JP7656819B2 - Boost connection circuit, power conversion system - Google Patents

Description

This disclosure relates to a boost connection circuit and power conversion system for integrating the outputs of multiple DC power sources with different output voltages.

As renewable energy sources are gaining attention, the use of solar power generation systems is expanding. In solar power generation systems in which multiple solar cell strings are installed, a junction box is sometimes installed before the power conditioner to integrate the direct current generated by the multiple solar cell strings.

Due to factors such as the shape of the roof, 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 (see, for example, Patent Documents 1 and 2).

JP 2016-10232 A JP 2013-218503 A

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.

There are multiple models of power conditioners with different maximum input voltages, and the model is selected depending on 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 depending on the maximum input voltage of the power conditioner to be connected.

Providing multiple models of boost function junction boxes leads to higher manufacturing costs. In addition, there is a risk that human error will result in connecting the wrong model of boost function junction box to the power conditioner during installation.

This disclosure has been made in light of these circumstances, and its purpose is to provide a highly versatile boost connection circuit and power conversion system that can be connected to a variety of power conversion devices.

In order to solve the above problem, a boost connection circuit according to one 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 a lower open circuit voltage than a first DC power source, an output wiring of the boost circuit, a junction output wiring in which the output wiring of the first DC power source is joined, and 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, 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.

This disclosure makes it possible to realize a highly versatile boost connection circuit that can be connected to a variety of power conversion devices.

1 is a diagram illustrating a configuration example of a solar power generation system according to an embodiment. FIG. 2 is a diagram illustrating an example of a circuit configuration of a boost circuit. FIG. 1 is a diagram showing the power-voltage characteristics (PV curve) of a solar cell module. 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; 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. 6 is a diagram for explaining an example of use of the operation unit shown in FIG. 5 . FIG. 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. FIG. 11 is a diagram showing another example of a waveform transition when the booster automatically determines the maximum input voltage of the inverter. 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. 5 is a flowchart showing a flow of a process for switching a maximum output voltage by a booster according to an embodiment. 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. 10 .

Figure 1 is a diagram showing an example of the configuration of a solar power generation system according to an embodiment. The solar power generation system shown in Figure 1 includes multiple solar 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.

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 with 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.

Each solar cell module includes multiple solar cells connected in series. The solar cells can convert light energy directly into DC power using 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.

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.

The second solar cell string PV2 has a lower open circuit voltage than the first solar cell string PV1 because it has a smaller number of series connections than the first solar cell string PV1. The first solar cell string PV1 is connected to the first input terminal IN1, and the power input to the first input terminal IN1 is supplied to the output wiring W1. The first switch RY1 and the backflow prevention diode D1 are connected to the output wiring W1. The second solar cell string PV2 is connected to the second input terminal IN2, and the 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 the boost circuit 11.

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 the terminal block is connected to the input terminal of the power conversion device 20 by the joined output wiring Wm. Hereinafter, in this specification, the circuit between the first solar cell string PV1 and the terminal block is referred to as the standard circuit system, and the circuit between the second solar cell string PV2 and the terminal block is referred to as the boost circuit system.

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 the 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 it to the power conversion device 20 via the output terminal OUT.

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.

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

The operation unit 13 accepts operations by the installer or user and outputs an operation signal to the control unit 12.

The control unit 12 controls the boost circuit 11 based on the voltage and current input from each sensor. 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).

The control unit 12 can be realized by a combination of hardware 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.

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

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.

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 reverse current flow from the output side of the boost circuit 11.

The switching element S1 can 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 depending on whether the switching element S1 is on or off.

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 (generated power) of the second solar cell string PV2 is maximized.

Figure 3 shows the power-voltage characteristics (P-V 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 that the maximum output power Pmax is maintained.

The control unit 12 detects the output power of the second solar cell string PV2 based on the output voltage of the second solar cell string PV2 detected by the input voltage sensor V1 and the output current of the second solar cell 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 solar cell string PV2 based on the relationship between the output voltage and output power of the second solar cell string PV2.

