KR20110101336A - Ground fault detection device and method with direct current wire for system of photovoltaic power generation - Google Patents

Abstract

An object of the present invention is to provide a ground fault detection circuit device and a ground fault detection method which can solve a high manufacturing cost and malfunction problem by greatly simplifying the circuit configuration and are more accurate and easy to implement, and simply detect the presence of a ground fault. It does not, however, provide a means to pinpoint ground faults between multiple solar cell modules in series.
To this end, the ground fault detection circuit device of the DC line of the present invention includes a voltage divider R1 and R2 inserted in series between the P (+) side and the N (-) side of the DC line. A voltage divider resistance circuit portion 2 formed by grounding the common connection point G of R1 and R2; Receives the three voltages of the voltage (V _PG ) (V _GN ) and the voltage (V _PN ) applied to both the voltage divider (R1) and (R2), respectively. A voltage sensing unit 3 including a voltage divider 5 for stepping down a high voltage to a low voltage level and a low pass filter 6 for removing high frequency signal noise from a low voltage analog signal output from the voltage divider 5. ; And an A / D converter capable of receiving an analog signal from the low pass filter 6 of the voltage sensing unit 3 and converting the A / D into a digital value, and having the digital value digitized in real time. It is configured to include; and a control unit (4) having an MPU to send a signal to the solar generator or to generate an alarm in the event of a ground fault.

Description

Ground fault detection device and method with direct current wire for system of photovoltaic power generation}

The present invention provides a ground fault detection circuit device and a detection method of a direct current line, a ground fault detection circuit device capable of detecting a ground fault and a location of a fault point on a direct current line coming into an input of a power conversion device in a power plant, particularly a photovoltaic power generation system; It's about how.

Developed countries in response to international and global environmental problems, such as high oil prices, global efforts to reduce carbon dioxide due to global warming, and increased domestic power consumption and restructuring of the electric power industry. In addition, Korea is spurring the development of alternative energy sources, that is, new energy sources. Alternative energy is, for example, photovoltaic power generation, wind power generation, fuel cell power generation, bio, waste, solar power generation, small cogeneration.

Among them, photovoltaic power generation using sunlight as an energy source is under development to improve efficiency, or some are already widely used. 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.

For this reason, each country has been supporting a large number of photovoltaic power generation systems that are spotlighted as environmentally friendly energy because they emit little carbon dioxide among renewable energy. However, the photovoltaic power generation system has a limitation in that it cannot generate electricity at night, when there is a lot of clouds, or when it rains due to its characteristics, and the efficiency of solar cells is not high yet. The installation area of the solar cell module is inevitably larger. In most countries, the single installation capacity of the photovoltaic system is increasing due to the government-sponsored distribution project and power generation gap support system.

However, the solar cell module installed in the large area not only causes problems in the DC cable line but also needs to increase the voltage and current capacity by connecting the solar cell modules in series and in parallel, so that problems occur over time at each connection between the solar cell modules. There is no choice but to. Ground faults on DC lines can lead to life-saving accidents and can lead to major problems such as reduced efficiency of photovoltaic systems and shortened device life.

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 circuit device for detecting a ground fault of a 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 ground fault detection circuit devices have been proposed. Ground fault detectors, which have been commonly used in the past, generate an alarm compared to a set value when a ground fault occurs, and this ground fault detector has a DC voltage drop method and an AC voltage. There is a dropping method, where most of the AC dropping methods have an applied AC voltage of 20 [㎐], which greatly affects AC 60 [㎐] and causes a ripple frequency that causes noise in the DC. .

As a representative example of the DC line detection device, 'Korea Electric Power Corporation' filed under the name 'DC cable ground detector' on May 15, 1997, and disclosed on December 5, 1998 (public patent 1998). -0083497).

The prior art includes a sensor for detecting a ground fault in the direct current line; A predetermined number of low-pass filters for removing noise other than 11 [Hz] of the detected signals; A signal converter for detecting a phase of the removed signal and converting an effective value; A second central processing apparatus that receives the converted signal and compares the data collected before installing the system to determine the degree of ground fault; A self-diagnostic device for diagnosing whether the sensor operates normally; A first central processing unit which receives the determination result of the second central processing unit to control the ground state data output, to control the self-diagnosis unit, and to output a control signal for generating an 11 [㎐] square wave signal; A direct current-to-direct current (DC-DC) converter on the power plant side, which is applied to an 11 [kW] signal generator for converting the power supplied to the direct current line into a predetermined direct current operating voltage; And an 11 [kW] signal generator for generating an 11 [kW] square wave signal through a parallel resistor in response to the control signal for generating the 11 [kW] signal from the first central processing unit and the converted DC voltage. When a ground fault occurs in a DC line used in a power plant or the like, it is possible to detect not only the alarm but also the degree of the ground fault and the position of the ground fault by comparing with the set value. ㎐] minimizes the effects of AC 60 [㎐] and reduces the ripple frequency that causes noise in DC.

