JP2016025804A - Booster connection device for photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control output current of a booster connection box so that the output current does not exceed allowable input current of a power conditioner, where the booster connection box comprises a plurality of booster circuits individually corresponding to a plurality of solar cell strings.SOLUTION: When it is determined that a power conditioner 6 is performing input current limitation, in the case that one booster circuit 51 having the highest input voltage of those of a plurality of booster circuits 51, 52, 53 is stopped and booster operation of the other booster circuits 52, 53 are activated; booster operation of the one booster circuit 51 having the highest input voltage is made to start to gradually raise output voltage of a booster connection box until release of the input current limitation, releasing the input current limitation by decreasing output current of the booster connection box without decreasing output.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a step-up connection device for a photovoltaic power generation system for collecting power generation outputs of a plurality of photovoltaic power generation units.

  In recent years, in a solar power generation system, it is desired to obtain a large total power output by installing a plurality of solar cell strings (power generation units) on the roof of a building. In this case, all solar cell strings may not have the same maximum output operating voltage due to roof structure and area limitations. Therefore, for example, as disclosed in Patent Document 1 below, a plurality of solar cell strings having different maximum output operating voltages are installed on the roof so as to match the output voltage of the solar cell string having the highest maximum output operating voltage. The output voltage of the other solar cell strings is boosted by a booster circuit, and the outputs of the plurality of solar cell strings are connected in parallel and output to the converter of the power conditioner. The converter controls the input current and the input voltage so as to maximize the input power by MPPT control so that the maximum output of the solar cell can be obtained.

  In addition, since the maximum allowable input current is limited due to the hardware configuration of this inverter, an input current limiting function using a limiter is provided so that the input current does not exceed a predetermined upper threshold in the boost control of the converter. Is limited so as not to increase the output power of the inverter. The boost control of such a converter is disclosed in, for example, Patent Document 2 below.

JP2013-50850A International Publication No. 2008/029711

  FIG. 3 shows the same solar power as the first solar cell string (maximum output 1230 W) in which six solar cell panels with a maximum output of 205 W (maximum output operating voltage 24.8 V, maximum output operating current 8.26 A) are connected in series. Second and third solar cell strings are connected to a power conditioner via a step-up junction box with second and third solar cell strings (maximum output of 820 W each) in which four battery panels are connected in series. Of the I-V characteristic of the input of the power conditioner when the output of the inverter is boosted by the booster circuit in accordance with the output voltage of the first solar cell string, and the current limit line and power limit line of the power conditioner input And an example of a voltage limit line, and the allowable input current of the power conditioner is 18A.

  At the average amount of sunshine, the input current of the inverter at the maximum power point is less than the allowable input current, but the day of the day when the amount of sunshine is the highest in the year and the temperature is relatively low from May to June. During this year, the output of the solar cell is maximized throughout the year. At this maximum output, the output voltage of the first solar cell string is 24.8V × 6 = 148.8V, the output current is 8.26A, and the booster circuit that boosts the output of the second and third solar cell strings The output current is (205 W × 4 / 148.8 V) × 98% (step-up efficiency) = 5.39 A. Therefore, the output current of the entire booster junction box is 8.26A + 5.39A × 2 = 19A, but the current value exceeds 18A which is the allowable input current of the power conditioner. The limiter is applied at point A, which is 18A. At this time, the first to third solar cell strings as a whole can only generate power of 1528.8V × 19A = 2872W, but can generate only 152V × 18 = 2737W, In some cases, power generation efficiency was poor.

  On the other hand, installing a large-capacity power conditioner for a limited period in which the output becomes the maximum scale has a problem that the cost performance deteriorates.

  Therefore, the present invention is as large as possible even in a situation where the input current limitation of the power conditioner occurs in the step-up connection device for a photovoltaic power generation system that collects the power generated by a plurality of solar cell strings and outputs the collected power to the power conditioner. It aims at making it possible to obtain generated electric power.

  In order to achieve the above object, the present invention takes the following technical means.

  That is, the present invention collects generated power input from a plurality of photovoltaic power generation units (for example, solar cell strings) and performs predetermined power conversion for limiting input current so that the input current does not exceed a predetermined upper limit threshold. Step-up connection device for a photovoltaic power generation system that outputs to a power supply unit (for example, a power conditioner that converts DC generated power into AC power linked to AC system power). And a control unit that controls the boosting operation of the boosting circuit, and the control unit stops the boosting operation of one boosting circuit having the highest input voltage among the plurality of boosting circuits. And determining means for determining whether or not the power converter is performing input current limitation when the other booster circuit is being boosted, and based on the determination result of the determining means, And it is characterized in that it is configured to step-up operation to initiate (claim 1).

