Distributed Power Systems

Abstract

To provide a distributed power source system which is a full power home consumption type and in which occurrence of a reverse power flow to a power system side can be suppressed even when a steep load fluctuation occurs.SOLUTION: Provided is a distributed power source system including: a distributed power source; a power conversion device that converts power supplied from the distributed power source to AC power corresponding to a load; a control device that controls the power converting operation of the power conversion device; and a reverse power relay that stops operation of the power conversion device upon detection of an occurrence of a reverse flow. When receiving an input of a control signal for following control, a control unit of the power conversion device performs following control by controlling operation of a conversion circuit to output power according to the inputted control signal for following control. When receiving an input of a control signal for emergency control, the control unit performs emergency control by controlling operation of the conversion circuit to output predetermined power .SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a distributed power system. [Background technology]

[0002] There is known a fully self-consumption distributed power system that uses distributed power sources such as solar power generators, wind power generators, geothermal power generators, etc. The distributed power system includes a power conversion device that converts the power generated by the distributed power source into power according to the load and supplies the converted power to the load.

[0003] In a distributed power system that is entirely self-consumption, it is desirable to maximize the use of power generated by the distributed power sources and reduce the amount of power purchased from the power grid. For this reason, the power conversion device performs tracking control, which controls the power supplied from the distributed power sources to the load according to the power consumption of the load so that the power received (purchased) from the power grid remains constant at a set value. This makes it possible to reduce the amount of power purchased from the power grid while suppressing the occurrence of reverse power flow from the distributed power sources to the power grid.

[0004] However, even in a power conversion device that performs the above-described tracking control, when a sudden load fluctuation that cannot be tracked by the tracking control occurs, a reverse power flow to the power grid may occur, causing the power conversion device to stop operating. When the power conversion device stops operating, there is a risk that it will take time to restart the power conversion device, for example, by having a worker go to the power conversion device to restore operation. Furthermore, if power supply to a load is required even when the power conversion device is stopped, all of the power required by the load must be supplied from the power grid until the power conversion device restarts, which increases the amount of power purchased from the power grid.

[0005] For this reason, in a distributed power generation system in which all power is consumed by the user, it is desirable to be able to suppress the occurrence of reverse power flow to the power grid even when a sudden load fluctuation occurs. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-88135 [Patent Document 2] Patent No. 6950060 Summary of the Invention [Problem to be solved by the invention]

[0007] An embodiment of the present invention provides a distributed power generation system of a total self-consumption type that can suppress the occurrence of reverse power flow to the power grid even when a sudden load fluctuation occurs. [Means for solving the problem]

[0008] According to an embodiment of the present invention, there is provided a distributed power system of a total self-consumption type that is connected to a power grid and a load, and that reduces power purchases from the power grid to the load by supplying power generated by a distributed power source to the load, the distributed power source generating and supplying the generated power, a power conversion device that converts the power supplied from the distributed power source into AC power corresponding to the load and supplies the converted AC power to the load, a control device that controls the power conversion operation of the power conversion device, and a reverse power relay that detects reverse power flow from the power conversion device toward the power grid and stops the operation of the power conversion device that outputs AC power to the load in response to the detection of the occurrence of reverse power flow, and the control device, when the occurrence of reverse power flow is not detected by the reverse power relay, acquires information on load power consumption that indicates the amount of power required by the load and information on output power of the power conversion device that indicates the amount of power supplied from the power conversion device to the load, and when a difference obtained by subtracting the output power from the load power consumption is equal to or greater than a predetermined value, To perform tracking control to control the output power of the power conversion device so that the received power supplied from the power grid to the load is constant at a set value,A control signal for tracking control is input to the power conversion device so that a value obtained by subtracting a set value from the load power consumption is set as the output power of the power conversion device, and when the difference obtained by subtracting the output power from the load power consumption is less than the predetermined value, the output power of the power conversion device is limited. For emergency control a control unit that receives the control signal for emergency control from the control device by communicating with the control device and inputs the input control signal for emergency control to the control unit; and an input unit that is capable of receiving the control signal for emergency control from the control device faster than communication by the communication unit and inputs the input control signal for emergency control to the control unit, wherein the control unit of the power conversion device, upon receiving the control signal for emergency control via the communication unit, executes the tracking control by controlling the operation of the conversion circuit so as to output power based on the input control signal for emergency control, and, upon receiving the control signal for emergency control via the input unit, executes the emergency control. [Effects of the Invention]

[0009] A distributed power generation system of all-in-house consumption type is provided that can suppress the occurrence of reverse power flow to the power grid even when a sudden load fluctuation occurs. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram schematically illustrating a solar power generation system according to an embodiment. [Figure 2] 4 is a flowchart schematically illustrating an example of an operation of the solar power generation system according to the embodiment. [Figure 3] 4 is a graph schematically illustrating an example of the operation of the solar power generation system according to the embodiment.

