Power system inertia grasping device and method

Abstract

To provide useful information for system stabilization while increasing the amount of stoppage of a rotation type generator and increasing the amount of connection of an inverter type generator by correctly understanding the contribution of the simulated inertial force to maintaining the frequency.SOLUTION: The power system inertial grasping device includes an inverter-type power supply in which the electric output is connected to the power system via the inverter and has a simulated inertia function for adjusting electrical output in response to power system fluctuations. The power system inertial grasping device includes: an accident condition setting part that sets accident conditions of an assumed accident in the power system; an inertia performance calculation unit that estimates the amount of change in the inertia of the inverter-type power supply at the time of a hypothetical accident; an area inertia estimation unit that estimates the inertia in an area of the subsystem set in the power system; and an inertia database that stores the amount of change in inertia of the inverter type power supply, or the amount of inertia in the subsystem area or the amount of power control change.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an apparatus and method for grasping the inertia of a power system including power generation and charge / discharge facilities linked to a system via a power converter, and capable of providing useful information for frequency control of the system.

Background Art

[0002] The frequency of a power system is maintained by controlling generation and demand to match each other moment by moment. When the balance between generation and demand is no longer maintained, for example, due to the stoppage of a generator or demand, the frequency fluctuates. If the amount of fluctuation exceeds a certain level, protection is activated to disconnect generation and loads from the system by a protection relay, which may lead to a large-scale power outage. Therefore, it is necessary to quickly perform control such as changing the generation output or interrupting demand in order to maintain the balance between generation and demand (supply-demand balance).

[0003] At this time, for example, the greater the inertial energy (inertia force) of a rotating generator, the slower the change in frequency, the greater the time margin for operations to maintain the supply-demand balance, and the smaller the amount of load (demand) to be interrupted. Also, the greater the inertia present in the system, the smaller the maximum value of the frequency change with respect to the difference between demand and supply (supply-demand imbalance), making it easier to maintain the frequency.

[0004] Here, the rate of change of frequency (RoCoF) is used as an index representing the magnitude of the frequency change per unit time when a supply-demand imbalance occurs. Also, the frequency maximum deviation (Nadir) is used as an index representing the maximum value of the frequency change.

[0005] In recent years, due to system accidents caused by disasters or lightning strikes, generators have fallen off, making it difficult to maintain the frequency and leading to large-scale power outages (e.g., power outages due to the Hokkaido Iburi earthquake and the earthquake off the coast of Fukushima). Also in recent years, the number of inverter-type power generation facilities connected to the grid by power converters (inverters), such as solar power generation and wind power generation, has increased. As a result, the amount of rotational generators stopping has also increased, and the time periods when the inertia of the grid decreases have been increasing.

[0006] When the inertia of the grid decreases, the frequency becomes more likely to change. Therefore, measures may be taken such that the grid is operated so that the inertia is above a certain level. As described above, usually, since inertia is maintained by rotational generators, there may be restrictions where inverter-type solar and wind power generation cannot be connected beyond a certain amount.

[0007] On the other hand, recently, a simulated inertia control function has been developed that gives the transient movement of inverter-type generators (solar, wind) and energy storage facilities a movement with inertia similar to that of rotational generators. It is also possible to give this function to charging facilities, which are inverter-type loads.

[0008] On the other hand, simulated inertia control has the problem that it becomes difficult to simulate inertia as in normal times when the grid voltage drops during a system accident or immediately after accident removal. Therefore, it is important to grasp the degree of inertia maintained due to a system accident and reflect it in the determination of the frequency control amount for achieving power supply-demand balance.

[0009] The voltage drop during a system accident can be grasped by measuring during the accident, but it can also be grasped by transient stability simulations assuming the accident. When grasping the changes in voltage and frequency during a system accident in advance, it is effective to grasp the transient state changes by such transient stability simulations assuming the system accident.

[0010] The operation of the above-mentioned inverter-type generator during a grid fault depends on the control method of the power converter. For example, Non-Patent Document 1 shows the regulations for the Fault Ride Through (FRT) requirement (hereinafter referred to as the "FRT requirement"). According to this regulation, when an inverter-type power source is operated, whether the operation continues immediately after a grid fault depends on the grid state.

[0011] In addition, the grid voltage may fluctuate due to power fluctuations after a grid fault. When the voltage drops, the output of the inverter-type power source may be limited to a power smaller than the rated power due to the constraint of the maximum current capacity of the converter. In such cases, the above-mentioned simulated inertia control may become difficult due to the output constraint.

