JP6733818B1 - Power converter - Google Patents

Abstract

The power conversion device is a power conversion device that outputs an alternating current by converting a first direct current input from the first direct current input part and a first direct current input part constructed to accept the first direct current. The circuit, the first current detector provided in the first DC input unit, and the magnitude of the first reverse current flowing in the direction opposite to the first DC current through the first DC input unit is the first determination value. And a short-circuit detector configured to output a first short-circuit detection signal when the exceeding is detected based on the output of the first current detector. The power conversion device may further include a second DC input unit capable of receiving the second DC current, and a second current detector provided in the second DC input unit. The short-circuit detection unit outputs to the output of the second current detector that the magnitude of the second reverse current flowing in the opposite direction to the second DC current through the second DC input unit exceeds the predetermined second determination value. It may be configured to output a second short circuit detection signal when detected based on the above.

Description

The present invention relates to a power conversion device.

Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 2013-80731, there is known a power conversion system in which a solar cell string is provided with an ammeter. In particular, FIG. 9 of the above publication describes a configuration in which a plurality of solar cell strings is provided and an ammeter is provided for each solar cell string.

Japanese Patent Laid-Open No. 2013-80731

Generally, when a short circuit occurs between a positive electrode and a negative electrode in a power system, a large current flows through the short-circuited portion. This large current is generally blocked by a protective element such as a fuse.

However, in a power system that has a solar cell or other constant current power supply, the current that flows when a short circuit occurs between the positive and negative electrodes in the circuit is the current during rated operation compared to other general power systems. Does not increase significantly. Therefore, there is a problem that it is difficult to detect a short circuit. In this type of power system in which the current flowing at the time of short circuit does not change significantly, there is still room for improvement from the viewpoint of ensuring complete protection against short circuits between the positive and negative electrodes.

The present invention has been made to solve the above problems, and an object thereof is to provide a power conversion device having a function of detecting a short circuit between a positive electrode and a negative electrode.

The first power conversion device according to the present application is
A first direct current input part constructed to accept a first direct current,
A power conversion circuit that outputs an AC current by converting the first DC current input from the first DC input unit,
A first current detector provided in the first DC input section,
It was detected based on the output of the first current detector that the magnitude of the first reverse current flowing in the opposite direction to the first DC current through the first DC input unit exceeded the first determination value. In this case, a short-circuit detector configured to output the first short-circuit detection signal as a switch-on signal ,
Equipped with
The power conversion circuit,
A positive electrode input terminal connected to the positive electrode of the first DC input section,
A negative electrode input end connected to the negative electrode of the first DC input section,
Have
One end is connected to the positive electrode input end and the other end is connected to the negative electrode input end, and a switch for electrically connecting the positive electrode input end and the negative electrode input end in response to the switch-on signal output by the short circuit detection unit. ,
Further prepare.

The second power conversion device according to the present application,
A first direct current input part constructed to accept a first direct current,
A second DC input section constructed to accept a second DC current,
A positive electrode input terminal connected to each positive electrode of the first DC input section and the second DC input section, and a negative electrode connected to each negative electrode of the first DC input section and the second DC input section A power conversion circuit having an input end;
A first current detector provided in the first DC input section,
A second current detector provided in the second DC input section,
When the total current value obtained by summing the current value detected by the first current detector and the current value detected by the second current detector exceeds the judgment value, it is constructed to output a short circuit detection signal. Short circuit detector,
Equipped with.

According to the first power conversion device, the following effects can be obtained. When receiving the first DC current from the first solar cell string via the first DC input unit, the short-circuit detection unit can detect whether or not the first DC current is correctly flowing in the forward direction. .. If the first reverse current flowing in the reverse direction is generated and the magnitude of the first reverse current exceeds the reference value, the reverse current with a magnitude exceeding the normal range is usually assumed. Is flowing to the side of the first solar cell strings. In this case, there is a high possibility that a short circuit between the first positive electrode and the negative electrode, which is a short circuit on the side of the first solar cell string, has occurred. Therefore, the short circuit detection unit can output a short circuit detection signal indicating that such a short circuit between the first positive electrode and the negative electrode has occurred.

According to the second power converter, the following effects can be obtained. When the current from each of the first solar cell string and the second solar cell string is received via the first DC input section and the second DC input section, whether the magnitude of the total current is appropriate is determined. It can be determined by the short-circuit detector. If the magnitude of the total current exceeds the reference magnitude, the magnitude of the current that normally exceeds the expected range is flowing to the power conversion circuit side. In this case, there is a high possibility that a short circuit between the second positive electrode and the negative electrode in which the positive electrode and the negative electrode of the power conversion circuit are short-circuited has occurred. Therefore, the short circuit detection unit can output a short circuit detection signal indicating that such a short circuit between the second positive electrode and the negative electrode has occurred.

