Boost connection circuit, power conversion system

Abstract

To provide a versatile boost connection circuit capable of being connected to various power converters.SOLUTION: A boost circuit (11) is capable of boosting a voltage of DC power output from a second DC power supply (PV2) having an open circuit voltage lower than a first DC power supply (PV1). A confluence output wire (Wm) is a wire in which an output wire (Wb) of the boost circuit (11) and an output wire (W1) of the first DC power supply (PV1) are merged, and is connected to a power converter (20) that converts DC power supplied from a boost connection circuit (10) into AC power. The boost connection circuit (10) is capable of switching the setting of the maximum output voltage of the boost circuit (11) so as not to exceed the maximum input voltage of the power converter (20).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a boost connection circuit and a power conversion system for integrating outputs of a plurality of DC power supplies with different output voltages. [Background technology]

[0002] As renewable energy has been gaining attention, the use of photovoltaic power generation systems is expanding. In photovoltaic power generation systems in which multiple solar cell strings are installed, a junction box is sometimes installed in front of the power conditioner to integrate the direct current generated by the multiple solar cell strings.

[0003] Depending on the shape of the roof, etc., it may not be possible to standardize the number of solar cell modules that make up each of the multiple solar cell strings. In such cases, a junction box with a boost function is installed in front of the power conditioner. The junction box with a boost function has the function of boosting the voltage of a solar cell string with a small number of solar cell modules connected in series to the voltage of a standard solar cell string and integrating the direct current of each solar cell string (for example, see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-10232 A [Patent Document 2] JP 2013-218503 A Summary of the Invention [Problem to be solved by the invention]

[0005] Load fluctuations on the power conditioner may cause the output voltage of the boost junction box connected in front of the power conditioner to rise. If the output voltage of the boost junction box exceeds the maximum input voltage of the power conditioner, the power conditioner will issue an input overvoltage error. In addition, components used in the power conditioner may exceed their voltage resistance, causing malfunctions.

[0006] There are multiple models of power conditioners with different maximum input voltages, and the model is selected according to the open circuit voltage of the solar cell string to be connected. There are multiple models of junction boxes with boost function with different maximum output voltages, and the model is selected according to the maximum input voltage of the power conditioner to be connected.

[0007] Providing multiple models of boost-function junction boxes increases manufacturing costs and also poses the risk of connecting the wrong model of boost-function junction box to the power conditioner due to human error during installation.

[0008] The present disclosure has been made in consideration of these circumstances, and has an object to provide a highly versatile boost connection circuit and power conversion system that can be connected to various power conversion devices. [Means for solving the problem]

[0009] In order to solve the above problems, a boost connection circuit according to an embodiment of the present disclosure includes a boost circuit capable of boosting the voltage of DC power output from a second DC power source having an open circuit voltage lower than that of a first DC power source, an output wiring of the boost circuit, a merged output wiring in which the output wiring of the first DC power source is merged, and a control unit for controlling the boost circuit. The merged output wiring is connected to a power conversion device that converts the DC power supplied from the boost connection circuit into AC power, and the boost connection circuit is capable of switching the setting of the maximum output voltage of the boost circuit so as not to exceed the maximum input voltage of the power conversion device. Effect of the Invention

[0010] According to the present disclosure, it is possible to realize a highly versatile boost connection circuit that can be connected to various power conversion devices. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration example of a solar power generation system according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of a circuit configuration of a boost circuit. [Diagram 3] FIG. 1 is a diagram showing the power-voltage characteristics (PV curve) of a solar cell module. [Figure 4] 1 is a diagram showing an example of an operation unit of a boost junction box having a function of switching a maximum output voltage; [Diagram 5] 13 is a diagram showing another example of an operation unit of a boost junction box having a function of switching the maximum output voltage. FIG. [Figure 6] 6 is a diagram for explaining an example of how to use the operation unit shown in FIG. 5. FIG. [Figure 7] FIG. 13 is a diagram showing an example of a waveform transition when a booster automatically determines a maximum input voltage of a power conditioner. [Figure 8] FIG. 13 is a diagram showing another example of a waveform transition when the booster automatically determines the maximum input voltage of the inverter. [Figure 9] FIG. 1 is a graph summarizing the maximum output power Pmax (W), maximum output operating voltage Vpm (V), open circuit voltage Voc (V), maximum output current Imax (A), short circuit current Isc (A), and constant β of multiple types of solar cell modules. [Figure 10] 5 is a flowchart showing a flow of a process for switching a maximum output voltage by a booster according to an embodiment. [Figure 11] 11 is a flowchart showing a subroutine of the process of automatically determining the maximum input voltage of the inverter shown in step S20 of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Fig. 1 is a diagram showing a configuration example of a photovoltaic power generation system according to an embodiment. The photovoltaic power generation system shown in Fig. 1 includes a plurality of photovoltaic cell strings PV1 and PV2 and a power conversion system 1. The power conversion system 1 includes a junction box with a boost function (hereinafter, appropriately referred to as a boost junction box or simply a booster) 10 and a power conversion device 20.

