Power system, grid control device, and stability evaluation method

Abstract

An electric power system according to an embodiment of the present disclosure is provided with one or more pieces of equipment connected to an electrical grid and a grid control device which is connected to the one or more pieces of equipment over a network and which controls the electrical grid, the electric power system comprising: a first processing unit that repeatedly acquires harmonic information over time or when the electrical grid or the equipment changes state, the harmonic information being information pertaining to harmonics of frequencies other than the fundamental frequency of the electrical grid, based on voltage or current in the equipment or the operation or control of the equipment; and an evaluation unit that evaluates the stability of the electrical grid with respect to the harmonics on the basis of the harmonic information.

Description

[[Technical Field]]

[0001] Embodiments of the present invention relate to a power system, a grid control device, and a stability evaluation method. [[Background Art]]

[0002] A power system includes, for example, a plurality of devices such as power converters that convert alternating-current power and direct-current power. [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Patent No. 6157880 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] In grid-connected power converters, harmonic resonance occurs due to the interaction between the grid impedance caused by grid-side wiring, power loads, etc., and the control of the power converter, which destabilizes operation and in some cases may lead to protective shutdown. For example, in grids such as microgrids and offshore wind power generation systems where a large number of power converters are connected, the risk of serious harmonic resonance problems caused by these interactions increases. Therefore, there is a demand for more accurate evaluation of the stability related to harmonic resonance in power systems.

[0005] However, typical power system control devices primarily monitor the fundamental frequency of the power system (rated at 50Hz or 60Hz) and evaluate and monitor the stability of the balance between generated power and load power based on frequency fluctuations. In other words, harmonics at frequencies other than the fundamental frequency are not evaluated at all times or at appropriate points in time. Standards such as grid connection regulations only require operators of interconnected equipment to meet harmonic standards under specific conditions and at specific points in time, and do not adequately consider changes in the state of the power system (system impedance). Therefore, even if the operation of individual equipment becomes unstable due to harmonic resonance, it is not possible to grasp the risks that are in line with the actual situation regarding harmonic resonance, and even if the entire power system becomes unstable as a result, it is difficult to identify the cause.

[0006] One of the objectives of this embodiment is to provide a power system that can more accurately evaluate the stability of a power system with respect to harmonic resonance. [Means for solving the problem]

[0007] The power system of the embodiment comprises one or more devices connected to a power system, and a system control device connected to the one or more devices by a network to control the power system, the power system comprising: a first processing unit that repeatedly acquires harmonic information, which is information relating to the voltage or current of the devices, operation, or harmonics of the power system excluding the fundamental frequency based on the operation or control of the devices, over time or when the state of the power system or the devices changes; and an evaluation unit that evaluates the stability of the power system with respect to the harmonics based on the harmonic information, the devices comprising: the first processing unit and a transmitting unit that transmits the harmonic information to the system control device The system control device comprises a receiving unit for receiving the harmonic information and an evaluation unit, wherein the first processing unit detects an instantaneous value of voltage or current in the equipment, calculates a harmonic amount indicating harmonics as harmonic information from the detected instantaneous value of voltage or current, the receiving unit receives the harmonic amount, the evaluation unit evaluates the stability of the power system with respect to harmonics based on the harmonic amount, and the system control device further comprises an information storage unit for storing the harmonic amounts received in the past, the evaluation unit compares the past harmonic amounts stored in the information storage unit with the received harmonic amount, and evaluates that the stability of the equipment with respect to harmonics is low if the increase in the harmonic amount is above a certain level. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows an example of the overall configuration of a power system according to the first embodiment. [Figure 2] Figure 2 shows an example of the configuration of a power converter according to the first embodiment. [Figure 3] Figure 3 is an equivalent circuit diagram showing an example of a power conversion device and grid impedance according to the embodiment. [Figure 4] Figure 4 shows an example of an impedance characteristic diagram of a power conversion device according to an embodiment. [Figure 5]Figure 5 is a block diagram showing an example of the functional configuration of a system control device according to the first embodiment. [Figure 6] Figure 6 is a sequence diagram showing an example of the procedure for evaluating harmonic stability based on harmonic quantity in the first embodiment. [Figure 7] Figure 7 is a sequence diagram showing an example of the procedure for evaluating harmonic stability based on impedance information in the first embodiment. [Figure 8] Figure 8 is a sequence diagram showing an example of the procedure for evaluating the stability of harmonics based on the operation control information in the first embodiment. [Figure 9] Figure 9 is an equivalent circuit diagram showing an example of the power transmission impedance in the power conversion device according to Modification 4. [Modes for carrying out the invention]

[0009] The embodiments will be described below with reference to the drawings. (First Embodiment) Figure 1 shows an example of the overall configuration of a power system according to the first embodiment. As shown in Figure 1, the power system 1 according to this embodiment mainly comprises renewable energy power sources 40A, 40C, and 40D, a storage battery 30, power converters 300A, 300B, 300C, and 300D, a voltage and current detection device 20, a switchgear 10, and a grid control device 100.

[0010] The renewable energy power sources 40A, 40C, and 40D, and the battery 30 are examples of power sources or power source groups connected to a power grid. The power grid in Figure 1 may be small-scale, such as a general distribution grid, an offshore wind power grid, or an island grid, or it may be part of a large-scale power grid. Renewable energy power sources are referred to as "renewable energy power sources."

[0011] Power converter 300B is connected to battery 30. Power converters 300A, 300C, and 300D are connected to renewable energy sources 40A, 40C, and 40D, respectively. Here, when renewable energy sources 40A, 40C, and 40D are not distinguished, they are referred to as renewable energy source 40, and when power converters 300A, 300B, 300C, and 300D are not distinguished, they are referred to as power converter 300. The power converter 300 is generally a device that converts direct current to alternating current, but depending on the frequency of the power supply, it may also be a device that directly converts alternating current to alternating current. The voltage / current detection device 20 detects voltage and current in the power system. The switchgear 10 is a switch that switches connections to the power system. The switchgear 10 may be used to switch connections in the power transmission and distribution lines at any point in the power system. The power grid control device 100 is a device that monitors the stability of harmonic resonances in the power grid.

[0012] Next, we will describe the details of the power converter 300. Figure 2 shows an example of the configuration of a power converter 300 according to the first embodiment. The power converter 300 is installed at the interconnection point between the power system and the DC power supply 4, and converts between the AC power supplied by the power system and the DC power supplied by the DC power supply 4. As shown in Figure 2, the power converter 300 comprises an instrument transformer VT, a switch CB, an interconnection inductor I, an instrument current transformer CT, a converter control device 31, and a power converter 32.

[0013] DC power source 4 is a device that operates on DC power, such as a storage battery, generator, or load. A switch (CB) switches between having continuity with the power system.

[0014] The power converter 32 includes a switching element that switches connection to the DC power supply 4. The power converter 32 receives a gate signal from the converter control device 31, and mutually converts AC power and DC power. The power converter 32 outputs a voltage V. The power converter 32 is, for example, a circuit configured using a self-extinguishing switching element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor).

[0015] The converter control device 31 executes various controls such as providing operation commands to the switching elements of the power converter 32. As shown in Figure 2, the converter control device 31 mainly includes an arithmetic processing unit 320, a voltage / current control unit 311, a harmonic voltage command generation unit 313, and a gate signal generation unit 312.

[0016] The arithmetic processing unit 320 functions as a first processing unit that acquires harmonic information, which is information related to harmonics based on voltage or current. That is, the arithmetic processing unit 320 performs various arithmetic processes using the grid interconnection point voltage Vs obtained by the instrument transformer VT connected to the grid interconnection point P between the power grid and the interconnection inductor I, and the AC current Is obtained by the instrument current transformer CT provided between the interconnection inductor I and the power converter 32. Here, the grid interconnection point voltage Vs is the voltage of the power grid, and the AC current Is is the current of the power grid.

