Boost connection circuit, power conversion system

Abstract

To realize a boosting connection circuit capable of appropriately adjusting output power in accordance with output control of a power conversion device connected in a subsequent stage.SOLUTION: A boosting circuit (11) can boost a voltage of DC power output from a second DC power supply (PV2) having a lower open-circuit voltage than that of a first DC power supply (PV1). Combined output wiring (Wb) is wiring in which output wiring (Wb) of the boosting circuit (11) and output wiring (W1) of the first DC power supply (PV1) are combined, and is connected to a power conversion device (20) that converts DC power supplied from a boosting connection circuit (10) into AC power. A control unit (12) estimates whether or not the power conversion device (20) is under output control based on an output from the boosting connection circuit (10) or the first DC power supply (PV1) to the power conversion device (20).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] With the increasing attention to renewable energy, the popularity of photovoltaic power generation systems is expanding. In a photovoltaic power generation system in which a plurality of solar cell strings are installed, when a power conditioner is used, a connection box for integrating the DC currents generated by the plurality of solar cell strings may be installed in front of the power conditioner.

[0003] Due to the shape of the roof or the like, it may not be possible to unify the number of solar cell modules constituting each of the plurality of solar cell strings. In that case, a connection box with a boosting function is installed in front of the power conditioner. The connection box with a boosting function has a 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 DC currents of each solar cell string (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the power conditioner in the latter stage of the connection box with a boosting function performs output control (also referred to as output suppression), the power conditioner suppresses the power input to the power conditioner by increasing the input voltage. As the input voltage of the power conditioner increases, the output power from the standard first solar cell string is suppressed. On the other hand, the boosting circuit in the connection box with a boosting function boosts the output voltage from the second solar cell string, which has fewer series cells than the first solar cell string, to match the input voltage of the power conditioner and tries to push the output power of the second solar cell string into the power conditioner.

[0006] When the output voltage of the first solar cell string rises to the open-circuit voltage, the output of the first solar cell string stops. At this point, the input power to the power conditioner becomes only the output power of the second solar cell string boosted by the boosting circuit. The boosting circuit continues the boosting operation so that the maximum power is output from the second solar cell string.

[0007] The power conditioner further increases the input voltage to suppress the input power from the second solar cell string. As the input voltage of the power conditioner increases, when the output voltage of the boosting circuit rises to the limiter value, the boosting circuit stops, the input power to the power conditioner stops, and the power conditioner also stops.

[0008] The present disclosure has been made in view of such a situation, and an object thereof is to provide a boosting connection circuit and a power conversion system that can appropriately adjust the output power in accordance with the output control of the power conversion device connected to the latter stage.

Means for Solving the Problems

[0009] To solve the above problems, a boost connection circuit according to an aspect of the present disclosure includes a boost circuit capable of boosting the voltage of DC power output from a second DC power source having an open-circuit voltage lower than that of a first DC power source, an output wiring of the boost circuit, a combined output wiring where the output wiring of the first DC power source and the output wiring of the boost circuit merge, and a control unit for controlling the boost circuit. The combined output wiring is connected to a power conversion device that converts the DC power supplied from the present boost connection circuit into AC power and outputs it to the power grid. The control unit estimates whether the power conversion device is under output control based on the output from the present boost connection circuit or the first DC power source to the power conversion device.

Effect of the Invention

[0010] According to the present disclosure, it is possible to realize a boost connection circuit that can appropriately adjust the output power in accordance with the output control of a power conversion device connected to the subsequent stage.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Mode for Carrying Out the Invention

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

[0013] The first solar cell string PV1 includes a plurality of solar cell modules (solar panels) connected in series. The second solar cell string PV2 includes solar cell modules 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.

[0014] Each solar cell module includes a plurality of solar cells connected in series. The solar cell can utilize the photovoltaic effect and directly convert light energy into DC power. As the solar cell, 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, etc. can be used.

[0015] The step-up connection box 10 includes a step-up 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 reverse current prevention diode D1, an output terminal OUT, an input voltage sensor V1, an input current sensor A1, an output voltage sensor V2, and an output current sensor A2.

[0016] Since the second solar cell string PV2 has fewer series cells than the first solar cell string PV1, its open-circuit voltage is lower than that of 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 reverse current 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 further connected to the step-up circuit 11.

[0017] The output wiring W1 of the first solar cell string PV1 and the output wiring Wb of the step-up circuit 11 merge at a terminal block (not shown), and the connection between the terminal block and the input terminal of the power conversion device 20 is made by a merged output wiring Wm. 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 step-up circuit system.

[0018] The step-up circuit 11 is a DC / DC converter capable of stepping up the voltage of the DC power output from the second solar cell string PV2. By stepping up the output voltage of the second solar cell string PV2 to the voltage of the standard circuit system, the step-up circuit 11 can integrate the output power of the first solar cell string PV1 and the output power of the second solar cell string PV2 and supply it to the power conversion device 20 via the output terminal OUT.

[0019] The input voltage sensor V1 detects the voltage of the output wiring W2 of the second solar cell string PV2 and outputs it to the control unit 12. The input current sensor A1 detects the current flowing through the output wiring W2 of the second solar cell string PV2 and outputs it to the control unit 12. The combined wiring voltage sensor V5 detects the voltage of the combined output wiring Wm and outputs it to the control unit 12.

[0020] The input voltage sensor V1 and the combined wiring voltage sensor V5 are configured to include, for example, a voltage dividing resistor and a differential amplifier. The input current sensor A1 is configured to include, for example, a CT sensor or a Hall sensor.

[0021] Based on the voltage and current input from each sensor, the control unit 12 controls the boosting operation of the boost circuit 11, and by controlling the voltage detected by the input voltage sensor V1 and the current detected by the input current sensor A1, the generated power of the second solar cell string PV2 can be optimized (details will be described later).

[0022] The control unit 12 can be realized by the cooperation of hardware resources and software resources, or by hardware resources only. As hardware resources, analog elements, microcontrollers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs can be used. As software resources, programs such as firmware can be used.

[0023] FIG. 2 is a diagram showing a circuit configuration example of the boost circuit 11. The boost circuit 11 shown in FIG. 2 is a boost chopper including an input capacitor C1, a reactor L1, a diode D2, a switching element S1, and an output capacitor C2.

[0024] An input voltage sensor V1 and a smoothing input capacitor C1 are connected between the positive and negative wirings 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. Note that it may be installed on the positive wiring.

[0025] 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 boost circuit 11. A diode D2 is connected in series to the plus wiring between the switching element S1 and the output capacitor C2 of the boost circuit 11. An inductor L1 is connected to the node between the switching element S1 and the diode D2. The diode D2 prevents the reverse flow of current from the output side of the boost circuit 11.

