CN114204594B - Grid-connected system and insulation resistance detection method - Google Patents
Grid-connected system and insulation resistance detection method Download PDFInfo
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- CN114204594B CN114204594B CN202111487761.0A CN202111487761A CN114204594B CN 114204594 B CN114204594 B CN 114204594B CN 202111487761 A CN202111487761 A CN 202111487761A CN 114204594 B CN114204594 B CN 114204594B
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- 238000009413 insulation Methods 0.000 title claims abstract description 20
- 238000001514 detection method Methods 0.000 title abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 29
- 238000004146 energy storage Methods 0.000 claims description 4
- 210000000352 storage cell Anatomy 0.000 claims description 2
- 238000010248 power generation Methods 0.000 description 12
- 238000010586 diagram Methods 0.000 description 11
- 239000004065 semiconductor Substances 0.000 description 2
- 238000003491 array Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
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- 230000001681 protective effect Effects 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
- Inverter Devices (AREA)
Abstract
The application discloses a grid-connected system and a detection method of insulation resistance, comprising the following steps: an inverter, a controller, and a test circuit; the test circuit comprises a test resistor and a test voltage source which are connected in series; the input end of the inverter is used for connecting with a direct current power supply, and the output end of the inverter is used for connecting with an alternating current power grid; the test circuit is connected between the output end of the inverter and the ground; the controller obtains the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system, the grid-connected system realizes the detection of the ground impedance in real time, and the inverter is not required to be shut down to detect the direct current impedance and the alternating current impedance respectively, so that the method is simple and easy to operate. According to the technical scheme, the ground impedance is detected in real time, whether the grid-connected system has a ground fault or not is judged in time, and personal safety and equipment safety are protected.
Description
Technical Field
The application relates to the technical field of new energy, in particular to a grid-connected system and a detection method of insulation resistance.
Background
At present, as new energy is more and more emphasized, the development of new energy is more and more mature, such as photovoltaic power generation, wind power generation or hydroelectric power generation, etc., and the development of new energy is described by using photovoltaic power generation as an example. The photovoltaic power generation can be connected with the grid through the inverter, but in actual work, the ground insulation impedance of the photovoltaic system needs to be detected, for example, the input end of the inverter is direct current, and the output end of the inverter is alternating current, so that the insulation impedance comprises direct current ground impedance and alternating current ground impedance, the direct current ground impedance and the alternating current ground impedance can be separately detected before the grid connection operation of the inverter, and the direct current ground impedance and the alternating current ground impedance can be accurately detected.
However, when the inverter is in grid-connected operation, the direct current impedance to the ground and the alternating current impedance to the ground are coupled together, and cannot be separately detected, so that whether the grid-connected system has an insulation fault cannot be judged.
Disclosure of Invention
In order to solve the technical problems, the application provides a grid-connected system and an insulation resistance detection method, which can accurately detect the insulation resistance of the grid-connected system during grid connection, so that measures can be taken in time when a ground fault occurs.
In order to achieve the above object, the technical solution provided by the embodiments of the present application is as follows:
The application provides a grid-connected system, comprising: an inverter, a controller, and a test circuit; the test circuit comprises a test resistor and a test voltage source which are connected in series;
the input end of the inverter is used for being connected with a direct current power supply, and the output end of the inverter is used for being connected with an alternating current power grid;
the test circuit is connected between the output end of the inverter and the ground;
The controller is used for obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, and the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system.
Preferably, the controller is specifically configured to obtain the impedance to ground of the grid-connected system according to the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source.
Preferably, the controller is specifically configured to obtain the impedance to ground of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor, the voltage of the test voltage source, and the current flowing through the test resistor when the test circuit is connected to the grid-connected system.
Preferably, the controller is specifically configured to obtain the impedance to ground by the following formula;
Wherein V0 is the first voltage, V1 is the second voltage, vt is the voltage of the test voltage source, and Rt is the test resistance.
Preferably, the test circuit further comprises a test switch in series with the test resistor and the test voltage source; the first voltage is greater than 0;
when the test switch is closed, the test circuit is connected to the grid-connected system; when the test switch is disconnected, the test circuit is not connected to the grid-connected system.