[0017] The arithmetic processing unit 320 includes a transmission / reception unit 321, a detection unit 323, and an impedance calculation unit 322. The transmission / reception unit 321 transmits and receives various data to and from the grid control device 100. In the present embodiment, the transmission / reception unit 321 transmits harmonic information, which is information related to harmonics, to the grid control device 100. The transmission / reception unit 321 also receives an impedance calculation command from the grid control device 100. Here, the harmonic information includes the harmonic amount described later and also the impedance information calculated by the impedance calculation unit 322 described later.

[0018] The detection unit 323 detects the grid interconnection point voltage Vs obtained by the instrument transformer VT connected to the grid interconnection point P, and the alternating current Is obtained by the instrument current transformer CT installed between the interconnection inductor I and the power converter 32. The detection unit 323 sends the detected grid interconnection point voltage Vs and alternating current Is to the voltage / current control unit 311.

[0019] In this embodiment, the detection unit 323 detects the instantaneous values ​​of the grid connection point voltage Vs and AC current Is, and calculates the harmonic quantity as harmonic information by methods such as Fourier transforming the detected instantaneous values ​​of the grid connection point voltage Vs or AC current Is. Here, the harmonic quantity is the harmonic value itself of the grid connection point voltage Vs or AC current Is that exceeds a predetermined reference value, or, for example, the harmonic level indicating whether or not the reference value is exceeded. The harmonic value itself may be the total distortion (rate) obtained by summing the harmonic spectrum of a specific frequency range (which may be a regulated frequency range such as the 2nd to 40th order range based on the fundamental frequency of the AC system), or the amplitude value of the harmonic spectrum that obtained the maximum amplitude from within a specific frequency range. The detection unit 323 sends the calculated harmonic quantity to the transmitting / receiving unit 321.

[0020] Furthermore, when the detection unit 323 receives notification from the transmitting / receiving unit 321 that it has received an impedance calculation command from the grid control device 100, it sends the detected grid connection point voltage Vs and AC current Is to the impedance calculation unit 322.

[0021] The impedance calculation unit 322 calculates impedance information from the grid connection point voltage Vs and AC current Is detected by the detection unit 323. The impedance calculation unit 322 obtains impedance information (i.e., frequency characteristics) at that point by performing a frequency analysis of the grid connection point voltage Vs and AC current Is using a Fourier transform. If the voltage at frequency f is V(f) and the current at frequency f is I(f), the impedance calculation unit 322 calculates the impedance Z(f) at frequency f from the following formula. Amplitude |Z(f)|=|V(f)| / |I(f)| The phase ∠Z(f) = ∠V(f) - ∠I(f)

[0022] In this embodiment, the impedance calculation unit 322 calculates impedance information by intentionally outputting harmonic voltages or harmonic currents while changing the frequency using the harmonic voltage command generation unit 313, and sequentially calculating the impedance for each frequency.

[0023] The impedance calculation unit 322 sends the impedance information calculated in this way to the transmitting / receiving unit 321 as harmonic information.

[0024] Next, we will explain an example of a power converter 300 and grid impedance. Figure 3 is an equivalent circuit diagram showing an example of a power converter 300 and system impedance according to an embodiment. As shown in Figure 3, the AC system consists of an equivalent inductance Lgrid from the AC power source to the system connection point P and an equivalent capacitance Cgrid at the system connection point. In the following description, the impedance seen from the system connection point P towards the AC power source is referred to as the power system impedance Zgrid. The power converter 32 is connected to the system connection point via an interconnection inductor Lvsc. The impedance seen from the system connection point P towards the power converter 32 is referred to as the converter impedance Zvsc. Zvsc is the impedance obtained by adding the characteristics of the power converter 32 control to Lvsc.

[0025] Figure 4 shows an example of an impedance characteristic diagram of the power converter 300 according to the embodiment. In Figure 4, the horizontal axis of both the upper and lower graphs is frequency. The vertical axis of the upper graph is amplitude. In the lower graph, the vertical axis is phase. Details of the graphs in Figure 4 will be described later, but in the lower graph, if the phase difference Δφ between Zgrid and Zvsc at the amplitude intersection fres is within 180°, the phase margin φm = 180° - Δφ is positive and the system is stable. On the other hand, if the phase margin φm is negative, the system is unstable and harmonic resonance occurs.

[0026] In this embodiment, the impedance calculation unit 322 acquires impedance information, which is information about the impedance Zgrid of the power system, and the transmitting / receiving unit 321 transmits the impedance information to the system control device 100. The impedance Zvsc of the power converter 300 as a device can be acquired not only by measurement during grid connection, but also by testing and analysis, such as by applying a harmonic voltage from an external source before grid connection, and its characteristics can be stored. The power converter 300 may transmit the stored Zvsc to the system control device 100, or the system control device 100 may store Zvsc in advance. The system control device 100 can then determine the risk of harmonic resonance by calculating the phase margin.

[0027] The harmonic voltage command generation unit 313 outputs a voltage command value Vh* at frequency f. The amplitude of the voltage command value Vh* is set to a few percent of the rated voltage so as not to affect the operational stability of the power converter 300. The harmonic voltage command generation unit 313 receives an impedance calculation command from the transmitting / receiving unit 321 and, as described above, repeatedly changes the frequency f within a predetermined range. This allows the impedance calculation unit 322 to acquire impedance information in a predetermined frequency range. Note that when determining stability based on the harmonic amount described above, the impedance information calculation unit 322 may be omitted, or communication of impedance information and impedance calculation commands may be omitted.

[0028] The voltage / current control unit 311 receives the grid connection point voltage Vs and AC current Is from the detection unit 323 and outputs an AC voltage command value V1*.

[0029] The voltage command value Vh* output from the harmonic voltage command generation unit 313 and the AC voltage command value V1* output from the voltage / current control unit 311 are added together by the adder 314 and input to the gate signal generation unit 312.

[0030] The gate signal generation unit 312 receives an added signal of a voltage command value Vh* and an AC voltage command value V1*, generates a gate signal gate to control the switching operation of the power converter 32, and outputs the generated gate signal gate to the power converter 32.

[0031] The converter control device 31 implements each function by having a hardware processor, such as a CPU (Central Processing Unit), execute a program (software) stored in a memory unit (not shown). Furthermore, some or all of each function may be implemented by hardware such as an LSI (Large Scale Integration), ASIC (Application-Specific Integrated Circuit), or FPGA (Field Programmable Gate Array), or by the cooperation of software and hardware.

[0032] Next, the system control device 100 will be described. Figure 5 is a block diagram showing an example of the functional configuration of a system control device 100 according to the first embodiment. As shown in Figure 5, the system control device 100 of this embodiment mainly comprises an information input unit 101, an information evaluation unit 102, an information display unit 103, an information storage unit 106, an information learning unit 105, and an operation command unit 104.

[0033] The information input unit 101 receives harmonic information from equipment such as the power converter 300. Specifically, the information input unit 101 receives harmonic quantity and impedance information from the power converter 300. The information input unit 101 is an example of a receiving unit.

[0034] The information storage unit 106 is, for example, a storage medium such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The information storage unit 106 stores harmonic quantity and impedance information received in the past. The information storage unit 106 also stores stability information, which is information regarding the stability of harmonics evaluated by the information evaluation unit 102 described above. The stability information includes evaluation results of the stability evaluation of harmonics for each piece of equipment such as the power converter 300, and evaluation results of the stability evaluation of harmonics for the entire power system or a part of it. In addition, the information storage unit 106 stores the operation patterns of the power system and time and / or seasonal patterns as stability information, along with the evaluation results.

