Planning device and planning method

Abstract

To allow planning of the operating modes of inverters connected to the power grid.SOLUTION: A planning device 100 comprises an inverter power supply ratio calculation unit 112 that calculates an inverter power supply ratio, which is the ratio of the sum of the generated power and the demanded power of the inverter power supply to a predicted value of the sum of the total generated power and the total demanded power in a future time interval at a bus connecting the power grid and the inverter power supply, and a planning unit 113 that sets the operating mode of the inverter power supply connected to the bus in the time interval to a grid-constructing type if the inverter power supply ratio exceeds a first predetermined value, and sets the operating mode of the inverter power supply connected to the bus in the time interval to a grid-following type if the inverter power supply ratio is equal to or less than the first predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a planning device and a planning method for the operation of an inverter device connected to a power grid. [Background technology]

[0002] The use of renewable energy sources is essential as a measure against global warming, but it affects the stability of the power system. Renewable energy sources are connected to the power system using power electronics technology, including inverters. The stability of the grid (power system) depends on the impedance or admittance at the connection point (bus) between the renewable energy source and the power system. When a failure or outage occurs in the main power source (synchronous generation) such as a thermal power plant or in a transmission line, the interactions between renewable energy sources or between renewable energy sources and the power system can cause instability and fluctuations in voltage, active power, reactive power, frequency, and current.

[0003] For the operation and maintenance of power systems, power electronics technologies including inverters are used to connect wind power generation, BESS (Battery Energy Storage Systems), FACTS (Flexible Alternating Current Transmission Systems), STATCOM (Static Synchronous Compensators), series capacitors, HVDC (High Voltage Direct Current), etc. These technologies are expected to become increasingly adopted as they provide economical solutions for power system stability and transmission capacity.

[0004] However, as systems using power electronics, including wind power generation, are increasingly introduced, interference between these systems and with the power grid occurs, causing voltage and current oscillations. In particular, when wind power inverters resonate with the power grid or systems using power electronics, this can cause wind turbine failures. Without appropriate countermeasures, this can lead to power outages. Furthermore, dealing with current oscillations due to electrical resonance also affects the ability of the power grid to damp oscillations. This phenomenon is called inverter interaction. This inverter interaction amplifies current and voltage oscillations, destabilizing the power grid and ultimately threatening to disconnect wind power generation from the grid.

[0005] In the following, systems that use power electronics technology, including renewable energy power sources connected to the power grid and FACTS, will be referred to as inverter power sources (inverter-based resources). Inverter power sources are power sources that use power electronics technology to convert direct current or alternating current into alternating current with the frequency of the power grid. Inverter power sources include renewable energy power sources such as wind power and solar power, and BESSs.

[0006] Inverter power supplies have advantages such as reducing greenhouse gas emissions, improving power quality, and increasing the flexibility of power systems. However, inverter power supplies have problems in the planning and operation of power systems, such as protection coordination, fault ride-through capability, voltage and frequency stability, and inertia. Patent Document 1 describes a system and method for reducing oscillations in renewable energy power supplies and power systems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 10,855,079 Summary of the Invention [Problem to be solved by the invention]

[0008] According to the technology described in Patent Document 1, when oscillations in current, voltage, torque, active power, or reactive power are detected, inverter settings are changed to reduce the oscillations. However, this technology does not mention any technology for preventing oscillations. Furthermore, detecting oscillations in large-scale systems using simulations requires a great deal of time and computing power. This makes it difficult to monitor and control oscillations in real time.

[0009] The problem with inverter power supplies described above is a problem with grid-following (GFL) inverters, which are increasingly being introduced as renewable energy power sources. In the following, the operating mode of an inverter that operates by following the voltage and phase of the power grid is defined as "grid-following."

[0010] A solution to the grid-following problem is the grid-forming (GFM) inverter. In the following, "grid-forming" is defined as the operating mode of an inverter that autonomously establishes and controls the voltage and phase of the power grid and operates in synchronization with the grid. Because grid-forming inverters autonomously establish and control the voltage and phase of the power grid, they become stable reference points for the voltage and frequency of the power grid. Grid-forming inverters are needed to improve the resilience and stability of the power grid and to expand the interconnection of renewable energy sources.

