JPH0354366B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a solar power generation system that converts direct current from a solar cell into predetermined power, and in particular appropriately monitors the electromotive force of a solar cell and starts a power conversion device. This invention relates to a method for starting a solar power generation system that can perform the following steps.

[Technical background of the invention]

As shown in Figure 1, a solar cell plate that generates electricity when irradiated with sunlight generates electricity when the output current Is increases above a certain value when the amount of solar radiation and temperature of the solar cell plate are constant at a certain value. The output voltage Vs rapidly decreases to zero. Also, the maximum output power Pmax of a solar cell with such characteristics occurs when the output current is Iop, and the power value is calculated by Iop and the output voltage at this time.
given by the product of Vop.

A solar panel is constructed by connecting 40 to 50 solar panels in series or in parallel. For example, a solar cell panel is constructed as shown in FIG. In the figure, reference numeral 1 denotes a solar cell plate which, when irradiated with sunlight, generates an electromotive force with positive polarity at terminal 3 and negative polarity at terminal 4, thereby obtaining an output 5. The solar cell panel 2 having the configuration shown in FIG. 2 is equivalently represented by the circuit shown in FIG. 3 in an electromotive state. Here, the symbols shown in FIG. 3 that are the same as those in FIG. 2 indicate the same functions. In this solar panel 2, the relationship curve between the output current Is and the output voltage Vs when the temperature is constant (for example, 300〓) and the amount of solar radiation is changed is the fourth
As shown in the figure, it changes as the amount of solar radiation changes, and the maximum output point changes as shown by the dotted line a curve in the figure. Therefore, if you are operating a resistor connected to the solar panel 2 as a load that can produce maximum output when the solar radiation is 50 mW/cm ² , for example, if the solar radiation changes from 50 to 100 mW/cm 2 due to a change in the weather. ^cm2 , the operating point is the intersection point A of the load characteristic curve B and the output current vs. output voltage relationship curve when the solar radiation is 50 mW/cm2, and the operating point is the output current vs. output voltage when the solar radiation is 100 mW/ ^cm2. Move to the intersection point B with the relationship curve of
It is no longer possible to extract maximum output. Further, when the amount of solar radiation decreases from 50 mW/cm ² to, for example, 10 mW/cm ² , the operating point shifts to point C, which is significantly deviated from the maximum output point. As described above, the output of a solar cell panel group configured by connecting a plurality of solar cell panels 2 in series and parallel, whose output fluctuates as the amount of solar radiation changes, is also easily affected by the amount of solar radiation. Therefore, as it is, it is not possible to efficiently extract output from the solar panel group, resulting in a low efficiency solar power generation system. Normally, solar power generation systems use AC equipment as the load, or because they are connected to an AC power system, it is necessary to convert DC to AC. The output of the converter 11 is a self-commutated power converter 13 composed of an inverter.
(hereinafter abbreviated as power converter 13), it is connected to a variable current load or an AC power system 14. Fifth
In the figure, a solar power generator 11 is a solar battery panel group consisting of a plurality of solar battery panels 2.
is a backflow prevention diode.

[Problems with background technology]

When starting up the solar power generation system as described above, the electromotive force of the solar power generator 11 is transferred to the power conversion device 1.
Conventionally, a monitor circuit for monitoring the starting force of the solar power generator 11 is provided close to the solar power generator 11 in order to monitor whether it has enough electromotive force to start the solar power generator 11. A method has been considered in which the power conversion device 13 is activated by detecting that the output of the circuit has exceeded a predetermined value. As shown in FIG. 6, this monitor circuit consisted of a solar panel 2 or a device capable of measuring sunlight irradiation, in addition to the solar power generator 11. However, with the configuration shown in FIG. 6, the true electromotive force of the solar power generator 11 cannot be monitored. For example, in the figure, if the solar power generator 11 is blocked by clouds or the like and the monitor circuit 21 is receiving solar radiation, the electromotive force of the solar power generator 11 activates the power converter 13 due to the output of the monitor circuit 21. It is erroneously determined that the electromotive force is sufficient to cause the power converter 13 to start, and the start condition is satisfied and a start command is given to the power conversion device 13. However, since the solar power generator 11 does not have enough electromotive force to start the power conversion device 13, the control is performed to significantly deviate from the operating point shown in the explanation of FIG. This results in the disadvantage that the power converter 13 cannot be operated. This drawback is more likely to occur as the scale of the solar power generator 11 becomes larger, and it becomes more difficult to start up and operate the solar power generator 11.

