JP3762036B2 - Power conditioner in solar power generation system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conditioner in a photovoltaic power generation system.
[0002]
[Prior art]
An outline of a conventional solar power generation system will be described with reference to FIG. 9. Reference numeral 2 denotes a solar battery, reference numeral 4 denotes a system power supply, and a power conditioner 6 is provided between the solar battery 2 and the system power supply 4. . The power conditioner 6 includes a smoothing capacitor 8, a booster circuit 10, a discharge circuit 14, an inverter circuit 16, a power conditioner control unit 18, and the like.
[0003]
The power conditioner 6 smoothes the DC voltage of the solar cell 2 with the smoothing capacitor 8, boosts the switch element 10 b in the booster circuit 10 by turning it on and off under the control of the power conditioner controller 18, and then discharges the discharge circuit 14. The switching elements 16a to 16d in the inverter circuit 16 are on / off controlled under the control of the power conditioner control unit 18 to be converted into alternating current and supplied to the system power supply 4 side as a load. . The discharge circuit 14 discharges the electric charges of the smoothing capacitor 8 and the smoothing capacitor 10c in the booster circuit 10 through the discharge resistor 14a when the internal switch element 14b is turned on under the control of the power conditioner control unit 18.
[0004]
[Problems to be solved by the invention]
In such a photovoltaic power generation system, it is necessary that the solar cell has an output characteristic capable of supplying power necessary for its operation to the power conditioner. Since the output characteristics of solar cells change according to the illuminance, when starting the operation of the inverter, it is determined whether the solar battery has the output characteristics that can supply the minimum power that can be operated. It is first necessary to make a decision. Since the power conditioner is stopped during the determination of the start condition, if the DC voltage corresponding to the power consumption during the stop of the solar battery is equal to or higher than the set voltage, the solar battery can operate at the minimum power conditioner. The power conditioner determines the start of operation by determining that it has an output characteristic capable of supplying power. This will be further described with reference to FIG. In FIG. 10 for determining the starting condition, the vertical axis represents the generated power of the solar cell and the horizontal axis represents the DC voltage as the output characteristics of the solar cell 2. V0 is the set voltage. With this set voltage V0 as a reference, since the DC voltage V1 corresponding to the power consumption during stop of the output characteristic (1) is equal to or higher than the set voltage V0, the start condition is determined that the power conditioner can be operated. Further, since the DC voltage V2 corresponding to the power consumption during stop of the output characteristic (2) is equal to or lower than the set voltage V0, the start condition is determined that the power conditioner is not operable. In the case of output characteristic (1), the curve exceeds the minimum operable power, so the determination of the start condition is correct. In the case of the output characteristic (2), the start condition is correctly determined because the curve does not exceed the minimum operable power.
[0005]
However, the number of used solar cells 2 is changed depending on how the user uses, the temperature characteristics change, the number of solar cells 2 in series or the number of parallel changes, or the type of solar cell 2 Depending on various factors such as changes, the output characteristics may change, for example, to (3) or (4). Then, when the start condition is determined for the output characteristic (3) with reference to the set voltage V0, the DC voltage V3 corresponding to the power consumption during the stop is equal to or lower than the set voltage V0. If it is possible, the start condition is determined, but the curve of the output characteristic (3) exceeds the minimum operable power and should be operable. Similarly, if the start condition is determined for the output characteristic (4) based on the set voltage V0, the DC voltage V4 corresponding to the power consumption during the stop is equal to or higher than the set voltage V0, so that the power conditioner can be operated. If it is, the start condition is determined, but the curve of the output characteristic (3) should not be able to operate because it does not exceed the minimum operable power.
[0006]
Therefore, according to the conventional power conditioner, although it is possible to supply electric power that can be operated from the solar cell, it is determined that the operation cannot be performed in the determination of the start condition, and the operation is not started at any time. Then, even if it is determined that the operation is possible, since the solar cell cannot supply the operable electric power, the operation is not started at all, and the operation becomes extremely unstable.
