JP7611097B2 - Power control system, power control device, and power control method - Google Patents

Description

This disclosure relates to a power control system, a power control device, and a power control method.

For example, in the case of distributed power sources such as solar power generation, if the power supply from the grid is cut off due to a power outage or other reason while the power conditioner is operating, the power conditioner continues to be able to supply power, which is called an isolated operation state. When the power conditioner is in isolated operation, it is necessary to stop the power supply from the power conditioner (inverter) from the perspective of the safety of workers and others. For example, Patent Document 1 proposes a technology for detecting the isolated operation of an inverter connected to a power grid.

JP 2007-318928 A

It would be extremely advantageous to adopt distributed power sources that have measures in place to prevent islanding, while also increasing the utilization of the electricity they generate when operating independently.

In light of these circumstances, the purpose of this disclosure is to provide a power control system, a power control device, and a power control method that increase the utilization of the power generated by distributed power sources during independent operation.

A power control system according to an embodiment of the present disclosure includes:
A power control system capable of supplying power output from a first distributed power source and a second distributed power source to a load during an isolated operation in which the first distributed power source and the second distributed power source are disconnected from a grid,
a first power control device that controls the power output by the first distributed power source;
a second power control device that controls the power output by the second distributed power source,
The first power control device has a function of independent operation output,
the second power control device has an islanding prevention function that prevents the second distributed power source from operating alone,
The first power control device, during an independent operation,
An upper limit of output power is set for the second power control device so that the isolated operation prevention function is not activated, and
The first distributed power source is caused to output power equal to or greater than the power consumed by the load minus the power output by the second distributed power source, or the first distributed power source is caused to consume power equal to the power output by the second distributed power source minus the power consumed by the load.

A power control device according to an embodiment of the present disclosure includes:
A power control system capable of supplying power output from a first distributed power source and a second distributed power source to a load during isolated operation in which the first distributed power source and the second distributed power source are disconnected from a grid, the power control system comprising: a power control device for controlling the power output from the first distributed power source,
The power control device has a function of independent operation output,
The power control device, during an independent operation,
a second power control device that controls the power output by the second distributed power source has a function of preventing an islanding operation of the second distributed power source, and sets an upper limit of output power for the power output by the second distributed power source so that the islanding operation prevention function is not activated; and
The first distributed power source is caused to output power equal to or greater than the power consumed by the load minus the power output by the second distributed power source, or the first distributed power source is caused to consume power equal to the power output by the second distributed power source minus the power consumed by the load.

A power control method according to an embodiment of the present disclosure includes:
1. A power control method for controlling power output by a first distributed power source in a power control system capable of supplying power output by a first distributed power source and a second distributed power source to a load during isolated operation in which the first distributed power source and the second distributed power source are disconnected from a grid, comprising:
During autonomous operation,
a second power control device that controls the power output by the second distributed power source has a function of preventing an islanding operation of the second distributed power source, and sets an upper limit of output power for the power output by the second distributed power source so that the islanding operation prevention function is not activated; and
The first distributed power source is caused to output power equal to or greater than the power consumed by the load minus the power output by the second distributed power source, or the first distributed power source is caused to consume power equal to the power output by the second distributed power source minus the power consumed by the load.

The present disclosure provides a power control system, a power control device, and a power control method that increase the utilization of power generated by a distributed power source during independent operation.

FIG. 1 is a diagram showing an example of a schematic configuration and operation of a known power control system. FIG. 2 is a diagram showing an example of a schematic configuration and operation of a known power control system. FIG. 3 is a diagram showing an example of a schematic configuration and operation of a known power control system. FIG. 4 is a diagram illustrating an example of a schematic configuration and operation of a power control system according to an embodiment. FIG. 5 is a block diagram showing an example of a schematic configuration of a power control device. FIG. 6 is a flowchart illustrating an example of the operation of the power control device according to an embodiment. FIG. 7 is a diagram showing an example of a schematic configuration and operation of a power control system according to another embodiment.

Below, a power control system, a power control device, and a power control method according to an embodiment of the present disclosure will be described with reference to the drawings. To explain the power control system according to this embodiment, the operation of a known power control system will first be described.

Figures 1 and 2 are block diagrams showing an example of the schematic configuration of a known power control system. Figure 1 shows an example of the operation of a known power control system during grid-connected operation. Also, Figure 2 shows an example of the operation of the same known power control system as Figure 1 during independent operation.

The power control system shown in FIG. 1 includes a first distributed power source 100, a second distributed power source 20, and a distribution board 40. The first distributed power source 100 includes a first power source 11 and a first power control device 120. The second distributed power source 20 includes a second power source 21 and a second power control device 22.

The first distributed power source 100 may be a non-renewable energy power source, and may use, for example, a storage battery (referred to as BT in FIG. 1) as the power source. Hereinafter, the first distributed power source 100 will be described as a power storage device that uses, for example, a storage battery such as the first power source 11 as its power source. The second distributed power source 20 may be a renewable energy power source, and may use, for example, a solar cell (referred to as PV in FIG. 1) as its power source. Hereinafter, the second distributed power source 20 will be described as a photovoltaic power generation device that uses, for example, a solar cell such as the second power source 21 as its power source.

