CN116131341A - Photovoltaic system, insulation resistance detection method and inversion system - Google Patents

Photovoltaic system, insulation resistance detection method and inversion system Download PDF

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Publication number
CN116131341A
CN116131341A CN202310141573.5A CN202310141573A CN116131341A CN 116131341 A CN116131341 A CN 116131341A CN 202310141573 A CN202310141573 A CN 202310141573A CN 116131341 A CN116131341 A CN 116131341A
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Prior art keywords
voltage
neutral point
direct current
current source
ground
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Inventor
钱远东
梁城
李贺
汪晶晶
钱永恒
潘年安
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Sungrow Power Supply Co Ltd
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Sungrow Power Supply Co Ltd
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Priority to CN202310141573.5A priority Critical patent/CN116131341A/en
Publication of CN116131341A publication Critical patent/CN116131341A/en
Priority to US18/331,079 priority patent/US20230400489A1/en
Priority to EP23178194.9A priority patent/EP4293375A1/en
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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
    • 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
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
    • 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
    • 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
    • H02J2300/28—The renewable source being wind energy

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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)
  • Measurement Of Resistance Or Impedance (AREA)

Abstract

The application discloses photovoltaic system, insulation impedance's detection method and contravariant system, photovoltaic system includes: an inverter, a direct current source and a controller; the input end of the inverter is used for connecting the photovoltaic string; the direct current source is connected in series with the resistor and then is connected between the virtual neutral point of the inverter and the ground; a controller for changing the output voltage of the direct current source to change the voltage of the virtual neutral point; and obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change before and after the change. By adding a direct current source between the virtual neutral point of the inverter and the ground and outputting different voltages through the direct current source to disturb the voltage of the virtual neutral point to the ground, the insulation impedance of the system is obtained according to the different voltages output before and after the direct current source and the voltage before and after the virtual neutral point is disturbed. And the insulation impedance can be obtained in the grid-connected operation process of the inverter, and is the coupling impedance of the alternating current side and the direct current side.

Description

Photovoltaic system, insulation resistance detection method and inversion system
Technical Field
The application relates to the technical field of photovoltaic power generation, in particular to a photovoltaic system, an insulation impedance detection method and an inversion system.
Background
The impedance to the ground of the photovoltaic system comprises the impedance to the ground of the direct current side and the impedance to the ground of the alternating current side, and before grid-connected operation of the inverter, the impedance to the ground of the direct current side and the impedance to the ground of the alternating current side are separated, so that the impedance to the ground of the direct current side and the impedance to the ground of the alternating current side can be detected respectively.
However, when the inverter is operated in a grid-connected mode, the direct current side impedance to the ground and the alternating current side impedance to the ground are coupled together, and the method of respectively obtaining the direct current side impedance to the ground and the alternating current side impedance to the ground in the prior art is not applicable, so that the insulation impedance to the ground of the photovoltaic system cannot be accurately detected.
Disclosure of Invention
In view of the above, the present application provides a photovoltaic system, an insulation resistance detection method, and an inverter system, which can accurately detect insulation resistance of the photovoltaic system when the inverter is operated in a grid-connected mode.
The photovoltaic system that this application provided includes: an inverter, a direct current source and a controller;
the input end of the inverter is used for connecting the photovoltaic string;
the direct current source is connected in series with the resistor and then is connected between the virtual neutral point of the inverter and the ground;
a controller for changing the output voltage of the direct current source to change the voltage of the virtual neutral point; and obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change before and after the change.
Preferably, the controller is specifically configured to control the direct current source to output the first voltage and the second voltage sequentially; when the direct current source outputs a first voltage, the virtual neutral point voltage to the ground is the first neutral point voltage; when the direct current source outputs a second voltage, the virtual neutral point voltage to the ground is the second neutral point voltage;
and the controller is used for obtaining the insulation resistance of the photovoltaic system according to the resistance value of the resistor, the first voltage, the first neutral point voltage, the second voltage and the second neutral point voltage.
Preferably, the controller is specifically configured to change the output voltage of the direct current source until the virtual neutral point voltage is stable to the ground when the second neutral point voltage fluctuates, so as to obtain a stable second neutral point voltage.