It is a circuit diagram showing the composition of the power converter concerning an embodiment, and the first short circuit mode. It is a block diagram which shows the 1st short circuit detection part concerning embodiment. It is a circuit diagram which shows the structure of the power converter device and 2nd short circuit mode concerning embodiment. It is a block diagram which shows the 2nd short circuit detection part concerning embodiment. It is a figure for demonstrating operation|movement of the 2nd short circuit detection part concerning embodiment. It is a block diagram which shows the 2nd short circuit detection part concerning the modification of embodiment. 3 is a configuration example of a control unit according to the embodiment.

In the embodiment, two different short circuit modes are detected. The “first short-circuit mode” is a mode in which the first positive-negative electrode short-circuit X1 shown in FIG. 1 has occurred. The “second short-circuit mode” is a mode in which the second positive-negative electrode short-circuit X2 shown in FIG. 3 has occurred.

[System Configuration of Embodiment and First Short-Circuit Mode]
FIG. 1 is a circuit diagram showing a configuration and a first short-circuit mode of a power conversion device 6 according to an embodiment. A solar power generation system 1 including a power conversion device 6 is also illustrated in FIG. 1.

First, the configurations of the solar power generation system 1 and the power conversion device 6 will be described with reference to FIG. 1. The solar power generation system 1 includes a first solar cell string #1, a second solar cell string #2, a third solar cell string #3, a first connection box 4a, a second connection box 4b, and a third solar cell string #3. The connection box 4c, the power converter 6, and the transformer 16 are provided.

The first solar cell string #1 includes a plurality of solar cell panels 2a. The first DC current output from each of the plurality of solar cell panels 2a joins inside the first junction box 4a.

The second solar cell string #2 includes a plurality of solar cell panels 2b. The second DC current output from each of the plurality of solar cell panels 2b merges inside the second junction box 4b.

The third solar cell string #3 includes a plurality of solar cell panels 2c. The third DC current output from each of the plurality of solar cell panels 2c joins inside the third junction box 4c.

Hereinafter, the first solar cell string #1, the second solar cell string #2, and the third solar cell string #3 may be collectively referred to as “solar cell strings #1 to #3”.

In the solar power generation system 1, the DC power generated by the solar cell strings #1 to #3 is converted into AC power by the power conversion device 6. The solar power generation system 1 is grid-connected to the power grid 17. The AC power converted by the power converter 6 is supplied to the power grid 17.

As illustrated in FIG. 1, the power conversion device 6 includes a first DC input unit 91, a second DC input unit 92, a third DC input unit 93, a first current detector 10a, and a second current detection unit. Device 10b, third current detector 10c, DC side circuit breaker 11, power conversion circuit 12, DC smoothing capacitor 13, switch SW, AC filter circuit 14, AC side circuit breaker 15, and control unit. 20 is provided.

The first DC input unit 91, the second DC input unit 92, and the third DC input unit 93 each include a positive electrode terminal 9a and a negative electrode terminal 9b. The fuse 7 is provided inside each of the first DC input unit 91, the second DC input unit 92, and the third DC input unit 93. The fuse 7 is also provided inside the first connection box 4a, the second connection box 4b, and the third connection box 4c.

The positive electrode terminal 9a of the first DC input unit 91 and the positive electrode of the first connection box 4a are connected, and the negative electrode terminal 9b of the first DC input unit 91 and the negative electrode of the first connection box 4a are connected. The first DC input unit 91 is constructed to be able to receive the first DC current supplied from the first solar cell string #1.

The positive electrode terminal 9a of the second DC input unit 92 and the positive electrode of the second connection box 4b are connected, and the negative electrode terminal 9b of the second DC input unit 92 and the negative electrode of the second connection box 4b are connected. The second DC input unit 92 is constructed to be able to receive the second DC current supplied from the second solar cell string #2.

The positive electrode terminal 9a of the third DC input unit 93 and the positive electrode of the third connection box 4c are connected, and the negative electrode terminal 9b of the third DC input unit 93 and the negative electrode of the third connection box 4c are connected. The third DC input unit 93 is constructed to be able to receive the third DC current supplied from the third solar cell string #3.

The first current detector 10a is provided at the subsequent stage of the fuse 7 in the first DC input unit 91. The first current detector 10a detects a current flowing via the first DC input unit 91. The first current detector 10a outputs the first detected current value I _st1 which is the detected current value to the control unit 20.