[0026] For the switching element S1, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal - Oxide - Semiconductor Field - Effect Transistor) can be used. The inductor L1 accumulates and releases energy based on the output current from the second solar cell string PV2 in accordance with the on / off state of the switching element S1.

[0027] 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 on the boost circuit 11 so that the output power (generated power) of the second solar cell string PV2 is maximized.

[0028] FIG. 3 is a diagram showing the power - voltage characteristic (P - V curve) of the 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 maximum output power Pmax operates, the output power P increases as the operating voltage V decreases. In the voltage range below the maximum output operating voltage Vpm, the output power P decreases as the operating voltage V decreases. In MPPT control, the operating voltage V is controlled so that the maximum output power Pmax is maintained.

[0029] 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 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 generates a voltage command value to maximize the output power of the second solar cell string PV2.

[0030] For example, the control unit 12 operates according to the hill climbing method to change the operating voltage V by a predetermined step width to search for the operating point of the maximum output power Pmax. 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 is generated, and on the right side of the operating point of the maximum output power Pmax, a voltage command value for shifting the current operating voltage V to the left is generated. 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 a switching operation in response to a drive signal based on the generated voltage command value.

[0031] Returning to FIG. 1. The power conversion device 20 is a power conditioner that converts DC power into AC power in a solar power generation system. The power conversion device 20 includes a DC / DC converter 21, an inverter 22, and a control unit 23.

[0032] The DC / DC converter 21 is a converter capable of adjusting the voltage of the DC power integrated by the boost connection 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.

[0033] 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 (hereinafter referred to as the system) 2 via a distribution board (not shown). Note that a household 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.

[0034] The control unit 23 comprehensively controls the entire power conversion device 20. The control unit 23 can be realized by the cooperation of hardware resources and software resources, or by hardware resources only. As hardware resources, analog elements, microcontrollers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs can be used. As software resources, programs such as firmware can be used.

[0035] When the input voltage of the DC / DC converter 21 is lower than the target value, the control unit 23 boosts the voltage so that the input voltage of the inverter 22 becomes the target value, and performs MPPT control on the DC / DC converter 21 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 a switching operation in response to a drive signal based on the generated current command value.

[0036] In Japan, with the amendment of the Renewable Energy Special Measures Act in January 2015, it was stipulated that renewable energy power generation facilities connected to the grid beyond a certain amount are obliged to respond to requests for output control from power companies without limitation and without compensation. Along with the expansion of the feed-in tariff system for renewable energy, the number of renewable energy power generation facilities connected to the grid has increased, and the supply-demand balance of Grid 2 has become more likely to be disrupted than before. When the power supply to Grid 2 exceeds the power demand, the voltage and frequency of Grid 2 increase, and when the power supply to Grid 2 is less than the power demand, the voltage and frequency of Grid 2 decrease. The power transmission and distribution operator can utilize output control to keep the voltage and frequency of Grid 2 within a predetermined range.

[0037] The management server (not shown) of the power transmission and distribution operator predicts the power supply and demand of Grid 2 based on weather forecasts, load forecasts, etc., and determines whether output control is necessary. If output control is necessary, the management server of the power transmission and distribution operator determines the schedule of output control and the output upper limit value. The schedule is defined, for example, in 30-minute units. The output upper limit value is defined, for example, as a percentage [%] of the rated output power of the power generation facility and is specified in 1% units. The power conversion device 20 receives an output control command from the management server of the power transmission and distribution operator via a network (for example, the Internet).

[0038] When the start time of the target time zone of the output control command arrives, the control unit 23 of the power conversion device 20 decreases the output power of the DC / DC converter 21 at a predetermined output change rate (slope Ss). The output change rate is defined as the suppression amount [W / s] per unit time and is set, for example, to a rate of decrease of 10 - 20% of the rated output per minute.

[0039] Also, when the end time of the target time zone of the output control command arrives, the control unit 23 increases the output power of the DC / DC converter 21 at a predetermined output change rate (slope Se). The output change rate is defined as the suppression release amount [W / s] per unit time and is set, for example, to a rate of increase of 10 - 20% of the rated output per minute.

[0040] FIG. 4 is a diagram showing an example of the transition of the output power during the output control of the power conversion device 20. In the example shown in FIG. 4, an example is shown in which the power conversion device 20 with an input power of 5.5 [kW] and a rated output = 5.5 [kW] receives an output control command with an output upper limit value = 50%.

[0041] When it reaches the start time of the target time period of the output control command, the control unit 23 stops the MPPT control of the DC / DC converter 21 and duty-controls the DC / DC converter 21 so that the output power of the DC / DC converter 21 decreases to 2.75 [kW] at a predetermined output change rate (slope Ss). Since the output power of the DC / DC converter 21 decreases with respect to the input power of the DC / DC converter 21, the input voltage of the DC / DC converter 21 increases. As a result, the output voltage of the first solar cell string PV1 of the standard circuit system is shifted to the right from the maximum output operating voltage Vpm, and the output power of the first solar cell string PV1 decreases (see FIG. 3). The behavior of the output power of the second solar cell string PV2 of the boost circuit system will be described later.

[0042] When it reaches the end time of the target time period of the output control command, the control unit 23 duty-controls the DC / DC converter 21 so that the output power of the DC / DC converter 21 increases to 5.5 [kW] at a predetermined output change rate (slope Se). Since the output power of the DC / DC converter 21 increases with respect to the input power of the DC / DC converter 21, the input voltage of the DC / DC converter 21 decreases. As a result, the output voltage of the first solar cell string PV1 of the standard circuit system is shifted to the left toward the maximum output operating voltage Vpm, and the output power of the first solar cell string PV1 increases (see FIG. 3). When the output power of the DC / DC converter 21 reaches the target value of 5.5 [kW], the control unit 23 resumes the MPPT control of the DC / DC converter 21.

[0043] Note that FIG. 4 shows an example in which a power command value for linearly changing the output power of the DC / DC converter 21 is generated, but a power command value for changing the output power of the DC / DC converter 21 in a stepwise manner may be generated.

[0044] FIG. 5 is a diagram showing an example of the transition of the output power of the step-up connection box 10 during the output control of the power conversion device 20. Since the second solar cell string PV2 of the step-up circuit system has a smaller number of solar cell modules connected in series than the first solar cell string PV1 of the standard circuit system, the output power of the first solar cell string PV1 of the standard circuit system is larger during steady state.

