CN112881808B - Method and device for detecting ground insulation resistance of photovoltaic array - Google Patents
Method and device for detecting ground insulation resistance of photovoltaic array Download PDFInfo
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- CN112881808B CN112881808B CN202011636172.XA CN202011636172A CN112881808B CN 112881808 B CN112881808 B CN 112881808B CN 202011636172 A CN202011636172 A CN 202011636172A CN 112881808 B CN112881808 B CN 112881808B
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- 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
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- 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
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Abstract
The invention relates to a method and a device for detecting the insulation resistance of a photovoltaic array to ground. The method for detecting the insulation resistance of the photovoltaic array to the ground comprises the following steps: setting a detection resistor capable of being connected between a bus negative electrode of the N-path MPPT inverter and the ground; detecting voltages between the bus cathodes of the N paths of MPPT inverters and the ground under different connection states of the detection resistors, and accordingly detecting and calculating each path of MPPT based on the detection resistors and the voltages to obtain insulation impedance corresponding to each path of MPPT; and finally, calculating the insulation resistance value of the photovoltaic array to ground based on the insulation resistance corresponding to each path of MPPT, wherein the insulation resistance value of the photovoltaic array to ground is the parallel resistance value of the insulation resistance corresponding to each path of MPPT. The photovoltaic array insulation resistance to ground detection device includes: the device comprises a detection circuit capable of being connected or disconnected, a sampling module and a processor, wherein the detection circuit comprises a detection resistor and a switch which are connected in series. The invention can locate which path of group string has the problem of insulation resistance, 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 the insulation resistance of a photovoltaic array to the ground, which are particularly suitable for detecting the insulation resistance of a photovoltaic inverter with unequal potential topology of an input negative electrode or an input positive electrode of each MPPT device to the photovoltaic array.
Background
At present, most of insulation impedance detection methods adopted by N-path MPPT inverters are based on topology that inputs of all MPPT devices are connected together negatively or positively. For string inverters of 1500V DC systems, there are topologies where the input positive or negative poles of the respective MPPT devices are not directly connected, in which the previous 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 the insulation resistance of a photovoltaic array to ground by an N-path MPPT inverter with an input positive electrode and an input negative electrode not directly connected.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the method for detecting the insulation resistance of the photovoltaic array to the 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 being connected between a bus negative electrode of the N-path MPPT inverter and the ground;
detecting and calculating MPPT of each path based on the detection resistor to obtain insulation impedance corresponding to the MPPT of each path;
calculating a photovoltaic array ground insulation resistance value based on insulation resistance corresponding to each path of MPPT, wherein the photovoltaic array ground insulation resistance value is a parallel resistance value of insulation resistance corresponding to each path of MPPT;
the method for detecting and calculating the n-th MPPT to obtain the insulation impedance of the n-th MPPT comprises the following steps: controlling output voltages corresponding to all but N-th MPPT to be reduced to 0, disconnecting the detection resistor from a bus negative electrode of the N-way MPPT inverter and ground, measuring voltage between the bus negative electrode of the N-way MPPT inverter and ground as a first voltage, connecting the detection resistor between the bus negative electrode of the N-way MPPT inverter and ground, measuring voltage between the bus negative electrode of the N-way MPPT inverter and ground as a second voltage, and calculating insulation impedance of the N-th MPPT based on the first voltage, the second voltage and resistance values 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 MPPT comprises the following steps:
wherein R is ISO,n Insulation resistance for n-th path MPPT, V1 n For the first voltage corresponding to the nth MPPT, V2 n And R13 is the resistance value of the detection resistor for the second voltage corresponding to the nth MPPT.
The utility model provides a photovoltaic array insulation resistance to ground detection device for realize aforementioned photovoltaic array insulation resistance to ground detection method, photovoltaic array insulation resistance to ground detection device includes:
the detection circuit can be connected or disconnected, is connected between the bus negative electrode of the N-path MPPT inverter and the ground, and comprises the detection resistor and the switch which are connected in series;
the sampling module is used for sampling the voltage between the bus negative electrode of the N-path MPPT inverter and the ground;
and the processor is used for controlling the switch and calculating the insulation resistance value to ground of the photovoltaic array based on the voltage between the bus cathode of the N-path MPPT inverter and the ground, which is sampled by the sampling module.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention solves the ISO detection problem under the condition that the negative electrode or the positive electrode of each MPPT input of the inverter is not equal in potential, can locate to be specific to which path of group string has the problem of insulation resistance, 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 ground insulation resistance detection device according to the present invention.
Fig. 2 is a flowchart of a method for realizing the detection of the insulation resistance of the photovoltaic array to the ground by the insulation resistance detection device of the photovoltaic array.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings.