[0011] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0012] FIG. 1 is a block diagram schematically illustrating a solar power generation system according to an embodiment. As shown in FIG. 1, the solar power generation system 10 (distributed power system) includes a solar panel 12 (distributed power supply), a power conversion device 14, a control device 16, a monitoring device 18, a power receiving panel 20, and a power meter 22.

[0013] The solar power generation system 10 is connected to a power grid 2 and a load 4. The solar power generation system 10 is a total self-consumption system that supplies power generated by a solar panel 12 to the load 4, thereby reducing the amount of power purchased from the power grid 2 to the load 4. The power of the power grid 2 is AC power. The load 4 is an AC load. In other words, the load 4 is a consumer.

[0014] The solar panel 12 generates electricity and supplies the generated electricity. The solar panel 12 generates electricity by converting the light energy of sunlight into electrical energy using the photovoltaic effect. The power generated by the solar panel 12 is DC power. The solar panel 12 supplies the generated DC power to the power conversion device 14.

[0015] The power conversion device 14 is connected to the solar panel 12 and also connected to the load 4 via the transformer 6, the local grid 8, etc. The power conversion device 14 converts the power supplied from the solar panel 12 into AC power compatible with the load 4 and supplies the converted AC power to the load 4.

[0016] The load 4 is connected to the power conversion device 14, and is also connected to the power grid 2 via the on-site grid 8 and the power receiving panel 20. The load 4 receives a supply of power generated by the solar panels 12 from the power conversion device 14, and also receives a supply of power from the power grid 2 to compensate for the shortfall in the power generated by the solar panels 12 compared to the required power. The power conversion device 14 makes maximum use of the power generated by the solar panels 12, thereby reducing the amount of power purchased from the power grid 2.

[0017] The control device 16 controls the power conversion operation by the power conversion device 14. The monitoring device 18 monitors the operation of the power conversion device 14 and the control device 16. The monitoring device 18, for example, acquires various information from the power conversion device 14 and the control device 16 and displays the acquired information, thereby enabling an administrator of the solar power generation system 10 or the like to monitor whether the power conversion device 14 and the control device 16 are operating normally.

[0018] The power receiving panel 20 is provided between the power system 2 and the load 4. The power receiving panel 20 is provided, for example, between the power system 2 and the local grid 8. AC power from the power system 2 is supplied to the local grid 8 and the load 4 via the power receiving panel 20.

[0019] The power meter 22 measures the power supplied to the load 4. In other words, the power meter 22 measures the power required by the load 4. The power meter 22 is connected to the power receiving panel 20, for example, via a communication line 30. The power meter 22 communicates with the power receiving panel 20 via the communication line 30, and inputs the measurement result of the power supplied to the load 4 to the power receiving panel 20.

[0020] The power receiving panel 20 includes, for example, a power meter 24 and a reverse power relay (RPR) 26. The power meter 24 measures the power supplied from the power system 2 to the load 4. In other words, the power supplied from the power system 2 to the load 4 is the difference between the power required by the load 4 and the power supplied to the load 4 from the solar panel 12 side.

[0021] The power receiving panel 20 is connected to the control device 16, for example, via a communication line 31. The power receiving panel 20 communicates with the control device 16 via the communication line 31, thereby inputting the measurement results of the power meter 22 and the measurement results of the power meter 24 to the control device 16. Note that the measurement results of the power meter 22 may be input directly from the power meter 22 to the control device 16, for example, without going through the power receiving panel 20.

[0022] The reverse power relay 26 detects a reverse power flow from the power conversion device 14 toward the power grid 2. The power conversion device 14 is connected to the power grid 2 via the transformer 6, the on-site grid 8, the power receiving panel 20, and the like. For this reason, if the power generated by the solar panel 12 becomes greater than the power consumed by the load 4, there is a possibility that part of the output power of the power conversion device 14 will flow toward the power grid 2. The reverse power relay 26 detects the occurrence of such a reverse power flow and operates to suppress the reverse power flow.

[0023] Reverse power relay 26 is connected to power conversion device 14 via signal line 40 and to control device 16 via signal line 41. Reverse power relay 26 inputs a detection signal to power conversion device 14 and control device 16 in response to detecting the occurrence of reverse power flow. Reverse power relay 26 inputs a detection signal to power conversion device 14 and control device 16, for example, when a reverse power flow state continues for a predetermined time or more. In other words, reverse power relay 26 detects the occurrence of reverse power flow when a reverse power flow state continues for a predetermined time or more. The predetermined time is, for example, approximately 0.5 seconds or more and 2 seconds or less.

