CN115327231A - Sampling circuit, branch circuit insulation impedance detection circuit and method - Google Patents
Sampling circuit, branch circuit insulation impedance detection circuit and method Download PDFInfo
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- CN115327231A CN115327231A CN202210967331.7A CN202210967331A CN115327231A CN 115327231 A CN115327231 A CN 115327231A CN 202210967331 A CN202210967331 A CN 202210967331A CN 115327231 A CN115327231 A CN 115327231A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/08—Measuring resistance by measuring both voltage and current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
Abstract
The invention is suitable for the technical field of inverters, and provides a sampling circuit, a branch insulation impedance detection circuit and a method, wherein the sampling circuit is used for branch insulation impedance detection, and under the condition that the insulation impedance of a string inverter to the ground is abnormal, the sampling circuit is connected to the output end of any PV branch connected with the string inverter and is used for adjusting the impedance of the output end of the PV branch to the ground so as to obtain the corresponding sampling voltage of the output end of the PV branch to the ground.
Description
Technical Field
The invention belongs to the technical field of inverters, and particularly relates to a sampling circuit, a branch circuit insulation impedance detection circuit and a branch circuit insulation impedance detection method.
Background
At present, the application of a string-type photovoltaic inverter of a multi-path MPPT (Maximum Power Point Tracking) controller is more and more extensive. However, the photovoltaic cell module is affected by factors such as weather, equipment aging may occur, and insulation resistance to ground may change, and the change of the insulation resistance may cause a safety hazard. For example, when the insulation resistance is too small, a large leakage current is generated, which may cause an electric shock hazard, resulting in a grid-connected safety accident and personal and property loss.
In the related technology, the voltage of the BUS + or the BUS-or the BUS _ M and the earth is obtained by changing the impedance of the BUS positive terminal BUS +, the BUS negative terminal BUS-or the BUS midpoint BUS _ M to the earth, so that whether the insulation impedance of the prototype system to the earth is abnormal or not is judged. However, the current scheme cannot judge the insulation resistance condition of each PV branch, cannot accurately detect an abnormal PV branch for timely maintenance, and has a poor detection effect.
Therefore, there is a need in the art to solve the technical problem of accurately detecting abnormal PV branches.
Disclosure of Invention
The embodiment of the invention provides a sampling circuit for detecting branch insulation impedance, aiming at solving the problem of accurately detecting an abnormal PV branch.
The embodiment of the invention is realized in such a way that, in the case that the insulation impedance of the string combination inverter to the ground is abnormal, the sampling circuit is connected to the output end of any PV branch connected with the string combination inverter and is used for adjusting the impedance of the output end of any PV branch to the ground so as to obtain the corresponding sampling voltage of the output end of any PV branch to the ground.
Still further, the sampling circuit comprises a first impedance adjustment sub-circuit and/or a second impedance adjustment sub-circuit;
the first impedance adjusting sub-circuit is connected between the positive output end of any PV branch and the ground and used for increasing the impedance between the positive output end and the ground;
the second impedance adjusting sub-circuit is connected between the negative output end of any one PV branch and the ground and used for increasing the impedance between the negative output end and the ground.
Still further, the sampling circuit further comprises: a first voltage equalization subcircuit and a second voltage equalization subcircuit;
the first voltage balancing sub-circuit is connected between a positive output end of any one PV branch and the ground, the second voltage balancing sub-circuit is connected between a negative output end of any one PV branch and the ground, and the first voltage balancing sub-circuit and the second voltage balancing sub-circuit are used for balancing the voltage of the positive output end and the negative output end to the ground.
Still further, the first impedance adjustment sub-circuit includes a first resistor and a first switch; one end of the first resistor is connected with the positive output end of any one PV branch circuit, the other end of the first resistor is connected with one end of the first switch, the other end of the first switch is grounded, and the impedance between the positive output end of the PV branch circuit and the ground is adjusted by closing or opening the first switch;
the second impedance adjusting sub-circuit comprises a second resistor and a second switch; one end of the second resistor is grounded, the other end of the second resistor is connected with one end of the second switch, the other end of the second switch is connected with the negative output end of any PV branch circuit, and the impedance between the negative output end of the PV branch circuit and the ground is adjusted by closing or opening the second switch.
Still further, the first voltage equalization subcircuit includes at least one resistance, and the second voltage equalization subcircuit includes at least one resistance;
the at least one resistor in the first voltage balancing sub-circuit is connected between the positive output of the any PV branch and ground, and the at least one resistor in the second voltage balancing sub-circuit is connected between the negative output of the any PV branch and ground.
Furthermore, the first voltage balancing sub-circuit comprises a third resistor and a fourth resistor, one end of the third resistor is connected with the positive output end of any one of the PV branches, the other end of the third resistor is connected with one end of the fourth resistor, and the other end of the fourth resistor is grounded;
the second voltage balancing sub-circuit comprises a fifth resistor R5 and a sixth resistor R6, one end of the fifth resistor is grounded, the other end of the fifth resistor is connected with one end of the sixth resistor, and the other end of the sixth resistor is connected with the negative output end of any PV branch.