[0011] Adding grid-connected inverters to a power system is a major change that requires planning by power system operators. Operators need to determine how they will use grid-connected inverters to ensure the power system remains stable as grid-connected inverters are increasingly used.

[0012] Because the development of grid-connected inverters differs from grid-tracked inverters, manufacturers must also plan. Manufacturers must design and build devices that operate independently and control the power system. Planning is essential to ensure that grid-connected inverters perform well, are reliable, and meet the needs of both operators and the power sector.

[0013] When introducing grid-connected inverters, it is necessary to consider their coexistence with grid-tracking inverters and optimize the operating mode (control mode) that allows switching between grid-connected and grid-tracking inverters. For the sake of stability and high reliability of the power system, it is necessary to formulate a plan to allocate the operating modes of grid-connected and grid-tracking inverters.

[0014] The present invention has been made in view of the above background, and an object of the present invention is to provide a planning device and a planning method that enable planning of operation modes of inverters connected to a power grid. [Means for solving the problem]

[0015] In order to solve the above-mentioned problems, the planning device of the present invention includes an inverter power supply ratio calculation unit that calculates an inverter power supply ratio, which is the ratio of the sum of the generated power and the demanded power of the inverter power supply to a predicted value of the sum of the total generated power and the total demanded power in a future time interval at a bus that connects an electric power system and an inverter power supply, and a planning unit that, if the inverter power supply ratio exceeds a first predetermined value, sets the operating mode of the inverter power supply connected to the bus in that time interval to a grid-building type, and, if the inverter power supply ratio is equal to or less than the first predetermined value, sets the operating mode of the inverter power supply connected to the bus in that time interval to a grid-following type. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a planning device and a planning method that enable planning of the operation modes of inverters connected to a power grid. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a functional block diagram of the planning device according to the first embodiment. [Figure 2] FIG. 3 is a data configuration diagram of an operation mode plan according to the first embodiment. [Figure 3] 4 is a flowchart of a planning process according to the first embodiment. [Figure 4] FIG. 3 is a diagram illustrating the screen configuration of a management screen according to the first embodiment. [Figure 5] FIG. 10 is a functional block diagram of a planning device according to a second embodiment. [Figure 6] 10 is a flowchart of a planning process according to the second embodiment. [Figure 7] FIG. 2 is a hardware configuration diagram illustrating an example of a computer that realizes the functions of the planning device according to the embodiment described above. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Planning Device Overview> A planning device in a mode (embodiment) for carrying out the present invention will be described below. The planning device formulates a plan for the operation mode of the inverter power supply for each bus (bus line) that serves as a connection point between the inverter power supply and the power grid and for each time interval. Specifically, the planning device first predicts the generated power and demand power for all buses and all time intervals. Next, for each bus and time interval, if the ratio of the power of the inverter power supply exceeds a predetermined value, the planning device sets the operation mode of the inverter power supply for that bus and that time to a grid-building mode; if it is equal to or less than the predetermined value, it sets the operation mode to a grid-following mode.

[0019] Stable operation of the power grid can be achieved by switching the operation of inverter power sources according to the plan formulated by such a planning device. Note that inverter power sources are power sources that use power electronics technology, and include renewable energy sources, BESS, FACTS, STATCOM, series capacitors, and HVDC.

[0020] As explained above, the inverter power supply is a power supply that uses power electronics technology. The inverter power source can be a renewable energy source, BESS, FACTS, STATCOM, series capacitor, or HVDC.

[0021] <Configuration of the Planning Device> 1 is a functional block diagram of a planning device 100 according to a first embodiment. The planning device 100 is a computer, and includes a control unit 110, a storage unit 120, and an input / output unit 180. User interface devices such as a display, keyboard, and mouse are connected to the input / output unit 180. The input / output unit 180 includes a communication device, and is capable of transmitting and receiving data to and from a power system 200.

[0022] Renewable energy power sources and inverter power sources including BESSs are connected via connection points (buses, busbars) to the power system 200. In this embodiment, one bus is connected to one inverter power source. 1, the circled R in the power system 200 indicates a renewable energy power source, the circled G indicates a synchronous power source such as a thermal power plant or a nuclear power plant, the circled W indicates a transformer, the rectangular L indicates a load, and the thick line indicates a bus.