[Purpose of the invention]

Therefore, the present invention takes into consideration this point of the conventional method,
When the solar power generation system is stopped, the bridge of the inverter circuit, which is one component of the power converter 13, is operated to form a circuit that short-circuits the output of the solar power generator 11, thereby reducing the electromotive force of the solar power generator 11 itself. To provide a method for starting a solar power generation system that can reliably start the power converter 13 after monitoring the power converter 13 and confirming that the electromotive force is sufficient to start the power converter 13. That purpose.

[Summary of the invention]

To achieve this object, the present invention provides a solar power generation system consisting of a solar cell and a self-commutated power converter that converts the DC output of the solar cell into a predetermined alternating current. At least one set of the bridges of the inverter circuit, which is composed of a plurality of switch elements connected between the DC terminals of the self-excited power converter, is operated so as to short-circuit between the DC terminals, and to perform a short-circuit operation with the solar cell. It has a current detector that detects the current flowing through the short circuit formed from the bridge, and a current detection circuit that detects when the output of the current detector reaches a predetermined value. This is a method of starting a solar power generation system by using it as a starting signal for a self-excited power converter.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIG. Components in FIG. 7 with the same symbols as in FIG. 5 have the same functions. However, 14 shows the case of an AC power system. In the embodiment shown in FIG. 7, the inverter circuit 13 is shown as a single-phase inverter, but it may be a three-phase inverter. The basic configuration of the inverter circuit 13 is shown, and its operating principle for converting direct current to alternating current is well known, so a description thereof will be omitted. Further, the DC reactor 31 and the capacitor 32 form a filter circuit that suppresses voltage and current ripples caused by the operation of the inverter circuit 33.

Comparing FIG. 7 and FIG. 5, and describing the different means, in the conventional FIG. 5, as shown in FIG. The power conversion device 13 is started based on the detected value of the power converter 13, whereas in FIG. The electromotive force of the solar power generator 11 is monitored by operating at least one set of switch elements of the bridge to short-circuit the DC terminals 301 and 302 and detecting the current flowing through the short circuit. Conversion device 1
This is the point where 3 is activated.

That is, in the embodiment shown in FIG. 7, when the solar power generation system is stopped, the switch 34 is opened, the inverter circuit 33 is disconnected from the AC power system 14, and the switch elements 331 and 332 are
3 gives an ON command and connects the DC terminals 301 and 30.
2 are shorted. That is, solar power generator 1
1 is a backflow prevention diode 12-DC reactor 31-DC terminal 301-switch element 331,
332-DC terminal 302-current detector 41, an output current corresponding to the amount of solar radiation shown in FIG. 4 is caused to flow. In the case of a solar power generation system, daily startup and shutdown are performed by the solar power generator 1.
1, that is, the solar radiation level. In other words, to start up the solar power generation system, it is only necessary that the solar power generator 11 can supply power that is greater than the no-load loss of the power converter 13. Therefore, when starting up the system, the current in the short circuit described above is equal to or less than the rated DC current.
It is about 10 to 15%, and the switch elements 331 and 33
The current load of No. 2 is well within the rated value. 7th again
Returning to the explanation of the figure, the current flowing through the aforementioned short circuit is detected by the current detector 41, and the level of the current detection signal 411 is detected by the current detection circuit 42. Here, the current detection circuit 42 may be a well-known comparator, so a detailed explanation will be omitted.

When the amount of solar radiation increases and the electromotive force of the solar power generator 11 increases, the current flowing through the current detector 41 of FIG. 7 increases as shown in FIG. 4. This current detector 4
1 current detection signal 411 is detected by the current detection circuit 42 and when the set value, that is, the electromotive force of the solar power generator 11 reaches a value sufficient to start the power conversion device 13, the output signal 421 is activated. . When this output signal 421 is given as a starting command to the control circuit 43, the simultaneous firing of the switch elements 331 and 332 is stopped, and a gate signal 431 is given to the switch elements 311 to 334 to start them so that the main circuit operates as specified. . When the inverter circuit 33 operates and reaches a predetermined output, the switch 34 is operated to connect the power conversion device 13 and the AC power system 14, and predetermined control is performed. The above operation is shown in the time chart of FIG. To explain the operation of the present invention using a time chart, when the current detection signal 41 reaches a predetermined value, the simultaneous conduction of the switch elements 331 and 332 of the inverter circuit 33 is stopped. After the capacitor 32, which is essential for the operation of the inverter circuit 33, is charged by the solar power generator 11, the inverter circuit 33 is operated, and after the inverter output voltage reaches a predetermined value, the switch 34 is closed and the AC power grid is connected. Connect with. In the figure, time T ₁ indicates the time until the capacitor 32 is charged to a predetermined value by the solar power generator 11 after the simultaneous conduction of the switch elements 331 and 332 is stopped. this time
Since T ₁ changes with the amount of solar radiation, a DC voltage detection circuit (not shown) detects that the charging voltage of the capacitor 32 reaches a predetermined value and operates the gate signal 431 of the inverter circuit 33. Also, the 9th
As shown in the figure, when the amount of solar radiation decreases below a predetermined value after stopping the simultaneous conduction of switch elements 331 and 332, that is, when time T ₁ is equal to predetermined time T ₀ , the condition is that T ₁ > T ₀ . When this is established, the inverter circuit 33 is not operated in a predetermined manner, and the switch elements 331 and 332 are fired at the same time again to discharge the charge in the capacitor 32 and return the solar power generation system to the stopped state again. If the power conversion device 1 is operated due to insufficient electromotive force of the solar power generator 11,
It is possible to prevent the accident described in 3. When discharging the capacitor 32 by firing the switch elements 331 and 332 at the same time, if the discharge current exceeds the allowable value of the switch elements, the switch elements 333 and 334 are also fired at the same time to divide the discharge current. Good.

