Distributed power systems

Abstract

To provide a distributed power system of full self-consumption type that can more appropriately keep the power factor at the interconnection point within a specified range.SOLUTION: A distributed power system includes a distributed power source that supplies generated power, a power conversion device that converts the power supplied from the distributed power source into AC power corresponding to a load and supplies the converted AC power to the load, and a control device that performs tracking control to make the active power output from the power conversion device track a target value and to control the operation of the power conversion device such that the power factor at the interconnection point with a power grid tracks the target value, and the control device sets, for the power factor at the interconnection point, a lower limit that is set to a value lower than the target value and a threshold that is set between the target value and the lower limit, and performs control to prevent the power factor at the interconnection point from falling below the lower limit when the power factor at the interconnection point is equal to or greater than the lower limit and less than the threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a distributed power system.

Background Art

[0002] A fully self-consumption type distributed power system using distributed power sources such as solar power generators, wind power generators, and geothermal power generators is known. The distributed power system includes a power conversion device that converts the generated power of the distributed power source into power corresponding to the load and supplies the converted power to the load.

[0003] In a fully self-consumption type distributed power system, it is desirable to maximize the use of the generated power of the distributed power source and suppress power purchase from the power grid. For this reason, the power conversion device performs a tracking control to control the magnitude of the active power supplied from the distributed power source to the load so that the received power (power purchase) from the power grid becomes constant at a set value according to the power consumption at the load. Thereby, it is possible to suppress the occurrence of reverse power flow from the distributed power source to the power grid side and suppress power purchase from the power grid.

[0004] Also, in a fully self-consumption type distributed power system, it is required to keep the power factor at the connection point with the power grid within a predetermined range. For this reason, the power conversion device performs an active power tracking control to control the magnitude of the active power supplied from the distributed power source to the load, and also performs a power factor tracking control to control so that the power factor at the connection point is kept within a predetermined range.

[0005] However, even if the above-described tracking control is performed, when the effective power amount of demand fluctuates greatly due to the operating status of the load such as operation or stop, the power factor at the connection point also fluctuates and may deviate from the predetermined range.

[0006] Therefore, in a fully self-consumption type distributed power system, it is desirable to more appropriately keep the power factor at the connection point within a predetermined range.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2017-118721 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Embodiments of the present invention provide a fully self-consumption type distributed power supply system that can more appropriately keep the power factor of the interconnection point within a predetermined range. [Means for solving the problem]

[0009] According to an embodiment of the present invention, a fully self-consumption type distributed power supply system is connected to a power grid and a load, and supplies power generated by the distributed power supply to the load, thereby suppressing the purchase of power from the power grid to the load, comprising: a distributed power supply that generates power and supplies the generated power; a power converter that converts the power supplied from the distributed power supply into AC power corresponding to the load and supplies the converted AC power to the load; and a control device that performs tracking control to make the active power output from the power converter follow a target value and to control the operation of the power converter so that the power factor at the connection point with the power grid follows a target value. A power meter for measuring the power required by the aforementioned load, The control device is equipped with Based on the measurement results of the power meter, information on load power consumption, which represents the amount of active power required by the load, is obtained, and the value obtained by subtracting a set value from the load power consumption is set as the target value of the active power. A lower limit is set for the power factor of the interconnection point, which is lower than the target value, and a threshold is set between the target value and the lower limit. When the power factor of the interconnection point is greater than or equal to the lower limit and less than the threshold, control is executed to prevent the power factor of the interconnection point from falling below the lower limit. Furthermore, if the power factor at the interconnection point is below the lower limit, control is performed to stop the supply of power from the power system to the load, and when the power factor at the interconnection point returns to or above the lower limit, the supply of power from the power system to the load is resumed. A distributed power system will be provided. [Effects of the Invention]

[0010] A fully self-consumption type distributed power system is provided that can more appropriately keep the power factor of the interconnection point within a predetermined range. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram schematically representing a solar power generation system according to the embodiment. [Figure 2] This is a flowchart schematically illustrating an example of the operation of a solar power generation system according to the embodiment. [Figure 3] Figures 3(a) and 3(b) are schematic graphs illustrating an example of the operation of a photovoltaic power generation system according to the embodiment.

[0012] Each embodiment will be described below with reference to the drawings. Please note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, as well as the ratios of the sizes of the parts, are not necessarily identical to those of reality. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. In this specification and in each figure, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

[0013] Figure 1 is a block diagram schematically representing a photovoltaic power generation system according to an embodiment. As shown in Figure 1, the photovoltaic power generation system 10 (distributed power system) comprises a photovoltaic panel 12 (distributed power source), a power converter 14, a control device 16, a monitoring device 18, a power receiving panel 20, and a power meter 22.

