Power conversion system, power conversion device

Abstract

To effectively use generated power while preventing unnecessary stop of the entire power conversion system during power outage.SOLUTION: A first power conversion device (10) can convert electric power generated by a power generator (4a) that generates power by using renewable energy into an AC power having a predetermined voltage and output the AC power to a power receiving point of an electric power system (2). A second power conversion device (20) has a converter (21) that performs charge and discharge with respect to a power storage unit (5), an inverter (22), and a control unit (25). During power outage in the electric power system (2), an independent output path of the second power conversion device (20) and an interconnection output path of the first power conversion device (10) are connected to each other. When power input to an AC side of the inverter (22) exceeds or is predicted to exceed the chargeable maximum power of the power storage unit (5), the control unit (25) performs control to prevent or block output from the first power conversion device (10).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion system and a power conversion device that are capable of using power generated by a power generation device using renewable energy during a power outage. [Background technology]

[0002] In Japan, the need for self-consumption of electricity generated by solar power generation systems is increasing due to the reduction in the feed-in tariff for solar power generation. In order to store the electricity generated by solar power generation systems in storage batteries without reverse power flow, the number of solar power generation system installers introducing new energy storage systems is increasing.

[0003] During a power outage, if the existing photovoltaic power generation system and the newly installed storage system are independent and output power independently (for example, see Figure 4), the output of the power conditioner of the photovoltaic power generation system becomes unstable due to the influence of fluctuations in solar radiation. In addition, the power generated by the photovoltaic power generation system cannot be charged to the storage battery.

[0004] Therefore, a configuration may be considered in which the independent output of a newly installed power storage system and the interconnected output of an existing solar power generation system are linked during a power outage (see, for example, FIG. 5 of the present application and Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-180159 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned configuration, depending on the state of charge of the storage battery, the solar power generation may become excessive, causing the entire system to stop.

[0007] The present disclosure has been made in consideration of these circumstances, and its purpose is to provide a power conversion system and a power conversion device that can effectively utilize the generated power while preventing unnecessary shutdowns of the entire system during a power outage. [Means for solving the problem]

[0008] In order to solve the above problems, a power conversion system according to an embodiment of the present disclosure includes a first power conversion device capable of converting power generated by a power generation device that generates power using renewable energy into AC power of a predetermined voltage and outputting the AC power to a power receiving point of a power grid, a converter capable of charging and discharging a power storage unit, an inverter connected between a DC bus to which the converter is connected and the power receiving point, and a second power conversion device having a control unit that controls the inverter. During a power outage in the power grid, an independent output path of the second power conversion device and an interconnected output path of the first power conversion device are connected, and the control unit controls the first power conversion device to suppress or cut off the output when the power input to the AC side of the inverter exceeds or is predicted to exceed the maximum chargeable power of the power storage unit. Effect of the Invention

[0009] According to the present disclosure, during a power outage, unnecessary shutdown of the entire power conversion system can be prevented and generated power can be effectively utilized. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram for explaining a power conversion system according to an embodiment; [Diagram 2] FIG. 13 is a diagram for explaining excessive power generation. [Diagram 3] 6 is a flowchart for explaining an example of operation during a power outage of the second power conversion device according to the embodiment. [Figure 4] FIG. 2 is a diagram for explaining a power conversion system according to a first comparative example. [Diagram 5] FIG. 11 is a diagram for explaining a power conversion system according to a second comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] FIG. 1 is a diagram for explaining a power conversion system 1 according to an embodiment. The power conversion system 1 includes a first power conversion device 10 and a second power conversion device 20. The first power conversion device 10 is a power conditioner for a solar power generation system. The second power conversion device 20 is a power conditioner for a hybrid power storage system (also called a generation and storage linked system). The second power conversion device 20 is an integrated power conditioner (also called a power station (registered trademark)) that integrates a power conditioner function for a solar power generation system and a power conditioner function for a power storage system.

[0012] The power conversion system 1 according to the embodiment is a system in which an existing old-type first power conversion device 10 cooperates with a newly installed new-type second power conversion device 20. Note that in the present embodiment, it is assumed that the old-type first power conversion device 10 does not have a communication port, and the first power conversion device 10 and the second power conversion device 20 are not connected by a communication line.

[0013] The first power conversion device 10 includes a DC / DC converter 11, an inverter 12, a converter control circuit 13, an inverter control circuit 14, a control unit 15, a grid-connection relay RY1, an independent output relay RY2, and an AC outlet 16.

