SVC-linked grid forming system for providing stability and inertia to power system, and operation method thereof

Abstract

According to the present disclosure, provided are an SVC-linked grid forming system for providing stability and inertia to a power system, and an operation method thereof. The system may comprise: a grid forming device connected to a power system; an SVC device connected to the power system in parallel with the grid forming device; and a controller configured to monitor the power system and control the grid forming device and the SVC device. The controller may control the SVC device to provide reactive power and control the grid forming device to provide active power and ground reactive power so as to prevent the grid forming device from operating with a leading power factor on the basis of monitoring of the power system, and may control the grid forming device to immediately supply a fault current to the power system for a pre-configured period when an accident occurs in the power system.

Description

SVC-linked grid-forming system and its operating method for providing stability and inertia to a power system

[0001] The present disclosure relates to an SVC-linked grid forming system and its operating method for providing stability and inertia to a power system.

[0002] Recently, with the growing need for net-zero carbon neutrality by 2050, the amount and share of renewable energy generation in the power and energy sectors is increasing worldwide. In fact, even in power grids with a capacity of 10 GW or more, there are cases where more than 70% of instantaneous power and more than 30% of annual energy are connected to the grid, supplying electrical energy.

[0003] However, as the proportion of renewable energy in the power system increases, the proportion of synchronous generators decreases, the strength of the power system decreases, and the power system may become unstable. For this reason, a method to secure the stability of the power system is required even as the proportion of renewable energy in the power system increases.

[0004] As a solution to this, active research is being conducted on the connection, operation, and management of grid-forming inverter systems with distributed power sources.

[0005] The present disclosure aims to provide an SVC-linked grid forming system and an operating method thereof for providing stability and inertia to a power system.

[0006] According to the present disclosure, a gridforming system linked to a Static Var Compensator (SVC) is provided. The system may include: a gridforming device connected to a power system; an SVC device connected to the power system in parallel with the gridforming device; and a controller configured to monitor the power system and control the gridforming device and the SVC device. The controller may control the SVC device to provide reactive power so that the gridforming device does not operate in a leading state based on the monitoring of the power system, and control the gridforming device to provide active power and lagging reactive power, and may control the gridforming device to immediately supply a fault current to the power system for a preset period when a fault occurs in the power system.

[0007] In addition, the controller prevents the gridforming device from operating at a fault current (Q) generated by the SVC device. S ) is greater than a preset maximum value, the grid forming device can be controlled to provide active power and ground reactive power.

[0008] In addition, the controller controls the grid demand leading reactive power (Q) to prevent the grid forming device from driving leading. 진 ) is less than the preset real reactive power target setting value, the grid forming device can be controlled to provide real power and ground reactive power.

[0009] Additionally, the controller may be configured to monitor the frequency of the power system and determine that an accident has occurred in the power system when the frequency of the power system falls below a preset frequency threshold.

[0010] Additionally, the controller may be further configured to control the grid forming device to supply fault current for the preset period immediately after determining that an accident has occurred in the power system, and then monitor the power system again.

[0011] According to the present disclosure, a method of operating an SVC-linked gridforming system is provided. The system may include an SVC device and a gridforming device connected to a power system. The SVC device may be connected in parallel with the gridforming device. The method may include the steps of: monitoring the power system; controlling the SVC device to provide reactive power so that the gridforming device does not operate in a leading state based on the monitoring of the power system, and controlling the gridforming device to provide active power and lagging reactive power; and controlling the gridforming device to immediately supply a fault current to the power system for a preset period when a fault occurs in the power system.

[0012] In addition, the step of controlling the grid forming device so that it does not operate in the real state is to control the reactive power (Q) generated in the SVC device. S ) may include a step of controlling the grid forming device to provide active power and ground reactive power when the power is greater than a preset maximum value.

[0013] In addition, the step of controlling the grid forming device so that it does not operate in the real state is to control the reactive power (Q) generated in the SVC device. S ) is less than the preset maximum, the system demand leading reactive power (Q 진 ) may further include a step of controlling the grid forming device to provide real power and ground reactive power when the real reactive power target setting value set in advance is less than the target setting value.

[0014] Additionally, monitoring of the power system may include monitoring the frequency of the power system. If the frequency of the power system falls below a preset frequency threshold, it may be determined that an accident has occurred in the power system.

[0015] Additionally, the method may further include a step of re-monitoring the power system after the grid forming device immediately supplies fault current for the preset period when an accident occurs in the power system.

[0016] According to the present disclosure, an SVC-linked grid forming system can be provided that provides reactive power through an SVC during normal operation of the system while preventing the grid forming device from operating at a fault, and that provides stability and inertia to the system by supplying fault current when a fault occurs in the system.

