CN112881808A - Method and device for detecting ground insulation impedance of photovoltaic array - Google Patents
Method and device for detecting ground insulation impedance of photovoltaic array Download PDFInfo
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- CN112881808A CN112881808A CN202011636172.XA CN202011636172A CN112881808A CN 112881808 A CN112881808 A CN 112881808A CN 202011636172 A CN202011636172 A CN 202011636172A CN 112881808 A CN112881808 A CN 112881808A
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- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000001514 detection method Methods 0.000 claims abstract description 54
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/20—Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
- G01R27/205—Measuring contact resistance of connections, e.g. of earth connections
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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
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Abstract
The invention relates to a method and a device for detecting insulation resistance of a photovoltaic array to the ground. The method for detecting the insulation impedance of the photovoltaic array to the ground comprises the following steps: setting a detection resistor which can be connected between the negative pole of a bus of the N-path MPPT inverter and the ground; respectively detecting the voltage between the negative electrode of a bus of the N paths of MPPT inverters and the ground under different connection states of the detection resistors, so as to respectively detect and calculate each path of MPPT based on the detection resistors and the voltage, and obtain the insulation impedance corresponding to each path of MPPT; and finally, calculating the insulation resistance value of the photovoltaic array to the ground based on the insulation resistance corresponding to each MPPT, wherein the insulation resistance value of the photovoltaic array to the ground is the parallel resistance value of the insulation resistance corresponding to each MPPT. The photovoltaic array insulation resistance to ground detection device includes: the circuit comprises a detection circuit, a sampling module and a processor, wherein the detection circuit can be switched on or off and comprises a detection resistor and a switch which are connected in series. The method can position which path of the string insulation impedance has a problem, has simple detection logic and reliable method, and saves the system cost.
Description
Technical Field
The invention belongs to the technical field of distributed power generation, and particularly relates to a method and a device for detecting insulation impedance of a photovoltaic array to the ground, which are particularly suitable for detecting the insulation impedance of a photovoltaic inverter of which each MPPT device inputs an unequal potential topology of a negative electrode or a positive electrode to the photovoltaic array.
Background
At present, most insulation impedance detection methods adopted by N-path MPPT inverters are based on the topology that each MPPT device inputs negative or positive connection. For a string inverter of a 1500V DC system, there is a topology in which the input positive electrodes or negative electrodes of the MPPT devices are not directly connected, and in this topology, the conventional insulation resistance detection method is no longer applicable. Therefore, a new photovoltaic array ground insulation resistance detection scheme needs to be designed for this topology.
Disclosure of Invention
The invention aims to provide a method and a device for detecting insulation resistance of a photovoltaic array to the ground, which are suitable for an N-way MPPT inverter with an input anode and an input cathode not directly connected.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for detecting insulation resistance of a photovoltaic array to ground is based on an N-path MPPT inverter with an input positive electrode and an input negative electrode not directly connected, and comprises the following steps:
setting a detection resistor capable of connecting the negative pole of a bus of the N-path MPPT inverter with the ground;
respectively detecting and calculating each path of MPPT based on the detection resistor to obtain the insulation impedance corresponding to each path of MPPT;
calculating a ground insulation resistance value of the photovoltaic array based on insulation resistance corresponding to each MPPT, wherein the ground insulation resistance value of the photovoltaic array is a parallel resistance value of the insulation resistance corresponding to each MPPT;
the method for detecting and calculating the nth MPPT to obtain the insulation impedance of the nth MPPT comprises the following steps: controlling output voltages corresponding to each path of MPPT except the nth path of MPPT to be reduced to 0, disconnecting the detection resistor from the bus cathode of the N paths of MPPT inverters and the ground, measuring the voltage between the bus cathode of the N paths of MPPT inverters and the ground as a first voltage, connecting the detection resistor between the bus cathode of the N paths of MPPT inverters and the ground, measuring the voltage between the bus cathode of the N paths of MPPT inverters and the ground as a second voltage, and calculating the insulation impedance of the nth path of MPPT based on the first voltage, the second voltage and the resistance value of the detection resistor;
wherein N is an integer greater than 1, and N is a positive integer less than or equal to N.
The method for calculating the insulation resistance of the nth path of MPPT comprises the following steps:
wherein R isISO,nInsulation resistance of the n-th MPPT, V1nA first voltage corresponding to the n-th MPPT, V2nThe second voltage is corresponding to the nth MPPT, and R13 is a resistance value of the detection resistor.
A photovoltaic array ground insulation resistance detection device is used for realizing the photovoltaic array ground insulation resistance detection method, and comprises the following steps:
the detection circuit can be switched on or switched off and is connected between the negative pole of the bus of the N-path MPPT inverter and the ground, and the detection circuit comprises the detection resistor and a switch which are connected in series;
the sampling module is used for sampling the voltage between the negative pole of the bus of the N-path MPPT inverter and the ground;
and the processor is used for controlling the switch and calculating to obtain the insulation impedance value of the photovoltaic array to the ground based on the voltage between the negative electrode of the bus of the N-path MPPT inverter sampled by the sampling module and the ground.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention overcomes the ISO detection problem of the inverter under the condition that the MPPT inputs unequal potentials of the cathode or the anode, can position which path of the insulation impedance has the problem, has simple detection logic and reliable method, and greatly saves the system cost.
