JP2014225212A - Photovoltaic power generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic power generator capable of controlling the output from a solar cell without using any on-off switch at the output side of the solar cell.SOLUTION: The photovoltaic power generator includes: a solar cell 1; a DC/DC converter 2 for boosting the output voltage from the solar cell 1; a DC/AC converter 3 that converts the output from the DC/DC converter 2 into an AC current and outputs the same to a system power source 4; and a controller 6 that, when the output voltage Vb from the solar cell 1 gets higher than an output target voltage Va1 of the DC/DC converter 2, sets the input target voltage Va2 of the DC/AC converter 3 to be higher than the output voltage Vb from the solar cell 1.

Description

  The present invention relates to a power generation device using a solar cell.

  As an apparatus for supplying power generated by a solar cell to a system power source, for example, after boosting DC power generated by a solar cell with a DC / DC converter, the DC / AC converter converts it to AC and then to the system power source. Devices for feeding are known.

  Since the power generation capacity of solar cells is affected by the amount of sunlight irradiated to the solar cells and the temperature at which the solar cells operate, as a way to constantly optimize the power generation capacity of solar cells in an environment where the weather changes daily, There is a maximum power point tracking (MPPT) control. In addition, as a method of effectively using the generated power of the solar battery, for example, by combining the solar battery and the storage battery and charging the generated power of the solar battery to the storage battery, the generated power of the solar battery is used without surplus. The method is known.

  As described above, the power generation capacity of the solar cell is affected by the amount of sunlight and the ambient temperature. Therefore, in order to obtain as much power generation as possible even on a bad day, May be installed.

  In that case, on the contrary, when conditions suitable for power generation of the solar cell are established, a voltage exceeding the rating is applied to the DC / DC converter, and a voltage exceeding the voltage range that can be controlled by the DC / DC converter is output as it is. Therefore, there is a concern about the influence on the system power supply and the storage battery. In order to avoid this, in order to suppress the output of the solar cell, a device has been devised in which an open / close switch is provided on the output side of the solar cell and this is turned on / off according to a predetermined condition.

JP 2011-101455 A Japanese Patent Laid-Open No. 10-243575

  Since the solar cell is disconnected by the open / close switch, it may be frequently opened and closed depending on the environment and conditions, and the contact life is shortened because it is disconnected in the state where current flows, and the open / close switch is periodically replaced. Deterioration in maintainability such as occurrence of a problem becomes a problem. In addition, noise is generated each time opening and closing. Furthermore, when the switch is closed in a state where the solar cell can generate enough power once the switch is opened, a precharging resistor must be provided in parallel with the open / close switch because an excessive charging current flows to the capacitor in the device. There is a problem.

  An object of this invention is to provide the solar power generation device which suppresses the output of a solar cell, without using an opening / closing switch on the output side of a solar cell.

  In order to achieve the above object, a photovoltaic power generation apparatus according to an embodiment converts a solar cell, a DC / DC converter that boosts the output voltage of the solar cell, and an output of the DC / DC converter into alternating current. When the output voltage of the DC / AC converter to be output to the system power supply and the solar cell is higher than the output target voltage of the DC / DC converter, the input target voltage of the DC / AC converter is And a controller for setting higher than the output voltage of the battery.

  With this configuration, when the output voltage of the solar cell becomes higher than the rated voltage of the DC / DC converter, the output of the solar cell can be suppressed.

  In order to achieve the above object, a photovoltaic power generation apparatus according to another embodiment includes a solar cell, a first DC / DC converter that boosts an output voltage of the solar cell, power storage means, A second DC / DC converter for charging and discharging power storage means; and the first DC / DC converter connected in parallel with the first DC / DC converter and the second DC / DC converter. A DC / AC converter that converts a direct current output of at least one of the first and second DC / DC converters into an alternating current, or converts an alternating current output from the system power supply into a direct current and outputs the output, and an output voltage of the solar cell Is higher than the output target voltage of the first DC / DC converter, the target voltage on the system power supply side of the second DC / DC converter is set higher than the output voltage of the solar cell. And a controller.

  With this configuration, the output of the solar cell can be suppressed when the output voltage of the solar cell becomes higher than the rated voltage of the first DC / DC converter.

  According to the embodiment of the present invention, it is possible to provide a solar power generation device that suppresses the output of a solar cell without using an open / close switch on the output side of the solar cell.

The block diagram of the 1st Embodiment of this invention. The graph of an example of the VI characteristic and VP characteristic of a solar cell. The block diagram of the 2nd Embodiment of this invention.

(First embodiment)
FIG. 1 is a diagram showing the configuration of the first exemplary embodiment of the present invention. The DC power generated by the solar cell 1 is boosted to a predetermined voltage by the DC / DC converter 2, converted to AC by the DC / AC converter 3, and then supplied to the system power supply 4.