  The other booster circuit preferably performs MPPT control so that the input power (generated power) from the corresponding power generation unit is maximized, and the power conversion unit further includes the boost connection device of the present invention. In this case, the output voltage of the boosting connection device is a voltage determined by the MPPT control of the input power of the power converter. The output sides of the plurality of booster circuits can be connected to an output unit having a common capacitor, and the collected power can be output from the output unit to the power conversion unit. The one booster circuit can be constituted by a boost chopper circuit that can control the boosting rate by increasing / decreasing the on-duty ratio of the switching element, and the boosting operation is stopped when the on-time of the switching element is zero. The input power of one booster circuit is output to the power conversion unit without being boosted, and the IV characteristic curve of the input power of the power conversion unit is changed as the ON time of the switching element is increased, thereby converting the power The output voltage of the step-up connection device (input voltage of the power conversion unit) can be increased by MPPT control of the unit. In addition, the one booster circuit having the highest input voltage may be fixedly set in advance, and the one corresponding to the power generation unit having the highest output voltage according to the power generation status of each power generation unit. A booster circuit may be selectively set.

  According to the step-up connection device for a photovoltaic power generation system of the present invention, the one step-up circuit stops the step-up operation during normal operation and outputs the input power from the corresponding power generation unit to the power conversion unit without stepping up. Therefore, there is no loss due to boosting the generated power of the power generation unit having a high output voltage, and the power efficiency can be maintained as high as possible. On the other hand, when the determination unit of the control unit determines that the input current limitation is performed in the power conversion unit, the boosting operation of the one booster circuit is started. When one booster circuit is boosted, the IV characteristic of the output power of the boosting connection device changes, the voltage at the maximum power point increases and the current at the maximum power point decreases, and the allowable input of the power conversion unit Also in the current, it is possible to obtain larger generated power than before the boosting operation.

  Preferably, during the boosting operation of the one booster circuit, when the determination unit determines that the input current limitation is performed in the power converter, the on-time or the on-duty ratio of the switching element of the one booster circuit is increased by a predetermined amount. On the other hand, when the determination means determines that the input current limitation is not performed in the power conversion unit, the control unit can be configured to decrease the on-time or on-duty ratio of the switching element of one booster circuit by a predetermined amount. . The determination by the determination unit is preferably performed after a predetermined time (for example, several tens of milliseconds) has elapsed after increasing or decreasing the ON time or ON duty ratio of the switching element of one booster circuit. Alternatively, it is possible to avoid the determination based on the unstable state of the voltage and current due to the response delay immediately after the increase / decrease of the on-duty ratio.

  The step-up connection device for a photovoltaic power generation system according to the present invention further includes an output voltage sensor that detects an output voltage of the step-up connection circuit, and an output current sensor that detects an output current of the step-up connection circuit, and the determination unit When the output voltage detected by the output voltage sensor varies, but the output current detected by the output current sensor does not vary, it is determined that the power conversion unit is limiting the input current. (Claim 2). According to this, it is possible to determine whether or not the boosting connection device alone is in the input current limiting state.

  Moreover, in the step-up connection device for a photovoltaic power generation system according to the present invention, the determination unit is configured such that the power conversion unit is configured to limit the input current based on information acquired through communication with a control unit that controls the operation of the power conversion unit. (Claim 3). According to this, since it determines based on the information from the control part of the power converter which is performing input current restriction control, it can be judged correctly whether it is in an input current restriction state.

  Note that the step-up connection device for a photovoltaic power generation system of the present invention can be incorporated in the power conversion device. Further, in the present invention, each of the booster circuits is a circuit that outputs and outputs an input voltage when the boosting operation is stopped, such as a boost chopper circuit or a transformer having the same number of primary side windings as the number of primary side windings. An insulating flyback converter or the like can be suitably used.

  According to the step-up connection device for a photovoltaic power generation system according to claim 1 of the present invention, the one step-up circuit stops the step-up operation during normal operation, and does not boost the input power from the corresponding power generation unit. Since it outputs to a conversion part, there is no loss by boosting the generated electric power of the electric power generation part with a high output voltage, and it can maintain power efficiency as high as possible. On the other hand, when the determination unit of the control unit determines that the input current limitation is performed in the power conversion unit, the boosting operation of the one booster circuit is started. When one booster circuit is boosted, the IV characteristic of the output power of the boosting connection device changes, the voltage at the maximum power point increases and the current at the maximum power point decreases, and the allowable input of the power conversion unit Also in the current, it is possible to obtain larger generated power than before the boosting operation.