[0007]
[Means for Solving the Problems]
In the power conditioner of the present invention, the discharge circuit is provided inside, and after measuring the power consumption of the solar cell in operation stop, the power consumption of the solar cell is changed by the discharge operation by the discharge circuit. The operating point voltage of the solar cell is changed from the operating point voltage of the solar cell before discharging by the discharging circuit and the operating point voltage of the solar cell after discharging by the discharging circuit . A DC voltage expected value is calculated, and the DC voltage expected value is compared with a DC voltage capable of minimum operation, so that the DC voltage expected value is greater than the DC voltage capable of minimum operation. The above-described problem is solved by being configured to start operation based on the determination result .
In the power conditioner of the present invention, the booster circuit is provided inside, and after measuring the power consumption of the solar cell during operation stop, the power consumption of the solar cell is changed by the boosting operation by the booster circuit. The operating point voltage of the solar cell is changed with the operating point voltage of the solar cell before boosting by the boosting circuit and the operating point voltage of the solar cell after boosting by the boosting circuit. The estimated DC voltage value for power is calculated, and the estimated DC voltage value is compared with the DC voltage that can be operated at a minimum, and the estimated DC voltage value is larger than the DC voltage that can be operated at the minimum. The above-described problem is solved by being configured to start operation based on the determination result.
Further, in the power conditioner of the present invention, a capacitor for smoothing the DC voltage of the solar cell, a booster circuit having a switch element and a capacitor in parallel with the capacitor for boosting the smoothing capacitor output, a discharge resistor, A discharge circuit comprising a switch element controlled to discharge the charge of the capacitor via the discharge resistor; and an inverter circuit comprising a plurality of switch elements for converting the booster circuit output into alternating current; In a power conditioner in a solar power generation system including a power conditioner control unit that controls on / off of each switch element, the power conditioner control unit controls on / off of the switch element in the discharge circuit, and The power consumption of the solar cell when the inverter is stopped While changing the operating point voltage and the operating point voltage at the power consumption of the solar cell during the operation of the discharge circuit, the predicted DC voltage at the minimum operable power of the solar cell is calculated from the operating point voltage The DC voltage expected value is compared with the DC voltage capable of minimum operation, and the operation is started based on the determination result that the DC voltage expected value is larger than the DC voltage capable of the minimum operation. The above-described problem is solved by being configured as described above.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
FIG. 1 is a circuit diagram of a transformerless type power conditioner in a photovoltaic power generation system according to an embodiment of the present invention. The parts corresponding to those of the conventional one shown in FIG. As for the part related to the reference numeral, only names are listed, and detailed description thereof is omitted. In FIG. 1, 2 is a solar cell, 4 is a system power supply, 6 is a power conditioner, 8 is a smoothing capacitor, 10 is a booster circuit, 14 is a discharge circuit, 16 is an inverter circuit, 18 is a power conditioner controller, and 20 is a direct current. This is a resistance for current measurement. The booster circuit 10 includes an inductor 10a, a switch element 10b, a smoothing capacitor 10c, and a backflow prevention diode 10d, the discharge circuit 14 includes a discharge resistor 14a and a switch element 14b, and the inverter circuit 16 includes four switch elements 16a that are H-bridge connected. To 16d.
[0010]
The power conditioner control unit 18 controls on / off of the switch element 10b in the booster circuit 10, the switch element 14b in the discharge circuit 14, and the switch elements 16a to 16b in the inverter circuit 16 to supply the direct current of the solar battery 2 to the system power supply. 4 is supplied as an alternating current. Since this operation is well known, detailed description thereof is omitted.
[0011]
The power conditioner control unit 18 measures the DC voltage of the solar cell 2, measures the DC current from the voltage across the DC current measuring resistor 20 and the resistance value thereof, and based on these measurement data. Obtain power consumption measurement data.
[0012]
Hereinafter, the operation control in the power conditioner control unit 18 will be described with reference to FIGS. 2 to 4.