The control unit 12 searches for the operating point of the maximum output power Pmax, for example, by changing the operating voltage V in a predetermined step width according to the hill-climbing method. For example, to the left 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 to the right 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 control unit 12 captures the operating point of the maximum output power Pmax, it generates a voltage command value 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.

Returning to FIG. 1, the power conversion device 20 is a power conditioner that converts DC power to 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.

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. 2 can be used for the DC/DC converter 21, and this DC/DC converter 21 is connected to the inverter 22.

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.

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 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.

When the input voltage of the DC/DC converter 21 is low, the control unit 23 boosts the input voltage of the inverter 22 to the target value, 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.

In the above-mentioned boost circuit 11, a limiter value is set for the output voltage to protect downstream components. The control unit 12 controls the output voltage of the boost circuit 11 so that it does not 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.

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

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).

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 shut down.

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

However, due to an ordering error by the installer, a solar power generation system could be assembled with an inappropriate combination of inverter and boost junction box 10. In such cases, a product exchange or replacement is required, which places a heavy burden on the user and the installer.

Let us now consider the 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 connection box 10 with a maximum output voltage set to 380V (hereafter referred to as a 380V output booster). 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 will be no need to replace the product. However, this will increase the burden on the installer.

Next, consider a solar power generation system assembled with a 380V input inverter, a solar cell string with an open circuit voltage range of less than 380V, and a boost connection box 10 with a maximum output voltage set to 450V (hereafter referred to as a 450V output booster). In this case, since the 450V output booster allows an output voltage exceeding 38V, a voltage exceeding the maximum input voltage will be input to the 380V input inverter, which may cause the 380V input inverter to issue an error signal and shut down. This may also lead to component failure within the 380V input inverter.

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.

In response to this, this embodiment provides a booster 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.

Figure 4 is a diagram showing an example of the operation unit 13 of the boost connection box 10 having a maximum output voltage switching function. The operation unit 13 shown in Figure 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. Figure 4 shows an example in which the maximum output voltage can be set to 450V and 380V. 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 installation according to the maximum input voltage of the power conditioner.

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.

Figure 5 is a diagram showing another example of the operation unit 13 of the boost junction box 10 that has a maximum output voltage switching function. The operation unit 13 shown in Figure 5 includes a 7-segment display 13a and multiple 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.

Figure 6 is a diagram for explaining an example of how to use the operation unit 13 shown in Figure 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 Figure 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).

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

When the output voltage of the booster exceeds the set maximum output voltage according to the settings switched as described above, the booster stops boosting or reduces the boost ratio to control the output voltage so that it does not exceed the maximum output voltage.

Next, we will explain the automatic maximum output voltage switching function. 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 that uses 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 that uses 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.

Solar cell modules have the characteristic that their voltage rises above the nominal open circuit voltage at low temperatures. In many cases, taking into account the characteristics at low temperatures, 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 at least a certain value lower than the maximum input voltage of the inverter.

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.

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 booster (described in detail 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 booster 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 a decrease in power generation will not occur.

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 inverter.

In addition, if the maximum input voltage of the inverter to be connected can be confirmed in advance or if automatic switching is difficult, the installer can switch to manual settings and set the maximum output voltage of the booster to match the maximum input voltage value of the inverter to be connected.

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 circuit voltage of the connected solar cell string with the output voltage sensor V2. When the detection value of the output voltage sensor V2 is equal to or greater than the judgment threshold, the control unit 12 of the booster determines that a 450V input inverter is connected, and when it is less than the judgment threshold, determines that a 380V input inverter is connected. The judgment 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.

Figure 7 shows an example of the waveform transition when the booster automatically determines the maximum input voltage of the inverter. The example shown in Figure 7 is based on the assumption that a solar cell string with an open circuit voltage Voc of 420 V and a 450 V 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.

When the inverter is stopped, the output voltage Vout of the solar cell string increases with increasing solar radiation intensity. 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. Because 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.

Until the output voltage Vout of the solar cell string exceeds the judgment threshold Vth (380V), 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 380V. On the other hand, when the output voltage Vout of the solar cell string exceeds the judgment threshold Vth (380V), 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 450V.

When the MPPT control of the inverter starts, the output voltage Vout of the solar cell string drops to near the maximum operating output voltage Vpm, below 380 V. However, once the detection value of the output voltage sensor V2 exceeds the judgment 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 judgment threshold Vth (380 V).