[0045] When the output control is started by the power conversion device 20, the input voltage of the power conversion device 20 (≈ the output voltage of the first solar cell string PV1) rises, and the output power of the first solar cell string PV1 decreases. When the input voltage of the power conversion device 20 rises, since the control unit 12 of the step-up connection box 10 performs MPPT control on the step-up circuit 11, in order to continue to supply current to the power conversion device 20, the control unit 12 increases the boost ratio of the step-up circuit 11 to maintain the output voltage of the step-up circuit 11 higher than the input voltage of the power conversion device 20. Since the control unit 12 performs MPPT control on the step-up circuit 11 so that the maximum power is output from the step-up circuit 11 to the power conversion device 20 while current is flowing, the output power from the second solar cell string PV2 to the power conversion device 20 is maintained without decreasing. In response to the rise in the output voltage of the step-up circuit 11, the output current flowing into the power conversion device 20 decreases.

[0046] When the input voltage of the power conversion device 20 rises and reaches the open-circuit voltage Voc of the first solar cell string PV1, the output of the first solar cell string PV1 stops. When the output voltage of the step-up circuit 11 rises to the limiter value as the input voltage of the power conversion device 20 rises, the step-up circuit 11 stops due to overvoltage, and the output from the second solar cell string PV2 to the power conversion device 20 also stops. As a result, the input to the power conversion device 20 is interrupted, and the power conversion device 20 also stops once. After that, the power conversion device 20 resumes operation, and the output from the first solar cell string PV1 to the power conversion device 20 resumes. The step-up circuit 11 resumes operation with a delay in response to the resumption of operation of the power conversion device 20.

[0047] When the input voltage of the power conversion device 20 rises and reaches the open-circuit voltage Voc of the first solar cell string PV1, the output of the first solar cell string PV1 stops again. When the output voltage of the boost circuit 11 rises to the limiter value by MPPT control, the boost circuit 11 stops due to overvoltage, the output from the second solar cell string PV2 to the power conversion device 20 also stops again, and the power conversion device 20 also stops again. When the above process is repeated, a state where the output power from the power conversion device 20 is unstable occurs, and when it stops a predetermined number of times (for example, 8 times), it may be necessary to reset the power supply of the power conversion device 20.

[0048] In the present embodiment, the boost connection box 10 is equipped with a function of estimating whether the power conversion device 20 is in output control, thereby appropriately controlling the output power of the boost connection box 10 during the output control of the power conversion device 20.

[0049] FIG. 6 is a diagram showing a configuration example of a photovoltaic power generation system according to Embodiment 1. The photovoltaic power generation system according to Embodiment 1 is a voltage-based system that estimates from the voltage whether the power conversion device 20 is in output control. The photovoltaic power generation system according to Embodiment 1 shown in FIG. 6 is a configuration in which a standard circuit voltage sensor V3 is added to the basic configuration of the photovoltaic power generation system according to the embodiment shown in FIG. 1. The standard circuit voltage sensor V3 detects the voltage of the output wiring W1 of the first solar cell string PV1 and outputs it to the control unit 12. The standard circuit voltage sensor V3 is connected to the first solar cell string PV1 side from the reverse current prevention diode D1 of the output wiring W1 of the first solar cell string PV1.

[0050] When the voltage detected by the standard circuit voltage sensor V3 (hereinafter referred to as the standard circuit input voltage) is lower than the voltage detected by the confluence wiring voltage sensor V5 (hereinafter referred to as the output voltage of the boost connection box 10), the control unit 12 can estimate that the output from the first solar cell string PV1 to the power conversion device 20 has stopped, so it determines that the power conversion device 20 is in output control. When the control unit 12 determines that the power conversion device 20 is in output control, it stops the MPPT control of the boost circuit 11 and starts the suppression control of the boost circuit 11.

[0051] The control unit 12 controls the boost circuit 11 so that the output voltage of the boost connection box 10 coincides with the standard circuit input voltage (controlled to Voc when the output of the first solar cell string PV1 stops), or decreases to a voltage (Voc-α) that is lower than the standard circuit input voltage by a predetermined value. Specifically, the control unit 12 increases the operating voltage of the boost circuit 11 to decrease the output power and output voltage of the boost circuit 11.

[0052] When the standard circuit input voltage drops by a predetermined value from the voltage at the start of suppression of the boost circuit 11 (for example, when it drops to a value of 95% of the voltage at the start of suppression), the control unit 12 determines that the output control of the power conversion device 20 has been released, and resumes the MPPT control of the boost circuit 11.

[0053] FIG. 7 is a diagram showing an example of the transition of the voltage and power in the boost connection box 10 during the output control of the power conversion device 20 in the photovoltaic power generation system according to Embodiment 1. The example shown in FIG. 7 shows a case where the maximum output power of the boost connection box 10 is 5.5 [kW], the maximum output power of the standard circuit is 3.5 [kW], the maximum output power of the boost circuit 11 is 2.0 [kW], and the power conversion device 20 has received an output control command of 1.5 [kW].

[0054] At time t0, the power conversion device 20 and the boost connection box 10 start operating. The control unit 23 of the power conversion device 20 performs MPPT control on the DC / DC converter 21, so that the output power of the standard circuit increases. Accordingly, the standard circuit input voltage decreases. The control unit 12 of the boost connection box 10 performs MPPT control on the boost circuit 11, so that the output power of the boost circuit 11 increases. During normal operation, the standard circuit input voltage and the output voltage of the boost connection box 10 change in a consistent state.

[0055] At time t1, when the standard circuit input voltage drops to the maximum output operating voltage Vpm of the first solar cell string PV1, the standard circuit input power (the output power of the first solar cell string PV1) becomes maximum. When the input voltage of the boost circuit 11 detected by the input voltage sensor V1 (hereinafter referred to as the boost circuit input voltage) drops to the maximum output operating voltage Vpm of the second solar cell string PV2, the boost circuit input power (the output power of the second solar cell string PV2) becomes maximum. At this time, the output power of the boost connection box 10 becomes maximum.

[0056] At time t2, when the power conversion device 20 receives an output control command, the control unit 23 stops the MPPT control of the DC / DC converter 21 and starts the suppression control of the DC / DC converter 21. The control unit 23 raises the operating voltage of the DC / DC converter 21 to lower the input power of the power conversion device 20 toward the target value (1.5 [kW]). At this point, since the boost connection box 10 does not recognize that the power conversion device 20 is under output control, the output power of the boost circuit 11 maintains the maximum output power (2.0 [kW]). Due to the suppression control of the power conversion device 20, the standard circuit input voltage and the output voltage of the boost connection box 10 increase.

