CN114039544B - Photovoltaic inverter, insulation resistance detection method and photovoltaic power generation system - Google Patents
Photovoltaic inverter, insulation resistance detection method and photovoltaic power generation system Download PDFInfo
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- CN114039544B CN114039544B CN202111306955.6A CN202111306955A CN114039544B CN 114039544 B CN114039544 B CN 114039544B CN 202111306955 A CN202111306955 A CN 202111306955A CN 114039544 B CN114039544 B CN 114039544B
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- 238000009413 insulation Methods 0.000 title claims abstract description 126
- 238000001514 detection method Methods 0.000 title claims abstract description 83
- 238000010248 power generation Methods 0.000 title claims abstract description 41
- 238000000034 method Methods 0.000 claims description 34
- 238000005286 illumination Methods 0.000 description 19
- 239000003990 capacitor Substances 0.000 description 15
- 238000010586 diagram Methods 0.000 description 13
- 238000006243 chemical reaction Methods 0.000 description 8
- 238000007599 discharging Methods 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 3
- 239000000428 dust Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000005669 field effect Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 150000004706 metal oxides Chemical class 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 229910010271 silicon carbide Inorganic materials 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- -1 Silicon Carbide Metal Oxide Chemical class 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
- H02S40/30—Electrical components
- H02S40/32—Electrical components comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
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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
-
- 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
-
- 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
Abstract
A photovoltaic inverter, a detection method of insulation resistance and a photovoltaic power generation system relate to the technical field of photovoltaic power generation. The photovoltaic inverter includes a rectifier circuit, an insulation resistance detection circuit, and a controller. The first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, and the controllable switch is used for adjusting the size of the resistor connected into the insulation impedance detection circuit. The input end of the rectifying circuit is connected with an alternating current power grid, and the output end of the rectifying circuit is connected with a direct current bus. When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controller determines that the time when the voltage to the ground of the direct current bus reaches a stable state is a first time interval after the working state of the controllable switch is switched; and determining the ground insulation impedance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval. The scheme improves the accuracy of detecting the ground insulation resistance.
Description
Technical Field
The application relates to the technical field of photovoltaic power generation, in particular to a photovoltaic inverter, an insulation resistance detection method and a photovoltaic power generation system.
Background
Photovoltaic power generation is a technology for converting light energy into electric energy by utilizing the photovoltaic effect of a semiconductor interface, and has been rapidly developed. The photovoltaic power generation system generally comprises a photovoltaic module and a photovoltaic inverter, wherein the photovoltaic module is used for converting the light energy into direct current, and the photovoltaic inverter is used for converting the direct current transmitted by the photovoltaic module into alternating current and then outputting the alternating current.
The direct current input end of the photovoltaic inverter is connected with a direct current bus, and the direct current bus comprises a positive direct current bus and a negative direct current bus. The insulation resistance to ground of the positive and negative DC buses, namely the insulation resistance to ground of the DC end of the photovoltaic inverter. Because photovoltaic module and cable etc. are normally placed in the open air, receive dust, sleet and external force friction etc. influence, can lead to the direct current end of photovoltaic dc-to-ground insulation resistance of photovoltaic dc-to-ac converter to change, have influenced photovoltaic power generation system's safe operation, consequently before photovoltaic dc-to-ac converter begins work, need detect photovoltaic dc-to-ground insulation resistance of photovoltaic dc-to-ac converter to protect photovoltaic power generation system.
At present, when detecting the insulation resistance to the ground of the direct current end of the photovoltaic inverter, a bridge method is generally adopted, as shown in fig. 1, an insulation resistance detection circuit 201 is arranged between the positive direct current bus, the negative direct current bus and the ground, the insulation resistance detection circuit 201 comprises a resistor network and a controllable switch, the resistor connected in the resistor network is changed by switching the working state of the controllable switch, and the insulation resistance to the ground of the positive direct current bus and the negative direct current bus is determined according to the resistance value of the connected resistor and the voltages to the ground of the positive direct current bus and the negative direct current bus. However, as shown in C1 and C2 in fig. 1, the photovoltaic modules included in the photovoltaic array 01 have distributed capacitances to the ground, as the number of the photovoltaic modules increases along with the increase of the power level of the photovoltaic inverter 20, the distributed capacitances will become larger and larger, and when the controllable switch in the insulation resistance detection circuit 201 is controlled to be closed or opened at this time, the voltage to the ground of the collected positive and negative dc buses is affected by the discharge of the distributed capacitances, so that the insulation resistance to the ground of the positive and negative dc buses cannot be accurately obtained, which easily causes the error protection or the non-protection of the photovoltaic inverter, and reduces the safety of the photovoltaic power generation system.
Disclosure of Invention
In order to solve the technical problems, the application provides a photovoltaic inverter, an insulation impedance detection method and a photovoltaic power generation system, accuracy in detection of ground insulation impedance is improved, and safety of the photovoltaic power generation system is further improved.
In a first aspect, the present application provides a photovoltaic inverter for converting dc power into ac power, the input of the photovoltaic inverter being connected to a photovoltaic array through a dc bus, the dc bus comprising a positive dc bus and a negative dc bus, the output of the photovoltaic inverter being connected to an ac power grid, the photovoltaic inverter comprising: the device comprises a rectifying circuit, an insulation resistance detection circuit and a controller. The first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, the insulation impedance detection circuit can be a resistor network, and the insulation impedance detection circuit comprises a controllable switch which is used for adjusting the size of a resistor connected into the insulation impedance detection circuit. The input end of the rectifying circuit is used for being connected with an alternating current power grid, and the output end of the rectifying circuit is used for being connected with a direct current bus. When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controller determines that the time when the ground voltage of the direct current bus reaches a stable state after the working state of the controllable switch is switched is a first time interval, and the region time interval represents the influence time of the charge and discharge of the distributed capacitor of the photovoltaic module on voltage measurement. And then the controller determines the ground insulation resistance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval.
In summary, by using the technical scheme of the application, when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the output voltage of the photovoltaic module can be clamped to the output voltage of the rectifying circuit no matter how illumination changes in the detection process, so that the influence of illumination change on the voltage detection accuracy is eliminated. On the other hand, after the working state of the controllable switch is switched, for example, the direct current bus is switched to a closed state from opening or is switched to an open state from closing, namely, when the direct current bus is stable in ground voltage, namely, when the distributed capacitor of the photovoltaic module is charged and discharged, after the first time interval is detected, the distributed capacitor is charged and discharged, the detected ground voltage is a stable true value, then the direct current bus ground voltage obtained through detection at the moment is utilized for calculating the direct current bus ground impedance, the accuracy of the detection of the ground insulation impedance is improved, and the safety of the photovoltaic power generation system is further improved.