Furthermore, the first voltage balancing sub-circuit includes a third resistor and a fourth resistor, one end of the third resistor is connected to the positive output end of any PV branch, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded;
the second voltage balancing sub-circuit comprises a fifth resistor R5 and a sixth resistor R6, one end of the fifth resistor is grounded, the other end of the fifth resistor is connected with one end of the sixth resistor, and the other end of the sixth resistor is connected with the negative output end of any PV branch;
the first impedance adjustment sub-circuit comprises a first resistor and a first switch; one end of the first resistor is connected with the positive output end of any PV branch, the other end of the first resistor is connected with one end of the first switch, and the other end of the first switch is connected between the third resistor and the fourth resistor;
the second impedance adjusting sub-circuit comprises a second resistor and a second switch; one end of the second resistor is grounded, the other end of the second resistor is connected with one end of the second switch, and the other end of the second switch is connected between the fifth resistor and the sixth resistor.
Furthermore, the third resistor and the fifth resistor have the same resistance, and the fourth resistor and the sixth resistor have the same resistance.
The embodiment of the present invention further provides a branch insulation resistance detection circuit, including:
the sampling circuit; and
and the control logic circuit is connected to the sampling circuit and used for acquiring corresponding sampling voltage of the output end of any PV branch circuit to the ground when the impedance of the output end of any PV branch circuit to the ground is adjusted, determining the insulation impedance of any PV branch circuit based on different sampling voltages and the output voltage of any PV branch circuit, and determining whether the insulation impedance of any PV branch circuit is abnormal based on a preset threshold value.
The embodiment of the invention also provides a branch insulation impedance detection method, which is characterized in that the branch insulation impedance detection method is realized based on the branch insulation impedance detection circuit, and comprises the following steps:
under the condition that the insulation resistance of the string inverter to the ground is determined to be abnormal, closing each knob switch of the string inverter in turn, and determining whether the insulation resistance of the string inverter to the ground is abnormal again;
if the insulation impedance of the string inverter to the ground is determined to be abnormal again, connecting the sampling circuit to the output end of the PV branch corresponding to the currently closed knob switch, and adjusting the impedance of the output end of the PV branch to the ground to obtain the corresponding sampling voltage of the output end to the ground;
determining an insulation resistance of the PV branch based on the different sampling voltages and the output voltage of the PV branch;
and determining whether the insulation resistance of the PV branch circuit is abnormal or not based on a preset threshold value.
Further, the determining the insulation resistance of the PV branch based on the different sampling voltages and the output voltage of the PV branch comprises:
and acquiring a first voltage of the negative output end of the PV branch circuit to the ground in a state that the first switch is closed and the second switch is opened, a second voltage of the negative output end of the PV branch circuit to the ground in a state that the first switch is opened and the second switch is closed and the output voltage of the PV branch circuit, and calculating to obtain the insulation impedance of the PV branch circuit based on the first voltage, the second voltage and the output voltage.
Further, the insulation resistance of the PV branch is calculated based on the first voltage, the second voltage and the output voltage, using the following calculation formula:
wherein, R represents the insulation resistance of the PV branch, req0 represents the equivalent resistance of the positive output end of the PV branch to the ground, req1 represents the equivalent resistance of the negative output end of the PV branch to the ground, and the intermediate variable
G is determined according to the first voltage, the second voltage and the output voltage of the PV branch circuit.
Further, the determining whether the insulation resistance of the PV branch circuit is abnormal based on the preset threshold includes:
and if the insulation resistance of the PV branch circuit does not reach the preset threshold value, determining that the insulation resistance of the PV branch circuit is abnormal.
The invention achieves the following beneficial effects:
according to the invention, under the condition that the insulation impedance of the string inverter to the ground is abnormal, the sampling circuit is further connected to the output end of any PV branch circuit connected with the string inverter, and the sampling circuit can adjust the impedance of the output end of the PV branch circuit to the ground, so that different sampling voltages of the output end of the PV branch circuit to the ground can be obtained, the insulation impedance of the PV branch circuit can be accurately determined based on different sampling voltages and the output voltage of the PV branch circuit, the PV branch circuit with the abnormal insulation impedance can be accurately positioned, the detection efficiency is improved, and the maintenance cost is reduced.
Drawings
FIG. 1 is a block diagram of an insulation resistance detection scheme provided by the prior art;
FIG. 2 is a block diagram of a sampling circuit for branch insulation resistance detection according to an embodiment of the present invention;
FIG. 3 is an example of a sampling circuit provided by an embodiment of the invention;
FIG. 4 is another exemplary sampling circuit provided by embodiments of the present invention;
FIG. 5 is another exemplary sampling circuit provided by embodiments of the present invention;
FIG. 6 is another example of a sampling circuit provided by embodiments of the present invention;
FIG. 7 is an example of a high impedance circuit and a differential circuit provided by an embodiment of the present invention;
FIG. 8 is an example of a voltage sampling circuit provided by an embodiment of the present invention;
fig. 9 is a flowchart of a branch insulation resistance detection method according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the prior art, an insulation resistance detection scheme is provided, as shown in fig. 1, the voltage of BUS + or BUS-or BUS _ M and the earth is obtained by changing the resistance of BUS positive terminal BUS +, BUS negative terminal BUS-or BUS midpoint BUS _ M to the earth, so as to judge whether the insulation resistance of a prototype system to the earth is abnormal. However, the current scheme cannot judge the insulation resistance condition of each PV branch, cannot accurately detect an abnormal PV branch for timely maintenance, and has a poor detection effect.