[0014] The first solar cell 4a is a power generating device that utilizes the photovoltaic effect to directly convert light energy into DC power. As the first solar cell 4a, a silicon solar cell, a solar cell made of a material such as a compound semiconductor, a dye-sensitized solar cell, an organic thin-film solar cell, or the like is used. The first solar cell 4a is connected to a DC / DC converter 11 of the first power conversion device 10, and outputs the generated power to the first power conversion device 10. The DC / DC converter 11 is a converter that can adjust the voltage of the DC power output from the first solar cell 4a. The DC / DC converter 11 can be configured, for example, as a boost chopper.

[0015] The converter control circuit 13 controls the DC / DC converter 11. The converter control circuit 13 controls the DC / DC converter 11 by MPPT (Maximum Power Point Tracking) so that the output power of the first solar cell 4a is maximized. Specifically, the converter control circuit 13 measures the input voltage and input current of the DC / DC converter 11, which are the output voltage and output current of the first solar cell 4a, to estimate the power generated by the first solar cell 4a. The converter control circuit 13 generates a command value for making the power generated by the first solar cell 4a a maximum power point (optimum operating point) based on the measured output voltage of the first solar cell 4a and the estimated power generation. For example, the converter control circuit 13 changes the operating point voltage by a predetermined step width according to a hill-climbing method to search for the maximum power point, and generates a command value to maintain the maximum power point. The DC / DC converter 11 performs switching operation in response to a drive signal based on the generated command value.

[0016] The inverter 12 converts the DC power supplied from the DC / DC converter 11 into AC power and outputs it. The inverter control circuit 14 controls the inverter 12. As a basic control, the inverter control circuit 14 controls the inverter 12 so that the voltage of the DC bus between the DC / DC converter 11 and the inverter 12 maintains a target value. Specifically, the inverter control circuit 14 detects the voltage of the DC bus and generates a command value for matching the detected bus voltage with the target value. When the voltage of the DC bus is higher than the target value, the inverter control circuit 14 generates a current command value for increasing the output power of the inverter 12, and when the voltage of the DC bus is lower than the target value, the inverter control circuit 14 generates a current command value for decreasing the output power of the inverter 12. The inverter 12 performs a switching operation in response to a drive signal based on the generated current command value.

[0017] The output path of the inverter 12 branches into a grid-connected output path and an independent output path. A grid-connected relay RY1 is inserted into the grid-connected output path of the inverter 12. The grid-connected output path of the first power conversion device 10 is connected to a power receiving point of a commercial power system (hereinafter simply referred to as system 2) or an independent output path of the second power conversion device 20 via a parallel-off relay RY6 and an output switching relay RY5. A distribution board (not shown) is installed at the power receiving point. In this embodiment, a single-phase three-wire 100V / 200V power supply is assumed as the system power supply. A general load 3a is connected to the distribution board. The general load 3a is a general term for loads within the home.

[0018] The output switching relay RY5 is a C-contact relay that selectively connects the interconnection output path of the first power conversion device 10 to the power receiving point of the system 2 or the independent output path of the second power conversion device 20. The parallel-off relay RY6 is a relay for parallel-off the first power conversion device 10 from the system 2 and the power conversion system 1.

[0019] An independent output relay RY2 is inserted in the independent output path of the inverter 12. The independent output path of the first power conversion device 10 is connected to an AC outlet 16. During a power outage, a user can insert the outlet plug of a home appliance into the AC outlet 16 to use the appliance.

[0020] The control unit 15 performs overall control of the first power conversion device 10. The control unit 15 can be realized by a combination of hardware resources and software resources, or by hardware resources alone. Analog elements, microcontrollers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs can be used as hardware resources. Programs such as firmware can be used as software resources.

[0021] In the grid-connected mode, the control unit 15 controls the grid-connected relay RY1 to be on (closed) and the isolated output relay RY2 to be off (open). In the isolated operation mode during a power outage, the control unit 15 controls the grid-connected relay RY1 to be off and the isolated output relay RY2 to be on.

[0022] The second power conversion device 20 includes a DC / DC converter 21, an inverter 22, a converter control circuit 23, an inverter control circuit 24, a DC / DC converter 26, a converter control circuit 27, a control unit 25, a grid-connection relay RY3, and an independent output relay RY4.

[0023] The newly installed second solar cell 4b may be a solar cell of the same type as the existing first solar cell 4a, or may be a solar cell of a different type. The second solar cell 4b is connected to a DC / DC converter 26 of the second power conversion device 20 and outputs the generated power to the second power conversion device 20. The DC / DC converter 26 is connected between the second solar cell 4b and the DC bus Bd and is a converter capable of adjusting the voltage of the DC power output from the second solar cell 4b. The DC / DC converter 26 can be configured, for example, by a boost chopper.