[0057] At time t3, when the standard circuit input voltage reaches the open-circuit voltage Voc of the first solar cell string PV1, the standard circuit input power (the output power of the first solar cell string PV1) becomes zero, and the input power of the power conversion device 20 becomes 2.0 [kW] (= the maximum output power of the boost circuit 11). Since the power conversion device 20 needs to lower the input power to the target value (1.5 [kW]), the control unit 23 further raises the operating voltage of the DC / DC converter 21. In response to this, the control unit 12 of the boost connection box 10 tries to control by increasing the boost ratio of the boost circuit 11 to raise the output voltage of the boost circuit 11.

[0058] Since the standard circuit input voltage does not rise above the open-circuit voltage Voc of the first solar cell string PV1, the output voltage of the boost circuit 11 is higher than the standard circuit input voltage. When the output voltage of the boost circuit 11 becomes higher than the standard circuit input voltage, the control unit 12 of the boost connection box 10 determines that the power conversion device 20 is in output control. When the control unit 12 determines that the power conversion device 20 is in output control, it stops the MPPT control of the boost circuit 11 and starts the suppression control of the boost circuit 11.

[0059] The control unit 12 controls the boost circuit 11 so that the output voltage of the boost connection box 10 drops to a voltage (Voc-α) that is a predetermined value lower than the standard circuit input voltage. Specifically, the control unit 12 raises the operating voltage of the boost circuit 11 to reduce the output power and output voltage of the boost circuit 11. If the output voltage of the boost connection box 10 is reduced below the standard circuit input voltage, current can be more reliably drawn from the first solar cell string PV1.

[0060] At time t4, when the input power of the power conversion device 20 reaches the target value of 1.5 [kW], the increase in the operating voltage of the DC / DC converter 21 stops, and the output power of the boost connection box 10 becomes constant. As the output power of the boost circuit 11 decreases, the standard circuit input power (the output power of the first solar cell string PV1) increases from zero. After time t5, the output power of the first solar cell string PV1 and the output power of the boost circuit 11 change at a constant ratio.

[0061] FIG. 8 is a diagram showing a configuration example of a photovoltaic power generation system according to a modified example of Example 1. In the photovoltaic power generation system according to the modified example of Example 1 shown in FIG. 8, a boost circuit output voltage sensor V2 is used instead of the combined wiring voltage sensor V5 of the photovoltaic power generation system according to Example 1 shown in FIG. 6. The boost circuit output voltage sensor V2 detects the voltage of the output wiring Wb of the boost circuit 11 and outputs it to the control unit 12.

[0062] When the voltage detected by the standard circuit voltage sensor V3 is lower than the voltage detected by the boost circuit output voltage sensor V2, the control unit 12 can estimate that the output from the first solar cell string PV1 to the power conversion device 20 has stopped. Therefore, the control unit 12 determines that the power conversion device 20 is under output control. The control after determining that it is under output control is the same as the voltage-based control method described above.

[0063] FIG. 9 is a diagram showing a configuration example of a photovoltaic power generation system according to Embodiment 2. The photovoltaic power generation system according to Embodiment 2 is a current-based system that estimates whether the power conversion device 20 is under output control from the current. The photovoltaic power generation system according to Embodiment 2 shown in FIG. 9 has a configuration in which a standard circuit current sensor A3 is added to the basic configuration of the photovoltaic power generation system according to the embodiment shown in FIG. 1. The standard circuit current sensor A3 detects the current flowing through the output wiring W1 of the first solar cell string PV1 and outputs it to the control unit 12. The standard circuit current sensor A3 is connected to the combined output wiring Wm side from the reverse current prevention diode D1 of the output wiring W1 of the first solar cell string PV1.

[0064] When the current detected by the standard circuit current sensor A3 (hereinafter referred to as the standard circuit current) is zero and the current detected by the input current sensor A1 (hereinafter referred to as the boost circuit input current) is a positive value (greater than zero), the control unit 12 determines that the power conversion device 20 is under output control. When the control unit 12 determines that the power conversion device 20 is under output control, it stops the MPPT control of the boost circuit 11 and starts the suppression control of the boost circuit 11.

[0065] Note that when the standard circuit current is zero and the boost circuit input current is also zero, the control unit 12 determines that the power conversion device 20 has stopped and stops the operation of the boost circuit 11.

[0066] The control unit 12 raises the operating voltage of the boost circuit 11 until the ratio of the standard circuit current to the boost circuit input current reaches a predetermined ratio, thereby reducing the output power and output current of the boost circuit 11.

[0067] When the standard circuit current continuously increases for a preset period, the control unit 12 determines that the output control of the power conversion device 20 is released, and resumes the MPPT control of the boost circuit 11.

[0068] FIG. 10 is a diagram showing an example of the transition of current and power in the boost connection box 10 during the output control of the power conversion device 20 in the photovoltaic power generation system according to the second embodiment. The example shown in FIG. 10 is such that the maximum output power of the boost connection box 10 is 5.5 [kW], the maximum output power of the standard circuit is 3.5 [kW], the maximum output power of the boost circuit 11 is 2.0 [kW], and an example where the power conversion device 20 receives an output control command of 1.5 [kW] is shown.

[0069] At time t0, the power conversion device 20 and the boost connection box 10 start operating. The control unit 23 of the power conversion device 20 performs MPPT control on the DC / DC converter 21, whereby the output power of the standard circuit increases. Along with this, the standard circuit input voltage decreases. The control unit 12 of the boost connection box 10 performs MPPT control on the boost circuit 11, whereby the output power of the boost circuit increases. During normal operation, the standard circuit input voltage and the output voltage of the boost connection box 10 change in a consistent state, and both the standard circuit current and the boost circuit input current maintain positive values.

[0070] At time t1, when the standard circuit input voltage drops to the maximum output operating voltage Vpm of the first solar cell string PV1, the standard circuit current becomes the maximum output operating current Ipm of the first solar cell string PV1, and the standard circuit input power (the output power of the first solar cell string PV1) becomes maximum. When the boost circuit input voltage drops to the maximum output operating voltage Vpm of the second solar cell string PV2, the boost circuit input current becomes the maximum output operating current Ipm of the second solar cell string PV2, and the boost circuit input power (the output power of the second solar cell string PV2) becomes maximum. At this time, the output power of the boost connection box 10 becomes maximum.

[0071] At time t2, when the power conversion device 20 receives an output control command, the control unit 23 stops the MPPT control of the DC / DC converter 21 and starts the suppression control of the DC / DC converter 21. The control unit 23 increases the operating voltage of the DC / DC converter 21 to reduce the input power of the power conversion device 20 toward the target value (1.5 [kW]). As a result, the standard circuit current decreases. At this point, since the boost connection box 10 does not recognize that the power conversion device 20 is under output control, the output power of the boost circuit 11 maintains the maximum output power (2.0 [kW]). Due to the suppression control of the power conversion device 20, the standard circuit input voltage and the output voltage of the boost connection box 10 increase.