  According to the step-up connection device for a photovoltaic power generation system according to claim 2 of the present invention, it is possible to determine whether or not the step-up connection device alone is in the input current limiting state.

  According to the step-up connection device for a photovoltaic power generation system according to claim 3 of the present invention, since the determination is based on the information from the control unit of the power conversion unit that performs the input current limit control, whether or not the input current limit state exists Can be accurately determined.

It is a schematic circuit block diagram of a solar power generation system provided with the pressure | voltage rise connection apparatus which concerns on one Embodiment of this invention. It is operation | movement explanatory drawing of the same boost connection circuit. It is a characteristic graph for demonstrating the change of the IV characteristic of the input power of a power conditioner.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a photovoltaic power generation system according to an embodiment of the present invention. The photovoltaic power generation system includes first to third three solar cell strings 1, 2, 3 (solar power generation unit). A step-up connection device 5 connected to the plurality of solar cell strings 1, 2, 3 to collect the generated power of the solar cell strings 1, 2, 3 and output it from a common output unit 4; It is mainly composed of a power conditioner 6 (power conversion unit) that inputs the generated power output from the output unit 4 of the device 5.

  The power conditioner 6 includes a converter 7 that boosts the generated power input from the boost connection device 5 to a predetermined voltage corresponding to the system voltage, and AC power that is connected to the system power by the generated power boosted by the converter 7. The inverter 8 to be converted is mainly configured, and the output of the inverter 8 is connected to the system. Converter 7 is generally composed of a boost chopper circuit that can control the boost ratio by changing the on-duty ratio of the switching element. The inverter 8 is generally a full-bridge voltage source bridge inverter, and is configured by connecting four switching elements such as IGBTs in an H-bridge form and connecting a feedback diode in parallel to each switching element, The output current is controlled by performing so-called current mode control (current control of the voltage source inverter), and AC power is output. An input voltage sensor 9 for detecting an input voltage and an input current sensor 10 for detecting an input current are provided on the input side of the converter 7. The detection signals of these sensors 9 and 10 are controlled by a control unit. 11 is input. The operations of the converter 7 and the inverter 8 are controlled by a control signal from the control unit 11. In particular, in this embodiment, the hill-climbing method is performed with reference to the input voltage detection value and the input current detection value detected by the sensors 9 and 10. The input voltage target value is determined so that the input power of the converter 7 is maximized by the conventionally known MPPT control such as, and the input current target value is calculated based on the difference between the input voltage target value and the input voltage detection value. The on-duty ratio of the switching element of the converter 7 is controlled so that the input current target value is obtained. Further, for reasons of hardware configuration such as circuit components constituting the converter 7, an upper limit threshold is provided for the input current target value of the converter 7, and the input current of the converter 7 is a predetermined upper limit threshold (for example, 18A). The control is configured to limit the input current so as not to exceed.

  Each solar cell string 1, 2, 3 is formed by connecting a plurality of solar panels in series. In this embodiment, for example, the maximum output of the first solar cell string 1 is 1230 W, and the maximum output operating voltage is 148. .8V, the maximum output operating current is 8.26A, the maximum output of the second and third solar cell strings 2, 3 is 820W, the maximum output operating voltage is 99.2V, and the maximum output operating current is 8.26A. Has been.

  The booster connection device 5 includes a first booster circuit 51 that boosts the generated power input from the first solar cell string 1 and a second booster circuit 52 that boosts the generated power input from the second solar cell string 2. And a third booster circuit 53 that boosts the generated power input from the third solar cell string 3, and a control unit 54. The output sides of the first to third booster circuits 51, 52, 53 are connected in parallel to the output unit 4, and the output unit 4 is provided with a capacitor 41 (smoothing capacitor). The input voltage sensor 12 for detecting the input voltage from the second and third solar cell strings 2 and 3 and the input current are detected on the input side of the second and third booster circuits 52 and 53. The output current sensor 13 is provided with an output voltage sensor 14 and an output current sensor 15 for detecting the voltage across the capacitor 41 (the output voltage of the output unit 4). . These sensors 12, 13, 14, and 15 are connected to the control unit 54, and each detection value is input to the control unit 54. The control unit 54 calculates the power output from the output unit 4 to the power conditioner 6 based on the detection values of the output voltage sensor 14 and the output current sensor 15 of the output unit 4 and detects the output voltage per unit time. The power conditioner 6 monitors the fluctuation amount of the output current detection value with respect to the fluctuation amount of the value, and when the output current detection value does not fluctuate beyond a predetermined threshold despite the fluctuation in the output voltage detection value. A determination circuit or a determination program (determination unit) that determines that the input current is limited is provided. Note that the above determination is preferably performed based on the average value of the plurality of output current detection values acquired immediately before, thereby absorbing fluctuations in voltage and current due to MPPT control of the converter 7 of the power conditioner 6. Thus, it is possible to more accurately determine whether or not the input current is limited.