[0024] The converter control circuit 27 controls the DC / DC converter 26. As a basic control, the converter control circuit 27 performs MPPT control of the DC / DC converter 26 so that the output power of the second solar cell 4b is maximized. The converter control circuit 27 can also control the step-up ratio of the DC / DC converter 26 so that the voltage of the DC bus Bd is maintained at a target value, or so that the measured value of the power generation of the second solar cell 4b is maintained at a target value. This control may be invoked when it becomes necessary to suppress the amount of power generation of the second solar cell 4b.

[0025] The power storage unit 5 is capable of charging and discharging power, and includes a storage battery such as a lithium ion battery, a nickel metal hydride battery, a lead storage battery, etc. Instead of the storage battery, a capacitor such as an electric double layer capacitor or a lithium ion capacitor may be included.

[0026] The power storage unit 5 is connected to the DC / DC converter 21, and charging and discharging are controlled by the DC / DC converter 21. The DC / DC converter 21 is a bidirectional DC / DC converter connected between the power storage unit 5 and the DC bus Bd, and for charging and discharging the power storage unit 5.

[0027] The converter control circuit 23 controls the DC / DC converter 21. As a basic control, the converter control circuit 23 controls the charging and discharging of the DC / DC converter 21 based on a command value transmitted from the control unit 25. As the charging and discharging control, for example, constant current (CC) control or constant voltage (CV) control is possible. The converter control circuit 23 can also control the charging and discharging of the DC / DC converter 21 so that the voltage of the DC bus Bd maintains a target value.

[0028] The inverter 22 is a bidirectional inverter connected between the DC bus Bd and the distribution board. The inverter 22 converts DC power input from the DC bus Bd into AC power, and outputs the converted AC power to the distribution board via the interconnection relay RY3. The inverter 22 can convert AC power supplied from the system 2 via the distribution board and the interconnection relay RY3 into DC power, and output the converted DC power to the DC bus Bd. The inverter 22 can also convert AC power supplied from the first power conversion device 10 via the output switching relay RY5 and the independent output relay RY4 into DC power, and output the converted DC power to the DC bus Bd.

[0029] The inverter control circuit 24 controls the inverter 22. As a basic control, the inverter control circuit 24 controls the inverter 22 so that the voltage of the DC bus Bd maintains a target value. Specifically, the inverter control circuit 24 detects the voltage of the DC bus Bd and generates a command value for matching the detected bus voltage with the target value. The inverter 22 performs a switching operation in response to a drive signal based on the generated command value.

[0030] The output path of the inverter 22 is branched into a grid-connected output path and an isolated output path. A grid-connected relay RY3 is inserted in the grid-connected output path of the inverter 22. The grid-connected output path of the second power conversion device 20 is connected to a distribution board.

[0031] An independent output relay RY4 is inserted in the independent output path of the inverter 22. The independent output path of the second power conversion device 20 is connected to some of the branch distribution lines in the distribution board. During a power outage, power is supplied only to the AC outlet connected to that branch wiring. A specific load 3b (e.g., lighting fixture, refrigerator, etc.) to which it is desired to ensure a power supply even during a power outage may be connected to the AC outlet connected to that branch wiring. The independent output path of the second power conversion device 20 may be connected to all of the branch wiring in the distribution board. In that case, power can be supplied to the general load 3a even during a power outage.

[0032] The control unit 25 performs overall control of the entire second power conversion device 20. The control unit 25 can be realized by a combination of hardware resources and software resources, or by hardware resources alone. Analog elements, microcontrollers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs can be used as hardware resources. Programs such as firmware can be used as software resources.

[0033] In the grid-connected mode, the control unit 25 controls the grid-connected relay RY3 to be on and the isolated output relay RY4 to be off, and connects the output switching relay RY5 to the power receiving point side of the grid 2. In the isolated operation mode, the control unit 25 controls the grid-connected relay RY3 to be off and the isolated output relay RY4 to be on, and connects the output switching relay RY5 to the isolated output path side of the second power conversion device 20. Also, in the isolated operation mode, the control unit 25 controls the inverter control circuit 24 to cause the inverter 22 to output an AC voltage corresponding to the grid frequency and grid voltage.

[0034] The control unit 25 can detect a power outage in the system 2 based on the measured voltage on the AC side of the inverter 22. When the control unit 25 detects a power outage, it switches from the grid-connected mode to the isolated operation mode.

[0035] The control unit 25 can acquire the SOC (State Of Charge) of the power storage unit 5 from a control unit (not shown) in the power storage unit 5. The control unit 25 includes a SOC / SOP (State Of Power) table (not shown). The SOC / SOP table is a table that describes the relationship between the SOC of the power storage unit 5 and the maximum chargeable power (maximum charging rate) of the power storage unit 5. The maximum chargeable power for each SOC of the power storage unit 5 differs depending on the type and capacity of the storage battery and capacitor used in the power storage unit 5. The designer prepares the SOC / SOP table in advance according to the storage battery and capacitor to be used.

