Insulation resistance detection method and system for multi-path photovoltaic input system

Abstract

The invention relates to an insulation resistance detection method and system for a multi-path photovoltaic input system. The method comprises the following steps: acquiring an input voltage between a positive electrode and a negative electrode of each photovoltaic input module; respectively acquiring a first voltage and a second voltage corresponding to each photovoltaic input module; according to the first voltage, the second voltage and the input voltage of each photovoltaic input module, calculating positive electrode ground insulation resistance of each photovoltaic input module; the first voltage, the second voltage and the input voltage of one photovoltaic input module are selected to calculate the nominal negative electrode ground insulation resistance of the selected photovoltaic input module; and according to the nominal negative electrode ground insulation impedance of the selected photovoltaic input module and the positive electrode ground insulation impedance of the other photovoltaic input modules, calculating to obtain common negative electrode ground insulation impedance. According to the method, errors caused by simultaneous detection of multiple paths of input are avoided, and the detection precision is improved, so that the power utilization safety and the utilization efficiency of photovoltaic facilities are ensured, and the calculation process is simplified.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic insulation impedance detection, and in particular to a method and system for detecting the insulation impedance of a multi-channel photovoltaic input system. Background Art

[0002] A photovoltaic inverter grid-connected system is generally a non-isolated system. When grid-connected for power generation, there is a non-isolated connection between the photovoltaic input system and the grid. Therefore, it is required to detect the insulation impedance of the photovoltaic inverter grid-connected system before grid connection. For a multi-channel photovoltaic input system, the prior art usually detects the insulation impedance of multiple photovoltaic input modules to the ground simultaneously. This detection method requires complex calculation methods and has large detection errors. At the same time, because other electronic components (such as Y capacitors and varistors) of the photovoltaic input module will generate leakage current when withstanding the withstand voltage, these leakage currents will introduce greater errors when calculating using Kirchhoff's Current Law (KCL).

[0003] Large detection errors are likely to cause false alarms or missed alarms for insulation impedance problems. Under some humid conditions, the actual insulation impedance of the photovoltaic input module to the ground will decrease, but it can still meet the insulation impedance requirements for grid-connected power generation. At this time, large detection errors may lead to false alarms, and the photovoltaic inverter grid-connected system stops grid connection, reducing the utilization efficiency of photovoltaic facilities. When the actual insulation impedance of the photovoltaic input module to the ground decreases to a level that cannot meet the requirements, large detection errors may lead to missed alarms, which will endanger the power consumption safety of the grid. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for detecting the insulation impedance of a multi-channel photovoltaic input system to improve the detection accuracy.

[0005] The technical solution adopted by the present invention to solve its technical problems is: providing a method for detecting the insulation impedance of a multi-channel photovoltaic input system, the multi-channel photovoltaic input system includes a plurality of photovoltaic input modules, the negative electrodes of all photovoltaic input modules form a common negative electrode, the positive electrodes of all photovoltaic input modules are not co-polar, and an auxiliary detection module is connected between the common negative electrode and the ground; the method includes the following steps:

[0006] S1. Collect the input voltage between the positive electrode and the negative electrode of each photovoltaic input module.

[0007] S2. Respectively collect the first voltage and the second voltage corresponding to each photovoltaic input module; the first voltage and the second voltage are respectively: when the positive and negative electrodes of all photovoltaic input modules except the photovoltaic input module to be collected are short-circuited, the voltage of the ground to the common negative electrode when the auxiliary detection module is in the on or off state.

[0008] S3. Calculate the insulation impedance of the positive electrode of each photovoltaic input module to the ground according to the first voltage, the second voltage, and the input voltage of each photovoltaic input module;

[0009] S4. Select the first voltage, the second voltage, and the input voltage of one of the photovoltaic input modules to calculate the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground; the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground is: the parallel equivalent impedance of the insulation impedance of the common negative electrode to the ground and the insulation impedance of the positive electrodes of the remaining photovoltaic input modules;

[0010] S5. Calculate the insulation impedance of the common negative electrode to the ground according to the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground and the insulation impedance of the positive electrodes of the remaining photovoltaic input modules.

[0011] Further, step S3 includes: calculating the insulation impedance of the positive electrode to the ground based on a first preset formula; step S4 includes: calculating the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground based on a second preset formula.

[0012] Further, the first preset formula is:

[0013]

[0014] The second preset formula is:

[0015]

[0016] wherein, R― is the nominal insulation impedance of the negative electrode to the ground, R+ is the insulation impedance of the positive electrode to the ground, U PV is the input voltage, U1 is the first voltage, U0 is the second voltage, G3 = 1 / R0, and R0 is the resistance value of the auxiliary detection module.

[0017] Further, when the input voltage range of the photovoltaic input module is 60V to 550V, the resistance value range of the auxiliary detection module is 100kΩ to 1000kΩ.

[0018] Further, each photovoltaic input module is connected to a voltage conversion module. Before collecting the first voltage and the second voltage of the photovoltaic input module to be collected, the method further includes: by controlling the corresponding voltage conversion module, short-circuiting the positive electrode and the negative electrode of all photovoltaic input modules except the photovoltaic input module to be collected.

[0019] Further, the photovoltaic inverter grid-connected system is connected to the multi-channel photovoltaic input system, and the method further includes: sequentially performing step S2 and step S3 on each photovoltaic input module, and after obtaining the corresponding positive pole-to-ground insulation impedance, determining whether the corresponding positive pole-to-ground insulation impedance exceeds a preset insulation impedance range. If not, perform step S2 and step S3 on the next photovoltaic input module. If so, prohibit the photovoltaic inverter grid-connected system from being grid-connected to the multi-channel photovoltaic input system and stop the detection.