[0014] The solar power generation system 10 is connected to the power grid 2 and load 4. The solar power generation system 10 is a fully self-consumption type system that reduces the purchase of electricity from the power grid 2 to load 4 by supplying the electricity generated by the solar panels 12 to load 4. The electricity from power grid 2 is AC electricity. Load 4 is an AC load. In other words, load 4 is a consumer.

[0015] The solar panel 12 generates electricity and supplies the generated power. The solar panel 12 generates electricity by utilizing the photovoltaic effect and converting the light energy of sunlight into electrical energy. The generated power of the solar panel 12 is direct current power. The solar panel 12 supplies the generated direct current power to the power conversion device 14.

[0016] The power conversion device 14 is connected to the solar panel 12 and is also connected to the load 4 via a transformer 6, an in-plant system 8, etc. The power conversion device 14 converts the power supplied from the solar panel 12 into alternating current power corresponding to the load 4 and supplies the converted alternating current power to the load 4.

[0017] The load 4 is connected to the power conversion device 14 and is also connected to the power system 2 via the in-plant system 8, a switchboard 20, etc. The load 4 receives the supply of the generated power of the solar panel 12 from the power conversion device 14 and receives the supply of the power that is insufficient with the generated power of the solar panel 12 for the required power from the power system 2. The power conversion device 14 is configured to suppress the power purchase from the power system 2 by making the best use of the generated power of the solar panel 12.

[0018] The capacity of the solar panel 12 (power conversion device 14) is, for example, 500 kW or more and 2 MW or less. The contract power of the solar power generation system 10 with the power system 2 is, for example, 500 kW or more and 2 MW or less. In other words, the contract power of the solar power generation system 10 with the power system 2 is, for example, high-voltage power.

[0019] The control device 16 controls the operation of power conversion by the power conversion device 14. The monitoring device 18 monitors the operations 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 performs display of the acquired information, etc., so that the administrator of the solar power generation system 10 can monitor whether the power conversion device 14 and the control device 16 are operating normally.

[0020] The switchboard 20 is provided between the power system 2 and the load 4. The switchboard 20 is provided, for example, between the power system 2 and the on-site system 8. The alternating current power of the power system 2 is supplied to the on-site system 8 and the load 4 via the switchboard 20.

[0021] The wattmeter 22 measures the power supplied to the load 4. In other words, the wattmeter 22 measures the power required by the load 4. The wattmeter 22 is connected to the switchboard 20 via, for example, the communication line 30. The wattmeter 22 measures the power supplied to the load 4 and inputs the measurement result to the switchboard 20 by communicating with the switchboard 20 via the communication line 30.

[0022] The switchboard 20 has, for example, a wattmeter 24 and a reverse power relay 26 (RPR). The wattmeter 24 measures the power supplied from the power system 2 to the load 4. The power supplied from the power system 2 to the load 4 is, in other words, the difference in power between the power required by the load 4 and the power supplied from the solar panel 12 side to the load 4. Also, the wattmeter 24 measures the power supplied from the power system 2 to the load 4 and measures the power factor at the connection point with the power system 2.

[0023] The switchboard 20 is connected to the control device 16 via, for example, the communication line 31. The switchboard 20 communicates with the control device 16 via the communication line 31 and inputs the measurement results of the wattmeter 22 and the wattmeter 24 to the control device 16. Note that the measurement result of the wattmeter 22 may be directly input from the wattmeter 22 to the control device 16 without passing through the switchboard 20, for example. Also, the power supplied from the power system 2 to the load 4 and the power factor at the connection point may be obtained, for example, by measuring the voltage value and current value at the connection point and performing calculations on the control device 16 side based on the measurement results.

[0024] The reverse power relay 26 detects reverse power flow from the power converter 14 towards the power system 2. The power converter 14 is connected to the power system 2 via the transformer 6, the premises system 8, and the power receiving panel 20. Therefore, if the power generated by the solar panels 12 exceeds the power consumed by the load 4, some of the output power of the power converter 14 may flow to the power system 2. The reverse power relay 26 detects the occurrence of such reverse power flow and performs an operation to suppress it.

[0025] The reverse power relay 26 is connected to the power converter 14 via a signal line 35. The reverse power relay 26 inputs a detection signal to the power converter 14 in response to the detection of reverse power flow. For example, the reverse power relay 26 inputs a detection signal to the power converter 14 if the reverse power flow condition continues for a predetermined time or longer. In other words, the reverse power relay 26 detects the occurrence of reverse power flow if the reverse power flow condition continues for a predetermined time or longer. The predetermined time is, for example, about 0.5 seconds to 2 seconds.

