CN103558503A - Earth fault detection circuit of photovoltaic inverter - Google Patents

Abstract

The invention relates to an earth fault detection circuit of a photovoltaic inverter. The earth fault detection circuit comprises a detection unit, a first differential amplification unit, a second differential amplification unit, a third differential amplification unit and a processing unit. The detection unit is used for detecting positive-electrode earth faults and negative-electrode earth faults of inverter direct-current input or a photovoltaic battery and outputting a positive-electrode detection voltage and a negative-electrode detection voltage. The first differential amplification unit is used for performing differential amplification on the positive-electrode detection voltage and outputting a first differential amplification voltage. The second differential amplification unit is used for performing differential amplification on the negative-electrode detection voltage and outputting a second differential amplification voltage. The third differential amplification unit is used for performing differential amplification on the voltages of the positive electrode and the negative electrode of the inverter direct-current input or the photovoltaic battery and outputting a third differential amplification voltage. The processing unit is used for calculating the positive-electrode earth impedance and the negative-electrode earth impedance of the inverter direct-current input or the photovoltaic battery according to the first differential amplification voltage, the second differential amplification voltage and the third differential amplification voltage. The earth fault detection circuit of the photovoltaic inverter is simple and high in detection precision.

Description

Photovoltaic DC-to-AC converter ground fault detection circuit

Technical field

The present invention relates to photovoltaic power generation technology field, more particularly, relate to a kind of photovoltaic DC-to-AC converter ground fault detection circuit.

Background technology

Sun power is as a kind of clean reproducible energy, just by development and application widely.Solar electrical energy generation is divided into photo-thermal power generation and photovoltaic generation, and wherein photovoltaic generation is to utilize the photovoltaic effect of interface and a kind of technology of luminous energy directly being changed into electric energy.Existing photovoltaic generating system comprises the equipment such as solar panel, photovoltaic DC-to-AC converter.Inversion link is a key link in grid-connected photovoltaic power generation system, and the major equipment that this link is used is photovoltaic DC-to-AC converter, and it is converted to alternating current for the direct current that solar-energy photo-voltaic cell is produced, and sends into electrical network.In order fully to accept illumination, solar panel adopts outdoor mounted mode, and this has caused earth fault probability of happening very high.When solar panel generation earth fault, the photovoltaic DC-to-AC converter being attached thereto also may damage, even on fire.Therefore photovoltaic DC-to-AC converter Earth Fault Detection seems particularly important.

At present, photovoltaic arrays Earth Fault Detection both domestic and external, adopts Low frequency signal injection method, frequency variation signal injection method etc. conventionally.But these methods exist and realize the defects such as complicated, accuracy of detection is not high, detection effect is undesirable.For example Low frequency signal injection method injects a pair of low frequency signal by two capacitances to bus, although the relative busbar voltage of this low frequency signal is compared very little, but still can bring unsafe factor concerning the high system of security requirement, and the larger system of distributed capacitance is difficult to realize accurately detection, and implement more complicated.For another example frequency variation signal injection method can solve the impact of Low frequency signal injection method distributed capacitance in theory, but it is unsatisfactory to detect effect during practical application, and implements more complicated.

Summary of the invention

The technical problem to be solved in the present invention is, realization complexity and the not high defect of accuracy of detection for prior art, provide a kind of photovoltaic DC-to-AC converter ground fault detection circuit, realizes simple and accuracy of detection is higher.

The technical solution adopted for the present invention to solve the technical problems is: construct a kind of photovoltaic DC-to-AC converter ground fault detection circuit, comprise detecting unit, the first differential amplification unit, the second differential amplification unit, the 3rd differential amplification unit and processing unit; Described detecting unit is for plus earth fault, the minus earth fault of the input of inverter direct current or photovoltaic cell are detected, and difference output cathode detects voltage and negative pole detects voltage to described the first differential amplification unit and the second differential amplification unit; Described the first differential amplification unit is for carrying out differential amplification and export the first differential amplification voltage the described anodal voltage that detects; Described the second differential amplification unit carries out differential amplification and exports the second differential amplification voltage for described negative pole is detected to voltage; Described the 3rd differential amplification unit for to inverter direct current input or the positive pole of photovoltaic cell, the voltage at negative pole two ends carry out differential amplification and export the 3rd differential amplification voltage; Described processing unit is used for according to the plus earth impedance of described the first differential amplification voltage, described the second differential amplification voltage and described the 3rd differential amplification voltage calculating inverter direct current input or photovoltaic cell, minus earth impedance to judge whether to occur earth fault.

Preferably, described detecting unit comprises positive pole, the anodal detection module between negative pole and the negative pole detection module that is serially connected with the input of inverter direct current or photovoltaic cell; Tie point between described anodal detection module and described negative pole detection module connects protective ground line; Described anodal detection module comprises the first resistance and first switch member of series connection; Described negative pole detection module comprises the second resistance and the second switch part of series connection.

Preferably, described the 3rd differential amplification unit comprises the 3rd resistance, the 4th resistance, the 5th resistance, the 6th resistance and the first operational amplifier; Wherein, one end of described the 3rd resistance connects the positive pole of the input of inverter direct current or photovoltaic cell, and the other end connects the first input end of described the first operational amplifier; One end of described the 4th resistance connects the negative pole of the input of inverter direct current or photovoltaic cell, and the other end connects the second input end of described the first operational amplifier; One end of described the 5th resistance connects the first input end of described the first operational amplifier, and the other end connects the output terminal of described the first operational amplifier; One end of described the 6th resistance connects the second input end of described the first operational amplifier, other end ground connection.

