CN112595895A - Insulation impedance detection circuit and method of photovoltaic inverter - Google Patents

Insulation impedance detection circuit and method of photovoltaic inverter Download PDF

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CN112595895A
CN112595895A CN202011390629.3A CN202011390629A CN112595895A CN 112595895 A CN112595895 A CN 112595895A CN 202011390629 A CN202011390629 A CN 202011390629A CN 112595895 A CN112595895 A CN 112595895A
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switch
bus
insulation resistance
detection circuit
ground
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孙小龙
金海燕
孙佳明
吴生闻
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Esway New Energy Technology Jiangsu Co ltd
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Esway New Energy Technology Jiangsu Co ltd
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    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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Abstract

The invention discloses an insulation impedance detection circuit and method of a photovoltaic inverter. The insulation impedance detection circuit comprises a first bus capacitor and a second bus capacitor which are connected in series; the inverter circuit comprises a first switch, a second switch, a third switch, a fourth switch, a fifth switch and a sixth switch, wherein the first switch, the second switch, the third switch and the fourth switch are sequentially connected between a positive direct current bus and a negative direct current bus in series, one end of the fifth switch is electrically connected with a connection point of the first switch and the second switch, the other end of the fifth switch is electrically connected with one end of the sixth switch, the other end of the sixth switch is electrically connected with a connection point of the third switch and the fourth switch, and the insulation impedance detection circuit further comprises a disturbance resistor, wherein the first end of the disturbance resistor is electrically connected with a connection point of the fifth switch and the sixth switch, a connection point of the first bus capacitor and the second bus capacitor, and the second end of the disturbance resistor is grounded. The invention reduces the device cost, and is simple and reliable.

Description

Insulation impedance detection circuit and method of photovoltaic inverter
Technical Field
The invention belongs to the field of insulation impedance detection of photovoltaic inverters, and relates to an insulation impedance detection circuit and method of a photovoltaic inverter.
Background
In the photovoltaic system, the output PV + and PV-of the solar cell panel have earth impedance to the earth PE, and the inverter and other confluence energy equipment also have earth impedance to the earth PE, wherein the insulation impedance is the total equivalent resistance of the input end of the inverter PV to the earth. Before the inverter generates power, the insulation resistance of the PV end to the ground is detected, and when the insulation resistance is lower than a specific value, the inverter cannot be used, so that the damage to the whole photovoltaic system caused by the fact that the insulation resistance to the ground is too low is avoided.
In the prior art, devices such as a relay or an optical coupler are generally required to be additionally added, and the device such as the relay or the optical coupler is used for detecting the ground insulation impedance. For example, chinese patent CN105548719B discloses a circuit and a method for detecting insulation resistance to ground, which detect insulation resistance of a photovoltaic inverter based on the circuit for detecting insulation resistance to ground shown in fig. 1. The resistors R01 and R02 are equivalent resistors of the insulation resistance to the ground of the device to be detected, and the resistors R30, R40, R50, R60 and the switch Q10 form a topological structure of the detection circuit. The detection circuit solves the resistance value of the resistors R01 and R02 by introducing resistance disturbance and according to kirchhoff's law. However, in the insulation impedance detection circuit and method, the ground insulation impedance is obtained by solving the equivalent calculation formula, at least one switch needs to be assisted on hardware, the equivalent formula is solved by switching on and off the switch and the input side voltage, devices such as the switch are added on the original circuit of the photovoltaic inverter, the hardware cost is high, the algorithm is complex, and the calculation amount is large.
Disclosure of Invention
In view of the above technical problems, the present invention provides an improved insulation resistance detection circuit and method for a photovoltaic inverter, which reduces the cost and is simple and reliable.
The invention adopts the following technical scheme:
an insulation impedance detection circuit of a photovoltaic inverter comprises a positive direct current bus, a negative direct current bus, an inverter circuit, a first bus capacitor and a second bus capacitor, wherein the first bus capacitor and the second bus capacitor are connected between the positive direct current bus and the negative direct current bus in series; the inverter circuit comprises a first switch, a second switch, a third switch, a fourth switch, a fifth switch and a sixth switch, the first switch, the second switch, the third switch and the fourth switch are sequentially connected in series between the positive direct current bus and the negative direct current bus, one end of the fifth switch is electrically connected to the connection point of the first switch and the second switch, the other end of the fifth switch is electrically connected to one end of the sixth switch, the other end of the sixth switch is electrically connected to a connection point of the third switch and the fourth switch, the insulation impedance detection circuit further comprises a disturbance resistor, wherein a first end of the disturbance resistor is electrically connected to a connection point of the fifth switch and the sixth switch and a connection point of the first bus capacitor and the second bus capacitor, and a second end of the disturbance resistor is grounded.