[0013] The first solar cell string PV1 includes a plurality of solar cell modules (solar panels) connected in series. The second solar cell string PV2 includes solar cell modules having a smaller number of series connections than the first solar cell string PV1. For example, the first solar cell string PV1 may include five solar cell modules, and the second solar cell string PV2 may include three solar cell modules.

[0014] Each solar cell module includes a number of solar cells connected in series. The solar cells can convert light energy directly into DC power by utilizing the photovoltaic effect. The solar cells can be heterojunction solar cells, polycrystalline silicon solar cells, single crystal silicon solar cells, thin film silicon solar cells, compound solar cells, etc.

[0015] The boost connection box 10 includes a boost circuit 11, a control unit 12, an operation unit 13, a first input terminal IN1, a second input terminal IN2, a first switch RY1, a second switch RY2, a backflow prevention diode D1, an output terminal OUT, an input voltage sensor V1, an input current sensor A1, an output voltage sensor V2 and an output current sensor A2.

[0016] The second solar cell string PV2 has a smaller number of series connections than the first solar cell string PV1, and therefore has a lower open circuit voltage than the first solar cell string PV1. The first solar cell string PV1 is connected to a first input terminal IN1, and power input to the first input terminal IN1 is supplied to an output wiring W1. A first switch RY1 and a backflow prevention diode D1 are connected to the output wiring W1. The second solar cell string PV2 is connected to a second input terminal IN2, and power input to the second input terminal IN2 is supplied to the output wiring W2 via the second switch RY2, and is further connected to a boost circuit 11.

[0017] The output wiring W1 of the first solar cell string PV1 and the output wiring Wb of the boost circuit 11 are joined at a terminal block (not shown), and a joined output wiring Wm connects the terminal block to an input terminal of the power conversion device 20. Hereinafter, in this specification, the circuit between the first solar cell string PV1 and the terminal block is referred to as a standard circuit system, and the circuit between the second solar cell string PV2 and the terminal block is referred to as a boost circuit system.

[0018] The boost circuit 11 is a DC / DC converter capable of boosting the voltage of the DC power output from the second solar cell string PV2. The boost circuit 11 boosts the output voltage of the second solar cell string PV2 to the voltage of a standard circuit system, thereby integrating the output power of the first solar cell string PV1 and the output power of the second solar cell string PV2 and supplying the integrated power to the power conversion device 20 via the output terminal OUT.

[0019] The input voltage sensor V1 detects the voltage of the output wiring W2 of the second solar cell string PV2 and outputs it to the control unit 12. The input current sensor A1 detects the current flowing in the output wiring W2 of the second solar cell string PV2 and outputs it to the control unit 12. The output voltage sensor V2 detects the voltage of the junction output wiring Wm and outputs it to the control unit 12. The output current sensor A2 detects the current flowing in the junction output wiring Wm and outputs it to the control unit 12.

[0020] The input voltage sensor V1 and the output voltage sensor V2 are each configured to include, for example, a voltage dividing resistor and a differential amplifier. The input current sensor A1 and the output current sensor A2 are each configured to include, for example, a CT sensor or a Hall sensor.

[0021] The operation unit 13 receives operations from an installer or a user, and outputs an operation signal to the control unit 12 .

[0022] The control unit 12 controls the boost circuit 11 based on the voltages and currents input from the respective sensors. The control unit 12 controls the boost operation of the boost circuit 11 to control the voltage detected by the input voltage sensor V1 and the current detected by the input current sensor A1, thereby optimizing the power generation of the second solar cell string PV2 (details will be described later).

[0023] The control unit 12 can be realized by a combination of hardware and software resources, or by hardware resources alone. Examples of hardware resources that can be used include analog elements, microcontrollers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs. Examples of software resources that can be used include programs such as firmware.

[0024] Fig. 2 is a diagram showing an example of a circuit configuration of the boost circuit 11. The boost circuit 11 shown in Fig. 2 is a boost chopper including an input capacitor C1, a reactor L1, a diode D2, a switching element S1, and an output capacitor C2.

[0025] An input voltage sensor V1 and a smoothing input capacitor C1 are connected between the positive and negative wiring of the output wiring W2 of the second solar cell string PV2. A reactor L1 is inserted in the positive wiring of the output wiring W2 of the second solar cell string PV2. An input current sensor A1 is installed on the negative wiring of the output wiring W2 of the second solar cell string PV2. It may also be installed on the positive wiring.

[0026] A switching element S1 and a smoothing output capacitor C2 are connected between the positive and negative wiring of the output wiring Wb of the boost circuit 11. A diode D2 is connected in series to the positive wiring between the switching element S1 and the output capacitor C2 of the boost circuit 11. A reactor L1 is connected to the node between the switching element S1 and the diode D2. The diode D2 prevents a reverse current from flowing from the output side of the boost circuit 11.