In one possible implementation, the controller determines the time period when the voltage to ground of the negative dc bus or the positive dc bus reaches the steady state after the controllable switch is switched from the open state to the closed state when the current open voltage of the photovoltaic array is less than or equal to the output voltage of the rectifying circuit.
When the voltage to the ground of one direct current bus reaches a stable state, the distributed capacitance of the photovoltaic array can be determined to finish charging and discharging.
In one possible implementation, the photovoltaic inverter further comprises a transformer, an input terminal of the transformer is connected to the ac power grid, an output terminal of the transformer is connected to an input terminal of the rectifying circuit, and the transformer is used for boosting an input voltage of the transformer.
Through setting up the transformer, can promote the alternating current that rectifier circuit's input is connected, and then promote rectifier circuit output's voltage to with photovoltaic array's voltage clamp to higher voltage.
In one possible implementation, the output voltage of the rectifying circuit is equal to the maximum open circuit voltage of the photovoltaic array.
At this time, no matter how the illumination intensity changes, the voltage clock at the output end of the photovoltaic array is clamped to the maximum open-circuit voltage, so that the influence of the illumination intensity change on the voltage detection accuracy can be eliminated, and after the voltage is clamped to the maximum open-circuit voltage, the voltage can be directly detected at a first time interval, so that the convenience is improved.
In one possible implementation, the controller is configured to determine, after the controllable switch is turned off for a first time interval, a voltage to ground of the first dc bus as the first voltage; after the controllable switch is controlled to be closed for a first time interval, determining the grounding voltage of the first direct current bus as a second voltage, and determining the grounding insulation resistance of the direct current bus by utilizing the output voltage of the rectifying circuit, the first voltage and the second voltage, wherein the first direct current bus is a positive direct current bus or a negative direct current bus.
It is understood that the controller may also control the controllable switch to open the first time interval and then control the controllable switch to close the first time interval.
In one possible implementation, the output voltage of the rectifying circuit is less than the maximum open circuit voltage of the photovoltaic array.
At this time, the power consumption of the rectifying circuit and the step-up transformer can be properly reduced, so as to reduce the power consumption in the insulation impedance detection process.
In one possible implementation, the controller is specifically configured to determine, after a first time interval when the controllable switch is turned off, a voltage to ground of the first dc bus as the first voltage; after the controllable switch is controlled to be closed for a first time interval, determining the grounding voltage of the first direct current bus as the second voltage, and determining the grounding insulation impedance of the direct current bus by utilizing the output voltage of the rectifying circuit, the first voltage and the second voltage when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, wherein the first direct current bus is a positive direct current bus or a negative direct current bus.
When the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, namely, the direct current bus voltage is always clamped to the output voltage of the rectifying circuit, the influence of illumination intensity change on the direct current bus voltage is negligible.
In one possible implementation, the controller determines the voltage to ground of the first dc bus as the third voltage and determines the voltage between the dc buses as the fifth voltage when the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifying circuit, or when the voltage between the dc buses is greater than the output voltage of the rectifying circuit, after controlling the controllable switch to open for a first time interval. After the controller controls the controllable switch to be closed for a first time interval, determining the voltage to the ground of the first direct current bus as a fourth voltage, and determining the voltage between the direct current buses as a sixth voltage. When the difference value of the fifth voltage and the sixth voltage is in the preset voltage range, the change of the characteristic illumination intensity in the first time interval is small, the influence on the voltage of the direct current bus is small, and at the moment, the controller determines the insulation resistance to the ground of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.
In one possible implementation, the rectifying circuit is a bridge rectifying circuit employing diodes.
The diode bridge rectifier circuit is adopted to avoid common mode interference caused by the high-frequency on-off of the power switch device, so that the accuracy of the calculation of the ground insulation resistance can be improved.
In one possible implementation, the insulation resistance detection circuit includes a first branch, a second branch, and a third branch. The first end of the first branch is connected with the positive direct current bus, the first end of the second branch is connected with the negative direct current bus, and the second end of the first branch and the second end of the second branch are grounded through the third branch. The third branch includes a controllable switch for adjusting the resistance of the third branch.
In a second aspect, the present application provides an insulation resistance detection method applied to a photovoltaic inverter, the method including:
when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, determining that the time for stabilizing the ground voltage of the direct current bus is a first time interval after the working state of the controllable switch is switched;
and determining the ground insulation impedance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval.
In summary, by using the method provided by the application, when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifying circuit no matter how illumination changes in the detection process, so that the influence of illumination change on the voltage detection accuracy is eliminated. On the other hand, after the working state of the controllable switch is switched, for example, the direct current bus is switched to a closed state from opening or is switched to an open state from closing, namely, when the direct current bus is stable in ground voltage, namely, when the distributed capacitor of the photovoltaic module is charged and discharged, after the first time interval is detected, the distributed capacitor is charged and discharged, the detected ground voltage is a stable true value, then the direct current bus ground voltage obtained through detection at the moment is utilized for calculating the direct current bus ground impedance, the accuracy of the detection of the ground insulation impedance is improved, and the safety of the photovoltaic power generation system is further improved.
In one possible implementation manner, when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifying circuit, determining that the voltage to ground of the direct current bus is a first time interval after the working state of the controllable switch is switched, where the time interval is when the voltage to ground reaches a stable state, specifically includes:
when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controllable switch is controlled to be switched from an open state to a closed state, and the time when the voltage to the ground of the negative direct current bus or the positive direct current bus reaches a stable state is determined to be a first time interval.
In one possible implementation manner, determining the ground insulation resistance of the direct current bus by using the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval specifically includes:
after the controllable switch is controlled to be disconnected for a first time interval, determining the grounding voltage of the first direct current bus as a first voltage, wherein the first direct current bus is a positive direct current bus or a negative direct current bus;
after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as a second voltage;
and determining the ground insulation resistance of the direct current bus by using the output voltage, the first voltage and the second voltage of the rectifying circuit.