[0036] The maximum chargeable power of the power storage unit 5 is 0 W when SOC=100%. As the SOC decreases, the maximum chargeable power increases. For simplicity, the maximum chargeable power may be fixed to the rated charging power of the power storage unit 5 when the SOC is in the range of 98-0%. The control unit 25 refers to the SOC / SOP table and specifies the maximum chargeable power of the power storage unit 5 based on the SOC of the power storage unit 5 acquired from the control unit of the power storage unit 5.

[0037] The control unit 25 calculates the AC power output from the inverter 22 or the AC power input to the inverter 22 based on the measured voltage and current on the AC side of the inverter 22 .

[0038] During a power outage, when the power input to the AC side of the inverter 22 (hereinafter referred to as inverter input power) exceeds or is predicted to exceed the maximum chargeable power of the power storage unit 5, the control unit 25 controls so that the power obtained by subtracting the power consumption of the specific load 3b from the output power of the first power conversion device 10 becomes equal to or less than the maximum chargeable power of the power storage unit 5. In other words, the control is performed so as to prevent an overpower generation state. Methods for controlling so as to prevent an overpower generation state include a method of turning off the parallel-off relay RY6 and a method of changing the output voltage of the inverter 22.

[0039] First, a method of controlling the parallel-off relay RY6 to turn off so as not to cause an overpower generation state will be described. The control unit 25 turns off the parallel-off relay RY6 when the inverter input power has exceeded or is predicted to exceed the maximum chargeable power. As a method of detecting a state in which the inverter input power is predicted to exceed the maximum chargeable power, for example, it may be determined whether the inverter input power has exceeded the maximum chargeable power minus a predetermined margin. When the inverter input power exceeds the maximum chargeable power minus a predetermined margin, the control unit 25 determines that the inverter input power is in a state in which it is predicted to exceed the maximum chargeable power.

[0040] Also, it may be determined whether the maximum chargeable power is less than a first set value. When the maximum chargeable power is less than the first set value, the control unit 25 determines that the inverter input power is in a state where it is predicted to exceed the maximum chargeable power. For example, the first set value may be set to a value at which the maximum chargeable power starts to decrease rapidly.

[0041] Also, it may be determined whether the SOC of the power storage unit 5 has exceeded a second set value. When the SOC of the power storage unit 5 has exceeded the second set value, the control unit 25 determines that the inverter input power is predicted to exceed the maximum chargeable power. The second set value may be set to, for example, a value near full charge (e.g., 98%).

[0042] Next, a method of controlling the inverter 22 to prevent excessive power generation will be described. When the inverter input power exceeds or is predicted to exceed the maximum chargeable power, the control unit 25 reduces the output voltage of the inverter 22 based on the maximum chargeable power and the maximum output current of the first power conversion device 10 so that the output power of the first power conversion device 10 is equal to or less than the maximum chargeable power.

[0043] For example, when the maximum output current of the first power conversion device 10 is 30 A and the maximum chargeable power of the power storage unit 5 is 3000 W, the control unit 25 reduces the output voltage of the inverter 22 to 100 V (=3000 W / 30 A) or less. This makes it possible to prevent the inverter input power from exceeding the maximum chargeable power even in a no-load state.

[0044] When the inverter input power has exceeded or is predicted to exceed the maximum chargeable power, the control unit 25 may change the output voltage of the inverter 22 to a voltage at which the first power conversion device 10 detects an abnormality and stops operation.

[0045] The first power conversion device 10 includes an undervoltage relay (UVR) (not shown) as a protective relay for grid interconnection. The undervoltage relay (UVR) is installed to detect islanding and as a countermeasure against instantaneous voltage drops. The grid interconnection regulations stipulate that the condition for the undervoltage relay (UVR) to detect an undervoltage is that the output voltage of the first power conversion device 10 remains at or below 80% for one second. Note that the undervoltage relay (UVR) may be an interconnection relay RY1 or a gate block of the inverter 12.

[0046] As described above, when the control unit 25 of the second power conversion device 20 detects a power outage, it switches the connection destination of the output switching relay RY5 from the power receiving point side of the grid 2 to the independent output path side of the second power conversion device 20, and causes the inverter 22 to output an AC voltage corresponding to the grid frequency and grid voltage. As a result, even if a power outage occurs, the control unit 15 of the first power conversion device 10 determines that it is an instantaneous voltage drop, and when an independent AC voltage is output from the second power conversion device 20, it determines that the grid 2 has returned to normal.

[0047] When the control unit 25 of the second power conversion device 20 controls the output voltage of the inverter 22 to a level below the level at which the undervoltage relay (UVR) of the first power conversion device 10 detects an undervoltage for a period of time equal to or longer than the detection time limit, the first power conversion device 10 stops due to abnormality detection. After reducing the output voltage of the inverter 22, the control unit 25 returns the output voltage of the inverter 22 to its original state when a time equal to or longer than the detection time limit has elapsed.

