KR101011003B1 - Dc feeder groundfault detector - Google Patents

Abstract

The present invention relates to a ground fault detection device for a direct current line. In the present invention, a distribution resistor (R1) (R2) is connected between the P (+) side and the N (-) side of the DC line 120, the internal resistance at the common connection point of the distribution resistor (R1) (R2) The current detection unit 140 having an r _ct is connected. The current detector 140 is grounded. And even if a ground fault occurs at the P (+) side or the N (-) side of the DC line 120, the absolute signal is processed so that the detector output signal output through the current detector 140 is always a positive value. The value circuit unit 160 and the comparator 170 for comparing the detection unit output signal of the absolute value circuit unit 160 with a preset ground current reference value are sequentially connected. In addition, the control means 180 for controlling the driving of the power converter 110 is connected to the DC line 120 according to the comparison result of the comparison unit 170 is configured. According to the present invention having such a configuration, there is an advantage that the ground current can always be compared with the reference value in the positive region regardless of the current direction when a ground fault occurs.

Ground Current, DC Cable, Power Converter, Solar Power System

Description

DC line ground fault detection device {DC FEEDER GROUNDFAULT DETECTOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault detection device, and more particularly, to a direct current line fault detection device for detecting a ground fault state of an input current line of a power converter.

In response to international and global environmental issues, increased power consumption due to improved people's living standards, and the restructuring of the power industry, domestic and foreign countries are spurring the development of alternative energy, that is, new energy sources. Alternative energy may include, for example, photovoltaic power generation, wind power generation, fuel cell power generation, biotechnology, waste, solar power generation, cogeneration and the like.

Among them, photovoltaic power generation using sunlight as an energy source is under development to improve efficiency, or some of them have already been put into practical use.

A representative example of photovoltaic power generation is the use of solar cells. Photovoltaic power generation can not only use the generated power by itself, but also convert the DC power generated by the solar cell into AC power and supply it to the commercial power system.

In particular, the commercial power system boosts the voltage of the DC power generated by the solar cell by the booster circuit, and the inverter circuit controls the AC power of the same frequency as the AC power of the commercial power system.

The commercial power system is provided with a detection device for detecting a ground fault of the DC line connecting the solar cell and the commercial power system. If a ground fault does not occur properly, a system connected to the commercial power system may be stopped, and damage may occur to a boost circuit and an inverter configured for power conversion.

Therefore, various types of ground fault detection devices have been proposed, and as an example of the DC line detection device, 'Korea Electric Power Corporation' filed the name of 'DC cable ground fault detector' on May 15, 1997, There is a prior art published in 5 date (Japanese Patent No. 1998-0083497).

When the ground fault occurs in a DC line used in a power plant or the like, the alarm can be detected as well as the degree of the ground fault and the position of the ground fault compared to the set value, and the applied AC voltage used in the AC voltage drop method can be used. 11 [㎐] can be used to minimize the influence of AC 60 [㎐] and to reduce the ripple frequency that causes noise in DC.

However, the prior art that provides such a function is complicated in its construction.

That is, the configuration of the 11 [k] signal generator is necessary in order to supply the 11 [k] square wave signal constantly so as not to be affected by temperature and other environments.

The 11 [kW] signal generator supplies 11 [kW] square wave signals to the DC line, wherein the 11 [k] signal generator receives the converted device operating voltage to operate the photo coupler according to the control signal of the first central processing apparatus. It is supplied through the bridge rectifier. Therefore, a DC-DC converter for supplying power for driving the photo coupler should be configured in the 11 [k] signal generator.

In addition, it is also necessary to configure a bridge rectifier for rectifying the operation signal output from the photo coupler.

In addition, the signal conversion unit detects the signal phase removed through the low pass filter and converts the effective value. The signal conversion unit includes an AC amplifier amplifying the input signal and a gain amplifier amplifying the gain of the signal filtered by the low pass filter. And an effective value converter for converting this to the ground current effective value.

Such a complicated configuration increases the manufacturing cost of the ground fault detector, thereby weakening the competitiveness with the same product.

And as the configuration is complicated, the probability of occurrence of a malfunction increases, and coping with a failure may not be executed quickly.

Accordingly, the present invention has been made to solve the above problems, an object of the present invention is to provide a ground fault detection apparatus of a direct current line to detect a ground fault of the direct current line with a simpler configuration.

Another object of the present invention is to be able to compare the ground current reference value in the positive region at all times regardless of the current direction when a ground fault occurs.