Preferably, the test circuit further comprises a first switch, a second switch, a third switch and a fourth switch;
the first switch is connected between the positive electrode of the test voltage source and the first end of the test resistor; the second end of the test resistor is connected with the output end of the inverter; the second switch is connected between the negative electrode of the test voltage source and the ground; the third switch is connected between the negative electrode of the test voltage source and the first end of the test resistor; the fourth switch is connected between the positive electrode of the test voltage source and ground;
when the first voltage is smaller than 0, the controller is used for controlling the first switch and the second switch to be closed and controlling the third switch and the fourth switch to be opened;
and when the first voltage is greater than 0, the controller is used for controlling the first switch and the second switch to be opened and controlling the third switch and the fourth switch to be closed.
Preferably, when the grid-connected system comprises three phases, the test resistor comprises three test resistors with equal resistance values, each corresponding to one test resistor, and Rt is a test resistor of any one of the three phases.
Preferably, the controller is further configured to perform fault alarm when the impedance to ground of the grid-connected system is smaller than a preset impedance.
Preferably, the direct current power supply is from a photovoltaic array or a cluster of energy storage cells; the inverter includes a Boost circuit.
Preferably, the test circuit further comprises an inductance in series with the test resistor.
The application provides a detection method of insulation resistance, which is applied to a grid-connected system, wherein the grid-connected system comprises the following components: an inverter, a controller, and a test circuit; the test circuit comprises a test resistor and a test voltage source which are connected in series; the test circuit is connected between the output end of the inverter and the ground; the method comprises the following steps:
obtaining the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system;
Obtaining the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system;
obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, and the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system.
Preferably, the obtaining the impedance to ground of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source specifically includes:
And obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source.
Preferably, the obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source specifically includes:
obtaining the current flowing through the test resistor when the test circuit is connected to the grid-connected system;
and obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor, the voltage of the test voltage source and the current flowing through the test resistor when the test circuit is connected into the grid-connected system.
Preferably, the impedance to ground of the grid-connected system is obtained according to the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source, and in particular, the impedance to ground is obtained through the following formula;
Wherein V0 is the first voltage, V1 is the second voltage, vt is the voltage of the test voltage source, and Rt is the test resistance.
Preferably, the first voltage, the second voltage and the impedance to ground are all obtained during grid-connected operation of the inverter.
According to the technical scheme, the application has the following beneficial effects:
The grid-connected system comprises: an inverter, a controller, and a test circuit; the test circuit comprises a test resistor and a test voltage source which are connected in series; the test circuit is connected between the output end of the inverter and the ground; obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, and the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system.
The test circuit in the technical scheme provided by the embodiment of the application is only connected when the impedance of the grid-connected system to the ground is required to be tested, and the test circuit is disconnected from the grid-connected system when detection is not required, so that the grid-connected system is not affected, the normal operation of the grid-connected system is not affected, for example, the inverter is not required to be shut down, and the generated energy is further lost. The grid-connected system can realize the detection of the ground impedance in real time, and the direct current impedance and the alternating current impedance do not need to be detected respectively by the shutdown of the inverter, so that the grid-connected system is simple and easy to operate. According to the technical scheme, the detection of the ground impedance can be realized in real time, so that whether the grid-connected system has a ground fault or not is judged in time, and the personal safety and the equipment safety are protected.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a grid-tie system;
FIG. 2 is a schematic diagram of a grid-connected system according to the present application;
FIG. 3 is a schematic diagram of the switch of FIG. 2 when closed;
FIG. 4 is a schematic diagram of a grid-tie system including multiple inverters according to the present disclosure;
FIG. 5 is a schematic diagram of another grid-connected system according to the present application;
fig. 6 is a flowchart of a method for detecting insulation resistance according to the present application.
Detailed Description
In order to help better understand the scheme provided by the embodiment of the application, before introducing the method provided by the embodiment of the application, an application scene of the scheme of the embodiment of the application is introduced.
Referring to fig. 1, a schematic diagram of a grid-tie system is shown.
The embodiment of the application is not limited to a specific energy source of the grid-connected system, and can be used for photovoltaic power generation, wind power generation, hydroelectric power generation, an energy storage system and the like.
In order to facilitate understanding and implementation by those skilled in the art, photovoltaic power generation is described below as an example.
The photovoltaic array PV1 outputs direct current to the input of the inverter 101, and the output of the inverter 101 is connected to the ac grid through a switch. In fig. 1, a three-phase ac power grid is taken as an example, and it should be understood that the photovoltaic power generation may also be applied to a single-phase ac power grid for household use.