In an embodiment, the insulation resistance detection circuit further includes a sampling circuit for acquiring a voltage of the negative dc bus from the ground.
In an embodiment, the sampling circuit includes an operational amplifier, one input terminal of the operational amplifier is electrically connected to the second terminal of the disturbance resistor, and the other input terminal of the operational amplifier is electrically connected to the negative dc bus.
In an embodiment, the insulation resistance detection circuit further includes a control chip, and the control chip is electrically connected to the output terminal of the operational amplifier.
In an embodiment, the control chip is further electrically connected to the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch respectively to control on/off of each switch respectively.
In one embodiment, the insulation resistance detection circuit has a first detection state and a second detection state, and when the insulation resistance detection circuit is in the first detection state, the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch are all turned off; when the insulation resistance detection circuit is in a second detection state, the first switch, the second switch, the third switch and the fifth switch are turned off and the fourth switch and the sixth switch are turned on, or the second switch, the third switch, the fourth switch and the sixth switch are turned off and the first switch and the fifth switch are turned on.
In an embodiment, the control chip obtains the insulation resistance to ground Rx of the photovoltaic inverter according to the following formula (1) or (2):
Rx=(Vpe1-Vpe2)*R/Vpe2 (1)
Rx=R(Vpe1-Vpe2)/(Vpe2-Vbus) (2)
wherein Vpe1 is the voltage of the ground to the negative dc bus in the first detection state, Vpe2 is the voltage of the ground to the negative dc bus in the second detection state, R is the resistance of the disturbance resistor, and Vbus is the voltage of the positive dc bus to the negative dc bus.
In an embodiment, the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch are IGBTs or MOSFETs, respectively.
In one embodiment, the disturbance resistor has a resistance value of 100kohm to 800 kohm.
In an embodiment, the inverter circuit is a three-level midpoint clamped inverter (ANPC) including the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch.
The invention also adopts the following technical scheme:
an insulation resistance detection method of a photovoltaic inverter, the insulation resistance detection method using the insulation resistance detection circuit as described above, the insulation resistance detection method comprising the steps of:
turning off the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch, and detecting a voltage Vpe1 of the negative dc bus to the ground;
turning off the first switch, the second switch, the third switch, and the fifth switch, turning on the fourth switch and the sixth switch, and detecting a voltage Vpe2 of the negative dc bus from the ground;
calculating the insulation resistance Rx to the ground of the photovoltaic inverter according to the following formula (1):
Rx=(Vpe1-Vpe2)*R/Vpe2 (1)
wherein, R is the resistance value of the disturbance resistor.
The invention also adopts the following technical scheme:
an insulation resistance detection method of a photovoltaic inverter, the insulation resistance detection method using the insulation resistance detection circuit as described above, the insulation resistance detection method comprising the steps of:
turning off the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch, and detecting a voltage Vpe1 of the negative dc bus to the ground;
turning off the second switch, the third switch, the fourth switch, and the fifth switch, turning on the first switch and the fifth switch, and detecting a voltage Vpe2 of the negative dc bus to ground;
calculating the insulation resistance to ground Rx of the photovoltaic inverter according to the following formula:
Rx=R(Vpe1-Vpe2)/(Vpe2-Vbus) (2)
wherein, R is the resistance of the disturbance resistor, Rx1 is the total equivalent resistance of the positive dc bus input terminal to the ground, and Vbus is the voltage of the positive dc bus to the negative dc bus.