[0017] In addition, according to the present disclosure, by controlling the grid forming device not to operate in a fault state in conjunction with the SVC, it is possible to prevent the problem of overcurrent occurring when the grid forming device supplies fault current in the event of a system accident.

[0018] In addition, according to the present disclosure, there is an effect of being able to build a cost-saving grid forming system by preventing the risk of overcurrent occurring when supplying fault current, thereby reducing the capacity calculation of a grid forming device that requires a large cost compared to an SVC.

[0019] Figure 1 is an exemplary diagram showing a grid-forming inverter.

[0020] FIG. 2 is a schematic diagram of an exemplary SVC-linked grid forming system according to one embodiment of the present disclosure.

[0021] FIG. 3 is an exemplary flow chart illustrating an operation method of an SVC-linked grid forming system according to one embodiment of the present disclosure.

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. First, when assigning reference numerals to components in each drawing, it should be noted that, where possible, identical components are assigned the same reference numerals even if they appear in different drawings. Furthermore, when describing the present invention, if a detailed description of a related, well-known structure or function is judged to obscure the gist of the present invention, such detailed description will be omitted.

[0023] Various aspects of the present invention are described below. It is to be understood that the inventions presented herein may be embodied in a wide variety of forms, and that any specific structure, function, or both presented herein are merely exemplary. Based on the inventions presented herein, one of ordinary skill in the art will appreciate that one aspect presented herein may be implemented independently of any other aspects, and that two or more of these aspects may be combined in various ways. For example, a device may be implemented or a method may be implemented using any number of the aspects described herein. Furthermore, such a device may be implemented or such a method may be implemented using structures, functions, or structures and functions other than or in addition to one or more of the aspects described herein.

[0024] Figure 1 is an exemplary drawing showing a grid-forming inverter.

[0025] A grid-forming inverter (100) as illustrated in Fig. 1 is a device that independently generates power in a power system and can perform a role similar to a generator. The grid-forming inverter (100) can alleviate voltage and frequency instability of the power system by operating in a voltage source control method rather than a conventional current source control method. In addition, since the grid-forming inverter (100) can independently generate and apply voltage and phase, it can provide an inertial effect to a power system whose robustness has decreased as the proportion of renewable energy increases in a carbon-neutral environment where synchronous generators are scarce, thereby enhancing system stability.

[0026] Such a grid-forming inverter (100) is connected to an energy source (e.g., a battery, a super capacitor, a DC capacitor, etc.) and can operate to supply energy (fault current) to the power system immediately or within a very short time (e.g., within 10 ms) to restore the frequency and voltage to a normal range when an accident occurs in the power system. This fault current can be generated and supplied as a combination of active power and reactive power depending on the situation of the power system where the fault occurred to restore the normal state.

[0027] However, the grid forming inverter (100) may generate an overcurrent of 3 to 4 times when a fault current is supplied due to an accident in the system during the leading operation. Due to this overcurrent generation phenomenon, a grid forming inverter with a higher capacity than the rated capacity must be used for stable operation of the grid forming inverter (100). For example, if the required capacity of the grid forming inverter (100) is 1 MVAR, even if it can supply a fault current of 1.5 to 2 times the required capacity momentarily by taking into account the margin of the IGBT of the inverter, in actual application, an inverter of 2 MVAR or more must be applied considering an overcurrent of 3 to 4 times during the leading operation, which may cause excessive costs in building a relatively expensive grid forming system.

[0028] Therefore, if the grid forming inverter (100) can be maintained so as not to operate at a leading edge, excessive capacity calculation can be avoided when applying the grid forming system, thereby enabling construction of a grid forming system at a reduced cost.

[0029] Accordingly, the present disclosure proposes a system and an operating method thereof that can provide stability and inertia to a power system by operating in conjunction with an SVC to prevent leading-edge operation in a grid-forming inverter device (110) using a grid-forming inverter (100), as described later.

[0030] FIG. 2 is a schematic diagram of an exemplary SVC-linked grid forming system according to one embodiment of the present disclosure.

[0031] As illustrated in FIG. 2, the SVC (Static Var Compensator) linked grid forming system (101) may include a grid forming device (110), an SVC device (210), and a controller (300).

[0032] The grid forming device (110) can be connected to a power grid through a grid forming connection point (150) and a power grid connection point (350). The grid forming device (110) can include a grid forming inverter (100) and an energy source connected thereto. The grid forming device (110) can be configured to implement a grid forming function for supplying stability and inertia to the power grid based on the connected energy source. The energy source connected to the grid forming inverter (100) can be a super capacitor (120), a battery (130), a DC capacitor (140), etc., but is not limited thereto and can be another form of distributed power generation source or energy storage device capable of supplying energy.