[0012] In any case, the inertia of the grid will decrease, the frequency change due to the supply-demand imbalance will increase, and more countermeasures (load shedding and generator output change amount) required to maintain the grid frequency will be needed. Also, in the case of load shedding, a decrease in simulated inertia will occur due to the bottoming out of the inverter-type power generation included in the load shedding area, and frequency maintenance control considering such a decrease in inertia will be required.

[0013] For example, Non-Patent Document 2 shows a method for measuring the inertia constant of the grid. Here, the inertia H is defined as in Equation (1). Here, H represents the unit inertia constant (MW·s / MVA), df / dt represents the frequency change rate (Hz / s), and fs represents the fundamental frequency (Hz). [Equation 1] H = 0.5×(ΔP×fn) / (df / dt) (1) Thus, by incorporating control that changes the output according to the change in frequency into the inverter-type power source, simulated inertia control becomes possible.

[0014] For example, Patent Document 1 discloses a method of estimating the power imbalance amount of a local power system to which an electrical station to be monitored belongs by using the rate of change of frequency and the inertia constant of a generator within the local power system to which the electrical station to be monitored belongs, and determining a load limit amount or a power source limit amount according to the estimated power imbalance amount by a predetermined calculation.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Non-Patent Documents

[0016]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0017] The method described in the aforementioned Patent Document 1 shows a method of achieving frequency stabilization of the power system by using the inertia constant of a generator within the local power system, but does not show a method of grasping the amount of simulated inertia of inverter-type power generation equipment or frequency control according to changes in inertia.

[0018] From the above, there is a problem that the inertial force simulated by the inverter-type power source included in the local power system or its area cannot be grasped, and the accuracy of frequency control is reduced.

Means for Solving the Problems

[0019] To solve the above problems, the present invention provides "an inertia grasping device for a power system including an inverter-type power source having a simulated inertia function in which electrical output is connected to a power system via an inverter and the electrical output is adjusted according to fluctuations in the power system, the inertia grasping device for a power system comprising: an accident condition setting unit that sets accident conditions for an assumed accident in the power system; The above-mentioned an inertia performance calculation unit for the inverter-type power source during the assumed accident; a system simulation unit that grasps the voltage drop amounts of the inverter-type power source during and after an accident from the system analysis model, and an area inertia estimation unit within a partial system area set in the power system, calculate the reduction amount of the power control amount characterized by comprising an inertia amount database." aggregate the reduction amount of the power control amount of the inverter-type power source obtained by the inertia performance calculation unit, and the above-mentioned and aggregate the power control change amount an area inertia estimation unit within a partial system area set in the power system, store the information obtained by the area inertia estimation unit characterized by comprising an inertia amount database."

[0020] Further, the present invention provides "an inertia grasping method for a power system including an inverter-type power source having a simulated inertia function in which electrical output is connected to a power system via an inverter and the electrical output is adjusted according to fluctuations in the power system, the inertia grasping method executed using a computer comprising: setting accident conditions for an assumed accident in the power system; grasp the voltage drop amounts of the inverter-type power source during and after an accident from the system analysis model, calculating inertia performance of the inverter-type power source during the assumed accident; calculate the reduction amount of the power control amount, aggregate the calculated reduction amount of the power control amount of the inverter-type power source, and the above-mentioned estimating area inertia within a partial system area set in the power system; aggregate the power control change amount, and store the aggregated information characterized by the above."

Advantages of the Invention

[0021] According to the present invention, by correctly grasping the contribution of the simulated inertia force to frequency maintenance, it is possible to increase the amount of rotational generators stopped and increase the connection amount of inverter-type generators, and also provide information useful for achieving system stabilization. Further, the contribution amount of the simulated inertia control to frequency maintenance can be quantified, incentives can be provided, power generation income can be increased for power generation companies, and system stabilization effects can be obtained for system operators.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following are merely examples of implementation, and the present invention is not intended to be limited to the following specific contents.

Examples

[0024] First, an overview of a case where the simulated inertia of an inverter-type power source changes during a system accident will be described with reference to FIG. 4.

[0025] FIG. 4 shows an example of a power system including inverter-type power sources GI1, GI2, GI3, GI6, GI7, and GI8. The power system represented by this figure is composed of nodes (buses) N, transmission lines L connecting them, a generator G which is a rotating machine type power source connected to the nodes N, a load Ld, a transformer Tr, etc. The numbers enclosed in squares on the nodes (buses) N indicate node numbers set for convenience.