[0048] As described above, as a method for controlling to prevent an overpower generation state, a method for turning off the parallel-off relay RY6 and a method for changing the output voltage of the inverter 22 have been described. Either the former method or the latter method may be used, or both may be used in combination.

[0049] FIG. 2 is a diagram for explaining overpower generation. Overpower generation refers to a state in which "power generation amount of the first solar cell 4a + power generation amount of the second solar cell 4b - power consumption amount of the specific load 3b" > "maximum chargeable power of the power storage unit 5." In an overpower generation state, the generated power becomes surplus and has nowhere to go. When an overpower generation state occurs, the overcurrent detection function for the power storage unit 5 and the overvoltage detection function for the DC bus Bd are activated, causing the second power conversion device 20 to abnormally stop. When the output voltage of the second power conversion device 20 disappears, the first power conversion device 10 also abnormally stops.

[0050] 2, the amount of power generated by the first solar cell 4a cannot be controlled by the second power conversion device 20 because the first power conversion device 10 and the second power conversion device 20 are not connected by a communication line. On the other hand, the amount of power generated by the second solar cell 4b can be controlled by the second power conversion device 20. The amount of power consumed by the specific load 3b cannot basically be controlled by the second power conversion device 20. Note that, if a Home Energy Management System (HEMS) controller is installed in the house, it is possible to control the amount of power consumed by a load such as an air conditioner, but this embodiment is premised on a configuration in which the amount of power consumed by the specific load 3b cannot be controlled.

[0051] When the overpower generation state occurs, the voltage of the DC bus Bd of the second power conversion device 20 rises. The converter control circuit 27 of the second power conversion device 20 has a function of controlling the step-up ratio of the DC / DC converter 26 so that the voltage of the DC bus Bd maintains a target value. When the voltage of the DC bus Bd exceeds the target value, the converter control circuit 27 controls the step-up ratio of the DC / DC converter 26 to reduce the output power of the second solar cell 4b. If the voltage of the DC bus Bd does not become equal to or lower than the target value even when the output power of the second solar cell 4b is reduced, the converter control circuit 27 gate-blocks the DC / DC converter 26 to stop power generation by the second solar cell 4b.

[0052] This control is executed based on the measured voltage value of the DC bus Bd, and the amount of power generated by the second solar cell 4b can be instantly adjusted. The converter control circuit 27 does not need to receive an instruction signal for the amount of power generated by the second solar cell 4b from the control unit 25. Therefore, the control unit 25 does not need to monitor the charging power from the second solar cell 4b to the power storage unit 5.

[0053] 3 is a flowchart for explaining an example of operation of the second power conversion device 20 according to the embodiment during a power outage. During a power outage in the system 2 (Y in S10), the control unit 25 connects the output switching relay RY5 to the independent output path side of the second power conversion device 20 (S11). The control unit 25 compares the SOC of the storage unit 5 with a set value (e.g., 98%) (S12), and when the SOC exceeds the set value (Y in S12), turns off the parallel-off relay RY6 (S13). The process proceeds to step S10. While the SOC does not exceed the set value (N in S12), the process proceeds to step S14.

[0054] The control unit 25 specifies the maximum chargeable power of the power storage unit 5 based on the SOC of the power storage unit 5 (S14). The control unit 25 compares the maximum chargeable power of the power storage unit 5 with the power input to the AC side of the inverter 22 (hereinafter referred to as inverter input power) (S15). If the inverter input power exceeds the maximum chargeable power (Y in S15), the control unit 25 reduces the output voltage of the inverter 22 (S16). The control unit 25 turns off the parallel-off relay RY6 (S17). When the parallel-off relay RY6 is turned off, the control unit 25 restores the output voltage of the inverter 22 (S18). The process proceeds to step S10. If the inverter input power does not exceed the maximum chargeable power (N in S15), the process proceeds to step S10.

[0055] 3 is based on the assumption that the system configuration has a slow response of the parallel-off relay RY6. For example, a system configuration may be used in which the control unit 25 is realized by cooperation between a microcontroller in the housing of the second power conversion device 20 and a microcontroller of a remote control setting device outside the housing. In this system configuration, if the two microcontrollers are connected using a low-speed serial communication standard such as RS-485, it may take several seconds or more from when the inverter input power exceeds the maximum chargeable power until the parallel-off relay RY6 is actually turned off.