[0027] The switching element S1 may be an insulated gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). The reactor L1 stores and releases energy based on the output current from the second solar cell string PV2 according to the on / off state of the switching element S1.

[0028] The control unit 12 can control the boost ratio by controlling the on / off ratio (duty ratio) of the switching element S1. The control unit 12 can perform MPPT (Maximum Power Point Tracking) control of the boost circuit 11 so that the output power (power generation) of the second solar cell string PV2 is maximized.

[0029] 3 is a diagram showing the power-voltage characteristics (PV curve) of a solar cell module. In the voltage range between the open circuit voltage Voc of the solar cell module and the maximum output operating voltage Vpm at which the module operates at the maximum output power Pmax, the output power P increases as the operating voltage V is lowered. In the voltage range below the maximum output operating voltage Vpm, the output power P decreases as the operating voltage V is lowered. In MPPT control, the operating voltage V is controlled so as to maintain the maximum output power Pmax.

[0030] The control unit 12 detects the output power of the second photovoltaic string PV2 based on the output voltage of the second photovoltaic string PV2 detected by the input voltage sensor V1 and the output current of the second photovoltaic string PV2 detected by the input current sensor A1. The control unit 12 generates a voltage command value for maximizing the output power of the second photovoltaic string PV2 based on the relationship between the output voltage and output power of the second photovoltaic string PV2.

[0031] For example, the control unit 12 searches for an operating point of the maximum output power Pmax by changing the operating voltage V by a predetermined step width according to a hill-climbing method. For example, on the left side of the operating point of the maximum output power Pmax in Fig. 3, a voltage command value is generated for shifting the current operating voltage V to the right, and on the right side of the operating point of the maximum output power Pmax, a voltage command value is generated for shifting the current operating voltage V to the left. When the operating point of the maximum output power Pmax is captured, the control unit 12 generates a voltage command value so as to maintain the operating point of the maximum output power Pmax. The switching element S1 of the boost circuit 11 performs switching operation in response to a drive signal based on the generated voltage command value.

[0032] Returning to Fig. 1, the power conversion device 20 is a power conditioner that converts DC power into AC power in a solar power generation system. The power conversion device 20 includes a DC / DC converter 21, an inverter 22, and a control unit 23.

[0033] The DC / DC converter 21 is a converter capable of adjusting the voltage of the DC power integrated by the boost junction box 10. For example, a boost chopper as shown in FIG.

[0034] The inverter 22 can convert the DC power supplied from the DC / DC converter 21 into AC power and output the converted AC power to the commercial power system 2 via a distribution board (not shown). Note that a load (not shown) within the home is connected to the distribution board, and the inverter 22 can also supply the converted AC power to the load via the distribution board.

[0035] The control unit 23 performs overall control of the entire power conversion device 20. The control unit 23 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.

[0036] The control unit 23 boosts the input voltage of the DC / DC converter 21 to the target value when the input voltage of the DC / DC converter 21 is low, and controls the DC / DC converter 21 by MPPT so that the integrated input power of the first solar cell string PV1 and the second solar cell string PV2 is maximized. The control unit 23 controls the inverter 22 so that the voltage between the DC / DC converter 21 and the inverter 22 maintains the target value. Specifically, the control unit 23 generates a current command value for matching the input voltage of the inverter 22 to the target value. When the input voltage of the inverter 22 is higher than the target value, the control unit 23 generates a current command value for increasing the output power of the inverter 22, and when the input voltage of the inverter 22 is lower than the target value, the control unit 23 generates a current command value for decreasing the output power of the inverter 22. The inverter 22 performs switching operation in response to a drive signal based on the generated current command value.

[0037] In the above-mentioned boost circuit 11, a limiter value is set for the output voltage in order to protect the components in the subsequent stages. The control unit 12 controls the output voltage of the boost circuit 11 so as not to exceed the limiter value. Specifically, when the output voltage of the boost circuit 11 reaches the limiter value, the control unit 12 reduces the duty ratio of the switching element S1 to reduce the output voltage, or turns off the switching element S1 to stop the operation of the boost circuit 11.

[0038] The power conversion device 20 (hereinafter referred to as a power conditioner) controls the input power to be reduced when the output power is reduced due to output control (also referred to as output suppression) or load fluctuation. This control may cause the output voltage of the boost junction box 10 to increase.

[0039] As mentioned above, there are multiple models of inverters with different maximum input voltages. For example, there are models with a maximum input voltage of 450V (hereafter referred to as 450V input inverters) and models with a maximum input voltage of 380V (hereafter referred to as 380V input inverters).

[0040] For example, if a 380V input inverter is connected to a boost junction box 10 capable of boosting voltage up to 450V, when the output voltage of the boost circuit 11 exceeds 380V, it will exceed the maximum input voltage of the 380V input inverter. In this case, an input overvoltage error will occur and the 380V input inverter will stop.