However, in providing such a function, the prior art has a complicated circuit configuration. In other words, in order to supply 11 [㎐] square wave signals uniformly so as not to be influenced by temperature and other environments, the configuration of the 11 [㎐] signal generator is necessary, and the 11 [㎐] signal generator needs to generate 11 [㎐] square wave signals. The 11 [kW] signal generator receives the converted device operating voltage and operates the photo coupler according to the control signal of the first central processing apparatus to supply the bridge via the 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.

This prior art using the AC voltage drop method applying an AC voltage of 11 [Hz] is difficult to implement because the circuit configuration is too complicated and requires many peripheral devices, and the production cost of the ground fault detector increases significantly. There may be a problem that can weaken the competitiveness with the same product. And as the circuit configuration is complicated, the probability of occurrence of malfunction increases, and coping with the failure may not be executed quickly.

In view of these problems, Korean Laid-Open Patent Publication No. 10-2009-0129775 discloses a distribution resistor (R1) (R2) connected between a P (+) side and a N (-) side of a DC line; A current detector connected to a common connection point of the distribution resistors R1 and R2 and having an internal resistance rct; 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, according to the comparison result of the comparison unit has proposed a DC line ground fault detection device comprising a control unit for controlling the drive of the power converter connected to the DC line.

According to the above configuration, the line invention connects a current detection unit having an internal resistance rct to a common connection point of the distribution resistors R1 and R2 connected between the P (+) side and the N (-) side of the DC line. In case of ground fault in DC line, ground fault current can be detected by simple configuration. And even if ground fault occurs on P (+) side or N (-) side of DC line, it is always positive (+) area It is claimed that the ground fault current can be compared with the reference value, so that the ground fault current can be easily coped with regardless of the current direction.

However, the above-mentioned method detects the ground fault current and compares it with the ground fault current reference value. Therefore, it is difficult to detect the ground fault current due to seasonal factors and surrounding environmental factors. There is a disadvantage that the ground fault point between the photovoltaic modules cannot be detected.

Accordingly, the present invention has been made to solve the above problems of the prior art, and its object is to provide a ground fault detection circuit device that can solve the high manufacturing cost and malfunction problem by greatly simplifying the circuit configuration and is more accurate and easy to implement. In addition, it does not merely detect the occurrence of ground faults, but also provides a means for pinpointing the ground fault point between a plurality of solar cell modules connected in series.

In order to achieve the above object, the ground fault detection circuit device of the direct current line according to the present invention includes a voltage divider R1 and R2 inserted in series between the P (+) side and the N (-) side of the direct current line. The voltage dividing resistance A voltage divider resistance circuit portion 2 formed by grounding the common connection point G of R1 and R2; Receives the three voltages of the voltage (V _PG ) (V _GN ) and the voltage (V _PN ) across the voltage dividers (R P1) and (R2) respectively. A voltage sensing unit 3 including a voltage divider 5 for stepping down a high voltage to a low voltage level and a low pass filter 6 for removing high frequency signal noise from a low voltage analog signal output from the voltage divider 5. ; And an A / D converter capable of receiving an analog signal from the low pass filter 6 of the voltage sensing unit 3 and converting the A / D into a digital value, and having the digital value digitized in real time. It is configured to include; and a control unit (4) having an MPU to send a signal to the solar generator or to generate an alarm in the event of a ground fault.

According to a preferred embodiment of the present invention, there is provided an algorithm for detecting a ground fault occurring on the P (+) side or the N (−) side with a voltage value applied to the quantified voltage divider resistance; And it includes an algorithm for detecting the position of the ground fault point generated between the solar cell modules connected in series with the voltage difference across the voltage divider resistance.

