Protection system, control device, control method, and program

Abstract

This protection system comprises: a DC current sensor provided on a power line; an AC current sensor provided on the power line; a circuit breaker provided on the power line; a determination unit that determines that a specific event has occurred on the basis of a measurement value of the DC current sensor and a measurement value of the AC current sensor; and a control unit that executes a protection operation corresponding to the specific event.

Description

Protection system, control device, control method, and program

[0001] The present invention relates to power line protection systems.

[0002] In a DC bus through which a DC current flows, a short circuit current, an overload current, or the like may occur, and protective operations against these currents have been conventionally performed (for example, Non-Patent Document 1).

[0003] Conventional protective actions against short circuit current and overload current include opening a circuit breaker and stopping the output of a power conversion device.

[0004] Study on Short-Circuit Protection Methods for Bus-Wired Outdoor DC Power Supply Systems (IEEJ National Convention 2023, 4-153)

[0005] However, the conventional technology has a problem in that it may not be possible to take appropriate protective action in response to an event that occurs on the DC bus. Note that this problem is not limited to DC buses and can occur in power supply systems in general.

[0006] The present invention has been made in view of the above points, and has an object to provide a technique for performing an appropriate protective operation in response to an event that occurs in a power supply system.

[0007] According to the disclosed technology, there is provided a protection system comprising: a DC current sensor provided on a power line; an AC current sensor provided on the power line; a circuit breaker provided on the power line; a determination unit that determines that a specific event has occurred based on a measurement value of the DC current sensor and a measurement value of the AC current sensor; and a control unit that executes a protection operation corresponding to the specific event.

[0008] According to the disclosed technology, it is possible to perform an appropriate protective operation in response to an event that occurs in a power supply system.

[0009] FIG. 1 is a diagram for explaining problems of the prior art. FIG. 2 is a diagram for explaining an overview of an embodiment of the present invention. FIG. 3 is a diagram showing an example of the configuration of a DC bus protection system in an embodiment of the present invention. FIG. 4 is a diagram showing an example of the operation of the DC bus protection system 100. FIG. 5 is a diagram for explaining variations. FIG. 6 is a diagram showing a flow path in Example 1. FIG. 7 is a diagram showing examples of thresholds and measured values ​​in Example 1. FIG. 8 is a diagram showing a flow path in Example 2. FIG. 9 is a diagram showing examples of thresholds and measured values ​​in Example 2. FIG. 10 is a diagram showing the configuration of a control device 300. FIG. 11 is a diagram showing an example of the hardware configuration of the control device 300.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0011] In the following, a protection system for a DC bus will be described as an example of a protection system using the technology of the present invention, but the technology of the present invention is not limited to DC buses and can be applied to power supply systems in general. For example, the technology of the present invention may be applied to a branch line portion of a loop-type wiring.

[0012] Below, the problem will be explained in more detail first, and then the technology according to the present embodiment will be explained.

[0013] (Regarding the Problem) In the prior art, the protective action against a short circuit current and an overload current is to open a circuit breaker or to stop the output of a power conversion device. Here, opening a circuit breaker is referred to as protective action (1), and stopping the output of a power conversion device is referred to as protective action (2).

[0014] Problems that arise when conventional protective operations (1) and (2) are performed will be described with reference to Fig. 1. In the DC bus configuration shown in Fig. 1, power conversion devices A to D are connected via circuit breakers A to D.

[0015] As shown in Figure 1, suppose a short circuit or overload occurs on the side of power conversion device B, causing a large current to flow in the branch line (power line) to which power conversion device B is connected. If protective operation (1) (opening circuit breaker B) is performed at this time, the voltage input to power conversion device B will become 0 V, causing power conversion device B to stop. Furthermore, protective operation (2) (stopping the output of power conversion device A) will cause the voltage of the entire DC bus to become 0 V, causing power conversion devices C and D in the healthy system to also stop.

[0016] In the above case, if the cause of the large current is a short circuit near power conversion device B, protective action (2) would be an inappropriate action. In other words, the conventional technology has a problem in that when a large current flows through the DC bus, it may not be possible to take appropriate protective action against the current.