[0026] In FIG. 4, partial system areas A1 and A2 represent partial systems including the inverter-type power source GI, and this range is assumed to be set in advance by the system operator. Since many of the inverter-type power sources GI are installed in the distribution system, it is advisable to set the partial system areas A1 and A2 as areas including the entire lower-level distribution system for each substation, for example, in terms of the distribution system unit.

[0027] In addition, in the present invention, the inverter-type power source GI is a general term for facilities that connect electrical output to the power system via an inverter. Photovoltaic power generation, wind power generation, and energy storage facilities fall under this category, and those that generate electricity by a rotating machine such as a synchronous generator are distinguished as the generator G.

[0028] In such a system, when a system accident F such as lightning strike occurs, acceleration (increase in rotational speed) or fluctuation (vibration) of the generator G occurs, and accordingly, the frequency and voltage fluctuate. Also, for example, if the acceleration of this generator exceeds a certain amount or the fluctuation diverges, the operation of the generator cannot be continued, the generator stops, a supply-demand imbalance occurs, and the frequency fluctuates. The supply-demand imbalance occurs not only due to system accidents but also due to power generation stoppage caused by earthquakes or generator accidents.

[0029] During and after power system accidents caused by such factors, voltage dips may, depending on their magnitude, lead to temporary stoppage of operation or reduction in output of inverter-type power sources GI. In such cases, the expected movement as the simulated inertia of the inverter-type power source GI cannot occur, and the frequency stability of the entire power system will deteriorate. In this case, it becomes necessary to increase the control amount required for frequency maintenance to compensate for the lost simulated inertia. By performing transient stability simulations due to power system accidents or generator tripping and estimating the amount of simulated inertia lost, it becomes possible to correct the control amount required for frequency maintenance.

[0030] Thus, the movements of inverter-type power sources GI1, GI2, GI3, GI6, GI7, and GI8 during accidents will affect the calculation of frequency fluctuations by transient stability simulations of the power system. Also in the simulations, as described above, it is important to accurately simulate the operating characteristics during power system accidents (such as FRT characteristics and output upper limits during voltage dips) and correctly grasp the performance of the simulated inertia operation of the inverter-type power source.

[0031] FIG. 3 is a diagram showing a configuration example of an inertia grasping device 10 for a power system according to an embodiment of the present invention. The inertia grasping device 10 for a power system is composed of a computer system, and a display device 11, input means 12 such as a keyboard and a mouse, a computer CPU, communication means 14, a random access memory RAM 15, and various databases DB are connected to a bus line 30. Also, as the databases DB of the computer system, a system model database DB1, an inverter-type power source database DB2, an inertia amount database DB3, a frequency control database DB4, and a program database DB5 are provided.

[0032] Here, the computer CPU executes a calculation program to issue instructions for image data to be displayed, search for data in various databases, etc. The random access memory RAM15 is a memory that temporarily stores system model data used for simulation, inverter-type power source data such as inertia control characteristics and installation points, data such as the inertia amount and power control amount generated in each area of the system, and frequency control data such as the control amount of generators and loads with respect to frequency changes. Based on these data, the computer CPU generates necessary image data and displays it on the display device 11 (for example, a display screen).

[0033] In the power system inertia grasping device 10, there are roughly five databases DB installed. Among them, the system model database DB1 stores data related to facilities constituting the power system, such as lines L (resistance, reactance, shunt capacitance) and generators G (capacity, transient reactance, etc.). By using this data, power flow calculations, sensitivity coefficient calculations, and transient stability calculations of the power system can be performed, and voltage phase changes of main generators associated with system accidents can be grasped.

[0034] The inverter-type power source database DB2 stores data such as the installation node N of the inverter-type power source GI1, control configuration and control parameters, and FRT characteristics (operation continuation availability, active power output pattern). From this information and the calculation result information regarding the voltage mentioned above, the movement (operation continuation availability, output limitation amount, inertia reduction amount, etc.) of the inverter-type power source GI1 during and after a system accident is determined.

[0035] The inertia amount database DB3 stores the total inertia amount of the partial area A of the system and the power amount of the power source used to generate inertia. In addition, sensitivity indicators (for example, LoCoF, Nadir, etc.) indicating the degree of frequency change generated by the inverter-type power source GI in the partial area A of the system during a system accident are stored.