[0026] The power converter 14 stops outputting AC power to the load 4 in response to the input of a detection signal. In this way, the reverse power relay 26 detects reverse power flow and stops the operation of the power converter 14 that outputs AC power to the load 4 in response to the detection of the occurrence of reverse power flow. As a result, the reverse power relay 26 prevents reverse power flow from continuing to flow to the power system 2 side. In other words, the reverse power relay 26 performs the operation of stopping the operation of the power converter 14 as an operation to suppress reverse power flow.

[0027] The reverse power relay 26 may, for example, have a circuit breaker that opens and closes the connection to the power system 2. The reverse power relay 26 may suppress reverse power flow by stopping the operation of the power converter 14 and opening the circuit breaker in response to the detection of reverse power flow. The operation to suppress reverse power flow may also be the operation of stopping the operation of the power converter 14 and opening the circuit breaker. The reverse power relay 26 does not necessarily have to be installed in the power receiving panel 20. The reverse power relay 26 may be installed separately from the power receiving panel 20.

[0028] The power converter 14 includes a conversion circuit 50, a control unit 51, communication units 52 and 53, and an input unit 54.

[0029] 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 operation of the power conversion by the conversion circuit 50.

[0030] 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 control signals to the communication unit 52 via the communication line 32 to control the operation of the power converter 14. By communicating with the control device 16, the communication unit 52 receives control signals from the control device 16 and inputs the input control signals to the control unit 51. The control unit 51 controls the operation of the conversion circuit 50 based on the control signals input from the communication unit 52. This makes it possible to control the AC power output from the conversion circuit 50 (power converter 14) in accordance with the control signals input from the control device 16.

[0031] The communication unit 53 is connected to the control unit 51 and also 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.

[0032] The control unit 51 communicates with the monitoring device 18 via the communication unit 53 and the communication line 33 to transmit information to the monitoring device 18 for monitoring the operation of the power converter 14. The control device 16 communicates with the monitoring device 18 via the communication line 33 to transmit information to the monitoring device 18 for monitoring the operation of the control device 16. In this way, the monitoring device 18 monitors the operation of the power converter 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 converter 14, control communication and monitoring communication may be performed by a single communication unit.

[0033] The input unit 54 is connected to the reverse power relay 26 via the signal line 35. The input unit 54 is also connected to the control unit 51. The input unit 54 inputs a detection signal for the occurrence of reverse power flow, which is input from the reverse power relay 26 via the signal line 35, to the control unit 51. In response to the detection signal input from the input unit 54, the control unit 51 stops the power conversion operation by the conversion circuit 50.

[0034] In this manner, the reverse power relay 26 is connected to the input unit 54, for example, via the signal line 35, and stops the operation of the power converter 14 by inputting a detection signal to the input unit 54 in response to the detection of reverse power flow. As a result, as described above, the operation of the power converter 14 can be stopped in response to the detection of reverse power flow by the reverse power relay 26, thereby suppressing reverse power flow to the power system 2.

[0035] Communication via communication lines 30-33 requires communication circuits such as communication units 52 and 53. Communication via communication lines 30-33 allows for the transmission and reception of various types of information, such as control signals representing the output power of the power converter 14. On the other hand, communication via communication lines 30-33 suffers from delays due to processing by communication units 52 and 53. Communication via communication lines 30-33 conforms to communication standards such as Ethernet and RS485. In other words, communication units 52 and 53 are communication circuits conforming to predetermined communication standards.

[0036] Communication via signal line 35 can only handle binary inputs, such as the input and deactivation of a reverse power flow detection signal. The detection signal has two states: a reverse power flow detection state and a non-detection state. On the other hand, communication via signal line 35 can suppress delays caused by processing in the communication unit, allowing for faster input of each signal compared to communication via communication lines 30-33. Communication via signal line 35 is, for example, communication by switching the contacts of a relay on and off. Input unit 54 is a circuit that uses contact input, which is faster than communication via communication units 52 and 53. Input unit 54 is, for example, an input / output terminal (IO terminal). Signal line 35 is, for example, a hardwire.

[0037] In the solar power generation system 10, the power output from the power converter 14 (conversion circuit 50) is controlled by communication using communication lines 30-33. On the other hand, to stop the operation of the power converter 14 in response to the detection of reverse power flow by the reverse power relay 26, communication using signal line 35 is used. As a result, stopping the operation of the power converter 14 in response to the detection of reverse power flow can be done faster than communication using communication lines 30-33. Thus, the solar power generation system 10 uses a contact input that is faster than communication using communication lines 30-33 to stop the operation of the power converter 14 in response to the detection of reverse power flow.