[0056] In contrast, a drop in the output voltage of the inverter 22 is instantly reflected in the output voltage of the first power conversion device 10, so the first power conversion device 10 stops instantly after the inverter input power exceeds the maximum chargeable power. However, when the output voltage of the inverter 22 returns to normal, the first power conversion device 10 resumes operation. In this case, there is a possibility that the first power conversion device 10 will frequently repeat operation and stop.

[0057] 3, after the parallel-off relay RY6 is turned off, the output voltage of the inverter 22 is restored, thereby preventing the first power conversion device 10 from frequently repeating operation and stopping. Note that the control unit 25 may turn on the parallel-off relay RY6, for example, when the SOC of the power storage unit 5 drops to a predetermined value or when a time period with low solar radiation is entered. In either case, the possibility that the inverter input power will exceed the maximum chargeable power is reduced.

[0058] In the example of operation shown in FIG. 3, when priority is given to effective use of the power generated by the first solar cell 4a, the process of step S17 may be omitted.

[0059] As described above, according to this embodiment, during a power outage, unnecessary shutdown of the entire power conversion system 1 can be suppressed while efficiently utilizing the power generated by the first solar cell 4a. In addition, there is no need to improve the internal configuration of the existing first power conversion device 10, and the existing first power conversion device 10 can be used as is. Therefore, the cost of additionally introducing the second power conversion device 20 can be reduced.

[0060] FIG. 4 is a diagram for explaining the power conversion system 1 according to Comparative Example 1. In Comparative Example 1, the second power conversion device 20 is a power conditioner of a power storage system, and the second solar cell 4b is not installed. In addition, the independent output of the second power conversion device 20 and the grid-connected output of the first power conversion device 10 are not linked. In this configuration, the independent output of the first power conversion device 10 becomes unstable during a power outage. In addition, the power storage unit 5 cannot be charged from the first solar cell 4a.

[0061] 5 is a diagram for explaining the power conversion system 1 according to Comparative Example 2. In Comparative Example 2, the second power conversion device 20 is a power conditioner of a power storage system, and a second solar cell 4b is not installed. In this configuration, when the power supplied from the DC / DC converter 21 to the power storage unit 5 exceeds the maximum chargeable power, the control unit 25 changes the output voltage of the inverter 22, thereby making it possible to avoid an overpower generation state.

[0062] On the other hand, in the configuration of the power conversion system 1 shown in FIG. 1, if control is used to change the output voltage of the inverter 22 when the power supplied from the DC / DC converter 21 to the power storage unit 5 exceeds the maximum chargeable power, the output voltage of the inverter 22 will frequently fluctuate due to charging from the second solar cell 4b to the power storage unit 5.

[0063] In contrast, the technology disclosed in the above embodiment compares the inverter input power with the maximum chargeable power, thereby making it possible to prevent the output voltage of the inverter 22 from fluctuating frequently. Note that the technology disclosed in the above embodiment can also be applied to the power conversion system 1 according to the comparative example 2 shown in Fig. 5, and is a highly versatile technology.

[0064] The present disclosure has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each processing step, and that such modifications are also within the scope of the present disclosure.

[0065] In the above embodiment, the first solar cell 4a and the second solar cell 4b are an example of a power generation device that generates power using renewable energy. At least one of the first solar cell 4a and the second solar cell 4b may be replaced with a wind power generator, a micro hydroelectric power generator, or the like. When an AC output generator is used, an AC / DC converter is used instead of a DC / DC converter.

[0066] In the above-described embodiment, a semiconductor switch may be used for at least one of the interconnection relay RY1, the independent output relay RY2, the interconnection relay RY3, the independent output relay RY4, the output switching relay RY5, and the parallel-off relay RY6.

[0067] In the above embodiment, a method of lowering the output voltage of the inverter 22 has been described as a method of controlling the output voltage of the inverter 22 to prevent an overpower generation state by changing the output voltage of the inverter 22. In this regard, the overvoltage relay (OVR) provided in the first power conversion device 10 may be used. The grid interconnection regulations stipulate that the condition for the overvoltage relay (OVR) to detect an overvoltage is that the output voltage of the first power conversion device 10 must remain at or above 115% for one second.

[0068] When the control unit 25 of the second power conversion device 20 controls the output voltage of the inverter 22 to a level at which the overvoltage relay (OVR) of the first power conversion device 10 detects an overvoltage for a detection time limit or more, the first power conversion device 10 stops due to abnormality detection. After increasing the output voltage of the inverter 22, the control unit 25 returns the output voltage of the inverter 22 to its original state when a time equal to or greater than the detection time limit has elapsed.

[0069] In addition, an over-frequency relay (OFR) or an under-frequency relay (UFR) provided in the first power conversion device 10 may be used. The control unit 25 can change the frequency of the output voltage of the inverter 22 to stop the first power conversion device 10.