  Each of the first to third booster circuits 51, 52, and 53 can have a conventionally known appropriate booster circuit configuration. Specifically, the first to third booster circuits 51, 52, and 53 are output from the control unit 54 to the respective booster circuits 51, 52, and 53. It can be configured by a conventionally known boost chopper circuit capable of controlling the boost ratio by changing the on-duty ratio of the switching element by the control signal.

  In the present embodiment, the boost control method of the first booster circuit 51 (one booster circuit) corresponding to the first solar cell string 1 having the largest maximum output operating voltage, the second and third booster circuits 52, The step-up control method of 53 (another step-up circuit) is different. As the boost control method of the second and third boost circuits 52 and 53, conventionally known MPPT control is adopted, and the input voltage detection value and the input current detection value detected by the sensors 12 and 13 are referred to. On the other hand, the input voltage target value is determined so that the input power of each booster circuit 52, 53 is maximized by the conventionally known MPPT control such as the hill-climbing method, and the input is performed based on the difference between the input voltage target value and the input voltage detection value. A current target value is calculated, and the on-duty ratios of the switching elements of the booster circuits 52 and 53 are controlled so as to be the calculated input current target value.

  Next, the boost control method of the first booster circuit 51 will be described. The input current of the power conditioner 6 when the amount of sunshine is relatively small and the input power of the power conditioner 6 is operating near the maximum power point. Is less than the upper threshold value of 18A, the output current of the boosting connection device 5 varies along the IV characteristic curve, so that the control unit 54 (determination means) in the power conditioner 6 Without determining that the input current is limited, the switching element of the first booster circuit 51 is always off (on time 0), the boost operation is stopped, and the output of the first solar cell string 1 is output. The voltage is output to the power conditioner 6 via the output unit 4 without being boosted.

  On the other hand, when the solar cell outputs the maximum generated power throughout the year, the current at the maximum power point of the IV characteristic curve of the input power of the power conditioner 6 is the upper threshold value as described above with reference to FIG. 18A, the target input current value in the MPPT control of the converter 7 of the power conditioner 6 is limited to 18A, and the output current of the boosting connection device 5 is also limited to 18A. In the vicinity of the point A in FIG. Stagnant. In such an input current limiting state, even if the output voltage of the boosting connection device 5 increases or decreases due to the switching timing of the converter 7 or the second and third booster circuits 52 and 53, the balance of instantaneous passing power, etc., the output current is 18A. If the control unit 54 detects such a state, the power conditioner 6 determines that the input current is limited, and the on-time of the switching element of the first booster circuit 51 is set to a predetermined minute value. Increase the voltage by a small amount to start the boosting operation. Then, as shown in FIG. 2 which is an enlarged view between the points A and B in FIG. 3, the IV characteristic curve of the input power of the converter 7 slightly changes, and the same power as the point A before the boost operation starts. The voltage at point C1 rises by ΔV from the voltage at point A, and the current at point C1 decreases by ΔA from the current at point A. On the other hand, in the MPPT control of the converter 7, the input current and the input voltage are controlled so as to maximize the power along the changed IV characteristic curve. Therefore, after several milliseconds to several tens of milliseconds, By the MPPT control, the current and voltage converge at a point B1 where the changed IV characteristic curve and the input current upper limit threshold line intersect, and the input current limit state is entered again. When the control unit 54 determines that the input current limit state has been reached again, similarly, by increasing the on-time of the switching element of the first booster circuit 51 by a predetermined minute amount, the points C2, B2, C3,. The input voltage of the converter 7 (the output voltage of the boosting connection device 5) is gradually boosted, and the IV characteristic curve and the upper limit threshold line at which the current at the maximum power point becomes 18A (upper limit threshold) Is boosted to the vicinity of the point B where the points intersect (point B is the maximum power point).

  When the on-time of the switching element of the first booster circuit 51 is further increased by a predetermined small amount in the vicinity of the point B and the input current is limited, the intersection of the changed IV characteristic curve and the upper limit threshold line Is lower than the voltage at the intersection B between the IV characteristic curve before the change and the upper limit threshold line, and the current at the maximum power point at this time is lower than 18 A which is the upper limit threshold. Converter 7 does not limit the input current, and therefore control unit 54 of boost connection circuit 5 determines that the input current is not limited. Also, when the amount of sunshine decreases and the current at the maximum power point in the IV characteristic curve at that time becomes smaller than 18A which is the upper limit threshold, the control unit 54 determines that the input current is not limited. When it is determined that the input current is not limited, the control unit 54 gradually decreases the boosting amount by decreasing the ON time of the switching element of the first boosting circuit 51 by a predetermined minute amount. The control is configured as follows. Note that when the ON time of the switching element of the first booster circuit 51 is reduced to 0, the boosting operation is naturally stopped.

