CN112924753A - Detection apparatus for photovoltaic array is to ground insulation resistance - Google Patents
Detection apparatus for photovoltaic array is to ground insulation resistance Download PDFInfo
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- CN112924753A CN112924753A CN201911244847.3A CN201911244847A CN112924753A CN 112924753 A CN112924753 A CN 112924753A CN 201911244847 A CN201911244847 A CN 201911244847A CN 112924753 A CN112924753 A CN 112924753A
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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
- G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
- G01R27/18—Measuring resistance to earth, i.e. line to ground
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Abstract
The embodiment of the invention discloses a detection device for insulation resistance of a photovoltaic array to the ground, which comprises: the system comprises a relay, an access resistor and a sampling circuit which are sequentially connected in series, wherein the relay is also electrically connected with a positive electrode of a bus voltage, the sampling circuit is also electrically connected with a negative electrode of the bus voltage and connected with a common end in parallel, a first node is arranged between the access resistor and the sampling circuit and connected with a protection ground in parallel, and a second node is arranged between the protection ground and the sampling circuit; one end of the photovoltaic module is electrically connected with the ground insulation resistor and the power supply conversion unit respectively, the other end of the photovoltaic module is electrically connected with the negative electrode of the bus voltage, the power supply conversion unit is also electrically connected with the positive electrode of the bus voltage, and the ground insulation resistor is also electrically connected with the first node; the detection module controls the on-off of the relay, collects the voltage of the second node and the bus voltage and calculates the insulation resistance value to the ground, and controls the output of the disconnected photovoltaic module circuit when the insulation resistance value to the ground is smaller than the safety impedance value. The embodiment of the invention improves the detection precision.
Description
Technical Field
The embodiment of the invention relates to the inverter detection technology, in particular to a detection device for insulation resistance of a photovoltaic array to the ground.
Background
At present, a distributed photovoltaic power generation system is widely applied to power generation markets at home and abroad, a photovoltaic grid-connected inverter is one of key components of the photovoltaic power generation system, and converts direct current in a solar photovoltaic module matrix into alternating current through electric power and feeds the alternating current back to a power grid to realize grid-connected power generation.
In a photovoltaic power generation system, a photovoltaic grid-connected inverter must detect ground insulation resistance on the input side for safety reasons. If the ground insulation impedance is lower than a safety specified value, the photovoltaic grid-connected inverter is switched to an abnormal fault state, so that electric shock hazard is prevented, and personnel and equipment are protected.
However, the detection circuit of the existing ground insulation resistance detection circuit has a complex structure and a complex calculation process, which results in low detection precision.
Disclosure of Invention
The embodiment of the invention provides a detection device for insulation resistance of a photovoltaic array to the ground, which is used for simplifying a detection circuit structure and improving detection precision.
The embodiment of the invention provides a detection device for insulation resistance of a photovoltaic array to the ground, which comprises:
the bus voltage sampling circuit comprises a relay, an access resistor and a sampling circuit which are sequentially connected in series, wherein the other end of the relay is electrically connected with the positive electrode of a bus voltage, the other end of the sampling circuit is electrically connected with the negative electrode of the bus voltage and connected with a common end in parallel, a first node is arranged on a connecting line between the access resistor and the sampling circuit and is connected to a protection ground, and a second node is arranged on a connecting line between the protection ground and the sampling circuit;
the photovoltaic module circuit comprises photovoltaic modules, a ground insulation resistor and a power supply conversion unit, wherein a first end of each photovoltaic module is electrically connected with the ground insulation resistor and the power supply conversion unit respectively, a second end of each photovoltaic module is electrically connected with a negative electrode of the bus voltage and connected with the common end, the other end of each power supply conversion unit is electrically connected with a positive electrode of the bus voltage, and the other end of each ground insulation resistor is electrically connected with the first node;
the detection module is respectively electrically connected with the relay, the second node and the bus voltage, is used for controlling the disconnection or the conduction of the relay, is also used for collecting the voltage values of the second node and the bus voltage, calculating an earth insulation resistance value Rx according to a formula (1), and is also used for controlling the disconnection of an output path of the photovoltaic assembly line when detecting that the earth insulation resistance value is smaller than a safety impedance value,
wherein VeoffIs the voltage value of the second node Ve when the relay is offonIs the voltage value of the second node when the relay is switched on, Ra is the resistance value of the sampling circuit, VBusonThe voltage value of the bus voltage when the relay is switched on is shown, and R0 is the resistance value of the access resistor.