[0038] The solar power generation system 10 further comprises a phase-advancing capacitor 40 and a switch 42. The phase-advancing capacitor 40 improves the power factor at the connection point with the power system 2 by advancing the phase of the current at the connection point with the power system 2 when the phase of the current at the connection point with the power system 2 lags from the perspective of the power system 2 and the power factor at the connection point with the power system 2 decreases. The switch 42 switches the phase-advancing capacitor 40 on and off.

[0039] The power factor correction capacitor 40 is connected to the premises power system 8, for example, via a switch 42. In other words, the power factor correction capacitor 40 is connected in parallel with the load 4 via the switch 42. This allows for improvement of the lagging power factor at the interconnection point caused by the load 4 by switching on the power factor correction capacitor 40 via the switch 42. However, the configuration of the power factor correction capacitor 40 and the switch 42 is not limited to this, and any configuration that can appropriately improve the power factor at the interconnection point by switching on the power factor correction capacitor 40 is acceptable.

[0040] The switch 42 is connected to the control device 16 via a signal line 44. The control device 16 controls the switching of the switch 42 to open and close by inputting a control signal to the switch 42 via the signal line 44. In other words, the control device 16 controls the switching of the power factor correction capacitor 40 to open and close by inputting a control signal to the switch 42 via the signal line 44.

[0041] The solar power generation system 10 may include, for example, multiple power factor correction capacitors 40 and multiple switches 42. The control device 16 allows for individual control of switching each of the multiple power factor correction capacitors 40 on and off. In other words, the control device 16 allows for control of the number of power factor correction capacitors 40 that are turned on. This allows for more precise control of the power factor at the interconnection point by changing the number of power factor correction capacitors 40 that are turned on. In this case, the capacitances of each of the multiple power factor correction capacitors 40 may be different. This allows for even more precise control of the power factor at the interconnection point by changing the combination of power factor correction capacitors 40 that are turned on.

[0042] The control device 16 communicates with the power receiving panel 20 via the communication line 31 to obtain information on load power consumption, which represents the amount of active power required by the load 4, and information on the power factor at the connection point with the power system 2, based on the measurement results of the power meter 22. The control device 16 also obtains information on received power, which represents the amount of active power (purchased power) supplied from the power system 2 to the load 4, based on the measurement results of the power meter 24.

[0043] Furthermore, the control device 16 communicates with the power converter 14 via the communication line 32 or the communication line 33 to obtain information on the output power of the power converter 14, which represents the magnitude of the active power (generated power) supplied from the power converter 14 to the load 4.

[0044] However, the method for obtaining information on load power consumption, power factor, received power, and output power is not limited to the above, and any method that allows the control device 16 to appropriately obtain each piece of information is acceptable. For example, power factor information may be obtained by calculation within the control device 16, as described above. Furthermore, the magnitudes of load power consumption, received power, and output power refer, more specifically, to the effective values ​​of each power, which are AC power.

[0045] When the output power of the power converter 14 is less than the load power consumption (i.e., no reverse power flow occurs), the control device 16 performs tracking control, which controls the operation of the power converter 14 based on the acquired information, so that the active power and power factor follow the target value.

[0046] The target value of active power is set to the value obtained by subtracting a set value from the load power consumption. This allows the control device 16 to control the output power (active power) of the power converter 14 so that the received power supplied from the power system 2 to the load 4 remains constant at the set value. The set value is, for example, a constant value pre-set in the control device 16. The set value may be changed, for example, in response to operations on the control unit provided in the control device 16 or input from external devices such as the monitoring device 18.

[0047] The target power factor is, for example, 100%. If an upper limit on the power factor is specified, for example, by contract with the power company, it will be set to the specified value. In other words, the target power factor is the upper limit of the power factor. The target power factor is, for example, a fixed value set in advance in the control device 16. The target power factor may be made changeable, for example, by operation of an operating unit provided in the control device 16 or by input from an external device such as a monitoring device 18.

[0048] The control device 16 determines, for example, the magnitude of the reactive power to be output from the power converter 14 in order to bring the power factor at the interconnection point closer to the target value, based on information such as the target value of active power and the power factor at the interconnection point. The control device 16 then generates a control signal to cause the power converter 14 to output the target value of active power and the determined magnitude of reactive power, and inputs the generated control signal to the power converter 14 via the communication line 32.

[0049] When the control unit 51 of the power converter 14 receives a control signal via the communication line 32 and the communication unit 52, it controls the operation of the conversion circuit 50 to output active power and reactive power of magnitudes based on the input control signal. This allows the operation of the power converter 14 to be controlled so that the active power and power factor follow target values. In other words, the operation of the power converter 14 can be controlled so that the power received from the power system 2 is kept constant at a set value and the power factor at the interconnection point is kept within a predetermined range.