The input end of the inverter 101 is dc, and the impedance of the dc bus to the ground PE corresponds to the dc bus, including the following two: the direct current positive bus insulation resistance to ground is direct current resistance R11, and the direct current negative bus insulation resistance to ground is direct current resistance R12.
The output of the inverter 101 is three-phase ac, and the ac impedances of the three phases to ground PE are Ra, rb, and Rc, respectively.
Conventionally, the dc impedances R11 and R12 and the ac impedances Ra, rb and Rc may be obtained before the inverter 101 is connected to the grid, i.e. before the switch at the output of the inverter 101 is closed. However, after the inverter 101 is in grid-connected operation, the ac impedance and the dc impedance are coupled together, so that the impedance to ground of the grid-connected system cannot be accurately detected, and whether the grid-connected system has a fault to ground cannot be accurately determined.
Grid-connected system embodiment
In order to solve the technical problems, the application provides the grid-connected system, wherein the detection circuit is added in the grid-connected system, so that the ground impedance of the grid-connected system can be detected in real time in the running process of the grid-connected system, and whether the grid-connected system has a ground fault or not can be judged by utilizing the ground impedance.
In order that the above-recited objects, features and advantages of the present application will become more readily apparent, a more particular description of embodiments of the application will be rendered by reference to the appended drawings and appended drawings.
Referring to fig. 2, the schematic diagram of a grid-connected system provided by the application is shown.
In this embodiment, the grid-connected system includes one inverter as an example, and it should be understood that the number of inverters is not limited in this embodiment of the present application, and the grid-connected system may include a plurality of inverters, where output ends of the plurality of inverters are all connected to an ac power grid, and input ends of the plurality of inverters are connected to respective corresponding photovoltaic arrays.
The embodiment provides a grid-connected system, including: an inverter 101, a controller (not shown in the figure), and a test circuit; the test circuit comprises a test resistor and a test voltage source which are connected in series; the test circuit is connected between the output end of the inverter 101 and the ground PE;
In fig. 2, a three-phase power grid is taken as an example to illustrate, each of the three phases includes a test resistor, as shown in fig. 2, the corresponding resistors of the three phases are test resistors RA, RB and RC, respectively, where the test resistors of the three phases may be equal, for example ra=rb=rc, and the embodiment of the present application does not specifically limit the resistance of the test resistor, for example, may be 450k ohms.
The test resistor of each phase is grounded through a test voltage source Us, where Us is a dc voltage source, for example, when the voltage of the grid-connected system is 1500V or 1000V or higher, the voltage of Us may be 600V, which is only illustrated in the present embodiment, and it should be understood that the voltage of Us may take other values.
The input end of the inverter 101 is used for connecting to a dc power source, which is exemplified as a photovoltaic array PV1 in the present embodiment, and the dc power source may be from hydropower or wind power, or an energy storage battery cluster, which is not particularly limited in the embodiment of the present application. The output of the inverter 101 is used to connect to an ac grid. It should be understood that, for convenience of grid-connected control, a relay may be further connected between the output end of the inverter 101, i.e., the ac power grid, and the connection state of the inverter 101 and the ac power grid may be controlled by turning on and off the relay.
The controller is used for obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the test voltage source; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, and the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system.
In one possible implementation manner, the controller can control whether the current flowing through the test resistor is available or not by controlling the on-off of the switch, when the test circuit is not connected to the grid-connected system, the ground voltage of the alternating current power grid is collected, for example, the connection and the non-connection of the test circuit to the grid-connected system can be controlled by the switch K, the controller controls the switch K to be closed, and then the test circuit is connected to the grid-connected system; and the controller controls the switch K to be disconnected, so that the test circuit is not connected into the grid-connected system. And when the test circuit is connected into the grid-connected system, collecting the ground voltage of the alternating current power grid. It should be understood that, in addition to controlling the presence or absence of current by controlling the switch K as described above, the presence or absence of current may be controlled by other forms, and the present invention is not limited specifically herein.
The embodiment of the application is not particularly limited to a specific implementation form of the switch K, for example, a mechanical switch may be used to reduce leakage current, because the semiconductor switching device has leakage current. In addition, redundant contacts of an alternating current switch existing in the grid-connected system can be reused, and no additional switch is needed.
