Electric 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

Power system, system control device and stability evaluation method

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

[0002] The power system includes, for example, a plurality of devices such as power conversion devices that convert AC power and DC power.

[0003] Patent No. 6157880

[0004] In power conversion devices connected to a grid, harmonic resonance occurs due to the interaction between the system impedance caused by the grid wiring and power loads, etc., and the power conversion device control, causing operational instability and, in some cases, leading to a protective shutdown. For example, in systems such as microgrids and offshore wind power generation systems that interconnect many power conversion devices, the risk of serious harmonic resonance problems due to their interactions is increasing. For this reason, there is a demand for more accurate evaluation of the stability of power systems regarding harmonic resonance.

[0005] However, typical power system control devices primarily monitor the fundamental frequency of the power system (rated at 50 Hz or 60 Hz) 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 constantly or at appropriate times. Standards, including grid interconnection regulations, only require operators of interconnected equipment to meet harmonic standards under specific conditions and at specific times, but do not fully 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 difficult to grasp the actual risks related to 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 the power system with respect to harmonic resonance.

[0007] The power system of an embodiment is a power system comprising one or more devices connected to a power system, and a system control device connected to the one or more devices via a network to control the power system, and is also provided with a first processing unit that repeatedly acquires harmonic information, which is information regarding harmonics of frequencies excluding the fundamental frequency of the power system based on the voltage, current, or operation of the devices, or 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 harmonics based on the harmonic information.

[0008] FIG. 1 is a diagram illustrating an example of the overall configuration of a power system according to a first embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a power conversion device according to the first embodiment. FIG. 3 is an equivalent circuit diagram illustrating an example of a power conversion device and a grid impedance according to the embodiment. FIG. 4 is a diagram illustrating an example of an impedance characteristic diagram of the power conversion device according to the embodiment. FIG. 5 is a block diagram illustrating an example of a functional configuration of a grid control device according to the first embodiment. FIG. 6 is a sequence diagram illustrating an example of a procedure for evaluating stability regarding harmonics based on harmonic amounts in the first embodiment. FIG. 7 is a sequence diagram illustrating an example of a procedure for evaluating stability regarding harmonics based on impedance information in the first embodiment. FIG. 8 is a sequence diagram illustrating an example of a procedure for evaluating stability regarding harmonics based on operation control information in the first embodiment. FIG. 9 is an equivalent circuit diagram illustrating an example of a grid impedance in a power conversion device according to a fourth modification.

[0009] Hereinafter, embodiments will be described with reference to the drawings. (First Embodiment) Fig. 1 is a diagram showing an example of the overall configuration of a power system according to a first embodiment. As shown in Fig. 1, a power system 1 according to this embodiment mainly includes renewable energy power sources 40A, 40C, and 40D, a storage battery 30, power conversion devices 300A, 300B, 300C, and 300D, a voltage / current detection device 20, a switching device 10, and a system control device 100.

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

[0011] The power conversion device 300B is connected to a storage battery 30. The power conversion devices 300A, 300C, and 300D are connected to renewable energy power sources 40A, 40C, and 40D, respectively. When the renewable energy power sources 40A, 40C, and 40D are not distinguished from one another, they are referred to as renewable energy power sources 40. When the power conversion devices 300A, 300B, 300C, and 300D are not distinguished from one another, they are referred to as power conversion devices 300. The power conversion device 300 generally converts DC to AC, but may also directly convert AC to AC depending on the frequency of the power source. The voltage / current detection device 20 detects the voltage and current in the power system. The switchgear 10 is a switch that switches the connection to the power system. The switchgear 10 may be used to switch the connection of the transmission and distribution lines at any position in the power system. The system power control device 100 is a device that monitors the stability of harmonic resonance in the power system.

[0012] Next, details of the power conversion device 300 will be described. Fig. 2 is a diagram showing an example of the configuration of the power conversion device 300 according to the first embodiment. The power conversion device 300 is provided at an interconnection point between an electric power grid and a DC power source 4, and converts AC power supplied by the electric power grid into DC power supplied by the DC power source 4, and vice versa. As shown in Fig. 2 , the power conversion device 300 includes a voltage transformer VT, a switch CB, an interconnection inductor I, a current transformer CT, a converter control device 31, and a power converter 32.

[0013] The DC power source 4 is a device that operates on DC power, such as a storage battery, a generator, a load, etc. The switch CB switches between electrical continuity with the power grid.

[0014] The power converter 32 includes a switching element that switches the connection with the DC power supply 4. The power converter 32 receives a gate signal gate from the converter control device 31 and converts AC power to DC power and vice versa. The power converter 32 outputs a voltage V. The power converter 32 is a circuit configured using self-extinguishing switching elements 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 issuing operation commands to the switching elements of the power converter 32. As shown in Fig. 2 , the converter control device 31 mainly includes an arithmetic processing unit 320, a voltage / current control unit 311, a harmonic voltage command generating unit 313, and a gate signal generating 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 processing using the grid-tie point voltage Vs obtained by the voltage transformer VT connected to the grid-tie point P between the power grid and the grid-tie inductor I, and the AC current Is obtained by the current transformer CT provided between the grid-tie inductor I and the power converter 32. Here, the grid-tie point voltage Vs is the voltage of the power grid, and the AC current Is is the current of the power grid.