In one possible implementation manner, determining the ground insulation resistance of the direct current bus by using the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval specifically includes:
after the controllable switch is controlled to be disconnected for a first time interval, determining the grounding voltage of the first direct current bus as a first voltage, wherein the first direct current bus is a positive direct current bus or a negative direct current bus;
after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as a second voltage;
when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, the first voltage and the second voltage are used for determining the insulation resistance to the ground of the direct current buses.
In one possible implementation, the method further includes:
when the current open-circuit voltage of the photovoltaic array is larger than the output voltage of the rectifying circuit or when the voltage between the direct current buses is larger than the output voltage of the rectifying circuit, the controllable switch is controlled to be disconnected for a first time interval, the ground voltage of the first direct current bus is determined to be a third voltage, and the voltage between the direct current buses is determined to be a fifth voltage;
After the controllable switch is controlled to be closed for a first time interval, determining the voltage to the ground of the first direct current bus as a fourth voltage, and determining the voltage between the direct current buses as a sixth voltage;
and when the difference value of the fifth voltage and the sixth voltage is in the preset voltage range, determining the ground insulation resistance of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.
In a third aspect, the present application further provides a photovoltaic power generation system, which includes the photovoltaic inverter provided in the above implementation manner, and further includes a plurality of photovoltaic modules. The photovoltaic modules are used for converting light energy into direct current and transmitting the direct current to the input end of the photovoltaic inverter. The output end of the photovoltaic inverter is the output end of the photovoltaic power generation system. The plurality of photovoltaic modules may be connected in series to form a photovoltaic array, or the plurality of photovoltaic modules may be connected in series to form a plurality of photovoltaic strings, and the plurality of photovoltaic strings are connected in parallel to form the photovoltaic array.
The photovoltaic inverter of the photovoltaic power generation system can detect and obtain the time required by the completion of the charge and discharge of the distributed capacitor, and after the completion of the charge and discharge of the distributed capacitor, the ground insulation resistance of the direct current bus is determined by the detection value of the ground voltage, so that the accuracy in the detection of the ground insulation resistance is improved, and the safety of the photovoltaic power generation system is further improved.
Drawings
FIG. 1 is a schematic diagram of an insulation resistance detection circuit;
FIG. 2 is a schematic diagram of a photovoltaic power generation system;
FIG. 3 is a schematic diagram of another photovoltaic power generation system;
fig. 4 is a schematic diagram of a photovoltaic inverter according to an embodiment of the present disclosure;
fig. 5 is a schematic diagram of another photovoltaic inverter provided in an embodiment of the present application;
fig. 6 is a schematic diagram of an insulation resistance detection circuit according to an embodiment of the present application;
fig. 7 is a flowchart of a method for detecting insulation resistance according to an embodiment of the present application;
FIG. 8 is a flowchart of another method for detecting insulation resistance according to an embodiment of the present disclosure;
FIG. 9 is a flowchart of another method for detecting insulation resistance according to an embodiment of the present disclosure;
fig. 10 is a schematic diagram of a photovoltaic power generation system according to an embodiment of the present application.
Detailed Description
In order to make the person skilled in the art more clearly understand the application scheme, the application scenario of the application scheme is first described below.
Referring to fig. 2, a schematic diagram of a photovoltaic power generation system is shown.
The illustrated photovoltaic power generation system includes a photovoltaic inverter 20 and a plurality of photovoltaic modules 10. The output end of the photovoltaic module 10 is connected with the input end of the photovoltaic inverter 20, and the output end of the photovoltaic inverter 20 is connected with the alternating current power grid 40.
The photovoltaic module 10 is a direct current power supply formed by packaging solar cells in series and parallel.
The plurality of photovoltaic modules 10 can form a photovoltaic group string in a mode of connecting the positive electrode and the negative electrode in series end to end so as to form a photovoltaic array; the plurality of photovoltaic modules 10 may be connected in series to form a plurality of photovoltaic strings, and the photovoltaic strings may be connected in parallel to form a photovoltaic array.
Referring to fig. 3, a schematic diagram of another photovoltaic power generation system is shown.
The illustrated photovoltaic power generation system includes: an ac combiner box 30, a plurality of photovoltaic modules 10, and a plurality of photovoltaic inverters 20.
The dc side of the photovoltaic inverter 20 is connected to one or more photovoltaic modules 10, and in practical application, the dc side of the photovoltaic inverter 20 is generally connected to a plurality of photovoltaic modules 10.
The photovoltaic inverter 20 may include a two-stage power conversion circuit, in which the first stage is a Direct Current (DC) -DC conversion circuit and the second stage is a Direct Current-alternating Current (Alternating Current, AC) conversion circuit, i.e., an inverter circuit.
The ac power output from the plurality of photovoltaic inverters 20 is collected by the ac combiner box 30 and then connected to the ac power grid 904.
For the photovoltaic inverter 20 in each of the above photovoltaic power generation systems, the dc input terminal of the photovoltaic inverter is connected to a dc bus including a positive dc bus and a negative dc bus. The insulation resistance to ground of the positive and negative DC buses, namely the insulation resistance to ground of the DC end of the photovoltaic inverter.
Because photovoltaic module and cable etc. are normally placed in the open air, receive influence such as dust, sleet and external force friction, can lead to the direct current end of photovoltaic inverter to the ground insulation resistance change, have influenced photovoltaic power generation system's safe operation, consequently before photovoltaic inverter begins work, need detect photovoltaic inverter's direct current end to the ground insulation resistance to photovoltaic power generation system protects, and then ensures that photovoltaic inverter can the safety be incorporated into the power networks.
At present, when the insulation resistance to the ground of the direct current end of the photovoltaic inverter is detected, a bridge method is generally adopted, however, along with the improvement of the power level of the photovoltaic inverter 20, the number of the photovoltaic modules 10 is continuously increased, so that the distributed capacitance of the photovoltaic modules 10 is larger and larger, when a controllable switch in the insulation resistance detection circuit 201 is controlled to be closed or opened, the influence of the discharge of the distributed capacitance is caused, the collected insulation resistance to the ground of the positive and negative direct current buses is inaccurate, the insulation resistance to the ground of the positive and negative direct current buses cannot be accurately obtained, the error protection or the non-protection of the photovoltaic inverter is easily caused, and the safety of a photovoltaic power generation system is reduced.