Further, the sampling circuit comprises a first sampling resistor and a second sampling resistor which are connected in series, the other end of the first sampling resistor is electrically connected with the access resistor, and the other end of the second sampling resistor is electrically connected with the negative electrode of the bus voltage and connected with the common end;
Ra＝R1+R2，
r1 is the resistance of the first sampling resistor, and R2 is the resistance of the second sampling resistor.
Furthermore, a third node is arranged on a connecting line between the first sampling resistor and the second sampling resistor;
the detection module is further used for acquiring a voltage value of the third node and calculating a voltage value of the second node according to formulas (2) and (3);
wherein, VisooffIs the voltage value of the third node, Viso, when the relay is offonThe voltage value of the third node when the relay is conducted is obtained.
Further, the detection module comprises an acquisition unit and a control chip;
the acquisition unit is electrically connected with the third node and used for acquiring the voltage value of the third node, and the acquisition unit is also electrically connected with the bus voltage and used for acquiring the voltage value of the bus voltage;
the control chip is respectively electrically connected with the acquisition unit and the relay, is used for controlling the disconnection or the connection of the relay, is used for calculating the earth insulation resistance value according to the voltage values of the third node and the bus voltage, and is also used for controlling the disconnection of the output path of the photovoltaic module circuit when detecting that the earth insulation resistance value is smaller than the safety impedance value.
Further, the output end of the photovoltaic module circuit is electrically connected with the input end of the photovoltaic grid-connected inverter;
the detection module is used for controlling to disconnect the transmission path of the photovoltaic module line and the photovoltaic grid-connected inverter when detecting that the ground insulation resistance value is smaller than the safety resistance value, or is used for controlling to connect the transmission path of the photovoltaic module line and the photovoltaic grid-connected inverter when detecting that the ground insulation resistance value is larger than or equal to the safety resistance value.
Further, the power conversion unit is a non-isolation type boost direct current switch circuit.
In the embodiment of the invention, when one or more photovoltaic arrays are connected into the photovoltaic grid-connected inverter, the circuit structure of the detection device is simple, and the Rx calculation processes of the detection module are as follows: and voltage values of the second node and the bus voltage are collected before and after the relay is switched on and switched off, and Rx can be calculated according to the voltage values and a formula. In the embodiment of the invention, the relay and the sampling circuit are respectively connected with the positive electrode and the negative electrode of the bus voltage, but not the output end of the photovoltaic array, namely the input end of the photovoltaic grid-connected inverter, when one or more photovoltaic component circuits exist, only one relay and one sampling circuit are connected into the photovoltaic grid-connected inverter, the input end of the photovoltaic grid-connected inverter is connected with one sampling circuit, but not the multiple sampling circuits, the hardware circuit design is greatly optimized, the cost is reduced, the circuit cost is reduced, the control logic of one relay is very simple and easy to realize, the algorithm is simplified, a complex calculation process is not needed, the error between the obtained impedance value and the actual value is small, and the impedance detection precision is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief description will be given below of the drawings required for the embodiments or the technical solutions in the prior art, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of a circuit for detecting insulation resistance to ground provided by the prior art;
FIG. 2 is a schematic diagram of a device for detecting insulation resistance to ground of a photovoltaic array according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a device for detecting insulation resistance to ground of a photovoltaic array according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of the opening of a relay of the detection device of the insulation resistance of the photovoltaic array to the ground in the embodiment of the invention;
FIG. 5 is a schematic diagram of the conduction of a relay of the detection device of the insulation resistance of the photovoltaic array to the ground in the embodiment of the invention;
FIG. 6 is a schematic diagram of a device for detecting insulation resistance to ground of a photovoltaic array according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a detection module of the detection device for detecting the insulation resistance of the photovoltaic array to the ground in the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described through embodiments with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic diagram of a conventional ground insulation resistance detection circuit. The detection circuit comprises a plurality of photovoltaic arrays 1', one photovoltaic array 1' is arranged corresponding to one relay ISO, and a positive end PV + and a negative end PV-of the photovoltaic array 1 'are respectively connected with a sampling circuit 2' in series in a ground mode. By a certain detection algorithm, the impedance of PV + or PV-to-ground can be calculated, and whether the impedance to ground exceeds a safe specified value or not can be further judged.