[0017] The calculation processing unit 320 includes a transmitting / receiving unit 321, a detecting unit 323, and an impedance calculating unit 322. The transmitting / receiving unit 321 transmits and receives various data to and from the system control device 100. In this embodiment, the transmitting / receiving unit 321 transmits harmonic information, which is information related to harmonics, to the system control device 100. The transmitting / receiving unit 321 also receives an impedance calculation command from the system control device 100. Here, the harmonic information includes the amount of harmonic waves, which will be described later, and impedance information calculated by the impedance calculating unit 322, which will be described later.

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

[0019] In this embodiment, the detector 323 detects the instantaneous values ​​of the grid-connection point voltage Vs and the AC current Is and calculates the amount of harmonic waves as harmonic information by, for example, Fourier transforming the detected instantaneous values ​​of the grid-connection point voltage Vs or the AC current Is. Here, the amount of harmonic waves refers to the harmonic value of the grid-connection point voltage Vs or the AC current Is that exceeds a predetermined reference value, or, for example, a harmonic level indicating whether or not the reference value is exceeded. The harmonic value itself may be a total distortion (rate) obtained by adding up 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 with the maximum amplitude within the specific frequency range. The detector 323 sends the calculated amount of harmonic waves to the transmitter / receiver 321.

[0020] In addition, when the detection unit 323 receives a notification from the transmission / reception unit 321 that an impedance calculation command has been received from the system control device 100, the detection unit 323 sends the detected system interconnection point voltage Vs and AC current Is to the impedance calculation unit 322.

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

[0022] In this embodiment, the impedance calculation unit 322 intentionally outputs a harmonic voltage or harmonic current while changing the frequency using the harmonic voltage command generation unit 313, and calculates the impedance for each frequency in sequence to calculate impedance information.

[0023] The impedance calculation unit 322 sends the calculated impedance information to the transmission / reception unit 321 as harmonic information.

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

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

[0026] As described above, in this embodiment, the impedance calculation unit 322 acquires impedance information, which is information on the impedance Zgrid of the power grid, and the transmitter / receiver 321 transmits the impedance information to the system control device 100. The impedance Zvsc of the power conversion device 300 as a device can be obtained not only by measurement during grid connection, but also by test and analysis, such as by applying a harmonic voltage from outside and measuring, before grid connection, and the characteristics can be stored. The power conversion device 300 may transmit the stored Zvsc to the system control device 100, or the system control device 100 may store the Zvsc in advance. Then, the system control device 100 can calculate the phase margin to determine the risk of harmonic resonance occurring.

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

[0028] The voltage / current control unit 311 receives the grid-tied point voltage Vs and the 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 generating unit 313 and the AC voltage command value V1* output from the voltage / current control unit 311 are added by an adder 314 and input to the gate signal generating unit 312.

[0030] The gate signal generating unit 312 receives the sum signal of the voltage command value Vh* and the AC voltage command value V1*, generates a gate signal gate for controlling 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 realizes each function by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software) stored in a storage unit (not shown). Furthermore, some or all of the functions may be realized by hardware such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array), or may be realized by a combination of software and hardware.

[0032] Next, the system control device 100 will be described. Fig. 5 is a block diagram showing an example of the functional configuration of the system control device 100 according to the first embodiment. As shown in Fig. 5, the system control device 100 of this embodiment mainly includes 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 a device such as the power conversion device 300. Specifically, the information input unit 101 receives harmonic amount and impedance information from the power conversion device 300. The information input unit 101 is an example of a receiving unit.

[0034] The information storage unit 106 is a storage medium such as a hard disk drive (HDD) or a solid state drive (SSD). The information storage unit 106 stores harmonic amounts and impedance information received in the past. The information storage unit 106 also stores stability information, which is information regarding harmonic stability evaluated by the information evaluation unit 102 described above. The stability information includes the evaluation results of harmonic stability evaluation for each device, such as the power conversion device 300, and the evaluation results of harmonic stability evaluation for the entire power system or a part of the power system. The information storage unit 106 also stores, as stability information, the operation pattern of the power system and time and / or seasonal patterns, 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 amount 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 device such as the power conversion device 300, and the harmonic stability of the entire power system or a part of the power system.

[0036] That is, the information evaluation unit 102 evaluates the harmonic stability of each device, such as the power conversion device 300, based on the harmonic amount as harmonic information received by the information input unit 101. Specifically, when the harmonic amount is a harmonic value, the information evaluation unit 102 determines that an unstable state in which harmonic resonance occurs exists when the average of the harmonic values ​​exceeds a predetermined threshold. Also, when the harmonic amount is a harmonic level, the information evaluation unit 102 determines that an unstable state in which harmonic resonance occurs exists when the exceedance of the harmonic level exceeds a predetermined threshold.

[0037] The information evaluation unit 102 compares the amount of harmonics for a certain period of time in the past stored in the information storage unit 106 with the amount of harmonics received, and if the increase in the amount of harmonics received is equal to or greater than a certain level, or if the difference between the amount of harmonics for a certain period of time in the past and the amount of harmonics received is equal to or greater than a certain level, evaluates that the stability of the transmitting device with respect to harmonics is low.

[0038] The information evaluation unit 102 performs aggregation or statistical processing, such as calculating the average or maximum value of multiple harmonic quantities for each device, and evaluates the stability of the entire power system or a part of it based on the harmonic quantities after aggregation or statistical processing. Specifically, the information evaluation unit 102 evaluates that the stability of the entire power system or a part of it is low when the harmonic quantity after aggregation or statistical processing is equal to or greater than a predetermined reference value.