In order to solve the above problems, embodiments of the present application provide a photovoltaic inverter, a method for detecting insulation resistance, and a photovoltaic power generation system. When the current open-circuit voltage of the photovoltaic inverter is smaller than or equal to the output voltage of the rectifying circuit, the controller of the photovoltaic inverter determines that the time for reaching a stable state is a first time interval after the working state of the controllable switch is switched, namely, determines the charging and discharging time of the distributed capacitor when the working state of the switch is switched, and determines the ground insulation impedance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for the first time interval and the ground voltage after the controllable switch is opened for the first time interval, so that the accuracy of the detection of the ground insulation impedance of the positive and negative direct current buses is improved, and the safety of the photovoltaic power generation system is further improved.
In order to make the technical solution more clearly understood by those skilled in the art, the following description will refer to the technical solution in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application.
The words "first," "second," and the like in the description herein are used for descriptive purposes only and are not to be interpreted as indicating or implying a relative importance or implicitly indicating the number of features indicated
In the present application, unless explicitly specified and limited otherwise, the term "coupled" is to be construed broadly, and for example, "coupled" may be either fixedly coupled, detachably coupled, or integrally formed; may be directly connected or indirectly connected through an intermediate medium.
The embodiment of the application provides a photovoltaic inverter, and the output end of the photovoltaic inverter can be connected with a three-phase alternating current power grid or a two-phase alternating current power grid, and in the following figures, the three-phase alternating current power grid is connected with the output end of the photovoltaic inverter for illustration, and when the two-phase alternating current power grid is connected, the principle is similar and will not be repeated.
Referring to fig. 4, a schematic diagram of a photovoltaic inverter according to an embodiment of the present application is shown.
The input end of the illustrated photovoltaic inverter 20 is connected with the photovoltaic array 01 through a direct current bus, and the output end of the photovoltaic inverter 20 is connected with the alternating current power grid 40. The photovoltaic inverter 20 includes: an insulation resistance detection circuit 201, a rectification circuit 202, a controller 203, and an inverter circuit 204.
The inverter circuit 204 may be a two-level inverter circuit or a multi-level inverter circuit, which is not specifically limited in the embodiment of the present application. The inverter circuit 204 is configured to convert dc power into ac power, and the specific implementation and the working principle of the inverter circuit 204 are mature technologies, which are not described herein.
The first point of the insulation resistance detection circuit 201 is connected to a dc line, i.e. to a positive dc BUS (bus+ in the figure) and to a negative dc BUS (BUS-in the figure). The second terminal of the insulation resistance detection circuit 201 is grounded. The insulation resistance detection circuit 201 includes a resistor network and a controllable switch S1. When the operating state of the controllable switch S1 is changed, the resistance connected to the insulation resistance detection circuit 201 can be adjusted, so as to change the detection value of the voltage of the dc bus to the ground.
The controller 203 is capable of controlling the operating state of the controllable switch S1. When the current open-circuit voltage of the photovoltaic array 01 is less than or equal to the output voltage of the rectifying circuit 202, the voltage between the dc buses is clamped to be equal to the output voltage of the rectifying circuit 202, and the controller 203 controls the controllable switch S1 to switch from off to on state at this time, or controls the controllable switch S1 to switch from on to off state, that is, controls the controllable switch S1 to switch to the working state, and then determines that the time when the voltage to ground of the dc buses reaches a stable state is the first time interval. The first time interval is when the distributed capacitance of the photovoltaic array 01 is charged or discharged.
In practical applications, the controller 203 may switch the operating state of the controllable switch S1 multiple times, further obtain multiple first time intervals, and reduce the measurement error by averaging.
After determining the first time interval, the controller 203 controls the controllable switch S1 to close the first time interval, so that the distributed capacitance of the photovoltaic array 01 is charged and discharged completely, and the voltage to ground of a direct current bus is obtained; and then the controllable switch S1 is controlled to be disconnected for a first preset time interval, so that the distributed capacitance of the photovoltaic array 01 is charged and discharged, and the voltage to the ground of the direct current bus is obtained again. The obtained direct current voltages are the real voltage of the direct current bus to the ground, so that the influence of the distributed capacitance of the photovoltaic array on the detection value of the direct current bus to the ground voltage is reduced. The obtained voltage may be a positive dc bus voltage or a negative dc bus voltage, which is not limited in the embodiment of the present application.
In other embodiments, the controller 203 may also control the controllable switch S1 to be opened for a first time interval, and then control the controllable switch S1 to be closed for the first time interval, which is not described herein.
In summary, by using the technical scheme provided by the embodiment of the application, when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifying circuit no matter how the illumination changes in the detection process, so that the influence of the illumination change on the voltage detection accuracy is eliminated. On the other hand, after the working state of the controllable switch is switched, for example, the direct current bus is switched to a closed state from opening or is switched to an open state from closing, namely, when the direct current bus is stable in ground voltage, namely, when the distributed capacitor of the photovoltaic module is charged and discharged, after the first time interval is detected, the distributed capacitor is charged and discharged, the detected ground voltage is a stable true value, then the direct current bus ground voltage obtained through detection at the moment is utilized for calculating the direct current bus ground impedance, the accuracy of the detection of the ground insulation impedance is improved, and the safety of the photovoltaic power generation system is further improved.
The type of controllable switch S1 may be any one or a combination of the following: relays, insulated gate bipolar transistors (Insulated Gate Bipolar Transistor, IGBTs) or metal oxide semiconductor field effect transistors (Metal Oxide Semiconductor Filed Effect Transistor, MOSFETs, hereinafter referred to as MOS transistors), silicon carbide field effect transistors (Silicon Carbide Metal Oxide Semiconductor, siC MOSFETs), and the like, embodiments of the present application are not particularly limited.
The controller 203 may be an application specific integrated circuit (Application Specific Integrated Circuit, ASIC), a programmable logic device (Programmable Logic Device, PLD), a digital signal processor (Digital Signal Processor, DSP), or a combination thereof. The PLD may be a complex programmable logic device (Complex Programmable Logic Device, CPLD), a Field programmable gate array (Field-programmable Gate Array, FPGA), a general-purpose array logic (Generic Array Logic, GAL), or any combination thereof, and embodiments of the present application are not particularly limited.
The following description is made in connection with specific implementations.
Referring to fig. 5, a schematic diagram of another photovoltaic inverter provided in the implementation of the present application is shown.
The embodiment of the present application differs from the embodiment corresponding to fig. 4 in that it further includes: a transformer 205.
The input end of the transformer 205 is connected to an ac power grid, the output end of the transformer 205 is connected to the input end of the rectifying circuit 202, and the transformer 205 is used for boosting to boost the input voltage of the rectifying circuit 202 and further boost the output voltage of the rectifying circuit.