In addition, the method for detecting the ground fault of the direct current line provided for power generation by the solar cell module of the present invention, the voltage applied to the voltage divider resistors V _R1 and V _R2 of the voltage sensing unit for receiving the divided voltage of the solar cell module. Measuring; Voltage module V _Module by dividing series voltage V _PV by series number of solar cell module Obtaining a value; Comparing the values of the voltage divider V _R1 and V _R2 ; When to equal the value of the dividing resistor V _R1 and V _R2 at the step returns to the initial measurement step, and compare the series voltage V _PV and V _R1 both are the same, and it is determined that the ground fault occurred in the N-side track of the two If the values are different, the series voltage V _PV and V _R2 are compared with each other, and if they are the same, it is determined that a ground fault occurs at the P side line, and if they are different, the absolute value obtained by subtracting the value of the voltage divider resistance V _R1 from V _R2 is Determining whether the value is greater than or equal to a module V _Module value; The net of the absolute value | V _R1 - V _R2 | when the module voltage is larger than or equal to the value V _Module comprising: a determination value V _R1 to V _R2 is greater than and; If the values V _R1 at the step is greater than the value V _R2 to V _R1 V _Module After dividing the value obtained for the integer n, based on the P-side n-th cell is determined to have occurred a fault in the module and, in the case where in the step V _R1 value is smaller than V _R2 by dividing the V _R2 value in V _Module value obtained for the integer n And determining that a ground fault has occurred in the nth battery module based on the N side.

Since the present invention knows the voltage characteristics of the solar cell module provided by the solar cell module manufacturer and knows exactly whether the ground fault occurs as well as the location of the accident by only the voltage value of the series number of the solar cell module and the voltage divider resistor 2. Compared to the existing proposed methods and devices, the circuit configuration is extremely simple, so it is easy and cheap to implement, and it is very efficient because it provides an accurate ground detection method and device.

1 is a block diagram of a photovoltaic system to which the ground fault detection circuit device of the present invention is applied.
2 is a circuit diagram showing a voltage divider resistor and a low pass filter for the purpose of voltage drop of the voltage sensing unit 3 according to the present invention.
Fig. 3 is a circuit diagram showing the voltage applied to the voltage divider resistance when a ground fault occurs on the P (+) side of the DC line.
Fig. 4 is a circuit diagram showing the voltage applied to the voltage divider resistance when a ground fault occurs on the N (-) side of the DC line.
5 is a circuit diagram showing the voltage applied to the voltage divider resistance when a ground fault occurs between series connected solar cell modules.
6 is a flowchart representing an algorithm for detecting ground fault with the voltage measured at the voltage divider resistance.

In order to fully understand the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Embodiment of the present invention may be modified in various forms, the scope of the invention should not be construed as limited to the embodiments described in detail below. This embodiment is provided to more completely explain the present invention to those skilled in the art. Therefore, the shape of the elements in the drawings and the like may be exaggerated to emphasize a more clear description. It should be noted that the same members in each drawing are sometimes shown with the same reference numerals. In addition, detailed descriptions of well-known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention are omitted.

Hereinafter, the ground fault detection apparatus of the direct current line of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of a photovoltaic power generation system to which the ground fault detection device of the present invention is applied, and FIG. 2 is a circuit diagram showing a voltage divider resistance and a low pass filter for voltage drop purposes of the voltage sensing unit 3 according to the present invention. Fig. 3 is a circuit diagram showing the voltage applied to the voltage divider resistance when a ground fault occurs on the P (+) side of the DC line. 4 is a circuit diagram showing the voltage applied to the voltage dividing resistor when a ground fault occurs on the N (-) side of the DC line. FIG. 5 is a voltage applied to the voltage dividing resistor when a ground fault occurs between the solar cell modules connected in series. Fig. 6 is a flowchart showing an algorithm for detecting ground fault with the voltage measured at the voltage divider resistance.

The present invention is to detect the ground fault in the DC line that can occur in the photovoltaic power generation system can be detected in three locations where the ground fault can occur.

In general, a photovoltaic power generation system includes a solar cell module (1, connected) connected in parallel and a power converter 11 for converting DC power generated from the solar cell module 1 according to characteristics of a consumer. There is a direct current line to connect between them. In order to meet the input voltage range of the power converter, the DC line should be connected in series with the solar cell modules (1), and also in parallel with the solar cell modules connected in series to increase the current capacity. These multiple parallel groups are installed to be gathered in the junction box (1) to enter the input of the power converter 11 through a single DC line (10, 10). However, as installation capacity increases, the number of junction boxes (1) connected by a series-parallel combination increases, so when a ground fault occurs, it is difficult to identify the ground fault occurrence and the location of the ground fault. A ground fault detection circuit device is normally provided between the box 1 and the power converter 11.

The ground fault detection circuit device 20 employed in the present invention is largely composed of a voltage divider resistor circuit 2, a voltage sensing unit 3, and a controller 4.

The voltage dividing resistor circuit portion 2 includes voltage dividing resistors R1 and R2 inserted in series between the P (+) side and the N (-) side of the DC line, and the voltage dividing resistor The common connection point G between R1 and R2 is grounded to form a circuit.