[0039] The information evaluation unit 102 may be configured to compare the amount of harmonic waves for each device with a predetermined reference value, and if the number of devices whose amount of harmonic waves exceeds the predetermined reference value is equal to or greater than a certain number, determine that the entire or part of the power system is unstable 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 occurrence by calculating a phase margin from the impedance information. That is, the information evaluation unit 102 evaluates the harmonic stability of the device by calculating a phase margin from the impedance information.

[0041] Furthermore, the information evaluation unit 102 obtains stability determination information by performing tabulation or statistical processing such as calculating the average value or maximum value of the impedance information of each device, and evaluates the stability of the entire power system or a part of it with respect to harmonics. Specifically, the information evaluation unit 102 evaluates that the stability of the entire power system or a part of it is low when the stability determination information after tabulation or statistical processing is equal to or greater than a predetermined reference value.

[0042] The information evaluation unit 102 may be configured to compare the impedance information for each device with a predetermined reference value, and if the number of devices whose impedance information exceeds the predetermined reference value is equal to or greater than a certain number, determine that the entire or part of the power system is unstable with respect to harmonics.

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

[0044] The information learning unit 105 obtains learning information that learns patterns with high stability and / or patterns with low stability based on the stability information stored in the information storage unit 106. Furthermore, the information learning unit 105 calculates a recommended pattern that stabilizes the power system based on the learning information.

[0045] The information storage unit 106 stores stability information, making it possible to predict operation patterns that are likely to cause harmonic resonance. The information learning unit 105 learns based on the stability information, making it possible to present operation patterns with high stability regarding harmonics and automatically control to stable operation patterns. Here, operation patterns include, for example, the open / closed state of the power system switchgear 10 (device connection and line usage status), the operation / stop of the power generation device and power conversion device 300, and power, and can be used by the operation command unit 104 described later.

[0046] In addition, since power demand and the operating conditions of the renewable energy power source 40 vary depending on the time and season, the information storage unit 106 can associate time information with operation patterns and stability information, store them in the information storage unit 106, and learn from them.

[0047] The operation command unit 104 sends operation commands to each device in the power system based on the learned information and the above operation pattern. Examples of operation commands include an opening / closing command to the switchgear 10, an operation / stop command and / or a power generation command to a power generation device, an operation / stop command and / or a power conversion command to a power conversion device, etc.

[0048] In addition, when multiple power generation devices are connected to a power system, the operation command unit 104 can issue operation commands to reduce the power generation power so that the individual power generation devices have equal opportunities to reduce the power generation power.

[0049] Here, when stopping the power generation device or the power conversion device 300, the operation command unit 104 is configured to send an operation command to stop devices with a high amount of harmonic waves first, for example, and by preventing the high harmonic levels from spreading to the system, it is possible to stabilize the entire power system.

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

[0051] Next, a process for evaluating the stability of harmonics performed by the power system 1 according to the first embodiment configured as described above will be described. First, a process for evaluating the stability of harmonics based on the amount of harmonics in a device will be described.

[0052] 6 is a sequence diagram showing an example of a procedure for evaluating the stability regarding harmonics based on the amount of harmonics in the first embodiment. In the example of FIG. 6, a plurality of power electronics devices 300 will be described as an example of the devices.

[0053] First, in each of the multiple power conversion devices 300, the calculation processing unit 320 detects the grid-connection point voltage Vs and the AC current Is (S101A, S101B). The calculation processing unit 320 then calculates the amount of harmonic waves using the detected grid-connection point voltage Vs or AC current Is (S102A, S102B). The transceiver unit 321 of each power conversion device 300 transmits the calculated amount of harmonic waves to the grid control device 100 (S103A, S103B). The timing of transmission may be limited to a predetermined time, time interval, or when the change in the amount of harmonic waves exceeds a predetermined standard. This makes it possible to grasp changes in harmonic trends while reducing network load. It is necessary to repeatedly transmit information at multiple points in time when the amount of harmonic waves may change over time or when the state of the power grid or equipment changes, enabling evaluation.

[0054] In the system control device 100, the information input unit 101 receives the amount of harmonics from each of the power conversion devices 300, and the information evaluation unit 102 evaluates the harmonic stability of each device based on each amount of harmonics (S104A, S104B).The information evaluation unit 102 then compiles 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 of the power system, and generates learning information (S106). After that, the operation command unit 104 issues operation commands to each device as necessary (S107A, S107B).

[0056] Next, a description will be given of a process for evaluating the stability of harmonics based on the impedance information in the power conversion device 300. Fig. 7 is a sequence diagram showing an example of a procedure for evaluating the stability of harmonics based on the 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 plurality of power conversion devices 300 (S201A, S201B). The timing of transmission may be limited to a predetermined time, time interval, or only when the operational status of the power system (such as the state of the switching devices, the amount of power generated, or the amount of load) changes. In each of the plurality of power conversion devices 300 that received the impedance calculation command, the calculation processing unit 320 detects the grid interconnection point voltage Vs and the AC current Is (S202A, S202B). Then, the calculation processing unit 320 calculates impedance information using the detected grid interconnection point voltage Vs and the AC current Is (S203A, S203B). The transmission / reception unit 321 of each power conversion device 300 transmits the calculated impedance information to the grid control device 100 (S204A, S204B). Note that the power conversion device 300 may also be configured to determine the timing of the impedance calculation in a similar manner. It is necessary to be able to repeatedly calculate and evaluate impedance at multiple points in time when the amount of harmonics can change over time or when the state of the power system or equipment changes.