[0050] However, the method of controlling the power converter 14 is not limited to the above. For example, the control device 16 may transmit information on the target value of active power and the power factor of the interconnection point to the power converter 14, and the calculation of the magnitude of reactive power may be performed on the power converter 14 side. The method of controlling the power converter 14 may be any method that is capable of making the active power and power factor follow the target value based on each piece of information.

[0051] Furthermore, the control device 16 sets a target value for the power factor at the connection point with the power system 2, and also sets a lower limit and a threshold value. The lower limit is set to a value lower than the target value. For example, the lower limit is 85%. For example, depending on the contract with the power company, a surcharge may be incurred when the power factor at the connection point falls below a predetermined value. For example, a surcharge may be incurred when the lagging power factor as seen from the power system 2 side falls below 85%. The lower limit is set to a value that would result in such a surcharge. The lower limit is not limited to 85% and can be set appropriately according to the contract with the power company, etc.

[0052] The threshold is set between the target value (upper limit) and the lower limit. For example, the threshold is set to a value closer to the lower limit than the target value. The threshold is used to detect when the power factor at the interconnection point approaches the lower limit. For example, if the target value is 100% and the lower limit is 85%, the threshold will be set to around 90%.

[0053] The lower limit and threshold values ​​of the power factor may be fixed values ​​pre-set in the control device 16, similar to the target value, or they may be changeable in response to operations on the control unit provided in the control device 16 or input from external devices such as the monitoring device 18.

[0054] When the output power of the power converter 14 is less than the load power consumption, the control device 16 performs tracking control as described above, and also determines whether the power factor at the interconnection point is above the lower limit and below the threshold, and whether the power factor at the interconnection point is below the lower limit, based on the power factor information.

[0055] If the control device 16 determines that the power factor at the interconnection point is above the lower limit but below the threshold, it executes control to prevent the power factor at the interconnection point from falling below the lower limit.

[0056] The control device 16, for example, outputs a signal to issue an alarm indicating that the power factor at the interconnection point is approaching the lower limit, as a control to suppress the power factor at the interconnection point from falling below the lower limit.

[0057] The control device 16, for example, outputs a signal to the monitoring device 18 to issue an alarm in response to a determination that the power factor of the interconnection point is above the lower limit value but below a threshold value, thereby causing the monitoring device 18 to issue an alarm. The monitoring device 18, for example, issues an alarm by displaying an alarm on its display unit or by outputting an alarm sound from its speaker in response to receiving a signal from the control device 16.

[0058] This allows the administrator of the solar power generation system 10, who monitors each part of the solar power generation system 10 via the monitoring device 18, to be notified that the power factor at the interconnection point is approaching the lower limit. This prompts the administrator to take measures such as reducing the output power of the power converter 14 or turning on the power factor correction capacitor, thereby preventing the power factor at the interconnection point from falling below the lower limit.

[0059] The manner in which the monitoring device 18 issues an alarm is not limited to the above, and may be any manner that appropriately notifies administrators, etc., that the power factor at the interconnection point is approaching the lower limit. Furthermore, the output destination of the signal for issuing the alarm is not limited to the monitoring device 18. For example, the signal may be output to a mobile device such as a smartphone or tablet owned by an administrator, etc., to notify the administrator, etc. The output destination of the signal may also be, for example, a warning light or speaker that notifies people around the control device 16 or monitoring device 18 that the power factor is approaching the lower limit. The output destination of the signal may also be, for example, any device that appropriately prompts administrators, etc., to take measures against the power factor decline.

[0060] Furthermore, the control device 16, for example, executes the closing of the power factor correction capacitor 40 as a control to suppress the power factor at the interconnection point from falling below the lower limit. For example, when the power factor correction capacitor 40 is open, the control device 16 determines that the power factor at the interconnection point in the lagging direction as seen from the power system 2 side is above the lower limit but below the threshold, and inputs a control signal to the switch 42 to close the power factor correction capacitor 40. This makes it possible to more effectively suppress the power factor at the interconnection point from falling below the lower limit.

[0061] After the power factor correction capacitor 40 is turned on, the control device 16 turns off the power factor correction capacitor 40 by inputting a control signal to the switch 42, for example, when the power factor at the interconnection point exceeds a predetermined value, or when the power factor at the interconnection point changes to a leading side.

[0062] In this way, the control device 16 performs, for example, the output of a signal for issuing an alarm and the closing of the power factor correction capacitor 40 as controls to prevent the power factor at the interconnection point from falling below the lower limit. This prevents the power factor at the interconnection point from falling below the lower limit and allows the operation of the power converter 14 to be controlled so that the power factor at the interconnection point is kept within a predetermined range. In other words, the operation of the power converter 14 can be controlled so that the power factor at the interconnection point is kept within the range between the target value and the lower limit.