Embodiment one: the method for detecting the insulation resistance of the photovoltaic array to the ground is aimed 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, and comprises the following steps:
setting a detection resistor capable of being connected between a bus negative electrode of the N-path MPPT inverter and the ground;
detecting and calculating MPPT of each path based on the detection resistor to obtain insulation impedance corresponding to the MPPT of each path;
and calculating the insulation resistance value of the photovoltaic array to ground based on the insulation resistance corresponding to each path of MPPT, wherein the insulation resistance value of the photovoltaic array to ground is the parallel resistance value of the insulation resistance corresponding to each path of MPPT.
In the above scheme, the method for detecting and calculating the nth path MPPT (N is a positive integer less than or equal to N) to obtain the insulation impedance of the nth path MPPT includes: and controlling output voltages corresponding to all MPPT except the nth MPPT to be reduced to 0, disconnecting the detection resistor from the bus negative electrode of the N MPPT inverter, measuring the voltage between the bus negative electrode of the N MPPT inverter and the ground as a first voltage, connecting the detection resistor between the bus negative electrode of the N MPPT inverter and the ground, measuring the voltage between the bus negative electrode of the N MPPT inverter and the ground as a second voltage, and calculating the insulation impedance of the nth 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 with reference to a specific device for detecting the insulation resistance to ground of the photovoltaic array.
As shown in fig. 1, a 4-path MPPT device is used as an illustration, wherein R9 and R11 are positive and negative insulation impedances of the first path MPPT, R10 and R12 are positive and negative insulation impedances of the second path MPPT, R15 and R17 are positive and negative insulation impedances of the third path MPPT, and R16 and R18 are positive and negative insulation impedances of the fourth path MPPT.
Based on the above, the photovoltaic array insulation resistance detection device comprises a detection line, a sampling module and a processor.
The detection circuit can be connected or disconnected, is connected between a BUS negative electrode BUS-of the N-path MPPT inverter and the ground PE, and comprises a detection resistor R13 and a switch (a control signal is Relay 1) which are connected in series.
The sampling module is used for sampling the voltage between the BUS negative BUS-of the N-path MPPT inverter and the ground PE.
The processor is respectively connected with the switch and the sampling module and is used for controlling the switch, and the voltage between the BUS negative electrode BUS-of the N-path MPPT inverter sampled by the sampling module and the ground PE is calculated to obtain the insulation resistance value R of the photovoltaic array to the ground ISO . The functions of the processor may be implemented by a controller of the multi-path MPPT inverter.
The flow of the method for realizing the detection of the photovoltaic array insulation resistance to ground based on the photovoltaic array insulation resistance to ground detection device is shown in the accompanying figure 2:
for the 1 st path MPPT, the output currents utilized by the 2 nd path MPPT, the 3 rd path MPPT and the 4 th path MPPT are increased by controlling the DC/DC current of the 2 nd path MPPT, the 3 rd path MPPT and the 4 th path MPPT, thereby controlling the output voltages V corresponding to the 2 nd path MPPT, the 3 rd path MPPT and the 4 th path MPPT PV2 、V PV3 、V PV4 Decreasing to 0. The processor outputs a control signal of Relay 1=0 to open the switch, and at this time, the voltage between the BUS negative electrode BUS-of the N-way MPPT inverter and the ground PE is measured as a first voltage V1. The processor outputs a control signal of Relay 1=1 to close the switch, at this time, the voltage between the BUS negative electrode BUS-of the N-path MPPT inverter and the ground PE is measured as a second voltage V2, and then the processor outputs a control signal of Relay 1=0 to open the switch.
After the measurement process, the insulation impedance of the nth path MPPT can be calculated.
By R ISO,n ＝F(V1 n ,V2 n ) The method for calculating the insulation resistance of the nth path MPPT comprises the following steps:
wherein R is ISO,n Insulation resistance for n-th path MPPT, V1 n For the first voltage corresponding to the nth MPPT, V2 n And R13 is the resistance value of the detection resistor for the second voltage corresponding to the nth MPPT.
The insulation impedance of each MPPT is calculated by the method, which comprises R ISO,1 ,R ISO,2 ,...,R ISO,n (R is included in the present embodiment) ISO,1 ,R ISO,2 ,R ISO,3 ,R ISO,4 ) Then the insulation resistance value R of the photovoltaic array to the ground ISO Parallel resistance values of insulation resistance corresponding to MPPT of each path, namely R ISO ＝R ISO,1 //R ISO,2 //...//R ISO,n (R in this embodiment) ISO ＝R ISO,1 //R ISO,2 //R ISO,3 //R ISO,4 ). Judging the insulation resistance value R of the photovoltaic array to the ground ISO Whether the resistance is larger than the resistance threshold (such as 50 k), if so, the resistance value R of the photovoltaic array to ground is indicated ISO An abnormality.