[0023] <Planning Device: Memory Unit> The storage unit 120 is configured to include storage devices such as a read-only memory (ROM), a random access memory (RAM), and a solid-state drive (SSD). The storage unit 120 stores a power supply model 121, power prediction data 130, past data 140, inverter power prediction data 150, an operation mode plan 160, and a program 128. The program 128 includes a description of the processing of functional units included in the control unit 110, which will be described later. Note that the contents of the storage unit 120 may be stored in an external storage device, such as a cloud server, and may be read as needed.

[0024] The power supply model 121 is a mathematical model of the inverter power supply used to perform time-domain simulations of voltage, current, frequency, active power, reactive power, and the like based on predicted values ​​of the total power generation and total power demand in the bus (see power forecast data 130, described later). By using the power supply model 121, the behavior of the inverter power supply can be predicted with high accuracy, and predicted values ​​of the power generation and power demand of the inverter power supply can be obtained. Note that the power demand of the inverter power supply is, for example, the power consumed by household appliances at night when there is no power generation, if a house equipped with solar panels is considered to be the inverter power supply.

[0025] The power forecast data 130 is a forecast value of the total power generation and total power demand of each bus in the future. The power forecast data 130 may include the power generation and power demand of the entire power system 200. The power forecast data 130 is a forecast value of the power generation and power demand predicted based on, for example, the season, time period, weather forecast, and past records of power generation and power demand. The total power generation and total power demand include all power generation and power demand, including inverter power supplies, non-inverter power supplies, and loads connected to the bus. Historical data 140 is a record of past weather events and events such as power outages. The inverter power supply prediction data 150 is a predicted value of the generated power and the demanded power of the inverter power supply predicted by a prediction unit 111 (described later) using a power supply model 121.

[0026] FIG. 2 is a data configuration diagram of the operation mode plan 160 according to the first embodiment. The operation mode plan 160 is data in a table format, and each column indicates the operation mode of the inverter power supply connected to a certain bus for each time interval of the bus. Note that a time interval is a predetermined length of time into the future. For example, for bus 3, it indicates that the operation mode switches between grid-building, grid-following, and grid-building modes.

[0027] <Planning Device: Control Unit> Returning to FIG. 1, the control unit 110 will be described. The control unit 110 includes a CPU (Central Processing Unit), and includes a prediction unit 111, an inverter power supply ratio calculation unit 112, a planning unit 113, a collection unit 114, and a display control unit 115.

[0028] <Control unit: Prediction unit> The prediction unit 111 calculates predicted values ​​of the generated power and the demanded power by simulating the inverter power supply using the power supply model 121 based on the total generated power and the total demanded power (see the power prediction data 130). The prediction unit 111 stores the predicted values ​​in the inverter power supply prediction data 150.

[0029] As described above, the planning device 100 includes the prediction unit 111 that calculates the power generated by the inverter power supply and the power demand in a future time interval. The prediction unit 111 predicts and calculates the generated power and demanded power of the bus in a future time interval using a power supply model 121, which is a mathematical model of the inverter power supply used to perform a time domain simulation of at least one of voltage, current, frequency, active power, and reactive power.

[0030] <<Control unit: Inverter power supply ratio calculation unit>> The inverter power supply ratio calculation unit 112 calculates the inverter power supply ratio (sum of generated power and demanded power of inverter power supplies / sum of total generated power and total demanded power), which is the ratio of the sum of the generated power and demanded power of the inverter power supplies to the sum of the total generated power and total demanded power, for each bus and each time interval. The total generated power and total demanded power are included in the power prediction data 130.

[0031] As described above, the planning device 100 includes an inverter power supply ratio calculation unit 112 that calculates an inverter power supply ratio, which is the ratio of the sum of the generated power and the demanded power of the inverter power supply to the predicted value of the sum of the total generated power and the total demanded power (see the power prediction data 130) in a future time interval on a bus connecting the power system 200 and the inverter power supply.

