JP2023018368A - Boost connection circuit and power conversion system - Google Patents

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 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.

As attention is focused on renewable energy, the spread of photovoltaic power generation systems is expanding. 2. Description of the Related Art In a photovoltaic power generation system in which a plurality of solar cell strings are installed, a junction box may be installed upstream of a power conditioner for integrating direct currents generated by the plurality of solar cell strings.

Depending on the shape of the roof or the like, it may not be possible to unify the number of solar cell modules that constitute each of the plurality of solar cell strings. In that case, a junction box with boost function is installed in the front stage of the power conditioner. Junction boxes with boosting functions have the function of boosting the voltage of a solar cell string with a small number of series-connected solar cell modules to the voltage of a standard solar cell string and integrating the direct current of each solar cell string (for example, patented References 1 and 2).

JP 2016-10232 A JP 2013-218503 A

Due to the load fluctuation of the power conditioner, the output voltage of the junction box with boost function connected to the front stage of the power conditioner may rise. If the output voltage of the junction box with boost function exceeds the maximum input voltage of the inverter, the inverter will report an input overvoltage error. In addition, the parts used in the power conditioner may exceed the withstand voltage, resulting in malfunction of the parts.

Power conditioners have a plurality of models with different maximum input voltages, and the model is selected according to the open-circuit voltage of the connected solar cell string. Multiple models with different maximum output voltages were prepared for the junction box with boost function, and the model was selected according to the maximum input voltage of the connected power conditioner.

Preparing a plurality of models as a junction box with boosting function leads to an increase in manufacturing cost. In addition, there is a risk of connecting the wrong type of connection box with boost function to the power conditioner during installation due to human error.

The present disclosure has been made in view of such circumstances, and an object thereof is to provide a highly versatile booster connection circuit and power conversion system that can be connected to various power converters.

In order to solve the above problems, a booster connection circuit according to one aspect of the present disclosure includes a booster circuit capable of boosting the voltage of DC power output from a second DC power supply having an open-circuit voltage lower than that of a first DC power supply; The output wiring of the booster circuit and the combined output wiring in which the output wirings of the first DC power supply join together, and a control section for controlling the booster circuit. The combined output wiring is connected to a power converter that converts DC power supplied from the booster connection circuit into AC power, and the booster connection circuit is configured so as not to exceed the maximum input voltage of the power converter. It is possible to switch the setting of the maximum output voltage of the booster circuit.

According to the present disclosure, it is possible to realize a highly versatile booster connection circuit that can be connected to various power converters.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structural example of the photovoltaic power generation system which concerns on embodiment. It is a figure which shows the circuit structural example of a booster circuit. FIG. 4 is a diagram showing power-voltage characteristics (PV curve) of a solar cell module; FIG. 4 is a diagram showing an example of an operating portion of a boost junction box having a maximum output voltage switching function; FIG. 10 is a diagram showing another example of the operating portion of the boost junction box having a maximum output voltage switching function; 6A and 6B are diagrams for explaining a usage example of the operation unit shown in FIG. 5; FIG. FIG. 4 is a diagram showing an example of waveform transition when the booster automatically determines the maximum input voltage of the power conditioner; FIG. 10 is a diagram showing another example of waveform transition when the booster automatically determines the maximum input voltage of the power conditioner; 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), constant β of multiple types of solar cell modules FIG. 10 is a diagram showing a summarized graph; 7 is a flow chart showing the flow of switching processing of the maximum output voltage by the booster according to the embodiment. FIG. 11 is a flow chart showing a subroutine of automatic determination processing of the maximum input voltage of the power conditioner shown in step S20 of FIG. 10; FIG.

FIG. 1 is a diagram illustrating 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 strings PV1 and PV2 and a power conversion system 1 . The power conversion system 1 includes a connection box with a boost function (hereinafter referred to as a boost connection 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 having a smaller number of series connections than the first solar cell string PV1. For example, the first photovoltaic string PV1 may include five photovoltaic modules, and the second photovoltaic string PV2 may include three photovoltaic modules.

Each solar module includes multiple solar cells connected in series. Solar cells utilize the photovoltaic effect and can convert light energy directly into direct current power. A heterojunction solar cell, a polycrystalline silicon solar cell, a single crystal silicon solar cell, a thin film silicon solar cell, a compound solar cell, or the like can be used as the solar cell.

The boost junction 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, and 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.