The voltage sensing unit 3 receives three voltages from the voltage dividing resistor circuit 2, and the voltage V _PG across the voltage divider resistor R1 and the voltage V across the voltage divider resistor R2. _GN ) and the voltage V _PN across the voltage divider resistors R1 and R2. In general, since a plurality of solar cell modules are connected in series, these three voltages are high voltages of up to 1000 V. Therefore, the three voltages must be stepped down to a low voltage level that can be recognized by the MPU of the controller 4.

For this reason, each voltage V _PG (V _GN ) (V _PN ) introduced into the voltage sensing unit 3 is once again stepped down to a low voltage level through the voltage divider resistor 5 and then a low pass filter for high frequency blocking purpose ( 6) is output. This output, which is converted into an analog signal of low voltage, is converted into a digital value through an A / D converter of the control unit 4 and digitized. The MPU of the control unit 4 determines whether there is a ground fault using the numerical value digitized in real time, and when a ground fault occurs, it can signal a solar generator or generate an alarm.

As such, the control unit 4 includes a relay capable of generating a contact signal with the MPU. The control unit 4 digitally converts the analog signal of the low voltage level from the voltage sensing unit 3 through an A / D converter built in the MPU. It is converted to a value and digitized. The MPU determines whether there is a ground fault using three numerical values. The MPU inputs the open voltage and operating voltage of one solar cell module and the number of series of modules.

Under normal conditions, the voltage across the voltage divider resistors R1 and R2 is equally distributed in the series voltage of the solar cell module. That is, although the series voltage V _PN may change or change, the voltages V _PG and V _GN applied to the divided resistors R1 and R2 are equally divided.

V _R1 = (R1 / R1 + R2) * V _PN ,

V _R2 = (R2 / R1 + R2) * V _PN ,

V _R1 = V _R2

However, when a ground fault occurs, it appears differently depending on where it occurs. 3 is a situation in which a ground fault occurs on the P (+) side line of a DC line, and both ends of the voltage divider resistor R1 have an equipotential between the common ground terminal G and the ground fault point F: 7. V] is applied. On the contrary, the entire series voltage V _PN is applied to both ends of the voltage divider resistor R2.

FIG. 4 assumes that a ground fault occurs on the N (-) side line of the DC line, and the entire series voltage V _PN is applied to both ends of the voltage divider resistor R1, and a common ground terminal is formed at both ends of the voltage divider resistor R2. G) and the ground fault (F: 8) become equipotential and take 0 [V].

FIG. 5 assumes a ground fault occurring between the solar cell modules connected in series. The common ground terminal G and the ground fault point F: 9 form a loop as if connected through the ground. Voltage appears as

V _R1 = V _PF , V _R2 = V _FN

That is, even if a ground fault occurs, the series voltage (V _PN ) does not change, but the voltage across the voltage divider resistor is different. Consequently, the sum of the voltage V _PG and V _GN across the voltage divider resistor is equal to the series voltage V _PN .

V _PN = V _PG + V _GN

Therefore, the MPU measures the voltage in real time and monitors V _PG and V _GN to find the location of the ground fault by the difference.

The MPU of the control unit 4 detects these three ground faults, and thus can detect the position of the ground fault point. Due to the characteristics of the solar cell module 1, there are many environmental influences such as air condition, temperature, season, etc. Therefore, the open voltage and operating voltage of the solar cell module are fluctuated, and the maximum power is output from the power converter 11. In order to change the operating voltage from time to time, the controller 4 must know the voltage of one solar cell module in real time.

Voltage per Photovoltaic Module = V _PN / Number of Solar Modules in Series

When the above equation is applied, the power converter 11 is stopped and the open voltage is applied or the power converter 11 operates so that the voltage per one solar panel module can be known even if the operating voltage is applied, regardless of the operation state of the power converter. It is possible to know exactly whether a ground fault occurred and the location of the ground fault point. When the controller 4 detects a ground fault, a signal is sent to the power converter and an alarm is generated to take measures to protect the system such as stopping the power converter.

Hereinafter, the control algorithm of the present invention will be described in detail with reference to the flowchart of FIG.