[0032] <Control Unit: Planning Division> The planner 113 determines the operation mode of the inverter power supply connected to the bus for each bus and for each time interval, and formulates the operation mode plan 160. The planner 113 determines the operation mode as a grid-building type if the inverter power supply ratio is greater than a predetermined value (first predetermined value), and determines the operation mode as a grid-following type if the inverter power supply ratio is equal to or less than the first predetermined value.

[0033] The planner 113 transmits the operation mode of each bus in the operation mode plan 160 to the inverter power supply connected to that bus via the network 290. The inverter power supply switches the operation mode in accordance with the received operation mode. The first predetermined value is a threshold value that is obtained by a simulation using the power supply model 121, for example, and at which no oscillation occurs in voltage, frequency, or the like.

[0034] As described above, the planning device 100 includes a planning unit 113 that sets the operating mode of the inverter power supply connected to the bus in the time interval to a grid-constructing type if the inverter power supply ratio exceeds a first predetermined value, and sets the operating mode of the inverter power supply connected to the bus in the time interval to a grid-following type if the inverter power supply ratio is equal to or less than the first predetermined value.

[0035] <<Control unit: Collection unit, display control unit>> The collection unit 114 collects measured values ​​such as voltage, current, and frequency at each bus of the power system 200 via the network 290 . The display control unit 115 displays a management screen 310 (see FIG. 4) to be described later on a display connected to the input / output unit 180.

[0036] <Planning Process> 3 is a flowchart of the planning process according to the first embodiment. The planning process is executed at a predetermined timing, for example, periodically. The period for which the operation mode is planned is assumed to be divided into time sections of a predetermined length.

[0037] In step S11 , the prediction unit 111 predicts the generated power and demand power of the inverter power supply for all buses and time intervals, and stores the predicted power in the inverter power supply prediction data 150 . In step S12, the planner 113 starts the process of repeating steps S13 to S17 for each bus. Hereinafter, the bus that is the processing target of this repeated process will be referred to as the processing target bus.

[0038] In step S13, the planner 113 starts the process of repeating steps S14 to S17 for each time interval. Hereinafter, the time interval that is the processing target of this repeated process will be referred to as the processing target time interval. In step S14, the inverter power supply ratio calculation unit 112 calculates the inverter power supply ratio for the bus to be processed and the time interval to be processed.

[0039] In step S15, if the inverter power supply ratio (denoted as "ratio" in FIG. 3) calculated in step S14 is greater than a first predetermined value (step S15→YES), the planning unit 113 proceeds to step S16, and if it is equal to or less than the first predetermined value (step S15→NO), the planning unit 113 proceeds to step S17.

[0040] In step S16 , the planner 113 sets the operation mode for the bus to be processed and the time interval to be processed as the grid construction type, and records this in the corresponding column of the operation mode plan 160 . In step S17 , the planner 113 sets the operation mode for the bus to be processed and the time interval to be processed as grid-following type, and records this in the corresponding column of the operation mode plan 160 .

[0041] 4 is a diagram showing the screen configuration of the management screen 310 according to the first embodiment. The management screen 310 is displayed by the display control unit 115 on a display connected to the input / output unit 180 (see FIG. 1). Area 311 of management screen 310 displays a system diagram of power system 200. When a date and time is selected from the drop-down list in area 312, the operation mode plan 160 for that date and time is displayed in area 313. When one of the items such as voltage, current, or frequency is selected from the drop-down list in area 314, a graph of the measured value of that item is displayed in area 315.

[0042] <Features of the Planning Device> For each bus and each time interval, if the inverter power supply ratio exceeds a first predetermined value, the planning device 100 sets the operation mode of the inverter power supply for that bus and that time to a grid-building type, and if the inverter power supply ratio is equal to or less than the first predetermined value, to a grid-following type. Switching the operation mode of the inverter power supply in accordance with the operation mode plan 160 formulated by the planning device 100 enables stable operation of the power system 200. Furthermore, by referring to the management screen 310, the operator of the power system 200 can know values ​​such as the operation mode and voltage of each bus and grasp the status of the power system 200.