[0036] The frequency control database DB4 stores the power generation / load control amount or control correction amount for ensuring that the system frequency change is within the specified range with respect to the change amount of the inertia of the inverter-type power source calculated by this algorithm.

[0037] The program database DB5 stores the power flow calculation program PR1, transient stability calculation program PR2, and sensitivity coefficient calculation program PR3, which are calculation programs. These programs are read out to the computer CPU as needed, and calculations are executed.

[0038] Using FIG. 1, the processing function configuration of the power system inertia grasping device 10 according to an embodiment of the present invention will be described. The power system inertia grasping device 10 includes functions of an accident condition setting unit 31, a system simulation unit 32, an inertia performance calculation unit 33, an area inertia estimation unit 34, a frequency fluctuation index calculation unit 35 during a system accident, and a frequency stabilization control amount calculation unit 36, and is composed of the four aforementioned databases: the system model database DB1, the inverter-type power source database DB2, the inertia amount database DB3, and the frequency control database DB4.

[0039] The accident condition setting unit 31 determines a virtual system accident F in the power system of FIG. 4, and is a part that sets the location, appearance, generators to be disconnected, etc. as system accident conditions. It may be set by input from the user, or the system accident F may be appropriately selected from pre-prepared patterns.

[0040] The system simulation unit 32 creates a system analysis model from the information in the system model database DB1 and the inverter-type power source database DB2, and uses it as input to execute the power flow calculation PR1 and transient stability calculation PR2, which are calculation programs. From the calculation results, the voltage drop amount of each inverter-type power source GI during and after the accident is grasped, and the value is passed to the inertia performance calculation unit 33.

[0041] The inertia performance calculation unit 33 calculates the operability of the inverter-type power source GI, the reduction amount of inertia performance after an accident, and the reduction amount of power control amount from the voltage drop amount at the connection point of each inverter-type power source GI, and passes them to the area inertia estimation unit 34.

[0042] The area inertia estimation unit 34 aggregates the reduction amount of inertia performance of the inverter-type power source GI and the reduction amount of power control change amount within each area A of the power grid, aggregates the inertia amount and power control change amount within area A, stores them in the inertia amount database DB3, and passes them to the frequency fluctuation index calculation unit 35 during a grid accident.

[0043] The frequency fluctuation index calculation unit 35 during a grid accident calculates the evaluation index of frequency fluctuation when considering the change amount of inertia performance of the inverter-type power source GI under the set conditions, and passes it to the frequency stabilization control amount calculation unit 36.

[0044] The frequency stabilization control amount calculation unit 36 calculates the power source cut-off amount (power control amount) and load cut-off amount (load control amount) necessary for the frequency and frequency fluctuation index to fall within the specified range based on the evaluation index of frequency fluctuation, and stores the results in the frequency control database DB4.

[0045] Using FIG. 2, a processing flow showing an example of the processing algorithm of the inertia grasping device for the power grid will be described. This processing flow corresponds to the processing of the accident condition setting unit 31, the grid simulation unit 32, the inertia performance calculation unit 33, the area inertia estimation unit 34, and the frequency fluctuation index calculation unit 35 during a grid accident in FIG. 1.

[0046] First, in processing step S1, grid accident conditions are set. In processing step S2, a grid analysis model is created from the information in the grid model database DB1 and the inverter-type power source database DB2, and the power flow calculation program PR1 and the transient stability calculation program PR2, which are calculation programs, are executed using this as an input.

[0047] In processing step S3, the voltage drop amount during and after an accident of each inverter-type power source GI is grasped. In processing step S4, the output change characteristics with respect to the voltage change of each inverter-type power source GI are grasped (such as the inertia operation characteristics with respect to the magnitude and phase change of the voltage). In processing step S5, the output power change amount and the change amount of inertia of each inverter-type power source GI are calculated.

[0048] In processing step S6, as an initial setting, the power grid area Aj = 1 is set, and the processes of steps S7 to S11 are performed for each of the following power grid areas. In processing step S7, the power change amount and the change amount of inertia of the inverter-type power sources within the power grid area Aj are calculated. In processing step S8, the sensitivity coefficients Lj and Nj of the indexes representing the influence of the power change of the inverter-type power sources in area Aj on the system frequency change rate LoCoF and the frequency maximum deviation Nadir are calculated.

