System stabilization system and system stabilization method

Abstract

To provide a grid stabilization system and a grid stabilization method that avoids grid frequency fluctuations and power outages by controlling the rate of change of power received at consumers in response to changes in a grid condition.SOLUTION: The grid stabilization system is for stabilizing an on-premise power system 13 when the premise power system 13 that is disconnected from a commercial power grid 10 is in stand-alone operation and the entire grid is in low inertia. The grid stabilization system has low-inertia grid detection means (power receiving power detection unit 41) that detects that the entire grid to which the premise power system 13 is connected has become low inertia, a backup power source 21 with a PCS 23 that is connected to the premise power system 13 and controls charging and discharging of a power storage device 22, and a power receiving power monitoring and control device 40 that controls the output power from the backup power source 21 to the premise power system 13 to adjust the rate of change of the power receiving power to a predetermined value so that the fluctuation of the frequency of the premise power system 13 is within an acceptable range on the basis of at least the power receiving power detection value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] , , , , , , ,

[0001] The present invention relates to a system stabilization system and a system stabilization method for preventing fluctuations and power outages in system frequency when the load suddenly changes due to the inertia of the power system. In particular, the present invention relates to a technique for stabilizing the load when the load suddenly changes in a power system with inherently low inertia, such as when an accident occurs in the power system and it enters an islanded operation state, or in a small-scale independent power system in an isolated island or a remote area.

Background Art

[0002] For example, Patent Document 1 discloses a technique for continuing power supply to a load while adjusting the supply-demand balance within an in-plant power system when an accident occurs in the power transmission and distribution system and the in-plant power system of a factory that has been receiving power from the power transmission and distribution system enters an islanded operation state. In this Patent Document 1, when an in-plant power system having a plurality of generators and loads is disconnected from the power transmission system and enters an islanded operation state, the adjustment amount (the difference between the total power generation amount and the total load amount) required for stabilizing the in-plant power system is calculated based on the power flow state of the tie line between the two systems. When the deviation rate between the total power generation amount and the total load amount is equal to or greater than a predetermined value, high-priority loads are disconnected according to the magnitude relationship (forward or reverse power flow) between the two, or measures such as apportioning the above adjustment amount to each generator are taken to adjust the supply-demand balance and achieve the stabilization of the in-plant power system.

[0003] In addition, Patent Document 2 discloses a technique for stabilizing the frequency of an islanded operation system by operating the PCSs in the customers' homes that constitute the islanded operation system and feeding power from distributed power sources to the load when the power system monitoring unit in an external server constantly monitors the stability of the power system (inertia, reserve power, etc.) and the commercial power supply drops due to a system accident and the system stability decreases.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0010] to

[0026] , Figures 1 to 3, etc.) [Patent Document 2] Japanese Patent Publication No. 2019-201453 (

[0013] to

[0105] , Figures 1 to 4, etc.) [Overview of the project] [Problems that the invention aims to solve]

[0005] Figure 4 is a diagram illustrating the configuration when an accident occurs between a commercial power system 10, consisting of large-scale thermal power generators, etc., and a circuit breaker 12, and the power transmission system 11, which was disconnected from the commercial power system 10 by the operation of the circuit breaker 12, becomes an isolated power system for the factory 20. The commercial power system 10 is assumed to be sufficiently large in scale and have sufficient inertia. This system configuration is basically the same as that assumed in Patent Documents 1 and 2 for the occurrence of a system failure.

[0006] In Figure 4, 30 is a distributed power source connected to the power transmission system 11, and is composed of, for example, a combination of a solar cell 31 and a PCS (Power Conditioning System) 32 that converts its DC output into AC power of a predetermined magnitude and frequency, or a diesel generator (not shown). This distributed power source 30 may also be installed as an on-site facility of the factory 20.

[0007] The backup power supply 21 installed within the factory 20 consists of an energy storage device 22 such as a battery or capacitor, and a power converter 23 which controls the charging and discharging of the energy storage device 22 and exchanges power between the factory power system 13 and the energy storage device 22. Furthermore, loads such as AC motors are connected to the on-site power system 13.