[0013]
First, the case where the solar cell 2 has the output characteristic {circle around (1)} in FIG. 2 will be described. The power conditioner control unit 18 first determines the start condition, and first, the discharge circuit 14 is stopped during operation stop at step n1. The switch element 14b is turned off, and the power consumption Pa during stoppage of the solar cell 2 and the corresponding DC voltage Va (= V1) are measured in step n2, and then the switch element 14b is turned on in step n3. Then, the discharge circuit 14 is operated. In step n4, the power consumption Pb of the solar cell 2 during operation of the discharge circuit 14 and the corresponding DC voltage Vb (= V1 ′) are obtained. When the DC voltages Va (= V1) and Vb (= V1 ′) are obtained when the operation is stopped and when the discharge circuit is operated, the power conditioner control unit 18 performs a calculation for determining the starting condition in step n5. . The calculated value based on the determination formula for the start condition shown in step n5 is the expected DC voltage Vc (determination voltage) of the solar cell 2 at the minimum operable power Pc. Here, the minimum operable power Pc is a known value. Therefore, the power conditioner control unit 18 substitutes each value of Va (= V1), Vb = (V1 ′), Pa, Pb, and Pc in this calculation formula, so that the DC voltage expected value Vc, that is, the determination voltage Vc. Can be obtained.
[0014]
After calculating the determination voltage Vc in step n5 in this way, in step n6, it is determined whether or not the determination voltage Vc is greater than a DC voltage that enables the minimum operation of the power conditioner 6. As a result of this determination, if the determination voltage Vc is larger than the DC voltage that allows the minimum operation, the power conditioner control unit 18 can operate when the solar cell 2 has the output characteristic 1 (circled 1 in FIG. 2). Operation is started at step n7.
[0015]
Similarly, when the solar cell 2 has the output characteristic {circle around (2)}, the power conditioner control unit 18 executes the flowchart of FIG. 4 and Va is V2 and Vb is V2 ′. In the case of {circle around (2)}, in step n6, it is determined that the determination voltage Vc is not within the minimum operable voltage range, and the operation is not started.
[0016]
Similarly, when the solar cell 2 has the output characteristic (3), the power conditioner control unit 18 executes the flowchart of FIG. 4 and Va is V3 and Vb is V3 ′. In the case of {circle around (3)}, in step n6, it is determined that the determination voltage Vc is within the minimum operable voltage range, and the operation is started.
[0017]
Similarly, when the solar cell 2 has the output characteristic (4), the power conditioner control unit 18 executes the flowchart of FIG. 4 and Va is V4 and Vb is V4 ′. In the case of (4), at step n6, it is determined that the determination voltage Vc is not within the minimum operable voltage range, and the operation is not started.
[0018]
It is to be noted that the power conditioner control unit 18 similarly determines the start condition that the operation is started or not started by turning on / off the switch element 10b in the booster circuit 10 instead of operating the discharge circuit 14 in the above-described embodiment. Is possible.
[0019]
In the above-described embodiment, the power consumption by the discharge resistor 14a is controlled by turning on and off the switch element 14b in the discharge circuit 14, and the DC voltage Va at the stopped power consumption Pa and the power consumption Pb during the discharge circuit operation. However, the rechargeable battery 14c may be connected in series with the discharge resistor 14a and the switch element 14b in the discharge circuit 14 as shown in FIG. Since it is uneconomical to consume power by the discharge resistor 14a, the rechargeable battery 14c is charged with the discharge current from the discharge resistor 14a, while the measurement operating point is changed by the rechargeable battery 14c. I do not care. When the rechargeable battery 14c is used in this way, the power conditioner can be used for other purposes using the power charged in the rechargeable battery 14c while determining the activation condition for starting operation. The operational efficiency of 6 is improved.