[0063] Furthermore, it is not necessary to output a signal for issuing an alarm and to switch on the power factor correction capacitor 40. The control device 16 may perform at least one of the following actions as a control to prevent the power factor at the interconnection point from falling below the lower limit: outputting a signal for issuing an alarm and switching on the power factor correction capacitor 40. Moreover, the control to prevent the power factor at the interconnection point from falling below the lower limit is not limited to the above, and may be any control capable of preventing the power factor at the interconnection point from falling below the lower limit.

[0064] If the control device 16 determines that the power factor at the interconnection point is below the lower limit, it outputs a signal to issue an alarm indicating that the power factor at the interconnection point has fallen below the lower limit. For example, in response to the determination that the power factor at the interconnection point is below the lower limit, the control device 16 outputs a signal to the monitoring device 18 to issue an alarm. However, as with the case of issuing an alarm indicating that the power factor is approaching the lower limit, the manner of alarm issuance and the alarm output device may be arbitrary.

[0065] Furthermore, if the control device 16 determines that the power factor at the connection point is below the lower limit, it will, for example, perform control to stop the supply of power from power system 2 to load 4. The control to stop the supply of power from power system 2 to load 4 is, for example, a control that disconnects the solar power generation system 10 and load 4 from power system 2 by opening a circuit breaker (not shown) installed at the connection point with power system 2. In other words, the control to stop the supply of power from power system 2 to load 4 is a control that stops the connection of the solar power generation system 10 with power system 2. The control to stop the supply of power from power system 2 to load 4 is not limited to the above, and may be any control that is capable of stopping the supply of power from power system 2 to load 4.

[0066] For example, if the control device 16 determines that the power factor at the interconnection point is below a lower limit and stops supplying power from the power system 2 to the load 4, it will resume supplying power from the power system 2 to the load 4 when the power factor at the interconnection point returns to or above the lower limit. The control device 16 may also resume supplying power from the power system 2 to the load 4 when the power factor at the interconnection point returns to or above a threshold higher than the lower limit, or to a target value. This prevents the power factor at the interconnection point from falling below the lower limit again after it has risen above the lower limit and then returning to below the lower limit when the interconnection is resumed.

[0067] Thus, if the control device 16 determines that the power factor at the interconnection point is below the lower limit, it may, for example, output a signal to issue an alarm and stop the supply of power from power system 2 to load 4. However, the control device 16 may only perform one of either outputting a signal to issue an alarm or stopping the supply of power from power system 2 to load 4. When the power factor at the interconnection point falls below the lower limit, the control device 16 may not necessarily stop the supply of power from power system 2 to load 4, but may instead connect the solar power generation system 10 to power system 2 while the power factor remains low and continue operating the power converter 14. The operation of the control device 16 when it determines that the power factor at the interconnection point is below the lower limit is not limited to the above, and may be any operation appropriate for when the power factor at the interconnection point falls below the lower limit.

[0068] Figure 2 is a flowchart schematically illustrating an example of the operation of a solar power generation system according to the embodiment. Figures 3(a) and 3(b) are schematic graphs illustrating an example of the operation of a photovoltaic power generation system according to the embodiment. Figure 3(a) schematically shows an example of the power factor at the interconnection point. Figure 3(b) schematically shows an example of the load power consumption required by load 4 and an example of the output power of power converter 14.

[0069] As shown in Figure 2, in the solar power generation system 10, the reverse power relay 26 detects reverse power flow from the power converter 14 toward the power grid 2 (step S101 in Figure 2). In response to the detection of reverse power flow, the reverse power relay 26 inputs a detection signal to the power converter 14 and the control device 16.

[0070] The power converter 14 and the control device 16 stop outputting AC power to the load 4 in response to the input of the detection signal (step S102 in Figure 2). This prevents reverse power flow from continuing to flow to the power system 2.

[0071] The control device 16 acquires information on load power consumption, power factor, and received power when the reverse power relay 26 has not detected the occurrence of reverse power flow (step S103 in Figure 2). The control device 16 acquires information on load power consumption, power factor, and received power from the power receiving panel 20 by communicating with the power receiving panel 20, for example, via the communication line 31.

[0072] After acquiring each piece of information, the control device 16 determines whether the power factor at the interconnection point is below a threshold based on the acquired power factor information (step S104 in Figure 2).

[0073] If the control device 16 determines that the power factor at the interconnection point is above a threshold, it communicates with the power converter 14 via the communication line 32 to monitor the status of the power converter 14 (step S105 in Figure 2). By communicating with the power converter 14, the control device 16 obtains information on the output power of the power converter 14 from the power converter 14.