[0008] Currently, when the circuit breaker 12 is not operating and is connected to the commercial power grid 10, the inertia of the power transmission grid 11 is sufficiently large. As shown in Figure 5, even if the load suddenly decreases at time t1 and the power received by the factory 20 decreases sharply, the frequency of the power received does not fluctuate much, as shown by arrow a, and remains within the allowable level (allowable value for the magnitude of the frequency, or allowable value for the range of frequency fluctuation).

[0009] However, if, for example, an accident occurs between the commercial power grid 10 and the circuit breaker 12, causing the circuit breaker 12 to operate and the on-site power grid 13 to become an isolated system, the on-site power grid 13 will enter a low-inertia state if the PCS 32 does not have a control function as a pseudo-synchronous generator or if the distributed power source 30 is a small-capacity diesel generator.

[0010] Figure 6 shows the waveform when the received power decreases sharply due to a sudden change in load in a low-inertia state. In this scenario, it is assumed that the output of the distributed power supply 30 does not immediately start up after time t1, and that the output of the backup power supply 21 remains unchanged (zero) before and after time t1.

[0011] In this case, the frequency of the on-site power system 13 fluctuated as shown by arrow b in Figure 6, exceeding the permissible level, and there was a risk that relays and other equipment (not shown) would activate, causing a power outage for load 24. In other words, conventionally, no measures were taken to address the decrease in system inertia, resulting in insufficient stabilization measures for the on-site power system 13.

[0012] Therefore, the problem to be solved by the present invention is to avoid fluctuations in the frequency of the power grid and power outages during sudden changes in load by adjusting the rate of change of the power received by consumers, and in particular to provide a grid stabilization system and grid stabilization method that can stably maintain a low-inertia grid. [Means for solving the problem]

[0013] To solve the above problems, the grid stabilization system of the present invention is a grid stabilization system for stabilizing the on-site power system of a consumer connected to the commercial power grid, A power receiving means for detecting the power received by the consumer from the commercial power grid, A backup power supply connected to the aforementioned on-site power system and equipped with a power converter that controls the charging and discharging of the energy storage device, A power receiving monitoring and control means adjusts the rate of change of the customer's power receiving power to a predetermined value by controlling the power supplied from the backup power supply to the on-site power system based at least on the value detected by the power receiving power detection means, It possesses the following characteristics. More specifically, in order to ensure that fluctuations in the frequency of the on-site power system remain within an acceptable range during sudden changes in the load within the customer, the power supplied to the on-site power system from a backup power source capable of charging and discharging a power storage device is controlled based on the detected power received by the customer and the magnitude of inertia of the entire system to which the on-site power system is connected, thereby adjusting the rate of change of the power received by the customer to a predetermined value.

[0014] Furthermore, the grid stabilization system of the present invention further comprises low-inertia grid detection means for detecting when the entire grid to which the in-house power grid is connected has entered a low-inertia state. When the load changes abruptly while the low-inertia system detection means detects that the entire system has become low-inertia, the power receiving monitoring and control means adjusts the rate of change of the power received by the customer to a predetermined value.

[0015] Furthermore, the grid stabilization method of the present invention is a grid stabilization method for stabilizing the on-premises power system of a consumer connected to a commercial power grid, In order to ensure that fluctuations in the frequency of the on-site power system remain within an acceptable range during sudden changes in the load within the customer, the power supplied to the on-site power system from a backup power source capable of charging and discharging a power storage device is controlled based on the detected power received by the customer and the magnitude of inertia of the entire system to which the on-site power system is connected, thereby adjusting the rate of change of the power received by the customer to a predetermined value.

[0016] Further, the system stabilization method of the present invention is a system stabilization method for stabilizing the in-house power system when the load amount suddenly changes in a state where the entire system to which the in-house power system of the consumer is connected has become low-inertia, when the load amount suddenly changes, at least based on the detected value of the received power of the consumer, by controlling the charge and discharge power of the energy storage device by a backup power source connected to the in-house power system, the change rate of the received power of the consumer is controlled to a predetermined value so that the fluctuation of the frequency of the in-house power system falls within an allowable range. [Effect of the Invention]