[0017] (Outline of the embodiment) In this embodiment, in order to solve the above problem, it is possible to perform separate protective operations for short-circuit current and overload current by determining whether a large current flowing in a branch line of a DC bus is a short-circuit current or an overload current.

[0018] That is, when a short circuit occurs, the circuit breaker through which the short circuit current flows is opened, allowing the power conversion devices in the healthy system to continue operating. On the other hand, when an overload current occurs, control is implemented to reduce the current in the power conversion devices, allowing the operation of each power conversion device to continue.

[0019] More specifically, as shown in Fig. 2, a DC current sensor 110 and an AC current sensor 120 are provided on a branch line of a DC bus. The AC current sensor 120 is, for example, a current transformer. Fig. 2 also shows the actual DC current waveform, the waveform detected by the DC current sensor 110, and the waveform detected by the AC current sensor 120 for each of a short-circuit current and an overload current.

[0020] Note that a large current that exceeds the allowable current of a "power line, power conversion device, or load device" is called an overcurrent (excluding short-circuit current here). Since an overload current is an example of an overcurrent, it is written as "overcurrent (overload current)" in the diagram.

[0021] As shown in FIG. 2, the DC current sensor 110 detects waveforms similar to the actual DC current waveforms for both short-circuit current and overload current.

[0022] On the other hand, the AC current sensor 120 detects the amount of change in current (differential value). Therefore, when the current changes suddenly, such as in a short-circuit current, the output value of the sensor becomes large. On the other hand, when the current changes slowly, such as in an overload current, the output value of the sensor becomes small.

[0023] 2, the DC current sensor 110 and the AC current sensor 120 output different values ​​for short-circuit current and overload current. Therefore, by comparing the output value from the DC current sensor 110 and the output value from the AC current sensor 120 with respective threshold values, it is possible to determine whether the current is a short-circuit current or an overload current.

[0024] The determination method using the output value from the DC current sensor 110 and the output value from the AC current sensor 120 can be applied to the detection of events other than short-circuit current and overload current.

[0025] The configuration and operation of this embodiment will be described in detail below.

[0026] (System Configuration Example) Fig. 3 shows an example of a system configuration of a DC bus according to this embodiment. As shown in Fig. 3, in the DC bus, a power conversion device 200 is connected to each branch line connected to a trunk line via a DC bus protection system 100. Note that both the trunk line and the branch line are power lines. The DC bus protection system may also be referred to as a protection system. The following describes the DC bus protection system 100 on the left side in Fig. 3, but the configuration and operation of the other DC bus protection systems 100 are similar to those of the DC bus protection system 100 on the left side.

[0027] 3, the DC bus protection system 100 includes a DC current sensor 110, an AC current sensor 120, a determination unit 130, a control unit 140, and a circuit breaker 150. The DC current sensor 110, the AC current sensor 120, and the circuit breaker 150 are provided on a branch line (on a power line).

[0028] The determination unit 130 is connected by signal lines to each of the DC current sensor 110 and the AC current sensor 120. The control unit 140 is connected by signal lines to each of the determination unit 130, the circuit breaker 150, and the power conversion device 200.

[0029] The determination unit 130 determines whether a short circuit current or an overload current has occurred based on the measurement value of the DC current sensor 110 and the measurement value of the AC current sensor 120 .

[0030] If the determining unit 130 determines that a short-circuit current has occurred, the control unit 140 opens the circuit breaker 150. If the determining unit 130 determines that an overload current has occurred, the control unit 140 commands the power conversion device 200 to reduce the current.

[0031] The power conversion device to be instructed to reduce the current does not have to be power conversion device 200 connected to DC bus protection system 100 on the left side in Fig. 3. For example, a command to reduce the current may be sent to a power conversion device that supplies power to power conversion device 200 connected to DC bus protection system 100 on the left side in Fig. 3.

[0032] (Operation of DC bus protection system 100) An example of the operation of the DC bus protection system 100 will be described with reference to the flowchart of Fig. 4. In the following operation, each threshold value is set in advance in the determination unit 130.

