JP6357638B2 - Power converter - Google Patents

Description

The present invention relates to a power conversion device capable of connecting a plurality of solar cell assemblies including a plurality of solar cells, for example, solar cell strings.

In general, the power converter operates to generate AC power when the solar cell is generating power, and when the solar cell stops generating power or when the amount of power generation decreases (for example, when sunset is judged)
The generation of AC power is terminated. For example, a plurality of solar cell modules (corresponding to solar cell strings) integrated open-circuit voltage (corresponding to the output voltage of the solar cell) is switched to the AC power after a predetermined time for status confirmation from the time when it becomes equal to or higher than the starting initial value There was something that started the conversion. (Patent Document 1)

Japanese Patent No. 3218878

In the case of the configuration described in Patent Document 1, when a solar cell power generation device or system is configured using a plurality of solar cell modules, that is, a plurality of solar cell strings, the power generation voltage of the entire power generation device is used to start output of AC power. Must be greater than the initial startup value.

At sunrise, the position of the sun is low, so there are solar cell strings that are in the shade and have a low power generation voltage even though the power generation voltage of some solar cell strings is above the initial startup value. There is a case. In this case, the output of the entire solar cell string is integrated, and the generated voltage does not reach the starting initial value, and the output start of the AC power may be delayed.

The present invention provides a power conversion device that can start conversion to AC power and quickly start supplying AC power if there is a solar cell string in which the generated voltage reaches a predetermined value.

The power conversion device of the present invention includes a booster circuit that boosts the output of a solar battery assembly composed of a plurality of solar cells for each of the plurality of solar battery assemblies, and combines the outputs of the respective booster circuits into a single unit. In a power conversion device including a conversion circuit for converting to AC power after that, the input voltage of at least one of the boost circuits is maintained at a state equal to or higher than a first predetermined voltage for a first predetermined time or longer. At least one of the booster circuit and the converter circuit is started, and the operation can be started for each solar cell assembly that can be converted into AC power. .

In the power conversion device of the present invention, since the operation can be started for each solar cell assembly that can be converted into AC power, the utilization rate of solar cells is improved.

FIG. 1 is an explanatory view showing an embodiment of the present invention. FIG. 2 is an explanatory diagram showing the operation of the embodiment shown in FIG.

In the present invention, a plurality of solar cell assemblies (for example, solar cell strings) can be connected, and the operation is started for each solar cell assembly that can be converted into AC power.

FIG. 1 is an explanatory view showing an embodiment of the present invention, A to E are solar cell strings,
A plurality of solar cells are electrically connected in series / parallel to form a single module, or this module is electrically connected in series / parallel to form a single solar cell assembly. . Hereinafter, the embodiments will be described simply as strings A to E. In FIG. 1, reference numeral 1 denotes a power converter, and the output of the power converter 1 is superimposed on the grid G.

The strings A to E are configured by connecting a plurality of solar cell modules (panels) in parallel and / or in series so as to match the specifications (input ratings) of the corresponding input circuits 2a to 2e. The number of strings to be connected is not limited to five from A to E, and it is not necessary to connect the strings to all the input circuits 2a to 2e, and at least two input circuits are configured to be effective. That's fine.

Since the same circuit can be used for the input circuits 2a to 2e, the input circuit 2a will be described and the description of the input circuits 2b to 2e will be omitted. A string A of solar cells is connected to the input circuit 2a via positive and negative input terminals. The input voltage of the input circuit 2a (corresponding to the DC output voltage of the string A) is detected by the voltage detector 3 and input. The current detector 4 detects the input current of the circuit 2a (corresponding to the DC output current of the string A).

The voltage detector 3 divides the applied voltage as necessary, performs A / D (analog / digital) conversion, and supplies it to the control unit 5 as a digital voltage value. The control unit 5 or the control unit 5
When the control element such as the microprocessor has an A / D conversion unit, the voltage detector 3 may be configured by a voltage dividing unit by resistance voltage division.

The current detector 4 detects a supplied current, and there are a detector that detects a voltage drop due to a shunt resistor, a non-contact type that uses the Hall effect, and the like, and outputs a voltage corresponding to the detected current amount. Is. This voltage is supplied to the control unit 5 in the same manner as the output of the voltage detector 3.