According to a feature of the present invention for achieving the above object, a distribution resistor (R1) (R2) connected between the P (+) side and the N (-) side of the DC line; A current detector connected to a common connection point of the distribution resistors R1 and R2 and having an internal resistance r _ct ; An absolute value circuit unit for processing an output signal output through the current detector to always be a positive value; A comparison unit comparing the output signal of the absolute value circuit unit with a preset ground current reference value; And a control unit for controlling the driving of the power converter connected to the DC line according to the comparison result of the comparison unit.

According to another feature of the invention, the distribution resistor (R1) (R2) connected between the P (+) side and the N (-) side of the DC line; A current detector connected to a common connection point of the distribution resistors R1 and R2 and having an internal resistance r _ct ; A comparison unit comparing the output signal of the current detection unit with a preset ground current reference value; And, according to the comparison result of the comparison unit includes a control unit for controlling the drive of the power converter connected to the DC line, the output signal output as a (+) or (-) value according to the ground fault occurrence position of the DC line Ground fault current reference values of (+) and (-) shall be provided for comparison respectively.

The ground fault detection device may further include a low pass filter for removing high frequency components included in the output signal of the current detection unit.

According to the ground fault detection apparatus of the DC line of the present invention having the above-described configuration has the following effects.

First, connect the current detector with the internal resistance (r _ct ) to the common connection point of the distribution resistors (R1) and (R2) connected between the P (+) side and the N (-) side of the DC line, and cause a ground fault in the DC line. At the time of occurrence, the ground fault current can be detected by a simple configuration.

And even if a ground fault occurs on the P (+) side or N (-) side of the DC line, the ground fault current can always be compared with the reference value in the positive region by means of the absolute value circuit section, so it is easy to cope with the ground fault regardless of the current direction. It can be effective.

In addition, when the ground fault occurs, the output of the comparator may be directly used, and in this case, the solar power generation system in which the ground fault detection device is installed may be safely protected without the control of the control unit.

Hereinafter, a ground fault detection apparatus for a DC line according to the present invention will be described in detail with reference to a preferred embodiment shown in the accompanying drawings.

The ground fault detection device can be used in various fields, but in the present embodiment, the DC power generated from the solar cell is received by the power converter through the DC cable line, and the solar power generator converts the AC power into the AC power in the commercial power system. The system will be described as an example.

1 is a block diagram of a photovoltaic power generation system including a ground fault detection apparatus of a DC line according to a first embodiment of the present invention.

Referring to FIG. 1, a solar module 100 in which at least one solar cell is modularized for solar power generation is configured. The photovoltaic module 100 provides power from several W to several thousand kW, depending on the combination of solar cells.

DC power generated from the solar module 100 is supplied to the power converter 110. As described above, the power converter 110 converts the DC power into AC power and outputs the same to the commercial power system. To this end, the power converter 110 includes a booster circuit and an inverter for converting DC power into AC power. In general, four or six switching elements including diodes are connected to the inverter circuit in the form of a bridge, which converts DC power boosted by the booster circuit into AC power having the same frequency and in phase as the commercial power system. Perform.

In order to supply the DC power generated from the solar module 100 to the power converter 110, the solar module 100 and the power converter 110 are connected to the DC wire path 120.

The DC wire path 120 is provided with a ground fault detection device 130 to detect a ground fault of the DC wire path 120. The ground fault detecting apparatus 130 may detect a ground fault in any one of the P (+) side and the N (−) side of the DC line 120.

The ground fault detection device 130 has the following configuration.

Two distribution resistors R1 and R2 are connected between the P (+) side and the N (−) side of the DC line 120.

In addition, the current detector 140 is connected to a common connection point of the resistor R1 and the resistor R2. The current detector 140 detects a ground current when a ground fault occurs in the DC line 120. The current detector 140 has an internal resistance r _ct connected thereto and is grounded.

The current detector 140 is connected to a filter 150 for removing high frequency components from the ground current detected by the current detector 140. The filter 150 uses a low pass filter.

The absolute value circuit unit 160 is connected to the filter 150 so that the signal removed by the filter 150 can always be compared with a preset ground current reference value in a positive region. That is, since the directions of ground fault currents are opposite to each other when a ground fault occurs on the P (+) side or the N (-) side of the DC line 120, a negative value may occur, but in this case, This is to always detect a positive signal.

A comparator 170 for comparing a signal output from the absolute value circuit unit 160, that is, a (+) signal value with a preset ground current reference value, is connected.