Figure 8 shows another example of the waveform transition when the booster automatically determines the maximum input voltage of the inverter. The example shown in Figure 8 also assumes 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.

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 has risen to the open-circuit voltage Voc. In addition, the response performance of inverters has improved in recent years, 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.

In this way, even if the open circuit voltage Voc of a solar cell string is 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 judgment threshold Vth (380V) and remains below the judgment 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.

Below, we will explain the control to prevent such erroneous judgment. 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. Note that 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 obtained 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.

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 the 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.

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). If 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, if 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.

Figure 9 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 for multiple types of solar cell modules. According to the inventors' research, it was found that the constant (β) for many types of solar cell modules is about 1.2. For this reason, in this embodiment, the constant β is set to 1.2. Note that, taking into account the power conversion efficiency and circuit constants of the booster, a value corrected from 1.2 may be set as the constant β.

Figure 10 is a flowchart showing the flow of the process of switching the maximum output voltage by the booster according to the embodiment. In the example shown in the flowchart of Figure 10, it is assumed that the operation unit 13 shown in Figure 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).

When automatic is selected with the first slide switch SW1 (automatic in S11), the control unit 12 executes an automatic process for determining the maximum input voltage of the connected inverter (S20). When the power supply of the booster is turned off (N in S10), the process for switching the maximum output voltage ends.

Figure 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 Figure 10. In the flowchart of Figure 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).

When the inverter 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). When 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). When 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).

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 processing of step S27 is skipped, and the control unit 12 always updates the voltage value to obtain the maximum power.

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

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 greater 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).

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

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 process, and that such modifications are also within the scope of the present disclosure.

In the above embodiment, the boost connection 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 regard, the scope of this disclosure also includes a boost connection box 10 equipped with only an automatic determination function or a boost connection box 10 equipped with only a manual setting function. In the latter case, the first slide switch SW1 shown in FIG. 4 is omitted.

Also, without providing the first slide switch SW1 shown in FIG. 4, only the manual setting function may be provided to the installer or user, and the automatic determination function may operate 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 connection 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 connection 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.

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, multiple 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 installed in each string. The current (power) output from the multiple first solar cell strings PV1 to the junction output wiring Wm is the sum of the output currents (output power) of the multiple first solar cell strings PV1.

Similarly, multiple 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 installed in each string. The current (power) output from the multiple boost circuits 11 to the merged output wiring Wm is the sum of the output currents (output power) of the multiple second solar cell strings PV2.

In the above embodiment, an example has been described in which a first solar cell string PV1 and a second solar cell string PV2 having a lower open-circuit voltage than 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 having a lower open-circuit voltage than 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.

The embodiment may be specified by the following:

[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 the output wiring (Wb) of the boost circuit (11) and the output wiring (W1) of the first DC power source (PV1) are joined;
A control unit (12) that controls the boost circuit (11),
The junction output wiring (Wb) is connected to a power conversion device (20) that converts DC power supplied from the boost connection circuit (10) into AC power,
This boost connection circuit (10) is characterized in that it is possible to switch the setting of the maximum output voltage of the boost circuit (11) so that it does not 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, a voltage sensor (V2) is provided to detect a voltage of the junction output wiring (Wb),
The boost connection circuit (10) described in item 1 is 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) according to the voltage detected by the voltage sensor (V2), and determines a setting value of the 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);
The boost connection circuit (10) described in item 2 is characterized in that, 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 the 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 conversion device (20) for the solar cells (PV1, PV2) with high accuracy.
[Item 4]
2. The boost connection circuit (10) according to claim 1, wherein the control unit (12) determines a set 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, a voltage sensor (V2) is provided to detect a voltage of the junction output wiring (Wb),
5. The boost connection circuit (10) according to claim 4, characterized in that, when a setting 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 setting value of the maximum output voltage of the boost circuit (11) to a voltage value 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 conversion device (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.

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 Joint output wiring, L1 Reactor, C1 Input capacitor, C2 Output capacitor, D2 Diode, S1 Switching element.

Claims (6)

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