[0017] According to the present invention, by adjusting the change rate of the received power of the consumer at the time of sudden change of the load amount, fluctuations and power outages of the frequency of the power system can be avoided, and in the case of an islanded operation system, the islanded operation state can be stably maintained. [Brief Description of the Drawings]

[0018] [Figure 1] It is a configuration diagram of a system stabilization system according to an embodiment of the present invention. [Figure 2] It is an operation explanatory diagram when the circuit breaker operates in FIG. 1 (when a low-inertia system is configured by an islanded operation state). [Figure 3] It is an operation explanatory diagram when the circuit breaker operates in FIG. 1 (when a low-inertia system is configured by an islanded operation state), and particularly, it is an operation explanatory diagram when the remaining charge capacity of the energy storage device is smaller than a predetermined value. <00000�5>It is a configuration diagram when the in-house power system becomes an islanded operation system. [Figure 5] It is an operation explanatory diagram when the power transmission system is healthy in FIG. 4. [Figure 6] It is an operation explanatory diagram when the circuit breaker operates in FIG. 4 (when a low-inertia system is configured by an islanded operation state). [Mode for Carrying Out the Invention]

[0019] Embodiments of the present invention will be described below with reference to the figures. Figure 1 is a diagram of the system stabilization system according to this embodiment. Parts identical to those in Figure 4 are given the same reference numerals and their descriptions are omitted. The following explanation will focus on the differences from Figure 4.

[0020] Furthermore, the power converter in the distributed power source 30 in Figure 1 may be an inverter that converts the DC output of the solar cell 31 into AC power, and the power converter in the backup power source 21 may be an inverter that performs forward and reverse conversion (bidirectional power conversion) between the energy storage device 22 and the on-site power system 13 to exchange power. In other words, the types of these power converters are not limited to so-called PCS.

[0021] In Figure 1, a power receiving unit 41 is installed at the power receiving point of the factory 20. This power receiving unit 41 has the function of detecting the power received by the factory 20 based on the current and voltage input from the power transmission system 11 or distributed power source 30, and transmitting the detection result to the power receiving monitoring and control device 40 via a wireless or wired line. The power receiving monitoring and control device 40 is also capable of acquiring the on / off status of the circuit breaker 12.

[0022] The power receiving control device 40 includes a CPU or other processing unit, memory, and a communication interface, which execute a predetermined program based on the power receiving detection value received from the power receiving detection unit 41 and the on / off state of the circuit breaker 12. The power receiving control device 40 may be installed attached to the factory 20, but the functions of the power receiving control device 40 may also be provided to a higher-level system monitoring control device that monitors and controls the entire power system, including other consumers.

[0023] The power receiving monitoring and control device 40 adjusts the rate of change of the power receiving power of the factory 20 when the load suddenly decreases, based on the magnitude of the inertia of the entire system to which the in-house power system 13 (PCS 23 in the backup power supply 21) is connected, as well as the detected power receiving value and the on / off state of the circuit breaker 12. Specifically, the power receiving control device 40 generates a charge / discharge control signal corresponding to the power that the backup power supply 21 should output to the on-site power system 13, and transmits this charge / discharge control signal to the PCS 23 to charge and discharge the energy storage device 22, thereby adjusting the rate of change in the power flow of the power received by the factory 20. Furthermore, a sudden decrease in load can be detected based on the detected power reception value and information from load 24.

[0024] The adjustment operation for the rate of change of received power during sudden load changes described above is: (a) If an accident occurs in the power transmission system 11 (including the transmission path between the commercial power system 10 and the circuit breaker 12), the circuit breaker 12 is turned off, the premises power system 13 enters an isolated state, and the entire system to which the premises power system 13 is connected becomes a low-inertia system, (b) When the on-premises power system 13 is operating in an isolated state, and the entire system to which the on-premises power system 13 is connected becomes a low-inertia system, and the remaining energy storage capacity of the energy storage device 22 in the backup power supply 21 is small (when the rated capacity of the energy storage device 22 is small or when the SOC is large), (c) When the power transmission system 11 is in good condition, the circuit breaker 12 is in the ON state, and the inertia of the entire system to which the on-premises power system 13 is connected is sufficiently large, It will be executed in either case.