One photovoltaic array can correspond to one sampling circuit, the sampling circuit is used for sampling signals corresponding to the photovoltaic array, the detection algorithm is simple, when the photovoltaic grid-connected inverter is connected into a plurality of photovoltaic arrays, a plurality of sampling circuits and a plurality of relays are needed, the structure of the detection circuit is complex, correspondingly, the control logic of the relays of different photovoltaic arrays is also complex, and the detection precision is possibly low.
One sampling circuit can correspond to a plurality of photovoltaic arrays, the positive end and the negative end of each photovoltaic array are connected to the sampling circuit, and the detection circuit needs to control the switching of different photovoltaic arrays, so that the circuit structure and the control logic thereof are complex, the calculation amount is large, errors are easy to occur, the error between the finally calculated impedance value and the actual value is large, and the accuracy is low.
Referring to fig. 2, a schematic diagram of a device for detecting insulation resistance to ground of a photovoltaic array is provided in an embodiment of the present invention. The detection device provided by the embodiment is suitable for detecting the insulation resistance to ground of one or more paths of photovoltaic modules.
The detection device for the insulation resistance of the photovoltaic array to the ground provided by the embodiment comprises: the device comprises a relay 1, an access resistor 2 and a sampling circuit 3 which are sequentially connected in series, wherein the other end of the relay 1 is electrically connected with the positive electrode of a BUS voltage BUS, the other end of the sampling circuit 3 is electrically connected with the negative electrode of the BUS voltage BUS and connected with a common end GND, a first node N1 is arranged on a connecting line between the access resistor 2 and the sampling circuit 3, the first node N1 is connected with a protection ground PE, and a second node N2 is arranged on a connecting line between the protection ground PE and the sampling circuit 3; the photovoltaic module circuit 4 comprises a plurality of photovoltaic module circuits 4 connected in parallel, each photovoltaic module circuit 4 comprises a photovoltaic module PV, a ground insulation resistor 41 and a power conversion unit 42, the first end of each photovoltaic module PV is electrically connected with the ground insulation resistor 41 and the power conversion unit 42 respectively, the second end of each photovoltaic module PV is electrically connected with the negative electrode of a BUS voltage BUS and connected with a common end GND, the other end of each power conversion unit 42 is electrically connected with the positive electrode of the BUS voltage BUS, and the other end of each ground insulation resistor 41 is electrically connected with a first node N1; the detection module 5 is respectively electrically connected with the relay 1, the second node N2 and the BUS voltage BUS, is used for controlling the relay 1 to be switched off or switched on, is also used for collecting the voltage values of the second node N2 and the BUS voltage BUS, calculating the ground insulation resistance value Rx according to a formula (1), and is also used for controlling the output path of the photovoltaic module circuit 4 to be switched off when the ground insulation resistance value Rx is detected to be smaller than the safety resistance value,
wherein VeoffIs the voltage value, Ve, of the second node N2 when the relay 1 is switched offonThe voltage value of the second node N2 when the relay 1 is turned on, Ra is the resistance value of the sampling circuit 3, VBusonThe value of the BUS voltage BUS when the relay 1 is conducted is R0, which is the resistance value of the access resistor 2.
As shown in fig. 2, the detection device for insulation resistance to ground of the optional photovoltaic array comprises: and one photovoltaic module line 5. In other embodiments, as shown in fig. 3, the apparatus for detecting insulation resistance to ground of the photovoltaic array may further include: the photovoltaic module circuit that the multichannel is parallelly connected.
Referring to fig. 2, the detection device comprises a relay 1, an access resistor 2 and a sampling circuit 3 which are connected in series in sequence. It can be understood that the other end of the relay 1 is electrically connected with the positive electrode of the BUS voltage BUS, and the other end of the sampling circuit 3 is electrically connected with the negative electrode of the BUS voltage BUS and connected with the common end GND, wherein the BUS voltage BUS is the BUS voltage of the photovoltaic grid-connected inverter. Obviously, the relay 1 is in a disconnected state, the BUS voltage BUS is disconnected with the transmission path of the sampling circuit 3, and the BUS voltage BUS is not connected to the circuit; relay 1 is in the on-state, and BUS voltage BUS switches on with sampling circuit 3's transmission path, is inserted the circuit. It will be appreciated that the detection module 5 controls the relay 1 to be open or closed.