The input circuit 2a includes a DC voltage boosting unit (boosting circuit). The boosting unit includes at least a reactor 6, a switching element 7, a diode 8, and a capacitor 9. The terminal voltage of the capacitor 9 becomes a target voltage. A general DC / DC converter that feedback-controls the on-duty ratio of the switching element 7 (for example, the switching period is 1 to 3 kHz) can be used. The configuration of the boosting unit is not limited to this configuration, and for example, it can be configured by an insulating boosting circuit using a transformer.

The diode 10 is used to prevent backflow when a plurality of input circuits are used. This diode 1
The DC power output through 0 is combined with the outputs of the other input circuits 2b to 2e into a single unit and supplied to the capacitor 11 that outputs an intermediate voltage. This intermediate voltage is supplied to an inverter unit 12 (corresponding to a conversion unit that converts direct current into alternating current) that performs D / A (digital / analog) conversion by connecting four switching elements in a single-phase bridge shape.

The inverter unit 12 turns on / off each switching element based on a switching signal obtained by comparing the magnitude of a modulated wave having a frequency equivalent to the frequency of the system G and the carrier wave, so that the frequency is substantially the same as that of the system G. The pseudo sine wave AC is output. This pseudo sine wave is attenuated by a filter circuit including reactors 13 and 14 and a capacitor 15 and then a high frequency component is attenuated.
Is to be superimposed. In addition, the waveform shaping of this pseudo sine wave is not limited to this method,
Other methods such as a neutral point clamp method can be used.

Reference numeral 16 denotes a display unit. The display unit 16 may be any general-purpose 7-segment / 8-segment display or liquid crystal display that can display numbers, symbols, characters, and the like, and is based on a signal from the control unit 5. , Numbers, symbols, and letters are combined to display a specific code.

The control unit 5 has a maximum (or near or maximum) AC power for superimposing the target voltage of the boosting unit, the peak value of the AC voltage superimposed on the system G (or an effective voltage or an average voltage), etc. on the system G. Value). At this time, the generated power of the string A is calculated from the detection values of the voltage detector 3 and the current detector 4, and the target voltage of the boosting unit is adjusted so that the generated power is maximized. Is a general MPPT (Maximum Power P
It is possible to use an oint tracking method.

FIG. 2 is an explanatory diagram showing the operation of the embodiment shown in FIG.
If the input voltage of a (boost circuit), that is, the voltage detected by the voltage detector 3 is maintained at or above the first predetermined voltage for the first predetermined time or more and there is no activation flag Fa, this flag Fa is set. If the flag Fa is already set, the flag Fa is maintained. Further, the voltage detected by the voltage detector 3 is maintained at a state equal to or lower than a second predetermined voltage lower than the first predetermined voltage for a second predetermined time or more.
If the flag Fa is set, the flag Fa is deleted. If there is no flag Fa, the flag Fa
Maintain the state without. A series of these operations is based on “determination of flag Fa” in step S1.

Further, when the flag Fa is set, the control unit 5 starts the operation of the boosting unit of the input circuit 2a.
If the state where a is standing continues, the operation of the booster is maintained as it is, and if the flag 2a is not present, the operation of the booster is stopped.

In step S2, the flag Fb corresponding to the input circuit 2b is determined in the same manner as in step S1, similarly in step S3, the flag Fc is determined, in step S4, the flag Fd is determined, and in step S5, the flag Fe is determined. I do.

The first predetermined voltage varies depending on the characteristics of the solar battery cell. For example, if the rated output of the string is about 1.5 Kw or less, it can be set in the range of 70V to 100V. Similarly, the first predetermined time can be set to about 100 to 200 seconds.

The determination at the time of setting the flags in steps S1 to S5 is made by a combination of the first predetermined voltage and the first predetermined time. In parallel, the third predetermined voltage higher than the first predetermined voltage is the first predetermined voltage. It is also possible to add a determination to set a flag even when the time is maintained for a fourth predetermined time which is shorter than one predetermined time. In this case, for example, the third predetermined voltage can be about 1.5 times the first predetermined voltage, and the fourth predetermined time can be about 1/10 of the first predetermined time. It is not limited to these values.