As shown in FIG. 1, power from the first power source 11 is output to the first power control device 120. The first power control device 120 can be configured with a known power conditioner. The first power control device 120 converts the voltage of DC power output (discharged) from the storage battery, which is the first power source 11, into AC power by stepping up or stepping down the voltage. The power converted to AC by the first power control device 120 is output to the distribution board 40 via the grid interconnection relay 32 or the independent operation relay 34. The distribution board 40 is connected to the grid 50 and the load 60.

The grid-connection relay 32 and the independent operation relay 34 can be configured with any switch or the like. The grid-connection relay 32 and the independent operation relay 34 are basically controlled so that one is open and the other is closed. That is, during grid-connection, the grid-connection relay 32 is closed and the independent operation relay 34 is open (see FIG. 1). During independent operation, the grid-connection relay 32 is opened and the independent operation relay 34 is closed (see FIG. 2). Such control may be performed by the first power control device 120 or by another control unit or control device, etc.

The distribution board 40 includes a main breaker 31 that separates the grid 50 from the load 60, the first distributed power source 100, and the second distributed power source 20. The first distributed power source 100 operates in an independent manner when the grid 50 is disconnected by the main breaker 31. In this example, the distribution board 40 further includes a switching relay 42 that switches between grid-connected operation and independent operation according to an instruction (control signal) from the first distributed power source 100. This allows the distribution board 40 to supply the output of the independent operation of the first distributed power source 100 to the load 60. In this example, the main breaker 31 and the switching relay 42 are controlled by the first power control device 120.

As shown in FIG. 1, the line connecting the grid-connection relay 32 and the switching relay 42 is called the power transmission line PL1. The power transmission line PL1 is further connected to the grid 50. The line connecting the independent operation relay 34 and the switching relay 42 is called the power transmission line PL2. The line connecting the switching relay 42 and the load 60 is called the power transmission line PL3. The switching relay 42 connects the power transmission line PL1 and the power transmission line PL3 during grid-connection operation (see FIG. 1). The switching relay 42 connects the power transmission line PL2 and the power transmission line PL3 during independent operation in which the grid is disconnected from the grid 50 (see FIG. 2). Here, the control of the switching relay 42 may be performed by the first power control device 120, or may be performed by another control unit or control device, etc.

System 50 can be a typical commercial power system (grid).

The load 60 can be various devices such as home appliances used by a user that are supplied with power from the power control system. In FIG. 1, the load 60 is shown as one configuration, but is not limited to one configuration and can be any number of various devices. The load 60 can also be various devices connected via an outlet in the indoor wiring.

The first power control device 120 may also be a bidirectional inverter. In this case, the first power control device 120 can convert AC power from the grid 50 to DC, for example, and boost or lower the voltage of the DC power to supply (charge) the storage battery, which is the first power source 11.

The power from the second power source 21 is output to the second power control device 22. The second power control device 22 can also be configured with a known power conditioner. The second power control device 22 converts the voltage of the DC power output from the second power source 21 into AC power by stepping up or stepping down. The power converted to AC by the second power control device 22 is output to the distribution board 40 via the interconnection relay 33. The second distributed power source 20 is connected to the transmission line PL1 so that the AC power from the second power control device 22 is output to the distribution board 40 via the transmission line PL1. Here, the control of the interconnection relay 33 may be performed by the first power control device 120 or by another control unit or control device.

As described above, the power control system shown in FIG. 1 shows a state during grid-connected operation. The main breaker 31, grid-connected relay 32, and grid-connected relay 33 are closed, the independent operation relay 34 is open, and the switching relay 42 connects the power transmission line PL1 and the power transmission line PL3. In this operating state, at least one of the output of the first distributed power source 100 and the output of the second distributed power source 20 can be supplied to the load 60. The load 60 can also be supplied with power from the grid 50. Furthermore, the first distributed power source 100 can also be charged with power supplied from at least one of the grid 50 and the second distributed power source 20. The power generated by the second distributed power source 20 can also be sold to the grid 50. In this way, the power control system shown in FIG. 1 can control the power of multiple distributed power sources.

When, for example, a power outage is detected, the power control system shown in FIG. 1 goes into an operating state as shown in FIG. 2. As described above, the power control system shown in FIG. 2 shows a state during independent operation. The main breaker 31, the grid-connection relay 32, and the grid-connection relay 33 are opened, the independent operation relay 34 is closed, and the switching relay 42 connects the power transmission line PL2 and the power transmission line PL3.

More specifically, when a power outage or the like is detected in the power control system shown in FIG. 1, the first power control device 120 opens the main breaker 31, the grid-connection relay 32, and the grid-connection relay 33. Then, when the power transmission line PL2 and the power transmission line PL3 are connected by the switching relay 42 and the independent operation relay 34 is closed (see FIG. 2), the first distributed power source 100 starts outputting independent operation and supplies power to the load 60. In the power control system shown in FIG. 1, the operation from when a power outage is detected until the switching relay 42 is activated can be about 10 seconds. In this operating state, even during a power outage, the power charged in the storage battery of the first distributed power source 100 can be supplied to the load 60 by the independent operation output.

Also, as shown in FIG. 2, because the interconnection relay 33 and the main breaker 31 are open, the power generated by the second distributed power source 20 during a power outage does not flow back to the grid 50. Furthermore, the second power control device 22 has an islanding prevention function that prevents islanding, and can independently detect a power outage in the grid 50. Therefore, even if the grid 50 is not disconnected by the main breaker 31, the islanding operation of the second distributed power source 20 is avoided, and the power generated by the second distributed power source 20 during a power outage does not flow back to the grid 50.