[0020]
In the above-described embodiment, the measurement operation point is changed by controlling the power consumption by the discharge resistor 14a in the discharge circuit 14, but the power consumption Pb during the discharge circuit operation is illustrated as a reference example . 6, the DC voltage Vb at that time is in a voltage range Vzone in which the power conditioner 6 can operate (operation is stopped outside this range). You may make it start operation by. In this case, it is not necessary to use the complicated calculation formula as described above, and erroneous determination of the start condition due to the calculation error of the calculation formula in the power conditioner control unit 18 is reduced. In FIG. 6, when the solar cell 2 has an output characteristic 5 (circled 5 in FIG. 6) , the DC voltage Vb during operation of the discharge circuit 14 is within the operable voltage range Vzone, so that the power of the solar cell 2 Means that the power conditioner 6 maintains the minimum power that can be operated, and the determination of the start condition is that the power conditioner 6 can be operated, and the solar cell 2 has other output characteristics 6 (circled in FIG. 6). 6) and 7 (circled 7 in FIG. 6) , since the DC voltage Vb during operation of each discharge circuit 14 is not within the operable voltage range Vzone, the determination of the start condition is performed by the power conditioner 6 Cannot be started.
[0021]
In the above-described embodiment, the measurement operating point is changed by controlling the power consumption by the discharge resistor 14a in the discharge circuit 14, but the type of the solar cell 2 when it is once installed. Since the output characteristics change according to the illuminance, the DC voltage in the power consumption during the stop should remain as it is. Therefore, when the solar cell 2 has such output characteristics, the slope of the output characteristics increases as the illuminance increases and decreases as the illuminance decreases, but it follows a certain correlation. Therefore, once the operation of the power conditioner 6 is started and the change in the measurement operation point of the solar cell 2 is measured as in the above-described embodiment, the output of the solar cell 2 is shown as a reference example in FIG. The shape of the characteristic 8 (circled 8 in FIG. 7) or 9 (circled 9 in FIG. 7) is predicted, and the predicted data is stored. In this case, the slopes α8 and α9 of the change in the operating point voltage of the output characteristics 8 (circled 8 in FIG. 7) and 9 (circled 9 in FIG. 7) when the operation is started from the stop time, respectively. The operating point voltages β8 and β9 at the time of stopping are stored, and if the operating point voltages β8 and β9 at the time of stopping are constant and the slopes α8 and α9 are different, the output characteristics of the solar cell 2 are different as shown in FIG. Will have occurred. Therefore, the start condition may be determined from the inclinations α8, α9 and the operating point voltages β8, β9 at the time of stop.
[0022]
In the above-described embodiment, the operating point is changed by controlling the power consumption by the discharge resistor 14a in the discharge circuit 14, but the periphery of the solar cell 2 becomes dark during the evening or the like during operation. Then, the DC voltage of the solar cell 2 when the operation is stopped when the DC voltage of the solar cell 2 is below the minimum operable voltage and the operation of the power conditioner 6 is stopped is stored. When the surroundings of the solar cell 2 become brighter in the morning, the start condition is that the power conditioner 6 starts operation when the DC voltage of the solar cell 2 exceeds the stored DC voltage at the time of stop. The determination condition may be used.
[0023]
In the above-described embodiment, the operating point is changed by controlling the power consumption by the discharge resistor 14a in the discharging circuit 14, but a plurality of operating points are measured as shown in FIG. The operating point voltage at the minimum power that can be operated from the operating point may be calculated by curve approximation, and the operation may be started when the operating point voltage exceeds the minimum operating voltage range.
[0024]
In the above-described embodiment, the operating point is changed by controlling the power consumption by the discharge resistor 14a in the discharge circuit 14, but the solar cell 2 at the start of operation of the power conditioner 6 is changed. The determination value of the DC voltage may be changed depending on whether the operation is successful or unsuccessful so that the power conditioner 6 can start the operation when the operation is possible.
[0025]
In the above-described embodiment, the operating point is changed by controlling the power consumption by the discharge resistor 14a in the discharge circuit 14, but from the maximum generated power during operation and the DC voltage at the time of stoppage. A conversion table for obtaining a voltage for determining start-up is created in advance, and the maximum generated power is measured when operation is actually possible. At that time, the operation is temporarily stopped and the DC voltage at this time is measured. From the two measured values of the measured maximum generated power and the measured DC voltage, the voltage required for activation is determined and stored using the conversion table. When stopping, the operation may be started when the determination value exceeds the DC voltage. In this case, of course, the calculation may be performed using mathematical formulas instead of the conversion table for activation determination.