[0033] The SVC device (210) can be connected to the power system through the SVC connection point (250) and the power system connection point (350), and can be connected in parallel with the grid forming device (110). The SVC device (210) can be configured to provide reactive power to the power system. For example, the SVC device (210) can include a reactive power providing device (e.g., TCR, TSR, etc.) that is configured with a reactor (220) and a thyristor (225) that can provide ground reactive power to the power system, and / or a reactive power providing device (e.g., TSC, etc.) that is configured with a capacitor (230) and a thyristor (235) that can provide leading reactive power to the power system.

[0034] The controller (300) may be configured to monitor the power system and control the grid forming device (110) and the SVC device (210). Specifically, the controller (300) may analyze the power status of the bus connected through the power system connection point (350), and the power status may include the active power, reactive power, frequency, etc. of the bus. The controller (300) may be part of an operating system such as an HMI (Human Machine Interface) or may operate in conjunction therewith. In addition, the controller (300) may calculate the system required active power, the system required reactive power, the system required fault current, etc. based on the monitoring of the power system, and use the calculated values ​​for the linked control of the grid forming device (100) and the SVC device (210), which will be described later.

[0035] The controller (300) can control the grid forming device (110) and the SVC device (210) to prevent the grid forming device (110) from operating abnormally based on monitoring of the power system. For example, the controller (300) can control the SVC device (210) to provide reactive power and the grid forming device (110) to provide active power. Alternatively, for example, the controller (300) can control the SVC device (210) to provide reactive power and the grid forming device (110) to provide active power and ground reactive power.

[0036] The controller (300) prevents the grid forming device (110) from operating at the reactive power (Q) generated in the SVC device (210). S) is greater than a preset maximum value, the grid forming device (110) can be controlled to provide active power or active power and ground reactive power. Here, the preset maximum value may mean a reactive power of a value that can be generated at the maximum level in the SVC device (210), which may be determined by the capacity of the reactor (220) included in the SVC device (210) and / or the capacity of the AC capacitor (230).

[0037] Additionally, the controller (300) prevents the grid forming device (110) from operating at the reactive power (Q) generated in the SVC device (210). S ) is not more than the preset maximum, the system demand leading reactive power (Q 진 ) is less than the preset leading reactive power target setting value, the grid forming device (110) can be controlled to provide active power or active power and ground reactive power. Here, the preset leading reactive power target setting value may mean the minimum value of the leading reactive power targeted in the power system. For example, the preset leading reactive power target setting value may be set through the HMI.

[0038] The controller (300) may control the grid forming device (110) to not operate normally as described above, and when a fault occurs in the power system, the grid forming device (110) may be controlled to immediately (or within a very short time (e.g., within 10 ms)) supply a full load fault current to the power system for a preset period. Here, the preset period may be set to be less than or equal to the time required to remove the fault in the power system (e.g., within 5-6 cycles). For example, the preset period may be 2 cycles, and the length of one cycle may be 1 / 60 of a second. Depending on the implementation, the controller (300) may control the grid forming device (110) to supply both active power and reactive power corresponding to the fault current, or may control the grid forming device (110) to supply a portion of active power and reactive power corresponding to the fault current, and then control the SVC device (210) to supply a portion of the remaining reactive power after the preset period. If the SVC device (210) can supply a portion of the reactive power of the fault current, the active power supply capability for frequency regulation provided by the grid forming device (110) can be additionally increased.

[0039] The controller (300) can monitor the frequency of the power system to determine whether a power system accident has occurred, and if the frequency of the power system falls below a preset frequency threshold, it can determine that a power system accident has occurred. For example, the rated frequency of the power system may be 60 Hz, and the frequency threshold may be set to 59.8 Hz.

[0040] Furthermore, the controller (300) may be additionally configured to control the grid forming device (110) to supply fault current for a preset period of time (i.e., after two cycles) after determining that a fault has occurred in the power system, and then monitor the power system again. Due to this additional operation of the controller (300), the SVC-linked grid forming system (101) can supply active and reactive power additionally required in the power system after the supply of fault current, and can continue to supply stability and inertia to the power system.

[0041] As described above, the SVC-linked grid forming system (101) according to the present disclosure can prevent overcurrent from occurring when an accident occurs in the system and the grid forming device (110) supplies fault current by controlling the grid forming device (110) not to operate while providing reactive power through the linked SVC device (210) during the normal operation of the system.

[0042] FIG. 3 is an exemplary flow chart illustrating an operation method of an SVC-linked grid forming system according to one embodiment of the present disclosure.

