JP3832573B2 - Power conditioner for photovoltaic power generation - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conditioner for photovoltaic power generation.
[0002]
[Prior art]
A solar power generation system is a system that converts DC power generated by a solar cell into AC power using a power conditioner, and generally supplies the power to a load linked to a grid. Since this system uses renewable energy such as sunlight, it is extremely clean and has been put to practical use worldwide because it does not run out of resources.
[0003]
FIG. 3 shows a configuration example of such a photovoltaic power generation system, in which 1 is a solar cell, 2 is a power conditioner, 3 is a load, and 4 is a system. In the present configuration example, the power conditioner 2 converts the generated power of the solar cell 1 into AC power, which is connected to the system 4 and supplied to the load 3. At this time, when the generated power of the solar cell 1 is smaller than the power consumption of the load 3, all the generated power is consumed by the load 3, and the shortage is supplied from the system 4, but the generated power is the power consumption of the load 3. If it is larger, surplus power is generated and supplied to the grid 4 as reverse power flow.
[0004]
In FIG. 3, the power conditioner 2 includes switching means such as an inverter, a protection device, and the like in order to convert the DC power of the solar cell 1 into AC power and supply it to the load 3 and the system 4. FIG. 4 shows a configuration example of such a power conditioner, in which 21 and 22 are noise filters, 23 is a protection diode, 24 is a switching means, 25 is a reactor, 26 is an insulation transformer, and 27 is a protection device. In the present configuration example, the DC power of the solar cell 1 is converted into AC power by the switching means 24 and supplied to the load 3 and the system 4 via the reactor 25 and the insulation transformer 26. The protection device 27 is installed to stop the switching means 24 when a failure occurs in the system 4. The protective diode 23 is installed to prevent the power from flowing back from the switching means 24 to the solar cell 1. Further, noise filters 21 and 22 are incorporated in order to prevent high frequency components accompanying switching of the switching means 24 from flowing out to the solar cell 1 or the system 4.
[0005]
FIG. 5 shows another configuration example of the power conditioner, in which the voltage of the solar cell 1 is boosted. In order to omit the insulation transformer, a reactor 28 and other switching means 29 are added as a step-up chopper. That is, in order to directly connect to the grid 4, when the voltage of the grid 4 is 200V, a voltage of 300V or more is required as a DC voltage, and when the voltage of the solar cell 1 is lower than this, the reactor 28 and The voltage is boosted by the switching means 29.
[0006]
[Problems to be solved by the invention]
In the conventional system, a relatively high voltage of 200 V or higher is usually adopted as the voltage of the solar cell 1 in order to improve the system efficiency. Moreover, the characteristic of the solar cell 1 has a constant current characteristic as shown in FIG. 6, and the open circuit voltage Voc is higher than the maximum output operating voltage Va.
[0007]
In order to obtain the maximum power from the solar cell 1, the power conditioner 2 normally has its switching means controlled so that its DC input voltage becomes the maximum output operating voltage Va. In this case, in the unlikely event, a circuit extending from the DC input terminal (A) of the power conditioner 2 to the input terminal (B) of the switching means, that is, the noise filter 21 and the protection diode 23 in FIG. When a connection failure occurs in the connection part of the diode 23, the reactor 28, etc., the difference voltage (several tens of volts) between the open circuit voltage Voc and the maximum output voltage Va is instantaneously applied to the part, and the current continues to flow. As a result, arc discharge occurs at the connection failure site. That is, normally, the switching means is controlled so that the input voltage of the power conditioner 2 becomes the point A in FIG. 6, but when a connection failure occurs, a voltage drop due to arc discharge occurs, and the operation of the solar cell 1 The point moves to B.
[0008]
At this time, power corresponding to the product of the current Ib at point B and the voltage drop Vd is generated at the poorly connected portion. For example, if the power is 20 A and 20 V, respectively, the power is 400 W, which is a considerable amount. An exotherm occurs. Further, as is well known, since direct current has no zero point of current, there is a problem that once arc discharge starts, it does not disappear until a certain amount of spatial distance is secured.