Drawings
FIG. 1 is a partial circuit diagram of a photovoltaic array insulation resistance to ground detection device of the present invention.
FIG. 2 is a flow chart of a method for detecting insulation resistance to ground of a photovoltaic array by using the apparatus for detecting insulation resistance to ground of a photovoltaic array according to the present invention.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.
The first embodiment is as follows: a method for detecting insulation resistance of a photovoltaic array to the ground aiming at an N (N is an integer larger than 1) path MPPT inverter with an input positive electrode and an input negative electrode not directly connected comprises the following steps:
setting a detection resistor which can be connected between the negative pole of a bus of the N-path MPPT inverter and the ground;
respectively detecting and calculating each path of MPPT based on the detection resistor to obtain the insulation impedance corresponding to each path of MPPT;
and calculating the insulation resistance value of the photovoltaic array to the ground based on the insulation resistance corresponding to each MPPT, wherein the insulation resistance value of the photovoltaic array to the ground is the parallel resistance value of the insulation resistance corresponding to each MPPT.
In the above scheme, the method for detecting and calculating the nth (N is a positive integer less than or equal to N) MPPT to obtain the insulation resistance of the nth MPPT includes: and controlling the output voltage corresponding to each path of MPPT except the nth path of MPPT to be reduced to 0, disconnecting the detection resistor from the bus cathode of the N paths of MPPT inverters and the ground, measuring the voltage between the bus cathode of the N paths of MPPT inverters and the ground as a first voltage, connecting the detection resistor between the bus cathode of the N paths of MPPT inverters and the ground, measuring the voltage between the bus cathode of the N paths of MPPT inverters and the ground as a second voltage, and calculating the insulation impedance of the nth path of MPPT based on the first voltage, the second voltage and the resistance value of the detection resistor.
The method for detecting the insulation resistance to ground of the photovoltaic array is described below by combining a specific device for detecting the insulation resistance to ground of the photovoltaic array.
As shown in FIG. 1, a 4-way MPPT device is taken as an illustration, wherein R9 and R11 are insulation resistance of a first way MPPT, R10 and R12 are insulation resistance of a second way MPPT, R15 and R17 are insulation resistance of a third way MPPT, and R16 and R18 are insulation resistance of a fourth way MPPT.
Based on this, photovoltaic array insulation resistance to ground detection device includes detection circuitry, sampling module and processor.
The detection line can be switched on or off and is connected between a BUS negative electrode BUS-of the N-way MPPT inverter and the ground PE, and the detection line comprises a detection resistor R13 and a switch (a control signal is Relay1) which are connected in series.
The sampling module is used for sampling voltage between a BUS cathode BUS-and ground PE of the N MPPT inverters.
The processor is respectively connected with the switch and the sampling module, is used for controlling the switch, and obtains a photovoltaic array ground insulation resistance value R through calculation based on the voltage between the BUS cathode BUS-ground PE of the N-path MPPT inverter sampled by the sampling moduleISO. The functions of the processor may be implemented by a controller of the multi-way MPPT inverter.
The process of implementing the photovoltaic array ground insulation impedance detection method based on the photovoltaic array ground insulation impedance detection device is shown in the attached figure 2:
aiming at the 1 st path MPPT, the DC/DC current of the 2 nd path MPPT, the 3 rd path MPPT and the 4 th path MPPT is controlled to increase the output current used by the 2 nd, the 3 rd and the 4 th paths MPPT, thereby controlling each path of MPPT except the 1 st path MPPT, namely the output voltage V corresponding to the 2 nd path MPPT, the 3 rd path MPPT and the 4 th path MPPTPV2、VPV3、VPV4The decrease is 0. The processor outputs a control signal that the Relay1 is equal to 0 to turn off the switch, and at the moment, the bus of the N-path MPPT inverter is measuredThe voltage between the negative BUS and ground PE is taken as the first voltage V1. The processor outputs a control signal with Relay1 being 1 to close the switch, measures the voltage between the BUS negative electrode BUS-of the N-path MPPT inverter and the ground PE as a second voltage V2, and then outputs a control signal with Relay1 being 0 to open the switch.
After the measurement process, the insulation resistance of the n-th path of MPPT can be calculated.
By means of RISO,n＝F(V1n,V2n) The method for calculating the insulation resistance of the nth path of MPPT comprises the following steps:
in the formula, RISO,nInsulation resistance of the n-th MPPT, V1nA first voltage corresponding to the n-th MPPT, V2nThe second voltage is corresponding to the nth MPPT, and R13 is a resistance value of the detection resistor.