[0033] In S1 (step 1), the DC current sensor 110 and the AC current sensor 120 each measure a current value, and the determination unit 130 acquires each measurement value.

[0034] In S2, the determination unit 130 determines whether the measurement value (magnitude of current) of the DC current sensor 110 is greater than the threshold value of the DC current sensor 110. If the determination result in S2 is Yes, the process proceeds to S3, and if No, the process returns to S1.

[0035] In S3, the determination unit 130 determines whether the measurement value of the AC current sensor 120 is greater than the threshold value of the AC current sensor 120. If the determination result in S3 is Yes, the process proceeds to S11, and if No, the process proceeds to S21.

[0036] In S11, the determination unit 130 determines that a short-circuit current has occurred. In S12, the control unit 140 transmits a signal to open the circuit breaker 150 to the circuit breaker 150. As a result, the circuit breaker 150 is opened in S13.

[0037] In S21, which is reached if the determination result in S3 is No, the determination unit 130 determines that an overload current has occurred. In S22, the control unit 140 transmits a current reduction command (a command to reduce the magnitude of the current) to the power conversion device 200. This causes the power conversion device 200 to perform an operation to reduce the current.

[0038] (Variations of Operation in S2) Two thresholds may be set in the determination unit 130 for the measurement value of the DC current sensor 110. When two thresholds are used, the operation of the determination unit 130 in S2 is as follows: A to C. The larger of the two thresholds is set as the sensor threshold (large), and the smaller is set as the sensor threshold (small).

[0039] A: If the "current value>sensor threshold value (large)", the flow proceeds to S11, which is a flow for opening the circuit breaker 150.

[0040] B: If "sensor threshold (large)>current value>sensor threshold (small)", the process proceeds to S3, which is the determination flow for the AC current sensor 120.

[0041] C: If the "sensor threshold (small)>current value", the process returns to S1, which is the measurement flow.

[0042] An image of the current value, the sensor threshold (large), and the sensor threshold (small) is shown in Fig. 5. Note that setting two thresholds is just an example, and three or more thresholds may be set.

[0043] As more specific examples of the flow, a flow in the case where a short circuit current occurs will be described as Example 1, and a flow in the case where an overload current occurs will be described as Example 2.

[0044] (Example 1) Fig. 6 shows the flow path in Example 1. That is, in Example 1, processing is performed along the line shown in Fig. 6. Also, the graph of "short circuit current" shown in the upper part of Fig. 7 corresponds to the graph of Example 1. The processing in Example 1 is as follows.

[0045] In S1, the DC current sensor 110 and the AC current sensor 120 each measure a current value, and the determination unit 130 acquires each measurement value.

[0046] In S2, the determination unit 130 determines that the measurement value of the DC current sensor 110 is greater than the threshold value of the DC current sensor 110 (FIG. 7B). In S3, the determination unit 130 determines that the measurement value of the AC current sensor 120 is greater than the threshold value of the AC current sensor 120 (FIG. 7C).

[0047] In S11, the determination unit 130 determines that a short-circuit current has occurred. In S12, the control unit 140 transmits a signal to the circuit breaker 150 to open the circuit breaker 150, and in S13, the circuit breaker 150 is opened.

[0048] Then, the process returns to S1. Since the circuit breaker 150 is open, no current flows, and the determination in S2 is No. Therefore, the loop flow of S1 and S2 is repeated, and the control ends.

[0049] (Example 2) Figure 8 shows the flow path in Example 2. That is, in Example 2, processing is performed along the line shown in Figure 8. Also, the graph of "overcurrent (overload current)" shown in the lower part of Figure 9 corresponds to the graph of Example 2. The processing in Example 2 is as follows.

[0050] In S1, the DC current sensor 110 and the AC current sensor 120 each measure a current value, and the determination unit 130 acquires each measurement value.