[0049] In processing step S9, if the calculation for each power grid area Aj is not completed, a branch process to return to S6 is performed. In processing step S10, the power change amount, the change amount of inertia, and the sensitivity coefficients of each area Aj and each inverter-type power source GI calculated so far are stored in the inertia amount database DB3.

[0050] FIG. 5 is a diagram showing an example of the simulation of the inverter-type power source GI in the power system analysis model. The inverter-type power source GI model is configured as a model for controlling the magnitude and phase of the current source 510 connected to the node N of the power grid. Also, the node voltage measurement value is taken into each control model via the voltage measurement device 530.

[0051] The control part of the inverter-type power source GI is composed of a generator-converter model 540, a converter control model 550, and a solar PV / wind turbine / battery model 560. The generator-converter model 540 receives the active / reactive current command values from the converter control model 550, and also receives the voltage measurement value from the voltage measurement device 530, and passes the generator active / reactive power amounts to the converter control model 550 and the generator active power amount to the solar PV / wind turbine / battery model 560, respectively.

[0052] The converter control model 550 determines the active and reactive current command values from the active and reactive power of the generator received from the generator-converter model, the power command received from the solar PV / wind turbine / battery model 560, and the voltage measurement value received from the voltage measurement device 530, and passes them to the generator-converter model 540.

[0053] Based on the active power of the generator received from the generator-converter model 540, the solar PV / wind turbine / battery model 560 gives an active power control command to the converter control model 550. Note that this inverter-type power source GI model is of a type that executes simulated inertia control. For example, the solar PV / wind turbine / battery model 560 is adjusted so that a power command in a form reflecting the simulated inertia control amount calculated by equation (1) is given to the converter control model 550.

[0054] By preparing such an inverter-type power source model, it becomes possible to simulate the output change and operability of wind power generation in consideration of the system voltage and the response of the converter. Combined with the FRT characteristics described later, there is an effect that the operability during a system accident can be simulated more realistically. Note that an analysis using the inverter-type power source GI model has been performed for all inverter-type power sources GI in the partial system area of FIG. 4.

[0055] Figures 6, 7, and 8 are diagrams for explaining the FRT characteristics of the inverter-type power source GI. The FRT characteristics of the inverter-type power source GI in FIGS. 6, 7, and 8 show the time after the accident on the horizontal axis and the voltage drop amount (remaining voltage) at the time of the accident on the vertical axis.

[0056] According to Non-Patent Document 1, as an FRT requirement for three-phase power generation facilities in a high-voltage system, for those connected after the end of March 2017, a system that satisfies the following matters is desired when the voltage drops due to an accident or the like. The first of these matters is that for a voltage drop with a remaining voltage of 20% or more and a duration of 0.3 seconds or less, the operation is continued (the area (a) in FIG. 6), and the output returns to 80% or more of the output before the voltage drop within 0.1 seconds after the voltage recovery. An example of the output pattern at this time is shown in FIG. 7.

[0057] Second, for a balanced voltage drop with a residual voltage of less than 20% and a duration of 0.3 seconds or less, the operation continues or is handled by the gate block (the area in (b) of FIG. 6). In this case, it is required to return to an output of 80% or more of the output before the voltage drop within 1.0 second (preferably within 0.2 seconds) after the voltage recovery. An example of the output pattern at this time is shown in FIG. 8.

[0058] Thus, when the voltage drop is 0.3 seconds or less, or the output recovery pattern after voltage recovery varies depending on the system state and the generator state. Therefore, the inverter-type power source GI connected to a node with a large voltage drop will stop once or significantly reduce its output after a system accident, and the expected inertial performance cannot be exerted and will be lost.

[0059] Therefore, for example, in the partial system area A2 relatively close to accident F, when it is predicted that all the inverter-type power sources GI6 - GI8 do not satisfy the conditions of item 1 and item 2 and will be disconnected, the contribution of the simulated inertia of the inverter-type power sources GI6 - GI8 to improving the power system stability cannot be expected. Conversely, for example, in the partial system area A1 far from accident F, when it is predicted that all the inverter-type power sources GI1 - GI3 satisfy the conditions of item 1 and item 2 and continue to operate, the contribution of the simulated inertia of the inverter-type power sources GI1 - GI3 to improving the power system stability can be expected. This makes it possible to grasp the inertial performance that changes due to a system accident and the amount of power that the inverter power source stops.