[0009]
Therefore, when such a situation occurs, the inside of the power conditioner may instantaneously become a high temperature, which may cause a safety problem.
An object of the present invention is to provide a power conditioner having high safety by preventing arc discharge by detecting such a connection failure.
[0010]
[Means for Solving the Problems]
To solve the above problems, photovoltaic power conditioner of the present invention is a photovoltaic power conditioner having a switching means for converting the power generated by the solar battery into AC power, characteristics of the solar cell the The switching means is controlled such that the open circuit voltage is higher than the maximum output operating voltage, and the voltage at the DC input terminal of the power conditioner becomes the maximum output operating voltage. The voltage at the DC input terminal of the power conditioner and the switching Detecting the voltage at the input end of the means, and when the voltage at the DC input end of the power conditioner is higher than the voltage at the input end of the switching means, the switching means is turned off , Connection failure occurring in the circuit leading to the DC input terminal of the inverter and the input terminal of the switching means Voltage difference between the open-circuit voltage and the maximum output operating voltage so as to extinguish the arc discharge generated is applied instantaneously position.
[0011]
Further, another photovoltaic power conditioner of the present invention is a photovoltaic power having a boost chopper that boosts the generated power of the solar cell and switching means that converts the boosted generated power into AC power. In the conditioner, the step-up chopper includes other switching means, and the characteristics of the solar cell are higher in open circuit voltage than the maximum output operating voltage, and the voltage at the DC input terminal of the power conditioner becomes the maximum output operating voltage. The switching means is controlled to detect the voltage at the DC input terminal of the power conditioner and the voltage at the input terminal of the other switching means, and the voltage at the DC input terminal of the power conditioner is the other switching voltage. The switching means and / or when the voltage rises by a predetermined value or more compared to the voltage at the input terminal of the means Turns off the serial other switch means, the voltage difference between the open-circuit voltage and the maximum output operating voltage connection failure site occurred in the circuit leading to the input of the other switching means and the DC input end of the power conditioner instantaneous The arc discharge generated when applied to is extinguished .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the voltage at the DC input terminal of the power conditioner and the voltage at the input terminal of the switching means are detected. When the voltage at the input terminal of the switching means is pulse width modulated, the average value is obtained by a filter. Next, the difference between these voltages is obtained and compared with a predetermined value, and if it is greater than this value, the switching means is stopped. That is, normally, the difference between the above voltages is a value determined by the product of the DC resistance of the circuit and the DC current of the power conditioner, and is a value of several volts at most even during rated operation of the power conditioner. In the unlikely event that a connection failure occurs, this difference voltage rises to several tens of volts, so that the connection failure can be easily detected.
[0013]
IGBT or FET can be applied as the switching means, and the switching means can convert DC power into AC power. Preferably, it is combined with a step-up chopper.
[0014]
The step-up chopper is preferably provided with other switching means using IGBT or FET, and more preferably constituted by a reactor and the other switching means. When the other switching means is provided, the voltage is detected at the input terminal of the other switching means. And it compares with the voltage of the DC input terminal of a power conditioner.
[0015]
【Example】
FIG. 1 shows an embodiment according to the present invention, in which 51 and 52 are voltage dividing circuits, 53 is a constant voltage diode, and 54 is a comparison circuit. Others are the same as the conventional configuration example. In the present embodiment, the voltage at the DC input terminal of the power conditioner 2 is normally several V higher than the voltage at the input terminal of the switching means 24 made of IGBT for converting DC power into AC power. If the voltage is equal to or lower than the voltage of the constant voltage diode 53 (here, 10 V is used), the output voltage of the voltage dividing circuit 51 is lower than the output voltage of the voltage dividing circuit 52 and the output of the comparison circuit 54 is L. Yes.
[0016]
If a connection failure occurs in the DC circuit of the power conditioner 2 and this voltage drop exceeds the voltage of the constant voltage diode 53, the output voltage of the voltage dividing circuit 51 becomes higher than the output voltage of the voltage dividing circuit 52. The output of the circuit 54 becomes H and the switching means 24 is stopped.