The second current detector 10b is provided at a stage subsequent to the fuse 7 in the second DC input section 92. The second current detector 10b detects the current flowing through the second DC input unit 92. The second current detector 10b outputs the second detected current value I _st2 , which is the detected current value, to the control unit 20.

The third current detector 10c is provided at a stage subsequent to the fuse 7 in the third DC input section 93. The third current detector 10c detects a current flowing via the third DC input unit 93. The third current detector 10c outputs the detected third current value I _st3 , which is the detected current value, to the control unit 20.

In the embodiment, the direction of the current flowing into the input side of the power conversion circuit 12 is the “forward direction”. In the embodiment, the direction of the current flowing out from the input side of the power conversion circuit 12 is “reverse direction”. The first current detector 10a, the second current detector 10b, and the third current detector 10c measure the forward current flowing into the power conversion circuit 12 as a positive value, and reverse the reverse direction of the forward current. The current can be measured as a negative value.

The DC circuit breaker 11 is provided on the input side of the power conversion circuit 12. A DC smoothing capacitor 13 is provided between the DC circuit breaker 11 and the power conversion circuit 12. The AC side circuit breaker 15 is provided on the output side of the power conversion circuit 12. An AC filter circuit 14 is provided between the power conversion circuit 12 and the AC circuit breaker 15.

The power conversion circuit 12 is an inverter circuit that converts DC power into three-phase AC power. The power conversion circuit 12 is constructed by a plurality of semiconductor switching elements (not shown). The power conversion circuit 12 includes a positive electrode input end 12a and a negative electrode input end 12b.

The positive electrode input end 12a is connected to the positive electrode DC wiring 61a in the power converter 6. The positive electrode DC wiring 61a is connected to the positive electrode terminal 9a of the first DC input unit 91, the positive electrode terminal 9a of the second DC input unit 92, and the positive electrode terminal 9a of the third DC input unit 93.

The negative electrode input end 12b is connected to the negative electrode DC wiring 61b in the power converter 6. The negative electrode DC wiring 61b is connected to the negative electrode terminal 9b of the first DC input unit 91, the negative electrode terminal 9b of the second DC input unit 92, and the negative electrode terminal 9b of the third DC input unit 93.

The power conversion circuit 12 converts the first DC current to the third DC current input via the first DC input unit 91, the second DC input unit 92, and the third DC input unit 93, thereby converting the AC current. Output current.

The control unit 20 includes a first short circuit detection unit 21 and a second short circuit detection unit 22. When detecting the first short circuit X1 between the positive and negative electrodes shown in FIG. 1, the first short-circuit detector 21 outputs a switch-on signal S1, breaker trip signals S2, S3, and an alarm signal S4a.

More specifically, the first short circuit detection unit 21 includes a first block 21a, a second block 21b, and a third block 21c. The alarm signal S4a includes an alarm signal S41 output by the first block 21a, an alarm signal S42 output by the second block 21b, and an alarm signal S43 output by the third block 21c.

The short circuit X1 between the first positive electrode and the negative electrode has the first current detector 10a, the second current detector 10b, and the third current detector 10c as reference positions, and is closer to the solar cell strings #1 to #3 than the reference position. This is a short circuit between the positive and negative electrodes that occurs. Specifically, between the first connection box 4a and the first DC input section 91, between the second connection box 4b and the second DC input section 92, the third connection box 4c and the third DC input section 93. A short circuit X1 between the first positive electrode and the negative electrode occurs in at least one of The first positive-negative electrode short-circuit X1 may occur further on the solar cell strings #1 to #3 side than the first connection box 4a to the third connection box 4c.

In FIG. 1, as an example, a case where a first positive-negative electrode short circuit X1 occurs between the first junction box 4a and the first DC input unit 91 is shown. When the short circuit X1 between the first positive and negative electrodes occurs as in FIG. 1, the current Ix1 flows to the short-circuited portion of the short circuit X1 between the first positive and negative electrodes. The current Ix1 is the sum of the DC currents input from the second DC input unit 92 and the third DC input unit 93.

Details of the configuration and operation of the first short-circuit detector 21 will be described later with reference to FIG.

When the second short-circuit between the positive and negative electrodes X2 (see FIG. 3, which will be described later) is detected, the second short-circuit detector 22 outputs a switch-on signal S1, breaker trip signals S2, S3, and an alarm signal S4b. The configuration and operation of the second short circuit detection unit 22 will be described later with reference to FIGS. 3 and 4.