[0041] In response to this, manufacturers prepare multiple boost junction boxes 10 according to the specifications of the inverters. Installers select the boost junction box 10 that matches the specifications of the inverter they are using and install the solar power generation system.

[0042] However, due to an ordering mistake by the installer, a solar power generation system may be assembled with an inappropriate combination of the inverter and the boost junction box 10. In such cases, a product exchange or replacement is required, which is a significant burden for the user and the installer.

[0043] Here, consider a case where a solar power generation system is assembled with a 450V input power conditioner, a solar cell string with an open-circuit voltage range of 380 to 450V, and a boost junction box 10 (hereinafter referred to as a 380V output booster) with a maximum output voltage set to 380V. In this case, if the solar cell module allocation is reviewed and the string configuration is changed so that the open-circuit voltage is less than 380V, there is no need to replace the product. However, this will increase the burden on the installer.

[0044] Next, consider a case where a solar power generation system is assembled with a 380V input inverter, a solar cell string whose open circuit voltage range is less than 380V, and a boost junction box 10 (hereinafter referred to as a 450V output booster) whose maximum output voltage is set to 450V. In this case, since the 450V output booster allows an output voltage exceeding 38V, a voltage exceeding the maximum input voltage is input to the 380V input inverter, which may cause the 380V input inverter to generate an error signal and shut down. This may also lead to component failure within the 380V input inverter.

[0045] For manufacturers that provide step-up units, offering a lineup of multiple types of products based on the specifications of each inverter places a burden on them in terms of production, service, and management.

[0046] In contrast, in this embodiment, a booster is provided that is equipped with a function that allows the booster itself to switch the maximum output voltage. This relieves the installer from the need to be concerned about the combination of the inverter and the booster, reducing the burden on the installer. On the manufacturer's side, it is no longer necessary to have a lineup of multiple types of products according to the inverter specifications, reducing the burden on production, service, and management.

[0047] FIG. 4 is a diagram showing an example of the operation unit 13 of the boost junction box 10 having a function of switching the maximum output voltage. The operation unit 13 shown in FIG. 4 includes a first slide switch SW1 and a second slide switch SW2. The first slide switch SW1 is a switch for switching between an automatic determination mode and a manual setting mode. The second slide switch SW2 is a switch for switching the maximum output voltage of the booster. FIG. 4 shows an example in which 450V and 380V can be set as the maximum output voltage. Selection by the second slide switch SW2 is effective when the manual setting mode is selected by the first slide switch SW1. The installer can set the maximum output voltage of the booster during construction according to the maximum input voltage of the power conditioner.

[0048] When there are two or more types of maximum input voltages for the inverter, the number of slide switches or the number of selection points for the slide switches can be increased accordingly to increase the number of selectable types.

[0049] Fig. 5 is a diagram showing another example of the operation unit 13 of the boost junction box 10 having a function for switching the maximum output voltage. The operation unit 13 shown in Fig. 5 includes a 7-segment display 13a and a plurality of push buttons B1 to B4. The first push button B1 is a "MODE" button, the second push button B2 is an "UP" button, the third push button B3 is a "DOWN" button, and the fourth push button B4 is an "ENTER" button.

[0050] FIG. 6 is a diagram for explaining an example of use of the operation unit 13 shown in FIG. 5. The installer presses the "MODE" button several times to select the maximum output voltage setting mode. The selection is confirmed by pressing the "ENTER" button. Next, the setting value is selected. The desired setting value is selected by pressing the "UP" button and the "DOWN" button. In the example shown in FIG. 6, "450" ​​is selected from three patterns: "AUto" (= automatic determination), "380" (maximum output voltage setting of 380V), and "450" ​​(maximum output voltage setting of 450V).

[0051] The maximum output voltage may be set in 10V increments within the set range. After selecting a desired voltage value, the "ENTER" button is pressed to confirm the maximum output voltage setting. In this manner, in the example shown in Fig. 5 and Fig. 6, the 7-segment display 13a and the multiple push buttons B1 to B4 are used to switch the maximum output voltage setting.

[0052] According to the settings switched as described above, when the output voltage of the booster exceeds the set maximum output voltage, the booster stops boosting operation or reduces the boost ratio so that the maximum output voltage is not exceeded.

[0053] Next, the automatic maximum output voltage switching function will be explained. The inverters used in photovoltaic power generation systems have input voltage limitations, and the number of solar cell modules in series is determined so that the open-circuit voltage of the solar cell string does not exceed the inverter's maximum input voltage. For example, in a system using a 380V input inverter, the number of solar cell modules in series is determined so that the open-circuit voltage of the solar cell string is less than 380V. Also, in a system using a 450V input inverter, the number of solar cell modules in series is determined so that the open-circuit voltage of the solar cell string is less than 450V.