When the photovoltaic module 1 generates electric power, the resistance applied to the voltage divider circuit unit 3 is measured (step (a)). The module voltage (V _Module), as in step (b) is seeking into the V _PV to be series of modules, the value of both the ground surface as compared to the resistance values V _R1 and V _R2 the next step (c) of When generating this determines that there is no progress to return to the initial step, and by comparing the V _PV value and the V _R1 value in step ten thousand and one if the value of the two do not match (d) detecting that the value of both, such as ground fault in the N-side track Is determined (step (e)), and if both values are not equal, if the value of both is detected in step (f) by comparing the V _PV value with the value of V _R2 , a ground fault has occurred in the P-side line. (Step (g)) and if the values of both are not equal, the V _module obtained in step (b) is the absolute value of V _R1 -V _R2 in step (h). If the value is equal to or greater than the value, if the equation of the notation is not satisfied, the process returns to the initial stage.

If it is detected in step ( _R ) that the value of V _R1 is greater than the value of V _R2, an integer n is obtained by dividing the resistance value V _R1 by the V _Module value, and it is determined that a ground fault has occurred in the nth module on the P side. 4) controls to alert the fact that the ground fault has occurred (step (K)) and to display the ground fault occurrence point through a separate display unit.

However, if V _R1 value is detected to be smaller than the value of V _R2 in the above step (I), the resistance value of V _R2 to V _Module By determining an integer n divided by a value, it is determined that a ground fault has occurred in the nth module with reference to the N side (step (ta)), and the control unit 4 alerts that the ground fault has occurred in the same manner as before. Step (k)) and the ground fault occurrence point are controlled to be displayed through a separate display unit.

The embodiment of the ground fault detection circuit device of the present invention described above is merely exemplary, and it is well understood that various modifications and equivalent other embodiments are possible to those skilled in the art. You will know. Therefore, it will be understood that the present invention is not limited to the forms mentioned in the above detailed description. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims. It is also to be understood that the present invention includes all modifications, equivalents, and substitutes within the spirit and scope of the invention as defined by the appended claims.

1: Solar cell module (connection box) 2: Voltage divider circuit
3: voltage sensing unit 4: control unit
5: Voltage divider 6: Low pass filter
7,8,9 (F): Girak Branch 10: DC Cable
11: Solar generator (power converter)
20: Ground fault detection circuit device

Claims (3)

A circuit device for detecting a ground fault in a DC line provided for generation by a solar cell module, the voltage divider R1 being inserted in series between the P (+) side and the N (-) side of the DC line. ) And (R2), the divided resistance A voltage divider resistance circuit portion 2 formed by grounding the common connection point G of R1 and R2; Receives the three voltages of the voltage (V _PG ) (V _GN ) and the voltage (V _PN ) applied to both the voltage divider (R1) and (R2), respectively. A voltage sensing unit 3 including a voltage divider 5 for stepping down a high voltage to a low voltage level and a low pass filter 6 for removing high frequency signal noise from a low voltage analog signal output from the voltage divider 5. ; And an A / D converter capable of receiving an analog signal from the low pass filter 6 of the voltage sensing unit 3 and converting the A / D into a digital value, and having the digital value digitized in real time. And a control unit (4) having an MPU which sends a signal to a solar generator or generates an alarm when a ground fault occurs.
2. The system of claim 1, further comprising: an algorithm for detecting a ground fault occurring on the P (+) side or the N (−) side with a voltage value applied to the numerically divided voltage resistance; And an algorithm for detecting the position of the ground fault point generated between the solar cell modules connected in series with the voltage applied to the voltage divider resistor.
In the method for detecting the ground fault of the direct current line provided for power generation by the solar cell module,
Measuring voltages applied to the divided resistors V _R1 and V _R2 of the voltage sensing unit to receive the divided voltage of the solar cell module;
Obtaining the voltage module V _Module value by dividing the series voltage V _PV by the series number of the solar cell modules;
Comparing the values of the voltage divider V _R1 and V _R2 ;
When to equal the value of the dividing resistor V _R1 and V _R2 at the step returns to the initial measurement step, and compare the series voltage V _PV and V _R1 both are the same, and it is determined that the ground fault occurred in the N-side track of the two If the value is different as compared to the series voltage V _PV and V _R2 is an absolute value determined that the ground fault occurs in the P-side line, and when both are different from subtracting the value of V _R2 in the voltage-dividing resistor V _R1 if both are the same Voltage Modules V _Module Determining whether greater than or equal to a value;
The net of the absolute value | V _R1 - V _R2 | when the module voltage is larger than or equal to the value V _Module comprising: a determination value V _R1 to V _R2 is greater than and;
If the values V _R1 at the step is greater than the value V _R2 to V _R1 V _Module After dividing the value obtained for the integer n, based on the P-side n-th cell is determined to have occurred a fault in the module and, in the case where in the step V _R1 value is smaller than V _R2 by dividing the V _R2 value in V _Module value obtained for the integer n And determining that a ground fault has occurred in the n-th battery module based on the N side.

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