Preferably, the controller is specifically configured to change the output voltage of the direct current source to the first voltage or adjust the output voltage to an opposite value of the second voltage when the second neutral point voltage fluctuates, until the virtual neutral point voltage is stable to the ground, and obtain a stable second neutral point voltage.
Preferably, the method further comprises: a first switch in series with the DC source;
the controller is specifically configured to control the first switch to be turned off, so that the first voltage is 0.
Preferably, the direct current source comprises: the device comprises a constant voltage source, a first diode, a second switch, a third switch, a fourth switch and a fifth switch;
the positive electrode of the constant voltage source is connected with the first end of the direct current source through the second switch and the first diode which are connected in series, and the first end of the direct current source is connected with the virtual neutral point through the first switch and the resistor which are connected in series; the negative electrode of the constant voltage source is grounded through a fourth switch; a fifth switch is connected between the negative electrode of the constant voltage source and the first end of the direct current source, and the positive electrode of the constant voltage source is grounded through a second diode and a third switch which are connected in series;
and the controller is used for controlling the second switch and the fourth switch to be closed, and the third switch and the fifth switch to be opened so that the constant voltage source outputs positive voltage, and controlling the second switch and the fourth switch to be opened, and the third switch and the fifth switch to be closed so that the constant voltage source outputs negative voltage.
The application also provides a method for detecting insulation impedance in a photovoltaic system, wherein the photovoltaic system comprises a direct current source and an inverter; the direct current source is connected in series with the resistor and then is connected between the virtual neutral point of the inverter and the ground;
the method comprises the following steps:
changing the output voltage of the direct current source to change the voltage of the virtual neutral point;
obtaining output voltages before and after the direct current source is changed, and respectively corresponding virtual neutral point voltages to ground before and after the direct current source is changed;
and obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change before and after the change.
Preferably, obtaining the output voltage before and after the change of the direct current source and the virtual neutral point voltage to ground corresponding to the change before and after the change specifically includes:
controlling a direct current source to output a first voltage and a second voltage respectively; when the direct current source outputs a first voltage, obtaining a virtual neutral point voltage to the ground as a first neutral point voltage; when the direct current source outputs the second voltage, the virtual neutral point voltage to the ground is obtained as the second neutral point voltage;
obtaining insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change of the direct current source, wherein the method specifically comprises the following steps:
and obtaining the insulation resistance of the photovoltaic system according to the resistance value of the resistor, the first voltage, the first neutral point voltage, the second voltage and the second neutral point voltage.
Preferably, when the direct current source outputs the second voltage, the second neutral point voltage of the power grid to the ground is obtained, which specifically includes:
when the second phase voltage fluctuates, the output voltage of the direct current source is changed until the virtual neutral point voltage is stable to the ground, and the stable second neutral point voltage is obtained.
Preferably, the method comprises the steps of changing the output voltage of the direct current source until the virtual neutral point is stable to the ground voltage, and obtaining a stable second phase voltage, specifically comprising:
and changing the output voltage of the direct current source into the first voltage or adjusting the output voltage into the opposite value of the second voltage until the virtual neutral point voltage is stable to the ground, and obtaining the stable second neutral point voltage.
Preferably, the direct current source outputs a first voltage, specifically including:
and controlling the direct current source to disconnect from the virtual neutral point so that the first voltage is 0.
Preferably, the second neutral point voltage fluctuates, specifically including:
and acquiring the second neutral point voltage for a plurality of times in a preset time period, obtaining an average value of the second neutral point voltage, and judging the fluctuation of the second neutral point voltage when the average value of the second neutral point voltage exceeds a set value.
The application also provides an inversion system, comprising: an inverter, a direct current source and a controller;
the input end of the inversion system is used for connecting a direct current power supply;
the direct current source is connected in series with the resistor and then is connected between the virtual neutral point of the inverter and the ground;
a controller for changing the output voltage of the direct current source to change the voltage of the virtual neutral point; and obtaining the insulation impedance of the inverter system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the output voltage before and after the change.
From this, this application has following beneficial effect:
according to the photovoltaic system, the direct current source is added between the virtual neutral point of the inverter and the ground, and different voltages are output through the direct current source to disturb the voltage of the virtual neutral point to the ground, so that the insulation impedance of the system is obtained according to the different voltages output before and after the direct current source and the voltage before and after the virtual neutral point is disturbed. And the insulation impedance can be obtained in the grid-connected operation process of the inverter, and is the coupling impedance of the alternating current side and the direct current side.