As shown in FIG. 1, one end of the switch SW is connected to the positive electrode input end 12a via the positive electrode DC wiring 61a. The other end of the switch SW is connected to the negative electrode input end 12b via the negative electrode DC wiring 61b. The switch SW is turned on in response to the switch-on signal S1 output by the first short circuit detection unit 21. When the switch SW is turned on, the positive electrode input end 12a and the negative electrode input end 12b become conductive.

When the short circuit X1 between the first positive electrode and the negative electrode in the first short-circuit mode occurs, the switch SW is turned on, so that the "other current path" for intentionally flowing the current can be created while avoiding the short-circuit path. If the switch SW remains off, the short circuit current Ix2 flows due to the current Ix1 heading for the first positive electrode negative electrode short circuit X1. In this respect, in the embodiment, the current Ix1 can be made to flow so as to generate the flow of the current Ix3 of FIG. 1 via the switch SW. As a result, it is possible to prevent the short-circuit current Ix2 from flowing in the short-circuit path generated by the first positive-negative electrode short-circuit X1.

The DC side circuit breaker 11 is tripped in response to the circuit breaker trip signal S2. The AC side circuit breaker 15 is tripped in response to the circuit breaker trip signal S3. As a result, the protection operation can be performed when a short circuit occurs.

The alarm signal S4a and the alarm signal S4b may be transmitted to a monitoring device (not shown) provided outside the power conversion device 6. In response to the alarm signal S4a and the alarm signal S4b, an alarm display may be displayed on an alarm device (not shown) provided in or around the housing of the power conversion device 6.

[Configuration of First Short Circuit Detection Unit of Embodiment]
FIG. 2 is a block diagram showing the first short circuit detection unit 21 according to the embodiment. Each of the first block 21a, the second block 21b, and the third block 21c includes a determination value acquisition block 33 and a first comparison block 34.

In each of the first block 21a, the second block 21b, and the third block 21c, the determination value acquisition block 33 multiplies a predetermined determination reference value I _str by a negative coefficient of −1 to determine the first reverse current. The value I _ref1a , the second reverse current determination value I _ref1b, and the third reverse current determination value I _ref1c are calculated.

The first reverse current determination value I _ref1a , the second reverse current determination value I _ref1b, and the third reverse current determination value I _ref1c are values determined from a predetermined determination reference value I _str . The first reverse current determination value I _ref1a , the second reverse current determination value I _ref1b, and the third reverse current determination value I _ref1c may be common values or different values.

The first reverse current determination value I _ref1a , the second reverse current determination value I _ref1b, and the third reverse current determination value I _ref1c are the first solar cell string #1, the second solar cell string #2, and the third solar cell string #. It is preferable to set it on the basis of the rated currents corresponding to the respective power generation capacities of 3 and 3. Specifically, when the rated current of the first solar cell string #1 is 100 A, a reverse current can be allowed as long as the magnitude is equal to or less than the rated current. That is, it is possible to allow up to minus 100A.

As an example, the first reverse current determination value I _ref1a may be set to any value within the range of 1 to 2 times the rated current of the first solar cell string #1. The second reverse current determination value I _ref1b and the third reverse current determination value I _ref1c can be determined by the same policy as the first reverse current determination value I _ref1a .

The “first reverse current” is a current that flows through the first DC input unit 91 in a direction opposite to the first DC current output by the first solar cell string #1. The first reverse current is measured as a negative current in the first current detector 10a. When it is detected based on the first detected current value I _st1 of the first current detector 10 a that the magnitude of the first reverse current exceeds the first reverse current determination value I _{ref1 a} , the first block 21 a is set to the first block 21 a. The one short-circuit detection signal SX1a is output.

In the embodiment, the detection operation of the first block 21a is realized by the following specific logic by considering the direction of current flow, that is, the positive/negative of the detected current value. In the first block 21a, the first comparison block 34 compares the first reverse current determination value I _ref1a with the first detected current value I _st1 . When the first detected current value I _st1 becomes smaller than the first reverse current determination value I _ref1a , the output of the first comparison block 34 becomes high.

For example, it is _assumed that the first reference value I _{ref1a of the} reverse current is set to _{−200 A} by setting the determination reference value I _str to 200 _A. When the short circuit X1 between the first positive electrode and the negative electrode occurs, the first detected current value I _st1 becomes, for example, _{−300 A.} At this time, the first detected current value I _st1 exceeds the negative reverse current determination value I _ref1a of _{−200 A} and becomes a large value toward the negative side. That is, a situation occurs in which a reverse current is flowing and the absolute value of the measured value of the reverse current exceeds the determination reference value. In this case, since the magnitude of the first reverse current exceeds the allowable range, the output of the first comparison block 34 becomes high. The high output of the first comparison block 34 is the first short circuit detection signal SX1a.