[0035] The information evaluation unit 102 evaluates the harmonic stability of the power system based on the harmonic information (i.e., harmonic quantity and impedance information) received by the information input unit 101. Here, the harmonic stability of the power system refers to the harmonic stability of each piece of equipment, such as the power converter 300, and the harmonic stability of the entire power system or a part of it.

[0036] In other words, the information evaluation unit 102 evaluates the stability of harmonics for each piece of equipment, such as the power converter 300, based on the harmonic quantity as harmonic information received by the information input unit 101. Specifically, if the harmonic quantity is a harmonic value, the information evaluation unit 102 determines that an unstable state in which harmonic resonance occurs occurs if the average of the harmonic values ​​exceeds a predetermined threshold. Also, if the harmonic quantity is a harmonic level, the information evaluation unit 102 determines that an unstable state in which harmonic resonance occurs occurs occurs if the excess of the harmonic level exceeds a predetermined threshold.

[0037] The information evaluation unit 102 compares the amount of harmonics stored in the information storage unit 106 for a certain past period with the amount of harmonics received. If the increase in the amount of harmonics received exceeds a certain level, or if the difference between the amount of harmonics for a certain past period and the amount of harmonics received exceeds a certain level, the unit evaluates that the stability of the source equipment regarding harmonics is low.

[0038] The information evaluation unit 102 performs aggregation or statistical processing, such as calculating the average or maximum value of multiple harmonics for each piece of equipment, and evaluates the stability of the entire power system or a part of it based on the aggregated or statistically processed harmonics. Specifically, the information evaluation unit 102 evaluates the stability of the entire power system or a part of it as low if the aggregated or statistically processed harmonics are above a predetermined standard value.

[0039] Furthermore, the information evaluation unit 102 may be configured to compare the harmonic output of each device with a predetermined standard value, and if the number of devices whose harmonic output exceeds a certain standard value is greater than or equal to a certain level, it may be determined that the entire power system or a part of it is in an unstable state with respect to harmonics.

[0040] Furthermore, the information evaluation unit 102 evaluates the harmonic stability of each device based on the impedance information received by the information input unit 101. Specifically, as described above, the information evaluation unit 102 determines the risk of harmonic resonance by calculating the phase margin from the impedance information. In other words, the information evaluation unit 102 evaluates the harmonic stability of the device by calculating the phase margin from the impedance information.

[0041] Furthermore, the information evaluation unit 102 obtains stability determination information by aggregating or statistically processing it, such as calculating the average or maximum value of the impedance information for each piece of equipment, and evaluates the stability of the harmonics of the entire power system or a part of it. Specifically, the information evaluation unit 102 evaluates that the stability of the entire power system or a part of it is low if the stability determination information after aggregation or statistical processing is above a predetermined standard value.

[0042] Furthermore, the information evaluation unit 102 may be configured to compare the impedance information of each device with a predetermined reference value, and if the number of devices whose impedance information exceeds the predetermined reference value is above a certain level, it may be determined that the entire power system or a part of it is in an unstable state with respect to harmonics.

[0043] The information display unit 103 displays various information on a display device such as a display device. In this embodiment, it displays the evaluation results of the stability evaluation related to harmonics.

[0044] The information learning unit 105 obtains learned information, which includes highly stable and / or less stable patterns, based on the stability information stored in the information storage unit 106. Furthermore, the information learning unit 105 calculates a recommended pattern for a stable power system based on the learned information.

[0045] The information storage unit 106 stores stability information, making it possible to predict operating patterns that are prone to harmonic resonance. The information learning unit 105 learns based on the stability information, enabling it to present highly stable operating patterns related to harmonics or to automatically control to a stable operating pattern. Here, the operating patterns include, for example, the open / closed state of the power system switchgear 10 (connection of equipment and usage of lines), the operation / stop of the power generator and power converter 300, power, etc., and can be used by the operation command unit 104, which will be described later.

[0046] Furthermore, the information storage unit 106 can store and learn by associating time information with operating patterns and stability information, as power demand and the operating status of renewable energy sources 40 differ depending on the time and season.

[0047] The operation command unit 104 sends operation commands to each device in the power system based on the learned information and the operation patterns described above. Examples of operation commands include switching commands for the switchgear 10, operation / stop commands and / or power generation commands for the power generator, operation / stop commands and / or power conversion commands for the power converter.

[0048] Furthermore, when multiple power generation devices in a power grid are interconnected, the operation command unit 104 can issue operation commands to reduce the generated power in a way that equalizes the opportunity for each individual power generation device to reduce its generated power.

[0049] In this case, when stopping the power generation equipment or power conversion equipment 300, for example, the operation command unit 104 is configured to send operation commands to prioritize stopping equipment with high harmonic levels, thereby preventing the propagation of high harmonic levels to the power grid and stabilizing the entire power grid.

[0050] Furthermore, the operation command unit 104 transmits an impedance calculation command to the power converter 300.

[0051] Next, we will describe the stability evaluation process for harmonics by the power system 1 according to the first embodiment configured as described above. First, we will describe the process for evaluating the stability of harmonics based on the amount of harmonics in the equipment.

[0052] Figure 6 is a sequence diagram showing an example of the procedure for evaluating harmonic stability based on harmonic quantity in the first embodiment. In the example in Figure 6, multiple power converters 300 are used as examples of equipment.

[0053] First, in multiple power converters 300, the arithmetic processing unit 320 detects the grid connection point voltage Vs and AC current Is (S101A, S101B). Then, the arithmetic processing unit 320 calculates the harmonic amount using the detected grid connection point voltage Vs or AC current Is (S102A, S102B). Each transmitting / receiving unit 321 of the power converter 300 transmits the calculated harmonic amount to the grid control device 100 (S103A, S103B). The timing of transmission may be limited to a predetermined time, time interval, or only when the change in harmonic amount exceeds a predetermined standard. By doing so, it is possible to grasp changes in harmonic trends while reducing the network load. It is necessary to repeatedly transmit information at multiple points in time when the harmonic amount may change over time or when the state of the power system or equipment changes, and to make it possible to evaluate.

[0054] In the power system control device 100, the information input unit 101 receives harmonic values ​​from each of the power converters 300, and the information evaluation unit 102 evaluates the harmonic stability of each device based on each harmonic value (S104A, S104B). The information evaluation unit 102 then aggregates and statistically processes the evaluation results of the harmonic stability of each device to evaluate the harmonic stability of the entire power system or a part of it (S105).

[0055] Next, the information learning unit 105 learns the evaluation results of the harmonic stability of each device and the evaluation results of the harmonic stability of the entire power system or a part thereof, and generates learning information (S106). After this, the operation command unit 104 issues operation commands to each device as needed (S107A, S107B).

[0056] Next, we will describe the process of evaluating the stability of harmonics based on impedance information in the power converter 300. Figure 7 is a sequence diagram showing an example of the procedure for evaluating harmonic stability based on impedance information in the first embodiment.

[0057] First, the operation command unit 104 of the grid control device 100 transmits an impedance calculation command to each of the multiple power converters 300 (S201A, S201B). The timing of transmission may be limited to only when a preset time, time interval, or power system operation status (such as the state of switchgear, power generation amount, load amount, etc.) changes. In each of the multiple power converters 300 that have received the impedance calculation command, the calculation processing unit 320 detects the grid connection point voltage Vs and AC current Is (S202A, S202B). Then, the calculation processing unit 320 calculates impedance information using the detected grid connection point voltage Vs and AC current Is (S203A, S203B). The transmitting / receiving unit 321 of each power converter 300 transmits the calculated impedance information to the grid control device 100 (S204A, S204B). It is also possible to configure the power converters 300 to similarly determine the timing of impedance calculation. It is necessary to be able to repeatedly calculate and evaluate impedance at multiple points in time where the harmonic content may change over time or due to changes in the state of power systems or equipment.