Drawings
Fig. 1 is a schematic diagram of a photovoltaic system according to an embodiment of the present disclosure;
FIG. 2 is an equivalent circuit diagram corresponding to FIG. 1;
FIG. 3 is a schematic diagram of another photovoltaic system according to an embodiment of the present disclosure;
fig. 4 is a schematic diagram of an inverter system according to an embodiment of the present disclosure;
fig. 5 is a flowchart of a method for detecting insulation resistance in a photovoltaic system according to an embodiment of the present application;
fig. 6 is a flowchart of another method for detecting insulation resistance in a photovoltaic system according to an embodiment of the present application.
Detailed Description
In order to make the above objects, features and advantages of the present application more comprehensible, embodiments accompanied with figures and detailed description are described in further detail below.
The embodiment of the application does not specifically limit whether the input end of the inverter is connected with the photovoltaic string or other direct current power sources, for example, the input end of the inverter can be from wind power or energy storage batteries. As long as the system includes an inverter and the inverter is in operation, the insulation impedance of the system can be detected, it being understood that the insulation impedance of the system is the total impedance of the dc and ac coupling together when the inverter is in operation.
The embodiment of the application is not particularly limited to the single-phase inverter or the three-phase inverter, and the insulation impedance detection mode provided by the embodiment of the application is applicable.
The application of the inverter to the photovoltaic system will be described first, namely, the photovoltaic system will be described first.
Referring to fig. 1, a schematic diagram of a photovoltaic system according to an embodiment of the present application is shown.
The photovoltaic system provided in this embodiment includes: inverter 100, dc source 200, and controller 300;
the input end of the inverter 100 is used for connecting a photovoltaic group string PV;
the dc source 200 is connected in series with the resistor R and then connected between the virtual neutral point N of the inverter 100 and ground;
the direct current source 200 may include a constant voltage source DC, wherein the positive electrode of the constant voltage source DC may be connected to the virtual neutral point N through a resistor R, and the negative electrode of the constant voltage source DC may also be connected to the virtual neutral point N through the resistor R.
A controller 300 for changing the output voltage of the direct current source 200 to change the virtual neutral point to ground voltage; and the insulation impedance of the photovoltaic system is obtained according to the resistance value of the resistor R, the output voltage before and after the change of the direct current source 200 and the virtual neutral point to ground voltage corresponding to the change before and after the change.
And the output end of the inverter is connected with a power grid to perform grid-connected power generation. It should be appreciated that the virtual neutral point to ground voltage is equal to the grid's relative ground voltage.
For convenience of description, the controller is specifically configured to control the direct current sources to sequentially output the first voltages V 1 And a second voltage V 2 The method comprises the steps of carrying out a first treatment on the surface of the The DC source outputs a first voltage V 1 When the virtual neutral point voltage to the ground is the first neutral point voltage V N1 The method comprises the steps of carrying out a first treatment on the surface of the The DC source outputs a second voltage V 2 When the virtual neutral point voltage to the ground is the second neutral point voltage V N2 ；
A controller for controlling the voltage according to the resistance R of the resistor 1 First neutral point voltage V N1 Second voltage V 2 And a second neutral point voltage V N2 The insulation resistance of the photovoltaic system is obtained.
Specific derivation processes are described below with reference to the drawings.
Referring to fig. 2, the equivalent circuit diagram corresponding to fig. 1 is shown.
As can be seen from the equivalent circuit diagram of fig. 2, DC is the constant voltage source described above in this application, R 0 Resistance of known resistance, R f The insulation resistance, inductance L, capacitance C, resistance R, and voltage source of the system are shown on the right side of the dotted line as the influence on the left circuit loop when the inverter is connected, and the influence on the ac side from the dc side when the inverter is connected is uniformly shown by current I.