According to the invention, by utilizing the characteristic that an I-V curve of a photovoltaic panel can be short-circuited, and combining a topological structure that the input anodes or the input cathodes of all MPPT of a 1500V DC system inverter are not directly connected, a method for controlling all other MPPT input currents is adopted, under the condition of reducing all other MPPT input voltages, the current MPPT insulation impedance is detected, and finally the insulation impedance of all individual MPPT is connected in parallel to calculate the system insulation impedance.
In summary, the core idea of the invention is that: by utilizing the characteristics of the PV curve of the photovoltaic panel and the characteristic that the input negative electrode and the input positive electrode of each MPPT device of the inverter of the 1500V DC system are not directly connected, the insulation impedance of each path of MPPT is independently detected, and finally the total insulation impedance is calculated according to the insulation impedance of each path of MPPT.
The insulation impedance detection method provided by the invention does not need to directly connect the input negative electrode or the positive electrode of each MPPT device, and solves the problem that the prior art cannot be applied to the situation that the input negative electrode or the positive electrode of each MPPT device of a 1500V DC system string inverter is not connected. Compared with the prior art, the invention can be positioned to a specific way which has the problem of string insulation resistance, and has the advantages of no hardware device, simple detection logic, reliable method and great system cost saving.
The above embodiments are provided to illustrate the technical concept and features of the present invention and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.
Claims (3)
1. The utility model provides a photovoltaic array insulation resistance to ground detection method, carries out photovoltaic array insulation resistance to ground detection based on the N way MPPT dc-to-ac converter that does not connect directly between each way input positive pole and does not connect directly between each way input negative pole, its characterized in that: the method for detecting the insulation resistance of the photovoltaic array to the ground comprises the following steps:
setting a detection resistor capable of being connected between a bus negative electrode of the N-path MPPT inverter and the ground;
detecting and calculating MPPT of each path based on the detection resistor to obtain insulation impedance corresponding to the MPPT of each path;
calculating a photovoltaic array ground insulation resistance value based on insulation resistance corresponding to each path of MPPT, wherein the photovoltaic array ground insulation resistance value is a parallel resistance value of insulation resistance corresponding to each path of MPPT;
the method for detecting and calculating the n-th MPPT to obtain the insulation impedance of the n-th MPPT comprises the following steps: controlling output voltages corresponding to all but N-th MPPT to be reduced to 0, disconnecting the detection resistor from a bus negative electrode of the N-way MPPT inverter and ground, measuring voltage between the bus negative electrode of the N-way MPPT inverter and ground as a first voltage, connecting the detection resistor between the bus negative electrode of the N-way MPPT inverter and ground, measuring voltage between the bus negative electrode of the N-way MPPT inverter and ground as a second voltage, and calculating insulation impedance of the N-th MPPT based on the first voltage, the second voltage and resistance values 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 a photovoltaic array according to claim 1, wherein the method comprises the following steps: the method for calculating the insulation resistance of the nth path MPPT comprises the following steps:
wherein R is ISO,n Insulation resistance for n-th path MPPT, V1 n For the first voltage corresponding to the nth MPPT, V2 n And R13 is the resistance value of the detection resistor for the second voltage corresponding to the nth MPPT.
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 comprises:
the detection circuit can be connected or disconnected, is connected between the bus negative electrode of the N-path MPPT inverter and the ground, and comprises the detection resistor and the switch which are connected in series;
the sampling module is used for sampling the voltage between the bus negative electrode of the N-path MPPT inverter and the ground;
and the processor is used for controlling the switch and calculating the insulation resistance value to ground of the photovoltaic array based on the voltage between the bus cathode of the N-path MPPT inverter and the ground, which is sampled by the sampling module.
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| SU771568A1 (en) * | 1974-07-02 | 1980-10-15 | Предприятие П/Я В-2156 | Method of measuring insulation resistance of dc mains relatively to the case (earth) |
| CN107305224A (en) * | 2016-04-19 | 2017-10-31 | 台达电子企业管理（上海）有限公司 | Insulation resistance detection circuit, detection method and the photovoltaic DC-to-AC converter of photovoltaic DC-to-AC converter |
| CN106603007B (en) * | 2016-12-16 | 2018-09-28 | 阳光电源股份有限公司 | Photovoltaic array ground insulation impedance detection circuit |
| CN109541368A (en) * | 2018-11-08 | 2019-03-29 | 贵阳英纳瑞电气有限公司 | A kind of circuit and detection method for the detection of direct current system bus insulation |
| CN111505381A (en) * | 2020-05-12 | 2020-08-07 | 爱士惟新能源技术(江苏)有限公司 | Insulation impedance detection circuit and method for non-isolated photovoltaic inverter |
| CN111812406A (en) * | 2020-07-21 | 2020-10-23 | 上海正泰电源***有限公司 | Insulation impedance detection circuit and method for multi-path non-common-pole input circuit |
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