However, in the power control system shown in FIG. 2, the second distributed power source 20 is not connected to the load 60 because the interconnection relay 33 is open. Therefore, in the operating state shown in FIG. 2, even if the second power source 21 is in a state where it can generate power, the power output by the second distributed power source 20 cannot be supplied to the load 60.

Figure 3 is a block diagram showing an example of the schematic configuration of another known power control system, and shows an example of operation during independent operation. The same components as those in Figures 1 and 2 are given the same reference numerals and will not be described. The other known power control system shown in Figure 3 is a so-called multi-DC link type energy storage system, and includes a first power control device 120 in which a first distributed power source 100 controls a first power source 11 and a second power source 21. In other words, the first power control device 120 in Figure 3 also functions as the second power control device 22 in Figures 1 and 2.

In the power control system shown in FIG. 3, when the second distributed power source 20 is in a state where it can generate power during independent operation, the power output by the second distributed power source 20 can be supplied to the load 60. However, the second power source 21 is controlled by the first distributed power source 100 from the beginning. The power control system shown in FIG. 3 cannot be configured as a power control system that combines the first distributed power source 100 and the second distributed power source 20, each of which functions independently, as in FIG. 1 and FIG. 2.

Therefore, in one embodiment of the power control system of the present disclosure, it is possible to configure a combination of distributed power sources that each function independently.

The power control system according to this embodiment will be described below. Figure 4 is a block diagram showing an example of the general configuration of the power control system 1 according to this embodiment.

As shown in FIG. 4, the power control system 1 according to this embodiment includes a first power control device 12 instead of the first power control device 120 shown in FIG. 1. The first power control device 12 is a power conditioner. The power control system 1 includes a first distributed power source 10 and a second distributed power source 20. The first distributed power source 10 includes a first power source 11 and a first power control device 12. The second distributed power source 20 includes a second power source 21 and a second power control device 22. Here, the first power control device 12 controls the power output by the first power source 11. The second power control device 22 controls the power output by the second power source 21.

In addition, in the power control system 1 according to this embodiment, there is no switching relay 42 in the distribution board 40, and the power transmission line PL1 and the power transmission line PL2 are connected to the power transmission line PL3.

In addition, in the power control system 1 according to this embodiment, the first power control device 12 can set the upper limit of output power by sending a command (dummy command) in the form of a remote output control to the second power control device 22. Details of the dummy command will be described later.

Furthermore, as shown in FIG. 4, a current detection unit CT may be provided to detect the current flowing through the power transmission line PL1. The current detection unit CT is, for example, a current sensor such as a current transformer, but any element capable of detecting a current may be used. The second power control device 22 detects a reference voltage waveform based on a detection signal from the current detection unit CT. The current detection unit CT may be built into the second distributed power source 20 as long as it can detect the reference voltage waveform. When the second power control device 22 detects the reference voltage waveform during independent operation, it closes the interconnection relay 33, which was open. When the interconnection relay 33 is closed, the AC power (power A in FIG. 4) from the second power control device 22 is output to the distribution board 40 via the power transmission line PL1 and supplied to the load 60.

Here, FIG. 4 shows the operation of the power control system 1 during independent operation, with the interconnection relay 33 closed. In the following, the AC power from the second power control device 22 output to the power transmission line PL1 is referred to as power A. The AC power from the first power control device 12 output to the power transmission line PL2 is referred to as power B. The AC power input to the first power control device 12 on the power transmission line PL2 is referred to as power B'. The AC power supplied to the load 60 on the power transmission line PL3 is referred to as power C.

The other components of the power control system 1 are similar to those described with reference to FIG. 1, and therefore will not be described again in order to avoid duplication. In addition, the control of opening and closing of the main breaker 31 by the first power control device 12 is similar to that described above with reference to FIG. 1, and therefore will not be described again.

Next, the first power control device 12 and the second power control device 22 included in the power control system 1 according to this embodiment will be further described. FIG. 5 is a block diagram showing an example of the schematic configuration of the first power control device 12 and the second power control device 22.

As shown in FIG. 5, the first power control device 12 includes a first DC/DC converter 13, a first inverter 14, a first control unit 15, a first memory unit 16, and a first communication unit 17. The second power control device 22 includes a second DC/DC converter 23, a second inverter 24, a second control unit 25, a second memory unit 26, and a second communication unit 27.

The first DC/DC converter 13 steps up or down the voltage of the DC power from the first power source 11. The DC power whose voltage has been stepped up or down by the first DC/DC converter 13 is output to the first inverter 14. The first DC/DC converter 13 can be configured using a known component.

The first inverter 14 converts the DC power from the first DC/DC converter 13 into AC power. During grid-connected operation, the AC power converted by the first inverter 14 is supplied to the load 60 via the grid-connection relay 32 and the power transmission line PL1, and via the distribution board 40. During independent operation, the AC power converted by the first inverter 14 is supplied to the load 60 via the independent operation relay 34 and the power transmission line PL2, and via the distribution board 40.