[0051] In S2, the determination unit 130 determines that the measurement value of the DC current sensor 110 is greater than the threshold value of the DC current sensor 110 (FIG. 9B). In S3, the determination unit 130 determines that the measurement value of the AC current sensor 120 is equal to or less than the threshold value of the AC current sensor 120 (FIG. 9C).

[0052] In S21, the determination unit 130 determines that an overload current has occurred. In S22, the control unit 140 sends a command to reduce the current to the power conversion device 200. In response, in S23, the power conversion device 200 performs an operation to reduce the current.

[0053] Thereafter, the loop of "S1 to S3 -> S21 to S23" is repeated until the determination in S2 becomes No (that is, until the DC current sensor measurement value falls below the DC current sensor threshold value).

[0054] If the determination in S2 is No, the loop flow of S1 and S2 is repeated, and the control ends.

[0055] (Other Configuration Examples) A ​​configuration including the determination unit 130 and the control unit 140 may be referred to as a control device 300. The control device 300 may be provided within the DC bus protection system 100 as shown in FIG. 3 , or may be provided outside the DC bus protection system 100.

[0056] 10 shows a configuration diagram of the control device 300. As shown in FIG. 10, the control device 300 includes a determination unit 130 and a control unit 140.

[0057] The determination unit 130 determines that a specific event has occurred based on the measurement values ​​of the DC current sensor 110 and the AC current sensor 120. The control unit 140 executes a protective operation corresponding to the specific event. The specific event may be, for example, the occurrence of a short circuit current or an overload current.

[0058] (Hardware Configuration Example) The control device 300 described in this embodiment can be realized, for example, by causing a computer to execute a program. This computer may be a physical computer or a virtual machine on the cloud.

[0059] That is, the control device 300 can be realized by executing a program corresponding to the processing performed by the control device 300 using hardware resources such as a CPU and memory built into a computer. The program can be recorded on a computer-readable recording medium (such as a portable memory) and can be saved or distributed. The program can also be provided via a network such as the Internet or email.

[0060] Fig. 11 is a diagram showing an example of the hardware configuration of the computer. The computer in Fig. 11 includes a drive device 1000, an auxiliary storage device 1002, a memory device 1003, a CPU 1004, an interface device 1005, a display device 1006, an input device 1007, an output device 1008, and the like, all of which are interconnected via a bus B. The computer may further include a GPU.

[0061] The program that realizes the processing on the computer is provided by a recording medium 1001, such as a CD-ROM or a memory card. When the recording medium 1001 storing the program is set in the drive device 1000, the program is installed from the recording medium 1001 to the auxiliary storage device 1002 via the drive device 1000. However, the program does not necessarily have to be installed from the recording medium 1001, but may be downloaded from another computer via a network. The auxiliary storage device 1002 stores the installed program as well as necessary files, data, etc.

[0062] The memory device 1003 reads and stores the program from the auxiliary storage device 1002 when an instruction to start the program is received. The CPU 1004 realizes functions related to the control device 300 in accordance with the program stored in the memory device 1003. The interface device 1005 is used as an interface for connecting to a network, etc. The display device 1006 displays a GUI (Graphical User Interface) or the like according to the program. The input device 1007 is composed of a keyboard, mouse, buttons, a touch panel, etc., and is used to input various operation instructions. The output device 1008 outputs the results of calculations.

[0063] As described above, the technology described in the present embodiment makes it possible to perform an appropriate protective action in response to an event that occurs in a power supply system. More specifically, since it is possible to determine whether a short-circuit current or an overload current has occurred, it becomes possible to perform an appropriate protective action in response to the event that has occurred.

[0064] The following additional notes are provided regarding the above-described embodiments.