According to the invention, under the condition that the insulation impedance of the string combination inverter to the ground is abnormal, the sampling circuit is further connected to the output end of any PV branch circuit connected with the string combination inverter so as to regulate the impedance of the output end of the PV branch circuit to the ground, the sampling voltage of the output end of the PV branch circuit to the ground is obtained, the insulation impedance of the PV branch circuit can be determined based on different sampling voltages and the output voltage of the PV branch circuit, and whether the insulation impedance of the PV branch circuit is abnormal or not is judged. According to the sampling circuit, the branch insulation impedance detection circuit and the method, different sampling voltages of the output end of the PV branch to the ground can be obtained by adjusting the insulation impedance of the PV branch, so that the PV branch with abnormal insulation impedance can be accurately positioned, the detection efficiency is improved, and the maintenance cost is reduced.
Example one
The present embodiment provides a sampling circuit for detecting branch insulation resistance, where in case of abnormal insulation resistance of a string inverter to ground, the sampling circuit is connected to an output end of any PV branch connected to the string inverter, and is configured to adjust impedance of the output end of the PV branch to ground, so as to obtain a corresponding sampling voltage of the output end of the PV branch to ground.
It should be understood that the abnormal insulation resistance of the string inverter to the ground can be realized by the prior art, and will not be described in detail here. In this embodiment, when the insulation resistance of the entire string inverter to the ground is abnormal, the branch insulation resistance is detected, and the PV branch with the abnormal insulation resistance is determined.
As shown in fig. 2, the sampling circuit for detecting the branch insulation impedance provided in this embodiment is connected to the positive output terminal PV + and the negative output terminal PV-of any PV branch connected to the string inverter, it should be noted that PV + and PV-may refer to the positive output terminal and the negative output terminal of any PV branch in fig. 2, for example, PV2+ and PV2-, and then the control logic circuit may be connected to determine the insulation impedance of the PV branch according to different sampling voltages and the output voltage of the PV branch, and determine whether the insulation impedance of the PV branch is abnormal, thereby improving the detection efficiency and reducing the maintenance cost.
In this embodiment, when the insulation impedance of the string inverter to the ground is abnormal, the sampling circuit is connected to the output end of any PV branch connected to the string inverter to adjust the impedance of the output end of the PV branch to the ground, so as to obtain the sampling voltage of the output end of the PV branch to the ground, and the obtained adjusted different sampling voltages are used to implement the insulation impedance detection of the PV branch, so as to provide a calculation basis for determining the insulation impedance of the PV branch.
Example two
On the basis of the first embodiment, as shown in fig. 3, the sampling circuit for branch insulation impedance detection includes a first impedance adjusting sub-circuit 201 and/or a second impedance adjusting sub-circuit 202;
the first impedance adjusting sub-circuit 201 is connected between the positive output end PV + of any PV branch and the ground, and is used for increasing the impedance between the positive output end PV + and the ground;
a second impedance adjusting sub-circuit 202 is connected between the negative output terminal PV-of the PV branch and ground for increasing the impedance between the negative output terminal PV-and ground.
In fig. 3, the equivalent resistance to ground of the positive output terminal PV + is represented as Req0, the equivalent resistance to ground of the negative output terminal PV-is represented as Req1, the positive output terminal PV + of the PV branch is connected to one end of the equivalent resistance Req0, and the other end of the equivalent resistance Req0 is grounded; the negative output end PV-is connected with one end of the equivalent resistor Req1, the other end of the equivalent resistor Req1 is grounded, the insulation impedance of the PV branch circuit needs to be obtained through the two equivalent resistors and the output voltage of the PV branch circuit, the two equivalent resistors are unknown, the output voltage of the PV branch circuit can be measured, different data of the impedance between the output end and the ground and the sampling voltage can be obtained by changing the impedance between the output end and the ground, and the insulation impedance of the PV branch circuit can be further determined based on different sampling voltages.
In some cases, the sampling circuit may include both the first impedance adjusting sub-circuit 201 and the second impedance adjusting sub-circuit 202, and the impedance between the positive output terminal PV + and the ground and the impedance between the negative output terminal PV-and the ground are adjusted by the first impedance adjusting sub-circuit 201 and the second impedance adjusting sub-circuit 202, respectively, so that the impedances between the two sets of output terminals and the ground and corresponding sampling voltages can be obtained, and the insulation impedance of the PV branch circuit can be further determined based on different sampling voltages.
In other cases, the sampling circuit may only include the first impedance adjusting sub-circuit 201 or the second impedance adjusting sub-circuit 202, and when only one impedance adjusting sub-circuit is included, the impedance between the output terminal and the ground may also be obtained to obtain different data of the impedance between the output terminal and the ground and the sampling voltage, and the insulation impedance of the PV branch may be further determined based on the different sampling voltages.
In this embodiment, the impedance between the output end of the PV branch and the ground is changed through the first impedance adjusting sub-circuit and/or the second impedance adjusting sub-circuit, so as to obtain different sampling voltages corresponding to different impedances, and then the insulation impedance of the PV branch can be further determined based on the different sampling voltages, thereby realizing the insulation impedance detection of the PV branch.
EXAMPLE III
On the basis of the second embodiment, as shown in fig. 3, the sampling circuit for detecting branch insulation resistance further includes: a first voltage equalization sub-circuit 203 and a second voltage equalization sub-circuit 204;
the first voltage equalization subcircuit 203 is connected between the positive output terminal PV + of any PV branch and ground, the second voltage equalization subcircuit 204 is connected between the negative output terminal PV-of the PV branch and ground, and the first voltage equalization subcircuit 203 and the second voltage equalization subcircuit 204 are used for equalizing the voltages of the positive output terminal and the negative output terminal to the ground.