[0070] If the first power conversion device 10 has a voltage rise suppression function, the control unit 25 can suppress the output power of the first power conversion device 10 by increasing the output voltage of the inverter 22 to a voltage rise suppression value or higher of the first power conversion device 10. In this case, the first power conversion device 10 is less likely to be in an overpower generation state.

[0071] The embodiment may be specified by the following items.

[0072] [Item 1] a first power conversion device (10) capable of converting electric power generated by a power generation device (4a) that generates electric power using renewable energy into AC power of a predetermined voltage and outputting the AC power to a power receiving point of a power grid (2); a second power conversion device (20) including a converter (21) capable of charging and discharging a power storage unit (5), an inverter (22) connected between a DC bus (Bd) to which the converter (21) is connected and the power receiving point, and a control unit (25) that controls the inverter (22), When a power outage occurs in the power grid (2), an independent output path of the second power conversion device (20) and a grid-connected output path of the first power conversion device (10) are connected to each other; The power conversion system (1), characterized in that the control unit (25) controls the output of the first power conversion device (10) to be suppressed or cut off when the power input to the AC side of the inverter (22) exceeds or is predicted to exceed a maximum chargeable power of the storage unit (5). This makes it possible to effectively utilize the power generated by the power generation device (4a) during a power outage while preventing unnecessary shutdown of the entire power conversion system (1). [Item 2] The power conversion system (1) according to item 1, characterized in that, when power input to the AC side of the inverter (22) exceeds or is predicted to exceed the maximum chargeable power of the power storage unit (5), the control unit (25) reduces the output voltage of the inverter (22) based on the maximum chargeable power of the power storage unit (5) and a maximum output current of the first power conversion device (10) so that the output power of the first power conversion device (10) becomes equal to or less than the maximum chargeable power of the power storage unit (5). This makes it possible to limit the power input to the AC side of the inverter (22) to equal to or less than the maximum chargeable power of the power storage unit (5), thereby making it possible to avoid an overpower generation state. [Item 3] The power conversion system (1) described in item 1, characterized in that, when power input to the AC side of the inverter (22) exceeds or is predicted to exceed a maximum chargeable power of the storage unit (5), the control unit (25) changes the output voltage of the inverter (22) to a voltage at which the first power conversion device (10) stops. According to this, by stopping the first power converter (10), it is possible to avoid an excessive power generation state. [Item 4] 4. The power conversion system (1) according to any one of items 1 to 3, wherein the control unit (25) turns off a switch (RY6) inserted in an output path of the first power conversion device (10) when power input to an AC side of the inverter (22) has exceeded or is predicted to exceed a maximum chargeable power of the power storage unit (5). According to this, by releasing the link with the first power converter (10), it is possible to avoid an excessive power generation state. [Item 5] 4. The power conversion system (1) according to any one of items 1 to 3, wherein the control unit (25) turns off a switch (RY6) inserted in an output path of the first power conversion device (10) when a maximum chargeable power of the storage unit (5) becomes less than a first set value. According to this, by releasing the link with the first power converter (10), it is possible to prevent the occurrence of an excessive power generation state. [Item 6] 4. The power conversion system (1) according to any one of items 1 to 3, wherein the control unit (25) turns off a switch (RY6) inserted in an output path of the first power conversion device (10) when a State Of Charge (SOC) of the power storage unit (5) exceeds a second set value. According to this, by releasing the link with the first power converter (10), it is possible to prevent the occurrence of an excessive power generation state. [Item 7] the second power conversion device (20) further includes a converter (26) for another power generation device (4b) that generates power using renewable energy and that is capable of adjusting a voltage of the power generated by the power generation device (4b) and outputting the power to the DC bus (Bd); The power conversion system (1) according to any one of items 1 to 6, wherein the converter (26) for the power generation device (4b) reduces output power when the voltage of the DC bus (Bd) exceeds a target value. This makes it possible to instantly prevent an excessive power generation state caused by the power generated by the other power generation device (4b). [Item 8] A power conversion device (20) connectable to another power conversion device (10) capable of converting electric power generated by a power generation device (4a) that generates electric power using renewable energy into AC power of a predetermined voltage and outputting the AC power to a power receiving point of an electric power system (2), a converter (21) capable of charging and discharging the power storage unit (5); an inverter (22) connected between a DC bus (Bd) to which the converter (21) is connected and the power receiving point; and a control unit (25) that controls the inverter (22), When a power outage occurs in the power system (2), an independent output path of the power conversion device (20) and a grid-connected output path of the other power conversion device (10) are connected to each other; The power conversion device (20) is characterized in that the control unit (25) controls the output of the other power conversion device (10) to be suppressed or cut off when the power input to the AC side of the inverter (22) exceeds or is predicted to exceed the maximum chargeable power of the storage unit (5). This makes it possible to effectively utilize the electric power generated by the power generation device (4a) during a power outage while preventing unnecessary shutdown of the power conversion device (20) and the power conversion device (10) separate from each other. [Explanation of symbols]