[0058] In the power system control device 100, the information input unit 101 receives impedance information from each of the power converters 300, and the information evaluation unit 102 evaluates the harmonic stability of each device based on the impedance information (S205A, S205B). The information evaluation unit 102 then aggregates and statistically processes the evaluation results of the harmonic stability of each device to evaluate the harmonic stability of the entire power system or a part of it (S206).

[0059] Next, the information learning unit 105 learns the evaluation results regarding the harmonic stability of each device and the evaluation results regarding the harmonic stability of the entire power system or a part thereof, and generates learning information (S207). After this, the operation command unit 104 issues operation commands to each device as needed (S208A, S208B).

[0060] Conventional power system control devices primarily monitor the fundamental frequency of the power system (rated at 50Hz or 60Hz) and evaluate and monitor the stability of the balance between generated power and load power based on frequency fluctuations. In other words, harmonics at frequencies other than the fundamental frequency are not evaluated at all times or at appropriate points in time. Standards such as grid connection regulations only require operators of interconnected equipment to meet harmonic standards under specific conditions and at specific points in time, and do not adequately consider changes in the state of the power system (system impedance). Consequently, even if the operation of individual equipment becomes unstable due to harmonic resonance, it is not possible to grasp the risks that are in line with the actual situation regarding harmonic resonance, and even if the entire power system becomes unstable as a result, it is difficult to identify the cause.

[0061] In contrast, in this embodiment, harmonic information, which is information about harmonics based on voltage and current in equipment such as a power converter 300 connected to the power grid, is acquired, and the stability of the power grid with respect to harmonics is evaluated based on the harmonic information. Specifically, the equipment repeatedly acquires harmonic information, which is information about harmonics based on voltage and current in the equipment, and transmits it to the grid control device 100. The grid control device 100 receives the harmonic information and evaluates the stability of the power grid with respect to harmonics based on the harmonic information.

[0062] Therefore, according to this embodiment, the stability of the power system with respect to harmonic resonance can be evaluated more accurately. Furthermore, according to this embodiment, the state and risks of harmonic resonance can be visualized, a stable operating method can be selected, and equipment shutdown or burnout due to the expansion of harmonic resonance can be prevented. In other words, in this embodiment, whether the operation of individual equipment becomes unstable due to harmonic resonance or harmonic resonance is induced by the operation of multiple pieces of equipment, it is possible to grasp the risks related to harmonic resonance in a manner that is in line with the actual situation, so even if the entire power system becomes unstable, it becomes easier to identify the cause. Accordingly, according to this embodiment, it is possible to achieve stabilization of the entire power system with respect to harmonics.

[0063] Furthermore, according to this embodiment, by repeatedly acquiring harmonic information, when the operating state of the power system changes, the risk of unstable conditions due to harmonic resonance when adding generators, loads, power converters 300, etc., or when expanding the power system can be visualized and predicted. Therefore, according to this embodiment, it is possible to select a method for stable operation of the power system or a method for expanding the power system, thereby improving the reliability of the power system.

[0064] Furthermore, in this embodiment, devices such as the power converter 300 detect instantaneous values ​​of voltage and current in the device, calculate harmonic quantities indicating harmonics as harmonic information from the detected instantaneous values ​​of voltage and current, and transmit them to the system control device 100. The system control device 100 receives the harmonic quantities and evaluates the stability of the power system in terms of harmonics based on the received harmonic quantities. Therefore, according to this embodiment, since the judgment is based on actual values ​​such as instantaneous values ​​of voltage and current in devices connected to various points in the power system, the stability of the power system in terms of harmonic resonance can be evaluated more accurately.

[0065] Furthermore, in this embodiment, the system control device 100 compares past harmonic values ​​with the received harmonic values, and evaluates that the stability of the equipment with respect to harmonics is low if the increase in harmonic values ​​exceeds a certain level. Therefore, according to this embodiment, since the judgment is made based on past harmonic values, the increasing trend of harmonic values ​​can be grasped, and the stability of the power system with respect to harmonic resonance can be evaluated more accurately.

[0066] Furthermore, in this embodiment, the system control device 100 aggregates or statistically processes multiple harmonics for each piece of equipment and evaluates the stability of the entire power system or a part of it based on the aggregated or statistically processed harmonics. Specifically, the system control device 100 evaluates the stability of the entire power system or a part of it as low if the aggregated or statistically processed harmonics are above a predetermined threshold. Therefore, according to this embodiment, the stability of harmonics can be evaluated more accurately not only for each piece of equipment, but also for the entire power system or a part of it based on the harmonics.

[0067] In this embodiment, the power converter 300 and other devices detect voltage and current, calculate impedance information as harmonic information from the detected voltage and current, and transmit the calculated impedance information to the power grid control device. Specifically, the power converter 300 and other devices intentionally output harmonic voltage or harmonic current while changing the frequency, and calculate impedance information by sequentially calculating the impedance for each frequency. In this embodiment, the power grid control device 100 receives impedance information from the devices and evaluates the stability of the power grid regarding harmonics based on the received impedance information. Therefore, according to this embodiment, since the judgment is made based on impedance information, the stability of the power grid regarding harmonic resonance can be evaluated more accurately. For example, even if the state of the power grid or connected devices changes and the impedance changes, the judgment is made based on the impedance actually measured at that time, so the stability of the power grid regarding harmonic resonance can be evaluated more accurately.

[0068] Furthermore, in this embodiment, the system control device 100 evaluates the harmonic stability of each device based on the received impedance information, aggregates or statistically processes the evaluation results for each device, and evaluates the harmonic stability of the entire power system or a part thereof. Therefore, according to this embodiment, the harmonic stability can be evaluated more accurately not only for each device, but also for the entire power system or a part thereof based on the impedance information.

[0069] Furthermore, in this embodiment, the system control device 100 stores information regarding harmonic stability in the information storage unit 106, and based on the stored stability information, it obtains learned information that identifies patterns with high stability and / or low stability. Therefore, according to this embodiment, it is possible to make a more accurate determination of harmonic stability by utilizing the learned information. In addition, in this embodiment, by learning information regarding stability including the determination results, it is possible to accurately determine the harmonic stability of the power system over time, thereby improving reliability.

[0070] Furthermore, in this embodiment, the system control device 100 sends operation commands to the power system equipment based on the learned information. Therefore, according to this embodiment, by providing feedback and issuing operation commands based on the learned information regarding stability, it is possible to make the power system equipment operate more appropriately and automatically prevent instability related to harmonics.

[0071] (modified version) The first embodiment described above can be modified in various ways. In Modification 1, for example, in a device such as a power converter 300, the transmitting / receiving unit 321 can be configured to transmit the instantaneous value of the grid connection point voltage Vs or AC current Is calculated by the calculation processing unit 320 to the grid control device 100. In this case, the grid control device 100 can be configured to calculate the harmonic amount from the received instantaneous value of the grid connection point voltage Vs or AC current Is, and to evaluate the stability of the power system in terms of harmonics based on the calculated harmonic amount, by configuring the evaluation unit 102. This reduces the processing load on devices such as the power converter 300.

[0072] As another variation, in a device such as a power converter 300, the calculation processing unit 320 is configured to detect the grid connection point voltage Vs and AC current Is, calculate impedance information from the detected grid connection point voltage Vs and AC current Is, and further evaluate the stability of the device with respect to harmonics based on the impedance information. The transmitting and receiving unit 321 is configured to transmit the evaluation result of the stability with respect to harmonics as harmonic information to the grid control device 100.