  The DC / DC converter 2 has a chopper circuit, and boosts the output voltage Vb of the solar cell 1 so as to become the boost target voltage Va1. Moreover, MPPT (Maximum Power Point Tracking) control for optimizing the power generation capability of the solar cell of the solar cell 1 is performed.

  Here, the outline of the MPPT control will be described. Since the operating point for generating the maximum power differs depending on the solar radiation intensity and the temperature, the optimum operation that changes every moment is used in order to effectively use the generated power of the solar cell. It is important to generate power by following the points. In order to obtain such an optimal operating point for extracting the maximum power, maximum power tracking control {MPPT (Maximum Power Point Tracking) control) for tracking control to the optimal operating point at which the output of the solar cell is maximum is used. For example, the output power obtained at the current operating point is compared with the output power obtained at the operating point slightly moved from the current operating point to determine the direction to the optimal operating point, and to the optimal operating point. The hill-climbing method to follow is used.

  FIG. 2 is a graph of an example of the V-I characteristic showing the relationship between the output voltage V and the output current I of the solar cell and the V-P characteristic showing the relationship between the output voltage V and the output power P of the solar cell. is there. As shown in FIG. 2, the solar cell has a constant VI characteristic curve C1 and a constant VP characteristic curve P1 when the solar radiation intensity and temperature are constant, and is on the VI characteristic curve C1. The output power becomes the maximum output P1max at the optimum operating point C11 {coordinate C11 (V1, I1)}. In normal times, the output voltage Vb of the solar cell 1 is MPPT-controlled by the DC / DC converter 2 so as to reach the optimum operating point C11.

  The DC / AC converter 3 converts the direct current output of the DC / DC converter 2 into alternating current and supplies power to the system power supply 4. Further, the DC / AC converter 3 operates to adjust the output power so that the main circuit voltage Va becomes the input target voltage Va2.

  The DC / AC converter 3 is set so that the control processing cycle is earlier than that of the DC / DC converter 2, and the input target voltage Va2 for voltage control of the DC / AC converter 3 is set to a value lower than Va1. A voltage difference is generated by stepping up the voltage to Va1 by the DC / DC converter and stepping down to Va2 by voltage control of the DC / AC converter 3, whereby the generated power of the solar cell 1 flows to the system power supply 4. Become. Actually, when Va1 is 365V and Va2 is 355V, Va changes to a value of about 357V.

  Here, in order to ensure the amount of power generated by the solar cell 1 even in the case of some bad weather, a large number of solar panels of the solar cell 1 may be installed, exceeding the rating of the DC / DC converter 2. The solar cell 1 which becomes may be installed. In such a case, when conditions suitable for power generation of the solar cell 1 are satisfied, a voltage exceeding the rating of the DC / DC converter 2 is generated, and the boosting function of the DC / DC converter 2 is lost. The generated power of the solar cell 1 is directly input to the DC / AC converter 3 through a diode that is originally inside the DC / DC converter 2 and prevents backflow from the system power supply 4 side. Since the boosting function of the DC / DC converter 2 is lost and the function of suppressing the generated power of the solar cell 1 is also lost, the power generation is continued through the DC / AC converter 3 and the voltage is increased to the system power supply 4. There is a risk of adverse effects.

  In order to avoid this adverse effect on the system power supply 4, it is conceivable that an open / close switch is provided on the output side of the solar cell 1 and the system power supply 4 is protected by turning it off. Therefore, there is a problem such as exhaustion and breakdown of the open / close switch.

  Therefore, in this embodiment, a controller 6 is provided instead of the open / close switch. The controller 6 monitors the output voltage Vb of the solar cell 1 and the boost target voltage Va1 of the DC / DC converter 2, and when Vb> Va1, the input target voltage Va2 of the DC / AC converter 3 is Va2. Change the setting so that> Vb. As a result, the voltage control in the DC / AC converter 3 operates so that Vb becomes higher. As is apparent from FIG. 2, when the generated voltage increases as the characteristics of the solar cell, the current and power become zero. Since it becomes or approaches 0, the output to the system power supply 4 can be suppressed.

  If Vb <Va1, the controller 6 returns to the normal control state by restoring the input target voltage Va2 of the DC / AC converter 3. At this time, a hysteresis or an on-delay timer may be provided for determination to prevent hunting.

(Effects of the first embodiment)
According to the present embodiment, since the open / close switch is not provided on the output side of the solar cell 1, the generated power of the solar cell 1 itself can be directly suppressed in order to suppress the power supplied to the system power supply 4. A solar power generation device with excellent maintainability can be provided without being influenced by the life of the on / off switch, and waste of generated power can be reduced because it is not mechanically disconnected. This is because voltage adjustment by a semiconductor with respect to the open / close switch is fast, so that time for wasting power generation is shortened, and electric power for operating the open / close switch is not required.