When the first power source 11 is a storage battery, it can be charged with power supplied from the second distributed power source 20. In this case, the first inverter 14 converts AC power from the second distributed power source 20 into DC power. Then, the first DC/DC converter 13 steps up or down the voltage of the DC power from the first inverter 14 and supplies it to the first power source 11, which is a storage battery. The first power source 11 can charge the power supplied in this manner. When the first power source 11 is a storage battery, it can similarly be charged with power supplied from the grid 50.

The first control unit 15 controls and manages each functional unit of the first power control device 12 and the entire system. The first control unit 15 can be configured to include, for example, a CPU (Central Processing Unit) and the like. The first control unit 15 controls the switching of the grid-connection relay 32 and the independent operation relay 34. During grid-connected operation, the first control unit 15 closes the grid-connection relay 32 and opens the independent operation relay 34. When switching from grid-connected operation to independent operation due to a power outage or the like, the first control unit 15 opens the grid-connection relay 32 and closes the independent operation relay 34. The operation of the first control unit 15 will be described further below.

The first power control device 12 may include at least one processor as a first control unit 15 to provide control and processing power for performing various functions. According to various embodiments, the at least one processor may be implemented as a single integrated circuit (IC), or as multiple communicatively connected integrated circuits. The at least one processor may be implemented according to various known techniques.

In one embodiment, a processor includes one or more circuits or units configured to perform one or more data computational procedures or processes. For example, a processor may include one or more microprocessors, microcontrollers, application specific integrated circuits (ASICs), digital signal processors, programmable logic devices, field programmable gate arrays, or combinations thereof.

The first storage unit 16 may be configured with a semiconductor memory, a magnetic memory, or the like. The first storage unit 16 stores various information and programs executed by the first control unit 15. The first storage unit 16 may function as a work memory for the first control unit 15. The first storage unit 16 may also be included in the first control unit 15.

The first communication unit 17 includes one or more communication modules that communicate with the communication device 70. The first communication unit 17 may include, for example, a communication module that supports a wired or wireless LAN standard. In this embodiment, the communication device 70 is a network hub, and the first communication unit 17 and the communication device 70 are connected via a wired LAN. As another example, the first communication unit 17 may include a communication module that supports a mobile communication standard such as 4G (4th Generation) or 5G (5th Generation).

The second DC/DC converter 23 boosts or lowers the voltage of the DC power from the second power source 21. The DC power whose voltage has been boosted or lowered by the second DC/DC converter 23 is output to the second inverter 24. The second DC/DC converter 23 can be configured using a known converter.

The second inverter 24 converts the DC power from the second DC/DC converter 23 into AC power. The AC power converted by the second inverter 24 passes through the grid-connection relay 33 and the power transmission line PL1, and is supplied to the load 60 via the distribution board 40.

The second control unit 25 controls and manages each functional unit of the second power control device 22 and the entirety. The second power control device 22 may include at least one processor as the second control unit 25 to provide control and processing power for executing various functions. The configuration of the second control unit 25 may be the same as or different from the first control unit 15.

As described above, the second control unit 25 closes the interconnection relay 33 when it detects the reference voltage waveform based on the detection signal of the current detection unit CT.

The second storage unit 26 may be configured with a semiconductor memory or a magnetic memory, etc. The second storage unit 26 stores various information and programs executed by the second control unit 25, etc. The various information includes an execution schedule and an update schedule for remote output control. The second storage unit 26 may function as a work memory for the second control unit 25. In addition, the second storage unit 26 may be included in the second control unit 25.

The second communication unit 27 includes one or more communication modules that communicate with the communication device 70. The second communication unit 27 may include, for example, a communication module that supports a wired or wireless LAN standard. In this embodiment, the communication device 70 is a network hub, and the second communication unit 27 and the communication device 70 are connected via a wired LAN. As another example, the second communication unit 27 may include a communication module that supports a mobile communication standard such as 4G or 5G. The configuration of the second communication unit 27 may be the same as or different from that of the first communication unit 17.

Here, the second power control device 22 has an islanding prevention function. Therefore, when the first control unit 15 of the first power control device 12 detects, for example, a power outage and opens the interconnection relay 32 and closes the independent operation relay 34 to switch from interconnected operation to independent operation, the second power control device 22 keeps the interconnection relay 33 open until it detects the reference voltage waveform from the grid 50. In this embodiment, the first power control device 12 generates a reference voltage waveform when switching from interconnected operation to independent operation. In order for the second power control device 22 to recognize the reference voltage waveform generated by the first power control device 12 as being from the grid 50 (to determine that it is equivalent to the reference voltage waveform sent from the grid 50), the power of the generated reference voltage waveform needs to be sufficiently large. More specifically, the second power control device 22 determines that it has detected the reference voltage waveform from the grid 50 when there is a phase difference between the voltage waveform that the second power control device 22 itself is to generate and output and the detected reference voltage waveform. The phase difference is maintained when the power magnitude of the reference voltage waveform is equal to or greater than the power magnitude of the voltage waveform generated by the second power control device 22 itself. Therefore, the first control unit 15 of the first power control device 12 sets an upper limit on the output power of the second power control device 22 so that the islanding prevention function of the second power control device 22 does not operate. The first control unit 15 then generates and outputs a reference voltage waveform equal to or greater than the output power of the second power control device 22.