In one possible implementation, the rectifying circuit 202 is a diode full bridge rectifying circuit, i.e. rectifying the alternating current with a diode bridge, and the use of controllable switching devices in the rectifying circuit 202 is avoided. The controllable switch device brings common-mode interference when being switched on or off at high frequency, so that the sampling result of the direct-current bus to the ground voltage can be influenced by a distributed capacitance loop, and the detection error of the direct-current bus to the ground insulation impedance is improved.
The following specifically describes a method of detecting the insulation resistance of the dc bus to ground.
First, an implementation in which the output voltage of the rectifying circuit 202 is equal to the maximum open circuit voltage of the photovoltaic array 01 will be described.
At this time, the output voltage of the photovoltaic array 01 is always clamped to be equal to the output voltage of the rectifying circuit 202 no matter how the illumination intensity changes, so that the influence of the illumination intensity changes on the detection result is eliminated.
At this time, the controller 203 determines that the time when the voltage to ground of the positive dc bus or the negative dc bus reaches the steady state is the first time interval after the controllable switch S1 is switched from open to closed.
The first time interval is stored when the distributed capacitance of the photovoltaic array 01 is charged or discharged, and the influence time caused by the distributed capacitance is determined.
After the controller 203 controls the controllable switch S1 to turn off for a first time interval, it is determined that the voltage to ground of the first dc bus is the first voltage. After the controller 203 controls the controllable switch S1 to close for a first time interval, it determines the voltage to ground of the first dc bus as the second voltage, and determines the insulation resistance to ground of the dc bus by using the output voltage of the rectifying circuit, the first voltage and the second voltage, where the first dc bus is a positive dc bus or the negative dc bus.
The following describes a specific implementation of the insulation resistance detection circuit 201.
Referring to fig. 6, a schematic diagram of an insulation resistance detection circuit according to an embodiment of the present application is shown.
The insulation resistance detection circuit 201 includes a first branch, a second branch, and a third branch. The first end of the first branch is connected with the positive direct current bus, the first end of the second branch is connected with the negative direct current bus, and the second end of the first branch and the second end of the second branch are grounded through the third branch. The third branch includes a controllable switch for adjusting the resistance of the third branch.
For the purpose of illustration, the present application only takes, as an example, the first branch having a resistance R1, the second branch having a resistance R2, and the third branch having a resistance R3, where the controllable switches S1 and R2 are connected in parallel.
The insulation resistance to ground of the positive direct current bus is R+, and the insulation resistance to ground of the negative direct current bus is R-. After the controllable switch S1 is continuously disconnected for a first time interval, R1 is connected into the first branch, R2 is connected into the second branch, R3 is connected into the third branch, and at the moment, the equivalent parallel resistance R4 of R+ meets the following conditions:
R4＝R1+R3+R1*R3/R2 (1)
the equivalent parallel resistance R5 of R-at this time satisfies:
R5＝R2+R3+R2*R3/R1 (2)
at this time, the voltage to ground of the positive dc bus is V1, the voltage to ground of the negative dc bus is V2, and the voltage between the dc buses is Vo, the following formula exists:
V1-V2＝Vo (3)
when the controllable switch S1 is continuously closed for a first time interval, R1 is connected into the first branch, R2 is short-circuited, R3 is connected into the third branch, and at the moment, the equivalent parallel resistance of R+ is changed from R4 to be infinitely large, and the equivalent parallel resistance of R-is changed from R5 to R3. At this time, the voltage to ground of the positive dc bus is V3, the voltage to ground of the negative dc bus is V4, and the voltage between the dc buses is Vo, the following formula exists:
V3-V4＝Vo (5)
the ground insulation resistance R+ of the positive direct current bus and the ground insulation resistance R-of the negative direct current bus can be determined by solving the equation.
The voltage between the dc buses is Vo, that is, the output voltage of the rectifying circuit 202, which is a known value, and the voltage to ground of one dc bus is determined at this time, that is, the voltage to ground of the other dc bus is determined. That is, the first voltage is V1, and the second voltage is V3; alternatively, the first voltage is V2 and the second voltage is V4.
The foregoing is only one possible implementation of the insulation resistance detection circuit 201, and the calculation principle of other implementations of the insulation resistance detection circuit 201 is similar, and will not be repeated here.
It can be appreciated that in practical applications, the output voltage of the rectifying circuit 202 may be set to be slightly smaller than the maximum open-circuit voltage of the photovoltaic array 01, so as to achieve protection of the photovoltaic array 01.
The implementation when the output voltage of the rectifying circuit 202 is less than the maximum open circuit voltage of the photovoltaic array 01 is described below.
When the current open-circuit voltage of the photovoltaic array 01 is less than or equal to the output voltage of the rectifying circuit 202, the voltage between the dc buses is clamped to be equal to the output voltage of the rectifying circuit 202, and the controller 203 controls the controllable switch S1 to switch from off to on state at this time, or controls the controllable switch S1 to switch from on to off state, that is, controls the controllable switch S1 to switch to the working state, and then determines that the time when the voltage to ground of the dc buses reaches a stable state is the first time interval. The first time interval is when the distributed capacitance of the photovoltaic array 01 is charged or discharged.
After the controller 203 stores the first time interval, the controllable switch S1 is controlled to be turned off for the first time interval, and then the voltage to ground of the first dc bus is determined to be the first voltage; after the controllable switch is controlled to be closed for a first time interval, the ground voltage of the first direct current bus is determined to be the second voltage, and when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit 202, the ground insulation impedance of the direct current bus is determined by using the output voltage of the rectifying circuit, the first voltage and the second voltage, and the first direct current bus is a positive direct current bus or a negative direct current bus.
That is, the controller 203 needs to ensure that the voltage between the dc buses is always clamped to be equal to the output voltage of the rectifying circuit 202 during the detection process, so as to eliminate the influence of abrupt illumination intensity variation on the voltage detection. When the voltage between the dc buses satisfies the condition that the voltage is always equal to the output voltage of the rectifying circuit 202, it is characterized that the illumination intensity is not suddenly increased at this time, that is, the output voltage of the photovoltaic array 01 is not suddenly increased to exceed the output voltage of the rectifying circuit 202, and the controller 203 can determine the ground insulation resistance r+ of the positive dc bus and the ground insulation resistance R-of the negative dc bus according to the processes of the formulas (1) to (6) above.