When the test circuit is not connected into the grid-connected system, the current flowing on the ground impedance of the grid-connected system can be obtained through the ground voltage and the ground impedance of the alternating current power grid; when the test circuit is connected to the grid-connected system, the current flowing through the ground impedance of the grid-connected system is unchanged, or the ground voltage of the alternating current power grid is divided by the ground impedance, but at the moment, the current flowing through the test circuit branch also exists, namely, the current flowing through the test resistor is the difference between the ground voltage of the alternating current power grid and the voltage of the test voltage source and is positioned in the test resistor; therefore, the impedance to ground of the grid-connected system can be obtained by the above relation. It should be appreciated that this impedance to ground is the overall impedance to ground of the grid-tie system.
The following describes a process of obtaining the impedance of the grid-connected system to the ground according to the technical scheme provided by the embodiment of the application with reference to fig. 2 and 3.
Referring to fig. 3, a schematic diagram of the switch K of fig. 2 is shown when it is closed.
For convenience of description, in this embodiment, R iso represents the impedance to ground of the grid-connected system, that is, the total impedance after coupling the ac impedance and the dc impedance, before the test circuit is connected to the grid-connected system, that is, as shown in fig. 2, when K is disconnected, it is detected that the voltage to ground of the ac grid is the first voltage V0, and then the current I 0 flowing through the impedance to ground R iso can be obtained by the following formula:
When the test circuit is connected to the grid-connected system, the K shown in fig. 3 is closed, and the voltage to ground of the ac power grid is detected to be the second voltage V1, the current flowing through the impedance to ground R iso includes two parts, one part is the current I 0 on the impedance to ground, and the other part is the current flowing through the branch of the test circuit, namely the test resistor, and is named as I iso.
The voltage difference between the test circuit before being connected to the grid-connected system and the test circuit after being connected to the grid-connected system can be used for deducing the expression of the current flowing through the test resistor:
V1-V0＝(I0+Iiso)*Riso-I0*Riso＝Iiso*Riso
In addition, when the test circuit is connected to the grid-connected system, the current flowing through the test resistor can be calculated, wherein Vt, V1 and Rt are all known:
thus, by combining the above expression (1) and expression (2) expressing the total current, the expression of R iso can be found as the following expression (3):
Wherein V0 is the first voltage, V1 is the second voltage, vt is the voltage of the test voltage source, and Rt is the test resistance.
In fig. 2 and 3, a three-phase ac power grid is taken as an example to describe the inverter, which is also a three-phase inverter, where the test resistor Rt may be any one of the three-phase resistors RA, RB and RC, and the current I iso is also a current flowing through one of the three-phase resistors.
It should be understood that, the test circuit in the technical scheme provided by the embodiment of the application only needs to be connected when the impedance of the grid-connected system to the ground is required to be tested, and the test circuit is disconnected from the grid-connected system when the impedance is not required to be detected, so that the grid-connected system is not affected, the normal operation of the grid-connected system is not affected, for example, the inverter is not required to be shut down, and the generated energy is further lost. The grid-connected system can realize the detection of the ground impedance in real time, and the direct current impedance and the alternating current impedance do not need to be detected respectively by the shutdown of the inverter, so that the grid-connected system is simple and easy to operate. According to the technical scheme, the ground impedance can be detected in real time, so that whether the grid-connected system has a ground fault or not is judged in time, and when the ground fault occurs, the grid-connected system alarms in time and is maintained in time, and therefore personal safety and equipment safety are protected.
In fig. 2 and 3, the grid-connected system including one inverter is described as an example, and in the following, the grid-connected system including a plurality of inverters is described as an example. The grid-connected system can comprise a plurality of inverters, the output ends of the inverters are connected with an alternating current power grid, and the input end of each inverter is connected with a corresponding photovoltaic array.
For convenience in fig. 4, the grid-connected system is described by taking an example that includes two inverters.
Referring to fig. 4, a schematic diagram of another grid-connected system provided by the present application is shown.
The embodiment includes a first inverter 101 and a second inverter 102, where an input end of the first inverter 101 is connected to a first photovoltaic array PV1, an input end of the second inverter 102 is connected to a second photovoltaic array PV2, where resistances to ground of a direct current positive bus and a direct current negative bus of the input end of the first inverter 101 are R11 and R12, respectively, and resistances to ground of a direct current positive bus and a direct current negative bus of the input end of the second inverter 102 are R21 and R22, respectively.