[0072] At time t3, the standard circuit input voltage reaches the open-circuit voltage Voc of the first solar cell string PV1, the standard circuit current becomes zero, and the input power of the power conversion device 20 becomes 2.0 [kW] (= the maximum output power of the boost circuit 11). At this time, the boost circuit 11 maintains the maximum output power (2.0 [kW]), and the current corresponding to the maximum output power flows from the boost circuit 11 to the power conversion device 20. When a current flows from the boost circuit 11 to the power conversion device 20 when the standard circuit current becomes zero, the control unit 12 of the boost connection box 10 determines that the power conversion device 20 is under output control. When the control unit 12 determines that the power conversion device 20 is under output control, it stops the MPPT control of the boost circuit 11 and starts the suppression control of the boost circuit 11.

[0073] The control unit 12 increases the operating voltage of the boost circuit 11 until the ratio of the standard circuit current to the boost circuit input current reaches a predetermined ratio (1:1 in FIG. 10) to reduce the output power and output current of the boost circuit 11. Note that the predetermined ratio is not limited to 1:1 and may be set to 4:1, the number ratio of the solar modules in the standard circuit system and the boost circuit system, etc.

[0074] At time t4, when the input power of the power conversion device 20 reaches the target value of 1.5 [kW], the increase in the operating voltage of the DC / DC converter 21 stops, and the output power of the boost connection box 10 becomes constant. After time t4, the output power of the first solar cell string PV1 and the output power of the boost circuit 11 change at a constant ratio (1:1 in FIG. 10).

[0075] FIG. 11 is a diagram showing a configuration example of a photovoltaic power generation system according to a modified example of Example 2. In the photovoltaic power generation system according to the modified example of Example 2 shown in FIG. 11, a boost circuit output current sensor A2 and a combined wiring current sensor A5 are added to the basic configuration of the photovoltaic power generation system according to the embodiment shown in FIG. 1. The boost circuit output current sensor A2 detects the current flowing through the output wiring Wb of the boost circuit 11 and outputs it to the control unit 12. The combined wiring current sensor A5 detects the current flowing through the combined output wiring Wm and outputs it to the control unit 12.

[0076] In the modified example, the standard circuit current can be calculated by subtracting the current detected by the boost circuit output current sensor A2 (referred to as the boost circuit output current) from the current detected by the combined wiring current sensor A5. When the standard circuit current is zero and the boost circuit input current or the boost circuit output current is a positive value (greater than zero), the control unit 12 determines that the power conversion device 20 is under output control. The control after determining that it is under output control is the same as the control method of the current method described above. Note that as the current of the boost system, either the boost circuit input current or the boost circuit output current may be used.

[0077] FIG. 12 is a diagram showing a configuration example of a photovoltaic power generation system according to Embodiment 3. The photovoltaic power generation system according to Embodiment 3 is a power-based system that estimates whether the power conversion device 20 is under output control from the power. The photovoltaic power generation system according to Embodiment 3 shown in FIG. 12 has a configuration in which a boost circuit output voltage sensor V2, a boost circuit output current sensor A2, and a combined wiring current sensor A5 are added to the basic configuration of the photovoltaic power generation system according to the embodiment shown in FIG. 1. The boost circuit output voltage sensor V2 detects the voltage of the output wiring Wb of the boost circuit 11 and outputs it to the control unit 12. The boost circuit output current sensor A2 detects the current flowing through the output wiring Wb of the boost circuit 11 and outputs it to the control unit 12. The combined wiring current sensor A5 detects the current flowing through the combined output wiring Wm and outputs it to the control unit 12.

[0078] The control unit 12 detects the output power of the boost circuit 11 based on the voltage detected by the boost circuit output voltage sensor V2 and the current detected by the boost circuit output current sensor A2. The control unit 12 detects the output power of the boost connection box 10 based on the voltage detected by the combined wiring voltage sensor V5 and the current detected by the combined wiring current sensor A5.

[0079] The control unit 12 estimates whether the power conversion device 20 is under output control based on the transition of the output power of the boost connection box 10. For example, when the output power of the boost connection box 10 decreases at a substantially constant rate over a predetermined period (e.g., 3 to 5 minutes), the control unit 12 determines that the power conversion device 20 has started output control. Conversely, when the output power of the boost connection box 10 increases at a substantially constant rate over a predetermined period (e.g., 3 to 5 minutes), the control unit 12 determines that the power conversion device 20 has released output control. Note that the control unit 12 determines that output control has been started or released not only when the output power of the boost connection box 10 is linearly increasing or decreasing, but also when it is increasing or decreasing stepwise.

[0080] When the control unit 12 determines that the power conversion device 20 is under output control, it stops the MPPT control of the boost circuit 11 and controls the output power of the boost circuit 11 so that the output power of the boost circuit 11 changes corresponding to the change rate of the output power of the boost connection box 10. The change rate of the output power of the boost circuit 11 and the change rate of the output power of the boost connection box 10 may be made to coincide, or the change rate of the output power of the boost connection box 10 may be multiplied by a predetermined coefficient so that the two change rates are different.

[0081] For example, at the start of output control, if the change rate of the output power of the boost circuit 11 is controlled to be faster than the change rate of the output power of the boost connection box 10, the power output from the first solar cell string PV1 to the power conversion device 20 can be maintained within a possible range. When the control unit 12 determines that the output control of the power conversion device 20 has been released, it resumes the MPPT control of the boost circuit 11.

[0082] FIG. 13 is a diagram showing a configuration example of a photovoltaic power generation system according to a modification of Example 3. In the photovoltaic power generation system according to the modification of Example 3 shown in FIG. 13, instead of the combined wiring current sensor A5 of the photovoltaic power generation system according to Example 3 shown in FIG. 12, a standard circuit current sensor A3 is used. The standard circuit current sensor A3 detects the current in the output wiring W1 of the first solar cell string PV1 and outputs it to the control unit 12. The control unit 12 detects the output power of the standard circuit system based on the voltage detected by the combined wiring voltage sensor V5 and the current detected by the standard circuit current sensor A3.

[0083] The control unit 12 estimates whether the power conversion device 20 is under output control based on the transition of the output power of the standard circuit system. For example, when the output power of the standard circuit system decreases at a substantially constant rate over a predetermined period (for example, 3 to 5 minutes), the control unit 12 determines that the power conversion device 20 has started output control. Conversely, when the output power of the standard circuit system increases at a substantially constant rate over a predetermined period (for example, 3 to 5 minutes), the control unit 12 determines that the output control of the power conversion device 20 has been released.