Referring to fig. 2, a first node N1 is provided on a connection line between the access resistor 2 and the sampling circuit 3, the first node N1 is connected to a protection ground PE, and a second node N2 is provided on a connection line between the protection ground PE and the sampling circuit 3. The protective ground PE specifically means that a wire is directly connected to the ground, and here, the access resistor 2 is electrically connected to the sampling circuit 3 and then connected to the ground, and it can be understood that the first node N1 is equivalent to an electrical connection point between the access resistor 2 and the sampling circuit 3, and the first node N1 is connected to the ground through a wire. A second node N2 is provided on the connection between the protection ground PE and the sampling circuit 3, and a second node N2 is provided on the connection between the first node N1 and the sampling circuit 3, and the second node N2 is a virtual node and is defined only as the connection between the first node N1 and the sampling circuit 3.
Referring to fig. 2, the detection device includes a photovoltaic module circuit 4. If the detection device comprises a plurality of photovoltaic module circuits, the plurality of photovoltaic module circuits are connected in parallel. For any one path of photovoltaic module line 4, the photovoltaic module line 4 comprises a photovoltaic module PV, a ground insulation resistor 41 and a power conversion unit 42, a first end of the photovoltaic module PV is electrically connected with the ground insulation resistor 41 and the power conversion unit 42 respectively, a second end of the photovoltaic module PV is electrically connected with a negative electrode of a BUS voltage BUS and connected with a common end GND, the other end of the power conversion unit 42 is electrically connected with a positive electrode of the BUS voltage BUS, and the other end of the ground insulation resistor 41 is electrically connected with a first node N1. The photovoltaic module PV may optionally be a solar panel for converting light energy into electrical energy. The insulation resistance to ground 41 can be characterized as the impedance of any point of the photovoltaic module PV to the ground PE.
The output end of the optional photovoltaic module circuit 4 is electrically connected with the input end of a photovoltaic grid-connected inverter (not shown); the detection module 5 is used for controlling to disconnect the transmission path of the photovoltaic module line 4 and the photovoltaic grid-connected inverter when detecting that the ground insulation resistance value is smaller than the safety resistance value, or controlling to connect the transmission path of the photovoltaic module line 4 and the photovoltaic grid-connected inverter when detecting that the ground insulation resistance value is larger than or equal to the safety resistance value. It is understood that the output terminal of the pv module line 4 is electrically connected to the input terminal of the pv grid-connected inverter, and the ground insulation resistor 41 can also be characterized as the impedance of the input terminal of the pv grid-connected inverter to the ground PE.
The optional power conversion unit 42 is a non-isolated boost dc switch circuit, and is configured to convert a high-frequency dc signal of the photovoltaic module PV into a high-voltage dc signal and transmit the high-voltage dc signal to the photovoltaic grid-connected inverter.
Referring to fig. 2, the detection device further includes a detection module 5, and the detection module 5 is electrically connected to two ends of the relay 1 and is used for controlling the on/off of the relay 1. The detection module 5 is also electrically connected to the second node N2, and is configured to collect a voltage value of the second node N2 in an off state of the relay 1 and collect a voltage value of the second node N2 in an on state of the relay 1. Detection module 5 is still connected with busbar voltage BUS electricity, and busbar voltage BUS's negative pole meets common terminal GND, and the common terminal GND that detection module 5 shown in FIG. 2 is connected promptly for being the common terminal GND with busbar voltage BUS's negative pole connection, and the positive pole of busbar voltage BUS is connected with relay 1's first end electricity, and then detection module 5's the wire of being connected with relay 1's first end electricity is still multiplexing as the anodal wire of connecting busbar voltage BUS. When the relay 1 is in a conducting state, the BUS voltage BUS is connected into the circuit, and then the detection module 5 can detect the voltage value of the BUS voltage BUS; when the relay 1 is in an off state, the BUS voltage BUS is in an open circuit state and is not connected to the circuit.