[0073] In this case, the system control device 100 can be configured with an information input unit 101 to receive evaluation results from each device, and an evaluation unit 102 to aggregate or statistically process the evaluation results from each device to evaluate the stability of the entire power system or a part of it regarding harmonics. This reduces the processing load on the system control device 100.

[0074] As a third modification, in a device such as a power converter 300, the transmitting / receiving unit 321 can be configured to transmit the grid connection point voltage Vs and AC current Is detected by the calculation processing unit 320 to the grid control device 100 as harmonic information. In this case, the grid control device 100 can be configured to have an information input unit 101 that receives the grid connection point voltage Vs and AC current Is from each device, calculate impedance information from the grid connection point voltage Vs and AC current Is, evaluate the harmonic stability of each device based on the impedance information, and configure an evaluation unit 102 to aggregate or statistically process the evaluation results for each device to evaluate the harmonic stability of the entire power system or a part of it. This reduces the processing burden on devices such as the power converter 300.

[0075] (Second embodiment) In the first embodiment, the stability with respect to harmonics was evaluated using voltage and harmonic quantities and impedance information calculated from the voltage in the equipment. In this second embodiment, the stability with respect to harmonics of the power system is evaluated indirectly based on operation control information related to the operation and control of the power converter 300 as equipment.

[0076] In the second embodiment, the overall configuration of the power system 1, the functional configuration of the power converter 300, and the functional configuration of the grid control device 100 are the same as in the first embodiment.

[0077] In the power converter 300 of this embodiment, the detection unit 323 of the arithmetic processing unit 320 acquires operation control information related to the operation or control of the power converter 300 from the voltage / current control unit 311, etc. The transmitting / receiving unit 321 transmits the acquired operation control information to the system control device 100 as harmonic information.

[0078] In this embodiment, the power converter 300 can be switched between a first control mode for normal operation and a second control mode for suppressing harmonic resonance, via the voltage / current control unit 311.

[0079] As a first example, the first and second control modes are current control modes. A current control mode is a control mode that provides feedback control of the alternating current flowing between the power system and the power converter 300. The second control mode is a control mode within this current control mode that aims to suppress harmonic resonance by shaping the impedance of the power converter 300. The control mode taken by the second control mode is called the current control mode (harmonic resonance suppression). The current control mode taken by the first control mode is called the current control mode (normal). Details of the current control mode (harmonic resonance suppression) are disclosed in Japanese Patent Application Publication No. 2022-18864. In this embodiment, the voltage / current control unit 311 is configured to switch to the highly stable current control mode (harmonic resonance suppression) when the amplitude of the vibration component, arbitrarily converted based on the harmonic amount and voltage / current detection values, exceeds a predetermined threshold during the current control mode (normal).

[0080] As a second example, the first control mode is a current control mode that, as described above, provides feedback control of the alternating current flowing between the power system and the power converter 300. The second control mode is a voltage control mode. The voltage control mode is a control mode that adjusts the voltage phase output to the power system side in synchronization with the voltage of the power system, without directly providing feedback control of the current. The voltage control mode is sometimes also called grid forming control.

[0081] In this embodiment, the voltage / current control unit 311 is switchable between a current control mode and a voltage control mode. When the amplitude of the vibration component, arbitrarily converted based on the harmonic amount and voltage / current detection values, exceeds a predetermined threshold in the current control mode, the unit switches to the more stable voltage control mode for reasons described later.

[0082] More specifically, the voltage / current control unit 311 may be configured to include: a functional unit that receives the grid connection point voltage Vs and AC current Is output by the detection unit 323, generates and outputs an AC voltage command value V1* in current control mode; a functional unit that receives the grid connection point voltage Vs and AC current Is output by the detection unit 323, generates and outputs an AC voltage command value V1* in voltage control mode; and a changeover switch that switches either the AC voltage command value V1* output in current control mode or the AC voltage command value V1* output in voltage control mode to the gate signal generation unit 312 and outputs it based on a predetermined control switching signal.

[0083] Here, we will explain the relationship between each control mode and harmonic resonance using Figure 4. In Figure 4, Zvsc0 represents the current control mode (normal), Zvsc1 represents the current control mode (harmonic resonance suppression), and Zvsc2 represents the voltage control mode. As mentioned above, if the phase difference Δφ between Zgrid and Zvsc at the amplitude intersection fres is within 180°, the phase margin φm = 180° - Δφ is positive and the system is stable. On the other hand, if the phase margin φm is negative, the system is unstable and harmonic resonance occurs.

[0084] Furthermore, unstable conditions that cause harmonic resonance are more likely to occur when the impedance of the power converter 300 includes negative resistance. The presence of negative resistance occurs when the phase exceeds ±90°, as shown in the lower graph of Figure 4, Zvsc0. Since the phase of Zgrid is usually within ±90°, if the phase of Zvsc exceeds ±90°, the phase margin φm = 180° - Δφ can take a negative value.

[0085] Qualitatively, when the impedance of the power converter 300 includes normal resistance, a counteracting voltage is generated when harmonic current flows in, suppressing the harmonic current. On the other hand, when the impedance of the power converter 300 includes negative resistance, when harmonic current flows in, the voltage decreases and the harmonic current increases. For this reason, when the impedance of the power converter 300 includes negative resistance, it is prone to becoming unstable and prone to harmonic resonance.

[0086] In current control mode, a frequency range exhibiting negative resistance can occur mainly due to the effects of high gain and control delay. However, in voltage control mode (virtual generator control), the current is not directly controlled, thus reducing negative resistance. Therefore, as shown in the lower graph of Figure 4, at the amplitude intersection fres, the phase of Zvsc0, which represents the current control mode (normal), becomes unstable, exceeding the ±90° range. On the other hand, at the amplitude intersection fres, the phases of Zvsc1, which represents the current control mode (harmonic resonance suppression), and the voltage control mode are stable, within the ±90° range.

[0087] In other words, even when the power converter 300 is operating in a current control mode (normal), which is a general current feedback control, it can switch to the current control mode (harmonic resonance suppression) shown in Zvsc1 of Figure 4, and by shaping its impedance through control in this mode, it is possible to reduce negative resistance in certain frequency bands and suppress harmonic resonances.

[0088] Furthermore, by switching the control mode of the power converter 300 from current control mode to the power control mode shown as Zvsc2 in Figure 4, the negative resistance over a wider frequency range can be reduced, thereby suppressing harmonic resonance.

[0089] The power converter 300 autonomously detects harmonic resonance and switches the control mode from the current control mode (normal) indicated by Zvsc0 to the current control mode (harmonic resonance suppression) indicated by Zvsc1 or the voltage control mode indicated by Zvsc2. In such cases, the effect of the switched control mode can reduce harmonic resonance, but the power system can be judged to be inherently prone to generating harmonic resonance. For this reason, the information evaluation unit 102 of the system control device 100, described later, judges that the stability of the power converter 300 with respect to harmonics is low when the current control mode is the current control mode (harmonic resonance suppression) or the voltage control mode.

[0090] In this embodiment, the detection unit 323 obtains the current control mode from the voltage / current control unit 311 and sends it to the transmitting / receiving unit 321.

[0091] Furthermore, if protective shutdowns occur frequently in equipment such as the power converter 300, it is considered that the power system is unstable. When harmonic resonance occurs, the amplitude of the harmonics is added to the normal AC voltage or AC current, increasing the voltage or current value. This causes the equipment's overvoltage or overvoltage protection function to activate, and the equipment stops operating. Therefore, the detection unit 323 acquires protective shutdown information indicating that a protective shutdown has occurred in the power converter 300 from the voltage / current control unit 311, etc., and sends it to the transmitting / receiving unit 321. The transmitting / receiving unit 321 then transmits the acquired current control mode as operation control information to the system control device 100.