In addition, the controller 180 may be configured to check whether a ground fault occurs through the output of the comparator 170 and to stop driving of the booster circuit and the inverter configured in the power converter 110.

By such a control operation, even if a ground fault occurs in the DC line 120, the safety of the power converter 110 may be secured and the commercial power system may be protected.

Next, the operation of the ground fault detection apparatus of the DC line having the above configuration will be described.

As described above, the ground fault detection device 130 is configured in the photovoltaic power generation system, so when the photovoltaic power generation system operates normally, the direct current power generated by the photovoltaic module 100 is the direct current line 120. The power converter 110 is supplied through the power converter 110, and the power converter 110 converts it into AC power and supplies the power to the commercial power system or the load.

At this time, since a ground fault does not occur during normal operation of the photovoltaic power generation system, a current detection unit installed between the distribution resistors R1 and R2 of the DC line 120 located on the output side of the photovoltaic module 100 and the ground. The ground current does not flow to the 140.

Then, when a ground fault occurs on the P (+) side or the N (−) side of the DC line 120, the ground resistance Rg, the distribution resistor R1, R2, and the internal resistance of the current detector 140 are detected. Ground current flows through (r _ct ).

A process of detecting the occurrence of a ground fault at the P (+) side or the N (−) side of the DC line 120 will be described with reference to FIGS. 2 and 3.

First, FIG. 2 shows a state diagram (a) and an equivalent circuit configuration diagram (b) thereof for detecting the occurrence of a ground fault in the N (-) side of the DC line 120.

2, when a ground fault occurs on the N (-) side of the DC line 120, the ground current is P (+) line → resistance (R1) → current detector → internal resistance (r _ct ) → ground (GND) → ground fault resistance (Rg) → N (-) side.

In this case, the current detector 140 generates a detector output signal against the ground current as a positive value.

The detector output signal having the positive value is transmitted to the filter 150, and the filter 150 removes the noise signal included in the detector output signal and then transmits the noise signal to the absolute value circuit unit 160.

The absolute value circuit unit 160 transmits this value to the comparator 170 as it is because the current detector output signal has a positive value.

The comparison unit 170 compares the output signal output from the absolute value circuit unit 160 with a preset ground current reference value. The comparison unit 170 transmits the comparison result value to the control unit 180.

Then, the controller 180 checks whether a ground fault occurs according to the comparison result of the comparison unit 170, and controls to stop driving of the booster circuit and the inverter configured in the power converter 110.

The control operation of the controller 180 is to ensure the safety of the power converter when a ground fault occurs and to protect the commercial power system.

Next, FIG. 3 shows a state diagram (a) and an equivalent circuit configuration diagram (b) thereof for detecting when a ground fault occurs on the N (-) side of the DC line.

3, when a ground fault occurs on the P (+) side of the DC line 120, the ground current is the P (+) side line → ground resistance (Rg) → ground (GND) → (r _ct ) → Current detector → resistance (R2) → N (-) side flows in the direction of the line.

In other words, the ground current is reversed from the case where a ground fault occurs in the N (-) side of FIG.

Therefore, the current detector 140 generates a detector output signal against the ground current as a negative value.

The output signal of the negative value is transmitted to the filter 150, and the filter 150 removes the noise signal included in the output signal of the negative value and then transmits the noise signal to the absolute value circuit unit 160.

However, in the absolute value circuit unit 160, the output signal has a negative value. Since the ground fault current reference value can be compared by the comparing unit 170 when the output signal has a positive value, the output signal having the current negative value is transmitted to the absolute value circuit unit 160. The absolute value is processed to a positive value and output to the comparator 170.

The comparison unit 170 compares an output signal output from the absolute value circuit unit 160, that is, an output signal converted from (−) to (+) with a preset ground current reference value.

The comparison signal of the comparison unit 170 is transmitted to the control unit 180.

Then, the controller 180 checks whether there is a ground fault according to the comparison result of the comparison unit 170, and controls to stop driving of the booster circuit and the inverter configured in the power converter 110.

FIG. 4 is a block diagram of the photovoltaic power generation system including the block diagram of the DC line ground fault detecting apparatus according to the second embodiment of the present invention.

The second embodiment differs only in the configuration of the absolute value circuit portion compared with the configuration of the first embodiment described above.

That is, to briefly describe the configuration, a ground fault detection device 230 is provided to detect a ground fault in the DC line 220 connecting the solar module 200 and the power converter 210.