[0073] 1 power conversion system, 2 system, 3a general load, 3b specific load, 4a first solar cell, 4b second solar cell, 5 power storage unit, 10 first power conversion device, 11 DC / DC converter, 12 inverter, 13 converter control circuit, 14 inverter control circuit, 15 control unit, 16 AC outlet, 20 second power conversion device, 21 DC / DC converter, 22 inverter, 23 converter control circuit, 24 inverter control circuit, 25 control unit, 26 DC / DC converter, 27 converter control circuit, RY1 grid-connection relay, RY2 independent output relay, RY3 grid-connection relay, RY4 independent output relay, RY5 output switching relay, RY6 parallel-off relay, Bd DC bus.

Claims

1. a first power conversion device that converts electric power generated by a power generation device that generates electric power using renewable energy into AC power of a predetermined voltage and outputs the AC power to a power receiving point of the electric power grid; a second power conversion device including: a converter capable of charging and discharging a power storage unit; an inverter connected between a DC bus to which the converter is connected and the power receiving point; and a control unit that controls the inverter; When a power outage occurs in the power grid, an independent output path of the second power conversion device and an interconnection output path of the first power conversion device are connected to each other, a control unit that, when the power input to the AC side of the inverter exceeds or is predicted to exceed the maximum chargeable power of the power storage unit, reduces the output voltage of the inverter based on the maximum chargeable power of the power storage unit and the maximum output current of the first power conversion device so that the output power of the first power conversion device is equal to or less than the maximum chargeable power of the power storage unit.

2. A first power conversion device capable of converting electric power generated by a power generation device that generates electric power using renewable energy into AC power of a predetermined voltage and outputting the AC power to a receiving point of a power grid; a second power conversion device including: a converter capable of charging and discharging a power storage unit; an inverter connected between a DC bus to which the converter is connected and the power receiving point; and a control unit that controls the inverter; When a power outage occurs in the power grid, an independent output path of the second power conversion device and an interconnection output path of the first power conversion device are connected to each other, a control unit that changes the output voltage of the inverter to a voltage at which the first power conversion device stops when the power input to the AC side of the inverter exceeds or is predicted to exceed the maximum chargeable power of the storage unit.

3. 3. The power conversion system according to claim 1, wherein the control unit turns off a switch inserted in an output path of the first power conversion device when power input to the AC side of the inverter has exceeded or is predicted to exceed a maximum chargeable power of the power storage unit.

4. 3. The power conversion system according to claim 1, wherein the control unit turns off a switch inserted in an output path of the first power conversion device when a maximum chargeable power of the storage unit becomes less than a first set value.

5. 3. The power conversion system according to claim 1, wherein the control unit turns off a switch inserted in an output path of the first power conversion device when a state of charge (SOC) of the power storage unit exceeds a second set value.

6. the second power conversion device further includes a converter for a power generation device that is capable of adjusting a voltage of electric power generated by another power generation device that generates electric power using renewable energy and outputting the electric power to the DC bus; 6. The power conversion system according to claim 1, wherein the converter for the power generation device reduces output power when the voltage of the DC bus exceeds a target value.

7. A power conversion device that can be connected to another power conversion device that can convert power generated by a power generation device that generates power using renewable energy into AC power of a predetermined voltage and output the AC power to a receiving point of a power grid, A converter capable of charging and discharging the power storage unit; an inverter connected between the DC bus to which the converter is connected and the power receiving point; and a control unit that controls the inverter, When the power grid is interrupted, the independent output path of the power conversion device and the interconnection output path of the other power conversion device are connected to each other, a control unit that, when the power input to the AC side of the inverter exceeds or is predicted to exceed the maximum chargeable power of the power storage unit, reduces the output voltage of the inverter based on the maximum chargeable power of the power storage unit and the maximum output current of the other power conversion device so that the output power of the other power conversion device is equal to or lower than the maximum chargeable power of the power storage unit.

8. A power conversion device that can be connected to another power conversion device that can convert electric power generated by a power generation device that generates electric power using renewable energy into AC power of a predetermined voltage and output the AC power to a receiving point of an electric power grid, A converter capable of charging and discharging the power storage unit; an inverter connected between the DC bus to which the converter is connected and the power receiving point; and a control unit that controls the inverter, When the power grid is interrupted, the independent output path of the power conversion device and the interconnection output path of the other power conversion device are connected to each other, a control unit that changes the output voltage of the inverter to a voltage at which the other power conversion device stops when the power input to the AC side of the inverter exceeds or is predicted to exceed the maximum chargeable power of the storage unit.

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