[0026]
【The invention's effect】
As described above, according to the present invention, the operating point voltage of the solar cell is changed by changing the power consumption of the solar cell, and the curve of the output characteristics of the solar cell exceeds the minimum operable power from each operating point voltage. The start condition for starting the operation is determined based on the predicted value of whether or not the start condition is determined. It is extremely unstable, such as it does not start anytime after it has been made possible, or even if it is determined that it can be driven by the start condition determination, it can not be driven at all because the solar cell can not supply the power that can be driven There is no longer driving, and stable driving is possible.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a power conditioner according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing a relationship between power consumption of a solar cell and a DC voltage. FIG. 3 is a characteristic diagram showing a relationship between power consumption of the solar cell and a DC voltage.
FIG. 4 is a flowchart for explaining the operation of the embodiment of the present invention.
FIG. 5 is a circuit diagram of a power conditioner according to another embodiment of the present invention.
FIG. 6 is a characteristic diagram showing the relationship between the power consumption of the solar cell and the DC voltage in the embodiment of the reference example .
FIG. 7 is a characteristic diagram showing the relationship between the power consumption of a solar cell and a DC voltage in an embodiment of another reference example .
FIG. 8 is a characteristic diagram showing the relationship between the power consumption of a solar cell and a DC voltage in still another embodiment of the present invention.
FIG. 9 is a circuit diagram of a conventional power conditioner.
FIG. 10 is a characteristic diagram showing the relationship between the power consumption of a solar cell and a DC voltage in a conventional power conditioner 1;

Claims (3)

While having a discharge circuit inside, after measuring the power consumption of the solar cell in operation stop, changing the operating point voltage of the solar cell by changing the power consumption of the solar cell by the discharge operation by the discharge circuit, Calculate an expected DC voltage value at the minimum operable power of the solar cell from the operating point voltage of the solar cell before discharging by the discharging circuit and the operating point voltage of the solar cell after discharging by the discharging circuit , A comparison is made between the predicted DC voltage value and the DC voltage at which the minimum operation is possible, and the operation is started based on the determination result that the predicted DC voltage value is greater than the DC voltage at which the minimum operation is possible. It is comprised, The power conditioner in a solar power generation system characterized by the above-mentioned. Inside the booster circuit and after measuring the power consumption of the solar cell in operation stop, by changing the power consumption of the solar cell by the boost operation by the booster circuit, change the operating point voltage of the solar cell, Calculate an expected DC voltage value at the minimum operable power of the solar cell from the operating point voltage of the solar cell before boosting by the boosting circuit and the operating point voltage of the solar cell after boosting by the boosting circuit , A comparison is made between the predicted DC voltage value and the DC voltage at which the minimum operation is possible, and the operation is started based on the determination result that the predicted DC voltage value is greater than the DC voltage at which the minimum operation is possible. It is comprised, The power conditioner in a solar power generation system characterized by the above-mentioned. A capacitor for smoothing the DC voltage of the solar cell, a booster circuit having a switch element and a capacitor in parallel with the capacitor for boosting the output of the smoothing capacitor, a discharge resistor and the charge of the capacitor through the discharge resistor A discharge circuit including a switch element that is controlled to discharge the electric power, an inverter circuit including a plurality of switch elements for converting the booster circuit output into an alternating current, and power for controlling on / off of each switch element In a power conditioner in a photovoltaic power generation system equipped with a conditioner control unit,
The switching element in the discharge circuit is controlled to be turned on / off by the power conditioner control unit, the operating point voltage at the power consumption of the solar cell when the power conditioner is stopped, and the solar power when the discharge circuit is operating. The operating point voltage at the power consumption of the battery is changed, and the predicted DC voltage value at the minimum operable power of the solar cell is calculated from each operating point voltage , and the predicted DC voltage value and the minimum operation are possible. Comparing and determining a direct current voltage, the direct current voltage expected value is configured to start operation based on a result of determination that the minimum operation is possible than the direct current voltage. Power conditioner for photovoltaic system.

Images