The ground insulation resistor 41 can be characterized as the impedance of the input end of the photovoltaic grid-connected inverter to the ground PE, and when the impedance of the ground insulation resistor 41 is infinite, the impedance to the ground is normal, and when the impedance of the ground insulation resistor 41 is small (for example, 100K Ω), the impedance to the ground is abnormal. The safety impedance value is the impedance value of the input end of the photovoltaic grid-connected inverter specified by the national safety, obviously, the impedance of the ground insulation resistor 41 is smaller than the safety impedance value, which indicates that the input end of the photovoltaic grid-connected inverter is abnormal, and the photovoltaic grid-connected inverter gives an alarm and breaks the electric connection with the photovoltaic module circuit, so that the safety of the photovoltaic grid-connected inverter and personnel can be protected, and personnel contact can be prevented. The impedance of the ground insulation resistor 41 is larger than or equal to the safety impedance value, which indicates that the input end of the photovoltaic grid-connected inverter is normal, the electrical connection between the photovoltaic grid-connected inverter and the photovoltaic module circuit is normal, and the photovoltaic grid-connected inverter continues to work, so that grid-connected power generation is realized.
In this embodiment, the detection module 5 can calculate the ground insulation resistance Rx according to the formula (1), and compare the ground insulation resistance Rx with the safety impedance value to determine the line status,
wherein VeoffIs the voltage value, Ve, of the second node N2 when the relay 1 is switched offonThe voltage value of the second node N2 when the relay 1 is turned on, Ra is the resistance value of the sampling circuit 3, VBusonThe value of the BUS voltage BUS when the relay 1 is conducted is R0, which is the resistance value of the access resistor 2.
It will be appreciated that the detection module 5 controlling the relay 1 to open can derive a formula for Rx, which is related to Ra, R0, Ve and PV; the detection module 5 controls the relay 1 to be conducted, and an Rx formula is obtained, wherein the Rx formula is related to Ra, R0, Ve, VBus and PV. In the detection device, Ra and R0 are known values, the detection module 5 can acquire voltage values of Ve and VBus, and the voltage value of the photovoltaic module PV is fixed and unknown, so that the detection module 5 can eliminate the unknown parameter PV according to two Rx formulas under the on-off state of the relay 1 to obtain a formula (1), and at the moment, the Rx formulas are related to parameters such as Ra, R0, Ve and VBus. The specific formula derivation process is not described herein.
Based on this, formula (1) is preset in the detection module 5, and in actual detection, the detection module 5 only needs to collect the voltage values of Ve and VBus and calculate according to formula (1) to obtain the specific value of Rx. The working process of the detection module 5 is as follows:
step1, the detection module 5 controls the relay 1 to be disconnected, and then the BUS voltage BUS is not connected to the circuit. Referring to fig. 4, the detection module 5 collects the voltage value Ve of the second node N2 to obtain Veoff。
Step2 and the detection module 5 control the relay 1 to be conducted, and then the BUS voltage BUS is connected into the circuit. Referring to fig. 5, the detection module 5 collects the voltage value Ve of the second node N2 to obtain VeonThe detection module 5 acquires the voltage value VBus of the BUS voltage BUS to obtain VBuson。
Step3, calculating Rx according to the formula (1) by the detection module 5 according to the data obtained from Step 1-Step 2, wherein Rx is characterized by the ground insulation resistance of the photovoltaic module PV. The optional detection module 5 controls the relay 1 to open.
Step4, the detection module 5 compares Rx with its pre-stored safety impedance value.
Step5, if Rx detected by the detection module 5 is smaller than the safety impedance value, the transmission path between the photovoltaic module circuit and the photovoltaic grid-connected inverter is controlled to be disconnected, and the photovoltaic grid-connected inverter gives an alarm and switches to an abnormal fault state; or, when the detection module 5 detects that Rx is greater than or equal to the safety impedance value, the line of the photovoltaic module is normally conducted with the transmission path of the photovoltaic grid-connected inverter, and the photovoltaic grid-connected inverter continues to work, so that grid-connected power generation is realized.
In this embodiment, when one or more photovoltaic arrays are connected to the photovoltaic grid-connected inverter, the circuit structure of the detection device is simple, and the calculation processes of the detection module on Rx are as follows: and voltage values of the second node and the bus voltage are collected before and after the relay is switched on and switched off, and Rx can be calculated according to the voltage values and a formula. In this embodiment, the relay and the sampling circuit are respectively connected to the positive and negative poles of the bus voltage, rather than the output end of the photovoltaic array, that is, the input end of the photovoltaic grid-connected inverter, when one or more lines of the photovoltaic module exist, only one relay and one line of the sampling circuit are connected to the photovoltaic grid-connected inverter, the input end of the photovoltaic grid-connected inverter is connected to one line of the sampling circuit, rather than multiple lines of the sampling circuit, the hardware circuit design is greatly optimized, the cost is reduced, the circuit cost is reduced, the control logic of one relay is very simple, the implementation is easy, the algorithm is simplified, a complex calculation process is not needed, the error between the obtained impedance value and the actual value is small, and the impedance detection.