[0065] <Additional Notes> (Additional Item 1) A protection system comprising: a DC current sensor provided on a power line; an AC current sensor provided on the power line; a circuit breaker provided on the power line; a determination unit that determines that a specific event has occurred based on a measurement value of the DC current sensor and a measurement value of the AC current sensor; and a control unit that executes a protection operation corresponding to the specific event. (Additional Item 2) The protection system according to Additional Item 1, wherein the specific event is the occurrence of a short-circuit current or an overload current. (Additional Item 3) The protection system according to Additional Item 2, wherein when the occurrence of the short-circuit current is detected, the control unit executes control to open the circuit breaker, and when the occurrence of the overload current is detected, the control unit executes control to reduce the current of a power conversion device. (Supplementary Item 4) The protection system according to Supplementary Item 2, wherein the determination unit determines that the short-circuit current has occurred when the measurement value of the DC current sensor is greater than a first threshold value and the measurement value of the AC current sensor is greater than a second threshold value, or determines that the short-circuit current has occurred when the measurement value of the DC current sensor is greater than a third threshold value. (Supplementary Item 5) The protection system according to Supplementary Item 2, wherein the determination unit determines that the overload current has occurred when the measurement value of the DC current sensor is greater than the first threshold value and the measurement value of the AC current sensor is less than a second threshold value. (Supplementary Item 6) A control device that executes control over a protection system including a DC current sensor provided on a power line, an AC current sensor provided on the power line, and a circuit breaker provided on the power line, the control device comprising: a determination unit that determines that a specific event has occurred based on the measurement value of the DC current sensor and the measurement value of the AC current sensor; and a control unit that executes a protection operation corresponding to the specific event.(Supplementary Item 7) A control method by a control device that executes control over a protection system including a DC current sensor provided on a power line, an AC current sensor provided on the power line, and a circuit breaker provided on the power line, the control method comprising the steps of: determining that a specific event has occurred based on a measurement value of the DC current sensor and a measurement value of the AC current sensor; and executing a protection operation corresponding to the specific event. (Supplementary Item 8) A non-transitory storage medium that stores a program for causing a computer to function as a determination unit and a control unit in the control device described in Supplementary Item 6.

[0066] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0067] REFERENCE SIGNS LIST 100 DC bus protection system 110 DC current sensor 120 AC current sensor 130 Determination unit 140 Control unit 150 Circuit breaker 200 Power conversion device 300 Control device 1000 Drive device 1001 Recording medium 1002 Auxiliary storage device 1003 Memory device 1004 CPU 1005 Interface device 1006 Display device 1007 Input device 1008 Output device

Claims

1. A protection system comprising: a DC current sensor provided on a power line; an AC current sensor provided on the power line; a circuit breaker provided on the power line; a determination unit that determines that a specific event has occurred based on a measurement value of the DC current sensor and a measurement value of the AC current sensor; and a control unit that executes a protection operation corresponding to the specific event.

2. The protection system according to claim 1, wherein the specific event is the occurrence of a short circuit current or an overload current.

3. The protection system according to claim 2, wherein, when the occurrence of the short-circuit current is detected, the control unit executes control to open the circuit breaker, and when the occurrence of the overload current is detected, the control unit executes control to reduce the current in the power conversion device.

4. The protection system according to claim 2, wherein the determination unit determines that the short-circuit current has occurred when the measurement value of the DC current sensor is greater than a first threshold value and the measurement value of the AC current sensor is greater than a second threshold value, or determines that the short-circuit current has occurred when the measurement value of the DC current sensor is greater than a third threshold value.

5. The protection system according to claim 2, wherein the determination unit determines that the overload current has occurred when the measurement value of the DC current sensor is greater than a first threshold value and the measurement value of the AC current sensor is less than a second threshold value.

6. A control device that executes control over a protection system that includes a DC current sensor provided on a power line, an AC current sensor provided on the power line, and a circuit breaker provided on the power line, the control device comprising: a determination unit that determines that a specific event has occurred based on the measurement value of the DC current sensor and the measurement value of the AC current sensor; and a control unit that executes protection operation corresponding to the specific event.

7. A control method by a control device that executes control over a protection system that includes a DC current sensor provided on a power line, an AC current sensor provided on the power line, and a circuit breaker provided on the power line, the control method comprising: a step of determining that a specific event has occurred based on a measurement value of the DC current sensor and a measurement value of the AC current sensor; and a step of executing a protection operation corresponding to the specific event.

8. A program for causing a computer to function as the determining unit and the control unit in the control device according to claim 6.

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