When the constant voltage source outputs the first voltage V 1 When the virtual neutral point voltage to the ground is the first neutral point voltage V N1 The method can obtain:
Figure BDA0004088092540000051
when the constant voltage source outputs the second voltage V 2 When the virtual neutral point voltage to the ground is the second neutral point voltage V N2 The method can obtain:
Figure BDA0004088092540000052
when the impedance of the inverter to the ground is unchanged, the fluctuation of the circuit I is assumed to be ignored
I 1 ＝I 2
By the simultaneous equation, the current I is eliminated, and the following can be obtained:
Figure BDA0004088092540000053
thus, the system-to-ground impedance at the time of inverter grid connection can be represented by the above known parameters.
In addition, to ensure greater detection accuracy, the first voltage may be set to 0, and specific implementation is described below.
When V is 1 When the voltage is 0 (namely, the constant voltage source is disconnected with the virtual neutral point of the inverter), the voltage is a special working condition at the moment, and the voltage has high practical significance.
V N1 ＝R f *I 1
When the output voltage is V 2 When the virtual neutral point voltage to the ground is the second neutral point voltage V N2 The method can obtain:
V N2 ＝R f *(I 2 +I R )
at this time
Figure BDA0004088092540000061
At the same time
I 1 ＝I 2
Simultaneous availability:
Figure BDA0004088092540000062
according to the embodiment of the application, the first voltage is set to be 0, the change of the virtual neutral point to ground voltage of the inverter can be determined, fault location and other processing are facilitated, meanwhile, high detection precision can be guaranteed when a direct current source is not required to output high power, and insulation impedance detection is more accurate.
According to the photovoltaic system provided by the embodiment of the application, the direct current source is added between the virtual neutral point of the inverter and the ground, and different voltages are output through the direct current source to disturb the voltage of the virtual neutral point to the ground, so that the insulation impedance of the system is obtained according to the different voltages output before and after the direct current source and the voltage before and after the virtual neutral point is disturbed. And the insulation impedance can be obtained in the grid-connected operation process of the inverter, and is the coupling impedance of the alternating current side and the direct current side.
It should be understood that the dc source provided in the embodiments of the present application may apply a positive voltage disturbance to the virtual neutral point, and may also apply a negative voltage disturbance, which is described in detail below with reference to the accompanying drawings.
Referring to fig. 3, a schematic diagram of another photovoltaic system according to an embodiment of the present application is shown.
The photovoltaic system provided in this embodiment further includes: a first switch K1 connected in series with the DC source;
the controller is specifically configured to control the first switch K1 to be turned off, so that the first voltage is 0.
The direct current source 200 includes: a constant voltage source DC, a first diode D1, a second diode D2, a second switch K2, a third switch K3, a fourth switch K4, and a fifth switch K5;
the positive electrode of the constant voltage source DC is connected with the first end of the direct current source 200 through a second switch K2 and a first diode D1 which are connected in series, and the first end of the direct current source 200 is connected with a virtual neutral point through a first switch K1 and a resistor R which are connected in series; the negative electrode of the constant voltage source DC is grounded through a fourth switch K4; a fifth switch K5 is connected between the negative electrode of the constant voltage source DC and the first end of the direct current source 200, and the positive electrode of the constant voltage source DC is grounded through a second diode D2 and a third switch K3 which are connected in series;
the embodiment of the present application is not specifically limited, and the specific positions of K2 and D1 are shown in fig. 3, where D1 is close to DC, and K2 may be close to DC.
In fig. 3, for example, the anode of D1 is connected to the positive electrode of DC, and the cathode of D1 is connected to K2. The anode of D2 is connected to the positive pole of DC, and the cathode of D2 is connected to K3.
The controller 300 is configured to control the second switch K2 and the fourth switch K4 to be closed, and the third switch K3 and the fifth switch K5 to be opened, so that the constant voltage source DC outputs a positive voltage, that is, the positive electrode of the DC is connected to the virtual neutral point N; and controlling the second switch K2 and the fourth switch K4 to be opened, and controlling the third switch K3 and the fifth switch K5 to be closed, so that the constant voltage source DC outputs negative voltage, namely the negative electrode of the DC is connected with the virtual neutral point N.
It should be appreciated that when the virtual neutral point voltage to ground changes, the impedance of the system may change abruptly, and thus the output voltage of the constant voltage source may be controlled until the virtual neutral point voltage to ground stabilizes.
The controller is specifically configured to change the output voltage of the direct current source until the virtual neutral point voltage is stable to the ground when the second phase voltage fluctuates, so as to obtain a stable second neutral point voltage.