  The control speed for increasing / decreasing the ON time of the switching element of the first booster circuit 51 described above is sufficiently slower than the control speed in the MPPT control of the converter 7, and the ON time of the switching element of the first booster circuit 51 is reduced. It is preferable not to increase or decrease the ON time of the switching element of the first booster circuit 51 until the input voltage and input current of the converter 7 are stabilized by the MPPT control of the converter 7 immediately after the increase and decrease.

  The operation of this embodiment will be described below. As described above, when the first booster circuit 51 is not boosted, the power output is 2736 W at point A. However, according to the present embodiment, it is assumed that the voltage at point B is xV and the boosting efficiency is 98%. The total output current of the first to third booster circuits 51 is (1230 W / x) × 98% + (820 W / x) × 98% = 18 A, and therefore x = 156.3 V, 156.3 V × 18 A = 2813 W Total power output can be obtained, and an output improvement of about 77 W can be achieved.

  The present invention is not limited to the above-described embodiments, and the design can be changed as appropriate. For example, in the above embodiment, the determination of the input current limit state in the control unit 54 of the boost connection device 5 is performed based on the fluctuation state of the output current and the output voltage of the boost connection device 5, but the control unit 11 of the power conditioner 6 is used. Is connected to the control unit 54 of the booster connection device 5 to output a determination signal indicating whether or not the control unit 11 of the power conditioner 6 is limiting the input current to the control unit 54 of the booster connection device 5. The control unit 54 of the step-up connection device 5 may be configured to determine whether or not the power conditioner 6 is performing input current limitation based on the determination signal (information acquired through communication). it can. When the allowable input current of the connected power conditioner 6 is known, the power conditioner is determined based on whether or not the output current of the boosting connection device 5 has reached the allowable input current of the power conditioner 6. It is also possible to determine whether or not the na 6 is limiting the input current.

  In the above embodiment, the boost control is performed so as to gradually increase or decrease the boost amount after the start of the boost operation of the first boost circuit 51 of the boost connection device 5, but the switching element of the first boost circuit 51 is turned on. The time may be increased or decreased relatively. Moreover, although the increase / decrease control of the on-time is performed based only on whether or not the power conditioner 6 is in the input current limit state, has the output power of the booster connection device 5 increased / decreased by increasing / decreasing the on-time? It can also be based on whether or not. That is, when the output power is not increased or decreased before and after the on-time is increased, the on-time may be decreased even when it is determined that the input current is in the limited state.

DESCRIPTION OF SYMBOLS 1 Solar power generation part 2 Solar power generation part 3 Solar power generation part 5 Boosting connection apparatus 51 One booster circuit 52 Other booster circuit 53 Other booster circuits 54 Control part 6 Power converter 14 Output voltage sensor 15 Output current sensor

Claims (3)

Step-up connection device for photovoltaic power generation system that collects generated power input from a plurality of photovoltaic power generation units and outputs the collected power to a predetermined power conversion unit that limits the input current so that the input current does not exceed a predetermined upper limit threshold Because
A plurality of booster circuits provided corresponding to the respective power generation units, and a control unit for controlling the boosting operation of the booster circuit, the control unit having the highest input voltage among the plurality of booster circuits. Determining means for determining whether or not the power conversion unit is performing input current limitation when stopping the boosting operation of the boosting circuit and boosting the other boosting circuit, and determining by the determining means A step-up connection device for a photovoltaic power generation system, configured to start a step-up operation of the one step-up circuit based on a result.   The boost connection device for a photovoltaic power generation system according to claim 1, further comprising: an output voltage sensor that detects an output voltage of the boost connection circuit; and an output current sensor that detects an output current of the boost connection circuit, The determination means determines that the power conversion unit performs input current limitation when the output voltage detected by the output voltage sensor varies but the output current detected by the output current sensor does not vary. A step-up connection device for a photovoltaic power generation system.   2. The step-up connection device for a photovoltaic power generation system according to claim 1, wherein the determination unit is configured to limit the input current of the power conversion unit based on information acquired by communication with a control unit that controls the operation of the power conversion unit. It is determined whether or not the step-up connection device for a photovoltaic power generation system is characterized.

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