Preferably, described the first differential amplification unit comprises the first differential amplification module, and described the first differential amplification module comprises the 7th resistance, the 8th resistance, the 9th resistance, the tenth resistance and the second operational amplifier; Wherein, one end of described the 7th resistance connects the positive pole of the input of inverter direct current or photovoltaic cell, and the other end connects the first input end of described the second operational amplifier; One end of described the 8th resistance is connected to the tie point between described anodal detection module and described negative pole detection module, and the other end connects the second input end of described the second operational amplifier; One end of described the 9th resistance connects the first input end of described the second operational amplifier, and the other end connects the output terminal of described the second operational amplifier; One end of described the tenth resistance connects the second input end of described the second operational amplifier, other end ground connection;

Described the second differential amplification unit comprises the second differential amplification module, and described the second differential amplification module comprises the 11 resistance, the 12 resistance, the 13 resistance, the 14 resistance and the 3rd operational amplifier; Wherein, an end of described the 11 resistance is connected to the tie point between described anodal detection module and described negative pole detection module, and the other end connects the first input end of described the 3rd operational amplifier; One end of described the 12 resistance connects the negative pole of the input of inverter direct current or photovoltaic cell, and the other end connects the second input end of described the 3rd operational amplifier; One end of described the 13 resistance connects the first input end of described the 3rd operational amplifier, and the other end connects the output terminal of described the 3rd operational amplifier; One end of described the 14 resistance connects the second input end of described the 3rd operational amplifier, other end ground connection.

Preferably, described the first differential amplification unit also comprises the first Isolation Amplifier Module, and described the first Isolation Amplifier Module comprises the 15 resistance and the first isolation operational amplifier; Wherein, one end of described the 15 resistance connects the output terminal of described the second operational amplifier, and the other end connects the first input end of described the first isolation operational amplifier; The second input end grounding of described the first isolation operational amplifier;

Described the second differential amplification unit also comprises the second isolation operation amplifier module, and described the second Isolation Amplifier Module comprises the 16 resistance and the second isolation operational amplifier; Wherein, one end of described the 16 resistance connects the output terminal of described the 3rd operational amplifier, the first input end of the second isolation operational amplifier described in another termination; The second input end grounding of described the second isolation operational amplifier.

Preferably, described the first differential amplification unit also comprises the 3rd differential amplification module, and described the 3rd differential amplification module comprises the 17 resistance, the 18 resistance, the 19 resistance, the 20 resistance and four-operational amplifier; Wherein, one end of described the 17 resistance connects the first output terminal of described the first isolation operational amplifier, and the other end connects the first input end of described four-operational amplifier; One end of described the 18 resistance connects the second output terminal of described the first isolation operational amplifier, and the other end connects the second input end of described four-operational amplifier; One end of described the 19 resistance connects the first input end of described four-operational amplifier, and the other end connects the output terminal of described four-operational amplifier; One end of described the 20 resistance connects the second input end of described four-operational amplifier, other end ground connection;

Described the second differential amplification unit comprises the 4th differential amplification module, and described the 4th differential amplification module comprises the 21 resistance, the 22 resistance, the 23 resistance, the 24 resistance and the 5th operational amplifier; Wherein, one end of described the 21 resistance connects the first output terminal of described the second isolation operational amplifier, and the other end connects the first input end of described the 5th operational amplifier; One end of described the 22 resistance connects the second output terminal of described the second isolation operational amplifier, and the other end connects the second input end of described the 5th operational amplifier; One end of described the 23 resistance connects the first input end of described the 5th operational amplifier, and the other end connects the output terminal of described the 5th operational amplifier; One end of described the 24 resistance connects the second input end of described the 5th operational amplifier, other end ground connection.

Preferably, described processing unit comprises the 25 resistance, the 26 resistance, the 27 resistance, the first analog-to-digital conversion module, the second analog-to-digital conversion module, the 3rd analog-to-digital conversion module and processor; Wherein, one end of described the 25 resistance connects the output terminal of described the first differential amplification unit, and the other end connects the input end of described the first analog-to-digital conversion module; One end of described the 26 resistance connects the output terminal of described the second differential amplification unit, and the other end connects the input end of described the second analog-to-digital conversion module; One end of described the 27 resistance connects the output terminal of described the 3rd differential amplification unit, and the other end connects the input end of described the 3rd analog-to-digital conversion module; The output terminal of the output terminal of the output terminal of described the first analog-to-digital conversion module, described the second analog-to-digital conversion module and described the 3rd analog-to-digital conversion module is all connected with processor.

Preferably, the resistance of described the 3rd resistance equals the resistance of described the 4th resistance, and the resistance of described the 5th resistance equals the resistance of described the 6th resistance.

Preferably, the resistance of described the 7th resistance equals the resistance of described the 8th resistance, the resistance of described the 9th resistance equals the resistance of described the tenth resistance, the resistance of described the 11 resistance equals the resistance of described the 12 resistance, and the resistance of described the 13 resistance equals the resistance of described the 14 resistance.

Preferably, the resistance of described the 17 resistance equals the resistance of described the 18 resistance, the resistance of described the 19 resistance equals the resistance of described the 20 resistance, the resistance of described the 21 resistance equals the resistance of described the 22 resistance, and the resistance of described the 23 resistance equals the resistance of described the 24 resistance.

Implement photovoltaic DC-to-AC converter ground fault detection circuit of the present invention, can bring following useful technique effect: realize simply, accuracy of detection is higher.

Further, the present invention can also effectively eliminate the coupling influence of other testing circuits to photovoltaic DC-to-AC converter ground fault detection circuit, safe and reliable, and can according to impedance ground fault threshold values, regulate the enlargement factor of each differential amplification unit, without the analog to digital converter of degree of precision, also can realize the Earth Fault Detection of degree of precision.