Since the output terminals of the first inverter 101 and the second inverter 102 are both connected to the ac power grid, only one set of ac-side ground impedances, i.e., ac-to-ground impedances, are shown in fig. 4. At this time, the two inverters may share a set of test resistors, and the test resistors of each phase are the same, i.e., ra=rb=rc.
It should be understood that, since the output ends of the plurality of inverters are all connected to the ac power grid, the obtaining manner of the impedance to ground of the grid-connected system is the same as that of the grid-connected system shown in fig. 2, and the impedance to ground of the grid-connected system can be obtained by the test circuit added in the embodiment of the present application.
It should be noted that, the grid-connected system described in the above embodiment is implemented in the topology shown in fig. 2-4, provided that the voltage of the test voltage source is larger, and the first voltage is larger than 0. Another implementation is described below, that is, the voltage of the test voltage source is not limited, and may be larger or smaller, for example, 300V or 100V. The grid-connected system described below utilizes a plurality of switches to realize that the test voltage source can be connected into the grid-connected system by a positive voltage source or can be connected into the grid-connected system by a negative voltage source.
Referring to fig. 5, a schematic diagram of another grid-connected system according to an embodiment of the present application is shown.
The test circuit further comprises a first switch K1, a second switch K2, a third switch K3 and a fourth switch K4;
The first switch K1 is connected between the positive electrode of the test voltage source and the first end of the test resistor; the second end of the test resistor is connected with the output end of the inverter; the second switch K2 is connected between the negative electrode of the test voltage source Us and the ground; the third switch K3 is connected between the negative electrode of the test voltage source Us and the first end of the test resistor; the fourth switch K4 is connected between the positive electrode of the test voltage source Us and the ground;
When the first voltage is smaller than 0, the controller is used for controlling the first switch K1 and the second switch K2 to be closed and controlling the third switch K3 and the fourth switch K4 to be opened; the voltage Vt of the test voltage source is a positive value, such as 100V, and is merely illustrative, and the Vt is not specifically limited.
When the first voltage is greater than 0, the controller is used for controlling the first switch K1 and the second switch K2 to be opened and controlling the third switch K3 and the fourth switch K4 to be closed. At this time, the voltage Vt of the test voltage source is negative, for example, -100V. When the voltage source is negative, the voltage source outputs lower voltage, so that the insulation fault detection can be accurately finished.
In the above embodiments, the test circuit includes the test resistor and the test voltage source connected in series, and in addition, the test circuit may also include other devices, such as an inductor connected in series with the test resistor.
In addition, after the ground impedance of the grid-connected system is obtained, the ground impedance can be compared with a preset impedance, and if the ground impedance is smaller than the preset impedance, the grid-connected system is indicated to have the ground fault. At this time, each inverter can judge whether the corresponding branch has a fault to ground, and the inverter can further obtain direct current impedance and alternating current impedance to judge whether the alternating current side has a fault to ground or the direct current side has a fault to ground.
According to the grid-connected system provided by the embodiment of the application, before the test circuit is not connected into the grid-connected system, namely does not participate in work, the ground voltage of the alternating current power grid is measured. And after the test circuit is connected into the grid-connected system to participate in work, measuring the ground voltage of the alternating current power grid. The voltage difference between the voltages before and after the test circuit is connected and not connected with the AC power grid is the voltage of the test voltage source which is obtained by dividing the impedance of the grid-connected system to the ground, so that the impedance of the grid-connected system to the ground is obtained through calculation, and the impedance of the grid-connected system to the ground is understood to be the insulation impedance of the grid-connected system.
It should be noted that, when the grid-connected system provided in the above embodiment detects a ground fault, the normal operation of the inverter is not affected, and the first voltage, the second voltage and the impedance to the ground can be obtained in the grid-connected operation process of the inverter, so that grid-connected power generation is not affected, and the power generation efficiency can be improved.
Method embodiment
Based on the grid-connected system provided by the embodiment, the embodiment of the application also provides a detection method of insulation resistance.
Referring to fig. 5, a flowchart of a method for detecting insulation resistance according to an embodiment of the present application is shown.