[0084] When the control unit 12 determines that the power conversion device 20 is in output control, it stops the MPPT control of the boost circuit 11 and controls the output power of the boost circuit 11 so that the output power of the boost circuit 11 changes corresponding to the change rate of the output power of the standard circuit system. The change rate of the output power of the boost circuit 11 and the change rate of the output power of the standard circuit system may be made to coincide, or a predetermined coefficient may be multiplied by the change rate of the output power of the standard circuit system so that the change rates of both are different.

[0085] For example, at the start of output control, if the change rate of the output power of the boost circuit 11 is controlled to be faster than the change rate of the output power of the standard circuit system, the power output from the first solar cell string PV1 to the power conversion device 20 can be maintained as much as possible. When the control unit 12 determines that the output control of the power conversion device 20 has been released, it resumes the MPPT control of the boost circuit 11.

[0086] FIG. 14 is a diagram showing a configuration example of a photovoltaic power generation system according to Embodiment 4. The photovoltaic power generation system according to Embodiment 4 is a system of a communication method that acquires control information indicating whether or not the power conversion device 20 is in output control through communication. The photovoltaic power generation system according to Embodiment 4 shown in FIG. 14 has a communication line CL added to the basic configuration of the photovoltaic power generation system according to the embodiment shown in FIG. 1 for transmitting and receiving control information between the control unit 23 of the power conversion device 20 and the control unit 12 of the boost connection box 10.

[0087] For the communication line CL, for example, an RS-485 cable or a LAN cable can be used. Instead of installing the communication line CL, wireless communication may be performed between the control unit 23 of the power conversion device 20 and the control unit 12 of the boost connection box 10.

[0088] Before the start of output control, the control unit 23 of the power conversion device 20 transmits to the control unit 12 of the step-up connection box 10 the start time of output control, the output change rate at the start (suppression amount [W / s]), the output upper limit value = X%, the end time of output control, and the output change rate at release (suppression release amount [W / s]). Note that the control unit 23 of the power conversion device 20 may transmit the power command value from the start to the release of output control to the control unit 12 of the step-up connection box 10 each time.

[0089] Based on the control information obtained from the power conversion device 20, the control unit 12 of the step-up connection box 10 specifies the target value of the output power of the power conversion device 20 at each time during the period when the power conversion device 20 is under output control, and duty-controls the step-up circuit 11 so that the output power of the step-up connection box 10 becomes the target value of the output power of the power conversion device 20.

[0090] At this time, by adding the standard circuit current sensor A3 or the combined wiring current sensor A5 and the step-up circuit output current sensor A2, the control unit 12 may duty-control the step-up circuit 11 so that the output current of the standard circuit system and the output current of the step-up circuit system maintain a predetermined ratio, as described in the current method.

[0091] As described above, according to Embodiments 1-3, by estimating whether the power conversion device 20 is under output control based on the output from the step-up connection box 10 to the power conversion device 20, appropriate power can be output from the step-up connection box 10 to the power conversion device 20 in accordance with the output control of the power conversion device 20. Thereby, it is possible to avoid the sudden stop of the step-up circuit 11 due to the output voltage of the step-up circuit 11 rising to the limiter value, and it is possible to avoid the unintended stop of the power conversion device 20.

[0092] In the second control method in the current method, during the output control of the power conversion device 20, by maintaining the output current from the standard circuit system within a possible range, the power that the DC / DC converter 21 of the power conversion device 20 can control can be left.

[0093] In principle, the output power of the standard circuit system is controlled by the DC / DC converter 21 of the power conversion device 20, and the output power of the boost circuit system is controlled by the boost circuit 11 of the boost connection box 10. Therefore, it can be said that the higher the ratio of the output current of the standard circuit system to the output current of the boost circuit system, the more power can be controlled on the power conversion device 20 side. Generally, since the DC / DC converter 21 of the power conversion device 20 is designed to have higher responsiveness than the boost circuit 11 of the boost connection box 10, the higher the power that can be controlled on the power conversion device 20 side, the better the response performance of the power control input to the power conversion device 20.

[0094] Also, according to Embodiments 1-3, since it is not necessary to connect between the boost connection box 10 and the power conversion device 20 with the communication line CL as in Embodiment 4, the cost can be reduced. Also, the installation flexibility can be enhanced. Also, it is easy to retrofit the boost connection box 10 to the power conversion device 20 that does not have a communication function.

[0095] In Embodiments 1-3, the boost connection box 10 that connects a plurality of solar cell strings (PV1, PV2) in parallel and the power conversion device 20 are made into separate devices. Thereby, depending on the combination of the boost connection box 10 and the power conversion device 20, it is possible to respond to the installation configurations of various solar cell strings, and it is possible to respond to various installation forms with a small number of device types. Therefore, the costs of the devices including the boost connection box 10 and the power conversion device 20 can be reduced.

[0096] As described above, the present disclosure has been described based on the embodiments. The embodiments are examples, and it is understood by those skilled in the art that various modifications are possible for each of the components and the combinations of each processing process, and such modifications are also within the scope of the present disclosure.

[0097] In the above embodiment, an example in which the power conversion device 20 activates output control due to receiving an output control command from the management server of the power transmission and distribution operator has been described. In this regard, the output control is also activated due to, for example, the output voltage of the inverter 22 rising beyond the limiter value, the output power of the inverter 22 rising beyond the limiter value, or the temperature inside the power conversion device 20 rising beyond the limiter value. The control unit 23 of the power conversion device 20 controls the output power of the power conversion device 20 at an output change rate corresponding to each cause of output control occurrence.

[0098] In the above embodiment, an example in which the control unit 23 of the power conversion device 20 controls the output power of the DC / DC converter 21 in order to control the output power of the power conversion device 20 has been described. In this regard, the control unit 23 may fix the boost ratio of the DC / DC converter 21 at 1 and control the output power of the power conversion device 20 by the duty control of the inverter 22. Also in this case, when the output power of the inverter 22 increases, the input voltage of the power conversion device 20 increases as the output power of the step-up connection box 10 becomes larger.

[0099] In the above embodiment, for the sake of simplicity of explanation, an example 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 step-up circuit system has been described. In this regard, a plurality of first solar cell strings PV1 may be connected in parallel to the standard circuit system. In this case, the first switch RY1 and the 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 powers) of the plurality of first solar cell strings PV1.