Accompanying drawing explanation

Below in conjunction with drawings and Examples, the invention will be further described, in accompanying drawing:

Fig. 1 is the structured flowchart of photovoltaic DC-to-AC converter ground fault detection circuit of the present invention;

Fig. 2 is the circuit theory diagrams of photovoltaic DC-to-AC converter ground fault detection circuit the first embodiment of the present invention;

Fig. 3 is the circuit theory diagrams of photovoltaic DC-to-AC converter ground fault detection circuit the second embodiment of the present invention;

Fig. 4 is the circuit theory diagrams of photovoltaic DC-to-AC converter ground fault detection circuit the 3rd embodiment of the present invention.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.

Fig. 1 is the structured flowchart of photovoltaic DC-to-AC converter ground fault detection circuit of the present invention.As shown in Figure 1, photovoltaic DC-to-AC converter ground fault detection circuit comprises detecting unit 400, the first differential amplification unit 100, the second differential amplification unit 200, the 3rd differential amplification unit 300 and processing unit 500.Detecting unit 400 is directly connected to anodal DC+, the negative pole DC-(of the input of inverter direct current or photovoltaic cell or anodal DC+, the negative pole DC-of inverter input).The first differential amplification unit 100 and the second differential amplification unit 200 are all connected between detecting unit 400 and processing unit 500.Two input ends of the 3rd differential amplification unit 300 connect respectively anodal DC+, the negative pole DC-of the input of inverter direct current or photovoltaic cell, and output terminal connects processing unit 500.Wherein, detecting unit 400 is for plus earth fault, the minus earth fault of the input of inverter direct current or photovoltaic cell are detected, and difference output cathode detects voltage and negative pole detects voltage to the first differential amplification unit 100 and the second differential amplification unit 200.The first differential amplification unit 100 carries out differential amplification and exports the first differential amplification voltage for positive pole is detected to voltage.The second differential amplification unit 200 detects voltage for anticathode to carry out differential amplification and exports the second differential amplification voltage.The 3rd differential amplification unit 300 for to inverter direct current input or the positive pole of photovoltaic cell, the voltage at negative pole two ends carry out differential amplification and export the 3rd differential amplification voltage.Processing unit 500 for the plus earth impedance, minus earth impedance of calculating the input of inverter direct current or photovoltaic cell according to the first differential amplification voltage, the second differential amplification voltage and the 3rd differential amplification voltage to judge whether to occur earth fault.

Fig. 2 is the circuit theory diagrams of photovoltaic DC-to-AC converter ground fault detection circuit the first embodiment of the present invention.As shown in Figure 2, in the present embodiment, detecting unit 400 comprises positive pole, the anodal detection module 401 between negative pole and the negative pole detection module 402 that is serially connected with the input of inverter direct current or photovoltaic cell.Tie point between anodal detection module 401 and negative pole detection module 402 meets protective ground line PE.Anodal detection module 401 comprises the first resistance R 1 and the first switch member K1 of series connection.Negative pole detection module 402 comprises the second resistance R 2 and the second switch part K2 of series connection.The switch member here can be relay, and attracting electric relay K1, K2 when inverter starts detection of ground faults, disconnect relay K 1, K2 after detection.Certainly, those skilled in the art can know, the present invention is not limited to this, and switch member K1, K2 can be also other electronic switch parts such as triode, metal-oxide-semiconductor.In detecting unit 400 of the present invention, between ohmically voltage and the input of inverter direct current or photovoltaic cell input, meet electric resistance partial pressure relation, therefore, when there is earth fault, due to anodal DC+ and the negative pole DC-variation of equiva lent impedance over the ground, the first resistance R 1, voltage in the second resistance R 2 also changes, according to the first resistance R 1, voltage in the second resistance R 2 and the relation of DC input voitage, can be calculated by processing unit 500 the plus earth impedance of the input of inverter direct current or photovoltaic cell, the size of minus earth impedance, to judge whether to occur earth fault.

In the present embodiment, the first differential amplification unit 100 comprises that the first differential amplification module 101, the first differential amplification modules 101 comprise the 7th resistance R 7, the 8th resistance R 8, the 9th resistance R 9, the tenth resistance R 10 and the second operational amplifier U2.Wherein, one end of the 7th resistance R 7 connects the positive pole of the input of inverter direct current or photovoltaic cell, and the other end connects the first input end of the second operational amplifier U2.One end of the 8th resistance R 8 is connected to the tie point between anodal detection module 401 and negative pole detection module 402, and the other end connects the second input end of the second operational amplifier U2.One end of the 9th resistance R 9 connects the first input end of the second operational amplifier U2, and the other end connects the output terminal of the second operational amplifier U2.One end of the tenth resistance R 10 connects the second input end of the second operational amplifier U2, other end ground connection.Preferably, the positive supply termination power supply VCC1 of the second operational amplifier U2, negative supply termination power supply VEE1, the tenth resistance R 10 ground connection GND1, and power supply VCC1, VEE1 and GND1 form the first power pack, itself and other testing circuit isolation.In addition, preferably, the resistance of the 7th resistance R 7 equals the resistance of the 8th resistance R 8, and the resistance of the 9th resistance R 9 equals the resistance of the tenth resistance R 10, i.e. R7=R8, and R9=R10, the enlargement factor of the first differential amplification module 101 is G1=R9/R7.In the present embodiment, the output terminal of the second operational amplifier U2, as the output terminal of the first differential amplification unit 100, connects one end of the 25 resistance R 25 in processing unit 500.

