CN211830697U - Grounding detection circuit for non-isolated photovoltaic inverter - Google Patents
Grounding detection circuit for non-isolated photovoltaic inverter Download PDFInfo
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- CN211830697U CN211830697U CN202020775496.0U CN202020775496U CN211830697U CN 211830697 U CN211830697 U CN 211830697U CN 202020775496 U CN202020775496 U CN 202020775496U CN 211830697 U CN211830697 U CN 211830697U
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Abstract
The utility model discloses a ground connection detection circuitry for non-isolation photovoltaic inverter. A grounding detection circuit for a non-isolated photovoltaic inverter comprises an inversion unit, wherein the inversion unit comprises a first resistor and a first capacitor which are connected in parallel, one end of the first resistor and one end of the first capacitor are electrically connected to the AC side of the inversion unit, and the inversion unit further comprises a second resistor and a switch; the other end of the first resistor and the other end of the first capacitor are electrically connected to one end of the second resistor, and the one end of the second resistor is electrically connected with a shell of the photovoltaic inverter; the switch is provided with a first contact, a second contact and a movable contact, the first contact is used for being electrically connected with the positive electrode of the output end of the photovoltaic module, the second contact is used for being electrically connected with the negative electrode of the output end of the photovoltaic module, and the movable contact is electrically connected with the other end of the second resistor. The utility model discloses no detection blind spot, the testing result is accurate reliable.
Description
Technical Field
The utility model belongs to the photovoltaic inverter field relates to a ground connection (PE is connected) detection circuitry for non-isolation photovoltaic inverter.
Background
Under the global background of energy shortage and environmental deterioration, the utilization of new clean energy is very important, and solar energy is widely developed and applied due to the renewable property and abundant resources. With the popularization of photovoltaic grid-connected power generation application, the safety of a photovoltaic grid-connected power generation system is more and more emphasized. The photovoltaic inverter PE connection detection function is necessary for ensuring safe and reliable operation of a photovoltaic system and preventing personal electric shock. How to realize a simple and reliable detection function is significant for meeting safety requirements and reducing inverter cost.
In the existing non-isolated three-phase grid-connected inverter, the voltage between a power grid N and ground PE is the most reliable and visual method for judging whether the connection of the PE is good or not. However, in many operating conditions, even if the chassis is not well grounded, a situation may occur in which no voltage is substantially detected between the chassis and the neutral point N of the grid, because the chassis is balanced on the neutral point potential by the three-phase grid through charging and discharging due to the symmetry of the components such as EMC and surge inside the inverter. When the inverter is not well connected with the ground, the detection result of the PE connection detection circuit is inaccurate, and the machine grid connection can affect the machine and the human body.
SUMMERY OF THE UTILITY MODEL
In order to solve the technical problem, the utility model aims at providing a ground connection detection circuitry for non-isolation photovoltaic inverter, it does not have the detection blind spot, and the testing result is accurate reliable.
In order to achieve the above purpose, the utility model adopts the following technical scheme:
a grounding detection circuit for a non-isolated photovoltaic inverter comprises an inverter unit, wherein the inverter unit comprises a first resistor and a first capacitor which are connected in parallel, one end of the first resistor and one end of the first capacitor are electrically connected to the AC side of the inverter unit,
the inversion unit further comprises a second resistor and a switch;
the other end of the first resistor and the other end of the first capacitor are electrically connected to one end of the second resistor, and the one end of the second resistor is electrically connected with a shell of the photovoltaic inverter;
the switch is provided with a first contact, a second contact and a movable contact, the first contact is used for being electrically connected with the positive electrode of the output end of the photovoltaic module, the second contact is used for being electrically connected with the negative electrode of the output end of the photovoltaic module, and the movable contact is electrically connected with the other end of the second resistor.
In an embodiment, the inverter unit further includes a second capacitor connected in parallel to two ends of the second resistor.
In an embodiment, the ground detection circuit further includes a first dc voltage sampling unit and a first ac voltage sampling unit electrically connected between the positive electrode of the output terminal of the photovoltaic module and the ground.
In an embodiment, the ground detection circuit further includes a second dc voltage sampling unit and a second ac voltage sampling unit electrically connected between the negative electrode of the output terminal of the photovoltaic module and the ground.
In one embodiment, the switch is a relay.