In this embodiment, the voltage between the positive output terminal of the PV branch and the ground and the voltage between the negative output terminal of the PV branch and the ground are symmetric through the two voltage balancing sub-circuits, so as to achieve the balancing effect.
Example four
On the basis of the second embodiment, as shown in fig. 3, the first impedance adjusting sub-circuit 201 includes a first resistor R1 and a first switch SW1; one end of the first resistor R1 is connected to the positive output terminal PV + of any PV branch, the other end of the first resistor R1 is connected to one end of the first switch SW1, the other end of the first switch SW1 is grounded, and the impedance between the positive output terminal PV + of the PV branch and the ground is adjusted by closing or opening the first switch SW1, for example, the impedance between the positive output terminal PV + of the PV branch and the ground is increased by closing the first switch SW1;
the second impedance adjusting sub-circuit 202 includes a second resistor R2 and a second switch SW2; one end of the second resistor R2 is grounded, the other end of the second resistor R2 is connected to one end of the second switch SW2, the other end of the second switch SW2 is connected to the negative output terminal PV of the PV branch, the impedance between the negative output terminal PV of the PV branch and the ground is adjusted by closing or opening the second switch SW2, for example, the impedance between the negative output terminal PV-of the PV branch and the ground is increased by closing the second switch SW 2.
In the first impedance adjusting sub-circuit 201 and the second impedance adjusting sub-circuit 202, the corresponding resistors can be connected by closing or opening the switches, so that the impedance of the corresponding lines is increased. For the first impedance adjusting sub-circuit 201, closing the first switch SW1 can enable the first resistor R1 to be connected, so that the impedance between the positive output terminal PV + and the ground is increased, and when the first switch SW1 is opened, the state of only connecting the first voltage equalizing sub-circuit 203 is restored; similarly, with the second impedance adjustment sub-circuit 202, closing the second switch SW2 can switch in the second resistor R2, so that the impedance between the negative output terminal PV-and ground increases.
It should be understood that the sampling circuit may include both the first impedance adjusting sub-circuit 201 and the second impedance adjusting sub-circuit 202, or may include only the first impedance adjusting sub-circuit 201 or only the second impedance adjusting sub-circuit 202, for example, the sampling circuit shown in fig. 4 includes only the first impedance adjusting sub-circuit 201.
In this embodiment, an impedance adjusting sub-circuit structure of a resistor and a switch connected in series is adopted, and the impedance between the output end and the ground is adjusted by turning on or off the switch, so as to obtain different sampling voltages for determining the insulation impedance of the PV branch.
EXAMPLE five
On the basis of the fourth embodiment, as shown in fig. 3, the first voltage equalization sub-circuit 203 includes at least one resistor, and the second voltage equalization sub-circuit 204 includes at least one resistor;
at least one resistor in the first voltage balancing sub-circuit 203 is connected between the positive output terminal PV + of any PV branch and ground, and at least one resistor in the second voltage balancing sub-circuit 204 is connected between the negative output terminal PV-of that PV branch and ground.
It should be understood that, in other implementations, the first voltage equalization subcircuit 203/the second voltage equalization subcircuit 204 may include one resistor, two resistors, three resistors, four resistors, and so on, and through setting of the resistance values of the resistors, the voltage of the negative output terminal PV of the PV branch to the ground, and the voltage of the positive output terminal PV + of the PV branch to the ground can be equalized.
In this embodiment, the voltage balancing sub-circuits are implemented by using resistors, and by setting the resistance of at least one resistor in the two voltage balancing sub-circuits, the voltage between the positive output terminal of the PV branch and the ground and the voltage between the negative output terminal of the PV branch and the ground can be symmetric, thereby achieving the balancing effect.
Example six
Based on the fifth embodiment, as shown in fig. 3, the first voltage equalizing sub-circuit 203 includes a third resistor R3 and a fourth resistor R4, one end of the third resistor R3 is connected to the positive output terminal PV + of any PV branch, the other end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the fourth resistor R4 is grounded;
the second voltage equalizing sub-circuit 204 comprises a fifth resistor R5 and a sixth resistor R6, one end of the fifth resistor R5 is grounded, the other end of the fifth resistor R5 is connected to one end of the sixth resistor R6, and the other end of the sixth resistor R6 is connected to the negative output terminal PV-of the PV branch.
Preferably, the third resistor R3 and the fifth resistor R5 have the same resistance, and the fourth resistor R4 and the sixth resistor R6 have the same resistance. With R3= R5, R4= R6, a voltage symmetry between the positive output of the PV branch and ground, and between the negative output and ground can be achieved.
In this embodiment, two resistors connected in series are respectively disposed between the positive output terminal PV + and the ground and between the negative output terminal PV-and the ground, and the voltages between the positive output terminal of the PV branch circuit and the ground and between the negative output terminal of the PV branch circuit and the ground can be symmetric by setting the resistance values of the four resistors, so as to achieve a balancing effect.