Since the second solar cell string PV2 has a smaller number of series connections than the first solar cell string PV1, it has a lower open-circuit voltage than the first solar cell string PV1. The first solar cell string PV1 is connected to the first input terminal IN1, and power input to the first input terminal IN1 is supplied to the 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 the second input terminal IN2, and the power input to the second input terminal IN2 is supplied to the output wiring W2 through the second switch RY2 and further connected to the booster circuit 11. be.

The output wiring W1 of the first solar cell string PV1 and the output wiring Wb of the booster circuit 11 are merged at a terminal block (not shown), and the terminal block and the input terminal of the power conversion device 20 are connected by a merged output wiring Wm. be done. Hereinafter, in this specification, the circuit between the first solar cell string PV1 and the terminal block is called the standard circuit system, and the circuit between the second solar cell string PV2 and the terminal block is called the boost circuit system.

The booster 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 booster circuit 11 boosts the output voltage of the second photovoltaic string PV2 to the voltage of the standard circuit system, thereby integrating the output power of the first photovoltaic string PV1 and the output power of the second photovoltaic string PV2. It can be supplied to the power converter 20 via the output terminal OUT.

The input voltage sensor V<b>1 detects the voltage of the output wiring W<b>2 of the second solar cell string PV<b>2 and outputs it to the controller 12 . The input current sensor A<b>1 detects current flowing through the output wiring W<b>2 of the second solar cell string PV<b>2 and outputs the detected current to the control unit 12 . The output voltage sensor V<b>2 detects the voltage of the merged output wiring Wm and outputs it to the controller 12 . The output current sensor A<b>2 detects the current flowing through the merged output wiring Wm and outputs the detected current to the control unit 12 .

The input voltage sensor V1 and the output voltage sensor V2 include, for example, voltage dividing resistors and differential amplifiers. The input current sensor A1 and the output current sensor A2 include, for example, CT sensors and Hall sensors.

The operation unit 13 receives an operation by a builder or a user and outputs an operation signal to the control unit 12 .

The control unit 12 controls the booster circuit 11 based on the voltage and current input from each sensor. The control unit 12 controls the boosting operation of the booster circuit 11 to control the voltage detected by the input voltage sensor V1 and the current detected by the input current sensor A1, thereby controlling the generated power of the second solar cell string PV2. can be optimized (details below).

The control unit 12 can be realized by cooperation of hardware resources and software resources, or only by hardware resources. Analog devices, 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.

FIG. 2 is a diagram showing a circuit configuration example of the booster circuit 11. As shown in FIG. A booster circuit 11 shown in FIG. 2 is a booster chopper including 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 wiring and the negative wiring of the output wiring W2 of the second solar cell string PV2. A reactor L1 is inserted into 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. In addition, you may install on positive wiring.

A switching element S1 and a smoothing output capacitor C2 are connected between the plus wiring and the minus wiring of the output wiring Wb of the booster circuit 11 . A diode D2 is connected in series to the positive wiring between the switching element S1 of the booster circuit 11 and the output capacitor C2. Reactor L1 is connected to a node between switching element S1 and diode D2. Diode D<b>2 prevents backflow of current from the output side of booster circuit 11 .

An IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used for the switching element S1. Reactor L1 stores and releases energy based on the output current from second solar cell string PV2 in response to ON/OFF of switching element S1.

The controller 12 can control the step-up ratio by controlling the ON/OFF ratio (duty ratio) of the switching element S1. The controller 12 can MPPT (Maximum Power Point Tracking) control the booster circuit 11 so that the output power (generated power) of the second solar cell string PV2 is maximized.

FIG. 3 is a diagram showing 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 operating at the maximum output power Pmax, the lower the operating voltage V, the more the output power P increases. In the voltage range below the maximum output operating voltage Vpm, the lower the operating voltage V, the lower the output power P. In MPPT control, operating voltage V is controlled such that maximum output power Pmax is maintained.

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 detects the second solar cell Detect the output power of the string PV2. 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 the output power of the second photovoltaic string PV2.

For example, the control unit 12 searches for the operating point of the maximum output power Pmax by changing the operating voltage V by a predetermined step width according to the 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 for shifting the current operating voltage V to the right side is generated, Generate a voltage command value for shifting V to the left. When the operating point of the maximum output power Pmax is detected, 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 booster circuit 11 performs switching operation according to the drive signal based on the generated voltage command value.