Compared with the prior art, the invention has the following advantages by adopting the scheme:
according to the insulation impedance detection circuit and the insulation impedance detection method of the photovoltaic inverter, disclosed by the invention, the switch of the inverter circuit is used for controlling resistance disturbance without depending on an additional relay or an isolation device, so that the insulation impedance of a photovoltaic inverter system to the ground is calculated, the cost of devices such as a relay or an optical coupler is reduced, and the circuit and the detection method are simple and reliable.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a hardware topology of an insulation resistance detection circuit according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method for insulation resistance detection according to an embodiment of the present invention;
fig. 3 is a flow chart of another insulation resistance detection method according to an embodiment of the invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the invention may be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment provides an insulation resistance detection circuit of a photovoltaic inverter, which is used for detecting the insulation resistance of a photovoltaic inverter system to the ground. Referring to fig. 1, the insulation resistance detection circuit includes a positive dc bus1, a negative dc bus2, a first bus capacitor Cbus1, a second bus capacitor Cbus2, and an inverter circuit 3. The positive dc BUS1 has an input BUS-for connection to the photovoltaic panel and the negative dc BUS2 has an input BUS-for connection to the photovoltaic panel. A first bus capacitor Cbus1 and a second bus capacitor Cbus2 are connected in series between the positive dc bus1 and the negative dc bus 2. The inverter circuit 3 is a three-level midpoint clamped inverter topology including a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, and a sixth switch S6. The first switch S1, the second switch S2, the third switch S3 and the fourth switch S4 are sequentially connected in series between the positive dc bus1 and the negative dc bus2, one end of the fifth switch S5 is electrically connected to a connection point of the first switch S1 and the second switch S2, the other end of the fifth switch S5 is electrically connected to one end of the sixth switch S6, and the other end of the sixth switch S6 is electrically connected to a connection point of the third switch S3 and the fourth switch S4. The connection point of the first bus capacitor Cbus1 and the second bus capacitor Cbus2 is electrically connected to the connection point of the fifth switch S5 and the sixth switch S6. The switches are all switching transistors. In specific embodiments, the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5 and the sixth switch S6 are IGBTs or MOSFETs, respectively.
The insulation resistance detection circuit further comprises a disturbance resistor R, wherein a first end of the disturbance resistor R is electrically connected to a connection point of the fifth switch S5 and the sixth switch S6, and a second end of the disturbance resistor R is grounded PE. The disturbance resistor R is a designed and selected resistor, the resistance range of the disturbance resistor R is 100-800 kohm, the time detection precision of the ground insulation resistance detection is low when the resistance is larger than the range, and the system leakage current is large when the resistance is smaller than the range.
The insulation resistance detection circuit further comprises a sampling circuit for acquiring the voltage of the ground PE to the negative direct current bus 2. Specifically, the sampling circuit comprises an operational amplifier AMP, one input end of the operational amplifier AMP is electrically connected with the second end of the disturbance resistor R, and the other input end of the operational amplifier AMP is electrically connected with the negative direct current bus 2. The operational amplifier AMP is used for collecting voltage signals of the earth to the negative direct current bus2 and converting the voltage signals into digital signals in a differential or non-differential mode.
The insulation impedance detection circuit further comprises a control chip 4, and the control chip 4 is specifically an MCU chip for sampling detection and switch control. The control chip 4 is electrically connected with the output end of the operational amplifier AMP and is used for receiving the voltage signal output by the operational amplifier AMP. The control chip 4 is further electrically connected to the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5 and the sixth switch S6 respectively to control on/off of the switches respectively.
The insulation resistance detection circuit has a first detection state and a second detection state. When the insulation resistance detection circuit is in the first detection state, the control chip 4 controls the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5 and the sixth switch S6 to be turned off, and samples the voltage of the negative direct current bus2 through the ground PE; when the insulation resistance detection circuit is in the second detection state, the control chip 4 controls the first switch S1, the second switch S2, the third switch S3 and the fifth switch to be turned off, and controls the fourth switch S4 and the sixth switch S6 to be turned on, so as to sample the voltage of the negative direct current bus2 by the earth ground PE. Or, when the insulation resistance detection circuit is in the second detection state, the control chip 4 controls the second switch S2, the third switch S3, the fourth switch S4 and the sixth switch S6 to be turned off, the first switch S1 and the fifth switch S5 to be turned on, and the voltage of the PE negative dc bus2 is sampled to the ground.
The control chip 4 obtains the ground insulation impedance Rx of the photovoltaic inverter according to the following formula (1) or (2):
Rx=(Vpe1-Vpe2)*R/Vpe2 (1)
Rx=R(Vpe1-Vpe2)/(Vpe2-Vbus) (2)
wherein Vpe1 is the voltage of the ground to the negative dc bus2 in the first detection state, Vpe2 is the voltage of the ground to the negative dc bus2 in the second detection state, R is the resistance of the disturbance resistor, and Rx1 is the total equivalent resistance of the input terminal of the positive dc bus1 to the ground.