EXAMPLE seven
On the basis of the third embodiment, as shown in fig. 5, the first voltage equalizing sub-circuit 203 includes a third resistor R3 and a fourth resistor R4, one end of the third resistor R3 is connected to the positive output terminal PV + of any PV branch, the other end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the fourth resistor R4 is grounded;
the second voltage balancing sub-circuit 204 comprises a fifth resistor R5 and a sixth resistor R6, one end of the fifth resistor R5 is grounded, the other end of the fifth resistor R5 is connected with one end of the sixth resistor R6, and the other end of the sixth resistor R6 is connected with the negative output end PV-of the PV branch;
the first impedance adjusting sub-circuit 201 includes a first resistor R1 and a first switch SW1; one end of a first resistor R1 is connected with the positive output end PV + of the PV branch, the other end of the first resistor R1 is connected with one end of a first switch SW1, and the other end of the first switch SW1 is connected between a third resistor R3 and a fourth resistor R4;
the second impedance adjusting sub-circuit 202 includes a second resistor R2 and a second switch SW2; one end of the second resistor R2 is grounded, the other end of the second resistor R2 is connected to one end of the second switch SW2, and the other end of the second switch SW2 is connected between the fifth resistor R5 and the sixth resistor R6.
It should be understood that the sampling circuit in the present embodiment may include both the first impedance adjusting sub-circuit 201 and the second impedance adjusting sub-circuit 202 as shown in fig. 5, or may include only the first impedance adjusting sub-circuit 201 or only the second impedance adjusting sub-circuit 202, for example, the sampling circuit shown in fig. 6 includes only the first impedance adjusting sub-circuit 201.
Taking the first impedance adjusting sub-circuit 201 as an example, when the first switch SW1 is closed, the first resistor R1 is connected, so that the impedance between the positive output terminal PV + of the PV branch and the ground is changed, and when the first switch SW1 is open, the impedance between the positive output terminal PV + of the PV branch and the ground is restored to the condition of connecting the first voltage equalizing sub-circuit 203. The second impedance adjusting sub-circuit 202 is similar and will not be described in detail.
In this embodiment, an impedance adjusting sub-circuit structure of a resistor and a switch connected in series is adopted, and the impedance between the output end and the ground is adjusted by turning on or off the switch, so that different sampling voltages for determining the insulation impedance of the PV branch can be obtained.
Example eight
The present embodiment provides a branch insulation resistance detection circuit, including:
any of the sampling circuits provided in the previous embodiments; and
and the control logic circuit is connected with the sampling circuit and used for acquiring corresponding sampling voltage of the output end of the PV branch circuit to the ground when the impedance of the output end of any PV branch circuit to the ground is adjusted, determining the insulation impedance of the PV branch circuit based on different sampling voltages and the output voltage of the PV branch circuit, and determining whether the insulation impedance of the PV branch circuit is abnormal or not based on a preset threshold value.
In practical applications, the control logic circuit may be a control IC, such as a single chip, a DSP, and the like, which is not limited in this embodiment.
In the sampling circuit of the foregoing embodiment, a sampling point of the negative output terminal PV-of the PV branch is denoted as a, a sampling point of the ground (chassis) is denoted as B, a sampling voltage of the negative output terminal PV-to-ground of the PV branch is a high voltage, the connection between the control logic circuit and the sampling circuit can be realized by the high-resistance circuit 701 and the differential circuit 702 shown in fig. 7, the control logic circuit connects the a and the B through two high-resistance resistors in the high-resistance circuit 701, the high voltage is equalized through the high resistance value, and then the equalized high voltage is sent to the differential circuit 702 to output a low-voltage signal to a corresponding pin of the control IC, so as to determine the insulation impedance of the PV branch. The two high-resistance resistors may have a resistance of 56 mq, the differential circuit 702 may be a differential circuit formed by an operational amplifier and its peripheral circuits, and the operational amplifier may use TLV90641. In some implementations, the high impedance circuit 701 and the differential circuit 702 may be part of the sampling circuit in the foregoing embodiments, or may be part of the sampling circuit and the control logic circuit independently.
When acquiring the corresponding sampling voltage of the output end of the PV branch to the ground, different sampling voltages are measured through the high-resistance circuit 701 and the differential circuit 702, further, the output voltage of the PV branch may be measured through a high-voltage sensor, or through a voltage sampling circuit, specifically, the high-voltage sensor or the voltage sampling circuit, and the voltage sampling circuit may be, for example, the voltage sampling circuit shown in fig. 8, and is connected to the negative output end PV-and the positive output PV + of the PV branch to acquire the voltage between the negative output end PV-and the positive output PV +, that is, the output voltage of the PV branch.
In this embodiment, when the insulation impedance of the string inverter to the ground is abnormal, the sampling circuit is connected to the output terminal (positive output terminal PV +, negative output terminal PV-) of any PV branch connected to the string inverter, and when the impedance of the output terminal of any PV branch to the ground is adjusted by the sampling circuit, the control logic circuit can obtain the corresponding sampling voltage of the output terminal (negative output terminal PV-) of the PV branch to the ground, determine the insulation impedance of the PV branch based on the different sampling voltages and the output voltage of the PV branch, and determine whether the insulation impedance of the PV branch is abnormal based on the preset threshold. Therefore, the PV branch with abnormal insulation impedance can be accurately determined, the detection efficiency is improved, and the maintenance cost is reduced.