[0043] As shown in Fig. 3, the SVC-linked gridforming system (101) can analyze the bus power and HMI settings (301). The SVC-linked gridforming system (101) can monitor the power system to analyze the bus power status (302) and calculate the system required active power and system required reactive power required by the power system (303). The SVC-linked gridforming system (101) can control the SVC device (210) to provide reactive power (304). Here, the reactive power (Q) generated by the SVC device S) is greater than the preset maximum ('Yes' in 305), the SVC-linked grid forming system (101) can control the grid forming device (110) to provide active power and ground reactive power (307). The reactive power (Q) generated by the SVC device S ) is not more than the preset maximum ('No' in 305), the grid demand leading reactive power (Q 진 ) is less than the preset leading reactive power target setpoint ('Yes' at 306), the SVC-linked gridforming system (101) can control the gridforming device (110) to provide active power and grounding reactive power (307). The SVC-linked gridforming system (101) can analyze the bus frequency to monitor the frequency of the power system (308). If the measured frequency of the power system becomes lower than the preset frequency threshold ('Yes' at 309) (i.e., if it is determined that a fault has occurred in the power system), the SVC-linked gridforming system (101) can control the gridforming device (110) to immediately supply fault current to the power system (310). If the measured frequency of the power system is not lower than the preset frequency threshold ('No' at 309), the SVC-linked gridforming system (101) can monitor the power system again (302). After the grid forming device (110) supplies fault current for a preset period (e.g., 2 cycles) ('Yes' at 311), the SVC-linked grid forming system (101) can monitor the power grid again (302).

[0044] The description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments disclosed herein, but is to be construed in the broadest scope consistent with the principles and novel features disclosed herein.

[0045] (Explanation of symbols)

[0046] 100: Gridforming Inverter

[0047] 101: SVC-linked grid forming system

[0048] 110: Gridforming device

[0049] 120: Supercapacitor

[0050] 130: Battery

[0051] 140: DC capacitor

[0052] 150: Gridforming linkage

[0053] 210: SVC device

[0054] 220: Reactor

[0055] 225: Reactor-linked thyristor

[0056] 230: AC capacitor

[0057] 235: Capacitor-linked thyristor

[0058] 250: SVC linkage point

[0059] 300: Controller

[0060] 350: System connection point

Claims

1. As a grid forming system linked to SVC (Static Var Compensator), Gridforming device connected to the power grid; An SVC device connected in parallel with the grid forming device in the power system; and A controller configured to monitor the power system and control the grid forming device and the SVC device, The above controller, Based on the monitoring of the power system, the SVC device is controlled to provide reactive power so that the gridforming device does not operate in a fault state, and the gridforming device is controlled to provide active power and ground reactive power. When an accident occurs in the power system, the grid forming device is controlled to immediately supply fault current to the power system for a preset period. System.

2. In paragraph 1, The above controller, The reactive power (Q) generated in the SVC device is prevented from driving the grid forming device. S ) is greater than the preset maximum value, the grid forming device is controlled to provide active power and ground reactive power. System.

3. In paragraph 2, The above controller, The grid-forming device is designed to prevent the grid from operating at the required leading reactive power (Q). 진 ) is less than the preset real reactive power target setting value, the grid forming device is controlled to provide real power and ground reactive power. System.

4. In paragraph 1, The controller is configured to monitor the frequency of the power system and determine that an accident has occurred in the power system when the frequency of the power system falls below a preset frequency threshold. System.

5. In paragraph 4, The controller is further configured to monitor the power system again after controlling the grid forming device to immediately supply fault current for the preset period when it is determined that an accident has occurred in the power system. System.

6. In the operation method of the SVC linked grid forming system, The system comprises an SVC device and a gridforming device connected to a power grid, the SVC device being connected in parallel with the gridforming device, and the method comprising: A step of monitoring the above power system; A step of controlling the SVC device to provide reactive power so that the gridforming device does not operate based on monitoring of the power system and controlling the gridforming device to provide active power and ground reactive power; and Including a step of controlling the grid forming device to immediately supply fault current to the power grid for a preset period when an accident occurs in the power grid. method.

7. In paragraph 6, The step of controlling the above grid forming device so that it does not operate abnormally is as follows: The reactive power (Q) generated in the above SVC device S ) is greater than a preset maximum value, including a step of controlling the grid forming device to provide active power and ground reactive power. method.

8. In paragraph 7, The step of controlling the above grid forming device so that it does not operate abnormally is as follows: The reactive power (Q) generated in the above SVC device S ) is less than the preset maximum, the system demand leading reactive power (Q 진 ) further includes a step of controlling the grid forming device to provide real power and ground reactive power when the preset real reactive power target setting value is less than the preset real reactive power target setting value. method.

9. In paragraph 6, The monitoring of the power system includes monitoring the frequency of the power system, If the frequency of the power system falls below a preset frequency threshold, it is determined that an accident has occurred in the power system. method.

10. In paragraph 9, Further comprising a step of re-monitoring the power system after the grid forming device immediately supplies fault current for the preset period when an accident occurs in the power system. method.

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