It can be appreciated that when the first voltage is obtained, the operating state of the controllable switch is switched, and the second voltage value is obtained after the first time interval, that is, the above detection method generally requires that the illumination intensity is not suddenly and significantly increased within the time length of the first time interval.
In one possible implementation, when the controller 203 determines that the voltage between the dc buses is always greater than the output voltage of the rectifying circuit 202, the current voltage sampling result is discarded and the above detection process is restarted, so as to cycle until the first voltage and the second voltage satisfying the condition are obtained.
In another possible implementation manner, when it is determined that the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifying circuit, or when the voltage between the dc buses is greater than the output voltage of the rectifying circuit in the above detection process, the sudden change of the illumination intensity may have a greater influence on the voltage detection, and after the controller 203 controls the controllable switch S1 to turn off for a first time interval, determining the voltage to ground of the first dc bus as the third voltage, and determining the voltage between the dc buses as the fifth voltage; and after the controllable switch is controlled to be closed for a first time interval, determining the voltage to the ground of the first direct current bus as a fourth voltage, and determining the voltage between the direct current buses as a sixth voltage.
The controller 203 determines the ground insulation resistance of the dc bus using the third voltage, the fourth voltage, the fifth voltage, and the sixth voltage when the difference between the fifth voltage and the sixth voltage is within the preset voltage range.
It can be understood that the time interval between the fifth voltage and the sixth voltage is the first time interval, and when the difference between the fifth voltage and the sixth voltage is within the preset voltage range, that is, the voltage change of the dc bus is within the preset voltage range within the first time interval, the light intensity is relatively stable in the detection process, and no abrupt change occurs.
Since the voltage between the dc buses is greater than the output voltage of the rectifying circuit 202, it is necessary to collect the voltage between the dc buses, and collect the voltage to ground of one dc bus, so as to determine the voltage to ground of the other dc bus; or respectively collect the voltages to the ground of the two dc buses, and the insulation resistance detection circuit shown in fig. 6 will be further described as an example.
When the controllable switch S1 is continuously turned off for a first time interval, the voltage to ground of the positive dc bus is V1, the voltage to ground of the negative dc bus is V2, and at this time, the voltage between the dc buses, that is, the fifth voltage is Vo1, the following formula exists:
V1-V2＝Vo1 (7)
When the controllable switch S1 is continuously closed for a first time interval, the voltage to ground of the positive dc bus is V3, the voltage to ground of the negative dc bus is V4, and at this time, the voltage between the dc buses, that is, the sixth voltage is Vo2, the following formula exists:
V3-V4＝Vo2 (8)
when the difference between Vo1 and Vo2 is within the preset voltage range, the controller 203 determines that the detected value of the voltage to ground of the dc bus at this time is valid, and further determines the insulation resistance to ground r+ of the positive dc bus and the insulation resistance to ground R-of the negative dc bus.
When the first direct current bus is a positive direct current bus, the third voltage is V1, and the fourth voltage is V3; or when the first direct current bus is a negative direct current bus, the third voltage is V2, and the fourth voltage is V3.
In summary, by using the technical scheme provided by the embodiment of the application, when the bridge method is adopted to detect the insulation impedance of the direct current bus, the influence of the distributed capacitance and illumination intensity change of the photovoltaic array can be obviously reduced, the accuracy of detecting the insulation impedance to the ground is improved, and the safety of a photovoltaic power generation system is further improved.
Based on the photovoltaic inverter provided in the above embodiment, the embodiment of the present application further provides a method for detecting insulation of a dc line of the photovoltaic inverter, which is specifically described below with reference to the accompanying drawings.
Referring to fig. 7, a flowchart of an insulation detection method according to an embodiment of the present application is shown.
For a specific implementation of the photovoltaic inverter, reference may be made to the related description of the above embodiments, which will not be repeated herein, and the method includes the following steps:
s301: when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, determining that the time for reaching stability is a first time interval after the working state of the controllable switch is switched by the ground voltage of the direct current bus.
When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the voltage between the direct current buses is clamped to be equal to the output voltage of the rectifying circuit, at the moment, the controllable switch is controlled to be switched from the off state to the on state, or the controllable switch is controlled to be switched from the on state to the off state, namely the controllable switch is controlled to be switched to the working state, and then the time interval when the voltage to the ground of the direct current buses is stable is determined.
The first time interval is when the distributed capacitance of the photovoltaic array is charged or discharged.
S302: and determining the ground insulation impedance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval.
The controllable switch is controlled to be closed at first time intervals so that the charge and discharge of the distributed capacitor of the photovoltaic array are finished, and the ground voltage of one direct current bus is obtained; and then, the controllable switch is controlled to be disconnected for a first preset time interval, so that the charge and discharge of the distributed capacitance of the photovoltaic array are finished, and the voltage to the ground of the direct current bus is obtained again. The obtained direct current voltages are the real voltage of the direct current bus to the ground, so that the influence of the distributed capacitance of the photovoltaic array on the detection value of the direct current bus to the ground voltage is reduced. The obtained voltage may be a positive dc bus voltage or a negative dc bus voltage, which is not limited in the embodiment of the present application.
In other embodiments, the controllable switch may be controlled to be opened first for a first time interval, and then be closed for a first time interval, which is not described herein.
The following is a description of specific method steps.
Referring to fig. 8, a flowchart of another method for detecting insulation resistance according to an embodiment of the present application is shown.
The implementation mode when the output voltage of the rectifying circuit is equal to the maximum open-circuit voltage of the photovoltaic array is first described below, and the method includes the following steps:
s401: after the controllable switch is controlled to be disconnected for a first time interval, the ground voltage of the first direct current bus is determined to be the first voltage, and the first direct current bus is a positive direct current bus or a negative direct current bus.
S402: and after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as the second voltage.
S403: and determining the ground insulation resistance of the direct current bus by using the output voltage, the first voltage and the second voltage of the rectifying circuit.
Referring to fig. 9, a flowchart of another method for detecting insulation resistance according to an embodiment of the present application is shown.
The following describes an implementation manner when the output voltage of the rectifying circuit is smaller than the maximum open circuit voltage of the photovoltaic array, and the method includes the following steps:
s501: and judging whether the current open-circuit voltage of the photovoltaic array is larger than the output voltage of the rectifying circuit.
If not, S502 is executed, and if yes, S506 is executed.