[0043] Second Embodiment The planning device 100 according to the first embodiment determines the operation mode according to the inverter power supply ratio. The operation mode may be determined further taking into consideration the short-circuit ratio at the bus. FIG. 5 is a functional block diagram of a planning device 100A according to the second embodiment. Compared to the planning device 100 (see FIG. 1), a short-circuit ratio calculation unit 116 is added to the control unit 110, and the planning unit 113A is different.

[0044] The short circuit ratio calculation unit 116 calculates the short circuit ratio of the bus. The short circuit ratio is the ratio of the short circuit MVA capacity of the bus before the inverter power supply is connected to the rated megawatt value (generated power) of the inverter power supply (short circuit MVA capacity / rated megawatt value of the inverter power supply). The planning unit 113A determines the bus to be grid-following if the short-circuit ratio of the bus is equal to or greater than a predetermined value (second predetermined value) regardless of the time interval. If there is a time interval in which the short-circuit ratio is less than the second predetermined value, the system is treated as in the first embodiment. The second predetermined value is a threshold value that does not generate oscillations in voltage, frequency, etc., and is determined, for example, by simulation using the power supply model 121. The processing of the planning unit 113A can be summarized as follows.

[0045] (1) If the short-circuit ratio is greater than or equal to the second predetermined value in all time intervals, the grid-following type is used. (2) If "the short circuit ratio is less than the second specified value during a certain time period" and "the inverter power supply ratio is greater than the first specified value," then it is a grid-construction type. (3) If "short circuit ratio < second predetermined value in a certain time interval" and "inverter power supply ratio ≦ first predetermined value", it is a grid-following type.

[0046] As described above, planning device 100A includes short-circuit ratio calculation unit 116 that calculates the short-circuit ratio, which is the ratio of the short-circuit capacity to the power generated by the inverter power supply, for each bus and time interval. When the short circuit ratio in all time intervals in the bus is equal to or greater than the second predetermined value, the planning unit 113A sets the operation mode of the inverter power supply connected to the bus to the grid following type.

[0047] 6 is a flowchart of the planning process according to the second embodiment. Compared to the planning process according to the first embodiment (see FIG. 3), steps S24 and S25 are added. In step S24, if the short-circuit ratio is greater than or equal to the second predetermined value in all time intervals for the bus being processed (step S24 → YES), the planning unit 113A proceeds to step S25, and if there is a time interval in which the short-circuit ratio is less than the second predetermined value (step S24 → NO), the planning unit 113A proceeds to step S26. In step S25, the planner 113A sets the operation mode of the bus to be processed to grid following type for all time intervals, and records this in the corresponding column of the operation mode plan 160.

[0048] <<Second embodiment: Features of the planning device>> The planning device 100A determines the operation mode by referring to the short-circuit ratio in addition to the inverter power supply ratio. Compared to the planning device 100 according to the first embodiment, the operation of the power system 200 can be expected to be more stable.

[0049] Other variations Although several embodiments of the present invention have been described above, these embodiments are merely examples and do not limit the technical scope of the present invention. For example, although the power supply model 121 has been described as being one, a different model may be used depending on the type and capacity of the inverter power supply connected to the bus. The same applies to the first predetermined value and the second predetermined value.

[0050] The present invention can take on various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the present invention. These embodiments and modifications are included in the scope and spirit of the invention described in this specification, etc., and are also included in the invention described in the claims and their equivalents.

[0051] <Hardware configuration> The planning devices 100, 100A according to the above-described embodiments are realized by a computer 900 having a configuration as shown in FIG. 7, for example. FIG. 7 is a hardware configuration diagram showing an example of the computer 900 that realizes the functions of the planning devices 100, 100A according to the above-described embodiments. The computer 900 includes a CPU 901, a ROM 902, a RAM 903, an SSD 904, an input / output interface 905 (referred to as an input / output I / F (Interface) in FIG. 7), a communication interface 906 (referred to as a communication I / F in FIG. 7), and a media interface 907 (referred to as a media I / F in FIG. 7). The computer 900 may include an HDD (Hard Disc Drive) instead of the SSD 904, or may include an HDD in addition to the SSD 904.

