (or minimize) an objective function under certain setting constants and constraint conditions.

[0050] Specifically, the control decision unit 106 formulates a plan for maximizing the total amount of power generated by photovoltaic power generation using mixed integer linear programming as follows.

[0051] First, the set constants are the total inertia provided to the grid by the synchronous generators iner_SyncGen(i) calculated in S2, the power generation amount P_PV_MPPT(n,i) under MPPT control of the solar generator calculated in S4, the power generation amount P_PV_GFI(n,i) under GFI control of the solar generator, the inertia provided to the grid iner_GFI(n,i) under GFI control of the solar generator, the required inertia iner_Sys(i) used in S5, the power loss P_loss_change(n) generated when changing between MPPT control and GFI control of the solar generator, and a flag flag_change(n,i) indicating that MPPT control and GFI control of the solar generator have been changed.

[0052] Hereafter, n is a number assigned to each solar power generator, and i is the time of day expressed as an integer value. If data is taken every minute, i can take an integer value between 1 and 86400. The above setting constants are expressed as a function of both n and i, or either one of them.

[0053] The setting variable is the control variable for the solar power generator, cntl_GFI(n,i), which takes the value 1 when the solar power generator is under GFI control and takes the value 0 when the solar power generator is under MPPT control.

[0054] The constraint is iner_SyncGen(i)+Σiner_GFI(n,i)-iner_Sys(i)≧Σ((1-cntl_GFI(n,i))·iner_GFI(n,i)).

[0055] The left-hand side of the formula is the total system inertia, which is the sum of the inertia of the synchronous generators in the first term and the sum of the inertia of the GFI of the solar generators in the second term, minus the required inertia in the third term, which corresponds to the surplus inertia.

[0056] The right-hand side represents the sum of inertia provided to the grid by the GFI of a solar power generator that is not performing GFI control and is performing MPPT control when performing GFI control.

[0057] For the GFI of a solar power generator that is not under GFI control but is under MPPT control, the right-hand side (1-cntl_GFI(n,i)) is 1, and the inertia of that GFI is added. In other words, this constraint condition means that the control of the GFI of the solar power generator is changed from GFI control to MPPT control within the range of excess inertia.

[0058] The objective function is ΣP_PV_MPPT(n,i) · (1-cntl_GFI(n,i)) + ΣP_PV_GFI(n,i) · cntl_GFI(n,i)-P_loss_change(n) · flag_change(n,i).

[0059] The first term is the total power generation of the solar power generators under MPPT control, the second term is the power generation of the solar power generators under GFI control, and the third term is the power loss that occurs when switching between MPPT control and GFI control. In addition, the optimization calculation is determined by the solar power generator control cntl_GFI(n,i), which is a set constant, so that this objective function is maximized.

[0060] FIG. 5 is a graph showing an example of the power generation amount of the GFI control of the solar power generator, the power generation amount of the MPPT control, and a control plan of the solar power generator derived by the mixed integer linear programming method in the embodiment of the present invention.

[0061] For each of the photovoltaic generators 1 to 6, the thick line indicates the amount of power generated by MPPT control, the thin line indicates the amount of power generated by GFI control, and the dotted line indicates the result of the determination of whether or not GFI control is required. When the dotted line value is 0, it is determined that GFI control is not performed, and when the value is 1, it is determined that GFI control is performed.

[0062] For photovoltaic generators n=1 to 6 connected to the target grid, the left vertical axis shows the power generation amount P_PV_MPPT(n,i) under MPPT control used to maximize power generation using mixed integer linear programming, and the power generation amount P_PV_GFI(n,i) under GFI control of the photovoltaic generator, while the right vertical axis shows an example of the photovoltaic generator control cntl_GFI(n,i) obtained as a result of maximizing power generation using mixed integer linear programming.

[0063] The horizontal axis of the graph is the integer i, which represents the time every minute from 0:00 to 24:00. The photovoltaic generators n=1 to 6 are installed in different locations, have different weather conditions at those locations, and have different rated power generation capacities, so the power generation amount P_PV_MPPT(n,i) under MPPT control is different.