Example nine
The present embodiment provides a method for detecting branch insulation resistance, which is implemented based on the branch insulation resistance detection circuit in the foregoing embodiment, and as shown in fig. 9, the method for detecting branch insulation resistance in the present embodiment includes:
step 901, under the condition that the insulation impedance of the string inverter to the ground is determined to be abnormal, closing each knob switch of the string inverter in turn, and determining whether the insulation impedance of the string inverter to the ground is abnormal again;
step S902, if the insulation impedance of the string inverter to the ground is determined to be abnormal again, connecting the sampling circuit to the output end of the PV branch corresponding to the currently closed knob switch, and adjusting the impedance of the output end of the PV branch to the ground to obtain the corresponding sampling voltage of the output end to the ground;
step S903, determining the insulation resistance of the PV branch circuit based on different sampling voltages and the output voltage of the PV branch circuit;
step S904, determining whether the insulation resistance of the PV branch is abnormal based on a preset threshold.
In practice, the string inverter includes a plurality of knob switches, and each knob switch corresponds to at least one MPPT and at least one PV branch. In some cases, any PV branch may also be connected to other PV branches. When the string inverter self-tests and determines that the insulation impedance of the string inverter to the ground is abnormal, if the abnormal PV branch cannot be determined, all PV branches need to be overhauled, and a specific instrument needs to be overhauled in a specific time period (such as at night), so that the detection efficiency is low, and the maintenance cost is high. The method of the embodiment is applied to detection, time periods do not need to be considered, and the detection circuit is simple in structure and easy to achieve.
Specifically, under the condition that the insulation impedance of the string inverter to the ground is determined to be abnormal, all knob switches are turned off, each knob switch of the string inverter is turned on in turn, whether the insulation impedance of the string inverter to the ground is abnormal is determined again, so that the PV branch with the abnormality is determined to be the PV branch corresponding to which knob switch, when the insulation impedance of the string inverter to the ground is determined to be abnormal again after a certain knob switch is turned on, the PV branch corresponding to the currently-turned knob switch is determined to be abnormal, a sampling circuit is connected to the output end of any PV branch corresponding to the knob switch, the impedance of the output end of the PV branch to the ground is adjusted, so that the sampling voltage of the corresponding negative output end to the ground is obtained, and the insulation impedance of the PV branch is determined based on different sampling voltages and the output voltage of the PV branch; and finally, determining whether the insulation resistance of the PV branch circuit is abnormal or not based on a preset threshold value. The preset threshold may be set according to actual requirements, for example, 50K.
It should be understood that there may be more than one PV branch in which an abnormality occurs. And each time one knob switch is closed, the other knob switches are opened.
Taking fig. 2 as an example, the string inverter includes a plurality of knob switches 1 \8230 \ 8230and n/2, each knob switch corresponds to two MPPTs, for example, the knob switch 1 corresponds to the MPPT1 and the MPPT2, the knob switch 1 corresponds to 4 PV branches-PV 1, PV2, PV3 and PV4, wherein a positive output terminal PV1+ and a negative output terminal PV 1-of the PV1 are respectively connected to a positive output terminal PV2+ and a negative output terminal PV2+ of the PV2, when the knob switch 1 is closed, if it is determined again that the insulation impedance of the string inverter to the ground is abnormal, at least one of the PV branches PV1, PV2, PV3 and PV4 corresponding to the knob switch 1 has a detection impedance abnormality, and a sampling circuit is connected to the output terminal of any PV branch corresponding to the knob switch 1 to adjust the impedance of the output terminal of the PV branch to the ground, and it should be noted that, when the sampling circuit is connected between the connection point of the PV1 and the knob switch 1, the insulation impedance of the PV1 and the PV2 can be determined. PV3 and PV4 are similar and will not be described in detail.
In this embodiment, through the branch insulation impedance detection circuit with a simple structure and easy implementation, when it is determined that the insulation impedance of the string inverter to the ground is abnormal, the insulation impedance of the PV branch connected to the knob switch corresponding to the abnormality is detected, so that the PV branch with the abnormal insulation impedance can be accurately determined, the detection efficiency is improved, and the maintenance cost is reduced.
Example ten
In a case where the branch insulation resistance detection circuit includes the sampling circuit provided in embodiment six, determining the insulation resistance of the PV branch based on different sampling voltages and the output voltage of the PV branch includes:
and acquiring a first voltage of the negative output end PV-to-ground of the PV branch under the state that the first switch SW1 is closed and the second switch SW2 is opened, a second voltage of the negative output end PV-to-ground of the PV branch under the state that the first switch SW1 is opened and the second switch SW2 is closed and the output voltage of the PV branch, and calculating the insulation impedance of the PV branch based on the first voltage, the second voltage and the output voltage.
The sampling point of the negative output end PV-of the PV branch is marked as A, and the sampling point of the earth (chassis) is marked as B, which are respectively illustrated by the following figures 3 and 4:
referring to fig. 3, when the state quantity of the first switch SW1 is "ON" (closed) and the state quantity of the second switch SW2 is "OFF" (open), the sampling voltage (first voltage) at the two points AB at this time is Va, the output voltage of the PV branch is V1, and the inflow current and the outflow current are equal, and the relation a):
when the state quantity of the first switch SW1 is "OFF" (open) and the state quantity of the second switch SW2 is "ON" (closed), the sampling voltage (second voltage) at the two points AB at this time is Vb, the output voltage of the PV branch is V1, and the inflow current and the outflow current are equal, so that the relation b is obtained:
if R1= R2, R3= R5, R4= R6, the relation c) is obtained from the relations a) to b):
note book
Calculating the insulation impedance of the PV branch circuit based on the first voltage, the second voltage and the output voltage, and adopting the following calculation formula:
wherein, R represents the insulation resistance of the PV branch, req0 represents the equivalent resistance of the positive output end of the PV branch to the ground, req1 represents the equivalent resistance of the negative output end of the PV branch to the ground, and the intermediate variable
Va denotes a first voltage, vb denotes a second voltage, V1 denotes, R1 denotes a first resistance, R3 denotes a third resistance, and R4 denotes a fourth resistance.