In the ground fault detection device 230, two distribution resistors R1 and R2 are connected between the P (+) side and the N (−) side of the DC line 220, and the resistor R1 and the resistor ( The current detector 240 is connected to the common connection point of R2). The internal resistor r _ct is connected to the current detector 240 and is grounded.

A filter 250 for removing high frequency components from the output signal of the current detector 240 is connected.

A comparator 260 is applied to receive the output signal of the current detector 240 filtered by the filter 250, compare it with a preset ground current reference value, and supply a comparison output signal to the controller 270. In this case, when a ground fault occurs on the P (+) side or the N (−) side of the DC line 220, the detector output signal is output as a (+) value or a (−) value. 260 must be provided with two ground current reference values to compare the (+) or (-) values, respectively. In other words, when the absolute value circuit part is not configured, the ground fault current reference value should be provided by being divided into (+) and (-).

The operation of the second embodiment having such a configuration will be described.

When a ground fault occurs on the P (+) side or the N (-) side of the DC line 220 of the solar module 200, the ground fault resistor Rg, the distribution resistor R1, R2, and the current detector 240 Ground current flows through the internal resistance (r _ct ).

The current detector 240 generates an output signal of (+) or (-) depending on the current direction. The output signal is transmitted from the filter 250 to the comparator 260 with the noise signal included in the detector output signal removed.

When the comparator 260 is applied with the output signal of (+) or (-), the comparator 260 compares the ground fault current reference value of (+) or (−) corresponding to the corresponding output signal, and controls the control part through the output of the comparator 260. 270 confirms whether a ground fault has occurred.

The ground fault controller 270 controls to stop driving of the booster circuit and the inverter configured in the power converter 210.

Although described with reference to the illustrated embodiment of the present invention as described above, this is merely exemplary, those skilled in the art to which the present invention pertains various modifications without departing from the spirit and scope of the present invention. It will be apparent that other embodiments may be modified and equivalent. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

For example, in the present embodiment, the DC line fault detection device is described as operating in a photovoltaic power generation system, but the DC power generated by a predetermined energy source is transmitted to the system through the DC line, and the system On the side, it is applicable to any system provided with a converter for converting DC power into AC power or other DC power.
Further, in the embodiment of the present invention, the control unit stops driving of the booster circuit and the inverter configured in the power converter according to the result of the comparator, but it is not necessary to do so. That is, it is possible to protect the photovoltaic power generation system including the ground fault detection device of the DC line by directly using the output of the comparator. For example, a photovoltaic power generation system is provided with a protection device (not shown) to protect its operation. The output value of the comparator is directly transmitted to the protection device to control a switching element to cut off DC power supplied to a power converter. Alternatively, the protection algorithm provided in the protection device may cause the booster circuit of the DC converter and the drive of the inverter to be stopped. Such an embodiment can also be applied to the present invention.

1 is an overall configuration diagram of a photovoltaic power generation system including a ground fault detection apparatus for a DC line according to a first embodiment of the present invention.

FIG. 2 is a state diagram for detecting a ground fault in the N (-) side of the DC line of FIG. 1 and an equivalent circuit diagram thereof.

FIG. 3 is a state diagram for detecting a ground fault in the P (+) side of the DC line of FIG. 1 and an equivalent circuit diagram thereof.

Figure 4 is an overall configuration diagram of a photovoltaic power generation system including a schematic diagram of a DC line ground fault detection apparatus according to a second embodiment of the present invention.

Claims (3)

Distribution resistors R1 and R2 connected between the P (+) side and the N (−) side of the DC line; A current detector connected to a common connection point of the distribution resistors R1 and R2 and having an internal resistance r _ct ; An absolute value circuit unit for processing an output signal output through the current detector to always be a positive value; A comparison unit comparing the output signal of the absolute value circuit unit with a preset ground current reference value; And, And a control unit for controlling the driving of the power converter connected to the DC line according to the comparison result of the comparing unit. Distribution resistors R1 and R2 connected between the P (+) side and the N (−) side of the DC line; A current detector connected to a common connection point of the distribution resistors R1 and R2 and having an internal resistance r _ct ; A comparison unit comparing the output signal of the current detection unit with a preset ground current reference value; And, A control unit for controlling the driving of the power converter connected to the DC line in accordance with the comparison result of the comparison unit, DC ground fault detection device, characterized in that the ground fault current reference value of (+) and (-) is provided to compare the output signal output as (+) or (-) value according to the ground fault occurrence position of the DC line . The method according to claim 1 or 2, And a low pass filter for removing the high frequency components included in the output signal of the current detector.

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