Return to FIG. The power conversion device 20 is a power conditioner that converts DC power into AC power in a photovoltaic power generation system. The power converter 20 includes a DC/DC converter 21 , an inverter 22 and a controller 23 .

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

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). A home load (not shown) 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 controls the power converter 20 as a whole. The control unit 23 can be realized by cooperation of hardware resources and software resources, or only by hardware resources. Analog devices, 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 target value of the input voltage of the DC/DC converter 21 is low, the control unit 23 boosts the input voltage of the inverter 22 so that it reaches the target value, and also increases the voltage of the first solar cell string PV1 and the second solar cell string PV2. The DC/DC converter 21 is MPPT-controlled so that the integrated input power is maximized. Control unit 23 controls inverter 22 so that the voltage between DC/DC converter 21 and inverter 22 maintains a target value. Specifically, control unit 23 generates a current command value for matching the input voltage of inverter 22 with a target value. Control unit 23 generates a current command value for increasing the output power of inverter 22 when the input voltage of inverter 22 is higher than the target value, and controls the output of inverter 22 when the input voltage of inverter 22 is lower than the target value. Generate a current command value to reduce power. Inverter 22 performs a switching operation according to a drive signal based on the generated current command value.

In the booster circuit 11 described above, a limiter value is set for the output voltage in order to protect subsequent components. The control unit 12 controls the output voltage of the booster circuit 11 so as not to exceed the limiter value. Specifically, when the output voltage of the booster circuit 11 reaches the limiter value, the control unit 12 reduces the duty ratio of the switching element S1 to decrease the output voltage, or turns off the switching element S1 to increase the output voltage of the booster circuit 11. stop working.

The power conversion device 20 (hereinafter also referred to as a power conditioner as appropriate) controls to reduce the input power when the output power decreases due to output control (also referred to as output suppression) or load fluctuation. This control may increase the output voltage of the boost junction box 10 .

As described above, there are a plurality of models of power conditioners with different maximum input voltages. For example, there are models with a maximum input voltage of 450V (hereinafter referred to as 450V input power conditioner) and models with a maximum input voltage of 380V (hereinafter referred to as 380V input power conditioner).

For example, if a 380V input power conditioner is connected to a boost junction box 10 capable of boosting up to 450V, the output voltage of the booster circuit 11 exceeding 380V will exceed the maximum input voltage of the 380V input power conditioner. In this case, the 380V input inverter shuts down with an input overvoltage error.

On the other hand, manufacturers prepare a plurality of boost junction boxes 10 according to the specifications of inverters. The builder selects the boost junction box 10 that conforms to the specifications of the power conditioner to be used, and constructs the photovoltaic power generation system.

However, there have been cases where a photovoltaic power generation system has been assembled with an inappropriate combination of the power conditioner and the boost junction box 10 due to an order mistake by the builder. In that case, it is necessary to exchange the product or buy a new product, which is a heavy burden on the user and the installer.

Here, a photovoltaic power generation system is assembled with a 450V input power conditioner, a solar cell string with an open 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. Consider the case of In this case, if the allocation of the solar cell modules 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 increases the burden on the builder.

Next, a photovoltaic power generation system was assembled with a 380V input inverter, a solar cell string with an open-circuit voltage range of less than 380V, and a boost junction box 10 with a maximum output voltage set to 450V (hereinafter referred to as a 450V output booster). Consider the case. 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 power conditioner, and the 380V input power conditioner may report an error and stop. It also leads to component failure in the 380V input power conditioner.

For manufacturers who provide boosters, having a lineup of multiple types of products according to the specifications of inverters is a burden in terms of production, service, and management.

On the other hand, the present embodiment provides a booster having a function capable of switching the maximum output voltage in the booster itself. As a result, the builder does not need to be aware of the combination of the power conditioner and the booster, and the burden on the builder is reduced. On the manufacturer side as well, there is no need to line up a plurality of types of products according to the specifications of the inverter, and the burden of production, service and management can be reduced.

FIG. 4 is a diagram showing an example of the operating section 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 valid when the manual setting mode is selected by the first slide switch SW1. The builder can set the maximum output voltage of the booster according to the maximum input voltage of the inverter during construction.

When there are two or more types of maximum input voltage of the power conditioner, the number of selectable types can be increased by increasing the number of slide switches and the number of selection points of the slide switches according to the number of types.