And the controller is particularly used for changing the output voltage of the direct current source into the first voltage or adjusting the output voltage of the direct current source into the opposite value of the second voltage when the second neutral point voltage fluctuates until the virtual neutral point voltage is stable to the ground, and obtaining the stable second neutral point voltage.
For example, when the second neutral point voltage is unstable, the output voltage of the constant voltage source may be changed, for example, switched back from the second voltage to the first voltage, or the opposite number of the second voltage may be switched from the second voltage, for example, the second voltage is a positive voltage, and the second voltage is a negative voltage. The embodiment of the present application is not particularly limited until the stable second neutral point voltage is obtained.
According to the photovoltaic system provided by the embodiment of the application, the change of the neutral point voltage before and after disturbance is continuously detected by disturbing the virtual neutral point voltage of the inverter to the ground, so that high-precision insulation impedance is obtained. Specifically, each voltage in the detection process is updated continuously through circulation, so that the quick response after the system impedance fluctuates is ensured. In addition, because the real-time disturbance is adopted in the method, the problem of misinformation of impedance caused by environmental change in the insulation impedance detection process is solved, and the safety and the reliability of the system are ensured. Importantly, the technical scheme provided by the application can detect the insulation impedance of the AC-DC side coupled together in real time in the grid-connected state of the inverter, so that personal safety and equipment safety are protected.
Based on the photovoltaic system provided by the above embodiment, the embodiment of the application also provides an inversion system, and the embodiment of the application is not particularly limited to the specific application scene of the inversion system, and can be photovoltaic, wind power or energy storage.
Referring to fig. 4, a schematic diagram of an inverter system according to an embodiment of the present application is shown.
The inverter system provided in this embodiment includes: inverter 100, dc source 200, and controller 300;
the input end of the inversion system is used for connecting a direct current power supply;
DC source 200 and resistor R 0 Connected in series between the virtual neutral point of the inverter 100 and ground;
a controller 300 for changing the output voltage of the direct current source to change the voltage of the virtual neutral point N; and according to the resistance R 0 The resistance of the inverter system, the output voltage before and after the change of the direct current source 200, and the virtual neutral point-to-ground voltage corresponding to the output voltage before and after the change respectively.
Based on the photovoltaic system and the inverter system provided in the foregoing embodiments, the embodiments of the present application further provide a method for detecting insulation resistance in a photovoltaic system, which is described in detail below with reference to the accompanying drawings.
Referring to fig. 5, the flowchart of a method for detecting insulation resistance in a photovoltaic system according to an embodiment of the present application is shown.
The embodiment provides a method for detecting insulation impedance in a photovoltaic system, wherein the photovoltaic system comprises a direct current source and an inverter; the direct current source is connected in series with the resistor and then is connected between the virtual neutral point of the inverter and the ground;
the method comprises the following steps:
s501: changing the output voltage of the direct current source to change the voltage of the virtual neutral point;
s502: obtaining output voltages before and after the direct current source is changed, and respectively corresponding virtual neutral point voltages to ground before and after the direct current source is changed;
the method for obtaining the output voltage before and after the direct current source is changed and the virtual neutral point voltage to ground corresponding to the direct current source before and after the direct current source is changed specifically comprises the following steps:
controlling a direct current source to output a first voltage and a second voltage respectively; when the direct current source outputs a first voltage, obtaining a virtual neutral point voltage to the ground as a first neutral point voltage; and when the direct current source outputs the second voltage, obtaining the virtual neutral point voltage to the ground as the second neutral point voltage.
S503: and obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change before and after the change.
According to the photovoltaic system provided by the embodiment of the application, the direct current source is added between the virtual neutral point of the inverter and the ground, and different voltages are output through the direct current source to disturb the voltage of the virtual neutral point to the ground, so that the insulation impedance of the system is obtained according to the different voltages output before and after the direct current source and the voltage before and after the virtual neutral point is disturbed. And the insulation impedance can be obtained in the grid-connected operation process of the inverter, and is the coupling impedance of the alternating current side and the direct current side.
Obtaining insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change of the direct current source, wherein the method specifically comprises the following steps: and obtaining the insulation resistance of the photovoltaic system according to the resistance value of the resistor, the first voltage, the first neutral point voltage, the second voltage and the second neutral point voltage.