Insulation provided by the present embodiment the method of detecting the impedance of a semiconductor device, the method is applied to a grid-connected system, and the grid-connected system comprises the following steps: an inverter, a controller, and a test circuit; the test circuit comprises in series a test resistor and a test voltage source; the test circuit is connected between the output end of the inverter and the ground;
s501: obtaining the ground voltage of an alternating current power grid when the test circuit is not connected to the grid-connected system; a specific circuit diagram of the grid-connected system can be seen in fig. 2.
S502: obtaining the ground voltage of an alternating current power grid when the test circuit is connected into a grid-connected system;
S503: and obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source.
The first voltage and the second voltage can be obtained by sampling, and the voltages of the test resistor and the test voltage source are known, so that the ground impedance of the grid-connected system can be obtained by utilizing the four parameters, the ground impedance is the overall ground impedance of the grid-connected system in normal grid-connected operation, the direct current impedance and the alternating current impedance are not distinguished, and after the ground impedance is obtained, whether the grid-connected system has a ground fault or not can be judged, and therefore, protective measures can be timely taken, and personal safety and equipment safety are protected.
One possible implementation manner, obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the test voltage source specifically includes:
and obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor and the test voltage source.
In addition, the method for obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor and the test voltage source specifically comprises the following steps:
Obtaining the current flowing through the test resistor when the test circuit is connected into the grid-connected system;
and obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor, the test voltage source and the current flowing through the test resistor when the test circuit is connected into the grid-connected system.
The process of obtaining the impedance to ground is described in detail below in conjunction with the equations.
Obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor and the test voltage source, and specifically obtaining the ground impedance through the following formula;
wherein, V0 is the first voltage, V1 is the second voltage, vt is the voltage of the test voltage source, rt is the test resistance.
According to the method provided by the embodiment of the application, before the test circuit is not connected into the grid-connected system, namely does not participate in work, the voltage to ground of the alternating current power grid is measured. And after the test circuit is connected into the grid-connected system to participate in work, measuring the ground voltage of the alternating current power grid. The voltage difference between the voltages before and after the test circuit is connected and not connected with the AC power grid is the voltage of the test voltage source which is obtained by dividing the impedance of the grid-connected system to the ground, so that the impedance of the grid-connected system to the ground is obtained through calculation, and the impedance of the grid-connected system to the ground is understood to be the insulation impedance of the grid-connected system.
From the above description of embodiments, it will be apparent to those skilled in the art that all or part of the steps of the above described example methods may be implemented in software plus necessary general purpose hardware platforms. Based on such understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art in the form of a software product, which may be stored in a storage medium, such as ROM/RAM, a magnetic disk, an optical disk, etc., including several instructions for causing a computer device (which may be a personal computer, a server, or a network communication device such as a media gateway, etc.) to execute the method described in the embodiments or some parts of the embodiments of the present application.
It should be noted that, in the present description, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different manner from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the method disclosed in the embodiment, since it corresponds to the system disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the system part.
It should also be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The previous description of the disclosed embodiments, to enable any person skilled in the art to make or use the present application, will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (15)
1. A grid-tie system, comprising: an inverter, a controller, and a test circuit; the test circuit comprises a test resistor and a test voltage source which are connected in series;
the input end of the inverter is used for being connected with a direct current power supply, and the output end of the inverter is used for being connected with an alternating current power grid;
the test circuit is connected between the output end of the inverter and the ground;
The controller is used for obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source; the impedance to the ground of the grid-connected system is the overall impedance to the ground when the grid-connected system is in grid-connected operation; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, and the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system.
2. The system according to claim 1, wherein the controller is configured to obtain the ground impedance of the grid-tie system based in particular on the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source.
3. The system according to claim 2, wherein the controller is configured to obtain the impedance to ground of the grid-tie system based on the difference between the first voltage and the second voltage, the test resistor, the voltage of the test voltage source, and the current flowing through the test resistor when the test circuit is connected to the grid-tie system.
4. The system according to claim 2, wherein the controller is specifically configured to obtain the impedance to ground by the following formula;
Wherein V0 is the first voltage, V1 is the second voltage, vt is the voltage of the test voltage source, and Rt is the test resistance.