[0074] After acquiring information on the output power, the control device 16 performs calculations based on the acquired information to generate a control signal for tracking control, which controls the operation of the power converter 14 so that the active power and power factor follow the target values. The generated control signal is then input to the power converter 14 via the communication line 32 (step S106 in Figure 2).

[0075] When the control unit 51 of the power converter 14 receives a control signal via the communication line 32 and the communication unit 52, it controls the operation of the conversion circuit 50 based on the input control signal, thereby performing tracking control to make the active power and power factor follow the target value (step S107 in Figure 2). After the control device 16 has made the power converter 14 perform tracking control, it returns to the process in step S101.

[0076] If the control device 16 determines in step S104 that the power factor at the interconnection point is below a threshold, it then proceeds to determine whether the power factor at the interconnection point is below a lower limit (step S108 in Figure 2).

[0077] If the control device 16 determines that the power factor at the interconnection point is above the lower limit but below the threshold, it outputs a signal to trigger an alarm indicating that the power factor at the interconnection point is approaching the lower limit (step S109 in Figure 2, timings t1 and t2 in Figure 3). For example, in response to the determination that the power factor at the interconnection point is above the lower limit but below the threshold, the control device 16 outputs a signal to the monitoring device 18 to trigger an alarm, causing the monitoring device 18 to trigger an alarm.

[0078] The control device 16 issues an alarm indicating that the power factor at the interconnection point is approaching the lower limit, and then switches on the power factor correction capacitor 40 (step S110 in Figure 2).

[0079] If the control device 16 determines that the power factor at the interconnection point is above the lower limit but below the threshold, it performs control to prevent the power factor at the interconnection point from falling below the lower limit, such as issuing an alarm or turning on the power factor correction capacitor 40, and then starts the process in step S105.

[0080] In step S108, if the control device 16 determines that the power factor at the interconnection point is below the lower limit, it outputs a signal to issue an alarm indicating that the power factor at the interconnection point has fallen below the lower limit (step S111 in Figure 2, timing t3 in Figure 3). For example, in response to the determination that the power factor at the interconnection point is below the lower limit, the control device 16 outputs a signal to the monitoring device 18 to issue an alarm, thereby causing the monitoring device 18 to issue an alarm.

[0081] After issuing an alarm indicating that the power factor at the interconnection point has fallen below the lower limit, the control device 16 controls the system to stop supplying power from the power system 2 to the load 4 (step S112 in Figure 2). The control device 16 stops supplying power from the power system 2 to the load 4 by, for example, opening a circuit breaker installed at the interconnection point with the power system 2 and disconnecting the solar power generation system 10 and the load 4 from the power system 2.

[0082] If the control device 16 determines that the power factor at the interconnection point is below the lower limit, it will issue an alarm and control the shutdown of the power supply from power system 2 to load 4, and then start the process in step S105. The control device 16 will then repeatedly execute the above process.

[0083] As explained above, in the photovoltaic power generation system 10 according to this embodiment, the control device 16 executes control to prevent the power factor at the interconnection point from falling below the lower limit when the power factor at the interconnection point is above the lower limit but below the threshold. This makes it possible to more appropriately suppress the power factor at the interconnection point from falling outside the predetermined range, even when the amount of active power demand fluctuates greatly due to the operating status of the load, such as operation and shutdown, as shown in timings t1 and t2 in Figure 3, compared to when only tracking control is performed. In a fully self-consumption type photovoltaic power generation system 10 (distributed power source system), the power factor at the interconnection point can be more appropriately kept within the predetermined range. Furthermore, this makes it possible to suppress, for example, the occurrence of increased electricity charges due to a decrease in the power factor.

[0084] The control device 16, for example, outputs a signal to issue an alarm indicating that the power factor at the interconnection point is approaching the lower limit, and executes this as control to suppress the power factor at the interconnection point from falling below the lower limit. This makes it possible to more effectively suppress the power factor at the interconnection point from falling below the lower limit.

[0085] Furthermore, the control device 16, for example, performs the switching on of the power factor correction capacitor 40 as a control to suppress the power factor at the interconnection point from falling below the lower limit. This makes it possible to more effectively suppress the power factor at the interconnection point from falling below the lower limit.

[0086] In the above embodiment, a solar power generation system 10 is shown as an example of a distributed power system, using solar panels 12 as a distributed power source. The distributed power source is not limited to solar panels 12, but may also be, for example, a wind turbine or a geothermal generator. The distributed power source may be any power source capable of supplying the generated electricity. The electricity supplied by the distributed power source is not limited to DC power, but may also be AC ​​power, etc. The distributed power system is not limited to the solar power generation system 10, but may be any system using any distributed power source.