When the direct current source outputs the second voltage, the second neutral point voltage of the power grid to the ground is obtained, and the method specifically comprises the following steps: when the second phase voltage fluctuates, the output voltage of the direct current source is changed until the virtual neutral point voltage is stable to the ground, and the stable second neutral point voltage is obtained.
Changing the output voltage of the direct current source until the virtual neutral point is stable to the ground voltage, and obtaining a stable second phase voltage, specifically comprising: and changing the output voltage of the direct current source into the first voltage or adjusting the output voltage into the opposite value of the second voltage until the virtual neutral point voltage is stable to the ground, and obtaining the stable second neutral point voltage.
The direct current source outputs a first voltage, and specifically comprises: and controlling the direct current source to disconnect from the virtual neutral point so that the first voltage is 0.
The second neutral point voltage fluctuates, specifically including: and acquiring the second neutral point voltage for a plurality of times in a preset time period, obtaining an average value of the second neutral point voltage, and judging the fluctuation of the second neutral point voltage when the average value of the second neutral point voltage exceeds a set value.
The specific detection procedure is described below.
Referring to fig. 6, a flowchart of another method for detecting insulation resistance in a photovoltaic system according to an embodiment of the present application is shown.
S601: the constant voltage source outputs a first voltage V 1 。
S602: whether the neutral point voltage is stable or not, and if so, executing S603; and otherwise, waiting for the neutral point voltage to stabilize.
S603: recording neutral point voltage V N1 。
S604: the constant voltage source outputs a second voltage V 2 。
S605: if the neutral point voltage is stable, executing S606; and otherwise, waiting for the neutral point voltage to stabilize.
S606: recording neutral point voltage V N2 。
S607: according to V 1 、V N1 、V 2 、V N2 And a resistor, calculating insulation resistance.
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 system or device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant points refer to the description of the method section.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled 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 (13)

1. A photovoltaic system, comprising: an inverter, a direct current source and a controller;
the input end of the inverter is used for connecting a photovoltaic group string;
the direct current source is connected in series with a resistor and then is connected between a virtual neutral point of the inverter and the ground;
the controller is used for changing the output voltage of the direct current source so as to change the voltage of the virtual neutral point; and obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the direct current source is changed and the virtual neutral point grounding voltage respectively corresponding to the direct current source before and after the direct current source is changed.
2. The photovoltaic system of claim 1, wherein the controller is specifically configured to control the dc source to output a first voltage and a second voltage, respectively; when the direct current source outputs a first voltage, the virtual neutral point voltage to the ground is the first neutral point voltage; when the direct current source outputs a second voltage, the virtual neutral point voltage to the ground is the second neutral point voltage;
the controller is used for obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the first voltage, the first neutral point voltage, the second voltage and the second neutral point voltage.
3. The photovoltaic system according to claim 2, wherein the controller is configured to change the output voltage of the dc source until the virtual neutral point voltage is stabilized with respect to ground, when there is a fluctuation in the second neutral point voltage, to obtain a stabilized second neutral point voltage.
4. A photovoltaic system according to claim 3, wherein the controller is configured to change the output voltage of the dc source to the first voltage or to adjust to an opposite value of the second voltage until the virtual neutral point voltage is stabilized with respect to the ground voltage, thereby obtaining a stabilized second neutral point voltage when there is a fluctuation in the second neutral point voltage.
5. The photovoltaic system of any of claims 2-4, further comprising: a first switch in series with the dc source;
the controller is specifically configured to control the first switch to be turned off, so that the first voltage is 0.
6. The photovoltaic system of claim 5, wherein the dc source comprises: the device comprises a constant voltage source, a first diode, a second switch, a third switch, a fourth switch and a fifth switch;
the positive electrode of the constant voltage source is connected with the first end of the direct current source through the second switch and the first diode which are connected in series, and the first end of the direct current source is connected with the virtual neutral point through the first switch and the resistor which are connected in series; the negative electrode of the constant voltage source is grounded through the fourth switch; the negative electrode of the constant voltage source is connected with the first end of the direct current source, and the positive electrode of the constant voltage source is grounded through the second diode and the third switch which are connected in series;
the controller is used for controlling the second switch and the fourth switch to be closed, controlling the third switch and the fifth switch to be opened, enabling the constant voltage source to output positive voltage, and controlling the second switch and the fourth switch to be opened, and controlling the third switch and the fifth switch to be closed, enabling the constant voltage source to output negative voltage.