[0024] In response to the input of the detection signal, the power conversion device 14 and the control device 16 stop the operation of outputting AC power to the load 4. In this way, the reverse power relay 26 detects reverse power flow, and in response to the detection of the occurrence of reverse power flow, stops the operation of the power conversion device 14 that outputs AC power to the load 4. In this way, the reverse power relay 26 prevents the reverse power flow from continuing to the power grid 2 side. In other words, the reverse power relay 26 performs the operation of stopping the operation of the power conversion device 14 as an operation to suppress reverse power flow.

[0025] The reverse power relay 26 may have, for example, a circuit breaker that opens and closes the connection with the power grid 2. The reverse power relay 26 may suppress the reverse power flow by stopping the operation of the power conversion device 14 and opening the circuit breaker in response to detection of the occurrence of the reverse power flow. The operation of suppressing the reverse power flow may be an operation of stopping the operation of the power conversion device 14 and opening the circuit breaker. Note that the reverse power relay 26 does not necessarily have to be provided in the power receiving panel 20. The reverse power relay 26 may be provided separately from the power receiving panel 20.

[0026] The power conversion device 14 includes a conversion circuit 50, a control unit 51, communication units 52 and 53, and an input unit .

[0027] The conversion circuit 50 is a circuit that converts the power supplied from the solar panel 12 into AC power corresponding to the load 4. The conversion circuit 50 is, for example, an inverter circuit. The control unit 51 controls the power conversion operation by the conversion circuit 50.

[0028] The communication unit 52 is connected to the control unit 51 and also to the control device 16 via the communication line 32. The communication unit 52 communicates with the control device 16 via the communication line 32. The control device 16 inputs a control signal for controlling the operation of the power conversion device 14 to the communication unit 52 via the communication line 32. The communication unit 52 receives an input of a control signal from the control device 16 by communicating with the control device 16, and inputs the input control signal to the control unit 51. The control unit 51 controls the operation of the conversion circuit 50 based on the control signal input from the communication unit 52. This makes it possible to control the AC power output from the conversion circuit 50 (power conversion device 14) in accordance with the control signal input from the control device 16.

[0029] The communication unit 53 is connected to the control unit 51, and is also connected to the control device 16 and the monitoring device 18 via the communication line 33. The communication unit 53 communicates with the control device 16 and the monitoring device 18 via the communication line 33.

[0030] The control unit 51 communicates with the monitoring device 18 via the communication unit 53 and the communication line 33, thereby transmitting information to the monitoring device 18 for monitoring the operation of the power conversion device 14. The control device 16 communicates with the monitoring device 18 via the communication line 33, thereby transmitting information to the monitoring device 18 for monitoring the operation of the control device 16. In this way, the monitoring device 18 monitors the operations of the power conversion device 14 and the control device 16 by communicating with them via the communication line 33. The communication unit 52 is a communication unit used for control, and the communication unit 53 is a communication unit used for monitoring. Note that in the power conversion device 14, communication for control and communication for monitoring may be performed by a single communication unit.

[0031] The input unit 54 is connected to the reverse power relay 26 via a signal line 40, and is also connected to the control device 16 via two signal lines 42 and 43. The input unit 54 is also connected to the control unit 51.

[0032] The input unit 54 inputs the detection signal of the occurrence of reverse power flow input from the reverse power relay 26 to the control unit 51 via the signal line 40. The control unit 51 stops the power conversion operation by the conversion circuit 50 in response to the input of the detection signal from the input unit 54. In this way, the reverse power relay 26 is connected to the input unit 54 via the signal line 40, for example, and inputs the detection signal to the input unit 54 in response to the detection of the occurrence of reverse power flow, thereby stopping the operation of the power conversion device 14. In this way, as described above, the operation of the power conversion device 14 can be stopped in response to the detection of the occurrence of reverse power flow by the reverse power relay 26, thereby suppressing reverse power flow to the power grid 2 side.

[0033] The input unit 54 inputs a control signal input from the control device 16 to the control unit 51 via the signal lines 42 and 43. The control unit 51 controls the power conversion operation by the conversion circuit 50 based on the control signal input from the input unit 54. That is, the control unit 51 controls the power conversion operation by the conversion circuit 50 based on the control signal input via the communication unit 52 or the control signal input via the input unit 54.