S502: after the controllable switch is controlled to be disconnected for a first time interval, the ground voltage of the first direct current bus is determined to be the first voltage, and the first direct current bus is a positive direct current bus or a negative direct current bus.
S503: and after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as the second voltage.
S504: and judging whether the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit.
If yes, executing S505; if not, S506 is performed.
S505: and determining the ground insulation resistance of the direct current bus by using the output voltage, the first voltage and the second voltage of the rectifying circuit.
S506: and after the controllable switch is controlled to be disconnected for a first time interval, determining the voltage to the ground of the first direct current bus as a third voltage, and determining the voltage between the direct current buses as a fifth voltage.
S507: and after the controllable switch is controlled to be closed for a first time interval, determining the voltage to the ground of the first direct current bus as a fourth voltage, and determining the voltage between the direct current buses as a sixth voltage.
S508: it is determined whether a difference between the fifth voltage and the sixth voltage is within a preset voltage range.
If yes, executing S509; if not, S506 is performed.
S509: and determining the ground insulation resistance of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.
The above steps are merely for convenience of description, and do not limit the technical solution of the present application, and those skilled in the art may also make appropriate adjustments to the above steps when implementing the present application. For example, the order of S401 and S402 may be exchanged, i.e. the controllable switch is controlled to be closed first and then to be opened.
In summary, by using the method provided by the embodiment of the present application, when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifying circuit, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifying circuit no matter how the illumination changes in the detection process, so that the influence of the illumination change on the voltage detection accuracy is eliminated.
On the other hand, after the working state of the controllable switch is switched, for example, the direct current bus is switched to a closed state from opening or is switched to an open state from closing, namely, when the direct current bus is stable in ground voltage, namely, when the distributed capacitor of the photovoltaic module is charged and discharged, after the first time interval is detected, the distributed capacitor is charged and discharged, the detected ground voltage is a stable true value, then the direct current bus ground voltage obtained through detection at the moment is utilized for calculating the direct current bus ground impedance, the accuracy of the detection of the ground insulation impedance is improved, and the safety of the photovoltaic power generation system is further improved.
Based on the photovoltaic inverter provided in the above embodiment, the embodiment of the application also provides a photovoltaic power generation system, which is specifically described below with reference to the accompanying drawings.
Referring to fig. 10, a schematic diagram of a photovoltaic power generation system according to an embodiment of the present application is shown.
The illustrated photovoltaic power generation system 100 includes a photovoltaic array 01 and a photovoltaic inverter 20.
Wherein the photovoltaic array 01 comprises a plurality of photovoltaic modules 10, in some embodiments, the plurality of photovoltaic modules 10 may be connected in series to form the photovoltaic module 10; in other embodiments, the plurality of photovoltaic modules 10 may be connected in series to form a plurality of photovoltaic strings, and the plurality of photovoltaic strings may be connected in parallel to form the photovoltaic array 01.
The photovoltaic inverter 20 may include a single stage power conversion circuit, i.e., only a DC-AC conversion circuit; the photovoltaic inverter 20 may further include a two-stage power conversion circuit, the first stage being a DC-DC conversion circuit and the second stage being a DC-AC conversion circuit, i.e., an inverter circuit, which is not particularly limited in this embodiment of the present application.
With respect to the specific implementation and the working principle of the photovoltaic inverter 20, reference may be made to the related descriptions in the above embodiments, which are not repeated herein.
In summary, the controller of the photovoltaic inverter 20 provided in the embodiment of the present application can detect and obtain the time required for completing the charging and discharging of the distributed capacitor, and when the charging and discharging of the distributed capacitor are completed, the detection value of the ground voltage is used to determine the ground insulation impedance of the dc bus, so that the accuracy of the ground insulation impedance detection is improved, and the safety of the photovoltaic power generation system is further improved.
It should be understood that in this application, "at least one" means one or more, and "a plurality" means two or more. "and/or" for describing the association relationship of the association object, the representation may have three relationships, for example, "a and/or B" may represent: only a, only B and both a and B are present, wherein a, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, at least one (one) of a, b or c may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. The apparatus embodiments described above are merely illustrative, wherein the units and modules illustrated as separate components may or may not be physically separate. In addition, some or all of the units and modules can be selected according to actual needs to achieve the purpose of the embodiment scheme. Those of ordinary skill in the art will understand and implement the present invention without undue burden.
The foregoing is merely exemplary of the application and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the application and are intended to be comprehended within the scope of the application.
Claims (16)
1. The utility model provides a photovoltaic inverter, its characterized in that, photovoltaic array is connected through direct current busbar to photovoltaic inverter's input, direct current busbar includes positive direct current busbar and negative direct current busbar, photovoltaic inverter's output is connected the AC power grid, photovoltaic inverter includes: a rectifier circuit, an insulation resistance detection circuit and a controller;
The first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, the insulation impedance detection circuit comprises a controllable switch, and the controllable switch is used for adjusting the size of a resistor connected into the insulation impedance detection circuit;
the input end of the rectifying circuit is used for being connected with the alternating current power grid, and the output end of the rectifying circuit is used for being connected with the direct current bus;
the controller is used for determining that the time when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit is a first time interval after the working state of the controllable switch is switched and the ground voltage of the direct current bus is stable; and determining the ground insulation resistance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval.
2. The photovoltaic inverter of claim 1 wherein the controller is configured to determine the first time interval when the voltage to ground of the negative dc bus or the positive dc bus reaches a steady state after controlling the controllable switch to switch from an open to a closed state when the current open voltage of the photovoltaic array is less than or equal to the output voltage of the rectifying circuit.
3. The photovoltaic inverter of claim 1 further comprising a transformer;
the input end of the transformer is connected with the alternating current power grid, and the output end of the transformer is connected with the input end of the rectifying circuit;
the transformer is used for boosting.
4. A photovoltaic inverter according to claim 3, wherein the output voltage of the rectifying circuit is equal to the maximum open circuit voltage of the photovoltaic array.
5. The photovoltaic inverter of claim 4, wherein the controller is configured to determine a voltage to ground of a first dc bus as a first voltage after the controllable switch is turned off for the first time interval; and after the controllable switch is controlled to be closed for the first time interval, determining the grounding voltage of the first direct current bus as a second voltage, and determining the grounding insulation impedance of the direct current bus by utilizing the output voltage of the rectifying circuit, the first voltage and the second voltage, wherein the first direct current bus is the positive direct current bus or the negative direct current bus.