On the other hand, when the first detected current value I _st1 is _greater than or equal to the first reverse current determination value I _ref1a , the output of the first comparison block 34 becomes low. For example, _assume that the first reverse current determination value I _ref1a is set to _{−200 A} and the measured first detected current value I _st1 is ₋₁₀₀ A. In this case, although the reverse current is flowing, the “magnitude of the current flowing in the minus direction, that is, the reverse direction” in the first DC input unit 91 is 100 A, which is determined to be within the allowable range. That is, the situation in which the first detected current value I _st1 flows in the reverse direction so much that it exceeds the first reverse current determination value I _ref1a does not occur. In this case, the output of the first comparison block 34 remains low.

The first short-circuit detection signal SX1a is output to the outside of the controller 20 in the form of a switch-on signal S1, breaker trip signals S2 and S3, and an alarm signal S41 through the output interface of the first block 21a. The alarm signal S41 is a kind of the alarm signal S4a and indicates that there is a short circuit between the positive electrode and the negative electrode on the side of the first DC input unit 91.

When it is detected based on the second detected current value I _st2 of the second current detector 10 b that the magnitude of the second reverse current exceeds the second reverse current determination value I _ref1 b, the second block 21 b is set to the first block 21 b. The two short circuit detection signal SX1b is output. The second reverse current is a current that flows through the second DC input unit 92 in a direction opposite to the second DC current output by the second solar cell string #2. Also in the second block 21b, the detection operation considering the positive/negative of the current value is constructed by the same mechanism as the above-mentioned first block 21a.

The second short circuit detection signal SX1b is output to the outside of the controller 20 in the form of a switch-on signal S1, breaker trip signals S2 and S3, and an alarm signal S42 through the output interface of the second block 21b. The alarm signal S42 is a kind of the alarm signal S4a, and indicates that there is the first positive-negative electrode short circuit X1 on the side of the second DC input unit 92.

When it is detected that the magnitude of the third reverse current exceeds the third reverse current determination value I _ref1c based on the third detected current value I _st3 of the third current detector 10c, the third block 21c determines the third block 21c. Three short circuit detection signal SX1c is output. The third reverse current is a current flowing through the third DC input unit 93 in a direction opposite to the third DC current output by the third solar cell string #3. Also in the third block 21c, the detection operation in consideration of the positive/negative of the current value is constructed by the same mechanism as the first block 21a described above.

The third short circuit detection signal SX1c is output to the outside of the controller 20 in the form of a switch-on signal S1, breaker trip signals S2 and S3, and an alarm signal S43 through the output interface of the third block 21c. The alarm signal S43 is a kind of the alarm signal S4a, and indicates that there is the first positive-negative electrode short circuit X1 on the side of the third DC input unit 93.

According to the embodiment described above, when the current from the first solar cell string #1 is received via the first DC input unit 91, the current is the current of the first solar cell string #1. The first short-circuit detector 21 can detect whether or not the direct current is properly flowing in the forward direction. If the first reverse current flowing in the reverse direction is generated and the magnitude of the first reverse current exceeds the predetermined standard, the magnitude of the reverse current exceeding the normal range is usually exceeded. It flows to the side of the first solar cell string #1. In this case, there is a high possibility that the first positive-negative electrode short-circuit X1 in the first short-circuit mode has occurred on the side of the first solar cell string #1. Such a short circuit detection principle can be similarly applied to the current flowing through the second DC input unit 92 and the third DC input unit 93.

The first short-circuit detection unit 21 can output a first short-circuit detection signal SX1a indicating that the first positive-negative electrode short circuit X1 in the first short-circuit mode has occurred. Similarly, the first short-circuit detection unit 21 outputs a second short-circuit detection signal indicating that the first positive-negative electrode short circuit X1 in the first short-circuit mode has occurred in the second DC input unit 92 and the third DC input unit 93. The SX1b and the third short circuit detection signal SX1c can be output.

Since the first short-circuit detection signal SX1a, the second short-circuit detection signal SX1b, and the third short-circuit detection signal SX1c are separately output, the first DC input unit 91, the second DC input unit 92, and the third DC input unit. It is also possible to discriminately detect in which of 93 the short circuit has occurred.