In the present embodiment, the second differential amplification unit 200 comprises that the second differential amplification module 201, the second differential amplification modules 201 comprise the 11 resistance R the 11, the 12 resistance R the 12, the 13 resistance R the 13, the 14 resistance R 14 and the 3rd operational amplifier U3.Wherein, an end of the 11 resistance R 11 is connected to the tie point between anodal detection module 401 and negative pole detection module 402, and the other end connects the first input end of the 3rd operational amplifier U3.One end of the 12 resistance R 12 connects the negative pole of the input of inverter direct current or photovoltaic cell, and the other end connects the second input end of the 3rd operational amplifier U3.One end of the 13 resistance R 13 connects the first input end of the 3rd operational amplifier U3, and the other end connects the output terminal of the 3rd operational amplifier U3.One end of the 14 resistance R 14 connects the second input end of the 3rd operational amplifier U3, other end ground connection.Preferably, the positive supply termination power supply VCC2 of the 3rd operational amplifier U3, negative supply termination power supply VEE2, the 14 resistance R 14 ground connection GND2, and power supply VCC2, VEE2 and GND2 formation second source group, itself and other testing circuit is isolated.In addition, preferably, the resistance of the 11 resistance R 11 equals the resistance of the 12 resistance R 12, the resistance of the 13 resistance R 13 equals the resistance of the 14 resistance R 14, be R11=R12, R13=R14, the enlargement factor of the second differential amplification module 201 is G2=R13/R11.In the present embodiment, the output terminal of the 3rd operational amplifier U3, as the output terminal of the second differential amplification unit 200, connects one end of the 26 resistance R 26 in processing unit 500.

In the present embodiment, the 3rd differential amplification unit 300 comprises the 3rd resistance R 3, the 4th resistance R 4, the 5th resistance R 5, the 6th resistance R 6 and the first operational amplifier U1.Wherein, one end of the 3rd resistance R 3 connects the positive pole of the input of inverter direct current or photovoltaic cell, and the other end connects the first input end of the first operational amplifier U1.One end of the 4th resistance R 4 connects the negative pole of the input of inverter direct current or photovoltaic cell, and the other end connects the second input end of the first operational amplifier U1.One end of the 5th resistance R 5 connects the first input end of the first operational amplifier U1, and the other end connects the output terminal of the first operational amplifier U1.One end of the 6th resistance R 6 connects the second input end of the first operational amplifier U1, other end ground connection.Preferably, the positive supply termination power supply VCC of the first operational amplifier U1, negative supply termination power supply VEE, the 6th resistance R 6 ground connection GND, and power supply VCC, VEE and GND formation the 3rd power pack.In addition, preferably, the resistance of the 3rd resistance R 3 equals the resistance of the 4th resistance R 4, and the resistance of the 5th resistance R 5 equals the resistance of the 6th resistance R 6, i.e. R3=R4, and R5=R6, the enlargement factor of the 3rd differential amplification unit 300 is G3=R5/R3.In the present embodiment, the output terminal of the first operational amplifier U1, as the output terminal of the 3rd differential amplification unit 300, connects one end of the 27 resistance R 27 in processing unit 500.

In the present embodiment, processing unit 500 comprises the 25 resistance R the 25, the 26 resistance R the 26, the 27 resistance R 27, the first analog-to-digital conversion module 501, the second analog-to-digital conversion module 502, the 3rd analog-to-digital conversion module 503 and processor 504; Wherein, one end of the 25 resistance R 25 connects the output terminal of the first differential amplification unit 100, and the other end connects the input end of the first analog-to-digital conversion module 501.One end of the 26 resistance R 26 connects the output terminal of the second differential amplification unit 200, and the other end connects the input end of the second analog-to-digital conversion module 502.One end of the 27 resistance R 27 connects the output terminal of the 3rd differential amplification unit 300, and the other end connects the input end of the 3rd analog-to-digital conversion module 503.The output terminal of the output terminal of the output terminal of the first analog-to-digital conversion module 501, the second analog-to-digital conversion module 502 and the 3rd analog-to-digital conversion module 503 is all connected with processor 504.Preferably, the first analog-to-digital conversion module 501, the second analog-to-digital conversion module 502 and the 3rd analog-to-digital conversion module 503 all can have two input ends, comprise first input end and the second input end, wherein, first input end is input end recited above, and the second input end is for holding (first input end is only shown in figure) with reference to ground.Preferably, in the present embodiment, the first input end of the first analog-to-digital conversion module 501 connects the 25 resistance R 25, the second input end ground GND1; The first input end of the second analog-to-digital conversion module 502 connects the 26 resistance R 26, the second input end ground GND2; The first input end of the 3rd analog-to-digital conversion module 503 connects the 27 resistance R 27, the second input end ground GND.

Those skilled in the art can know, the first analog-to-digital conversion module 501, the second analog-to-digital conversion module 502, the 3rd analog-to-digital conversion module 503 can be all the electronic components such as analog to digital converter or the circuit that can realize analog-digital conversion function, can independently be arranged in processor 504 outsides, also can be integrated in processor 504 inside.The first analog voltage signal that the first analog-to-digital conversion module 501 is exported for receiving the first differential amplification unit 100, and convert the first received analog voltage signal to first digital voltage signal U _aD1, then by the first digital voltage signal U _aD1send to processor 504.The second analog voltage signal that the second analog-to-digital conversion module 502 is exported for receiving the second differential amplification unit 200, and convert the second received analog voltage signal to second digital voltage signal U _aD2, then by the second digital voltage signal U _aD2send to processor 504.The 3rd analog voltage signal that the 3rd analog-to-digital conversion module 503 is exported for receiving the 3rd differential amplification unit 300, and convert the 3rd received analog voltage signal to the 3rd digital voltage signal U _aD3, then by the 3rd digital voltage signal U _aD3send to processor 504.Processor 504 can be single-chip microcomputer, DSP or other operation processing unit, for according to the first digital voltage signal U _aD1, the second digital voltage signal U _aD2with the 3rd digital voltage signal U _aD2calculate plus earth impedance R+, the minus earth impedance R-of the input of inverter direct current or photovoltaic cell, to judge whether to occur earth fault.Concrete Computing Principle is as follows:

U _r1be the voltage at the first resistance R 1 two ends, U _r2be the voltage at the second resistance R 2 two ends, U is DC input voitage, U _r1, U _r2represent as the following formula respectively with U:

$U_{R1}=U_{\mathrm{AD}1}\×\frac{R7}{R9}---\left(1\right)$

$U_{R2}=U_{\mathrm{AD}2}\×\frac{R11}{R13}---\left(2\right)$

$U=U_{\mathrm{AD}3}\×\frac{R3}{R5}---\left(3\right)$

When inverter direct current input or photovoltaic cell positive pole exist earth fault over the ground, the input of inverter direct current or photovoltaic cell positive pole are the parallel connection of R+, R1, R7+R8 to the equiva lent impedance Req1 of protective ground line PE:

$\frac{1}{\mathrm{Req}1}=\frac{1}{R+}+\frac{1}{R1}+\frac{1}{R7+R8}---\left(4\right)$

U _r1meet the dividing potential drop relation of Req1 and R2:

$U_{R1}=\frac{\mathrm{Req}1}{\mathrm{Req}1+R2}\×U---\left(5\right)$

Like this, DC input voitage U can be obtained by formula (3), the voltage U at the first resistance R 1 two ends _r1can be obtained by formula (1); the input of inverter direct current or photovoltaic cell positive pole can be obtained by formula (5) the equiva lent impedance Req1 of protective ground line PE; so, the plus earth impedance R+ of the input of inverter direct current or photovoltaic cell can be obtained by formula (4).

In like manner, when inverter direct current input or photovoltaic cell negative pole exist earth fault over the ground, the input of inverter direct current or photovoltaic cell negative pole are the parallel connection of R-, R1, R7+R8 to the equiva lent impedance Req2 of protective ground line PE:

$\frac{1}{\mathrm{Req}2}=\frac{1}{R-}+\frac{1}{R2}+\frac{1}{R11+R12}---\left(6\right)$

U _r2meet the dividing potential drop relation of Req2 and R1:

$U_{R2}=\frac{\mathrm{Req}2}{\mathrm{Req}2+R1}\×U---\left(7\right)$

Like this, the voltage U at the second resistance R 2 two ends _r2can be obtained by formula (2); the input of inverter direct current or photovoltaic cell negative pole can be obtained by formula (7) the equiva lent impedance Req2 of protective ground line PE; so, the minus earth impedance R-of the input of inverter direct current or photovoltaic cell can be obtained by formula (6).

Fig. 3 is the circuit theory diagrams of photovoltaic DC-to-AC converter ground fault detection circuit the second embodiment of the present invention.The difference of photovoltaic DC-to-AC converter ground fault detection circuit the second embodiment of the present invention and the first embodiment is the first differential amplification unit 100 and the second differential amplification unit 200, the remaining element of the present embodiment is as identical with the first embodiment in the structure of detecting unit 400, the 3rd differential amplification unit 300 and processing unit 500, does not repeat them here.In the present embodiment, the first differential amplification unit 100 not only comprises the first differential amplification module 101, also comprises the first Isolation Amplifier Module 102.The second differential amplification unit 200 not only comprises the second differential amplification module 201, also comprises the second Isolation Amplifier Module 202.Wherein, the first differential amplification module 101 of the present embodiment is also identical with the first embodiment with the structure of the second differential amplification module 201, does not repeat them here.

Preferably, in the present embodiment, the first input end of the first analog-to-digital conversion module 501 in processing unit 500 connects the 25 resistance R 25, the second input end ground GND; The first input end of the second analog-to-digital conversion module 502 connects the 26 resistance R 26, the second input end ground GND; The first input end of the 3rd analog-to-digital conversion module 503 connects the 27 resistance R 27, the second input end ground GND.

In the present embodiment, the first Isolation Amplifier Module 102 comprises the 15 resistance R 15 and the first isolation operational amplifier U6.Wherein, one end of the 15 resistance R 15 connects the output terminal of the second operational amplifier U2, and the other end connects the first input end of the first isolation operational amplifier U6.The second input end grounding GND1 of the first isolation operational amplifier U6.The output that the enlargement factor G4 of the first isolation operational amplifier U6 equals the first isolation operational amplifier U6, to the enlargement factor of inputting, is depended on the first isolation operational amplifier U6 itself.In the present embodiment, the first output terminal of the first isolation operational amplifier U6 is as the output terminal of the first differential amplification unit 100, the one end that connects the 25 resistance R 25 in processing unit 500, the second output terminal of the first isolation operational amplifier U6 can ground connection GND.

In the present embodiment, the second Isolation Amplifier Module 202 comprises the 16 resistance R 16 and the second isolation operational amplifier U7.Wherein, one end of the 16 resistance R 16 connects the output terminal of the 3rd operational amplifier U3, the first input end of another termination the second isolation operational amplifier U7.The second input end grounding GND2 of the second isolation operational amplifier U7.The output that the enlargement factor G5 of the second isolation operational amplifier U7 equals the second isolation operational amplifier U7, to the enlargement factor of inputting, is depended on the second isolation operational amplifier U7 itself.In the present embodiment, the first output terminal of the second isolation operational amplifier U7 is as the output terminal of the second differential amplification unit 200, the one end that connects the 26 resistance R 26 in processing unit 500, the second output terminal of the second isolation operational amplifier U7 can ground connection GND.

Therefore, the Computing Principle of the present embodiment and the first embodiment are basic identical, only distinguish the voltage U at the first resistance R 1 two ends _r1u with the voltage at the second resistance R 2 two ends _r2calculating, the U of the present embodiment _r1and U _r2represent as the following formula respectively:

$U_{R1}=U_{\mathrm{AD}1}\×\frac{R7}{R9}\×\frac{1}{G4}---\left(8\right)$

$U_{R2}=U_{\mathrm{AD}2}\×\frac{R11}{R13}\×\frac{1}{G5}---\left(9\right)$

Therefore, in the present embodiment, DC input voitage U can be obtained by formula (3), the voltage U at the first resistance R 1 two ends _r1can be obtained by formula (8); the input of inverter direct current or photovoltaic cell positive pole can be obtained by formula (5) the equiva lent impedance Req1 of protective ground line PE; so, the plus earth impedance R+ of the input of inverter direct current or photovoltaic cell can be obtained by formula (4).In like manner, the voltage U at the second resistance R 2 two ends _r2can be obtained by formula (9); the input of inverter direct current or photovoltaic cell negative pole can be obtained by formula (7) the equiva lent impedance Req2 of protective ground line PE; so, the minus earth impedance R-of the input of inverter direct current or photovoltaic cell can be obtained by formula (6).