The second predetermined voltage is in the same range of 50V to 80V, and can be a voltage lower by about 20V than the first predetermined voltage. Similarly, the second predetermined time can be set to about 300 to 500 seconds, but is not limited to these values.
The first and second predetermined voltages and the first to third predetermined times are not limited to the values described above, and can be arbitrarily changed according to the specifications of the solar cell and the power converter.

In step S6, the state of the flag Fa to the flag Fe is determined. If at least one of the flags is set, the “system connection determination” is performed to determine whether to maintain or start the system connection. is there. When it is determined in step S6 that the grid connection is maintained or started, the process proceeds to step S7, and if the inverter unit 12 is not operating, the operation of the inverter unit 12 is started.
If the inverter unit 12 is operating, the operation is maintained. Therefore, at least one of them
When the two boosting units operate and the inverter unit 12 operates, the power generation output of the solar cell is converted into alternating current or alternating current power.

After step S8, the process proceeds to step S9, where it is determined whether or not the state where all of the flags Fa to Fe are lost is maintained for a third predetermined time (determination of cooperation stop),
When this condition is satisfied, the sunset is determined and the operation of the inverter unit 12 is stopped. The third predetermined time can be set to a value that takes into account variations in the amount of solar radiation, such as 10 minutes.

In the explanatory diagram shown in FIG. 2, after the operation of the boosting unit is determined in steps S1 to S5, the operation of the inverter unit 12 is determined in step S7, but all the states of the flags are determined. After that, the boosting unit and the inverter unit 12 may be operated simultaneously, or the boosting unit may be operated after the inverter unit 12 is activated. When the inverter unit 12 operates first, it is preferable from the viewpoint of control stability that the booster unit is operated within a short time, and when the booster unit operates first, the inverter 9 is operated after the terminal voltage of the capacitor 9 becomes high. It is preferable to actuate part 12.

Thus, in the present invention, conversion to alternating current is effectively started according to the power generation state of the solar cell string.

As mentioned above, although one Embodiment of this invention was described, the above description is for making an understanding of this invention easy, and does not limit this invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Power converter 2a-2e Input circuit 3 Voltage detector 4 Current detector 5 Control part 16 Display part

Claims (3)

A booster circuit that boosts the output of a solar battery assembly composed of a plurality of solar cells is provided for each of the plurality of solar battery assemblies, and the outputs of the respective booster circuits are combined into a single and then converted to AC power. In a power conversion device including a conversion circuit,
Maintaining a state where the input voltage of at least one of the respective booster circuits is equal to or higher than a first predetermined voltage for a first predetermined time and the input voltage is a first predetermined voltage
Maintaining a state higher than the third predetermined voltage for a fourth predetermined time shorter than the first predetermined time
When at least one of the above is satisfied , at least one of the booster circuit and the converter circuit is started to operate, and the input voltage of the booster circuit is lower than the first predetermined voltage and lower than the second predetermined voltage. The operation of the booster circuit that has maintained the state for the second predetermined time or more is stopped, and the operation of the conversion circuit is stopped when the state in which all the booster circuits have stopped operating is maintained for the third predetermined time. A power converter. The power converter according to claim 1, wherein sunset is determined when a state in which all the booster circuits are stopped is maintained for a third predetermined time. A booster circuit that boosts the output of a solar battery assembly composed of a plurality of solar cells is provided for each of the plurality of solar battery assemblies, and the outputs of the respective booster circuits are combined into a single and then converted to AC power. In a power conversion device including a conversion circuit,
Maintaining a state where the input voltage of at least one of the respective booster circuits is equal to or higher than a first predetermined voltage for a first predetermined time and the input voltage is a first predetermined voltage
Maintaining a state higher than the third predetermined voltage for a fourth predetermined time shorter than the first predetermined time
Power converter, characterized in that to initiate one of the operation one of at least the booster circuit or the converter circuit when the meets either of it.

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