In this embodiment, the first control unit 15 of the first power control device 12 sets the upper limit of output power by sending a dummy command in the form of remote output control to the second power control device 22. Here, in a distributed power system that has a contract for reverse power flow (power sales) with a power company, it is mandatory to have a function for receiving a remote output control command from the power company's power server 72. During grid-connected operation, the second communication unit 27 receives a remote output control command from the power server 72 via a network 71 such as the Internet and a communication device 70, and controls the output magnitude of the second power control device 22 according to a specified schedule. The first power control device 12 uses the remote output control command reception function of the second power control device 22 to transmit a dummy command in the form of remote output control that sets the upper limit of output power during independent operation.

The second power control device 22 detects the reference voltage waveform generated by the first power control device 12 based on the detection signal of the current detection unit CT, and when it recognizes this reference voltage waveform as equivalent to the grid 50, it closes the grid-connection relay 33. Figures 4 and 5 show the state of the power control system 1 in this case (grid-connection relay 33 is closed, grid-connection relay 32 is open, and independent operation relay 34 is closed). At this time, the second distributed power source 20 is connected to the load 60, and power A from the second power control device 22 can be supplied to the load 60.

In the state of the power control system 1 shown in Figures 4 and 5, the first power control device 12 causes the first distributed power source 10 to output power (power B) equal to or greater than the power (power C) consumed by the load 60 minus the power (power A) output by the second distributed power source 20, or causes the first distributed power source 10 to consume power (power B') obtained by subtracting the power (power C) consumed by the load 60 from the power (power A) output by the second distributed power source 20. Below, the control of this first power control device 12 will be specifically described assuming that the first power source 11 is a storage battery and the second power source 21 is a solar cell.

When the storage battery (first power source 11) is discharged during independent operation, the first power control device 12 discharges power B to the storage battery that is equal to or greater than the power C consumed by the load 60 minus the power A output by the solar cell (second power source 21). For example, the power C consumed by the load 60 is 3.9 kW, and the upper limit of the output power for the second power control device 22 is set to 1.9 kW. At this time, since the power A does not exceed 1.9 kW, the first power control device 12 outputs power B at 2.0 kW or more. During independent operation, the load 60 is supplied with a composite power including the power from the solar cell, thereby reducing the power consumption of the storage battery and enabling a long-term power supply, and the power generated by the solar cell can be effectively utilized. Here, the first power control device 12 sets the upper limit of the output power of the second power control device 22 to half or less of the power C consumed by the load 60. In addition, below, the above power relationship equation (power B ≧ power C - power A) when the storage battery is discharging during independent operation may be referred to as the "relationship equation between power A, power B, and power C."

When the storage battery (first power source 11) is charged during independent operation, the first power control device 12 charges the storage battery with power B' obtained by subtracting power C consumed by the load 60 from power A output by the solar cell (second power source 21). For example, the power C consumed by the load 60 is 1.0 kW, the upper limit of the output power for the second power control device 22 is set to 1.9 kW, and power A is 1.9 kW. At this time, the first power control device 12 charges the storage battery with power B' of 0.9 kW. During independent operation, the maximum power utilization is possible by charging the storage battery if there is surplus power while supplying power from the solar cell to the load 60. Here, the first power control device 12 sets the upper limit of the output power of the second power control device 22 to a power that is equal to or less than the power that can charge the storage battery. In other words, even if the power C consumed by the load 60 is zero, the power A output by the solar cell is set to be fully used for charging up to the level at which the storage battery can be charged. In addition, below, the above power relational equation (power B' = power A - power C) when the storage battery is charging during independent operation may be referred to as the "relational equation between power A, power B', and power C."

In this embodiment, the first power control device 12 executes constant voltage control so that the relational expression between power A, power B, and power C or the relational expression between power A, power B', and power C is satisfied. The constant voltage control is a control that keeps the voltage at point CP (see FIG. 4) on the power transmission line PL3 constant. The voltage at point CP corresponds to the output side voltage of the first inverter 14. For example, when power C is supplied to balance with the power consumed by the load 60, the voltage at point CP is 200V. When the power A output by the solar cell increases and the voltage at point CP exceeds 200V, the first power control device 12 charges the storage battery with the surplus power exceeding the power consumed by the load 60 as power B'. Also, when the power A output by the solar cell decreases and the voltage at point CP is 200V or less, the first power control device 12 discharges power B, which compensates for the power shortage with respect to the power consumed by the load 60, to the storage battery. By performing constant voltage control, the first power control device 12 is able to automatically switch between discharging and charging the storage battery without having to perform complex calculations.

The power control system 1 according to this embodiment is configured by combining a standard first distributed power source 10 and a standard second distributed power source 20, each of which functions independently, and does not require a special configuration (multiple DC link type) as shown in FIG. 3. Therefore, it is possible to easily change an existing system of distributed power sources that function independently to the power control system 1 according to this embodiment.

As described above, the first power control device 12 sets the upper limit of output power by sending a dummy command in the form of remote output control to the second power control device 22 during independent operation. In order to appropriately set the upper limit of the output power of the second power control device 22, the first power control device 12 may acquire information on the rated capacity of the second power control device 22 in advance before sending the dummy command in the form of remote output control. The information on the rated capacity may be stored, for example, in the first memory unit 16. At this time, the first power control device 12 can prevent the upper limit of the output power of the second power control device 22 that is set from exceeding the rated capacity, and can prevent an unstable state caused by a temporary voltage drop due to such an excess.