[0060] Next, with reference to FIGS. 9, 10, and 11, the effectiveness of the proposed method of the present invention will be explained by a schematic example. FIG. 9 shows the voltage of each node N during an accident when a system accident F (three-phase ground fault accident) occurs in the system of FIG. 4. According to this example, the voltages of the node numbers 81, 91, 910, 92, 920, 93, and 930 shown on the right side of FIG. 9 have dropped significantly, while the voltage drop is small for the node numbers shown on the left side of FIG. 9.

[0061] From these results, it is presumed that the node voltages in the partial system area A1 are all greater than 20% of the voltage, and thus the inverter-type power supplies GI1 to GI3 can also continue to operate. Therefore, it is presumed that the decrease in inertial performance is small in the partial system area A1.

[0062] On the other hand, for the partial system area A2, the node voltages of the inverter-type power supplies GI6, GI7, and GI8 are 0.2, 0.15, and 0.1 respectively. This indicates that it is assumed that the outputs of all the inverter-type power supplies GI6, GI7, and GI8 will stop once, and it is determined that inertia will be lost immediately after the accident. It is also presumed that the power generation amount before the accident is lost for the outputs of the inverter-type power supplies.

[0063] Fig. 10 shows an example of the voltage of node N being 930. During the accident from time 0.0 to 0.05 seconds, the voltage drops to 0.1 pu, and around time 0.4 seconds after the accident, the voltage drops to around 0.6 pu. Fig. 11 shows an example of the time variation of the output of the generator. Here, if the inverter-type power supply GI8 connected to node N being 930 could continue to operate, the output would drop to around 0.6 pu around 0.4 seconds.

[0064] In addition, assuming that a synchronous power supply (such as a thermal power generator) is connected to this node, depending on the inertia, synchronization power, and overload capacity, it is also possible to supply the rated output or more power generation amount to the system even when the voltage drops. Thus, for generators, the inverter-type power supply GI may have its original power output and inertia impaired due to voltage changes during an accident, and it is important to correctly grasp its value in frequency control.

[0065] Fig. 12 shows the change in the system frequency when a generator drops out. It is assumed that a certain amount of the generator stops at time 0 seconds. Immediately after the generator stops, the system frequency drops rapidly. The time change rate of this drop is defined by the index of the rate of change of frequency (RoCoF). Also, the value at which the frequency drops the most is defined by the index of the maximum deviation of frequency (Nadir) from the rated frequency.

[0066] Figure 12 shows graphs (a) when the inertia of the system is large and (b) when the inertia is small. When the inertia is smaller, the slope of the rate of change of frequency (RoCoF) is larger, and the value of the maximum frequency deviation (Nadir) is also larger.

[0067] During a system accident, it is necessary to maintain the power balance so that these indicators are below a certain amount. If the control fails, the power outage range of the system will expand, or in some cases, there is a concern that the system may experience a complete power outage. Therefore, it is important to grasp the amount (sensitivity) that the lost inertia and power of the inverter-type power source GI affect the indicators of the rate of change of frequency (RoCoF) and the maximum frequency deviation (Nadir), and reflect it in the determination of the frequency control amount.

[0068] Note that RoCoF can be calculated by Equation (2), and Nadir can be calculated by Equation (3). Here, △f is the frequency deviation from the reference frequency, △t is the time when the frequency is decreasing, fn is the reference frequency, and fb is the frequency at the maximum decrease. [Equation 2] RoCoF = △f / △t (2) [Equation 3] Nadir = fn - fb (3) Calculation examples of sensitivity are shown in Figures 13 and 14. Figure 13 shows an example of calculating the power reduction amount, rate of change of frequency (RoCoF), and maximum frequency deviation (Nadir) indicators of the inverter-type power source with respect to the voltage reduction amount after the accident. Figure 14 shows an example of calculating the rate of change of frequency (RoCoF) and maximum frequency deviation (Nadir) indicators when the inverter-type power source stops due to the FRT operation in response to the voltage reduction during the accident. These sensitivities are stored in the inertia amount database DB3.

[0069] In this way, by grasping the amount (sensitivity) that the lost inertia and power of the inverter-type power source during a system accident exert on indicators such as the rate of change of frequency (RoCoF) and the maximum frequency deviation (Nadir) and reflecting it in frequency control, the risk of power outages can be reduced, the excess or deficiency of the power generation and load control amounts required for frequency control can be reduced, and the effect of reducing power outages due to load restrictions can be obtained. Also, since the effect of inertia supply by the inverter-type power source can be calculated, it becomes possible to quantify the inertia control effect and provide incentives accordingly, which has the effect of improving the frequency stability due to the increase in inertia of the entire system.