[0054] Solar cell modules have a characteristic that their voltage rises above the nominal open circuit voltage at low temperatures. In many cases, the number of solar cell modules in series is determined so that the open circuit voltage of the solar cell string is not close to the maximum input voltage of the inverter, but is a voltage that is lower than the maximum input voltage of the inverter by a certain value or more, taking into account the characteristics at low temperatures.

[0055] Therefore, if the open circuit voltage of the solar cell string used in a solar power generation system exceeds 380V, it can be determined that the solar power generation system uses a 450V input inverter rather than a 380V input inverter. Also, if the open circuit voltage of the solar cell string is 380V or less, it can be determined that the solar power generation system uses a 380V input inverter.

[0056] Even when a 450V input inverter is used, there are photovoltaic power generation systems in which the open circuit voltage of the solar cell string is 380V or less. If the automatic determination function of the boost inverter (details to be described later) determines that a 380V input inverter is connected instead of a 450V input inverter and limits the maximum output voltage to 380V, the output voltage of the boost inverter will not exceed the maximum input voltage of the inverter. Therefore, problems such as the error shutdown mentioned above will not occur. In addition, because the system operates below the open circuit voltage, problems such as reduced power generation will not occur.

[0057] In this way, if the open circuit voltage of the solar cell string connected to the booster is known, the booster can automatically determine and set the maximum output voltage according to the maximum input voltage of the connected power conditioner.

[0058] In addition, if the maximum input voltage of the inverter to be connected can be confirmed in advance or if it is difficult to switch using automatic determination, the installer can switch to manual settings and set the maximum output voltage of the boost converter to a value that matches the maximum input voltage value of the inverter to be connected.

[0059] Next, a method for automatically determining the maximum input voltage of the inverter using the booster will be specifically described. When the inverter is stopped and the boost operation of the boost circuit 11 of the booster is stopped, the control unit 12 of the booster can detect the open voltage of the connected solar cell string with the output voltage sensor V2. When the detected value of the output voltage sensor V2 is equal to or greater than the determination threshold, the control unit 12 of the booster determines that a 450V input inverter is connected, and when it is less than the determination threshold, determines that a 380V input inverter is connected. The determination threshold is a threshold for determining whether a 380V input inverter or a 450V input inverter is connected to the output side of the booster, and is set to 380V in this example.

[0060] Fig. 7 is a diagram showing an example of waveform transition when the booster automatically determines the maximum input voltage of the inverter. The example shown in Fig. 7 is based on the assumption that a solar cell string with an open circuit voltage Voc of 420V and a 450V input inverter are used, and shows an example in which the booster determines the maximum input voltage of the inverter before the inverter starts operating.

[0061] When the inverter is stopped, the output voltage Vout of the solar cell string increases with an increase in the intensity of solar radiation. The output voltage Vout of the solar cell string is the output voltage of the first solar cell string PV1 in the standard circuit system. Since the boost circuit 11 has not yet started operating, the output voltage of the second solar cell string PV2 in the boost circuit system is lower than the output voltage of the first solar cell string PV1 in the standard circuit system.

[0062] Until the output voltage Vout of the solar cell string exceeds the judgment threshold Vth (380 V), the control unit 12 determines that a 380V input power conditioner is connected to the output side of the booster, and sets the maximum output voltage of the boost circuit 11 to 380 V. On the other hand, when the output voltage Vout of the solar cell string exceeds the judgment threshold Vth (380 V), the control unit 12 determines that a 450V input power conditioner is connected to the output side of the booster, and sets the maximum output voltage of the boost circuit 11 to 450 V.

[0063] When the MPPT control of the power conditioner starts, the output voltage Vout of the solar cell string drops to near the maximum operating output voltage Vpm and falls below 380 V. However, once the detection value of the output voltage sensor V2 exceeds the determination threshold Vth (380 V), the control unit 12 maintains the maximum output voltage of the boost circuit 11 at 450 V even if it subsequently falls below the determination threshold Vth (380 V).

[0064] Figure 8 is a diagram showing another example of waveform transition when the booster automatically determines the maximum input voltage of the inverter. The example shown in Figure 8 is also based on the premise that a solar cell string with an open circuit voltage Voc of 420 V and a 450 V input inverter are used. The example shown in Figure 8 shows a case where the inverter starts operating before the output voltage Vout of the solar cell string reaches the open circuit voltage Voc.

[0065] Immediately after sunrise, the power generated by the solar cell string is low, and the inverter may start operating before the output voltage Vout of the solar cell string rises to the open circuit voltage Voc. In addition, the response performance of recent inverters has improved, and MPPT control may start before the output voltage Vout of the solar cell string rises to the open circuit voltage Voc, and the output voltage may be controlled to near the maximum operating output voltage Vpm.