[0025] In (a) and (b) above, the fact that the entire system has become a low-inertia system can be detected by the power receiving control device 40 by receiving the off state of the circuit breaker 12 or the power receiving detection value from the power receiving detection unit 41. When the entire system becomes a low-inertia system, the power receiving control device 40 gradually reduces (slows down) the rate of change of power receiving when the load decreases sharply. Furthermore, in case (c) above, the received power should be reduced by a larger rate of change than in cases (a) and (b) above. Needless to say, when adjusting the rate of change of received power, a rate of change that can be achieved within the State of Charge (SOC) range of the energy storage device 22 should be considered.

[0026] Next, Figure 2 shows the operation when the load decreases sharply at time t1, in a case where an accident occurs in the power transmission system 11, the circuit breaker 12 turns off, and the on-site power system 13 is disconnected from the commercial power system 10, which has sufficiently large inertia, and becomes an isolated system (low inertia system). The power receiving control device 40 detects that the entire system to which the in-house power system 13 is connected has become low inertia, based on the power receiving detection value received from the power receiving detection unit 41 and the off information of the circuit breaker 12. If the load decreases sharply at time t1 in this state, the power receiving rate of change is set so that the power receiving power decreases gradually after time t1. Then, according to this set value, a charge / discharge control signal for the energy storage device 22 is generated and transmitted to the PCS 23 so that the power receiving power of the factory 20 decreases gradually. The PCS 23 charges the energy storage device 22, thereby controlling the output of the backup power supply 21 to match the power receiving rate of change to the set value.

[0027] In Figure 2, a charge / discharge control signal is given to the PCS 23 to increase the charging power to the energy storage device 22 at time t1, and then gradually decrease the charging power until time t2, thereby slowing down the rate of change of the received power. During this period (t1-t2), the charging power P1 to the energy storage device 22 is supplied by the power flow from the distributed power source 30 to the energy storage device 22 via the on-site power system 13 and the PCS 23.

[0028] As is clear from Figure 2, after time t1, the sum of the received power and the output of the backup power supply 21 (the power P1 used to charge the energy storage device 22) equals the load. In other words, the decrease in received power during the period (t1-t2) becomes the power P1 used to charge the energy storage device 22, and the power supplied to the load 24 (the load) remains constant after time t1. As a result of the operation of the power receiving control device 40 and the backup power supply 21 described above, the frequency of the power receiving power does not fluctuate as much as indicated by arrow c in Figure 2, thereby preventing power outages and stabilizing the on-site power system 13.

[0029] Next, Figure 3, similar to Figure 2, shows the operation when the load suddenly decreases at time t1 while the entire system to which the on-site power system 13 is connected is in a low-inertia state. In particular, it is an explanatory diagram of the operation when the remaining storage capacity of the energy storage device 22 is small. If the remaining storage capacity of the energy storage device 22 is less than a predetermined value (either because the capacity of the energy storage device 22 is originally small, or because the State of Charge (SOC) of the energy storage device 22 is large and therefore the amount of charge that can be further reduced), it may not be possible to secure the charging power P1 necessary to slow down the rate of change of the received power, as shown in Figure 2.

[0030] Therefore, in such cases, as shown in Figure 3, it is permissible to change the rate of change of the received power to a larger value than in the case of Figure 2, so that the charging power P2 to the energy storage device 22 during the period (t1 to t3) is smaller than the charging power P1 in Figure 2. In this case, the frequency of the received power will fluctuate as shown by arrow d, but as long as it does not exceed the permissible level, there is no particular problem in accepting this frequency fluctuation. The extent to which the rate of change of received power should be increased when the remaining energy storage capacity is less than a predetermined value should be determined based on the capacity of the energy storage device 22, the State of Charge (SOC), etc.

[0031] Here, the rate of change of received power shown in Figure 3 is applicable even when the load decreases sharply at time t1, assuming that the transmission system 11 is healthy, the circuit breaker 12 is ON, and the overall inertia of the system to which the premises power system 13 is connected is sufficiently large. In this case as well, even if the frequency of the received power fluctuates after time t1, there is no particular problem as long as it does not exceed the allowable level.