[0034] The control device 16 communicates with the power receiving panel 20 via the communication line 31 to obtain information on the load power consumption, which indicates the amount of power required by the load 4, based on the measurement results of the power meter 22, and also obtains information on the received power, which indicates the amount of power (purchased power amount) supplied from the power system 2 to the load 4, based on the measurement results of the power meter 24.

[0035] In addition, the control device 16 communicates with the power conversion device 14 via the communication line 32 or the communication line 33 to obtain information on the output power of the power conversion device 14, which indicates the magnitude of the power (generated power) supplied from the power conversion device 14 to the load 4.

[0036] However, the method of acquiring the information on the load power consumption, the information on the received power, and the information on the output power is not limited to the above, and any method may be used that can appropriately acquire each piece of information in the control device 16. In addition, the magnitude of the load power consumption, the received power, and the output power is, more specifically, the magnitude of the effective value of each power, which is AC power.

[0037] The control device 16 calculates the difference between the load power consumption and the output power based on the acquired information on the load power consumption and the output power. When the output power of the power conversion device 14 is lower than the load power consumption by a predetermined value or more, the control device 16 performs tracking control to control the output power of the power conversion device 14 so that the received power supplied from the power grid 2 to the load 4 is constant at a set value. In other words, the control device 16 performs tracking control when the difference obtained by subtracting the output power from the load power consumption is a predetermined value or more.

[0038] When performing tracking control, the control device 16 generates a control signal for tracking control in which the output power of the power conversion device 14 is set to, for example, the value obtained by subtracting a set value from the load power consumption, and inputs the generated control signal for tracking control to the power conversion device 14 via the communication line 32.

[0039] When the control unit 51 of the power conversion device 14 receives the input of the control signal for tracking control via the communication line 32 and the communication unit 52, it executes tracking control by controlling the operation of the conversion circuit 50 so as to output power based on the input control signal for tracking control. As a result, when the power generated by the solar panel 12 is equal to or greater than the power based on the control signal for tracking control, the power based on the control signal for tracking control can be output from the power conversion device 14, and the power received from the power grid 2 can be controlled to be constant at a set value.

[0040] On the other hand, when the difference obtained by subtracting the output power from the load power consumption is less than a predetermined value, the control device 16 performs emergency control to limit the output power of the power conversion device 14. The predetermined value for determining whether to perform follow-up control or emergency control is set to, for example, a value equal to or less than the set value of the received power in follow-up control. The predetermined value may be the same as the set value or may be lower than the set value. The predetermined value may be any value equal to or less than the set value.

[0041] If the difference obtained by subtracting the output power from the load power consumption falls below a predetermined value, it is considered that, due to a sudden change in the power consumption of the load 4 or the like, the control of the output power of the power conversion device 14 by tracking control is not enough in time, and the output power of the power conversion device 14 is heading in a direction toward becoming larger than the load power consumption. In other words, if the difference obtained by subtracting the output power from the load power consumption falls below a predetermined value, it is considered that reverse power flow is heading in the direction toward occurring. Therefore, the control device 16 performs emergency control to limit the output power of the power conversion device 14 and reduce the output power of the power conversion device 14 to a predetermined limit value. In this way, the power conversion device 14 and the control device 16 suppress the occurrence of reverse power flow.

[0042] The control device 16 has emergency controls including a first emergency process that limits the output power of the power conversion device 14 to a first limit value and a second emergency process that limits the output power of the power conversion device 14 to a second limit value that is lower than the first limit value. In the emergency control, the control device 16 determines whether the current output power of the power conversion device 14 is equal to or greater than a threshold value. If the current output power of the power conversion device 14 is equal to or greater than the threshold value, the control device 16 inputs a control signal for the first emergency process that instructs the execution of the first emergency process to the input unit 54 via the signal line 42 as a control signal for emergency control. On the other hand, if the current output power is less than the threshold value, the control device 16 inputs a control signal for the second emergency process that instructs the execution of the second emergency process to the input unit 54 via the signal line 43 as a control signal for emergency control. The control device 16 is connected to the input unit 54 via two signal lines 42, 43, and inputs a control signal for the first emergency processing to the input unit 54 via one signal line 42 of the two signal lines 42, 43, and inputs a control signal for the second emergency processing to the input unit 54 via the other signal line 43 of the two signal lines 42, 43.

[0043] The input unit 54 of the power conversion device 14 is capable of receiving an input of a control signal for emergency control from the control device 16 faster than communication by the communication units 52 and 53, and inputs the input control signal for emergency control to the control unit 51.