FIG. 5 is a diagram showing another example of the operation unit 13 of the boost junction box 10 having the function of 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 the "MODE" button, the second push button B2 is the "UP" button, the third push button B3 is the "DOWN" button, and the fourth push button B4 is the "ENTER" button. be.

FIG. 6 is a diagram for explaining a usage example of the operation unit 13 shown in FIG. 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. Then select the settings. Press the "UP" button and "DOWN" button to select the desired set value. In the example shown in FIG. 6, "450" is selected from three patterns of "AUto" (=automatic judgment), "380" (maximum output voltage 380V setting), and "450" (maximum output voltage 450V setting). is.

Note that the maximum output voltage may be set in increments of 10 V within the set range. With the desired voltage value selected, press the "ENTER" button to confirm the setting of the maximum output voltage. Thus, in the examples shown in FIGS. 5 and 6, the 7-segment display 13a and the plurality of push buttons B1 to B4 are used to switch the setting of the maximum output voltage.

When the output voltage exceeds the set maximum output voltage according to the settings switched as described above, the booster stops the boost operation or reduces the boost ratio to exceed the maximum output voltage. control to prevent

Next, the automatic switching function of the maximum output voltage will be explained. Inverters used in photovoltaic power generation systems have input voltage limits, and the number of solar cell modules connected in series is determined so that the open-circuit voltage of a solar cell string does not exceed the maximum input voltage of the inverter. For example, in a system using a 380V input power conditioner, the number of solar cell modules connected 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 power conditioner, the number of solar cell modules connected in series is determined so that the open-circuit voltage of the solar cell string is less than 450V.

A solar cell module has a characteristic that the voltage rises above the nominal open-circuit voltage at low temperatures. In many cases, considering the characteristics at low temperatures, the open-circuit voltage of the solar cell string is not near the maximum input voltage of the inverter, but is lower than the maximum input voltage of the inverter by a predetermined value or more. is determined.

Therefore, when the open-circuit voltage of a solar cell string used in a photovoltaic power generation system exceeds 380V, it can be determined that the photovoltaic power generation system uses a 450V input power conditioner instead of a 380V input power conditioner. Also, if the open-circuit voltage of the solar cell string is 380V or less, it can be determined that a 380V input power conditioner is being used.

Even if a 450V input power conditioner 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 booster's automatic determination function (details will be described later) determines that the booster is connected to a 380V input power conditioner instead of a 450V input power conditioner, and limits the maximum output voltage to 380V, the booster's output voltage does not exceed the inverter's maximum input voltage. Therefore, problems such as the above-mentioned error stop do not occur. In addition, since the system operates below the open-circuit voltage, problems such as a drop in power generation do not occur.

In this way, if the open-circuit voltage of the solar battery 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. becomes.

In addition, if the maximum input voltage of the connected inverter can be confirmed in advance, or if it is difficult to switch by automatic determination, the installer should switch to manual setting and set the maximum input voltage value that matches the maximum input voltage value of the connected inverter. It is possible to set the output voltage to the booster.

Next, the automatic determination method of the maximum input voltage of the power conditioner by the booster will be specifically described. When the power conditioner is stopped and the boosting operation of the booster circuit 11 of the booster is stopped, the controller 12 of the booster can detect the open-circuit voltage of the connected solar cell string with the output voltage sensor V2. The control unit 12 of the booster determines that the 450V input inverter is connected when the detection value of the output voltage sensor V2 is equal to or higher than the determination threshold, and determines that the 380V input inverter is connected when it is less than the determination threshold. do. 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.

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 power conditioner are used, and the booster determines the maximum input voltage of the power conditioner before the power conditioner starts operating. showing.

While the power conditioner is stopped, the output voltage Vout of the solar cell string increases as the intensity of the solar radiation increases. The output voltage Vout of the solar cell string is the output voltage of the first solar cell string PV1 of the standard circuitry. Since the booster circuit 11 has not started operating, the output voltage of the second solar cell string PV2 of the booster circuit system is lower than the output voltage of the first solar cell string PV1 of the standard circuit system.

Until the output voltage Vout of the solar cell string exceeds the determination threshold value Vth (380V), the control unit 12 determines that the 380V input inverter is connected to the output side of the booster, and sets the maximum output voltage of the booster circuit 11 to 380V. set to On the other hand, when the output voltage Vout of the solar cell string exceeds the determination threshold value Vth (380V), the control unit 12 determines that a 450V input power conditioner is connected to the output side of the booster, and reduces the maximum output voltage of the booster circuit 11. Set to 450V.