Respectively calculating the insulation resistance of each MPPT by using the method, including RISO,1,RISO,2,...,RISO,n(including R in this embodiment)ISO,1,RISO,2,RISO,3,RISO,4) Then the photovoltaic array is insulated from the ground by a resistance value RISOParallel resistance of insulation resistance, i.e. R, for each MPPTISO＝RISO,1//RISO,2//...//RISO,n(in this example RISO＝RISO,1//RISO,2//RISO,3//RISO,4). Judging the ground insulation resistance value R of the photovoltaic arrayISOWhether the resistance value is larger than a resistance threshold value (such as 50k), if so, the resistance value R of the photovoltaic array to the ground insulation is indicatedISOAnd (6) abnormal.
The invention utilizes the short-circuit characteristic of the photovoltaic panel I-V curve, combines a topological structure that each MPPT input anode or each input cathode of the 1500V DC system inverter is not directly connected, adopts a method for controlling all other MPPT input currents, detects the current MPPT insulation impedance under the condition of reducing all other MPPT input voltages, and finally calculates the system insulation impedance by connecting the insulation impedances of all the single MPPT in parallel.
In summary, the core idea of the invention is as follows: and (3) detecting the insulation impedance of each path of MPPT independently by utilizing the PV curve characteristic of a photovoltaic panel and the characteristic that the input cathode and the input anode of each MPPT device of the inverter of a 1500V DC system are not directly connected, and finally calculating the total insulation impedance according to the insulation impedance of each path of MPPT.
The insulation impedance detection method does not need direct connection of input cathodes or anodes of all MPPT devices, and solves the problem that the prior art cannot be applied to the situation that the input cathodes or the anodes of all MPPT devices of a 1500V DC system string inverter are not connected. The invention overcomes the ISO detection under the condition that the input negative electrode or positive electrode of each MPPT of the inverter is unequal in potential, compared with the prior art, the invention can position which path of the insulation impedance has the problem, in addition, no hardware device is added, the detection logic is simple, the method is reliable, and the system cost is greatly saved.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is 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 protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (3)
1. A photovoltaic array ground insulation impedance detection method is based on an N-path MPPT inverter with an input anode and an input cathode not directly connected, and is characterized in that the method comprises the following steps: the method for detecting the insulation impedance of the photovoltaic array to the ground comprises the following steps:
setting a detection resistor capable of connecting the negative pole of a bus of the N-path MPPT inverter with the ground;
respectively detecting and calculating each path of MPPT based on the detection resistor to obtain the insulation impedance corresponding to each path of MPPT;
calculating a ground insulation resistance value of the photovoltaic array based on insulation resistance corresponding to each MPPT, wherein the ground insulation resistance value of the photovoltaic array is a parallel resistance value of the insulation resistance corresponding to each MPPT;
the method for detecting and calculating the nth MPPT to obtain the insulation impedance of the nth MPPT comprises the following steps: controlling output voltages corresponding to each path of MPPT except the nth path of MPPT to be reduced to 0, disconnecting the detection resistor from the bus cathode of the N paths of MPPT inverters and the ground, measuring the voltage between the bus cathode of the N paths of MPPT inverters and the ground as a first voltage, connecting the detection resistor between the bus cathode of the N paths of MPPT inverters and the ground, measuring the voltage between the bus cathode of the N paths of MPPT inverters and the ground as a second voltage, and calculating the insulation impedance of the nth path of MPPT based on the first voltage, the second voltage and the resistance value of the detection resistor;
wherein N is an integer greater than 1, and N is a positive integer less than or equal to N.
2. The method for detecting the insulation resistance to ground of the photovoltaic array according to claim 1, wherein the method comprises the following steps: the method for calculating the insulation resistance of the nth path of MPPT comprises the following steps:
wherein R isISO,nInsulation resistance of the n-th MPPT, V1nA first voltage corresponding to the n-th MPPT, V2nThe second voltage is corresponding to the nth MPPT, and R13 is a resistance value of the detection resistor.
3. A photovoltaic array ground insulation resistance detection device for implementing the photovoltaic array ground insulation resistance detection method according to claim 1 or 2, characterized in that: the photovoltaic array insulation resistance to ground detection device includes:
the detection circuit can be switched on or switched off and is connected between the negative pole of the bus of the N-path MPPT inverter and the ground, and the detection circuit comprises the detection resistor and a switch which are connected in series;
the sampling module is used for sampling the voltage between the negative pole of the bus of the N-path MPPT inverter and the ground;
and the processor is used for controlling the switch and calculating to obtain the insulation impedance value of the photovoltaic array to the ground based on the voltage between the negative electrode of the bus of the N-path MPPT inverter sampled by the sampling module and the ground.
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| CN119125682A (en) * | 2024-11-15 | 2024-12-13 | 浙江华昱欣科技有限公司 | Multi-string photovoltaic inverter insulation impedance detection method, system and device |
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