[0058] In the system control device 100, the information input unit 101 receives impedance information from each of the power conversion devices 300, and the information evaluation unit 102 evaluates the harmonic stability of each device based on the impedance information (S205A, S205B). Then, the information evaluation unit 102 aggregates and statistically processes the evaluation results of the harmonic stability of each device, and evaluates 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 of the harmonic stability of each device and the evaluation results of the harmonic stability of the entire power system or a part of the power system, and generates learning information (S207). After that, the operation command unit 104 issues operation commands to each device as necessary (S208A, S208B).

[0060] Conventional power system control devices primarily monitor the fundamental frequency (rated 50 Hz or 60 Hz) of the power system 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 constantly or at appropriate times. Standards, including grid interconnection regulations, only require operators of interconnected equipment to meet harmonic standards under specific conditions and at specific times, but do not fully 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 actual risks associated with harmonic resonance. This makes it difficult to identify the cause of instability in the entire power system.

[0061] In contrast to this, in this embodiment, harmonic information, which is information about harmonics based on the voltage and current in devices such as the power conversion device 300 connected to the power system, is acquired, and the stability of the power system with respect to the harmonics is evaluated based on the harmonic information. Specifically, the devices repeatedly acquire harmonic information, which is information about harmonics based on the voltage and current in the devices, and transmit it to the system control device 100. The system control device 100 receives the harmonic information and evaluates the stability of the power system with respect to the harmonics based on the harmonic information.

[0062] Therefore, according to this embodiment, it is possible to more accurately evaluate the stability of a power system with respect to harmonic resonance. Furthermore, according to this embodiment, it is possible to visualize the state and risk of harmonic resonance, select a stable operation method, and prevent equipment shutdowns and burnout due to the expansion of harmonic resonance. That is, according to this embodiment, even when the operation of an individual device becomes unstable due to harmonic resonance or when harmonic resonance is induced by the operation of multiple devices, it is possible to grasp the risk of harmonic resonance in accordance with the actual situation, so that even if the entire power system becomes unstable, it is easy to identify the cause. Therefore, 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, when the operational state of the power system changes due to repeated acquisition of harmonic information, it is possible to visualize and predict the risk of an unstable state due to harmonic resonance when adding a generator, a load, a power conversion device 300, etc., or expanding the power system. Therefore, according to this embodiment, it is possible to select a method for stable operation of the power system or an expansion method of the power system, and it is possible to improve the reliability of the power system.

[0064] Furthermore, in this embodiment, devices such as the power conversion device 300 detect instantaneous values ​​of voltage and current in the device, calculate harmonic quantities indicating harmonics from the detected instantaneous values ​​of voltage and current as harmonic information, and transmit this to the system control device 100, which receives the harmonic quantities and evaluates the harmonic stability of the power system based on the received harmonic quantities. Therefore, according to this embodiment, since judgment is based on actual values, that is, instantaneous values ​​of voltage and current in devices connected to various locations in the power system, it is possible to more accurately evaluate the stability of the power system regarding harmonic resonance.

[0065] Furthermore, in this embodiment, the system control device 100 compares the past harmonic amount with the received harmonic amount, and if the increase in the harmonic amount is equal to or greater than a certain level, evaluates that the stability of the equipment with respect to harmonics is low. Therefore, according to this embodiment, since the judgment is based on the past harmonic amount, it is possible to grasp the increasing trend of the harmonic amount and more accurately evaluate the stability with respect to harmonic resonance of the power system.

[0066] Furthermore, in this embodiment, the system control device 100 aggregates or statistically processes multiple harmonic amounts for each device, and evaluates the stability of the entire power system or a portion thereof based on the aggregated or statistically processed harmonic amounts. Specifically, the system control device 100 evaluates that the stability of the entire power system or a portion thereof is low if the aggregated or statistically processed harmonic amounts are equal to or greater than a predetermined threshold. Therefore, according to this embodiment, it is possible to more accurately evaluate the stability regarding harmonics not only for each device, but also for the entire power system or a portion thereof based on the harmonic amounts.

[0067] In this embodiment, a device such as the power conversion device 300 detects voltage and current, calculates impedance information related to impedance from the detected voltage and current as harmonic information, and transmits the calculated impedance information to the grid control device. Specifically, the device such as the power conversion device 300 intentionally outputs harmonic voltages or harmonic currents while varying the frequency, and calculates the impedance information by sequentially calculating the impedance for each frequency. In this embodiment, the grid control device 100 receives impedance information from the device and evaluates the harmonic stability of the power grid based on the received impedance information. Therefore, according to this embodiment, since the determination is based on the impedance information, the stability of the power grid with respect to harmonic resonance can be more accurately evaluated. For example, even if the impedance changes due to changes in the state of the power grid or connected devices, the determination is based on the impedance actually measured at that time, so the stability of the power grid with respect to harmonic resonance can be more accurately evaluated.

[0068] In this embodiment, the system control device 100 evaluates the harmonic stability of each device based on the received impedance information, and aggregates or statistically processes the evaluation results for each device to evaluate the harmonic stability of the entire power system or a portion of it. Therefore, according to this embodiment, it is possible to more accurately evaluate the harmonic stability of the entire power system or a portion of it based on the impedance information, rather than just for each device.