[0100] Similarly, a plurality of second solar cell strings PV2 may be connected in parallel to the step-up circuit system. In this case, the second switch RY2 and the step-up circuit 11 are installed in each string. The current (power) output from the plurality of step-up circuits 11 to the combined output wiring Wm is the sum of the output currents (output powers) of the plurality of second solar cell strings PV2.

[0101] The control unit 12 performs duty control on each of the plurality of boost circuits 11 connected in parallel so that the output voltages of the plurality of boost circuits 11 connected in parallel are equalized. In the power system described above, the control unit 12 controls the output power of each of the plurality of boost circuits 11 connected in parallel so that the total output power of the plurality of boost circuits 11 connected in parallel changes corresponding to the change rate of the output power of the boost connection box 10.

[0102] In the above embodiment, an example in which the first solar cell string PV1 and the second solar cell string PV2 having an open-circuit voltage lower than that of the first solar cell string PV1 are connected to the boost connection box 10 has been described. In this regard, a plurality of DC power sources other than solar cells having different open-circuit voltages can also be connected to the boost connection box 10. For example, a first battery pack and a second battery pack having an open-circuit voltage lower than that of the first battery pack may be connected to the boost connection box 10. The second battery pack is a battery pack having a smaller number of cells or modules connected in series than the first battery pack.

[0103] Note that the embodiment may be specified by the following items.

[0104] [Item 1] A boost circuit (11) capable of boosting the 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), An output wiring (Wb) of the boost circuit (11) and a combined output wiring (Wb) where the output wiring (W1) of the first DC power source (PV1) merges, A control unit (12) for controlling the boost circuit (11), and The combined 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 and outputs it to the power grid, The control unit (12) estimates whether or not the power conversion device (20) is under output control based on the output from the boost connection circuit (10) or the first DC power source (PV1) to the power conversion device (20). A boost connection circuit (10) characterized by this. According to this, by the output control of the power conversion device (20), it is possible to prevent the output voltage of the boost connection circuit (10) from rising to the limiter value and suddenly stopping. [Item 2] The control unit (12) estimates whether or not the power conversion device (20) is under output control based on the transition of the output power of the boost connection circuit (10). The boost connection circuit (10) according to claim 1. According to this, it is possible to determine whether or not the power conversion device (20) is under output control without receiving a control signal by communication from the power conversion device (20). [Item 3] A first current sensor (A2) for detecting the current flowing through the output wiring (Wb) of the boost circuit (11); A first voltage sensor (V2) for detecting the voltage of the output wiring (Wb) of the boost circuit (11); A second current sensor (A5) for detecting the current flowing through the combined output wiring (Wb); A second voltage sensor (V5) for detecting the voltage of the combined output wiring (Wb), further comprising: The control unit (12) Detects the output power of the boost circuit (11) based on the current detected by the first current sensor (A2) and the voltage detected by the first voltage sensor (V2), and the current detected by the second current sensor (A5) and the second voltage sensor (V5). Detects the output power from the boost connection circuit (10) to the power conversion device (20) based on the voltage detected by the sensor (V5), When it is estimated that the power conversion device (20) is under output control, the boost circuit (11) is controlled so that the output power of the boost circuit (11) changes in accordance with the change in the output power from the boost connection circuit (10) to the power conversion device (20). The boost connection circuit (10) according to claim 2. According to this, it is possible to prevent excessive power from being output from the boost connection circuit (10) to the power conversion device (20) during the output control of the power conversion device (20). [Item 4] The boost connection circuit (10) according to item 1, wherein the control unit (12) estimates whether or not the power conversion device (20) is under output control based on the transition of the output power of the first DC power source (PV1). According to this, it is possible to determine whether or not the power conversion device (20) is under output control without receiving a control signal by communication from the power conversion device (20). [Item 5] A first current sensor (A2) for detecting a current flowing through the output wiring (Wb) of the boost circuit (11); A first voltage sensor (V2) for detecting the voltage of the output wiring (Wb) of the boost circuit (11); A second current sensor (A3) for detecting a current flowing through the output wiring (W1) of the first DC power source (PV1); Further comprising a second voltage sensor (V5 or V3) for detecting the voltage of the combined output wiring (Wb) or the voltage of the output wiring (W1) of the first DC power source (PV1), The control unit (12) detects the output power of the boost circuit (11) based on the current detected by the first current sensor (A2) and the voltage detected by the first voltage sensor (V2), and detects the output power of the first DC power source (PV1) based on the current detected by the second current sensor (A3) and the voltage detected by the second voltage sensor (V5 or V3). The boost connection circuit (10) according to item 4, wherein when it is estimated that the power conversion device (20) is under output control, the boost circuit (11) is controlled so that the output power of the boost circuit (11) changes in accordance with the change in the output power of the first DC power source (PV1). According to this, it is possible to prevent excessive power from being output from the boost connection circuit (10) to the power conversion device (20) during the output control of the power conversion device (20). [Item 6] The boost connection circuit (10) according to item 1, wherein the control unit (12) determines that the power conversion device (20) is under output control when no power is being output from the first DC power source (PV1), and performs suppression control on the boost circuit (11). According to this, by detecting that no power is output from the first DC power source (PV1), it is possible to determine whether the power conversion device (20) is under output control. [Item 7] A first voltage sensor (V2 or V5) that detects the voltage of the output wiring (Wb) of the boost circuit (11) or the voltage of the combined output wiring (Wb), A second voltage sensor (V3) that detects the output voltage of the first DC power source (PV1), and further includes: When the voltage detected by the second voltage sensor (V3) is lower than the voltage detected by the first voltage sensor (V2 or V5), the control unit (12) determines that the power conversion device (20) is under output control. The boost connection circuit (10) according to item 6, characterized in that. According to this, by detecting that the output voltage of the first DC power source (PV1) is low and no current is output from the first DC power source (PV1), it is possible to determine whether the power conversion device (20) is under output control. [Item 8] A first current sensor (A1 or A2) that detects the current flowing through the input wiring (W2) or the output wiring (Wb) of the boost circuit (11), A second current sensor (A5 or A3) that detects the current flowing through the combined output wiring (Wb) or the output wiring (W1) of the first DC power source (PV1), and further includes: Based on the current detected by the first current sensor (A2) and the current detected by the second current sensor (A5 or A3), when it can be determined that no current is flowing from the first DC power source (PV1) and current is flowing from the boost circuit (11), the control unit (12) determines that the power conversion device (20) is under output control. The boost connection circuit (10) according to item 6, characterized in that. According to this, by detecting that no current is output from the first DC power source (PV1) while current is flowing from the boost circuit (11), it is possible to determine whether the power conversion device (20) is under output control. [Item 9] When the control unit (12) determines that the power conversion device (20) is in output control, based on the current detected by the first current sensor (A1 or A2) and the current detected by the second current sensor (A5 or A3), the boost circuit (11) is controlled so that the ratio of the output current of the first DC power supply (PV1) to the output current of the boost circuit (11) becomes a predetermined ratio. The boost connection circuit (10) according to item 6. According to this, during output control of the power conversion device (20), the power output from the first DC power supply (PV1) to the power conversion device (20) can be maintained as much as possible. [Item 10] The first DC power supply (PV1) and the second DC power supply (PV2) are solar cells (PV1, PV2), When the control unit (12) determines that the power conversion device (20) is not in output control, the boost circuit (11) is controlled by MPPT (Maximum Power Point Tracking). The boost connection circuit (10) according to any one of items 1 to 9. According to this, when the power conversion device (20) is not in output control, the power generated by the solar cell (PV2) connected to the boost circuit (11) can be maximized. [Item 11] The boost connection circuit (10) according to any one of items 1 to 10, A power conversion device (20) that converts the DC power supplied from the boost connection circuit (10) into AC power, A power conversion system (1) characterized by comprising. According to this, by the output control of the power conversion device (20), it is possible to avoid the output voltage of the boost connection circuit (10) rising to the limiter value and suddenly stopping.