The first power control device 12 may change the upper limit of the output power of the second power control device 22 by a new dummy command in response to the fluctuation of the load 60. Here, a sensor that detects the current flowing through the power transmission line PL3 is provided (see the first current detection unit CT1 in FIG. 7), and the first power control device 12 may detect the fluctuation of the load 60 based on the detection signal of the sensor. At this time, when the power consumed by the load 60 decreases, the first power control device 12 can also lower the upper limit of the output power of the second power control device 22 by a dummy command. By responding to the fluctuation of the load 60 in this way, it is possible to avoid the power A becoming larger than the power B (the upper limit of the output power of the second power control device 22 is no longer half or less than the power C), and the islanding prevention function of the second power control device 22 being activated.

As described above, during independent operation, the power control system 1 supplies power to the load 60 with a composite power that includes power from the solar cell, thereby reducing the power consumption of the storage battery and enabling a long-term power supply. The available capacity and available time of the storage battery may be displayed on a display device of a HEMS (Home Energy Management System), for example.

Furthermore, the communication device 70 used to transmit the dummy command of the first power control device 12 is not limited to a network hub. As another example, the communication device 70 may be a router, a remote control for a HEMS or a distributed power source, etc. In other words, the communication device 70 may be a device having various communication functions used to receive commands for remote output control from the power server 72 of the power company.

For example, when the communication device 70 is a remote control for a HEMS or a distributed power source, the transmission of a dummy command may be executed in the following procedure. First, the remote control for the HEMS or the distributed power source is started by starting the independent operation of the first power control device 12. The first control unit 15 of the first power control device 12 instructs the remote control for the HEMS or the distributed power source to generate and transmit a dummy command. The second power control device 22, which receives the dummy command from the remote control for the HEMS or the distributed power source, sets an upper limit for the output power according to the dummy command. When the communication device 70 is a remote control for a HEMS or a distributed power source, the dummy command during independent operation can be generated by the same device as the command for normal remote output control during grid-connected operation.

In addition, during grid-connected operation, the contents of the remote output control command from the power server 72 (including, for example, an update schedule) may be managed as an electronic calendar associated with the date and time. The electronic calendar is stored, for example, in the second storage unit 26. The electronic calendar is also managed by the power server 72 or the HEMS. The second control unit 25 may, for example, read the electronic calendar from the second storage unit 26, control the second power source 21 according to the electronic calendar, and adjust the output power of the second power control device 22. Here, the contents of the electronic calendar stored in the second storage unit 26 may be changed by a dummy command during independent operation. At this time, the first control unit 15 of the first power control device 12 may request the power server 72 or the HEMS to transmit the electronic calendar to the second power control device 22, for example, when the power outage is resolved and the system returns from independent operation to grid-connected operation. Furthermore, if the communication device 70 is a HEMS, when returning from independent operation to grid-connected operation, the HEMS may transmit an electronic calendar to the second power control device 22 even if not requested by the first power control device 12.

In addition, during grid-connected operation, not only the second power control device 22 but also the first power control device 12 may acquire the contents of the remote output control command. At this time, the contents of the remote output control command may be stored in the first storage unit 16. When returning from independent operation to grid-connected operation, the first control unit 15 of the first power control device 12 may transmit the contents of the remote output control command stored in the first storage unit 16 to the second power control device 22 by a dummy command. Even if the contents of the electronic calendar stored in the second storage unit 26 are changed by a dummy command during independent operation, the first control unit 15 can restore the contents of the electronic calendar by further overwriting the contents of the remote output control command from the power server 72 by a dummy command. Here, the contents of the remote output control command transmitted by the first control unit 15 may be, for example, the contents of the schedule after power restoration, or may be, for example, the entire contents of the annual schedule.

Here, the first power control device 12 may apply an interlock that does not allow the electronic calendar in the second storage unit 26 to be updated, so that the contents of the electronic calendar stored in the second storage unit 26 are not erroneously changed. The first power control device 12 may release the interlock only when there is a command for remote output control from the power server 72 or when a dummy command is output.

Figure 6 is a flowchart explaining the operation (power control method) of the first power control device 12 and the second power control device 22 provided in the power control system 1 according to this embodiment during independent operation.

When the first power control device 12 detects a power outage or the like, it switches from grid-connected operation to independent operation (Yes in step S1). When switching from grid-connected operation to independent operation, the first power control device 12 opens the grid-connected relay 32 and closes the independent operation relay 34. When the first power control device 12 does not detect a power outage or the like and continues grid-connected operation (No in step S1), it does not perform the processes in steps S2 to S6 below.

The first power control device 12 outputs a reference voltage waveform (step S2). The first power control device 12 also sets an upper limit on output power for the second power control device 22 by sending a dummy command so that the islanding prevention function does not operate (step S3). The second power control device 22 detects the reference voltage waveform based on the detection signal of the current detection unit CT. When the second power control device 22 detects the reference voltage waveform, it closes the interconnection relay 33, which was open (see Figure 4).