5. A system according to any one of claims 1-3, wherein the test circuit further comprises a test switch in series with the test resistor and the test voltage source; the first voltage is greater than 0;
when the test switch is closed, the test circuit is connected to the grid-connected system; when the test switch is disconnected, the test circuit is not connected to the grid-connected system.
6. A system according to any of claims 1-3, wherein the test circuit further comprises a first switch, a second switch, a third switch, and a fourth switch;
the first switch is connected between the positive electrode of the test voltage source and the first end of the test resistor; the second end of the test resistor is connected with the output end of the inverter; the second switch is connected between the negative electrode of the test voltage source and the ground; the third switch is connected between the negative electrode of the test voltage source and the first end of the test resistor; the fourth switch is connected between the positive electrode of the test voltage source and ground;
when the first voltage is smaller than 0, the controller is used for controlling the first switch and the second switch to be closed and controlling the third switch and the fourth switch to be opened;
and when the first voltage is greater than 0, the controller is used for controlling the first switch and the second switch to be opened and controlling the third switch and the fourth switch to be closed.
7. The system of claim 4, wherein when the grid-tie system comprises three phases, the test resistors comprise three test resistors of equal resistance, each corresponding to one of the test resistors, and Rt is a test resistor of any one of the three phases.
8. A system according to any one of claims 1-3, wherein the controller is further configured to perform a fault alarm if the impedance to ground of the grid-tie system is less than a preset impedance.
9. A system according to any one of claims 1 to 3, wherein the dc power source is derived from a photovoltaic array or a cluster of energy storage cells; the inverter includes a Boost circuit.
10. A system according to any of claims 1-3, wherein the test circuit further comprises an inductance in series with the test resistor.
11. The method for detecting the insulation resistance is characterized by being applied to a grid-connected system, wherein the grid-connected system comprises the following components: an inverter, a controller, and a test circuit; the input end of the inverter is used for being connected with a direct current power supply, and the output end of the inverter is used for being connected with an alternating current power grid; the test circuit comprises a test resistor and a test voltage source which are connected in series; the test circuit is connected between the output end of the inverter and the ground; the method comprises the following steps:
Obtaining the ground voltage of an alternating current power grid when the test circuit is not connected to the grid-connected system;
Obtaining the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system;
Obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source; the impedance to the ground of the grid-connected system is the overall impedance to the ground when the grid-connected system is in grid-connected operation; the first voltage is the ground voltage of the alternating current power grid when the test circuit is not connected to the grid-connected system, and the second voltage is the ground voltage of the alternating current power grid when the test circuit is connected to the grid-connected system.
12. The method according to claim 11, wherein the obtaining the ground impedance of the grid-connected system according to the first voltage, the second voltage, the test resistor and the voltage of the test voltage source comprises:
And obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source.
13. The method according to claim 12, wherein the obtaining the ground impedance of the grid-tie system from the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source comprises:
obtaining the current flowing through the test resistor when the test circuit is connected to the grid-connected system;
and obtaining the ground impedance of the grid-connected system according to the difference between the first voltage and the second voltage, the test resistor, the voltage of the test voltage source and the current flowing through the test resistor when the test circuit is connected into the grid-connected system.
14. The method according to claim 12, wherein the obtaining the ground impedance of the grid-tie system from the difference between the first voltage and the second voltage and the voltages of the test resistor and the test voltage source is performed by;
Wherein V0 is the first voltage, V1 is the second voltage, vt is the voltage of the test voltage source, and Rt is the test resistance.
15. The method of any of claims 11-14, wherein obtaining the first voltage, the second voltage, and the impedance to ground are all obtained during grid-tie operation of the inverter.
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| US20230400489A1 (en) * | 2022-06-08 | 2023-12-14 | Sungrow Power Supply Co., Ltd. | Inverter and method for detecting insulation impedance of inverter |
| CN114720771B (en) * | 2022-06-08 | 2022-11-15 | 阳光电源股份有限公司 | Inverter and alternating current insulation impedance detection method thereof |
| CN115327234A (en) * | 2022-10-17 | 2022-11-11 | 阳光电源股份有限公司 | Alternating current-direct current ground insulation impedance monitoring device and method of inverter |
| CN115356540A (en) * | 2022-10-17 | 2022-11-18 | 阳光电源股份有限公司 | Alternating current-direct current ground insulation impedance monitoring device of inverter and self-checking method thereof |
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