[0066] In this way, even in a solar cell string with an open circuit voltage Voc of 420V, the output voltage Vout of the solar cell string may only rise to the maximum operating output voltage Vpm (near 350V). In the example shown in Fig. 8, the inverter starts operating when the output voltage Vout of the solar cell string is less than 380V, and the output voltage Vout of the solar cell string never exceeds the determination threshold Vth (380V) and remains below the determination threshold Vth (380V). In this case, the control unit 12 erroneously determines that a 380V input inverter is connected to the output side of the booster, even though a 450V input inverter is actually connected.

[0067] Control for preventing such erroneous judgment will be described below. During the operation of the power conditioner, the control unit 12 detects the output power of the booster by multiplying the output voltage detected by the output voltage sensor V2 and the output current detected by the output current sensor A2. The output power of the booster may be substituted by the input power obtained by multiplying the input voltage detected by the input voltage sensor (not shown) of the standard circuit system by the input current detected by the input current sensor (not shown) of the standard circuit system, and the input power of the boost circuit system by multiplying the input voltage detected by the input voltage sensor V1 of the boost circuit system by the input current detected by the input current sensor A1.

[0068] The control unit 12 performs MPPT control of the boost circuit 11 so that the output power of the booster is maximized. The control unit 12 multiplies the maximum output operating voltage when the output power of the booster is at the maximum output point by a predetermined constant β to calculate an estimated open circuit voltage Voc' of the solar cell string. The constant β is defined as the ratio of the open circuit voltage Voc to the maximum output operating voltage Vpm of the solar cell string.

[0069] During operation of the inverter, the control unit 12 compares the estimated open circuit voltage Voc' of the solar cell string with the judgment threshold Vth (380V). When the estimated open circuit voltage Voc' of the solar cell string is equal to or greater than the judgment threshold Vth (380V), the control unit 12 determines that a 450V input inverter is connected to the output side of the booster, and sets the maximum output voltage of the boost circuit 11 to 450V. On the other hand, when the estimated open circuit voltage Voc' of the solar cell string is less than the judgment threshold Vth (380V), the control unit 12 determines that a 380V input inverter is connected to the output side of the booster, and sets the maximum output voltage of the boost circuit 11 to 380V.

[0070] 9 is a graph showing the maximum output power Pmax (W), maximum output operating voltage Vpm (V), open circuit voltage Voc (V), maximum output current Imax (A), short circuit current Isc (A), and constant β of multiple types of solar cell modules. According to a study by the present inventors, it was found that the constant (β) of many types of solar cell modules is about 1.2. For the above reasons, in this embodiment, the constant β is set to 1.2. Note that, in consideration of the power conversion efficiency and circuit constants of the booster, a value corrected from 1.2 may be set to the constant β.

[0071] FIG. 10 is a flowchart showing a flow of a process of switching the maximum output voltage by the booster according to an embodiment. In the example shown in the flowchart of FIG. 10, it is assumed that the operation unit 13 shown in FIG. 4 is used. When the power supply of the booster is on (Y in S10), if the first slide switch SW1 selects manual and the second slide switch SW2 selects 450V (manual in S11, 450V in S12), the control unit 12 sets the maximum output voltage Vlim of the boost circuit 11 to 450V (S13). When the first slide switch SW1 selects manual and the second slide switch SW2 selects 380V (manual in S11, 380V in S12), the control unit 12 sets the maximum output voltage Vlim of the boost circuit 11 to 380V (S14).

[0072] When the first slide switch SW1 is set to automatic (S11: automatic), the control unit 12 executes an automatic process for determining the maximum input voltage of the connected inverter (S20). When the booster is turned off (S10: N), the process for switching the maximum output voltage ends.

[0073] Fig. 11 is a flowchart showing a subroutine of the automatic determination process of the maximum input voltage of the inverter shown in step S20 of Fig. 10. In the flowchart of Fig. 11, parameter Va is a parameter for holding the maximum value of the output voltage Vout of the solar cell string when the inverter is stopped. Parameter Vb is a parameter for holding the maximum value of the output voltage Vout of the solar cell string when the inverter is operating. Parameter Vc is a parameter for holding the target voltage to be compared with the determination threshold value Vth (380V).

[0074] If the power conditioner is stopped (Y in S21) and the boost circuit 11 is also stopped (Y in S22), the control unit 12 compares the value held in the parameter Va with the output voltage Vout detected by the output voltage sensor V2 (S23). If the output voltage Vout is greater than the value held in the parameter Va (Y in S23), the control unit 12 updates the value held in the parameter Va to the value of the detected output voltage Vout (S24). If the output voltage Vout is not greater than the value held in the parameter Va (N in S23), the process of step S24 is skipped. The control unit 12 assigns the value held in the parameter Va to the parameter Vc (S25).

[0075] When the power conditioner starts operating (N in S21), the boost circuit 11 also starts operating. The control unit 12 detects the output power of the booster by multiplying the output voltage detected by the output voltage sensor V2 by the output current detected by the output current sensor A2. If the output power of the booster is increasing (Y in S26), the control unit 12 updates the value held in the parameter Vb to the value of the output operating voltage Vout corresponding to the detected output power (S27). If the output power of the booster is not increasing (N in S26), the process of step S27 is skipped, and the control unit 12 always updates the voltage value to obtain the maximum power.