That is, in order to directly monitor the electromotive force of the solar power generator 11 that serves as the power source for the power conversion device 13, and start the power conversion device 13 based on the detection level,
Accurate startup can be performed without causing a difference between the detected value of the monitor circuit and the electromotive force of the solar power generator 11 unlike in the conventional system. In addition, unlike conventional methods, there is no need for an expensive monitor circuit such as a solar panel 2 or a device that can measure sunlight irradiation.
It can be realized with a cheap and simple circuit.

Next, other embodiments of the present invention will be described. 7th
In the illustrated embodiment, a current detector 41 for detecting the short-circuit current when the output of the solar power generator 11 is short-circuited by the switch elements 331 and 332 is provided on the solar power generator 11 side with respect to the capacitor 32. , may be provided on the inverter circuit 33 side. Also, current detector 41
can also be used as a direct current detector that is generally provided for protecting or controlling the inverter circuit 33.

Furthermore, in the embodiment shown in FIG. 7, when the solar power generation system is stopped, one of the switch elements 331 and 332 is turned off.
Although a set of bridges are operated, the present invention is not limited to a specific bridge, and a plurality or all of the bridges may be operated.

Further, the output signal 421 is given to the control circuit 43 as a condition for starting the power conversion device 13, and when an external signal (not shown) is given, the simultaneous conduction of the switch elements 331 and 332 is stopped, and the time T ₁
The inverter circuit 33 can also be activated later with a predetermined operation.

〔Effect of the invention〕

Thus, according to the present invention, in a solar power generation system composed of a solar cell having a photovoltaic force and a power converter that converts its DC output into a predetermined AC, one or more bridges are turned on when the system is stopped. It detects the current flowing through the short circuit that arcs and shorts the solar cells, accurately captures the electromotive force of the solar power generator, and starts the power conversion device. Therefore, there is no need for an expensive electromotive force monitor circuit. Stable startup can be performed without system malfunctions due to differences in electromotive force between the circuit and the solar power generator.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram of the relationship between the output current and output voltage of the solar cell plate, Figure 2 is a diagram of the configuration of the solar battery panel, and Figure 3 is a diagram of the solar battery panel configuration.
The figure shows the equivalent circuit of Fig. 2, and Fig. 4 shows the output voltage vs. output current characteristics of the solar cell plate when the amount of solar radiation changes.
Figure 5 is a block diagram of the solar power generation system, Figure 6
7 is a block diagram of a solar power generation system showing an embodiment of the present invention, and FIG. 8, FIG. 9 is a time chart of FIG. 7. 1... Solar cell plate, 2... Solar cell panel, 3, 4
...Terminal, 5...Output, 11...Solar power generator, 12...
Backflow prevention diode, 13...Power converter, 1
4... AC load or AC power system, 31... DC reactor, 32... Capacitor, 33... Inverter circuit, 34... Switch, 41... Current detector, 42
...Current detection circuit, 421...Output signal, 43...Control circuit, 431...Gate signal, 331-334...Switch element, 335-338...Diode, 44
1... Current detection signal, 301, 302... DC terminal.

Claims (1)

[Claims] 1. In a solar power generation system consisting of a solar cell having photovoltaic power and a self-excited power converter that converts the DC output of the solar cell into alternating current, when the solar power generation system is stopped, the self-excited power converter is activated. The DC terminals are short-circuited, and the detection that the current flowing through the closed circuit formed by the solar cell and the short circuit reaches a predetermined value is used as a start signal for the self-excited power converter. How to start a solar power generation system.