The utility model adopts the above scheme, compare prior art and have following advantage:
the utility model discloses a ground connection detection circuit and ground connection detection method eliminates the sampling interference that the three-phase self-balancing brought through increasing the second resistance, can utilize existing voltage in the system, and the principle is clear, does not have the detection blind spot, and is simple reliable.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic diagram of a ground detection circuit according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a ground fault detection circuit according to an embodiment of the present invention.
Detailed Description
The following detailed description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings, enables the advantages and features of the invention to be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. Furthermore, the technical features mentioned in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, an input terminal 1 of a photovoltaic module array (PV for short) is electrically connected to the DC side of the inverter through a PV side connection terminal 3. The chassis 4 of the inverter is in most cases well connected to the ground, and in some cases there may be a grounding abnormality, and the symbol of the chassis equipotential in fig. 1 indicates the inverter chassis potential, and the grounding point of the internal circuit of the inverter is considered to be the chassis potential. The AC side connection terminal 8 of the inverter is respectively and electrically connected with U, V, W phases of the power grid and a neutral point N, and the neutral point N at the far end of the power grid is grounded. 2. 5, 6, and 7 respectively represent PV side insulation resistance to ground integral equivalent, PV side wiring integral equivalent, AC side wiring integral equivalent, and voltage pattern between grid neutral points N and PE (ground point). U, V, W denotes a three-phase grid. Rinternal is the equivalent resistance of the DC side of the inverter with respect to the parasitic impedance present in the cabinet 1. The capacitance C3 and the resistance R3 are respectively equivalent to the parasitic capacitance and the parasitic resistance of the photovoltaic module array to the ground.
With reference to fig. 1 and fig. 2, the ground fault detection circuit for the non-isolated photovoltaic inverter of the present embodiment includes an inverter unit, where the inverter unit includes a first resistor R2 and a first capacitor C2, the first resistor R2 and the first capacitor C2 are connected in parallel, and one end of the first resistor R2 and one end of the first capacitor C2 are electrically connected to an AC side of the inverter unit, specifically, connected to a power grid through an AC side connection terminal of the inverter. The inverter unit further comprises a second resistor R1, and a connection point of the other ends of the first resistor R2 and the first capacitor C2 is electrically connected with one end of the second resistor R1. Furthermore, a second capacitor C1 may be connected in parallel to two ends of the second resistor R1. The inverter unit further comprises a switch K1, the switch K1 is provided with a first contact, a second contact and a movable contact, the first contact is electrically connected with the positive electrode PV + of the output end of the photovoltaic module, the second contact is electrically connected with the negative electrode PV-of the output end of the photovoltaic module, and the movable contact is electrically connected with the other end of the second resistor R1. The one end of the second resistor R1 is electrically connected to the cabinet 1 of the photovoltaic inverter, and as shown in fig. 1, the other ends of the first resistor R2 and the first torch C2 are also electrically connected to the cabinet 1 of the photovoltaic inverter. Thus, the first capacitor C2 and the first resistor R2 are capacitors and resistors connected to the AC side of the photovoltaic inverter with respect to the chassis 1 for implementing EMC and the like, and the second capacitor C1 and the second resistor R1 are capacitors and resistors added to the PV side terminal of the photovoltaic inverter with respect to the chassis 1. Through the arrangement of the second capacitor C1 and the second resistor R1, the potential self-balance between the shell 1 under the three-phase power grid and the neutral point N of the power grid is broken through by using the common-mode voltage of the direct-current side ground system, and when the shell 1 is not well grounded, a voltage which is enough to accurately realize the judgment function is generated between the shell 1 and the neutral point N of the power grid, so that the detection is realized.
As shown in fig. 2, the ground fault detection circuit further includes a first DC voltage sampling unit DC1 and a first AC voltage sampling unit AC1 electrically connected between the output end positive electrode PV + of the photovoltaic module and the ground; the grounding detection circuit comprises a second direct current voltage sampling unit DC2 and a second alternating current voltage sampling unit AC2 which are electrically connected between the output end negative electrode PV-of the photovoltaic module and the ground; the detection values of the four voltage sampling units DC1, DC2, AC1 and AC2 are used for representing the system common-mode voltage of the photovoltaic module array to the ground.