[0017]
FIG. 2 shows another embodiment according to the present invention, in which the power conditioner 2 has a built-in boost chopper composed of a reactor 28 for boosting generated power and other switching means 29 made of IGBT. . The configuration in this case is almost the same as that in FIG. 1, but a simple filter capacitor 55 is added to the voltage dividing circuit 52 because the input of the other switching means 29 in the boost chopper is pulse width modulated. As a result, the average voltage at the input terminal of the other switching means 29 can be detected, and similarly, a voltage drop due to poor connection can be detected to stop at least one of the switching means 24 or the other switching means 29. .
[0018]
In addition, if the switching means is stopped as described above, the current path from the solar cell is cut off, and arc discharge can be extinguished. Further, it has been confirmed that the differential voltage for detecting a connection failure, that is, the value of the constant voltage diode is preferably 5 to 20 V, more preferably about 10 V.
[0019]
【The invention's effect】
As described above, according to the present invention, the voltage at the DC input terminal of the power conditioner and the voltage at the input terminal of the switching means are detected, and the voltage at the DC input terminal of the power conditioner is the voltage at the input terminal of the switching means. Since the switching means is turned off when the value rises above a predetermined value compared to the above, even if a connection failure occurs, heat generation due to arc discharge can be prevented in advance, and an extremely safe power conditioner There is an effect that can be configured.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a power conditioner for photovoltaic power generation according to the present invention.
FIG. 2 is a diagram showing another embodiment of a power conditioner for photovoltaic power generation according to the present invention.
FIG. 3 is a diagram showing an outline of a photovoltaic power generation system.
FIG. 4 is a diagram showing an example of a conventional power conditioner for photovoltaic power generation.
FIG. 5 is a view showing another example of a conventional power conditioner for photovoltaic power generation.
FIG. 6 is a graph showing output characteristics of a solar cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Solar cell 2 Power conditioner 3 Load 4 System | systems 21, 22 Noise filter 23 Protection diode 24, 29 Switching means 25, 28 Reactor 26 Insulation transformer 27 Protection device 51, 52 Voltage dividing circuit 53 Constant voltage diode 54 Comparison circuit 55 Filter Capacitor

Claims (2)

In the photovoltaic power conditioner having switching means for converting the generated power of the solar cell into alternating current power, the characteristics of the solar cell are higher in open voltage than the maximum output operating voltage, and the DC input terminal of the power conditioner The switching means is controlled so that the voltage of the power supply becomes the maximum output operating voltage, and the DC input terminal voltage of the power conditioner and the input terminal voltage of the switching means are detected, and the DC input terminal of the power conditioner is detected. Is generated in a circuit that turns off the switching means and reaches the DC input terminal of the power conditioner and the input terminal of the switching means. The difference voltage between the open circuit voltage and the maximum output operating voltage is instantaneously applied to the connection failure site Power conditioner for solar power generation, which comprises eliminating the over arc discharge. A step-up chopper for boosting the power generated by the solar cell, the power conditioner for solar power generation and a switching means for converting the boosted generated power into AC power, the step-up chopper with other switching means, wherein The characteristic of the solar cell is that the open circuit voltage is higher than the maximum output operating voltage, and the switching means is controlled so that the voltage at the DC input terminal of the power conditioner becomes the maximum output operating voltage, and the DC input of the power conditioner When the voltage at the end and the voltage at the input end of the other switching means are detected, and the voltage at the DC input end of the power conditioner increases by a predetermined value or more compared to the voltage at the input end of the other switching means to, and turns off the switching means and / or the other switch means, the power conditioner Characterized in that it eliminated the arc discharge voltage difference occurs is applied instantaneously between the open-circuit voltage and the maximum output operating voltage connection failure site occurred in the circuit leading to the input of the other switching means and the DC input end Power conditioner for solar power generation.

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