[0069] Furthermore, in this embodiment, the system control device 100 stores information related to stability with respect to harmonics in the information storage unit 106, and obtains learning information that learns patterns with high and / or low stability based on the stored information on stability. Therefore, according to this embodiment, it is possible to use the learning information to more accurately determine stability with respect to harmonics. Furthermore, in this embodiment, by learning information related to stability including the determination results, it is possible to more accurately determine the stability with respect to harmonics in the power system as the operation period progresses, thereby improving reliability.

[0070] In this embodiment, the system control device 100 sends operation commands to the devices in the power system based on the learning information. Therefore, according to this embodiment, by providing feedback and issuing operation commands based on the learning information related to stability, the devices in the power system can be made to operate more appropriately, and harmonic instability can be automatically prevented.

[0071] (Modifications) There are various modifications to the first embodiment. In Modification 1, for example, in a device such as the power conversion device 300, the transmitter / receiver 321 can be configured to transmit the instantaneous value of the grid tie point voltage Vs or the 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 amount of harmonics from the received instantaneous value of the grid tie point voltage Vs or the AC current Is, and to evaluate the harmonic stability of the power grid based on the calculated amount of harmonics. This reduces the processing load on devices such as the power conversion device 300.

[0072] In addition, as a second modification, in a device such as the power conversion device 300, the calculation processing unit 320 can be configured to detect the grid interconnection point voltage Vs and the AC current Is, calculate impedance information related to the impedance from the detected grid interconnection point voltage Vs and AC current Is, and further evaluate the harmonic stability of the device based on the impedance information, and the transceiver unit 321 can be configured to transmit the evaluation result of the harmonic stability to the system control device 100 as harmonic information.

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

[0074] As a third modification, in a device such as the power conversion device 300, the transmitter / receiver 321 can be configured to transmit the grid tie point voltage Vs and AC current Is detected by the calculation processing unit 320 to the system control device 100 as harmonic information. In this case, in the system control device 100, the information input unit 101 can be configured to receive the grid tie point voltage Vs and AC current Is from each device, calculate impedance information from the grid tie point voltage Vs and AC current Is, evaluate the harmonic stability of each device based on the impedance information, and aggregate or statistically process the evaluation results of each device to evaluate the harmonic stability of the entire power system or a part of it. This reduces the processing load on devices such as the power conversion device 300.

[0075] Second Embodiment In the first embodiment, the stability of the power grid with respect to harmonics is evaluated using the voltage of the device and the amount of harmonics and impedance information calculated from the voltage. In the second embodiment, the stability of the power grid with respect to harmonics is evaluated indirectly based on operation control information related to the operation and control of the power conversion device 300 as the device.

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

[0077] In the power conversion device 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 conversion device 300 from the voltage / current control unit 311, etc. The transmission / reception unit 321 transmits the acquired operation control information to the system control device 100 as harmonic information.

[0078] The power conversion device 300 of this embodiment can switch, by the voltage / current control unit 311, the control mode in which it operates between a first control mode for normal operation and a second control mode for suppressing harmonic resonance.

[0079] As a first example, the first control mode and the second control mode are current control modes. The current control mode is a control mode that feedback controls the AC current flowing between the power grid and the power conversion device 300. The second control mode is a control mode among the current control modes that suppresses harmonic resonance by shaping the impedance of the power conversion device 300. The control mode adopted by the second control mode is referred to as the current control mode (harmonic resonance suppression). The current control mode adopted by the first control mode is referred to as the current control mode (normal). Details of the current control mode (harmonic resonance suppression) are disclosed in Japanese Patent Application Laid-Open 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 the 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 in which, similarly to the above, the AC current flowing between the power grid and the power conversion device 300 is feedback-controlled. The second control mode is a voltage control mode. The voltage control mode is a control mode in which the phase of the voltage output to the power grid is adjusted in synchronization with the voltage of the power grid without directly feedback-controlling the current. The voltage control mode is also sometimes called grid-forming control.

[0081] In this embodiment, the voltage / current control unit 311 is capable of switching between a current control mode and a voltage control mode, and when the amplitude of the vibration component arbitrarily converted based on the amount of harmonics and the voltage / current detection values ​​exceeds a predetermined threshold value in the current control mode, it is configured to switch to the more stable voltage control mode for reasons described below.

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

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

[0084] Furthermore, an unstable state in which harmonic resonance occurs is likely to occur when negative resistance is included in the impedance of the power conversion device 300. When negative resistance is included, the phase exceeds ±90°, as in Zvsc0 shown in the lower graph of Figure 4. Since the phase of Zgrid is usually within ±90°, when 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 conversion device 300 includes normal resistance, an opposing voltage is generated when a harmonic current flows in, and the harmonic current is suppressed. On the other hand, when the impedance of the power conversion device 300 includes negative resistance, when a harmonic current flows in, the voltage drops and the harmonic current increases. For this reason, when the impedance of the power conversion device 300 includes negative resistance, it is prone to an unstable state in which harmonic resonance occurs.

[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), negative resistance can be reduced because the current is not directly controlled. Therefore, as shown in the lower graph of Figure 4, at the amplitude intersection fres, the phase of Zvsc0, which indicates current control mode (normal), exceeds the ±90° range and becomes unstable. On the other hand, at the amplitude intersection fres, the phases of Zvsc1, which indicates current control mode (harmonic resonance suppression), and the voltage control mode are within the ±90° range and are stable.

[0087] That is, even when the power conversion device 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 in Figure 4 and shape the impedance by controlling this mode, thereby, for example, reducing the negative resistance in some frequency bands and suppressing harmonic resonance.