In the present embodiment, the PV side terminal of the photovoltaic inverter is added with only a resistor (i.e., the second resistor R1) with respect to the chassis 1, and then R11 in fig. 2 is the equivalent impedance of the second resistor R1; in other embodiments, the PV side terminal of the PV inverter has added resistance (i.e., the second resistor R1) and also added capacitance (i.e., the second capacitor C1) with respect to the chassis 1, and R11 is shown as the equivalent impedance of the second resistor R1 and the second capacitor C1 connected in parallel. The switch K1 and the resistor R11 can ensure that there is enough voltage between PE and N in case of poor inverter grounding, and the resistor R11 can be switched between the positive terminal PV + of the output terminal of the photovoltaic module and the cabinet 1 or between the negative terminal PV-of the output terminal of the photovoltaic module and the cabinet 1 by switching the switch K1. The resistors R21, R22, R23 and R24 in fig. 2 are used for characterizing the impedances of the neutral point, W phase, U phase and V phase of the power grid relative to the cabinet 1.
The switch K1 in this embodiment is specifically a relay, such as a single pole double throw relay.
The grounding detection circuit for the non-isolated photovoltaic inverter of the embodiment implements detection through the following steps:
A. switching a movable contact of the switch K1 to a first contact to connect the second resistor R1 between the output end positive electrode PV + of the photovoltaic module and the ground, detecting a voltage difference between the shell 1 of the photovoltaic inverter and a neutral point N of a power grid, judging whether the voltage difference falls into an error reporting range, and directly entering the step B when the voltage difference is not in the error reporting range; if not, continuously detecting until the pressure difference is not in the error reporting range, and entering the step B;
B. switching a movable contact of the switch K1 to a second contact to connect the second resistor R1 between the output end negative PV-of the photovoltaic module and the ground, detecting the voltage difference between the casing 1 of the photovoltaic inverter and the neutral point N of the power grid, judging whether the voltage difference falls into an error reporting range, and directly entering the step C when the voltage difference is not in the error reporting range; if not, continuously detecting until the pressure difference is not in the error reporting range, and entering the step B;
C. and C, keeping the switching state in the step B, continuously detecting the pressure difference between the shell 1 of the photovoltaic inverter and the neutral point N of the power grid after the photovoltaic inverter is connected to the power grid, and reporting error information when the pressure difference is judged to fall into an error reporting range.
The error reporting ranges in the step A, B, C are 30V respectively.
The operating state of the circuit in fig. 2 is described as follows:
considering the case without a good grounding condition,
when the switch K1 is switched off and the second resistor R1 is connected between the negative PV-of the output of the photovoltaic module and the enclosure, the voltage difference between the enclosure and the neutral point N of the grid is denoted as Ux, and then
The parameters R22, R21, R23 and R24 on the AC side of the inverter are mostly symmetrically set due to performance requirements, and considering practical application, the expression of the pressure difference Ux can be further optimized as follows:
when the switch K1 connects the second resistor R1 to the positive terminal PV + of the output terminal of the photovoltaic module and the chassis, the voltage difference Ux can be expressed as follows:
considering the symmetry of the actual arrangement of R22, R21, R23, R24, the pressure difference Ux can be further simplified to the following expression:
in the formula, (DC1+ AC1) and (DC2+ AC2) simplify the working condition under the condition that the inverter is connected to the grid, when the input voltage of the photovoltaic module array PV is equal to the BUS voltage, the absolute value is constantly |1/2BUS + Ucom |, Ucom is the relative common-mode voltage output by the inverter module, and different values are available when different modulation algorithms are adopted, and the value is generally near 1/6 BUS. It can be seen from the above description that the results of Ux are stable in the case of inverter grid-tie, whether K1 cuts R11 to PV-or PV +, respectively.
When (DC1+ AC1) and (DC2+ AC2) in the formula are off-grid, (DC1+ AC1) + (DC2+ AC2) ═ Upv, which refers to the PV input voltage of the inverter. However, the (DC1+ AC1) and (DC2+ AC2) voltage division ratios vary with the unexpected impedance of the output positive PV + and input negative PV-to earth of the photovoltaic module, but the two generally satisfy the trade-off total balance. From the above, before grid connection, the second resistor R1 needs to be connected to the output terminal negative electrode PV-of the photovoltaic module and the output terminal positive electrode PV + of the photovoltaic module respectively through the switch K1 to the ground, the differential pressure Ux values are read respectively, and the larger amplitude value is used for final judgment.