One detection principle of the insulation resistance detection circuit is as follows:
in the first detection state, namely when the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5 and the sixth switch S6 are all turned off, the voltage Vpe1 of the ground-to-negative dc bus2 is Rx2 Vbus/(Rx1+ Rx 2);
in the second detection state, i.e., when the first switch S1 and the fifth switch S5 are turned on and the other switches are turned off, the ground-to-negative dc bus2 voltage Vpe2 is (Rx2// R) × Vbus/(Rx1+ Rx2// R), i.e., the above equation (1);
according to the total impedance Rx of the PE, Rx1// Rx2 of the system, Rx is solved to be (Vpe1-Vpe2) R/Vpe 2. Vbus is the voltage of the BUS at the input end of the positive direct current BUS 1+ BUS at the input end of the negative direct current BUS 2; rx1 is the total equivalent resistance of the input end BUS + to the ground PE of the positive direct current BUS1 in the system, and comprises the resistance to the ground inside the inverter and the insulation resistance to the ground outside the inverter; rx2 is the total equivalent resistance of the input BUS of the negative DC BUS2 in the system to the earth PE, and comprises the resistance of the inside of the inverter to the earth and the insulation resistance of the outside of the inverter to the earth.
Another detection principle of the insulation resistance detection circuit is as follows:
in the first detection state, namely when the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5 and the sixth switch S6 are all turned off, the voltage Vpe1 of the ground-to-negative dc bus2 is Rx2 Vbus/(Rx1+ Rx 2);
in the second detection state, that is, when the fourth switch S4 and the sixth switch S6 are turned on and the other switches are turned off, the ground-to-negative dc bus2 voltage Vpe2 is (Rx2) × Vbus/(Rx1// R + Rx 2);
the total impedance Rx of the earth is Rx1// Rx2, which is solved by the system to obtain Rx R (Vpe1-Vpe2)/(Vpe2-Vbus), i.e., the above formula (2).
The embodiment also provides an insulation resistance detection method of the photovoltaic inverter, and the insulation resistance detection method adopts the insulation resistance detection circuit. Referring to fig. 2, the insulation resistance detection method specifically includes the following steps:
turning off a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5 and a sixth switch S6, and detecting a voltage Vpe1 of the ground to the negative direct current bus 2;
turning off the first switch S1, the second switch S2, the third switch S3 and the fifth switch S5, turning on the fourth switch S4 and the sixth switch S6, and detecting a voltage Vpe2 of the earth to the negative direct current bus 2;
calculating the insulation resistance Rx to the ground of the photovoltaic inverter according to the following formula (1):
Rx=(Vpe1-Vpe2)*R/Vpe2 (1)。
the embodiment also provides another insulation resistance detection method of the photovoltaic inverter, and the insulation resistance detection method adopts the insulation resistance detection circuit. The insulation resistance detection method specifically comprises the following steps:
turning off a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5 and a sixth switch S6, and detecting a voltage Vpe1 of the ground to the negative direct current bus 2;
turning off the second switch S2, the third switch S3, the fourth switch S4 and the fifth switch S5, turning on the first switch S1 and the fifth switch S5, and detecting a voltage Vpe2 of the ground to the negative dc bus 2;
calculating the insulation resistance Rx to the ground of the photovoltaic inverter according to the following formula (2):
Rx=R(Vpe1-Vpe2)/(Vpe2-Vbus) (2)。
the circuit and the method for detecting the ground insulation impedance of the photovoltaic inverter do not depend on an additional relay or an isolation device, and the resistance disturbance is controlled by using the switching tube of the ANPC inversion topology, so that the insulation impedance of a system to the ground is calculated, the cost of the additional relay or the optical coupler and other devices is reduced, and the circuit and the method are simple and reliable.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are preferred embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. An insulation impedance detection circuit of a photovoltaic inverter comprises a positive direct current bus, a negative direct current bus, an inverter circuit, a first bus capacitor and a second bus capacitor, wherein the first bus capacitor and the second bus capacitor are connected between the positive direct current bus and the negative direct current bus in series; the inverter circuit comprises a first switch, a second switch, a third switch, a fourth switch, a fifth switch and a sixth switch, wherein the first switch, the second switch, the third switch and the fourth switch are sequentially connected in series between the positive direct current bus and the negative direct current bus, one end of the fifth switch is electrically connected with a connection point of the first switch and the second switch, the other end of the fifth switch is electrically connected with one end of the sixth switch, and the other end of the sixth switch is electrically connected with a connection point of the third switch and the fourth switch, and the inverter circuit is characterized in that: the insulation impedance detection circuit further comprises a disturbance resistor, wherein a first end of the disturbance resistor is electrically connected to a connection point of the fifth switch and the sixth switch and a connection point of the first bus capacitor and the second bus capacitor, and a second end of the disturbance resistor is grounded.