[0070] Fig. 15 shows an example of a service utilizing the present invention. In this example, a configuration is shown in which an inertia force aggregator 601 provides a service using the value of inertia control by using the inertia amount estimation device 10 of the power system of the present invention. The inertia force aggregator 601 collects operation and control information of the inverter-type power source such as the control amount of inertia from an inverter-type power source operator 602 capable of performing simulated inertia control, and provides a control incentive commensurate with the control effect as a consideration. Also, to the system operator 603, it provides inertia control and system stabilization control and provides the operation information thereof, and receives a control incentive as a consideration commensurate with the control amount. Further, the inertia force aggregator 601 bids for inertia force control with respect to the inertia force trading market 604 and receives a consideration. By constructing the service relationship in this way, it becomes possible to exert the inertia forces of various inverter-type power sources, and it becomes possible to efficiently exert the inertia forces from a wide variety of inverter-type power sources.

Industrial Applicability

[0071] It can be used as a monitoring device, a frequency control device, and a simulation analysis device for maintaining the frequency stability of a power system in which distributed power sources including power converters for natural energy power generation are interconnected. It can also be used as a stabilization countermeasure decision-making device (frequency maintenance device) for assumed accidents used online. It can also be used as a system facility design support system for considering facility enhancements of the system in response to the addition of natural energy power generation and energy storage facilities, and the shutdown of rotating power generation facilities such as thermal power generators. It can also be used as a calculation support system for system stabilization incentives for giving inertial control to inverter-type power sources.

Explanation of Signs

[0072] 10: Inertia grasping device for power system 11: Display device 12: Input means such as keyboard and mouse 14: Communication means DB1: System model database DB2: Inverter-type power source database DB3: Inertia quantity database DB4: Frequency control database DB5: Program database 31: Accident condition setting section 32: System simulation section 33: Inertial performance calculation section 34: Area inertia estimation section 35: Frequency fluctuation index calculation section during system accident 36: Frequency stabilization control quantity calculation section N: Node G: Generator L: Transmission line Ld: Load Tr: Transformer GI1, GI2, GI3, GI4, GI6, GI7, GI8, GI9: Inverter-type power source F: System accident 510: Current source 530: Voltage measurement device 540: Generator / converter model 550: Converter control model 560: PV / windmill / battery model 601: Inertia force aggregator 602: Inverter type power operator 603: Power system operator 604: Inertia force trading market

Claims

1. An inertia grasping device for a power system including an inverter-type power source having an electric output connected to a power system via an inverter and having a simulated inertia function for adjusting the electric output according to fluctuations in the power system, an accident condition setting unit for setting accident conditions of an assumed accident in the power system, a system simulation unit for grasping voltage drop amounts of the inverter-type power source during and after an accident from a system analysis model, an inertia performance calculation unit for calculating a decrease amount of a power control amount of the inverter-type power source at the time of the assumed accident, an area inertia estimation unit for aggregating the decrease amount of the power control amount of the inverter-type power source obtained by the inertia performance calculation unit and aggregating a power control change amount within a partial system area set in the power system, An inertia grasping device for a power system, comprising an inertia amount database for storing information obtained by the area inertia estimation unit.

2. The inertia grasping device for a power system according to Claim 1, comprising a frequency fluctuation index calculation unit for calculating an evaluation index of frequency fluctuation of the power system from information of the area inertia estimation unit.

3. The inertia grasping device for a power system according to Claim 2, wherein the evaluation index of the frequency fluctuation is a rate of change of frequency (RoCoF) or a maximum frequency deviation (Nadir).

4. An inertia grasping method for a power system including an inverter-type power source having an electric output connected to a power system via an inverter and having a simulated inertia function for adjusting the electric output according to fluctuations in the power system, The inertia grasping method executed using a computer sets accident conditions of an assumed accident in the power system, grasps voltage drop amounts of the inverter-type power source during and after an accident from a system analysis model, calculates a decrease amount of a power control amount of the inverter-type power source at the time of the assumed accident, aggregates the calculated decrease amount of the power control amount of the inverter-type power source, aggregates a power control change amount within a partial system area set in the power system, and stores the aggregated information.

Images