Exemplarily, on the basis of the above technical solution, as shown in fig. 6, the sampling circuit 3 may include a first sampling resistor 31 and a second sampling resistor 32 connected in series, where the other end of the first sampling resistor 31 is electrically connected to the access resistor 2, and the other end of the second sampling resistor 32 is electrically connected to the negative electrode of the BUS voltage BUS and is connected to the common terminal GND; ra is R1+ R2, R1 is the resistance value of the first sampling resistor 31, and R2 is the resistance value of the second sampling resistor 32. In this embodiment, the sampling circuit 3 is composed of a first sampling resistor 31 and a second sampling resistor 32 which are connected in series, and two sampling resistors which are connected in series are arranged in the sampling circuit 3, so that the voltage between the sampling resistors can be conveniently acquired.
Optionally, a third node N3 is disposed on a connection line between the first sampling resistor 31 and the second sampling resistor 32; the detection module 5 is further configured to collect a voltage value of the third node N3 and calculate a voltage value of the second node N2 according to formulas (2) and (3);
wherein, VisooffIs the voltage value of the third node N3, Viso, when the relay 1 is switched offonThe voltage value of the third node N3 when the relay 1 is turned on.
In this embodiment, the access resistor 2 and the sampling resistors 31 and 32 in the sampling circuit 3 constitute a sampling conditioning circuit, so that the sampling voltage Viso of the relay ISO is acquired, the voltage of the third node N3 represents the sampling voltage Viso of the relay ISO, and the voltage Ve of the second node N2 represents the voltage of the earth ground PE and the ground inside the machine.
In this embodiment, the detection module 5 may not be capable of directly acquiring the voltage of the second node N2, the sampling circuit 3 is provided with the first sampling resistor 31 and the second sampling resistor 32, the detection module 5 may directly acquire the voltage of the third node N3, i.e., Viso, and then the selectable detection module 5 is electrically connected to the third node N3 to acquire the voltage value of the third node N3. The first sampling resistor 31 and the second sampling resistor 32 are connected in series, and the voltage of the second node N2 can be calculated according to equations (2) and (3), and then the detection module 5 substitutes the voltage of the second node N2 into equation (1) to calculate Rx.
It can be understood that the detection module 5 controls the relay 1 to be in the off state, and then collects the voltage value of the third node N3, that is, Visooff(ii) a The detection module 5 controls the relay 1 to be in a conducting state, and then the voltage value of the third node N3 is acquired, namely the Visoon。
Optionally, as shown in fig. 7, the detection module 5 includes an acquisition unit 51 and a control chip 52; the acquisition unit 51 is electrically connected with the third node N3 and is used for acquiring the voltage value of the third node N3, and the acquisition unit 51 is also electrically connected with the BUS voltage BUS and is used for acquiring the voltage value of the BUS voltage BUS; the control chip 52 is electrically connected to the acquisition unit 51 and the relay 1, and is configured to control the relay 1 to be turned off or turned on, calculate an insulation resistance to ground Rx according to the voltage values of the third node N3 and the BUS voltage BUS, and control an output path of a circuit of the photovoltaic module to be turned off when detecting that the insulation resistance to ground Rx is smaller than a safety impedance value.
In this embodiment, the acquisition unit 51 in the detection module 5 realizes the function of acquiring voltage signals, and the control chip 52 realizes the functions of controlling the on-off of the relay, calculating Rx, and detecting. It is understood that the collecting unit 51 may be any collecting unit capable of collecting voltage signals, and is not particularly limited in the present invention; the control chip 52 can be any one of control chips capable of controlling on/off of the relay, calculating Rx, detecting and the like.
In this embodiment, the detection module 5 may include one collection unit 51 for collecting the voltage values of the third node N3 and the BUS voltage BUS, and optionally include a plurality of collection units, where one collection unit is used for collecting the voltage value of the third node and another collection unit is used for collecting the voltage value of the BUS voltage. It can be understood that when the relay is switched on, the detection module collects the voltage value of the bus voltage.