[0076] The control unit 12 compares the value held in the parameter Va with the value held in the parameter Vb (S28). If the value held in the parameter Vb is equal to or less than the value held in the parameter Va (N in S28), the control unit 12 assigns the value held in the parameter Va to the parameter Vc (S25). If the value held in the parameter Vb becomes greater than the value held in the parameter Va as the solar radiation increases (Y in S28), the control unit 12 multiplies the value held in the parameter Vb by a constant β and assigns the value obtained as an estimate of the open circuit voltage Voc to the parameter Vc (S29).

[0077] The control unit 12 compares the value held in the parameter Vc with the judgment threshold Vth (380V) (S210). If the value held in the parameter Vc is smaller than the judgment threshold Vth (380V) (Y in S210), the control unit 12 sets the maximum output voltage Vlim of the boost circuit 11 to 380V (S211). If the value held in the parameter Vc is equal to or larger than the judgment threshold Vth (380V) (N in S210), the control unit 12 sets the maximum output voltage Vlim of the boost circuit 11 to 450V (S212).

[0078] As described above, according to this embodiment, by providing the boost junction box 10 with a function that can switch the maximum output voltage, it is possible to support multiple types of power conditioners with different maximum input voltages with one type of boost junction box 10. By realizing such a versatile boost junction box 10, the burden on manufacturers and installers can be reduced.

[0079] 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.

[0080] In the above embodiment, the boost junction box 10 is described as being equipped with an automatic determination mode and a manual setting mode as a maximum output voltage switching function. In this respect, the boost junction box 10 equipped with only the automatic determination function or the manual setting function is also included in the scope of the present disclosure. In the latter case, the first slide switch SW1 shown in FIG. 4 is omitted.

[0081] Also, the first slide switch SW1 shown in FIG. 4 may not be provided, and only the manual setting function may be provided to the installer or user, with the automatic determination function operating in the background. The installer may operate the second slide switch SW2 by mistake. For example, even if a 380V input power conditioner is connected to the boost junction box 10, the installer may set the second slide switch SW2 to the 450V side due to misrecognition or misoperation. In this case, when the automatic determination function of the boost junction box 10 determines that a 380V input power conditioner is connected, the control unit 12 changes the maximum output voltage Vlim of the boost circuit 11 from 450V to 380V.

[0082] In the above embodiment, in order to simplify the explanation, an example has been described in which one first solar cell string PV1 is connected to the standard circuit system, and one second solar cell string PV2 is connected to the boost circuit system. In this regard, a plurality of first solar cell strings PV1 may be connected in parallel to the standard circuit system. In this case, a first switch RY1 and a backflow prevention diode D1 are provided in each string. The current (power) output from the plurality of first solar cell strings PV1 to the junction output wiring Wm is the sum of the output currents (output power) of the plurality of first solar cell strings PV1.

[0083] Similarly, a plurality of second solar cell strings PV2 may be connected in parallel to the boost circuit system. In this case, a second switch RY2 and a boost circuit 11 are provided for each string. The current (power) output from the plurality of boost circuits 11 to the junction output wiring Wm is the sum of the output currents (output power) of the plurality of second solar cell strings PV2.

[0084] In the above embodiment, an example has been described in which the first solar cell string PV1 and the second solar cell string PV2, which has an open circuit voltage lower than that of the first solar cell string PV1, are connected to the boost junction box 10. In this regard, a DC power source other than a plurality of solar cells having different open circuit voltages can also be connected to the boost junction box 10. For example, a first storage battery pack and a second storage battery pack, which has an open circuit voltage lower than that of the first storage battery pack, may be connected to the boost junction box 10. The second storage battery pack is a storage battery pack in which the number of cells or modules connected in series is smaller than that of the first storage battery pack.

[0085] The embodiment may be specified by the following items.