[0044] When the control unit 51 of the power conversion device 14 receives an input of a control signal for emergency control via the input unit 54, it controls the operation of the conversion circuit 50 to output a predetermined power, thereby executing emergency control. When the control unit 51 receives an input of a control signal for first emergency processing via the signal line 42 and the input unit 54, it controls the operation of the conversion circuit 50 to output power of a first limit value. Similarly, when the control unit 51 receives an input of a control signal for second emergency processing via the signal line 43 and the input unit 54, it controls the operation of the conversion circuit 50 to output power of a second limit value.

[0045] The first limit value is set to, for example, about 20% of the rated output of the power conversion device 14 (conversion circuit 50). The second limit value is set to, for example, about 5% of the rated output of the power conversion device 14. However, the first limit value is not limited to the above and may be any value that can suppress the occurrence of reverse power flow. The second limit value is not limited to the above and may be any value lower than the first limit value.

[0046] When the control unit 51 receives an input of a control signal for the first emergency processing or a control signal for the second emergency processing, it executes control of the first emergency processing or control of the second emergency processing, giving priority to the control signal for the follow-up control.

[0047] After inputting the control signal for the first emergency processing to the power conversion device 14, the control device 16 stops inputting the control signal for the first emergency processing, for example, when the control of the first emergency processing is performed and the difference obtained by subtracting the output power from the load power consumption becomes equal to or greater than a predetermined value. Similarly, after inputting the control signal for the second emergency processing to the power conversion device 14, the control device 16 stops inputting the control signal for the second emergency processing, for example, when the control of the second emergency processing is performed and the difference obtained by subtracting the output power from the load power consumption becomes equal to or greater than a predetermined value.

[0048] When the control unit 51 of the power conversion device 14 performs the first emergency processing control or the second emergency processing control, for example, the control unit 51 performs the first emergency processing control or the second emergency processing control for a predetermined time and then returns to the tracking control. In other words, after executing the emergency control, the control unit 51 stops the emergency control when a predetermined time has elapsed since the start of the emergency control. In this case, the control unit 51 gradually changes the output power at a predetermined rate of change from the power of the first limit value or the second limit value to the power based on the control signal for the tracking control. This makes it possible to prevent, for example, a sudden change in output power from approaching a reverse power flow state again.

[0049] Communication via the communication lines 30 to 33 requires communication circuits such as communication units 52 and 53. Communication via the communication lines 30 to 33 allows transmission and reception of various information, such as a control signal for tracking control that indicates the magnitude of the output power of the power conversion device 14. On the other hand, communication via the communication lines 30 to 33 causes communication delays due to processing by the communication units 52 and 53. Communication via the communication lines 30 to 33 complies with communication standards such as Ethernet and RS485. In other words, the communication units 52 and 53 are communication circuits that comply with a predetermined communication standard.

[0050] In communication via the signal lines 40 to 43, only binary states can be input, such as inputting and stopping the input of a reverse power flow detection signal, and inputting and stopping the input of a control signal for the first emergency processing. The detection signal is a signal having two states, for example, a reverse power flow detection state and a non-detection state. The control signal for the first emergency processing is a signal having two states, for example, a state instructing execution of the first emergency processing and a state instructing stop of the first emergency processing. On the other hand, communication via the signal lines 40 to 43 can suppress communication delays due to processing by the communication unit, for example, and can input each signal more quickly than communication via the communication lines 30 to 33. Communication via the signal lines 40 to 43 is, for example, communication by switching on and off contacts such as relays. The input unit 54 is a circuit that uses contact inputs that are faster than communication via the communication units 52 and 53. The input unit 54 is, for example, an input / output terminal (IO terminal). The signal lines 40 to 43 are, for example, hard wires.

[0051] In the solar power generation system 10, tracking control is performed by communication using the communication lines 30 to 33. On the other hand, communication using the signal lines 40 to 43 is used to stop the operation of the power conversion device 14 and to execute emergency control in response to the detection of reverse power flow by the reverse power relay 26. This allows the operation of the power conversion device 14 to be stopped and emergency control to be executed faster than communication using the communication lines 30 to 33. In this way, the solar power generation system 10 uses contact input, which is faster than communication using the communication lines 30 to 33, to stop the operation of the power conversion device 14 in response to the detection of reverse power flow and to execute emergency control.

[0052] FIG. 2 is a flowchart schematically illustrating an example of the operation of the solar power generation system according to the embodiment. FIG. 3 is a graph schematically showing an example of the operation of the solar power generation system according to the embodiment. In the solar power generation system 10, the reverse power relay 26 detects a reverse power flow from the power conversion device 14 toward the power grid 2 (step S101 in FIG. 2). In response to detecting the occurrence of a reverse power flow, the reverse power relay 26 inputs a detection signal to the power conversion device 14 and the control device 16.