[0032] The rate of change of received power after time t1 in Figures 2 and 3 may be a value pre-calculated and stored according to the magnitude of the inertia of the entire system and the rate of change of load, taking into account the types and capacities of distributed power sources 30. If the load actually changes abruptly at time t1, it may be changed to the stored rate of change of received power.

[0033] In the above embodiment, the case where the customer is a factory 20 was described, but it goes without saying that the present invention is also applicable to customers such as office buildings and large-scale commercial facilities. Furthermore, in the above embodiment, an example of a low-inertia system was given in which a power system disconnected from the commercial power system 10 is operating independently. However, power systems supplied with electricity from diesel generators or the like, which inherently have low inertia, such as those on remote islands or in isolated areas, are also included in the definition of a low-inertia system. The present invention is effective when the load changes suddenly in these low-inertia systems. [Explanation of symbols]

[0034] 10: Commercial power system 11: Power transmission system 12: Circuit breaker 13: On-site power system 20: Factory 21: Backup power supply 22: Energy storage device 23: PCS 24: Load 30: Distributed power supply 31: Solar cells 32: PCS 40: Power reception monitoring and control device 41: Power receiving detection unit

Claims

1. A grid stabilization system for stabilizing the on-premises power grid of a customer connected to the commercial power grid, A power receiving means for detecting the power received by the consumer from the commercial power grid, A backup power supply connected to the aforementioned on-site power system and equipped with a power converter that controls the charging and discharging of the energy storage device, A power receiving monitoring and control means adjusts the rate of change of the customer's power receiving power to a predetermined value by controlling the power supplied from the backup power supply to the on-site power system based at least on the value detected by the power receiving power detection means, A system stabilization system characterized by having the following features.

2. In the system stabilization system described in claim 1, A grid stabilization system characterized by having distributed power sources connected to the power receiving point of the aforementioned consumer.

3. A grid stabilization method for stabilizing the on-premises power grid of a consumer connected to the commercial power grid, A grid stabilization method characterized by adjusting the rate of change of the power received by the customer to a predetermined value by controlling the power supplied to the on-site power system from a backup power source capable of charging and discharging a power storage device, based on the detected power received by the customer and the magnitude of inertia of the entire system to which the on-site power system is connected, so that when there is a sudden change in the load within the customer, the fluctuation of the frequency of the on-site power system remains within an acceptable range.

4. In the system stabilization system described in claim 1 or 2, The system further includes a low-inertia system detection means for detecting when the entire system to which the aforementioned on-site power system is connected has entered a low-inertia state. A grid stabilization system characterized in that, when the low-inertia grid detection means detects that the entire grid has become low-inertia, and the load within the customer changes abruptly, the power reception monitoring and control means adjusts the rate of change of the customer's power reception to a predetermined value.

5. In the system stabilization system described in claim 4, A grid stabilization system characterized in that the power receiving detection means functions as the low-inertia grid detection means.

6. In the system stabilization system described in claim 4, A grid stabilization system comprising means for detecting on / off information of circuit breakers installed between the commercial power grid and the consumer, wherein the means functions as the low-inertia grid detection means.

7. In the system stabilization system described in claim 2, A grid stabilization system characterized by supplying power to charge the energy storage device when the load within the customer changes suddenly, from the distributed power source via the on-site power grid.

8. In the system stabilization system described in claim 1 or 2, The power reception monitoring and control means is characterized by changing the rate of change of the power reception in accordance with the remaining storage capacity of the energy storage device.

9. A system stabilization method for stabilizing a customer's on-site power system when the load changes suddenly while the entire system, to which the customer's on-site power system is connected, is in a state of low inertia, A grid stabilization method characterized by controlling the rate of change of the power received by the customer to a predetermined value so that the fluctuation in the frequency of the on-site power system remains within an acceptable range, by controlling the charging and discharging power of the energy storage device with a backup power supply connected to the on-site power system, based at least on the detected power received by the customer, when the load changes abruptly.

10. In the system stabilization method described in claim 9, A grid stabilization method characterized by supplying the power to charge the energy storage device when the load changes suddenly from a distributed power source connected to the customer's power receiving point via the on-site power grid.

11. In the system stabilization method described in claim 9 or 10, A grid stabilization method characterized by changing the rate of change of the received power in accordance with the remaining storage capacity of the energy storage device.

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