In the embodiment, the input side detection of the photovoltaic grid-connected inverter is changed into bus side detection, the number of hardware sampling circuits and relays is reduced, the hardware design is simplified, the hardware cost is reduced, only three steps are needed in the whole detection process, and the detection efficiency is improved. And secondly, after the bus side detection is adopted, the insulation ground resistance of the input side of the photovoltaic grid-connected inverter and any point from the input side to the bus side can be detected, so that the detection range is expanded. Finally, the detection algorithm is simplified, the calculated amount is reduced, the impedance detection accuracy is improved, and the detection error is reduced by adjusting the detection circuit.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious modifications, rearrangements, combinations and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (6)
1. A detection device for insulation resistance of a photovoltaic array to ground is characterized by comprising:
the bus voltage sampling circuit comprises a relay, an access resistor and a sampling circuit which are sequentially connected in series, wherein the other end of the relay is electrically connected with the positive electrode of a bus voltage, the other end of the sampling circuit is electrically connected with the negative electrode of the bus voltage and connected with a common end in parallel, a first node is arranged on a connecting line between the access resistor and the sampling circuit and is connected to a protection ground, and a second node is arranged on a connecting line between the protection ground and the sampling circuit;
the photovoltaic module circuit comprises photovoltaic modules, a ground insulation resistor and a power supply conversion unit, wherein a first end of each photovoltaic module is electrically connected with the ground insulation resistor and the power supply conversion unit respectively, a second end of each photovoltaic module is electrically connected with a negative electrode of the bus voltage and connected with the common end, the other end of each power supply conversion unit is electrically connected with a positive electrode of the bus voltage, and the other end of each ground insulation resistor is electrically connected with the first node;
the detection module is respectively electrically connected with the relay, the second node and the bus voltage, is used for controlling the disconnection or the conduction of the relay, is also used for collecting the voltage values of the second node and the bus voltage, calculating an earth insulation resistance value Rx according to a formula (1), and is also used for controlling the disconnection of an output path of the photovoltaic assembly line when detecting that the earth insulation resistance value is smaller than a safety impedance value,
wherein VeoffIs the voltage value of the second node Ve when the relay is offonIs the voltage value of the second node when the relay is switched on, Ra is the resistance value of the sampling circuit, VBusonThe voltage value of the bus voltage when the relay is switched on is shown, and R0 is the resistance value of the access resistor.
2. The detection device according to claim 1, wherein the sampling circuit comprises a first sampling resistor and a second sampling resistor which are connected in series, the other end of the first sampling resistor is electrically connected with the access resistor, and the other end of the second sampling resistor is electrically connected with the negative pole of the bus voltage and connected with the common end;
Ra＝R1+R2，
r1 is the resistance of the first sampling resistor, and R2 is the resistance of the second sampling resistor.
3. The detection device according to claim 2, wherein a third node is arranged on a connecting line between the first sampling resistor and the second sampling resistor;
the detection module is further used for acquiring a voltage value of the third node and calculating a voltage value of the second node according to formulas (2) and (3);
wherein, VisooffIs the voltage value of the third node, Viso, when the relay is offonThe voltage value of the third node when the relay is conducted is obtained.
4. The detection device according to claim 3, wherein the detection module comprises an acquisition unit and a control chip;
the acquisition unit is electrically connected with the third node and used for acquiring the voltage value of the third node, and the acquisition unit is also electrically connected with the bus voltage and used for acquiring the voltage value of the bus voltage;
the control chip is respectively electrically connected with the acquisition unit and the relay, is used for controlling the disconnection or the connection of the relay, is used for calculating the earth insulation resistance value according to the voltage values of the third node and the bus voltage, and is also used for controlling the disconnection of the output path of the photovoltaic module circuit when detecting that the earth insulation resistance value is smaller than the safety impedance value.
5. The detection device according to claim 1, wherein the output end of the photovoltaic module line is electrically connected with the input end of a photovoltaic grid-connected inverter;
the detection module is used for controlling to disconnect the transmission path of the photovoltaic module line and the photovoltaic grid-connected inverter when detecting that the ground insulation resistance value is smaller than the safety resistance value, or is used for controlling to connect the transmission path of the photovoltaic module line and the photovoltaic grid-connected inverter when detecting that the ground insulation resistance value is larger than or equal to the safety resistance value.
6. The detection device according to claim 1, wherein the power conversion unit is a non-isolated boost dc switch circuit.
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