The present embodiment, on the basis of the first embodiment, has also adopted the first Isolation Amplifier Module 102 and the second Isolation Amplifier Module 202, can effectively eliminate the coupling influence of other testing circuits to ground fault detection circuit of the present invention, to realize more reliably, detects.

Fig. 4 is the circuit theory diagrams of photovoltaic DC-to-AC converter ground fault detection circuit the 3rd embodiment of the present invention.The difference of photovoltaic DC-to-AC converter ground fault detection circuit the 3rd embodiment of the present invention and the second embodiment is the first differential amplification unit 100 and the second differential amplification unit 200, the remaining element of the present embodiment is as identical with the first embodiment, the second embodiment in the structure of detecting unit 400, the 3rd differential amplification unit 300 and processing unit 500, does not repeat them here.In the present embodiment, the first differential amplification unit 100 not only comprises the first differential amplification module 101 and the first Isolation Amplifier Module 102, also comprises the 3rd differential amplification module 103.The second differential amplification unit 200 not only comprises the second differential amplification module 201 and the second Isolation Amplifier Module 202, also comprises the 4th differential amplification module 203.Wherein, the first differential amplification module 101 of the present embodiment is identical with the first embodiment, the second embodiment with the structure of the second differential amplification module 201, and first Isolation Amplifier Module 102 of the present embodiment is identical with the second embodiment with the structure of the second Isolation Amplifier Module 202, does not repeat them here.

Preferably, in the present embodiment, the first input end of the first analog-to-digital conversion module 501 in processing unit 500 connects the 25 resistance R 25, the second input end ground GND; The first input end of the second analog-to-digital conversion module 502 connects the 26 resistance R 26, the second input end ground GND; The first input end of the 3rd analog-to-digital conversion module 503 connects the 27 resistance R 27, the second input end ground GND.

In the present embodiment, the 3rd differential amplification module 103 comprises the 17 resistance R the 17, the 18 resistance R the 18, the 19 resistance R the 19, the 20 resistance R 20 and four-operational amplifier U4.Wherein, one end of the 17 resistance R 17 connects the first output terminal of the first isolation operational amplifier U6, and the other end connects the first input end of four-operational amplifier U4.One end of the 18 resistance R 18 connects the second output terminal of the first isolation operational amplifier U6, and the other end connects the second input end of four-operational amplifier U4.One end of the 19 resistance R 19 connects the first input end of four-operational amplifier U4, and the other end connects the output terminal of four-operational amplifier U4.One end of the 20 resistance R 20 connects the second input end of four-operational amplifier U4, other end ground connection.Preferably, the positive supply termination power supply VCC of four-operational amplifier U4, negative supply termination power supply VEE, the 20 resistance R 20 ground connection GND.In addition, preferably, the resistance of the 17 resistance R 17 equals the resistance of the 18 resistance R 18, the resistance of the 19 resistance R 19 equals the resistance of the 20 resistance R 20, be R17=R18, R19=R20, the enlargement factor of the 3rd differential amplification module 103 is G6=R19/R17.In the present embodiment, the output terminal of the 3rd differential amplification module 103, as the output terminal of the first differential amplification unit 100, connects one end of the 25 resistance R 25 in processing unit 500.

In the present embodiment, the 4th differential amplification module 203 comprises the 21 resistance R the 21, the 22 resistance R the 22, the 23 resistance R the 23, the 24 resistance R 24 and the 5th operational amplifier U5.Wherein, one end of the 21 resistance R 21 connects the first output terminal of the second isolation operational amplifier U7, and the other end connects the first input end of the 5th operational amplifier U5.One end of the 22 resistance R 22 connects the second output terminal of the second isolation operational amplifier U7, and the other end connects the second input end of the 5th operational amplifier U5; One end of the 23 resistance R 23 connects the first input end of the 5th operational amplifier U5, and the other end connects the output terminal of the 5th operational amplifier U5.One end of the 24 resistance R 24 connects the second input end of the 5th operational amplifier U5, other end ground connection.Preferably, the positive supply termination power supply VCC of the 5th operational amplifier U5, negative supply termination power supply VEE, the 24 resistance R 24 ground connection GND.In addition, preferably, the resistance of the 21 resistance R 21 equals the resistance of the 22 resistance R 22, the resistance of the 23 resistance R 23 equals the resistance of the 24 resistance R 24, be R21=R22, R23=R24, the enlargement factor of the 4th differential amplification module 203 is G7=R23/R21.In the present embodiment, the output terminal of the 4th differential amplification module 203, as the output terminal of the second differential amplification unit 200, connects one end of the 26 resistance R 26 in processing unit 500.

Therefore, the Computing Principle of the present embodiment and the first embodiment, the second embodiment are basic identical, only distinguish the voltage U at the first resistance R 1 two ends _r1u with the voltage at the second resistance R 2 two ends _r2calculating, the U of the present embodiment _r1and U _r2represent as the following formula respectively:

$U_{R1}=U_{\mathrm{AD}1}\×\frac{R7}{R9}\×\frac{1}{G4}\×\frac{R17}{R19}---\left(10\right)$

$U_{R2}=U_{\mathrm{AD}2}\×\frac{R11}{R13}\×\frac{1}{G5}\×\frac{R21}{R23}---\left(11\right)$

Therefore, in the present embodiment, DC input voitage U can be obtained by formula (3), the voltage U at the first resistance R 1 two ends _r1can be obtained by formula (10); the input of inverter direct current or photovoltaic cell positive pole can be obtained by formula (5) the equiva lent impedance Req1 of protective ground line PE; so, the plus earth impedance R+ of the input of inverter direct current or photovoltaic cell can be obtained by formula (4).In like manner, the voltage U at the second resistance R 2 two ends _r2can be obtained by formula (11); the input of inverter direct current or photovoltaic cell negative pole can be obtained by formula (7) the equiva lent impedance Req2 of protective ground line PE; so, the minus earth impedance R-of the input of inverter direct current or photovoltaic cell can be obtained by formula (6).