[0053] In response to the input of the detection signal, the power conversion device 14 and the control device 16 stop the operation of outputting AC power to the load 4 (step S102 in FIG. 2). This makes it possible to prevent reverse power flow from continuing to the power grid 2. Note that when the power conversion device 14 stops its operation in response to the input of the detection signal, for example, a worker must go to the power conversion device 14 to restore the operation, and it may take a long time to restart the power conversion device 14.

[0054] The control device 16 acquires information on the load power consumption, the received power, and the output power when the occurrence of reverse power flow has not been detected by the reverse power relay 26 (step S103 in FIG. 2). The control device 16 acquires information on the load power consumption and the received power from the power receiving panel 20 and acquires information on the output power from the power conversion device 14, for example, by communicating with the power receiving panel 20 via the communication line 31. Note that the control device 16 does not necessarily have to acquire information on the received power. The control device 16 only needs to acquire information on at least the load power consumption and the output power.

[0055] After acquiring each piece of information, the control device 16 determines whether or not a sudden load change has occurred (step S104 in FIG. 2). For example, if the difference obtained by subtracting the output power from the load power consumption is equal to or greater than a predetermined value, the control device 16 determines that there has been no sudden load change (the power consumption of the load 4 has not changed suddenly), and if the difference obtained by subtracting the output power from the load power consumption is less than the predetermined value, the control device 16 determines that there has been a sudden load change (the power consumption of the load 4 has changed suddenly).

[0056] If the control device 16 determines that there is no sudden change in the load, it generates a control signal for tracking control in which the output power of the power conversion device 14 is the value obtained by subtracting a set value from the load power consumption, and inputs the generated control signal for tracking control to the power conversion device 14 via the communication line 32 (step S105 in Figure 2).

[0057] When the control unit 51 of the power conversion device 14 receives the input of the control signal for tracking control via the communication line 32 and the communication unit 52, it performs tracking control by controlling the operation of the conversion circuit 50 so as to output power based on the input control signal for tracking control (step S106 in Figure 2).

[0058] When the control unit 51 is performing tracking control, if the power generated by the solar panel 12 is lower than the power based on the control signal for tracking control, the power based on the power generated by the solar panel 12 is output from the conversion circuit 50 (power conversion device 14) (for example, intervals P1 and P6 shown in Figure 3).

[0059] When the control unit 51 is performing tracking control, if the power generated by the solar panel 12 is equal to or greater than the power based on the control signal for tracking control, the power based on the control signal for tracking control is output from the conversion circuit 50 (power conversion device 14) (for example, in sections P3 and P5 shown in FIG. 3). This makes it possible to control the power received from the power grid 2 to be constant at a set value.

[0060] When it is determined in the process of step S104 that a sudden load change has occurred, the control device 16 continues to determine whether or not the current output power of the power conversion device 14 is equal to or greater than a threshold value (step S107 in FIG. 2).

[0061] When the control device 16 determines that the output power is less than the threshold value, it inputs a control signal for a second emergency processing to the input unit 54 via the signal line 43, instructing the execution of a second emergency processing that limits the output power of the power conversion device 14 to a second limit value that is lower than the first limit value.

[0062] When the control unit 51 of the power conversion device 14 receives the input of the control signal for the second emergency processing via the signal line 43 and the input unit 54, it executes the second emergency processing by controlling the operation of the conversion circuit 50 to output power of the second limit value (step S108 in FIG. 2). As a result, when the output power is less than the threshold, the power of the second limit value is output from the conversion circuit 50 (power conversion device 14) (for example, section P2 shown in FIG. 3). The control unit 51 executes control of the second emergency processing for a predetermined time and then stops control of the second emergency processing. In other words, after executing control of the second emergency processing, the control unit 51 stops control of the second emergency processing in response to the elapse of a predetermined time since the start of control of the second emergency processing.

[0063] If the control device 16 determines in the processing of step S107 that the output power is greater than or equal to the threshold value, it inputs a control signal for a first emergency processing to the input unit 54 via the signal line 42, instructing the execution of a first emergency processing that limits the output power of the power conversion device 14 to a first limit value.

[0064] When the control unit 51 of the power conversion device 14 receives the input of the control signal for the first emergency processing via the signal line 42 and the input unit 54, it executes the first emergency processing by controlling the operation of the conversion circuit 50 to output power of the first limit value (step S109 in FIG. 2). As a result, when the output power is equal to or greater than the threshold, power of the first limit value is output from the conversion circuit 50 (power conversion device 14) (for example, section P4 shown in FIG. 3). The control unit 51 executes control of the first emergency processing for a predetermined time and then stops control of the first emergency processing. In other words, after executing control of the first emergency processing, the control unit 51 stops control of the first emergency processing in response to the elapse of a predetermined time since the start of control of the first emergency processing.