[Configuration of Second Short Circuit Mode and Second Short Circuit Detection Unit of Embodiment]
FIG. 3 is a circuit diagram showing a configuration and a second short-circuit mode of the power conversion device 6 according to the embodiment. The configuration of the power conversion device 6 and the configuration of the solar power generation system 1 are the same in FIG. 1 and FIG. 3, and thus the description of the configuration is omitted.

As shown in FIG. 3, the second short-circuit mode, that is, the second short circuit X2 between positive and negative electrodes is a short circuit that occurs between the positive electrode DC wiring 61a and the negative electrode DC wiring 61b. When the short circuit X2 between the second positive and negative electrodes occurs, the short circuit current Ix4 flows to the short-circuited portion of the short circuit X2 between the second positive and negative electrodes. The short-circuit current Ix4 is the sum of the current input from the first DC input unit 91 and the sum of the currents input from the second DC input unit 92 and the third DC input unit 93 (that is, the current Ix1). Is.

FIG. 4 is a block diagram showing the second short circuit detection unit 22 according to the embodiment. The second short circuit detection unit 22 includes a total value calculation block 41, a low pass filter block 42, a gain block 43, and a second comparison block 44.

Total value calculation block 41, by adding the first detected current value _{I st1} and the second detected current value _{I st2} and a third detected current value _{I st3,} calculates a total current value _{I stsum.} The total current value I _stsum is input to the second comparison block 44 and the low pass filter block 42.

The low-pass filter block 42 can prevent the change from being transmitted to a subsequent circuit when the input value changes more rapidly than a predetermined speed. The time constant of the low-pass filter block 42 is set to a value that allows a gradual current change due to solar radiation fluctuation to pass through, and is set to an appropriate value that can cut off a sudden current change at the time of a short circuit.

The gain block 43 multiplies the input value by a predetermined gain coefficient K. In the second short-circuit detecting unit 22, the low-pass filter block 42 filters the total current value I _stsum . Next, the gain block 43 multiplies the value passed through the low-pass filter block 42 by the gain coefficient K.

As an example, the gain coefficient may be set to any value within the range of 1.1 to 1.5. The gain block 43 is preferably constructed so that the gain coefficient K can be variably set afterwards. The calculated value multiplied by the gain coefficient K is input to the second comparison block 44 as the total determination value I _sumref .

FIG. 5 is a diagram for explaining the operation of the second short circuit detection unit 22 according to the embodiment. In FIG. 5, a schematic graph of the total current value I _stsum is illustrated by a solid line, and a total determination value I _sumref corresponding to the graph is illustrated by a broken line.

The gradual fluctuation of the total current value I _stsum is a schematic representation of solar radiation fluctuation. Since the low-pass filter block 42 passes the current change due to the solar radiation fluctuation, the total current value I _stsum and the total determination value I _sumref change gently with the same tendency.

When a short circuit X2 between the second positive and negative electrodes occurs at time tx in FIG. 5, a short circuit current flows through the short circuit X2 between the second positive and negative electrodes. Since the current flowing from the solar cell strings #1 to #3 increases due to the short-circuit current, the current values measured by the first current detector 10a to the third current detector 10c increase. As a result, as shown in FIG. 5, the total current value I _stsum sharply increases at the time tx.

The low-pass filter block 42 stops a _sudden change in the total current value I _stsum at time tx. Therefore, even at time tx, the total determination value I _sumref holds the value immediately before the occurrence of the short circuit. Since the total determination value I _sumref is constant and the total current value I _stsum sharply increases, the total current value I _stsum increases beyond the total determination value I _sumref at the point indicated by the symbol Q.

The second comparison block 44 compares the total current value I _stsum with the total determination value I _sumref . The output of the first comparison block 34 is low during a period in which the total current value I _stsum before time tx is equal to or less than the total determination value I _sumref . However, when the total current value I _stsum becomes larger than the total judgment value I _{sumref at} the point Q in FIG. 5, the output of the second comparison block 44 becomes high. That is, the total current value I _stsum exceeds the total determination value I _sumref on the plus side. The high output of the second comparison block 44 is the short circuit detection signal SX2.

According to the embodiment described above, when the currents from the respective solar cell strings #1 to #3 are received via the first DC input unit 91 to the third DC input unit 93, the total current value I _{stsum is obtained.} The second short-circuit detection unit 22 can determine whether the size of is appropriate. If the magnitude of the total current exceeds the predetermined standard, a current larger than the original current is flowing to the power conversion circuit 12 side. In this case, there is a high possibility that the second positive-negative electrode short-circuit X2 in the second short-circuit mode has occurred in the preceding stage of the power conversion circuit 12. Therefore, the second short-circuit detection unit 22 can output a short-circuit detection signal SX2 indicating that such a second positive-negative electrode short circuit X2 in the second short-circuit mode has occurred.