The present embodiment is on the basis of the second embodiment, the 3rd differential amplification module 103 and the 4th differential amplification module 203 have also been adopted, further improve the enlargement factor of the first differential amplification unit 100 and the second differential amplification unit 200, can realize more high-precision detection.

In above-mentioned three embodiment of the present invention, all can calculate by processing unit 500 plus earth impedance R+ and the minus earth impedance R-of the input of inverter direct current or photovoltaic cell, according to the R+ calculating and R-, just can judge whether earth fault occurs.For example,, if the D.C. isolation impedance that inverter detects between photovoltaic arrays input end and ground before startup is less than R=V _maxpV/30mA, answers indication fault.For example a certain inverter maximum input voltage is 900V, when inverter detects R+ or R-<900V/30mA=30k Ω before starting so, just can judge plus earth fault or minus earth fault occur, and inverter is answered indication fault.

Photovoltaic DC-to-AC converter ground fault detection circuit of the present invention is mainly comprised of electronic components such as some resistance, amplifiers, implements very simple.And the first Isolation Amplifier Module 102 and the second Isolation Amplifier Module 202 have been adopted, and the first power pack (VCC1, VEE1, GND1) and the second source group (VCC2, VEE2, GND2) of employing and the isolation of other testing circuits, can effectively eliminate the coupling influence of other testing circuits to ground fault detection circuit, detect safe and reliable.In addition can according to impedance ground fault threshold values, regulate the enlargement factor of each amplifying unit, like this, without the analog to digital converter of degree of precision, also can realize the Earth Fault Detection of degree of precision.

Although the present invention describes by specific embodiment, it will be appreciated by those skilled in the art that, without departing from the present invention, can also carry out various conversion and be equal to alternative the present invention.Therefore, the present invention is not limited to disclosed specific embodiment, and should comprise the whole embodiments that fall within the scope of the claims in the present invention.

Claims (10)

1. a photovoltaic DC-to-AC converter ground fault detection circuit, is characterized in that, comprises detecting unit (400), the first differential amplification unit (100), the second differential amplification unit (200), the 3rd differential amplification unit (300) and processing unit (500); Described detecting unit (400) is for plus earth fault, the minus earth fault of the input of inverter direct current or photovoltaic cell are detected, and difference output cathode detects voltage and negative pole detects voltage to described the first differential amplification unit (100) and the second differential amplification unit (200); Described the first differential amplification unit (100) is for carrying out differential amplification and export the first differential amplification voltage the described anodal voltage that detects; Described the second differential amplification unit (200) carries out differential amplification and exports the second differential amplification voltage for described negative pole is detected to voltage; Described the 3rd differential amplification unit (300) for to inverter direct current input or the positive pole of photovoltaic cell, the voltage at negative pole two ends carry out differential amplification and export the 3rd differential amplification voltage; Described processing unit (500) for the plus earth impedance, minus earth impedance of calculating the input of inverter direct current or photovoltaic cell according to described the first differential amplification voltage, described the second differential amplification voltage and described the 3rd differential amplification voltage to judge whether to occur earth fault.

2. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 1, it is characterized in that, described detecting unit (400) comprises positive pole, the anodal detection module (401) between negative pole and the negative pole detection module (402) that is serially connected with the input of inverter direct current or photovoltaic cell; Tie point between described anodal detection module (401) and described negative pole detection module (402) connects protective ground line (PE); Described anodal detection module (401) comprises the first resistance (R1) and first switch member (K1) of series connection; Described negative pole detection module (402) comprises the second resistance (R2) and the second switch part (K2) of series connection.

3. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 2, it is characterized in that, described the 3rd differential amplification unit (300) comprises the 3rd resistance (R3), the 4th resistance (R4), the 5th resistance (R5), the 6th resistance (R6) and the first operational amplifier (U1); Wherein, one end of described the 3rd resistance (R3) connects the positive pole of the input of inverter direct current or photovoltaic cell, and the other end connects the first input end of described the first operational amplifier (U1); One end of described the 4th resistance (R4) connects the negative pole of the input of inverter direct current or photovoltaic cell, and the other end connects the second input end of described the first operational amplifier (U1); One end of described the 5th resistance (R5) connects the first input end of described the first operational amplifier (U1), and the other end connects the output terminal of described the first operational amplifier (U1); One end of described the 6th resistance (R6) connects the second input end of described the first operational amplifier (U1), other end ground connection.

4. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 3, it is characterized in that, described the first differential amplification unit (100) comprises the first differential amplification module (101), and described the first differential amplification module (101) comprises the 7th resistance (R7), the 8th resistance (R8), the 9th resistance (R9), the tenth resistance (R10) and the second operational amplifier (U2); Wherein, one end of described the 7th resistance (R7) connects the positive pole of the input of inverter direct current or photovoltaic cell, and the other end connects the first input end of described the second operational amplifier (U2); One end of described the 8th resistance (R8) is connected to the tie point between described anodal detection module (401) and described negative pole detection module (402), and the other end connects the second input end of described the second operational amplifier (U2); One end of described the 9th resistance (R9) connects the first input end of described the second operational amplifier (U2), and the other end connects the output terminal of described the second operational amplifier (U2); One end of described the tenth resistance (R10) connects the second input end of described the second operational amplifier (U2), other end ground connection;

Described the second differential amplification unit (200) comprises the second differential amplification module (201), and described the second differential amplification module (201) comprises the 11 resistance (R11), the 12 resistance (R12), the 13 resistance (R13), the 14 resistance (R14) and the 3rd operational amplifier (U3); Wherein, an end of described the 11 resistance (R11) is connected to the tie point between described anodal detection module (401) and described negative pole detection module (402), and the other end connects the first input end of described the 3rd operational amplifier (U3); One end of described the 12 resistance (R12) connects the negative pole of the input of inverter direct current or photovoltaic cell, and the other end connects the second input end of described the 3rd operational amplifier (U3); One end of described the 13 resistance (R13) connects the first input end of described the 3rd operational amplifier (U3), and the other end connects the output terminal of described the 3rd operational amplifier (U3); One end of described the 14 resistance (R14) connects the second input end of described the 3rd operational amplifier (U3), other end ground connection.

5. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 4, it is characterized in that, described the first differential amplification unit (100) also comprises the first Isolation Amplifier Module (102), and described the first Isolation Amplifier Module (102) comprises the 15 resistance (R15) and the first isolation operational amplifier (U6); Wherein, one end of described the 15 resistance (R15) connects the output terminal of described the second operational amplifier (U2), and the other end connects the first input end of described the first isolation operational amplifier (U6); The second input end grounding of described the first isolation operational amplifier (U6);

Described the second differential amplification unit (200) also comprises the second isolation operation amplifier module (202), and described the second Isolation Amplifier Module (202) comprises the 16 resistance (R16) and the second isolation operational amplifier (U7); Wherein, one end of described the 16 resistance (R16) connects the output terminal of described the 3rd operational amplifier (U3), the first input end of the second isolation operational amplifier (U7) described in another termination; The second input end grounding of described the second isolation operational amplifier (U7).

6. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 5, it is characterized in that, described the first differential amplification unit (100) also comprises the 3rd differential amplification module (103), and described the 3rd differential amplification module (103) comprises the 17 resistance (R17), the 18 resistance (R18), the 19 resistance (R19), the 20 resistance (R20) and four-operational amplifier (U4); Wherein, one end of described the 17 resistance (R17) connects the first output terminal of described the first isolation operational amplifier (U6), and the other end connects the first input end of described four-operational amplifier (U4); One end of described the 18 resistance (R18) connects the second output terminal of described the first isolation operational amplifier (U6), and the other end connects the second input end of described four-operational amplifier (U4); One end of described the 19 resistance (R19) connects the first input end of described four-operational amplifier (U4), and the other end connects the output terminal of described four-operational amplifier (U4); One end of described the 20 resistance (R20) connects the second input end of described four-operational amplifier (U4), other end ground connection;

Described the second differential amplification unit (200) comprises the 4th differential amplification module (203), and described the 4th differential amplification module (203) comprises the 21 resistance (R21), the 22 resistance (R22), the 23 resistance (R23), the 24 resistance (R24) and the 5th operational amplifier (U5); Wherein, one end of described the 21 resistance (R21) connects the first output terminal of described the second isolation operational amplifier (U7), and the other end connects the first input end of described the 5th operational amplifier (U5); One end of described the 22 resistance (R22) connects the second output terminal of described the second isolation operational amplifier (U7), and the other end connects the second input end of described the 5th operational amplifier (U5); One end of described the 23 resistance (R23) connects the first input end of described the 5th operational amplifier (U5), and the other end connects the output terminal of described the 5th operational amplifier (U5); One end of described the 24 resistance (R24) connects the second input end of described the 5th operational amplifier (U5), other end ground connection.

7. according to the photovoltaic DC-to-AC converter ground fault detection circuit described in claim 1-6 any one, it is characterized in that, described processing unit (500) comprises the 25 resistance (R25), the 26 resistance (R26), the 27 resistance (R27), the first analog-to-digital conversion module (501), the second analog-to-digital conversion module (502), the 3rd analog-to-digital conversion module (503) and processor; Wherein, one end of described the 25 resistance (R25) connects the output terminal of described the first differential amplification unit (100), and the other end connects the input end of described the first analog-to-digital conversion module (501); One end of described the 26 resistance (R26) connects the output terminal of described the second differential amplification unit (200), and the other end connects the input end of described the second analog-to-digital conversion module (502); One end of described the 27 resistance (R27) connects the output terminal of described the 3rd differential amplification unit (300), and the other end connects the input end of described the 3rd analog-to-digital conversion module (503); The output terminal of the output terminal of described the first analog-to-digital conversion module (501), described the second analog-to-digital conversion module (502) is all connected with processor with the output terminal of described the 3rd analog-to-digital conversion module (503).

8. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 3, it is characterized in that, the resistance of described the 3rd resistance (R3) equals the resistance of described the 4th resistance (R4), and the resistance of described the 5th resistance (R5) equals the resistance of described the 6th resistance (R6).

9. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 4, it is characterized in that, the resistance of described the 7th resistance (R7) equals the resistance of described the 8th resistance (R8), the resistance of described the 9th resistance (R9) equals the resistance of described the tenth resistance (R10), the resistance of described the 11 resistance (R11) equals the resistance of described the 12 resistance (R12), and the resistance of described the 13 resistance (R13) equals the resistance of described the 14 resistance (R14).

10. photovoltaic DC-to-AC converter ground fault detection circuit according to claim 6, it is characterized in that, the resistance of described the 17 resistance (R17) equals the resistance of described the 18 resistance (R18), the resistance of described the 19 resistance (R19) equals the resistance of described the 20 resistance (R20), the resistance of described the 21 resistance (R21) equals the resistance of described the 22 resistance (R22), and the resistance of described the 23 resistance (R23) equals the resistance of described the 24 resistance (R24).

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