When MPPT control of the power conditioner is started, the output voltage Vout of the solar cell string drops near the maximum operating output voltage Vpm and drops below 380V. However, once the detected value of the output voltage sensor V2 exceeds the determination threshold value Vth (380V), the control unit 12 sets the maximum output voltage of the booster circuit 11 to 450V even if it falls below the determination threshold value Vth (380V) thereafter. to maintain.

FIG. 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 FIG. 8 also assumes that a solar cell string with an open-circuit voltage Voc of 420V and a 450V input power conditioner are used. The example shown in FIG. 8 shows a case where the power conditioner starts operating before the output voltage Vout of the solar cell string reaches the open-circuit voltage Voc.

The power generated by the solar cell string immediately after sunrise is small, and the power conditioner may start operating before the output voltage Vout of the solar cell string rises to the open-circuit voltage Voc. Further, recent power conditioners have improved response performance, and there are cases where MPPT control is started before the output voltage Vout of the solar cell string rises to the open-circuit voltage Voc, and is controlled near the maximum operating output voltage Vpm.

Thus, even if the open-circuit voltage Voc of the solar cell string is 420V, the output voltage Vout of the solar cell string may rise only to the maximum operating output voltage Vpm (around 350V). In the example shown in FIG. 8, the power conditioner starts operating when the output voltage Vout of the solar cell string is less than 380 V, and the output voltage Vout of the solar cell string never exceeds the determination threshold Vth (380 V). It changes below the threshold Vth (380V). In this case, the control unit 12 erroneously determines that the 380V input power conditioner is connected although the 450V input power conditioner is connected to the output side of the booster.

Control for preventing such erroneous determination will be described below. During operation of the power conditioner, the controller 12 multiplies the output voltage detected by the output voltage sensor V2 and the output current detected by the output current sensor A2 to detect the output power of the booster. The output power of the booster is obtained by multiplying the input voltage detected by the input voltage sensor (not shown) of the standard circuit system and the input current detected by the input current sensor (not shown) of the standard circuit system. Substitute the input power obtained by adding the input power to the booster circuit system obtained by multiplying the input power by the input voltage detected by the input voltage sensor V1 of the booster circuit system and the input current detected by the input current sensor A1. good too.

The control unit 12 MPPT-controls the booster 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 reaches 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 by the ratio of the open-circuit voltage Voc to the maximum output operating voltage Vpm of the solar cell string.

During operation of the power conditioner, the controller 12 compares the estimated open-circuit voltage Voc' of the solar cell string with the determination threshold Vth (380 V). When the estimated open-circuit voltage Voc' of the solar cell string is equal to or higher than the determination threshold value Vth (380V), the control unit 12 determines that a 450V input inverter is connected to the output side of the booster, and increases the maximum output voltage of the booster circuit 11. Set to 450V. On the other hand, when the estimated open-circuit voltage Voc' of the solar cell string is less than the determination threshold value Vth (380V), the control unit 12 determines that the 380V input inverter is connected to the output side of the booster, and the maximum output of the booster circuit 11 is determined. Set the voltage to 380V.

FIG. 9 shows the maximum output power Pmax (W), maximum output operating voltage Vpm (V), open-circuit voltage Voc (V), maximum output current Imax (A), and short-circuit current Isc (A) of a plurality of types of solar cell modules. , a graph summarizing the constant β. According to investigations by the inventors, it has been found that the constant (β) of many types of solar cell modules is about 1.2. As described above, the constant β is set to 1.2 in the present embodiment. In view of the power conversion efficiency and circuit constants of the booster, a value obtained by correcting 1.2 may be set as the constant β.

FIG. 10 is a flowchart showing the flow of switching processing of the maximum output voltage by the booster according to the 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), manual operation is selected by the first slide switch SW1 and 450 V is selected by the second slide switch SW2 (manual operation in S11, 450 V in S12). The unit 12 sets the maximum output voltage Vlim of the booster circuit 11 to 450V (S13). When manual is selected by the first slide switch SW1 and 380V is selected by the second slide switch SW2 (manual in S11, 380V in S12), the control unit 12 sets the maximum output voltage Vlim of the booster circuit 11 to 380V. Set (S14).