Referring to fig. 4, when the state quantity of the first switch SW1 is OFF, the sampling voltage (first voltage) at the two points AB at this time is Va, the output voltage of the PV branch is V1, and the inflow current and the outflow current are equal, and the relation d is obtained:
when the state quantity of the first switch SW1 is "ON" (closed), the sampling voltage (second voltage) at the two points AB at this time is Vb, the output voltage of the PV branch is V1, and the relation e can be obtained according to the fact that the inflow current and the outflow current are equal):
if R3= R5, R4= R6, the relation f) is obtained from the relations d) to e):
note the book
Calculating the insulation impedance of the PV branch circuit based on the first voltage, the second voltage and the output voltage, and adopting the following calculation formula:
wherein, R represents the insulation resistance of the PV branch, req0 represents the equivalent resistance of the positive output end of the PV branch to the ground, req1 represents the equivalent resistance of the negative output end of the PV branch to the ground, and the intermediate variable
Va denotes a first voltage, vb denotes a second voltage, V1 denotes, R1 denotes a first resistance, R3 denotes a third resistance, and R4 denotes a fourth resistance.
In this embodiment, based on the branch insulation impedance detection circuit, the first voltage of the negative output terminal PV-to-ground of the PV branch in the state where the first switch SW1 is closed and the second switch SW2 is open, the second voltage of the negative output terminal PV-to-ground of the PV branch in the state where the first switch SW1 is open and the second switch SW2 is closed, and the output voltage of the PV branch are obtained, so that the insulation impedance of the PV branch can be calculated, the PV branch with abnormal insulation is determined, and timely maintenance is achieved.
EXAMPLE eleven
On the basis of the ninth embodiment, determining whether the insulation resistance of the PV branch circuit is abnormal based on a preset threshold includes:
and if the insulation resistance of the PV branch circuit does not reach the preset threshold value, determining that the insulation resistance of the PV branch circuit is abnormal.
It should be understood that if the insulation resistance of the PV branch reaches a preset threshold, it is determined that no abnormality has occurred in the insulation resistance of the PV branch. The preset threshold may be set according to actual requirements, and is, for example, 50K.
The sampling circuit, the branch insulation impedance detection circuit and the method provided by the embodiment of the invention have the advantages that under the condition that the insulation impedance of the string inverter to the ground is abnormal, the sampling circuit is further connected to the output end of any PV branch connected with the string inverter, and the sampling circuit can adjust the impedance of the output end of the PV branch to the ground, so that different sampling voltages of the output end of the PV branch to the ground can be obtained, the insulation impedance of the PV branch can be accurately determined based on the different sampling voltages and the output voltage of the PV branch, and the PV branch with the abnormal insulation impedance can be accurately positioned.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (13)
1. A sampling circuit for branch insulation impedance detection is characterized in that when insulation impedance of a string inverter to the ground is abnormal, the sampling circuit is connected to an output end of any PV branch connected with the string inverter and used for adjusting impedance of the output end of any PV branch to the ground so as to obtain corresponding sampling voltage of the output end of any PV branch to the ground.
2. The sampling circuit for branch insulation resistance detection according to claim 1, comprising a first impedance adjusting sub-circuit and/or a second impedance adjusting sub-circuit;
the first impedance adjusting sub-circuit is connected between the positive output end of any PV branch and the ground and used for increasing the impedance between the positive output end and the ground;
the second impedance adjusting sub-circuit is connected between the negative output end of any one PV branch and the ground and used for increasing the impedance between the negative output end and the ground.
3. The sampling circuit for branch insulation resistance detection according to claim 2, further comprising: a first voltage equalization subcircuit and a second voltage equalization subcircuit;
the first voltage balancing sub-circuit is connected between a positive output end of any PV branch and the ground, the second voltage balancing sub-circuit is connected between a negative output end of any PV branch and the ground, and the first voltage balancing sub-circuit and the second voltage balancing sub-circuit are used for balancing voltages of the positive output end and the negative output end to the ground.
4. The sampling circuit for branch insulation resistance detection according to claim 2,
the first impedance adjustment sub-circuit comprises a first resistor and a first switch; one end of the first resistor is connected with the positive output end of any one PV branch circuit, the other end of the first resistor is connected with one end of the first switch, the other end of the first switch is grounded, and the impedance between the positive output end of the PV branch circuit and the ground is adjusted by closing or opening the first switch;
the second impedance adjusting sub-circuit comprises a second resistor and a second switch; one end of the second resistor is grounded, the other end of the second resistor is connected with one end of the second switch, the other end of the second switch is connected with the negative output end of any PV branch, and the impedance between the negative output end of the PV branch and the ground is adjusted by closing or opening the second switch.