2. The insulation resistance detection circuit according to claim 1, wherein: the insulation resistance detection circuit further comprises a sampling circuit used for obtaining the voltage of the earth to the negative direct current bus.
3. The insulation resistance detection circuit according to claim 2, wherein: the sampling circuit comprises an operational amplifier, one input end of the operational amplifier is electrically connected with the second end of the disturbance resistor, and the other input end of the operational amplifier is electrically connected with the negative direct current bus.
4. The insulation resistance detection circuit according to claim 3, wherein: the insulation impedance detection circuit further comprises a control chip, and the control chip is electrically connected with the output end of the operational amplifier.
5. The insulation resistance detection circuit according to claim 4, wherein: the control chip is further electrically connected with the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch respectively to control the on-off of each switch respectively.
6. The ground insulation detection circuit according to claim 4, wherein: the insulation resistance detection circuit has a first detection state and a second detection state, and when the insulation resistance detection circuit is in the first detection state, the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch are all turned off; when the insulation resistance detection circuit is in a second detection state, the first switch, the second switch, the third switch and the fifth switch are turned off and the fourth switch and the sixth switch are turned on, or the second switch, the third switch, the fourth switch and the sixth switch are turned off and the first switch and the fifth switch are turned on.
7. The insulation resistance detection circuit according to claim 6, wherein: the control chip obtains the insulation resistance Rx to the ground of the photovoltaic inverter according to the following formula (1) or (2):
Rx=(Vpe1-Vpe2)*R/Vpe2 (1)
Rx=R(Vpe1-Vpe2)/(Vpe2-Vbus) (2)
wherein Vpe1 is the voltage of the ground to the negative dc bus in the first detection state, Vpe2 is the voltage of the ground to the negative dc bus in the second detection state, R is the resistance of the disturbance resistor, and Vbus is the voltage of the positive dc bus to the negative dc bus.
8. The insulation resistance detection circuit according to claim 1, wherein: the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch are respectively an IGBT or a MOSFET; the resistance value of the disturbance resistor is 100-800 kohm.
9. An insulation resistance detection method of a photovoltaic inverter is characterized in that: the insulation resistance detection method using the insulation resistance detection circuit according to any one of claims 1 to 8, the insulation resistance detection method comprising the steps of:
turning off the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch, and detecting a voltage Vpe1 of the negative dc bus to the ground;
turning off the first switch, the second switch, the third switch, and the fifth switch, turning on the fourth switch and the sixth switch, and detecting a voltage Vpe2 of the negative dc bus from the ground;
calculating the insulation resistance Rx to the ground of the photovoltaic inverter according to the following formula (1):
Rx=(Vpe1-Vpe2)*R/Vpe2 (1)
wherein, R is the resistance value of the disturbance resistor.
10. An insulation resistance detection method of a photovoltaic inverter is characterized in that: the insulation resistance detection method using the insulation resistance detection circuit according to any one of claims 1 to 8, the insulation resistance detection method comprising the steps of:
turning off the first switch, the second switch, the third switch, the fourth switch, the fifth switch and the sixth switch, and detecting a voltage Vpe1 of the negative dc bus to the ground;
turning off the second switch, the third switch, the fourth switch, and the fifth switch, turning on the first switch and the fifth switch, and detecting a voltage Vpe2 of the negative dc bus to ground;
calculating the insulation resistance Rx to the ground of the photovoltaic inverter according to the following formula (2):
Rx=R(Vpe1-Vpe2)/(Vpe2-Vbus) (2)
wherein, R is the resistance of the disturbance resistor, Rx1 is the total equivalent resistance of the positive dc bus input terminal to the ground, and Vbus is the voltage of the positive dc bus to the negative dc bus.
CN202011390629.3A 2020-12-02 2020-12-02 Insulation impedance detection circuit and method of photovoltaic inverter Pending CN112595895A (en)

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CN106597103A (en) * 2016-12-23 2017-04-26 阳光电源股份有限公司 Insulation resistance detection method of photovoltaic inverter direct current side and controller
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CN108427038A (en) * 2017-12-22 2018-08-21 深圳市中兴昆腾有限公司 A kind of multichannel input photovoltaic DC-to-AC converter ground insulation impedance detection
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CN111856144A (en) * 2020-09-04 2020-10-30 爱士惟新能源技术(扬中)有限公司 Ground insulation impedance detection circuit and method of photovoltaic inverter
CN111929505A (en) * 2020-09-07 2020-11-13 爱士惟新能源技术(扬中)有限公司 Ground insulation impedance detection circuit and method of grid-connected inverter

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