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

FIG. 11 is a flow chart showing a subroutine of automatic determination processing of the maximum input voltage of the power conditioner shown in step S20 of FIG. In the flowchart of FIG. 11, the parameter Va is a parameter for holding the maximum value of the output voltage Vout of the solar cell string while the power conditioner is stopped. The parameter Vb is a parameter for holding the maximum value of the output voltage Vout of the solar cell string during power conditioner operation. The parameter Vc is a parameter for holding a target voltage to be compared with the determination threshold Vth (380V).

When the power conditioner is stopped (Y of S21) and the booster circuit 11 is also stopped (Y of S22), the control unit 12 detects the value held in the parameter Va and the output detected by the output voltage sensor V2. The voltage Vout is compared (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 detected value of the output voltage Vout (S24). . If the output voltage Vout is not greater than the value held in the parameter Va (N of S23), the process of step S24 is skipped. The control unit 12 substitutes the value held in the parameter Va for the parameter Vc (S25).

When the inverter starts operating (N of S21), the booster circuit 11 also starts operating. The control unit 12 multiplies the output voltage detected by the output voltage sensor V2 and the output current detected by the output current sensor A2 to detect the output power of the booster. When 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 has not increased (N of S26), the process 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 the parameter Va with the value held in the parameter Vb (S28). If the value held in the parameter Vb is less than or equal to the value held in the parameter Va (N of S28), the control unit 12 substitutes the value held in the parameter Va into the parameter Vc (S25). When the value held in the parameter Vb becomes larger than the value held in the parameter Va as the insolation increases (Y in S28), the control unit 12 sets the value held in the parameter Vb to a constant A value obtained by multiplying by β is substituted for the parameter Vc as an estimated value of the open-circuit voltage Voc (S29).

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

As described above, according to the present embodiment, the step-up junction box 10 is provided with the function of switching the maximum output voltage, so that one type of step-up junction box 10 can handle a plurality of types of inverters with different maximum input voltages. can handle. By realizing such a highly versatile booster connection box 10, the burden on the manufacturer and the installer can be reduced.

The present disclosure has been described above based on the embodiments. It is to be understood by those skilled in the art that the embodiment is an example, and that various modifications are possible in the combination of each component and each treatment process, and such modifications are also within the scope of the present disclosure. .

In the above embodiment, the boost junction box 10 equipped with the automatic determination mode and the manual setting mode as the switching function of the maximum output voltage has been described. In this regard, the boost junction box 10 equipped with only the automatic determination function or the boost junction box 10 equipped with only the manual setting function are also included in the scope of the present disclosure. 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 the user, and the automatic determination function may be operated in the background. The installer may operate the second slide switch SW2 by mistake. For example, although 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, if the automatic determination function of the boost junction box 10 determines that a 380V input inverter is connected, the controller 12 changes the maximum output voltage Vlim of the booster circuit 11 from 450V to 380V.

In the above embodiment, for the sake of simplification, 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 an anti-backflow diode D1 are installed in each string. The current (power) output from the plurality of first solar cell strings PV1 to the combined output wiring Wm is the sum of the output currents (output power) of the plurality of first solar cell strings PV1.

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 booster circuit 11 are installed in each string. The current (power) output from the plurality of booster circuits 11 to the combined output wiring Wm is the sum of the output currents (output power) of the plurality of second solar cell strings PV2.

In the above embodiment, an example in which the first solar cell string PV1 and the 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 has been described. In this respect, the step-up junction box 10 can also be connected to a DC power source other than a plurality of solar cells with different open-circuit voltages. For example, the boost junction box 10 may be connected to a first battery pack and a second battery pack having a lower open-circuit voltage than the first battery pack. The second battery pack is a battery pack having fewer cells or modules in series than the first battery pack.

Note that the embodiment may be specified by the following items.