The first power control device 12 determines whether the storage battery is in a state requiring a discharge operation or a charge operation. In this embodiment, the first power control device 12 executes constant voltage control, and determines that the storage battery is in a state requiring a discharge operation when the voltage at point CP is equal to or lower than a reference value (for example, 200 V). Furthermore, the first power control device 12 determines that the storage battery is not in a state requiring a discharge operation (is in a state requiring a charge operation) when the voltage at point CP exceeds the reference value.

When the first power control device 12 determines that the storage battery is in a state requiring a discharge operation (Yes in step S4), it controls the storage battery to discharge power B equal to or greater than the power C consumed by the load 60 minus the power A output by the second power control device 22 (step S5).

When the first power control device 12 determines that the storage battery is in a state requiring charging (No in step S4), it controls the storage battery to be charged with power B', which is the power A output by the second power control device 22 minus the power C consumed by the load 60 (step S6).

As described above, the power control system 1, power control device (first power control device 12), and power control method according to this embodiment can continue to supply the output of a distributed power source such as a solar power generation device to the load 60 in accordance with the output of the independent operation of the power storage device, without activating the function for preventing the isolated operation of the distributed power source. This can therefore increase the utilization of the power generated by the distributed power source during independent operation.

The first power control device 12 according to this embodiment can set the upper limit of output power by sending a dummy command in the form of a remote output control to the second power control device 22. Since the function of receiving a command for remote output control is provided in an existing system, it is possible to easily change an existing system to the power control system 1 according to this embodiment by updating the control program, etc.

In addition, the first power control device 12 according to this embodiment can automatically switch between discharging and charging the storage battery without performing complex calculations by performing constant voltage control to keep the voltage in the power transmission line PL3 connected to the load 60 constant.

Although the present disclosure has been described based on various drawings and examples, it should be noted that a person skilled in the art would easily be able to make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications or corrections are included in the scope of the present disclosure. For example, the functions contained in each functional unit can be rearranged so as not to cause logical inconsistencies. Multiple functional units may be combined into one or divided. Each of the above-mentioned embodiments of the present disclosure is not limited to being implemented faithfully according to each of the embodiments described, but may be implemented by combining each feature or omitting some features as appropriate.

In the above embodiment, the first power control device 12 performed control to keep the voltage at point CP on the power transmission line PL3 constant (constant voltage control). Here, as shown in FIG. 7, the power control system 1 includes a first current detection unit CT1 and a second current detection unit CT2, and the first power control device 12 may perform control to adjust the power B or power B' based on the detection values from the first current detection unit CT1 and the second current detection unit CT2.

The first current detection unit CT1 detects the current flowing through the power transmission line PL3 to the load 60. The second current detection unit CT2 detects the current flowing through the power transmission line PL1 from the second power control device 22. The second current detection unit CT2 also functions as the current detection unit CT used to detect the reference voltage waveform in the above embodiment. The first control unit 15 of the first power control device 12 multiplies the detection value (current value) of the first current detection unit CT1 by a voltage value (for example, the output side voltage value of the first inverter 14) to calculate the power C. The first control unit 15 of the first power control device 12 also multiplies the detection value (current value) of the second current detection unit CT2 by a voltage value (for example, the output side voltage value of the first inverter 14) to calculate the power A. The first control unit 15 may then perform control to adjust the power B or the power B' so that the relational equation of the power A, the power B, and the power C or the relational equation of the power A, the power B', and the power C described above is satisfied.

In the above embodiment, the first distributed power source 10 is described as a power storage device. In the above embodiment, the second distributed power source 20 is described as a solar power generation device. Here, the first distributed power source 10 is not limited to a power storage device. In addition, the second distributed power source 20 is not limited to a solar power generation device. The first distributed power source 10 can be various non-renewable energy power sources capable of supplying and receiving power, such as a distributed power source system composed of a fuel cell device and a heat pump hot water supply device. In addition, the second distributed power source 20 can be various renewable energy power sources. For example, the second distributed power source 20 may be a fuel cell device such as a solid oxide fuel cell (SOFC) or a polymer electrolyte fuel cell (PEFC). In addition, for example, when the first distributed power source 10 is a power storage device, the second distributed power source 20 may be another power storage device.

In the above embodiment, the power control system 1 includes one first power control device 12 and one second power control device 22. Here, the power control system 1 may include multiple first power control devices 12. In this case, the power B is the total AC power of the multiple first power control devices 12. The power control system 1 may include multiple second power control devices 22. In this case, the power A is the total AC power of the multiple second power control devices 22. The same applies when some of the multiple second power sources 21 to which the multiple second power control devices 22 are connected are fuel cells. Here, in order to start the fuel cell during independent operation to obtain power, a known method such as a method using a pseudo current circuit can be adopted.

In the above embodiment, the power control system 1 is configured by combining a standard first distributed power source 10 and a standard second distributed power source 20, each of which functions independently. Here, the power control system 1 can use a storage device having an overload protection function and an overvoltage protection function as the first distributed power source 10 without changing the configuration. Here, the overload protection function and the overvoltage protection function are functions in which the first power control device 12 stops the output of power when the voltage in the power transmission line PL3 connected to the load 60 is undervoltage or overvoltage. As described above, in the power control system 1 according to this embodiment, the first power control device 12 performs constant voltage control. The first power control device 12 controls the voltage in the power transmission line PL3 to avoid being in a state of undervoltage (e.g., 180V or less) or overvoltage (e.g., 220V or more) and to maintain a constant reference voltage (e.g., 200V). Therefore, even if a storage device having an overload protection function and an overvoltage protection function is used as the first distributed power source 10, the power control system 1 can effectively utilize the power generated by the storage battery and the solar cell by avoiding the operation of the overload protection function and the overvoltage protection function. Even if the first power control device 12 does not perform constant voltage control, it is preferable that the power control system 1 controls the voltage in the power transmission line PL3 connected to the load 60 within an output voltage range in which the overload protection function and the overvoltage protection function do not operate.