In addition, the provision of the low-pass filter block 42 and the gain block 43 has the following advantages. The number of solar cell strings #1 to #3 and the current value for each solar cell string differ for each power system. As a result, the appropriate total determination value I _sumref for determining the total current is different for different power systems. In this regard, according to the embodiment, since the operation by the low-pass filter block 42 and the gain block 43 is subjected to the total current value _{I Stsum,} suitable total determination value _{I Sumref} is calculated. As a result, there is an advantage that the total determination value I _sumref does not have to be individually _reset for each system.

Further, according to the embodiment, since the gain coefficient K is 1.1 to 1.5, a value _1.1 to 1.5 times the actually input total current value I _stsum is set as the total determination value I _sumref . Can be set. As a result, the second positive-negative electrode short-circuit X2 can be detected quickly and with high accuracy even if the current flowing when the positive-negative electrode short-circuits is small. The gain coefficient K can be set to any value larger than 1.

In addition, in the embodiment, the switch SW becomes conductive in response to the switch-on signal S1 output by the second short-circuit detection unit 22. Since a path for intentionally flowing the short-circuit current when the second positive-negative electrode short-circuit X2 in the second short-circuit mode occurs can be created, and thus the current flowing to the generated short-circuited portion can be reduced. Therefore, the protection function is perfect for both the first short-circuit mode and the second short-circuit mode.

In the embodiment, the control unit 20 turns on at least one of the DC side circuit breaker 11 and the AC side circuit breaker 15 when at least one of the first short circuit detection unit 21 and the second short circuit detection unit 22 detects a short circuit. Built to trip. Therefore, the protection function can be further enhanced.

The control unit 20 according to the embodiment includes both the first short circuit detection unit 21 and the second short circuit detection unit 22. Therefore, the short circuit X1 between the first positive and negative electrodes in the first short-circuit mode and the short circuit X2 between the second positive and negative electrodes in the second short-circuit mode can be detected separately. In the embodiment, the alarm signal S4a (more specifically, S41, S42, S43) is output according to the first positive electrode negative electrode short circuit X1, and the alarm signal S4b is output according to the second positive electrode negative electrode short circuit X2. .. As a result, not only the short circuit detection but also the specific location of the short circuit can be notified to the outside.

[Modification of Embodiment]
A bandpass filter block may be used instead of the lowpass filter block 42 of FIG. It suffices that the bandpass filter block has a filter function of blocking signals in the high frequency band, like the lowpass filter block 42.

Note that the order of the low-pass filter block 42 and the gain block 43 may be the reverse of that of FIG. 4, that is, the gain block 43 may be in the preceding stage.

FIG. 6 is a block diagram showing the second short circuit detection unit 22 according to the modification of the embodiment. The judgment value setting unit 143 stores the total judgment value I _sumref in a rewritable manner. In the modification of FIG. 6, the total determination value I _sumref is a fixed value or a variable set value that is determined independently of the total current value I _stsum .

The power conversion device 6 including only one of the first short circuit detection unit 21 and the second short circuit detection unit 22 may be provided.

In addition, in embodiment, the solar power generation system 1 provided with three solar cell strings #1-#3 is provided. However, the number of solar cell strings is not limited to three. The number of solar cell strings may be one, two, or four or more. The above-described various determination values may be adjusted according to the number of solar cell strings connected.

FIG. 7 is a configuration example of the control unit 20 according to the embodiment. FIG. 7 is a hardware configuration diagram applicable to the control unit 20 in the embodiment of the present invention. As shown in FIG. 7, each function of the control unit 20 can be realized by the processing circuit 50. The processing circuit 50 includes a processor 51 and a memory 52.

For example, the processor 51 is a CPU (Central Processing Unit) such as a central processing unit, a processing unit, a microprocessor, a microcomputer, a processor, or a DSP. For example, the memory 52 is a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, an EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD. In the processing circuit 50, the program stored in the memory 52 is executed by the processor 51.

Although the solar power generation system 1 is provided in the embodiment, the power conversion device 6 is not limited to the solar power generation application. A constant current power source other than a solar cell may be connected to the power conversion device 6.