In conclusion, a pressure difference Ux which is more suitable for detection can be obtained by matching the casing with a proper impedance value R11 on the direct current side under the working conditions of grid connection, grid disconnection and unexpected impedance.
This embodiment is through analyzing and concluding up the earth system common mode voltage under the various operating modes of PV side (direct current side), ingenious utilization common mode voltage's characteristics, eliminate the sampling interference that the three-phase self-balancing brought through additionally increasing first electric capacity and first resistance, the utility model discloses in circuit and detection method can utilize existing voltage in the system, and the principle is clear, does not have the detection blind spot, and is simple reliable.
The method of this patent is considered to be a variation of this patent in that the second resistor R1 is connected to the equivalent path before the inverter grid-side relay via switch K1 to achieve the same function.
In other embodiments, a second capacitor C1 is connected in parallel across the second resistor R1; in the step A, the second resistor R1 and the second capacitor C1 are connected between the positive pole of the output end of the photovoltaic module and the ground; in the step B, the second resistor R1 and the second capacitor C1 are connected between the negative electrode of the output end of the photovoltaic component and the ground. In this case, R11 in the above formula is the equivalent resistance value of the second resistor R1 and the second capacitor C1.
The above embodiments are only for illustrating the technical concept and features of the present invention, and are preferred embodiments, which are intended to enable persons skilled in the art to understand the contents of the present invention and to implement the present invention, and thus, the protection scope of the present invention cannot be limited thereby. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (5)
1. The utility model provides a ground fault detection circuit for non-isolation photovoltaic inverter, includes the inverter unit, the inverter unit includes first resistance and the first electric capacity that connects in parallel each other, the one end of first resistance and the one end electric connection of first electric capacity are to the AC side of inverter unit, its characterized in that:
the inversion unit further comprises a second resistor and a switch;
the other end of the first resistor and the other end of the first capacitor are electrically connected to one end of the second resistor, and the one end of the second resistor is electrically connected with a shell of the photovoltaic inverter;
the switch is provided with a first contact, a second contact and a movable contact, the first contact is used for being electrically connected with the positive electrode of the output end of the photovoltaic module, the second contact is used for being electrically connected with the negative electrode of the output end of the photovoltaic module, and the movable contact is electrically connected with the other end of the second resistor.
2. The ground detection circuit of claim 1, wherein: the inversion unit further comprises a second capacitor connected in parallel to two ends of the second resistor.
3. The ground detection circuit of claim 1, wherein: the grounding detection circuit further comprises a first direct current voltage sampling unit and a first alternating current voltage sampling unit which are electrically connected between the positive electrode of the output end of the photovoltaic module and the ground.
4. The ground detection circuit of claim 1, wherein: the grounding detection circuit further comprises a second direct current voltage sampling unit and a second alternating current voltage sampling unit which are electrically connected between the negative electrode of the output end of the photovoltaic module and the ground.
5. The ground detection circuit of claim 1, wherein: the switch is a relay.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202020775496.0U CN211830697U (en) | 2020-05-12 | 2020-05-12 | Grounding detection circuit for non-isolated photovoltaic inverter |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202020775496.0U CN211830697U (en) | 2020-05-12 | 2020-05-12 | Grounding detection circuit for non-isolated photovoltaic inverter |
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| CN211830697U true CN211830697U (en) | 2020-10-30 |
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Address after: 200000 room 905b, 757 Mengzi Road, Huangpu District, Shanghai Patentee after: Asway Technology (Shanghai) Co.,Ltd. Address before: No.9 factory building, 198 Xiangyang Road, high tech Zone, Suzhou City, Jiangsu Province, 215011 Patentee before: Esway new energy technology (Jiangsu) Co.,Ltd. |
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Address after: 200000 room 905b, 757 Mengzi Road, Huangpu District, Shanghai Patentee after: Elsevier Technology Co.,Ltd. Address before: 200000 room 905b, 757 Mengzi Road, Huangpu District, Shanghai Patentee before: Esway Technology (Shanghai) Co.,Ltd. Address after: 200000 room 905b, 757 Mengzi Road, Huangpu District, Shanghai Patentee after: Esway Technology (Shanghai) Co.,Ltd. Address before: 200000 room 905b, 757 Mengzi Road, Huangpu District, Shanghai Patentee before: Asway Technology (Shanghai) Co.,Ltd. |
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