[0065] As described above, in the solar power generation system 10 according to this embodiment, when the control unit 51 of the power conversion device 14 receives an emergency control control signal via the input unit 54, the control unit 51 controls the operation of the conversion circuit 50 to output a predetermined power, thereby executing emergency control. As described above, the reverse power relay 26 detects the occurrence of reverse power flow when a reverse power flow state continues for a predetermined period of time or longer. Therefore, as described above, the control unit 51 receives an emergency control control signal via high-speed communication using the input unit 54, executes emergency control in response to the input emergency control control signal, and limits the output power of the power conversion device 14. This makes it possible to suppress the occurrence of reverse power flow to the power grid 2 even when a sudden load fluctuation occurs that cannot be followed up by the tracking control. In other words, the output power of the power conversion device 14 can be limited before the reverse power relay 26 detects the occurrence of reverse power flow, thereby preventing the power conversion device 14 from stopping due to the occurrence of reverse power flow. This prevents an increase in the amount of power purchased from the power grid 2 that would otherwise occur if the power conversion device 14 were to stop operating. This prevents the power generated by the solar panel 12 from being unable to be supplied to the load 4 due to the operation of the power conversion device 14 being stopped, and allows the power generated by the solar panel 12 to be used more effectively.

[0066] In the solar power generation system 10, the control device 16 has emergency controls including a first emergency process that limits the output power of the power conversion device 14 to a first limit value and a second emergency process that limits the output power of the power conversion device 14 to a second limit value that is lower than the first limit value, and when the current output power of the power conversion device 14 is equal to or greater than a threshold value, the control device 16 causes the power conversion device 14 to execute the first emergency process, and when it is less than the threshold value, the control device 16 causes the power conversion device 14 to execute the second emergency process.

[0067] In this way, by changing the value of the power to be limited in the emergency control in accordance with the current output power of the power conversion device 14, it is possible to prevent the power supplied from the power conversion device 14 to the load 4 from being excessively limited in the emergency control, for example. This makes it possible to more effectively utilize the power generated by the solar panel 12, for example.

[0068] The emergency control is not limited to two-stage control consisting of the first emergency process and the second emergency process, but may be one-stage control or three or more stages. However, if the number of stages for limiting power in the emergency control is too large, there is a concern that the amount of power limit may be insufficient even when emergency control is performed, resulting in reverse power flow. There is also a concern that the number of signal lines connecting the control device 16 and the input unit 54 may increase. For this reason, it is preferable that the number of stages for limiting power in the emergency control is about two stages, as described above.

[0069] In the solar power generation system 10, the control device 16 is connected to the input unit 54 via two signal lines 42 and 43. A control signal for the first emergency process is input to the input unit 54 via one of the two signal lines 42 and 43, the signal line 42, and a control signal for the second emergency process is input to the input unit 54 via the other of the two signal lines 42 and 43. This facilitates communication via contact input, which is faster than communication via the communication lines 30 to 33. However, the configuration of the input unit 54 is not necessarily limited to a configuration for communication via contact input. The configuration of the input unit 54 may be any configuration that allows it to receive an input of a control signal for emergency control from the control device 16 faster than communication via the communication units 52 and 53. The number of signal lines connecting the control device 16 and the input unit 54 is not limited to two and may be one.

[0070] In the solar power generation system 10, the control unit 51 executes emergency control and then stops the emergency control when a predetermined time has elapsed since the start of the emergency control. This makes it possible, for example, to prevent the system from approaching a reverse power flow state again due to the stopping of the emergency control. Furthermore, for example, after stopping the emergency control, the control unit 51 gradually changes the output power at a predetermined rate of change from the power of the emergency control to the power based on the control signal for tracking control. This makes it possible, for example, to further prevent the system from approaching a reverse power flow state again due to a sudden change in the output power.

[0071] In the solar power generation system 10, the reverse power relay 26 is connected to the input unit 54 via the signal line 40, and stops the operation of the power conversion device 14 by inputting a detection signal to the input unit 54 in response to detection of the occurrence of reverse power flow. By inputting the detection signal to the input unit 54 in this way, the detection signal can be input to the control unit 51 more quickly than by communication using the communication unit. This shortens the time from when the reverse power relay 26 detects the occurrence of reverse power flow to when the operation of the power conversion device 14 is stopped, and the occurrence of reverse power flow can be more appropriately suppressed.