1 solar power generation system, #1 first solar cell string, #2 second solar cell string, #3 third solar cell string, 2a, 2b, 2c solar cell panel, 4a first connection box, 4b second connection box 4c Third connection box, 6 Power converter, 7 Fuse, 9a Positive terminal, 9b Negative terminal, 10a First current detector, 10b Second current detector, 10c Third current detector, 11 DC breaker, 12 power conversion circuit, 12a positive electrode input terminal, 12b negative electrode input terminal, 13 DC smoothing capacitor, 14 AC filter circuit, 15 AC side circuit breaker, 16 transformer, 17 power system, 20 control unit, 21 first short-circuit detection unit, 21a 1st block, 21b 2nd block, 21c 3rd block, 22 2nd short circuit detection part, 33 judgment value acquisition block, 34 1st comparison block, 41 total value calculation block, 42 low-pass filter block, 43 gain block, 44 Second comparison block, 50 processing circuit, 51 processor, 52 memory, 61a positive DC wiring, 61b negative DC wiring, 91 first DC input section, 92 second DC input section, 93 third DC input section, 143 judgment value Setting unit, I _ref1a first reverse current determination value, I _ref1b second reverse current determination value, I _ref1c third reverse current determination value, I _st1 first detection current value, I _st2 second detection current value, I _st3 third Detection current value, I _str determination reference value, I _stsum total current value, I _sumref total determination value, S1 switch on signal, S2, S3 circuit breaker trip signal, S41, S42, S43, S4a alarm signal, S4b alarm signal, SW Switch, SX1a first short circuit detection signal, SX1b second short circuit detection signal, SX1c third short circuit detection signal, SX2 short circuit detection signal, X1 first short circuit between positive and negative electrodes, X2 second short circuit between positive and negative electrodes

Claims (6)

A first direct current input part constructed to accept a first direct current,
A power conversion circuit that outputs an AC current by converting the first DC current input from the first DC input unit,
A first current detector provided in the first DC input section,
It was detected based on the output of the first current detector that the magnitude of the first reverse current flowing in the opposite direction to the first DC current through the first DC input unit exceeded the first determination value. In this case, a short-circuit detector configured to output the first short-circuit detection signal as a switch-on signal ,
Equipped with
The power conversion circuit,
A positive electrode input terminal connected to the positive electrode of the first DC input section,
A negative electrode input end connected to the negative electrode of the first DC input section,
Have
One end is connected to the positive electrode input end and the other end is connected to the negative electrode input end, and a switch for electrically connecting the positive electrode input end and the negative electrode input end in response to the switch-on signal output by the short circuit detection unit. ,
A power converter further provided . A second DC input section capable of accepting a second DC current,
A second current detector provided in the second DC input section,
Further equipped with,
The short-circuit detection unit outputs to the output of the second current detector that the magnitude of the second reverse current flowing in the opposite direction to the second DC current through the second DC input unit exceeds a second determination value. When detected based on, is configured to output a second short circuit detection signal as the switch-on signal ,
The switch makes the positive electrode input end and the negative electrode input end electrically conductive in response to the first short-circuit detection signal output by the short-circuit detection unit as the switch-on signal, and the short-circuit detection unit outputs the switch-on signal. The power conversion device according to claim 1, wherein the power conversion device is constructed so as to conduct the positive electrode input end and the negative electrode input end in response to the second short circuit detection signal output as . A first direct current input part constructed to accept a first direct current,
A second DC input section constructed to accept a second DC current,
A positive electrode input terminal connected to each positive electrode of the first DC input section and the second DC input section, and a negative electrode connected to each negative electrode of the first DC input section and the second DC input section A power conversion circuit having an input end;
A first current detector provided in the first DC input section,
A second current detector provided in the second DC input section,
When the total current value obtained by summing the current value detected by the first current detector and the current value detected by the second current detector exceeds the judgment value, it is constructed to output a short circuit detection signal. Short circuit detector,
A power conversion device including. The short circuit detection unit,
A filter unit that damps a signal that changes more rapidly than a predetermined speed,
A gain unit that multiplies the input value by a predetermined gain coefficient,
Including
The electric power according to claim 3 , wherein the short-circuit detection unit is constructed so that a value obtained by applying filtering by the filter unit and multiplication of the gain coefficient by the gain unit to the total current value is the determination value. Converter. One end is connected to the positive electrode input terminal and the other end is connected to the negative electrode input terminal, and a switch for electrically connecting the positive electrode input terminal and the negative electrode input terminal in response to the short circuit detection signal output by the short circuit detection unit. The power conversion device according to claim 3 , further comprising: The short circuit detection unit,
By performing an arithmetic process for summing the current value detected by the first current detector and the current value detected by the second current detector, a total value calculation block that outputs the total current value,
A comparison block that outputs the result of comparing the total determination value and the total current value output by the total value calculation block as the short circuit detection signal,
The power conversion device according to claim 3, comprising:

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