[Item 1]
a booster circuit (11) capable of boosting the voltage of DC power output from a second DC power supply (PV2) having an open-circuit voltage lower than that of the first DC power supply (PV1);
a junction output wiring (Wb) in which the output wiring (Wb) of the booster circuit (11) and the output wiring (W1) of the first DC power supply (PV1) are merged;
A control unit (12) that controls the booster circuit (11),
The combined output wiring (Wb) is connected to a power conversion device (20) that converts DC power supplied from the booster connection circuit (10) into AC power,
The step-up connection circuit (10) is characterized in that the setting of the maximum output voltage of the step-up circuit (11) can be switched so as not to exceed the maximum input voltage of the power converter (20). A boost connection circuit (10).
According to this, by realizing a highly versatile booster connection circuit (10), it is possible to reduce the burden on manufacturers and installers.
[Item 2]
further comprising a voltage sensor (V2) that detects the voltage of the combined output wiring (Wb);
The control unit (12) controls the power conversion device (20) according to the voltage detected by the voltage sensor (V2) while the power conversion device (20) and the booster circuit (11) are stopped. A booster connection circuit (10) according to item 1, wherein a maximum input voltage is estimated, and a set value of the maximum output voltage of the booster circuit (11) is determined at a voltage value equal to or lower than the estimated maximum input voltage. .
According to this, by installing the automatic determination mode, the burden on the builder can be reduced, and human error can be reduced.
[Item 3]
The first DC power supply (PV1) and the second DC power supply (PV2) are solar cells (PV1, PV2),
While the power conversion device (20) is in operation and the booster circuit (11) is stopped, the control unit (12) changes the voltage detected by the voltage sensor (V2) to the solar cells (PV1, PV2 ), wherein the maximum input voltage of the power conversion device (20) is estimated according to the voltage obtained by multiplying the ratio of the open circuit voltage to the maximum output point voltage of the booster connection circuit (10 ).
According to this, the maximum input voltage of the power conversion device (20) for the solar cells (PV1, PV2) can be estimated with high accuracy.
[Item 4]
2. A booster connection circuit (10) according to item 1, characterized in that the controller (12) determines a set value of the maximum output voltage of the booster circuit (11) based on a user's operation.
According to this, it is possible to easily implement a switching function of the maximum output voltage.
[Item 5]
further comprising a voltage sensor (V2) that detects the voltage of the combined output wiring (Wb);
The control unit (12) estimates the set value of the maximum output voltage of the booster circuit (11) determined based on the user's operation from the voltage detected by the voltage sensor (V2). 5. Boosting connection according to item 4, characterized in that when the maximum input voltage of (20) is exceeded, the set value of the maximum output voltage of the booster circuit (11) is switched to a voltage value equal to or less than the maximum input voltage. circuit (10).
According to this, human error due to manual setting can be covered by the automatic determination function.
[Item 6]
a boost connection circuit (10) according to any one of items 1 to 5;
a power conversion device (20) for converting DC power supplied from the boost connection circuit (10) into AC power;
A power conversion system (1), characterized in that it comprises:
According to this, by realizing a highly versatile booster connection circuit (10), it is possible to reduce the burden on manufacturers and installers.

1 power conversion system 2 commercial power system 10 step-up junction box 11 step-up circuit 12 control unit 20 power conversion device 21 DC/DC converter 22 inverter 23 control unit PV1 first solar cell string PV2 second 2 solar cell strings, RY1 first switch, RY2 second switch, D1 backflow 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 (6)

a booster circuit capable of boosting the voltage of DC power output from a second DC power supply having an open-circuit voltage lower than that of the first DC power supply;
a combined output wiring in which the output wiring of the booster circuit and the output wiring of the first DC power supply are merged;
A control unit that controls the booster circuit,
The combined output wiring is connected to a power conversion device that converts DC power supplied from the boost connection circuit into AC power,
The booster connection circuit is characterized in that the setting of the maximum output voltage of the booster circuit can be switched so as not to exceed the maximum input voltage of the power converter. Further comprising a voltage sensor that detects the voltage of the combined output wiring,
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 booster circuit are stopped, and a voltage equal to or lower than the estimated maximum input voltage 2. The booster connection circuit according to claim 1, wherein the value determines the set value of the maximum output voltage of said booster circuit. The first DC power supply and the second DC power supply are solar cells,
When the power conversion device is in operation and the booster circuit is stopped, the control unit multiplies the voltage detected by the voltage sensor by the ratio of the open-circuit voltage to the maximum output point voltage of the solar cell. 3. The booster connection circuit according to claim 2, wherein the maximum input voltage of the power converter is estimated according to . 2. The booster connection circuit according to claim 1, wherein the controller determines a set value of the maximum output voltage of the booster circuit based on a user's operation. Further comprising a voltage sensor that detects the voltage of the combined output wiring,
When the set value of the maximum output voltage of the booster circuit determined based on the user's operation exceeds the maximum input voltage of the power converter estimated from the voltage detected by the voltage sensor 5. The booster connection circuit according to claim 4, wherein the set value of the maximum output voltage of the booster circuit is switched 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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