[0064] The power generation amount P_PV_GFI(n,i) under GFI control is smaller than the power generation amount P_PV_MPPT(n,i) under MPPT control by the amount of the boost required to provide inertia. When the control cntl_GFI(n,i) of these photovoltaic generators is 0, the photovoltaic generators perform GFI control, and when it is 1, the photovoltaic generators perform MPPT control.

[0065] By controlling this cntl_GFI(n,i), the amount of power generated by the solar power generator can be maximized.

[0066] FIG. 6 is a graph showing the amount of power generated by a solar power generator with and without excess inertia in an embodiment of the present invention.

[0067] The horizontal axis is time and the vertical axis is the total amount of power generated by multiple solar power generators. The thick line in the graph shows the total amount of power generated by the solar power generators when excess inertia is utilized to maximize the amount of solar power generated, and the thin line shows the total amount of power generated by the solar power generators when excess inertia is not utilized.

[0068] Comparing the two, the total amount of power generated by the former exceeds that of the latter, and it can be seen that power generation can be increased by maximizing the amount of solar power generated by utilizing surplus inertia. In this case, an increase in power generation of just over 4% was achieved.

[0069] Next, a power control device for a power conversion device that has an added function of avoiding instability of GFI control due to a sudden change in the amount of power generated by a solar power generator will be described.

[0070] In the case of the solar power generator shown in Fig. 3(c), the amount of power generated changes suddenly and repeatedly due to the passage of clouds. When such a sudden change in the amount of power generated is predicted, the excess inertia changes the control of the power conversion device of the solar power generator to MPPT control as a priority.

[0071] In the case of mixed integer linear programming, a variable β(n,i) representing a sudden change in power generation is added to the setting variables, and if there is no sudden change in power generation based on the power generation prediction, the variable is set to 1, and if a sudden change in power generation is predicted, the variable is set to a value greater than 1, for example 2.

[0072] The objective function is ΣP_PV_MPPT(n,i) · (1-cntl_GFI(n,i)) · β(n,i) + ΣP_PV_GFI(n,i) · cntl_GFI(n,i)-P_loss_change(n) · flag_change(n,i), and the first term is multiplied by β(n,i).

[0073] In this way, when a fluctuation in the amount of power generation is predicted, it becomes easier to select MPPT control, and destabilization of GFI control due to a sudden change in the amount of power generation can be avoided.

[0074] As shown in Figure 3(a), if GFI control is performed to prioritize solar power generators for which clear skies are expected, the inertia that can be supplied per solar power generator will be large, enabling more stable operation. EXAMPLES

[0075] A power control device of a power conversion device according to a second embodiment will be described with reference to Fig. 7. The power control device of the power conversion device according to the first embodiment formulates a control plan for the power conversion device so as to increase the total power generation amount of the photovoltaic power generator by using the surplus inertia predicted in advance, and controls the power conversion device, whereas the power control device of the power conversion device according to the second embodiment determines the control of the power conversion device to successively increase the power generation amount of the photovoltaic power generation by using the surplus inertia estimated in real time, and controls the power conversion device.

[0076] Hereinafter, differences between the power control device for the power conversion device of the first embodiment will be described.

[0077] FIG. 7 shows a control flow of the power control device of the power conversion device of the second embodiment.

[0078] First, in S9 to S12, the inertia of the grid is estimated in real time. In S9, the surplus inertia calculation unit 105 takes in real time power generation information of a synchronous generator such as a thermal power generator connected to the grid. The power generation information is obtained from a grid operator or a synchronous generator operator.

[0079] In S10, the surplus inertia calculation unit 105 calculates real-time inertia based on the real-time power generation information of the synchronous generator acquired in S9 in the same manner as in the embodiment 1. If there is a device supplying inertia to the system other than the synchronous generator and the grid forming inverter, and the inertia is large enough not to be ignored, the operating status of the device supplying inertia is acquired in real time in S9 and S10 to calculate the inertia.

[0080] In S11, the surplus inertia calculation unit 105 takes in the real-time power generation amount of the photovoltaic generator and the control state of GFI control or MPPT control. In S12, in the case of GFI control, the inertia provided to the grid in real time under GFI control and the power generation amount when switched to MPPT control are calculated from the real-time power generation amount in the case of GFI control.