(Second Embodiment)
FIG. 3 is a diagram showing the configuration of the second exemplary embodiment of the present invention. The difference in configuration compared to the first embodiment is that a storage battery 7 (power storage means) and a DC / DC converter 8 that charges and discharges the storage battery 7 are provided.

  As in the first embodiment, the DC / DC converter 2 performs MPPT control and operates so that the generated power of the solar cell 1 is maximized.

  The DC / AC converter 5 can perform bidirectional conversion from DC to AC (discharge direction) or from AC to DC (charge direction), and controls power to supply constant power to the system power supply 4 or the storage battery 7. I do. The direction of output can be switched by giving a switching command from the controller 9 to the DC / AC converter 5. For example, the grid power is connected to the system power supply from the solar battery 1 or / and the storage battery 7. 4 or when charging the storage battery 7 from the system power supply 4 or the like, by giving a command to the controller 9 from a setting means such as a PC (not shown) of the DC / AC converter 5 based on the time schedule. The output direction can be arbitrarily determined. Further, the power supply can be stopped in both the discharging direction and the charging direction by a stop command to the DC / AC converter 5.

  The storage battery 7 is a power source that can be charged and discharged, such as a lead storage battery or a lithium ion secondary battery. The DC / DC converter 8 controls charging and discharging of the storage battery 7 and operates so as to keep the voltage Va between the DC / DC converter 2 and the DC / AC converter 5 constant. In addition, the controller 6 monitors the state of charge of the storage battery 7 and changes the target voltage Va2 of the DC / DC converter 8 before overcharging or overdischarging in order to prevent battery performance deterioration or DC / AC. A stop command is given to the converter 5.

  When the generated power of the solar cell 1 is supplied to the system power supply 4 and the output to the system is stopped due to circumstances on the system side, the generated power of the solar cell 1 is effectively used to effectively use the generated power of the solar cell 1 Is charged into the storage battery 7. When the storage battery 7 is close to full charge, it is necessary to stop charging the storage battery 7. In order to stop the charging of the storage battery 7, it is conceivable to provide an open / close switch on the output side of the solar battery 1 and to turn it off to protect the overcharge of the storage battery 7. Therefore, there is a problem such as exhaustion and breakdown of the open / close switch.

  Therefore, in this embodiment, a controller 9 is provided instead of the open / close switch. By changing the target voltage (input target voltage in this case) Va2 of the DC / DC converter 8 higher than Va1 by the controller 9, it is possible to prevent inflow of power to the storage battery 7 and prevent overcharge of the storage battery 7. it can. Furthermore, when the solar cell 1 having a rating equal to or higher than that of the DC / DC converter 2 is installed, the same applies by setting Va2 higher than Vb. As a result, as apparent from FIG. 2, when the power generation voltage increases as the characteristics of the solar cell, the current and power become 0 or approach 0, so that charging of the storage battery 7 can be suppressed.

(Effect of 2nd Embodiment)
Therefore, according to the present embodiment, similarly to the first embodiment, even when the storage battery 7 is used, the storage battery 7 is overcharged without providing an open / close switch on the output side of the solar battery 1. In order to prevent this, the generated power of the solar cell 1 itself can be directly suppressed, so that it is possible to provide a solar power generation device with excellent maintainability without being affected by the life of the on / off switch, and mechanically disconnected. Therefore, waste of generated power can be reduced.

1 ... solar cell,
2,8 ... DC / DC converter,
3, 5 ... DC / AC converter,
4 ... System power supply,
6, 9 ... Controller 7 ... Storage battery

Claims (2)

Solar cells,
A DC / DC converter that boosts the output voltage of the solar cell;
A DC / AC converter for converting the output of the DC / DC converter into an alternating current and outputting it to a system power supply;
A controller that sets the input target voltage of the DC / AC converter higher than the output voltage of the solar cell when the output voltage of the solar cell becomes higher than the output target voltage of the DC / DC converter; A solar power generation apparatus comprising: Solar cells,
A first DC / DC converter that boosts the output voltage of the solar cell;
Power storage means;
A second DC / DC converter for charging and discharging the power storage means;
The first DC / DC converter and the second DC / DC converter are connected in parallel, and the direct current output of at least one of the first DC / DC converter and the second DC / DC converter is AC. Or a DC / AC converter that converts an alternating current output from the system power source into a direct current and outputs the direct current,
When the output voltage of the solar cell becomes higher than the output target voltage of the first DC / DC converter, the target voltage on the grid power supply side of the second DC / DC converter is And a controller for setting the output voltage higher than the output voltage.

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