[0092] When the transmitting / receiving unit 321 acquires protection stop information, it transmits the protection stop information to the system control device 100 as operation control information.

[0093] In the system control device 100, the information input unit 101 receives the current control mode and protection stop information as operation control information from the power converter 300.

[0094] The information evaluation unit 102 evaluates the stability of the power system with respect to harmonics based on the received operation control information. Specifically, the information evaluation unit 102 evaluates that the stability of equipment such as the power converter 300 is low when the current control mode is the second control mode, i.e., the current control mode (harmonic resonance suppression) or the voltage control mode. In addition, if the information input unit 101 receives protection shutdown information from equipment such as the power converter 300, the information evaluation unit 102 evaluates that the stability of the equipment that transmitted the protection shutdown information is low.

[0095] Furthermore, the information evaluation unit 102 aggregates or statistically processes the operation control information and evaluates the stability of the entire power system or a part thereof with respect to harmonics based on the processed operation control information. Specifically, the information evaluation unit 102 evaluates that the stability of the entire power system or a part thereof is low if there are more than a predetermined number of power converters 300 operating in the second control mode. Also, the information evaluation unit 102 evaluates that the stability of the entire power system or a part thereof is low if there are more than a predetermined number of devices such as power converters 300 that have transmitted protection stop information.

[0096] The functions of the information storage unit 106, the information learning unit 105, the information display unit 103, and the operation command unit 104 are the same as in the first embodiment. However, the operation patterns stored in the information storage unit 106 also include the control modes of the equipment.

[0097] Furthermore, the operation commands transmitted by the operation command unit 104 of this embodiment include, in addition to the same commands as in the first embodiment, commands for changing the control mode. In addition, the operation command unit 104 of this embodiment transmits a request command for operation control information to each device.

[0098] Next, we will describe the stability evaluation process for harmonics by the power system 1 according to the second embodiment configured as described above. Figure 8 is a sequence diagram showing an example of the procedure for evaluating the stability of harmonics based on operation control information in the first embodiment. In the example in Figure 8, multiple power converters 300 are used as examples of the equipment.

[0099] First, the operation command unit 104 of the grid control device 100 sends a request command for operation control information to each of the multiple power converters 300 (S301A, S301B). The timing of transmission may be limited to only when a preset time, time interval, or power system operation status (such as the state of switchgear, power generation amount, load amount, etc.) changes. In each of the multiple power converters 300 that have received a request command for operation control information, the arithmetic processing unit 320 acquires operation control information (i.e., the current control mode and protection stop information) (S302A, S302B). Then, the transmitting / receiving unit 321 of each power converter 300 transmits the acquired operation control information to the grid control device 100 (S303A, S303B). It may also be configured so that the operation control information is transmitted to the grid control device 100 when the operation control information from the power converter 300 changes. It is necessary to repeatedly transmit information at multiple points in time when the harmonic amount may change due to the passage of time or changes in the state of the power system or equipment, so that it can be evaluated.

[0100] In the power system control device 100, the information input unit 101 receives operation control information from each of the power converters 300, and the information evaluation unit 102 evaluates the harmonic stability of each device based on the operation control information (S304A, S304B). The information evaluation unit 102 then aggregates and statistically processes the evaluation results of the harmonic stability of each device to evaluate the harmonic stability of the entire power system or a part of it (S305).

[0101] Next, the information learning unit 105 learns the evaluation results regarding the harmonic stability of each device and the evaluation results regarding the harmonic stability of the entire power system or a part thereof, and generates learning information (S306). After this, the operation command unit 104 issues operation commands to each device as needed (S307A, S307B).

[0102] As described above, according to this embodiment, devices such as the power converter 300 acquire operation control information related to the operation or control of the device as harmonic information, transmit the acquired operation control information to the power grid control device 100, and the power grid control device 100 receives the operation control information from the device and evaluates the stability of the power grid with respect to harmonics based on the received operation control information. Therefore, according to this embodiment, since the stability of the power grid with respect to harmonics is evaluated indirectly, the stability of the power grid with respect to harmonic resonance can be evaluated more accurately and easily without detecting voltage or current.

[0103] Furthermore, in this embodiment, the system control device 100 aggregates or statistically processes the operation control information and evaluates the stability of the entire power system or a part of it regarding harmonics based on the processed operation control information. Therefore, according to this embodiment, the stability of harmonics can be evaluated more accurately and easily not only for each piece of equipment, but also for the entire power system or a part of it based on the operation control information.

[0104] Furthermore, in this embodiment, the power converter 300 can switch between a first control mode for normal operation and a second control mode for suppressing harmonic resonance. The power converter acquires the control mode in which it is operating and transmits the acquired control mode to the power grid control device 100. The power grid control device 100 receives the control mode and evaluates that the stability of the power converter 300 with respect to harmonics is low if the control mode is the second control mode. Specifically, the first and second control modes are current control modes that provide feedback control of the current flowing between the power grid and the power converter, and the second control mode is a control mode that aims to suppress harmonic resonance by shaping the impedance of the power converter 300. The first control mode is a current control mode that provides feedback control of the current flowing between the power grid and the power converter 300, and the second control mode is a voltage control mode that adjusts the voltage phase output to the power grid side in synchronization with the voltage of the power grid without directly providing feedback control of the current.

[0105] Therefore, according to this embodiment, since the stability of the power system with respect to harmonics is evaluated indirectly based on the second control mode, the stability of the power system with respect to harmonic resonance can be evaluated more accurately and easily without detecting voltage or current.

[0106] Furthermore, according to this embodiment, even if stability is ensured by the effect of the control when some power converters 300 are performing harmonic resonance suppression in the second control mode, there is a risk of rapid harmonics becoming unstable if the power converters 300 stop or if generators, loads, converters, etc. are added. In other words, the second control mode has the effect of temporarily stabilizing the power system, but as a result, the inherent stability of the power system becomes invisible. In this embodiment, since it is determined that the stability with respect to harmonics is low when operating in the second control mode of harmonic resonance suppression control, it is possible to accurately grasp the inherent instability risk of the power system and prevent instability before it occurs. Even when the entire power system is stable, the potential risk of instability can be grasped, and the stabilization effect of the second control mode of the power converters 300 can also be accurately grasped. Therefore, it becomes easier to take countermeasures in advance even when equipment stops or is added. Accordingly, according to this embodiment, similar to the first embodiment, even if the entire power system becomes unstable, it becomes easy to identify the cause and even predict the instability, making it possible to achieve harmonics stabilization of the entire power system.

[0107] Furthermore, in this embodiment, the system control device 100 evaluates that the stability of the entire power system or a part thereof is low when there are a predetermined number or more power converters 300 operating in the second control mode. Therefore, according to this embodiment, the stability of the entire power system or a part thereof can be evaluated more accurately and easily based on the second control mode, not just for each individual device.

[0108] Furthermore, in this embodiment, the operation control information is protective shutdown information for the equipment, and the system control device 100 determines that the equipment that transmitted the protective shutdown information has low harmonic stability. Therefore, according to this embodiment, the harmonic stability of the power system is evaluated indirectly based on the protective shutdown information of the equipment, so the harmonic resonance stability of the power system can be evaluated more accurately and easily without detecting voltage or current.

[0109] Furthermore, in this embodiment, the system control device 100 evaluates that the stability of the entire power system or a part thereof is low if the number of devices that have transmitted protective shutdown information exceeds a predetermined number. Therefore, according to this embodiment, the stability with respect to harmonics can be evaluated more accurately and easily not only for each device, but also for the entire power system or a part thereof based on the protective shutdown information of the devices.