[0081] In the case of MPPT control, the amount of power generated when switching to GFI control and the inertia provided to the grid under GFI control are calculated from the amount of power generated in real time. In this case, as in the first embodiment, the relationship between the amount of power generated under MPPT control set for each power conversion device and the inertia and amount of power generated to be supplied to the grid under GFI control is used.

[0082] In S13, the real-time excess inertia of the system is calculated by subtracting the required inertia of the system from the total inertia of the system in real-time.

[0083] The total inertia of the system in real time is calculated by adding the sum of the real-time inertia of the synchronous generators calculated in S9 and the sum of the real-time inertia when the power conversion device of the photovoltaic generator is under GFI control calculated in S11. If there is any device that supplies inertia to the system in addition to the synchronous generator and the grid forming inverter, the real-time inertia of the device that supplies inertia is added to this sum.

[0084] As in the first embodiment, the required inertia is the inertia required for the system frequency to fall within an allowable range (e.g., 50 Hz ± 0.2 Hz) when an accident such as a predicted power supply failure occurs, and is calculated in advance by system analysis or the like.

[0085] In S14, the control decision unit 106 determines whether there is surplus inertia in real time, i.e., whether the real-time surplus inertia calculated in S13 is positive. If there is surplus inertia in S14, in S15, a power conversion device that changes control to MPPT control among the power conversion devices of the photovoltaic generators that are performing GFI control so that the total power generation amount of the photovoltaic generators is increased within a range in which the surplus inertia does not become negative is determined.

[0086] When there are multiple solar power generators performing GFI control, the solar power generator is selected so that the increase in power generation resulting from switching to MPPT control will be the largest. In S16, the control transmission unit 107 sends a control change command to the power conversion device that performs the control change according to the control change determined in S15. If there is no excess inertia in S14, the processes of S15 and S16 are skipped.

[0087] In S17, it is determined whether or not it is sunset, and the flow from S9 to S16 is repeatedly executed until the sun sets and the solar power generator stops generating electricity.

[0088] As described above, the real-time inertia of the system is calculated as the sum of the inertia provided to the system by synchronous generators, grid forming inverters, etc. connected to the system. However, the inertia of the system may be calculated from the data by measuring the power flow and phase fluctuations of the system in real time at multiple locations.

[0089] Although a measuring instrument is required for the measurement, it is possible to determine the inertia provided by all devices, not just the main device that provides inertia to the system.

[0090] In the power control device of the power conversion device of the second embodiment, compared to the first embodiment in which a control plan for the power conversion device that increases the amount of power generated by solar power generation is formulated using surplus inertia predicted in advance, the control plan for the power conversion device that sequentially increases the amount of power generated by solar power generation is determined using surplus inertia estimated in real time. Although it is difficult to estimate in real time, it is possible to use surplus inertia without prediction error, and therefore it is possible to further increase the amount of power generated by solar power generation.

[0091] The power control device of the power conversion device of the second embodiment can also be added with a function for avoiding instability of GFI control due to a sudden change in the power generation amount of the solar power generator, as described in the power control device of the power conversion device of the first embodiment.

[0092] When the amount of power generation is suddenly changing in real time, or when a sudden change in the amount of power generation is predicted in the near future, the excess inertia changes the control of the power conversion device of that solar power generator to MPPT control as a priority.

[0093] In the first embodiment, a case has been described in which a plan for controlling a power conversion device that increases the amount of power generated by photovoltaic power generation is formulated using surplus inertia predicted in advance, and in the second embodiment, a case has been described in which a plan for controlling a power conversion device that successively increases the amount of power generated by photovoltaic power generation is determined using surplus inertia estimated in real time, but both may be combined.

[0094] By formulating a plan using the predicted surplus inertia, optimization over a long prediction period is possible, and by using the surplus inertia estimated in real time to sequentially determine the control of the solar power generation power conversion device, it is possible to use the surplus inertia without prediction error, further increasing the amount of power generated by solar power generation.