5. The sampling circuit for branch insulation resistance detection according to claim 4, wherein the first voltage equalization sub-circuit comprises at least one resistor, and the second voltage equalization sub-circuit comprises at least one resistor;
the at least one resistor in the first voltage balancing sub-circuit is connected between the positive output terminal of the any one PV branch and ground, and the at least one resistor in the second voltage balancing sub-circuit is connected between the negative output terminal of the any one PV branch and ground.
6. The sampling circuit for branch insulation resistance detection according to claim 5,
the first voltage balancing sub-circuit comprises a third resistor and a fourth resistor, one end of the third resistor is connected with the positive output end of any PV branch, the other end of the third resistor is connected with one end of the fourth resistor, and the other end of the fourth resistor is grounded;
the second voltage balancing sub-circuit comprises a fifth resistor and a sixth resistor, one end of the fifth resistor is grounded, the other end of the fifth resistor is connected with one end of the sixth resistor, and the other end of the sixth resistor is connected with the negative output end of any PV branch.
7. The sampling circuit for branch insulation resistance detection according to claim 3,
the first voltage balancing sub-circuit comprises a third resistor and a fourth resistor, one end of the third resistor is connected with the positive output end of any PV branch, the other end of the third resistor is connected with one end of the fourth resistor, and the other end of the fourth resistor is grounded;
the second voltage balancing sub-circuit comprises a fifth resistor and a sixth resistor, one end of the fifth resistor is grounded, the other end of the fifth resistor is connected with one end of the sixth resistor, and the other end of the sixth resistor is connected with the negative output end of any PV branch circuit;
the first impedance adjustment sub-circuit comprises a first resistor and a first switch; one end of the first resistor is connected with the positive output end of any PV branch, the other end of the first resistor is connected with one end of the first switch, and the other end of the first switch is connected between the third resistor and the fourth resistor;
the second impedance adjusting sub-circuit comprises a second resistor and a second switch; one end of the second resistor is grounded, the other end of the second resistor is connected with one end of the second switch, and the other end of the second switch is connected between the fifth resistor and the sixth resistor.
8. The sampling circuit for branch insulation resistance detection according to claim 6 or 7, wherein the third resistor and the fifth resistor have the same resistance value, and the fourth resistor and the sixth resistor have the same resistance value.
9. A branch insulation resistance detection circuit, comprising:
the sampling circuit of any one of claims 1 to 8; and
and the control logic circuit is connected to the sampling circuit and used for acquiring corresponding sampling voltage of the output end of any PV branch circuit to the ground when the impedance of the output end of any PV branch circuit to the ground is adjusted, determining the insulation impedance of any PV branch circuit based on different sampling voltages and the output voltage of any PV branch circuit, and determining whether the insulation impedance of any PV branch circuit is abnormal based on a preset threshold value.
10. A branch insulation resistance detection method implemented based on the branch insulation resistance detection circuit according to claim 9, the branch insulation resistance detection method comprising:
under the condition that the insulation resistance of the string inverter to the ground is determined to be abnormal, closing each knob switch of the string inverter in turn, and determining whether the insulation resistance of the string inverter to the ground is abnormal again;
if the insulation impedance of the group of series inverters to the ground is determined to be abnormal again, connecting the sampling circuit to the output end of the PV branch corresponding to the currently closed knob switch, and adjusting the impedance of the output end of the PV branch to the ground to obtain the sampling voltage of the corresponding output end to the ground;
determining an insulation resistance of the PV branch based on the different sampling voltages and the output voltage of the PV branch;
and determining whether the insulation resistance of the PV branch circuit is abnormal or not based on a preset threshold value.
11. The method according to claim 10, wherein, in the case where the branch insulation resistance detection circuit includes the sampling circuit according to claim 6, the determining the insulation resistance of the PV branch based on the different sampling voltages and the output voltage of the PV branch comprises:
and acquiring a first voltage of the negative output end of the PV branch circuit to the ground in a state that the first switch is closed and the second switch is opened, a second voltage of the negative output end of the PV branch circuit to the ground in a state that the first switch is opened and the second switch is closed and the output voltage of the PV branch circuit, and calculating to obtain the insulation impedance of the PV branch circuit based on the first voltage, the second voltage and the output voltage.
12. The method according to claim 11, wherein the calculating the insulation resistance of the PV branch based on the first voltage, the second voltage and the output voltage uses the following calculation formula:
wherein, R represents the insulation resistance of the PV branch, req0 represents the equivalent resistance of the positive output end of the PV branch to the ground, req1 represents the equivalent resistance of the negative output end of the PV branch to the ground, and the intermediate variable
G is based on the first voltage, secondAnd the second voltage is determined by the output voltage of the PV branch.
13. The method according to claim 10, wherein the determining whether the insulation resistance of the PV sub-circuit is abnormal based on a predetermined threshold comprises:
and if the insulation resistance of the PV branch circuit does not reach the preset threshold value, determining that the insulation resistance of the PV branch circuit is abnormal.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115792382A (en) * | 2022-11-29 | 2023-03-14 | 上能电气股份有限公司 | Light storage inverter ground insulation impedance detection device and method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115792382A (en) * | 2022-11-29 | 2023-03-14 | 上能电气股份有限公司 | Light storage inverter ground insulation impedance detection device and method |
| CN115792382B (en) * | 2022-11-29 | 2024-01-05 | 上能电气股份有限公司 | Device and method for detecting ground insulation resistance of light storage inverter |
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