[0110] (Modification 4) In cases where the power converter 300 is equipped with a harmonic filter, harmonic resonance may be reduced simply by changing the power converter 300 from a stopped state to an operating state. Figure 9 is an equivalent circuit diagram showing an example of the power and system impedance in the power converter 300 according to Modification 4. A power system is composed of, for example, an equivalent inductance Lgrid from the AC power source to the grid connection point P. The impedance when viewed from the grid connection point P towards the AC power source is called the system impedance Zgrid.

[0111] Furthermore, the impedance when viewed from the grid connection point towards the power converter 32 is called the converter impedance Zvsc. Zvsc is an impedance based on the connection inductor I (Lvsc), the harmonic filter F, and the characteristics of the converter control (Zsw).

[0112] For example, if the switch CB is conducting and the power converter 32 is in a switching-stopped state, the current Is in the power converter 32 becomes 0, and resonance occurs between the Lgrid and the harmonic filter (CFilter).

[0113] On the other hand, when the switch CB is conductive and the power converter 32 is in a switching operation state, the current Is of the power converter 32 is not 0, and resonance caused by the grid-side inductor Lgrid and the harmonic filter F is mitigated by the resistive action (-90°<phase of Zsw<+90°) included in Zsw on the power converter 32 side. In particular, Zsw often exhibits resistive action at relatively low frequencies, and this method is useful when the resonance frequency is low.

[0114] Even when the power converter device 300 is substantially in zero-power operation, the resistive action on the power converter 32 side can be obtained. As described above, harmonic resonance can be reduced merely by changing the power converter device 300 from a stopped state to an operating state. Therefore, when the power converter device 300 includes a harmonic filter, the operation command unit 104 of the grid control device 100 can be configured to transmit an operation command for changing the power converter device 300 from the stopped state to the operating state to the power converter device 300.

[0115] The grid control device 100 of the above embodiment and modified examples includes a control device such as a CPU, a storage device such as ROM (Read Only Memory) and RAM, an external storage device such as an HDD and a CD drive device, a display device such as a display device, and an input device such as a keyboard and a mouse, and has a hardware configuration provided with an arithmetic function like a computer.

[0116] A stability evaluation program executed by the grid control device 100 of the above embodiment and modified examples is provided as an installable or executable file recorded on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk), or the like.

[0117] Furthermore, the stability evaluation program executed by the system control device 100 of the above embodiment and its modified form may be stored on a computer connected to a network such as the Internet and provided by allowing users to download it via the network. Alternatively, the stability evaluation program executed by the system control device 100 of the above embodiment and its modified form may be provided or distributed via a network such as the Internet.

[0118] Furthermore, the stability evaluation program executed by the system control device 100 of the above embodiment and its modified form may be provided pre-installed in a ROM or the like.

[0119] The stability evaluation program executed by the system control device 100 of the above embodiment and modified example has a modular configuration including the above-mentioned parts (information input unit 101, information evaluation unit 102, information learning unit 105, and operation command unit 104). In actual hardware, the CPU (processor) reads the stability evaluation program from the storage medium and executes it, loading the above-mentioned parts onto the main memory, and generating the information input unit 101, information evaluation unit 102, information learning unit 105, and operation command unit 104 on the main memory.

[0120] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0121] (Note) In the above-described embodiment, the transmitting unit of the device transmits the instantaneous value of the voltage or current detected by the first processing unit as harmonic information to the system control device. The receiving unit of the system control device receives the instantaneous value of the detected voltage or current, The evaluation unit of the system control device calculates the amount of harmonics representing harmonics from the instantaneous value of the received voltage or current, and evaluates the stability of the power system with respect to harmonics based on the amount of harmonics.

[0122] In the above-described embodiment, the arithmetic processing unit of the device detects voltage and current in the device, calculates impedance information from the detected voltage and current, and evaluates the stability of the device with respect to harmonics based on the impedance information. The transmitting unit of the aforementioned device transmits the evaluation result of the stability of the harmonics as harmonic information to the system control device. The aforementioned system control device is The receiving unit of the system control device receives the evaluation results from each of the devices, The evaluation unit of the system control device aggregates or statistically processes the evaluation results of each of the devices to evaluate the stability of the harmonics of the entire power system or a part thereof.

[0123] In the above-described embodiment, the arithmetic processing unit of the device detects the voltage and current of the device, The transmitting unit of the system control device transmits the detected voltage and current to the system control device as harmonic information. The receiving unit of the system control device receives the detected voltage and current from each of the devices. The evaluation unit of the system control device calculates impedance information from the detected voltage and current, evaluates the stability of each of the devices with respect to harmonics based on the impedance information, and aggregates or statistically processes the evaluation results for each of the devices to evaluate the stability of the entire power system or a part of it with respect to harmonics.

[0124] In the above-described embodiment, the operation command is an opening / closing command for a switch. In the embodiments described above, the operation command is an operation / stop command for the power generation device and / or a power generation command.

[0125] In the above embodiment, when a plurality of the power generation devices are interconnected and the power generation is reduced by the operation command, The operation commands are given so that the opportunities for each of the aforementioned power generators to experience a decrease in power generation are equal.

[0126] In the embodiments described above, the operation command is an operation / stop command for the power converter and / or a power conversion command.

[0127] In the above-described embodiment, the operation command is a control mode change command relating to the suppression of harmonic resonance in the power converter.

[0128] In the above-described embodiment, the information storage unit stores the information relating to stability together with the operating pattern of the power system.

[0129] In the above-described embodiment, the information storage unit stores the information regarding stability along with the time and / or seasonal patterns. [Explanation of Symbols]

[0130] 1. Power Systems 4 DC power supply 20 Voltage / Current Detection Device 30 Storage batteries 31 Converter control device 32 Power Converters 40 Renewable energy sources 100-system control device 101 Information Input Section 102 Information Evaluation Department 103 Information display section 104 Operation command section 105 Information Learning Department 106 Information storage section 300 Power converter 311 Voltage / Current Control Unit 312 Gate signal generation unit 313 Harmonic Voltage Command Generation Unit 320 Arithmetic Processing Unit 321 Transmitter / Receiver 322 Impedance Calculation Section 323 Detection unit

Claims

1. A power system comprising one or more devices connected to a power grid, and a grid control device connected to the one or more devices via a network to control the power grid, A first processing unit repeatedly acquires harmonic information, which is information regarding the voltage or current in the equipment, or the harmonics of the power system excluding the fundamental frequency based on the operation or control of the equipment, over time or when the state of the power system or the equipment changes. The system includes an evaluation unit that evaluates the stability of the power system with respect to harmonics based on the harmonic information, The aforementioned device is The first processing unit and, The system includes a transmitting unit that transmits the harmonic information to the system control device, The aforementioned system control device is A receiving unit that receives the aforementioned harmonic information, The evaluation unit is provided, The first processing unit detects the instantaneous value of voltage or current in the device, and calculates the harmonic amount indicating harmonics as the harmonic information from the detected instantaneous value of voltage or current. The receiving unit receives the harmonics, The evaluation unit evaluates the stability of the power system with respect to harmonics based on the harmonic quantity, The aforementioned system control device is It further comprises an information storage unit that stores the aforementioned harmonics received in the past, The evaluation unit compares the past harmonic values ​​stored in the information storage unit with the received harmonic values, and evaluates that the device has low stability with respect to the harmonics if the increase in the harmonic values ​​exceeds a certain level. Power system.

2. The evaluation unit aggregates or statistically processes multiple harmonics for each device, and based on the aggregated or statistically processed harmonics, To evaluate the stability of the entire or a part of the aforementioned power system, The power system according to claim 1.