[0095] The power control devices for the power conversion devices in the first and second embodiments are intended for control of the power conversion devices connected to a grid, but may also be intended for control of a regional microgrid or a microgrid for an office or factory, instead of a grid.

[0096] By targeting a microgrid, it is possible to grasp the excess inertia more easily and more accurately, and it is also possible to more easily control the power conversion device using the excess inertia.

[0097] In the power control devices for the power conversion device of the first and second embodiments, a power conversion device for a solar power generator has been described as an example, but instead of a solar power generator, a generator that can provide inertia to the grid using a grid-forming inverter such as a wind power generator may also be used.

[0098] The power control devices of the power conversion device according to the first and second embodiments described above can provide a power control device for a power conversion device that increases the power generated by renewable energy sources such as solar power generation and wind power generation that control a grid-forming inverter while ensuring the inertia required for the grid, and prevents instability in the control of the grid-forming inverter due to a sudden change in the power generated by solar power generation, wind power generation, etc.

[0099] Furthermore, the embodiment of the present invention described above is merely an example of a method for providing a power control device for a power conversion device that uses excess inertia to increase the amount of power generated by a solar power generator, and is not limited thereto. [Explanation of symbols]

[0100] 101 Power control device 102 Power system 103 Power Converter (GFI) 104 Photovoltaic (PV) generator 105 Excess Inertia Calculation Unit 106 Control decision unit 107 Control transmission section

Claims

1. A power control device capable of controlling a plurality of power conversion devices that supply power generated by using renewable energy to a power grid, a power conversion device that performs a first control in which a part of the generated power is used for inertial supply and a second control in which the generated power is not used for inertial supply; a surplus inertia calculation unit that calculates a surplus inertia to be supplied to the power grid; a control decision unit that decides a first control and a second control for each power conversion device based on the surplus inertia calculated by the surplus inertia calculation unit; and a control transmission unit that transmits the operation control determined by the control determination unit to each of the power conversion devices.

2. The power control device according to claim 1 , wherein the first control is GFI control, and the second control is MPPT control.

3. 2. The power control device according to claim 1, wherein the excess inertia is a difference between a total sum of inertia supplied to the power system and an inertia required to keep the frequency of the power system within a predetermined range.

4. 4. The power control device according to claim 2, wherein the inertia supplied from the power conversion device is determined based on predicted weather information for a location where the power generation device is installed.

5. The power control device according to claim 1, characterized in that when a control decision unit decides on control for each power conversion device to increase the amount of power generation based on surplus inertia, the control decision unit uses the inertia supplied by the power conversion device to the grid when performing the first control, the amount of power generation of the renewable energy when performing the first control, and the amount of power generation of the renewable energy when performing the second control.

6. The power control device according to claim 1 , wherein the control decision unit uses optimization based on mixed integer linear programming when deciding control for each power conversion device so as to increase power generation based on surplus inertia.

7. The power control device according to claim 1 , wherein the control decision unit determines the surplus inertia in real time and decides the control for each power conversion device so as to increase the amount of power generation.

8. 7. The power control system of claim 6, wherein the excess inertia is determined using real-time obtained power flow information.

9. The power control device according to claim 1 , wherein the control decision unit decides to perform the second control by giving priority to a power conversion device in which a sudden change in power generation amount is predicted.

10. The power control device according to claim 1 , wherein the control decision unit decides on the first control by giving priority to a power conversion device that is predicted to have a stable amount of power generation.

11. The power control device according to claim 1 , wherein the renewable energy is renewable energy obtained by solar power generation.

12. The power control device according to claim 1 , wherein the power system is a microgrid.

13. A power control method capable of controlling a plurality of power conversion devices that supply power generated using renewable energy to a power grid, comprising: performing a first control in which a part of the electric power generated by the power conversion device is used for inertial supply and a second control in which the generated electric power is not used for inertial supply; The surplus inertia calculation unit calculates the surplus inertia to be supplied to the power grid, the control decision unit decides between the first control and the second control for each power electronics device based on the surplus inertia calculated by the surplus inertia calculation unit; The control transmission unit transmits the operation control determined by the control determination unit to each power conversion device.

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