7. The method for detecting the insulation resistance in the photovoltaic system is characterized in that the photovoltaic system comprises a direct current source and an inverter; the direct current source is connected in series with a resistor and then is connected between a virtual neutral point of the inverter and the ground;
the method comprises the following steps:
changing the output voltage of the direct current source to change the voltage of the virtual neutral point;
obtaining output voltages before and after the direct current source is changed and virtual neutral point grounding voltages respectively corresponding to the direct current source before and after the direct current source is changed;
and obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the direct current source is changed and the virtual neutral point grounding voltage respectively corresponding to the direct current source before and after the direct current source is changed.
8. The method according to claim 7, wherein the obtaining the output voltages of the dc source before and after the change and the virtual neutral point-to-ground voltages corresponding to the output voltages before and after the change respectively specifically includes:
controlling the direct current source to output a first voltage and a second voltage respectively; when the direct current source outputs a first voltage, the virtual neutral point voltage to the ground is obtained to be the first neutral point voltage; when the direct current source outputs a second voltage, the virtual neutral point voltage to the ground is obtained to be the second neutral point voltage;
the method for obtaining the insulation impedance of the photovoltaic system according to the resistance value of the resistor, the output voltage before and after the change of the direct current source and the virtual neutral point to ground voltage respectively corresponding to the change of the direct current source specifically comprises the following steps:
and obtaining the insulation resistance of the photovoltaic system according to the resistance value of the resistor, the first voltage, the first neutral point voltage, the second voltage and the second neutral point voltage.
9. The method according to claim 8, wherein obtaining the second neutral point voltage of the grid to ground when the dc source outputs the second voltage comprises:
and when the second phase voltage fluctuates, changing the output voltage of the direct current source until the virtual neutral point voltage is stable to the ground, and obtaining a stable second neutral point voltage.
10. The method according to claim 9, wherein said changing the output voltage of the dc source until the virtual neutral point voltage to ground stabilizes, resulting in a stabilized second phase voltage, comprises:
and changing the output voltage of the direct current source to be the first voltage or adjusting the output voltage to be the opposite value of the second voltage until the virtual neutral point voltage to the ground is stable, and obtaining the stable second neutral point voltage.
11. The method according to any one of claims 8-10, wherein the dc source outputs a first voltage, in particular comprising:
and controlling the direct current source to disconnect from the virtual neutral point so that the first voltage is 0.
12. The method according to claim 7, characterized in that there is a fluctuation in the second neutral point voltage, comprising in particular:
and acquiring the second neutral point voltage for a plurality of times in a preset time period, obtaining an average value of the second neutral point voltage, and judging that the second neutral point voltage fluctuates when the average value of the second neutral point voltage exceeds a set value.
13. An inverter system, comprising: an inverter, a direct current source and a controller;
the input end of the inversion system is used for being connected with a direct-current power supply;
the direct current source is connected in series with a resistor and then is connected between a virtual neutral point of the inverter and the ground;
the controller is used for changing the output voltage of the direct current source so as to change the voltage of the virtual neutral point; and obtaining the insulation impedance of the inverter system according to the resistance value of the resistor, the output voltage before and after the direct current source is changed and the virtual neutral point grounding voltage respectively corresponding to the output voltage before and after the direct current source is changed.
CN202310141573.5A 2022-06-08 2023-02-13 Photovoltaic system, insulation resistance detection method and inversion system Pending CN116131341A (en)

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CN202310141573.5A CN116131341A (en) 2023-02-13 2023-02-13 Photovoltaic system, insulation resistance detection method and inversion system
US18/331,079 US20230400489A1 (en) 2022-06-08 2023-06-07 Inverter and method for detecting insulation impedance of inverter
EP23178194.9A EP4293375A1 (en) 2022-06-08 2023-06-08 Inverter and method for detecting insulation impedance of inverter

Applications Claiming Priority (1)

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CN202310141573.5A CN116131341A (en) 2023-02-13 2023-02-13 Photovoltaic system, insulation resistance detection method and inversion system

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