[0088] Furthermore, by switching the control mode from the current control mode to the power control mode indicated by Zvsc2 in FIG. 4, the power conversion device 300 can reduce the negative resistance over a wider frequency range and suppress harmonic resonance.

[0089] When the power conversion device 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, the harmonic resonance can be reduced by the effect of the control mode after switching, but it can be determined that the power system is in a state that is inherently prone to harmonic resonance. For this reason, the information evaluation unit 102 of the system control device 100, which will be described later, determines that the stability of the power conversion device 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 acquires the current control mode from the voltage / current control unit 311 and sends it to the transmission / reception unit 321 .

[0091] Furthermore, if a number of protective shutdowns of devices such as the power conversion device 300 occur, the power system is considered unstable. When harmonic resonance occurs, the amplitude of harmonics is added to the normal AC voltage or AC current, increasing the voltage or current value. This activates the overvoltage or overvoltage protection function of the device, causing the device to stop operating. Therefore, the detection unit 323 acquires protection shutdown information indicating that a protective shutdown has occurred in the power conversion device 300 from the voltage / current control unit 311 or the like, and sends this information to the transmission / reception unit 321. The transmission / reception unit 321 then transmits the acquired current control mode to the system control device 100 as operation control information.

[0092] When the transmission / reception unit 321 acquires the 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 conversion device 300.

[0094] The information evaluation unit 102 evaluates the harmonic stability of the power system based on the received operation control information. Specifically, when the current control mode is the second control mode, i.e., the current control mode (harmonic resonance suppression) or the voltage control mode, the information evaluation unit 102 evaluates that the harmonic stability of the equipment such as the power conversion device 300 is low. Furthermore, when the information input unit 101 receives protection stop information from the equipment such as the power conversion device 300, the information evaluation unit 102 evaluates that the harmonic stability of the equipment that transmitted the protection stop 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 portion 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 portion thereof with respect to harmonics is low when a predetermined number or more of power electronics devices 300 operating in the second control mode are present. Furthermore, the information evaluation unit 102 evaluates that the stability of the entire power system or a portion thereof is low when a predetermined number or more of devices, such as power electronics devices 300, have transmitted protection stop information.

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

[0097] The operation commands transmitted by the operation command unit 104 of this embodiment include commands to change the control mode in addition to the commands similar to those in the first embodiment. Furthermore, the operation command unit 104 of this embodiment transmits a request command for operation control information to each device.

[0098] Next, a process for evaluating the stability regarding harmonics performed by the power system 1 according to the second embodiment configured as described above will be described. Fig. 8 is a sequence diagram showing an example of the procedure for evaluating the stability regarding harmonics based on the operation control information according to the first embodiment. In the example of Fig. 8, a plurality of power electronics devices 300 will be used as the devices.

[0099] First, the operation command unit 104 of the system control device 100 transmits a request for operation control information to each of the multiple power conversion devices 300 (S301A, S301B). The timing of transmission may be limited to a predetermined time, time interval, or only when the operational status of the power system (such as the state of the switching devices, the amount of power generated, or the amount of load) changes. In each of the multiple power conversion devices 300 that received the request 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 transceiver unit 321 of each power conversion device 300 transmits the acquired operation control information to the system control device 100 (S303A, S303B). Note that the system control device 100 may be configured to transmit the operation control information to the system control device 100 when the operation control information changes. It is necessary to repeatedly transmit information at multiple points in time when the amount of harmonic current may change over time or when the state of the power system or equipment changes, so that it can be evaluated.

[0100] In the system control device 100, the information input unit 101 receives operation control information from each of the power conversion devices 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 of the harmonic stability of each device and the evaluation results of the harmonic stability of the entire power system or a part of the power system, and generates learning information (S306). After that, the operation command unit 104 issues operation commands to each device as necessary (S307A, S307B).

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

[0103] Furthermore, in this embodiment, the power system control device 100 aggregates or statistically processes the operation control information and evaluates the harmonic stability of the entire power system or a part of it based on the processed operation control information. Therefore, according to this embodiment, it is possible to more accurately and easily evaluate the harmonic stability of the entire power system or a part of it based on the operation control information, not just for each device.

[0104] In the present embodiment, the power conversion device 300 can switch between a first control mode used during normal operation and a second control mode for suppressing harmonic resonance. The power conversion device 300 acquires the control mode in which the power conversion device is operating and transmits the acquired control mode to the grid control device 100. The grid control device 100 receives the control mode and, if the control mode is the second control mode, evaluates the power conversion device 300 as having low stability with respect to harmonics. Specifically, the first control mode and the second control mode are current control modes that perform feedback control of the current flowing between the power grid and the power conversion device, and the second control mode is a control mode that suppresses harmonic resonance by shaping the impedance of the power conversion device 300. The first control mode is a current control mode that performs feedback control of the current flowing between the power grid and the power conversion device 300, and the second control mode is a voltage control mode that adjusts the phase of the voltage output to the power grid in synchronization with the voltage of the power grid without directly feedback controlling the current.