[0087] This embodiment includes the following aspects. (Note 1) A fully self-consumption type distributed power system that is connected to a power grid and loads, and supplies electricity generated by distributed power sources to the loads, thereby suppressing the purchase of electricity from the power grid to the loads, A distributed power source that generates electricity and also supplies the electricity it generates, A power conversion device that converts 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 performs tracking control to control the operation of the power converter so that the active power output from the power converter follows a target value, and the power factor at the connection point with the power system follows a target value, Equipped with, The control device sets a lower limit value for the power factor of the interconnection point, which is set to a value lower than the target value, and a threshold value set between the target value and the lower limit value, and when the power factor of the interconnection point is greater than or equal to the lower limit value and less than the threshold value, it performs control to suppress the power factor of the interconnection point from falling below the lower limit value.

[0088] (Note 2) The distributed power supply system according to Appendix 1, wherein the control device outputs a signal for issuing an alarm indicating that the power factor of the interconnection point is approaching the lower limit, as a control to suppress the power factor of the interconnection point from falling below the lower limit.

[0089] (Note 3) A phase-advancing capacitor that improves the power factor at the aforementioned interconnection point, A switch for switching the power on and off of the aforementioned power factor correction capacitor, Furthermore, The distributed power supply system according to Appendix 1 or 2, wherein the control device controls the switching of the switch to turn on and off, thereby controlling the switching of the power factor correction capacitor to turn on, and the switching of the power factor correction capacitor to prevent the power factor at the interconnection point from falling below the lower limit.

[0090] (Note 4) The distributed power supply system according to any one of the appendices 1 to 3, wherein the control device outputs a signal for issuing an alarm indicating that the power factor of the interconnection point has fallen below the lower limit when the power factor of the interconnection point is below the lower limit.

[0091] (Note 5) The distributed power supply system according to any one of the appendices 1 to 4, wherein the control device controls the supply of power from the power system to the load when the power factor of the interconnection point is below the lower limit.

[0092] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0093] 2…Power system, 4…Load, 6…Transformer, 8…In-house system, 10…Solar power generation system (distributed power system), 12…Solar panels (distributed power source), 14…Power converter, 16…Control device, 18…Monitoring device, 20…Switchboard, 22, 24…Power meter, 30~33…Communication line, 35…Signal line, 40…Power factor correction capacitor, 42…Switch, 44…Signal line, 50…Conversion circuit, 51…Control unit, 52, 53…Communication unit, 54…Input unit

Claims

1. A fully self-consumption type distributed power system that is connected to a power grid and loads, and supplies electricity generated by distributed power sources to the loads, thereby suppressing the purchase of electricity from the power grid to the loads, A distributed power source that generates electricity and also supplies the electricity it generates, A power conversion device that converts 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 performs tracking control to control the operation of the power converter so that the active power output from the power converter follows a target value, and the power factor at the connection point with the power system follows a target value, A power meter for measuring the power required by the aforementioned load, Equipped with, The control device is Based on the measurement results of the power meter, information on load power consumption, which represents the amount of active power required by the load, is obtained, and the value obtained by subtracting a set value from the load power consumption is set as the target value of the active power. A lower limit is set for the power factor of the interconnection point, which is lower than the target value, and a threshold is set between the target value and the lower limit. When the power factor of the interconnection point is greater than or equal to the lower limit and less than the threshold, control is performed to prevent the power factor of the interconnection point from falling below the lower limit. If the power factor at the interconnection point is below the lower limit, control is performed to stop the supply of power from the power system to the load. A distributed power supply system that resumes supplying power from the power grid to the load in response to the power factor at the interconnection point returning to above the lower limit.

2. The distributed power supply system according to claim 1, wherein the control device outputs a signal for issuing an alarm indicating that the power factor of the interconnection point is approaching the lower limit, as a control to suppress the power factor of the interconnection point from falling below the lower limit.

3. A phase-advancing capacitor that improves the power factor at the aforementioned interconnection point, A switch for switching the power on and off of the aforementioned power factor correction capacitor, Furthermore, The distributed power supply system according to claim 1, wherein the control device controls the switching of the switch to turn on and off, thereby controlling the switching of the power factor correction capacitor to turn on, and the switching of the power factor correction capacitor to be performed as a control to suppress the power factor at the interconnection point from falling below the lower limit.

4. The distributed power supply system according to claim 1, wherein the control device outputs a signal for issuing an alarm indicating that the power factor of the interconnection point has fallen below the lower limit when the power factor of the interconnection point is below the lower limit.

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