[0052] The CPU 901 operates based on a program stored in the ROM 902 or the SSD 904, and performs control by the control unit 110 in Fig. 1. The ROM 902 stores a boot program executed by the CPU 901 when the computer 900 starts up, programs related to the hardware of the computer 900, and the like.

[0053] The CPU 901 controls an input device 910 such as a mouse or keyboard, and an output device 911 such as a display or printer, via an input / output interface 905. The CPU 901 acquires data from the input device 910 via the input / output interface 905, and outputs generated data to the output device 911.

[0054] The SSD 904 stores programs executed by the CPU 901 and data used by the programs. The communication interface 906 receives data from other devices (not shown) (e.g., the power system 200) via a communication network and outputs the data to the CPU 901, and also transmits data generated by the CPU 901 to other devices via the communication network.

[0055] The media interface 907 reads a program or data stored in the recording medium 912 and outputs it to the CPU 901 via the RAM 903. The CPU 901 loads the program from the recording medium 912 onto the RAM 903 via the media interface 907 and executes the loaded program. The recording medium 912 is an optical recording medium such as a DVD (Digital Versatile Disk), a magneto-optical recording medium such as an MO (Magneto Optical disk), a magnetic recording medium, a conductive memory tape medium, a semiconductor memory, or the like.

[0056] For example, when the computer 900 functions as the planning device 100, 100A according to the above-described embodiment, the CPU 901 of the computer 900 executes the program 128 (see FIG. 1) loaded onto the RAM 903, thereby realizing the functions of the planning device 100, 100A. The CPU 901 reads the program from the recording medium 912 and executes it. Alternatively, the CPU 901 may read the program from another device via a communication network, or may install the program 128 from the recording medium 912 onto the SSD 904 and execute it. [Explanation of symbols]

[0057] 100,100A planning device 111 Prediction Department 112 Inverter power supply ratio calculation unit 113,113A Planning Department 114 Collection Department 115 Display control unit 116 Short circuit ratio calculation section 121 Power Supply Model 128 programs 130 Power forecast data 140 historical data 150 Inverter Power Supply Forecast Data 160 Operational Mode Planning

Claims

1. an inverter power supply ratio calculation unit that calculates an inverter power supply ratio, which is the ratio of a sum of power generated by an inverter power supply and power demand to a predicted value of the sum of total power generated by the inverter power supply and total power demand in a future time interval, at a bus connecting the power grid and the inverter power supply; If the inverter power ratio is greater than a first predetermined value, the operation mode of the inverter power source connected to the bus during the time interval is set to a grid-building mode; a planning unit that sets the operation mode of the inverter power supply connected to the bus during the time interval to a grid following mode if the inverter power supply ratio is equal to or less than the first predetermined value. Planning device.

2. a short-circuit ratio calculation unit that calculates a short-circuit ratio, which is a ratio of a short-circuit capacity to a power generated by an inverter power supply, for the bus and the time interval; The planning unit When the short-circuit ratio in all time intervals is equal to or greater than a second predetermined value, the operation mode of the inverter power supply connected to the bus is set to grid following type. The planning device of claim 1 .

3. a prediction unit that calculates the generated power and the demanded power of the inverter power supply in the future time interval; The prediction unit Using a power supply model, which is a mathematical model of the inverter power supply used to perform a time domain simulation of at least one of voltage, current, frequency, active power, and reactive power, the generated power and demand power of the bus in the future time interval are predicted and calculated. The planning device of claim 1 .

4. The inverter power supply It is a power source that uses power electronics technology. The planning device of claim 1 .

5. The inverter power supply Renewable energy source, BESS, FACTS, STATCOM, series capacitor, or HVDC The planning device of claim 1 .

6. The planning device calculating an inverter power supply ratio, which is the ratio of the sum of the power generated by the inverter power supply and the power demand to a predicted value of the sum of the total power generated by the inverter power supply and the total power demand in a future time interval, at a bus connecting the power grid and the inverter power supply; If the inverter power ratio is greater than a first predetermined value, the operation mode of the inverter power source connected to the bus during the time interval is set to a grid-building mode; If the inverter power supply ratio is equal to or less than the first predetermined value, the operation mode of the inverter power supply connected to the bus during the time interval is set to grid following mode. Planning methods.

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