[0105] Therefore, according to this embodiment, the stability of the power system with respect to harmonics is evaluated indirectly based on the second control mode, so that 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, when some power conversion devices 300 are performing harmonic resonance suppression control in the second control mode, even if stability is ensured by the effect of that control, there is a risk of rapid harmonic instability if the power conversion device 300 is stopped or if a generator, load, converter, or the like is 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 the stability of the power system with respect to harmonics is determined to be low when operating in the second control mode of harmonic resonance suppression control, the inherent risk of instability in the power system can be accurately grasped and instability can be prevented. Even when the entire power system is stable, the potential risk of instability can be grasped, and the stabilizing effect of the second control mode of the power conversion device 300 can be accurately grasped. Therefore, it is easy to take measures in advance even when equipment is stopped or added. Therefore, according to this embodiment, as with the first embodiment, even if the entire power system becomes unstable, it is easy to identify the cause and even predict the instability, thereby achieving harmonic 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 of it with respect to harmonics is low when the number of power conversion devices 300 operating in the second control mode is equal to or greater than a predetermined number. Therefore, according to this embodiment, it is possible to more accurately and easily evaluate the stability of the entire power system or a part of it based on the second control mode, rather than just for each device.

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

[0109] In this embodiment, the power system control device 100 evaluates the stability of the entire or part of the power system as low when a predetermined number of devices have transmitted protection stop information. Therefore, according to this embodiment, it is possible to more accurately and easily evaluate the stability with respect to harmonics not only for each device but also for the entire or part of the power system based on the protection stop information of the devices.

[0110] (Modification 4) When the power conversion device 300 is equipped with a harmonic filter, harmonic resonance may be reduced simply by changing the power conversion device 300 from a stopped state to an operating state. Fig. 9 is an equivalent circuit diagram showing an example of the grid impedance in the power conversion device 300 according to Modification 4. The power grid is composed of, for example, an equivalent inductance Lgrid from the AC power source to the grid interconnection point P. The impedance seen from the grid interconnection point P toward the AC power source is referred to as grid impedance Zgrid.

[0111] The impedance seen from the grid interconnection point toward the power converter 32 is referred to as converter impedance Zvsc. Zvsc is an impedance based on the grid interconnection inductor I (Lvsc), the harmonic filter F, the converter control characteristics (Zsw), and the like.

[0112] For example, when the switch CB is conductive and the power converter 32 is in a switching stopped state, the current Is of the power converter 32 becomes 0, and resonance occurs due to 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 becomes ≠ 0, and the resistance action (-90 degrees < phase of Zsw < +90 degrees) included in Zsw on the power converter 32 side alleviates the resonance caused by Lgrid and the harmonic filter F. In particular, Zsw often exhibits a resistance action at relatively low frequencies, and this is a useful technique when the resonant frequency is low.

[0114] Even when the power conversion device 300 is operating at substantially zero power, a resistance effect can be obtained on the side of the power converter 32. In this way, harmonic resonance can be reduced simply by changing the power conversion device 300 from a stopped state to an operating state. For this reason, when the power conversion device 300 has a harmonic filter, the operation command unit 104 of the system control device 100 can be configured to transmit an operation command to the power conversion device 300 to change it from a stopped state to an operating state.

[0115] The system control device 100 of the above embodiment and modified example includes a control device such as a CPU, a storage device such as a ROM (Read Only Memory) or RAM, an external storage device such as a HDD or a CD drive, a display device such as a display device, and input devices such as a keyboard and a mouse, and has a hardware configuration with the calculation functions of a computer or the like.

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

[0117] The stability evaluation program executed by the system control device 100 of the above embodiment and modified example may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. The stability evaluation program executed by the system control device 100 of the above embodiment and modified example may be provided or distributed via a network such as the Internet.

[0118] The stability evaluation program executed by the system control device 100 of the above-described embodiment and modified example may be provided by being pre-installed in a ROM or the like.

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

[0120] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[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 to the system control device as the harmonic information; the receiving unit of the system control device receives the detected instantaneous value of the voltage or current; and the evaluating unit of the system control device calculates a harmonic amount indicating harmonics from the received instantaneous value of the voltage or current, and evaluates the stability of the power system with respect to the harmonics based on the harmonic amount.

[0122] In the above-described embodiment, the calculation processing unit of the device detects the voltage and current in the device, calculates impedance information related to impedance from the detected voltage and current, and evaluates the harmonic stability of the device based on the impedance information; the transmitting unit of the device transmits the evaluation result of the harmonic stability as the harmonic information to the system control device; the system control device: the receiving unit of the system control device receives the evaluation result from each of the devices; and the evaluation unit of the system control device aggregates or statistically processes the evaluation result of each of the devices to evaluate the harmonic stability of the entire or part of the power system.

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

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

[0125] In the above-described embodiment, when a plurality of the power generation devices are interconnected and the power generation is reduced by the operation command, the operation command is given so that the opportunity to reduce the power generation of each of the power generation devices is equalized.

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

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

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

[0129] In the above-described embodiment, the information storage unit stores the information on the stability together with time and / or seasonal patterns.

[0130] REFERENCE SIGNS LIST 1 Power system 4 DC power supply 20 Voltage / current detection device 30 Storage battery 31 Converter control device 32 Power converter 40 Renewable energy power source 100 System control device 101 Information input unit 102 Information evaluation unit 103 Information display unit 104 Operation command unit 105 Information learning unit 106 Information storage unit 300 Power conversion device 311 Voltage / current control unit 312 Gate signal generation unit 313 Harmonic voltage command generation unit 320 Arithmetic processing unit 321 Transmitting / receiving unit 322 Impedance calculation unit 323 Detection unit

Claims

1. A power system comprising one or more devices connected to a power system, and a system control device connected to the one or more devices via a network to control the power system, the power system comprising: a first processing unit that repeatedly acquires harmonic information, which is information regarding the voltage or current in the devices, or harmonics of frequencies excluding the fundamental frequency of the power system 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 harmonics based on the harmonic information.