In addition, in the power control system 1 according to this embodiment, an upper limit of output power is set for the second power control device 22, but the setting of the upper limit of the output power may be terminated at the following timing. The setting of the upper limit of the output power may be terminated when the system is no longer operating independently. In addition, the setting of the upper limit of the output power may be terminated when the first power source 11 loses the power it can supply (for example, when the first power source 11, which is a storage battery, becomes empty) when the power consumed by the load 60 is greater than the power generated by the second power source 21. In addition, the setting of the upper limit of the output power may be terminated when the first power source 11 can no longer consume power (for example, when the first power source 11, which is a storage battery, becomes fully charged) when the power generated by the second power source 21 is greater than the power consumed by the load 60.

REFERENCE SIGNS LIST 1 Power control system 10 First distributed power source 11 First power source 12 First power control device 13 First DC/DC converter 14 First inverter 15 First control unit 16 First memory unit 17 First communication unit 20 Second distributed power source 21 Second power source 22 Second power control device 23 Second DC/DC converter 24 Second inverter 25 Second control unit 26 Second memory unit 27 Second communication unit 31 Main breaker 32 Interconnection relay 33 Interconnection relay 34 Independent operation relay 40 Distribution board 42 Switching relay 50 System 60 Load 70 Communication device 71 Network 72 Power server 100 First distributed power source 120 First power control device CT Current detection unit CT1 First current detection unit CT2 Second current detection unit PL1 Power transmission line PL2 Power transmission line PL3 Power lines

Claims (11)

A power control system capable of supplying power output from a first distributed power source and a second distributed power source to a load during an isolated operation in which the first distributed power source and the second distributed power source are disconnected from a grid,
a first power control device that controls the power output by the first distributed power source;
a second power control device that controls the power output by the second distributed power source,
The first power control device has a function of independent operation output,
the second power control device has an islanding prevention function that prevents the second distributed power source from operating alone,
The first power control device, during an independent operation,
An upper limit of output power is set for the second power control device so that the isolated operation prevention function is not activated, and
A power control system that causes the first distributed power source to output power equal to or greater than the power consumed by a load minus the power output by the second distributed power source, or causes the first distributed power source to consume power equal to the power output by the second distributed power source minus the power consumed by the load. The power control system according to claim 1, wherein the first power control device sets the upper limit of output power by sending a command in the form of a remote output control to the second power control device. The power control system according to claim 1 or 2, wherein the first power control device performs constant voltage control to keep the voltage in the power transmission line connected to the load constant. the first distributed power source is a non-renewable energy power source;
The power control system according to claim 1 , wherein the second distributed power source is a renewable energy power source. The power control system according to any one of claims 1 to 4, wherein the first distributed power source is a storage battery. The power control system according to any one of claims 1 to 5, wherein the second distributed power source is a solar cell. The first power control device is
7. The power control system according to claim 1, wherein, during autonomous operation and when power output from the first distributed power source is required, the first distributed power source is caused to discharge power equal to or greater than the power consumed by the load minus the power output by the second distributed power source. The first power control device is
8. The power control system according to claim 1, wherein, when the system is operating autonomously and a supply of power to the first distributed power source is required, the first distributed power source is charged with power output by the second distributed power source minus power consumed by the load. The first power control device is
9. The power control system according to claim 1, wherein the voltage in the power transmission line connected to the load is controlled within an output voltage range in which an overload protection function and an overvoltage protection function do not operate. A power control system capable of supplying power output from a first distributed power source and a second distributed power source to a load during isolated operation in which the first distributed power source and the second distributed power source are disconnected from a grid, the power control system comprising: a power control device for controlling the power output from the first distributed power source,
The power control device has a function of independent operation output,
The power control device, during an independent operation,
a second power control device that controls the power output by the second distributed power source has a function of preventing an islanding operation of the second distributed power source, and sets an upper limit of output power for the power output by the second distributed power source so that the islanding operation prevention function is not activated; and
A power control device that causes the first distributed power source to output power equal to or greater than the power consumed by a load minus the power output by the second distributed power source, or causes the first distributed power source to consume power equal to the power output by the second distributed power source minus the power consumed by the load. 1. A power control method for controlling power output by a first distributed power source in a power control system capable of supplying power output by a first distributed power source and a second distributed power source to a load during isolated operation in which the first distributed power source and the second distributed power source are disconnected from a grid, comprising:
During autonomous operation,
a second power control device that controls the power output by the second distributed power source has a function of preventing an islanding operation of the second distributed power source, and sets an upper limit of output power for the power output by the second distributed power source so that the islanding operation prevention function is not activated; and
A power control method for causing the first distributed power source to output power equal to or greater than the power consumed by a load minus the power output by the second distributed power source, or for causing the first distributed power source to consume power equal to the power output by the second distributed power source minus the power consumed by the load.

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