Description of symbols

[0105] 1 Power conversion system, 2 systems, 10 step-up connection 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 solar cell string, RY1 first switch, RY2 second switch, D1 backflow prevention diode, V1 input voltage sensor, V2 step-up circuit output voltage sensor, V3 standard circuit voltage sensor, V5 confluence wiring voltage sensor, A1 input current sensor, A2 step-up circuit output current sensor, A3 standard circuit current sensor, A5 confluence wiring current sensor, W1, W2, Wb output wiring, Wm confluence output wiring, CL communication line, L1 reactor, C1 input capacitor, C2 output capacitor, D2 diode, S1 switching element.

Claims

1. A boost circuit capable of boosting the voltage of DC power output from a second DC power source having an open voltage lower than that of a first DC power source; The output wiring of the boost circuit and a combined output wiring where the output wiring of the first DC power source merges; A first current sensor for detecting the current flowing through the output wiring of the boost circuit; A first voltage sensor for detecting the voltage of the output wiring of the boost circuit; A second current sensor for detecting the current flowing through the combined output wiring; A second voltage sensor for detecting the voltage of the combined output wiring; And a control unit for controlling the boost circuit, The combined output wiring is connected to a power conversion device that converts the DC power supplied from this boost connection circuit into AC power and outputs it to the power grid, The control unit estimates whether the power conversion device is under output control based on the transition of the output power of this boost connection circuit, The control unit, Detects the output power of the boost circuit based on the current detected by the first current sensor and the voltage detected by the first voltage sensor, and detects the output power from this boost connection circuit to the power conversion device based on the current detected by the second current sensor and the voltage detected by the second voltage sensor. When it is estimated that the power conversion device is under output control, the boost circuit is controlled so that the output power of the boost circuit changes in response to the change in the output power from this boost connection circuit to the power conversion device. A boost connection circuit characterized by this.

2. A boost circuit capable of boosting the voltage of DC power output from a second DC power source having an open voltage lower than that of a first DC power source; The output wiring of the boost circuit and a combined output wiring where the output wiring of the first DC power source merges; A first current sensor for detecting the current flowing through the output wiring of the boost circuit; A first voltage sensor for detecting the voltage of the output wiring of the boost circuit; A second current sensor that detects a current flowing through the output wiring of the first DC power supply, A second voltage sensor that detects the voltage of the combined output wiring or the voltage of the output wiring of the first DC power supply, A control unit that controls the boost circuit, and The combined output wiring is connected to a power conversion device that converts DC power supplied from the boost connection circuit into AC power and outputs it to the power grid, Based on the transition of the output power of the first DC power supply, the control unit estimates whether the power conversion device is under output control, The control unit, Detects the output power of the boost circuit based on the current detected by the first current sensor and the voltage detected by the first voltage sensor, and detects the output power of the first DC power supply based on the current detected by the second current sensor and the voltage detected by the second voltage sensor. When it is estimated that the power conversion device is under output control, the boost circuit is controlled so that the output power of the boost circuit changes in response to the change in the output power of the first DC power supply. A boost connection circuit characterized by this.

3. A boost 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, The output wiring of the boost circuit and the combined output wiring where the output wiring of the first DC power supply merges, A first voltage sensor that detects the voltage of the output wiring of the boost circuit or the voltage of the combined output wiring, A second voltage sensor that detects the output voltage of the first DC power supply, A control unit that controls the boost circuit, and The combined output wiring is connected to a power conversion device that converts DC power supplied from the boost connection circuit into AC power and outputs it to the power grid, When no power is being output from the first DC power supply, the control unit determines that the power conversion device is under output control and suppresses the control of the boost circuit. The boost connection circuit is characterized in that when the voltage detected by the second voltage sensor is lower than the voltage detected by the first voltage sensor, the control unit determines that the power conversion device is under output control.

4. A boost circuit capable of boosting the voltage of DC power output from a second DC power source having an open voltage lower than that of a first DC power source; The output wiring of the boost circuit and a combined output wiring where the output wiring of the first DC power source merges; A first current sensor that detects a current flowing through the input wiring or output wiring of the boost circuit; A second current sensor that detects a current flowing through the combined output wiring or the output wiring of the first DC power source; A control unit that controls the boost circuit, and The combined output wiring is connected to a power conversion device that converts the DC power supplied from this boost connection circuit into AC power and outputs it to the power grid, When no power is being output from the first DC power source, the control unit determines that the power conversion device is under output control and performs suppression control on the boost circuit. Based on the current detected by the first current sensor and the current detected by the second current sensor, when the control unit can determine that no current is flowing from the first DC power source and current is flowing from the boost circuit, the control unit determines that the power conversion device is under output control. When it is determined that the power conversion device is under output control, based on the current detected by the first current sensor and the current detected by the second current sensor, the boost circuit is controlled so that the ratio of the output current of the first DC power source to the output current of the boost circuit becomes a predetermined ratio. The boost connection circuit is characterized by this.

5. The first DC power source and the second DC power source are solar cells, When the power conversion device is not under output control, the control unit performs MPPT (Maximum Power Point Tracking) control on the boost circuit. The boost connection circuit according to any one of claims 1 to 4, characterized by this.

6. The boost connection circuit according to any one of claims 1 to 5, a power conversion device that converts the DC power supplied from the boost connection circuit into AC power, and a power conversion system characterized by comprising the same.

Images