2. The power system according to claim 1, wherein the device comprises: the first processing unit; and a transmitting unit that transmits the harmonic information to the system control device; and the system control device comprises: a receiving unit that receives the harmonic information; and the evaluating unit.

3. The power system described in claim 2, wherein the first processing unit detects an instantaneous value of voltage or current in the equipment and calculates a harmonic amount indicating harmonics as the harmonic information from the detected instantaneous value of voltage or current; the receiving unit receives the harmonic amount; and the evaluation unit evaluates the stability of the power system with respect to harmonics based on the harmonic amount.

4. The power system according to claim 3, further comprising an information storage unit that stores the amount of harmonic waves received in the past, and the evaluation unit compares the amount of harmonic waves received with the amount of harmonic waves stored in the information storage unit in the past, and evaluates that the stability of the equipment with respect to harmonics is low if an increase in the amount of harmonic waves is equal to or greater than a certain level.

5. The power system according to claim 3, wherein the evaluation unit aggregates or statistically processes a plurality of harmonic quantities for each of the devices, and evaluates the stability of the entire or part of the power system based on the aggregated or statistically processed harmonic quantities.

6. The power system according to claim 5, wherein the evaluation unit evaluates the stability of the power system as a whole or a part thereof as low when the amount of harmonics after the tabulation or statistical processing is equal to or greater than a predetermined threshold value.

7. The power system according to claim 2, wherein the device comprises, as the first processing unit, a calculation processing unit that detects voltage and current and calculates impedance information related to impedance from the detected voltage and current as the harmonic information, the transmission unit transmits the calculated impedance information to the system control device, the reception unit receives the impedance information from the device, and the evaluation unit evaluates the stability of the power system with respect to harmonics based on the received impedance information.

8. The power system according to claim 7, wherein the calculation processing unit intentionally outputs a harmonic voltage or a harmonic current while changing a frequency, and calculates the impedance information by sequentially calculating the impedance for each frequency.

9. The power system according to claim 7, wherein the evaluation unit evaluates the stability of each of the devices with respect to the harmonics based on the received impedance information, and aggregates or statistically processes the evaluation results of each of the devices to evaluate the stability of the entire or part of the power system with respect to the harmonics.

10. The power system described in claim 2, wherein the first processing unit acquires operation control information related to the operation or control of the equipment as the 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 equipment, and the evaluating unit evaluates the stability of the power system with respect to the harmonics based on the received operation control information.

11. The power system according to claim 10, wherein the evaluation unit aggregates or statistically processes the operation control information, and evaluates the stability of the entire or part of the power system with respect to the harmonics based on the processed operation control information.

12. The power system described in claim 11, wherein the equipment is a power conversion device that converts AC power and DC power, the power conversion device is capable of switching between a first control mode for normal operation and a second control mode for suppressing harmonic resonance as a control mode in which it operates, the first processing unit obtains the control mode in which the power conversion device is operating, the transmitting unit transmits the obtained control mode to the system control device, the receiving unit receives the control mode, and the evaluating unit evaluates that the equipment has low stability with respect to harmonics when the control mode is the second control mode.

13. The power system according to claim 12, wherein the first control mode and the second control mode are current control modes for feedback-controlling a current flowing between the power grid and the power conversion device, and the second control mode is a control mode for suppressing harmonic resonance by shaping the impedance of the power conversion device.

14. The power system according to claim 12, wherein the first control mode is a current control mode in which a current flowing between the power grid and the power conversion device is feedback-controlled, and the second control mode is a voltage control mode in which a phase of a voltage output to the power grid side is adjusted in synchronization with a voltage of the power grid without directly feedback-controlling a current.

15. The power system according to claim 12, wherein the evaluation unit evaluates that the stability of the entire or part of the power system with respect to the harmonics is low when a predetermined number or more of the power conversion devices operating in the second control mode are present.

16. The power system of claim 11, wherein the operational control information is protection stop information for the equipment, and the evaluation unit determines that the equipment that transmitted the protection stop information has low stability with respect to harmonics, and further evaluates that the stability of the entire or part of the power system is low when there are a predetermined number or more of the equipment.

17. The power system according to claim 2, wherein the power system control device comprises: an information storage unit that stores information relating to the stability of the harmonics evaluated by the evaluation unit; and an information learning unit that obtains learning information for learning patterns of high stability and / or patterns of low stability based on the information relating to the stability stored in the information storage unit.

18. The power system according to claim 17, wherein the power system control device further comprises: an operation command unit that sends an operation command to the equipment of the power system based on the learning information.

19. A system control device that is connected to one or more devices via a network to control the power system, the system control device comprising: a receiving unit that repeatedly receives from the devices harmonic information, which is information regarding the voltage or current in the devices, or harmonics of a frequency excluding the fundamental frequency of the power system 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 harmonics based on the received harmonic information.

20. A stability evaluation method executed in a power system including one or more devices connected to a power system and a system control device connected to the one or more devices via a network to control the power system, the stability evaluation method including: repeatedly acquiring harmonic information, which is information about the voltage or current in the devices, or about harmonics of frequencies excluding the fundamental frequency of the power system based on the operation or control of the devices, over time or when the state of the power system or the devices changes; and evaluating the stability of the power system with respect to the harmonics based on the harmonic information.

Images