[0086] [Item 1] a boost circuit (11) capable of boosting a voltage of DC power output from a second DC power source (PV2) having an open circuit voltage lower than that of a first DC power source (PV1); a joined output wiring (Wb) in which an output wiring (Wb) of the boost circuit (11) and an output wiring (W1) of the first DC power source (PV1) are joined together; a control unit (12) that controls the boost circuit (11), The junction output wiring (Wb) is connected to a power converter (20) that converts DC power supplied from the boost connection circuit (10) into AC power, The boost connection circuit (10) is characterized in that the setting of the maximum output voltage of the boost circuit (11) can be switched so as not to exceed the maximum input voltage of the power conversion device (20). This makes it possible to realize a highly versatile boost connection circuit (10), thereby reducing the burden on manufacturers and installers. [Item 2] Further comprising a voltage sensor (V2) for detecting a voltage of the junction output wiring (Wb), The boost connection circuit (10) according to item 1, characterized in that, while the power conversion device (20) and the boost circuit (11) are stopped, the control unit (12) estimates a maximum input voltage of the power conversion device (20) in accordance with the voltage detected by the voltage sensor (V2), and determines a set value of a maximum output voltage of the boost circuit (11) to a voltage value equal to or lower than the estimated maximum input voltage. According to this, by incorporating an automatic judgment mode, the burden on the installer can be reduced and human error can be reduced. [Item 3] the first DC power source (PV1) and the second DC power source (PV2) are solar cells (PV1, PV2); 3. The boost connection circuit (10) according to item 2, wherein, when the power conversion device (20) is in operation and the boost circuit (11) is stopped, the control unit (12) estimates a maximum input voltage of the power conversion device (20) in accordance with a voltage obtained by multiplying a voltage detected by the voltage sensor (V2) by a ratio of an open circuit voltage to a maximum output point voltage of the solar cells (PV1, PV2). This makes it possible to estimate the maximum input voltage of the power converter (20) for the solar cells (PV1, PV2) with high accuracy. [Item 4] 2. The boost connection circuit (10) according to item 1, wherein the control unit (12) determines a setting value of a maximum output voltage of the boost circuit (11) based on a user operation. This allows the maximum output voltage switching function to be easily implemented. [Item 5] Further comprising a voltage sensor (V2) for detecting a voltage of the junction output wiring (Wb), 5. The boost connection circuit (10) according to item 4, characterized in that, when a set value of a maximum output voltage of the boost circuit (11) determined based on the user operation exceeds a maximum input voltage of the power conversion device (20) estimated from a voltage detected by the voltage sensor (V2), the control unit (12) switches the set value of the maximum output voltage of the boost circuit (11) to a voltage value that is equal to or lower than the maximum input voltage. This allows the automatic determination function to compensate for human errors that may occur due to manual settings. [Item 6] A boost connection circuit (10) according to any one of items 1 to 5; a power converter (20) that converts DC power supplied from the boost connection circuit (10) into AC power; A power conversion system (1) comprising: This makes it possible to realize a highly versatile boost connection circuit (10), thereby reducing the burden on manufacturers and installers. [Explanation of symbols]

[0087] 1 power conversion system, 2 commercial power system, 10 boost junction box, 11 boost circuit, 12 control unit, 20 power conversion device, 21 DC / DC converter, 22 inverter, 23 control unit, PV1 first solar cell string, PV2 second solar cell string, RY1 first switch, RY2 second switch, D1 reverse current prevention diode, V1 input voltage sensor, V2 output voltage sensor, A1 input current sensor, A2 output current sensor, A3 standard circuit output current sensor, T1 temperature sensor, W1, W2, Wb output wiring, Wm combined output wiring, L1 reactor, C1 input capacitor, C2 output capacitor, D2 diode, S1 switching element.

Claims

1. a boost circuit capable of boosting a voltage of DC power output from a second DC power source having an open circuit voltage lower than that of the first DC power source; a joined output wiring in which an output wiring of the boost circuit and an output wiring of the first DC power source are joined together; A control unit that controls the boost circuit, the junction output wiring is connected to a power conversion device that converts the DC power supplied from the boost connection circuit into AC power; This boost connection circuit is characterized in that it is possible to switch the setting of a maximum output voltage that serves as an upper limit voltage of the boost circuit so as not to exceed a maximum input voltage of the power conversion device.

2. A voltage sensor for detecting a voltage of the junction output wiring is further provided.

2. The boost connection circuit according to claim 1, wherein the control unit estimates a maximum input voltage of the power conversion device according to the voltage detected by the voltage sensor while the power conversion device and the boost circuit are stopped, and determines a setting value of the maximum output voltage of the boost circuit to a voltage value equal to or lower than the estimated maximum input voltage.

3. the first DC power source and the second DC power source are solar cells; 3. The boost connection circuit according to claim 2, wherein the control unit estimates a maximum input voltage of the power conversion device according to a voltage obtained by multiplying a voltage detected by the voltage sensor by a ratio of an open circuit voltage to a maximum output point voltage of the solar cell while the power conversion device is in operation and the boost circuit is stopped.

4. 2. The boost connection circuit according to claim 1, wherein the control unit determines a set value of the maximum output voltage of the boost circuit based on a user operation.

5. A voltage sensor for detecting a voltage of the junction output wiring is further provided.

5. The boost connection circuit according to claim 4, wherein when a setting value of the maximum output voltage of the boost circuit determined based on the user operation exceeds a maximum input voltage of the power conversion device estimated from a voltage detected by the voltage sensor, the control unit switches the setting value of the maximum output voltage of the boost circuit to a voltage value equal to or lower than the maximum input voltage.

6. A boost connection circuit according to any one of claims 1 to 5; a power conversion device that converts DC power supplied from the boost connection circuit into AC power; A power conversion system comprising:

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