3. The evaluation unit evaluates that the stability of the entire power system or a part thereof is low if the number of harmonics after aggregation or statistical processing is above a predetermined threshold. The power system according to claim 2.

4. A power system comprising one or more devices connected to a power grid, and a grid control device connected to the one or more devices via a network to control the power grid, A first processing unit repeatedly acquires harmonic information, which is information regarding the voltage or current in the equipment, or the harmonics of the power system excluding the fundamental frequency based on the operation or control of the equipment, over time or when the state of the power system or the equipment changes. The system includes an evaluation unit that evaluates the stability of the power system with respect to harmonics based on the harmonic information, The aforementioned device is The first processing unit and, The system includes a transmitting unit that transmits the harmonic information to the system control device, The aforementioned system control device is A receiving unit that receives the aforementioned harmonic information, The evaluation unit is provided, The first processing unit acquires operation control information relating to the operation or control of the equipment as harmonic information, The transmitting unit transmits the acquired operation control information to the system control device. The receiving unit receives the operation control information from the device, The evaluation unit evaluates the stability of the power system with respect to harmonics based on the received operation control information. Power system.

5. The evaluation unit aggregates or statistically processes the operation control information and evaluates the stability of the harmonics of the entire power system or a part thereof based on the processed operation control information. The power system according to claim 4.

6. The aforementioned device is a power converter that converts AC power to DC power, The power converter has a first control mode for normal operation and a second control mode for suppressing harmonic resonance as its operating control modes. It is possible to switch between these two modes. The first processing unit acquires the control mode in which the power converter is operating, The transmitting unit transmits the acquired control mode to the system control device. The receiving unit receives the control mode, The evaluation unit evaluates that the stability of the equipment with respect to harmonics is low when the control mode is the second control mode. The power system according to claim 5.

7. The first control mode and the second control mode are current control modes that provide feedback control of the current flowing between the power system and the power converter. The second control mode is a control mode that aims to suppress harmonic resonance by shaping the impedance of the power converter. The power system according to claim 6.

8. The first control mode is a current control mode that provides feedback control of the current flowing between the power system and the power converter. The second control mode is a voltage control mode that adjusts the voltage phase output to the power system in synchronization with the voltage of the power system without directly feedback-controlling the current. The power system according to claim 6.

9. The evaluation unit evaluates that the stability of the harmonics in the entire power system or a part thereof is low when there are a predetermined number or more power converters operating in the second control mode. The power system according to claim 6.

10. The aforementioned operation control information is protective shutdown information for the device, The evaluation unit determines that the stability of the equipment that transmitted the protection shutdown information is low with respect to harmonics, and further evaluates that the stability of the entire power system or a part thereof is low if the number of such equipment exceeds a predetermined number. The power system according to claim 5.

11. The aforementioned system control device is An information storage unit that stores information regarding the stability of the harmonics evaluated by the evaluation unit, An information learning unit that, based on the information information stored in the information storage unit, finds learned learning information of patterns with high stability and / or low stability, The power system according to claim 4, comprising:

12. The aforementioned system control device is An operation command unit that sends operation commands to the equipment of the power system based on the learned information. The power system according to claim 11, further comprising:

13. A power system control device comprising one or more devices connected to a power system, and the one or more devices connected to the power system via a network, A receiving unit that repeatedly receives harmonic information from the aforementioned device, which is information relating to the voltage or current in the device, or the harmonics of the power system excluding the fundamental frequency based on the operation or control of the device, over time or when the state of the power system or the device changes. The system includes an evaluation unit that evaluates the stability of the power system with respect to harmonics based on the received harmonic information, The receiving unit receives from the device a harmonic quantity representing a harmonic calculated as harmonic information from the instantaneous value of voltage or current in the device. The evaluation unit evaluates the stability of the power system with respect to harmonics based on the harmonic quantity, The aforementioned system control device is It further comprises an information storage unit that stores the aforementioned harmonics received in the past, The evaluation unit compares the past harmonic values ​​stored in the information storage unit with the received harmonic values, and evaluates that the device has low stability with respect to the harmonics if the increase in the harmonic values ​​exceeds a certain level. System control device.

14. A method for evaluating the stability of a power system, comprising one or more devices connected to a power grid, and a system control device connected to the one or more devices via a network to control the power grid, A first processing step in which the device repeatedly acquires harmonic information, which is information relating to the voltage or current in the device, or to the harmonics of the power system excluding the fundamental frequency based on the operation or control of the device, over time or when the state of the power system or the device changes. The equipment transmits the harmonic information to the system control device in a transmission step, The system control device performs a receiving step of receiving the harmonic information, The system control device includes an evaluation step of evaluating the stability of the power system with respect to harmonics based on the harmonic information, The first processing step involves detecting the instantaneous value of voltage or current in the device, and calculating the harmonic amount indicating a harmonic as the harmonic information from the detected instantaneous value of voltage or current. The receiving step involves receiving the harmonics, The evaluation step evaluates the stability of the power system with respect to harmonics based on the amount of harmonics, The system control device includes an information storage unit that stores the harmonic amounts received in the past, The evaluation step involves comparing the past harmonic values ​​stored in the information storage unit with the received harmonic values, and if the increase in the harmonic values ​​exceeds a certain level, the device is evaluated as having low stability with respect to the harmonics. Stability evaluation method.

15. The aforementioned device is The first processing unit includes a processing unit that detects voltage and current, and calculates impedance information relating to impedance as harmonic information from the detected voltage and current, The transmitting unit transmits the calculated impedance information to the system control device. The receiving unit receives the impedance information from the device, The evaluation unit evaluates the stability of the power system with respect to harmonics based on the received impedance information. The power system according to claim 4.

16. The processing unit intentionally outputs harmonic voltages or harmonic currents while changing the frequency, and calculates the impedance for each frequency sequentially to obtain the impedance information. The power system according to claim 15.

17. The evaluation unit evaluates the stability of each of the devices with respect to the harmonics based on the received impedance information, aggregates or statistically processes the evaluation results for each of the devices, and evaluates the stability of the entire power system or a part of it with respect to the harmonics. The power system according to claim 15.

18. A power system control device comprising one or more devices connected to a power system, and the one or more devices connected to the power system via a network, A receiving unit that repeatedly receives harmonic information from the aforementioned device, which is information relating to the voltage or current in the device, or the harmonics of the power system excluding the fundamental frequency based on the operation or control of the device, over time or when the state of the power system or the device changes. The system includes an evaluation unit that evaluates the stability of the power system with respect to harmonics based on the received harmonic information, The receiving unit receives operation control information relating to the operation or control of the equipment, which has been acquired from the equipment as harmonic information. The evaluation unit evaluates the stability of the power system with respect to harmonics based on the received operation control information. System control device.

19. A method for evaluating the stability of a power system, comprising one or more devices connected to a power grid, and a system control device connected to the one or more devices via a network to control the power grid, A first processing step in which the device repeatedly acquires harmonic information, which is information relating to the voltage or current in the device, or to the harmonics of the power system excluding the fundamental frequency based on the operation or control of the device, over time or when the state of the power system or the device changes. The equipment transmits the harmonic information to the system control device in a transmission step, The system control device performs a receiving step of receiving the harmonic information, The system control device includes an evaluation step of evaluating the stability of the power system with respect to harmonics based on the harmonic information, The first processing step involves acquiring operation control information relating to the operation or control of the equipment as harmonic information, The transmission step involves transmitting the acquired operation control information to the system control device. The receiving step involves receiving the operation control information from the device, The evaluation step evaluates the stability of the power system with respect to harmonics based on the received operation control information. Stability evaluation method.

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