[0072] In the above embodiment, a solar power generation system 10 in which solar panels 12 are used as distributed power sources is shown as an example of a distributed power generation system. The distributed power source is not limited to the solar panels 12, but may be, for example, a wind power generator or a geothermal power generator. The distributed power source may be any power source capable of supplying generated power. The power supplied by the distributed power source is not limited to DC power, but may be AC ​​power, etc. The distributed power generation system is not limited to the solar power generation system 10, but may be any system using any distributed power source.

[0073] 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. [Explanation of symbols]

[0074] 2...power system, 4...load, 6...transformer, 8...in-plant system 8, 10...photovoltaic power generation system (distributed power system), 12...solar panel (distributed power supply), 14...power conversion device, 16...control device, 18...monitoring device, 20...power receiving panel, 22...power meter, 30-33...communication line, 40-43...signal line, 50...conversion circuit, 51...control unit, 52, 53...communication unit, 54...input unit

Claims

1. A distributed power system of a total self-consumption type that is connected to a power grid and a load, and that supplies power generated by a distributed power source to the load, thereby suppressing power purchases from the power grid to the load, A distributed power source that generates electricity and supplies the generated electricity; a power conversion device that converts power supplied from the distributed power sources into AC power corresponding to the load and supplies the converted AC power to the load; a control device that controls the power conversion operation of the power conversion device; a reverse power relay that detects a reverse power flow from the power conversion device toward the power grid and stops the operation of the power conversion device that outputs AC power to the load in response to the detection of the occurrence of the reverse power flow; Equipped with The control device When the occurrence of reverse power flow is not detected by the reverse power relay, information on load power consumption indicating the amount of power required by the load and information on output power of the power conversion device indicating the amount of power supplied from the power conversion device to the load are acquired; When a difference obtained by subtracting the output power from the load power consumption is equal to or greater than a predetermined value, a control signal for tracking control is input to the power conversion device, in order to perform tracking control for controlling the output power of the power conversion device so that the received power supplied from the power grid to the load is constant at a set value, and the control signal for tracking control sets the output power of the power conversion device to a value obtained by subtracting the set value from the load power consumption; When a difference obtained by subtracting the output power from the load power consumption is less than the predetermined value, an emergency control signal is input to the power conversion device to perform emergency control that limits the output power of the power conversion device; The power conversion device is a conversion circuit that converts the power supplied from the distributed power sources into AC power corresponding to the load; a control unit that controls the power conversion operation by the conversion circuit; a communication unit that communicates with the control device to receive an input of the control signal for the tracking control from the control device and inputs the input control signal for the tracking control to the control unit; an input unit that can receive an input of the control signal for emergency control from the control device faster than communication by the communication unit and inputs the input control signal for emergency control to the control unit; and When the control unit of the power conversion device receives an input of the control signal for tracking control via the communication unit, it controls the operation of the conversion circuit to output power based on the input control signal for tracking control, thereby performing the tracking control, and when the control unit receives an input of the control signal for emergency control via the input unit, it controls the operation of the conversion circuit to output a predetermined power, thereby performing the emergency control. A distributed power supply system.

2. The control device has, as the emergency control, a first emergency process for limiting the output power of the power conversion device to a first limit value and a second emergency process for limiting the output power of the power conversion device to a second limit value lower than the first limit value, and in the emergency control, when the current output power of the power conversion device is equal to or greater than a threshold value, a control signal of the first emergency process instructing execution of the first emergency process is input to the power conversion device as a control signal for the emergency control, and when the current output power of the power conversion device is less than the threshold value, a control signal of the second emergency process instructing execution of the second emergency process is input to the power conversion device as a control signal for the emergency control, 2. The distributed power system according to claim 1, wherein the control unit of the power conversion device controls the operation of the conversion circuit so as to output the first limit value of power when receiving an input of the control signal for the first emergency processing, and controls the operation of the conversion circuit so as to output the second limit value of power when receiving an input of the control signal for the second emergency processing.

3. 3. The distributed power system according to claim 2, wherein the control device is connected to the input unit via two signal lines, and inputs the control signal for the first emergency processing to the input unit via one of the two signal lines, and inputs the control signal for the second emergency processing to the input unit via the other of the two signal lines.

4. The distributed power system according to claim 1 , wherein the control unit, after executing the emergency control, stops the emergency control when a predetermined time has elapsed since the start of the emergency control.

5. The distributed power system according to any one of claims 1 to 4, wherein the reverse power relay is connected to the input unit via a signal line, and stops operation of the power conversion device by inputting a detection signal to the input unit in response to detection of occurrence of reverse power flow.

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