6. A photovoltaic inverter according to any one of claims 1 to 3, wherein the output voltage of the rectifying circuit is less than the maximum open circuit voltage of the photovoltaic array.
7. The photovoltaic inverter of claim 6, wherein the controller is configured to determine a voltage to ground of a first dc bus as a first voltage after the controllable switch is turned off for the first time interval; and after the controllable switch is controlled to be closed for the first time interval, determining the grounding voltage of the first direct current bus as a second voltage, and determining the grounding insulation impedance of the direct current bus by utilizing the output voltage of the rectifying circuit, the first voltage and the second voltage when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, wherein the first direct current bus is the positive direct current bus or the negative direct current bus.
8. The photovoltaic inverter of claim 7, wherein the controller is further configured to determine that a voltage to ground of a first dc bus is a third voltage and determine that a voltage between the dc buses is a fifth voltage when a current open-circuit voltage of the photovoltaic array is greater than an output voltage of the rectifying circuit or when a voltage between the dc buses is greater than the output voltage of the rectifying circuit after the controllable switch is controlled to open for the first time interval; after the controllable switch is controlled to be closed for the first time interval, determining the voltage to the ground of the first direct current bus as a fourth voltage, and determining the voltage between the direct current buses as a sixth voltage; and when the difference value of the fifth voltage and the sixth voltage is in a preset voltage range, determining the ground insulation resistance of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.
9. The photovoltaic inverter of claim 1 wherein the rectifying circuit is a bridge rectifying circuit employing diodes.
10. The photovoltaic inverter of claim 1 wherein the insulation resistance detection circuit comprises a first leg, a second leg, and a third leg;
the first end of the first branch is connected with the positive direct current bus, the first end of the second branch is connected with the negative direct current bus, and the second end of the first branch and the second end of the second branch are grounded through the third branch;
the third branch includes a controllable switch for adjusting a resistance of the third branch.
11. The utility model provides a detection method of insulation impedance, characterized by is applied to photovoltaic inverter, photovoltaic inverter's input passes through the direct current busbar and connects photovoltaic array, the direct current busbar includes positive direct current busbar and negative direct current busbar, photovoltaic inverter's output is connected the alternating current electric wire netting, photovoltaic inverter includes rectifier circuit and insulation impedance detection circuit, insulation impedance detection circuit's first end is connected the direct current busbar, insulation impedance detection circuit's second end ground connection, insulation impedance detection circuit includes controllable switch, controllable switch is used for adjusting the size of the resistance that inserts in the insulation impedance detection circuit, rectifier circuit's input is used for connecting the alternating current electric wire netting, rectifier circuit's output is used for connecting the direct current busbar, the method includes:
When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, determining that the time for reaching stability is a first time interval after the working state of the controllable switch of the ground voltage of the direct current bus is switched;
and determining the ground insulation resistance of the direct current bus by utilizing the ground voltage of any direct current bus after the controllable switch is closed for a first time interval and the ground voltage after the controllable switch is opened for the first time interval.
12. The method for detecting insulation resistance according to claim 11, wherein when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifying circuit, determining that the time for reaching the steady state after the working state of the controllable switch is switched is a first time interval, specifically including:
when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controllable switch is controlled to be switched from an open state to a closed state, and the time when the voltage to the ground of the negative direct current bus or the positive direct current bus reaches a stable state is determined to be the first time interval.
13. The method for detecting insulation resistance according to claim 11 or 12, wherein determining the insulation resistance to ground of the dc bus by using the voltage to ground of any dc bus after the controllable switch is closed for a first time interval and the voltage to ground after the controllable switch is opened for the first time interval, specifically comprises:
after the controllable switch is controlled to be disconnected at the first time interval, determining the voltage to ground of a first direct current bus as a first voltage, wherein the first direct current bus is the positive direct current bus or the negative direct current bus;
after the controllable switch is controlled to be closed for the first time interval, determining the voltage to ground of the first direct current bus as a second voltage;
and determining the ground insulation resistance of the direct current bus by using the output voltage of the rectifying circuit, the first voltage and the second voltage.
14. The method for detecting insulation resistance according to claim 11 or 12, wherein determining the insulation resistance to ground of the dc bus by using the voltage to ground of any dc bus after the controllable switch is closed for a first time interval and the voltage to ground after the controllable switch is opened for the first time interval, specifically comprises:
After the controllable switch is controlled to be disconnected at the first time interval, determining the voltage to ground of a first direct current bus as a first voltage, wherein the first direct current bus is the positive direct current bus or the negative direct current bus;
after the controllable switch is controlled to be closed for the first time interval, determining the voltage to ground of the first direct current bus as a second voltage;
when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, the first voltage and the second voltage are utilized to determine the insulation resistance to ground of the direct current buses.
15. The method of detecting insulation resistance according to claim 14, further comprising:
when the current open-circuit voltage of the photovoltaic array is larger than the output voltage of the rectifying circuit or when the voltage between the direct current buses is larger than the output voltage of the rectifying circuit, after the controllable switch is controlled to be disconnected for the first time interval, determining the grounding voltage of the first direct current bus as a third voltage, and determining the voltage between the direct current buses as a fifth voltage;
after the controllable switch is controlled to be closed for the first time interval, determining the voltage to the ground of the first direct current bus as a fourth voltage, and determining the voltage between the direct current buses as a sixth voltage;
And when the difference value of the fifth voltage and the sixth voltage is in a preset voltage range, determining the ground insulation resistance of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.
16. A photovoltaic power generation system comprising the photovoltaic inverter of any one of claims 1 to 10, further comprising a plurality of photovoltaic modules;
the photovoltaic modules are used for converting light energy into direct current and transmitting the direct current to the input end of the photovoltaic inverter;
the output end of the photovoltaic inverter is the output end of the photovoltaic power generation system.
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| CN103105537A (en) * | 2012-12-26 | 2013-05-15 | 深圳创动科技有限公司 | Battery panel ground insulation impedance detection circuit and method |
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| WO2021180747A1 (en) * | 2020-03-11 | 2021-09-16 | Fronius International Gmbh | Method and photovoltaic inverter for determining the insulation resistance of a photovoltaic system to ground |
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| WO2021180747A1 (en) * | 2020-03-11 | 2021-09-16 | Fronius International Gmbh | Method and photovoltaic inverter for determining the insulation resistance of a photovoltaic system to ground |
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