[0020] Further, the photovoltaic inverter grid-connected system is connected to the multi-channel photovoltaic input system, and the method further includes: after obtaining the positive pole-to-ground insulation impedance of all photovoltaic input modules and the common negative pole-to-ground insulation impedance, respectively comparing them with a preset insulation impedance range; if the positive pole-to-ground insulation impedance of all photovoltaic input modules and the common negative pole-to-ground insulation impedance are all within the preset insulation impedance range, allow the photovoltaic inverter grid-connected system to be grid-connected to the multi-channel photovoltaic input system; if there is an insulation impedance that exceeds the preset insulation impedance range, prohibit the photovoltaic inverter grid-connected system from being grid-connected to the multi-channel photovoltaic input system.

[0021] There is also provided an insulation impedance detection system for a multi-channel photovoltaic input system. The multi-channel photovoltaic input system includes a plurality of photovoltaic input modules. The negative poles of all photovoltaic input modules form a common negative pole, and the positive poles of all photovoltaic input modules are not common. The insulation impedance detection system includes: a control module for performing the insulation impedance detection method of the multi-channel photovoltaic input system described in any one of the above; an auxiliary detection module, the first end of the auxiliary detection module is connected to the common negative pole, the second end of the auxiliary detection module is connected to the ground, and the third end is connected to the control module.

[0022] Further, the auxiliary detection module includes an auxiliary detection resistor and a detection switch. The auxiliary detection resistor is connected in series with the detection switch, and the control module controls the detection switch to turn on or off the auxiliary detection module.

[0023] Further, the insulation impedance detection system further includes: a plurality of first voltage detection units, each connected to a photovoltaic input module, for detecting the input voltage of the corresponding photovoltaic input module and transmitting it to the control module; a second voltage detection unit, connected between the negative poles of all photovoltaic input modules and the ground, for detecting a first voltage and a second voltage and transmitting them to the control module.

[0024] Implementing the present invention has the following beneficial effects: By independently detecting the positive pole-to-ground insulation impedance of each photovoltaic input module and detecting the common negative pole-to-ground insulation impedance, it avoids the errors caused by simultaneous detection of multiple inputs, improves the detection accuracy, thus ensuring the power consumption safety of the power grid and the utilization efficiency of photovoltaic facilities, and also simplifies the calculation process. Description of the Drawings

[0025] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0026] Figure 1 is a circuit schematic diagram of an embodiment of the insulation impedance detection system for a multi-channel photovoltaic input system of the present invention;

[0027] Figure 2 is a flowchart of the insulation impedance detection method for a multi-channel photovoltaic input system of the present invention. Detailed Embodiments

[0028] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the drawings. In the following description, it should be understood that unless otherwise clearly specified and defined, terms such as "connection" and "setting" should be understood in a broad sense. For example, they can be directly connected or indirectly connected through an intermediate medium. Terms such as "first" and "second" are only for the convenience of describing the present technical solution and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] The multi-channel photovoltaic input system is connected to the photovoltaic inverter grid-connected system and provides multiple direct current inputs to the photovoltaic inverter grid-connected system. The multi-channel photovoltaic input system includes multiple photovoltaic input modules, such as two, three, or more. A photovoltaic input module can include one photovoltaic panel or multiple photovoltaic panels. Each photovoltaic input module is connected to the photovoltaic inverter grid-connected system and provides an input voltage to the photovoltaic inverter grid-connected system. Among them, the negative electrodes of all photovoltaic input modules form a common negative electrode, which is then connected to the photovoltaic inverter grid-connected system, and the positive electrodes of all photovoltaic input modules are not common and are respectively connected to the photovoltaic inverter grid-connected system.

[0030] Furthermore, each photovoltaic input module is connected to a voltage conversion module. The voltage conversion module in this embodiment uses a boost circuit or a buck-boost circuit. Each photovoltaic input module is connected to the photovoltaic inverter grid-connected system through a voltage conversion module, and the voltage conversion module is used to convert the input voltage provided by the corresponding photovoltaic input module and then input it into the photovoltaic inverter grid-connected system.

[0031] The grid-connected system of a photovoltaic inverter includes a photovoltaic inverter, a grid-connected switch, etc., which can convert direct current into alternating current and incorporate the converted alternating current into the power grid. The grid-connected system of the photovoltaic inverter in this embodiment adopts the MPPT (Maximum Power Point Tracking) control method or other methods to adjust the power generation efficiency. To ensure the safety of the grid-connected power generation process, it is required to detect the insulation impedance of the multi-channel photovoltaic input system before the grid connection of the grid-connected system of the photovoltaic inverter.

[0032] In an embodiment of the insulation impedance detection system for a multi-channel photovoltaic input system of the present invention, the insulation impedance detection system includes: a control module and an auxiliary detection module.

[0033] The control module is used to execute the insulation impedance detection method for the multi-channel photovoltaic input system disclosed in any of the following embodiments. The first end of the auxiliary detection module is connected to the common negative pole, the second end of the auxiliary detection module is connected to the ground, and the third end is connected to the control module.

[0034] In an alternative embodiment, the multi-channel photovoltaic input system includes three photovoltaic input modules. As Figure 1 shown, R1+ is the insulation impedance between the positive pole PV1+ of the first photovoltaic input module and the ground PE, R1- is the insulation impedance between the negative pole PV1- of the first photovoltaic input module and the ground PE, R2+ is the insulation impedance between the positive pole PV2+ of the second photovoltaic input module and the ground PE, R2- is the insulation impedance between the negative pole PV2- of the second photovoltaic input module and the ground PE, R3+ is the insulation impedance between the positive pole PV3+ of the third photovoltaic input module and the ground PE, R3- is the insulation impedance between the negative pole PV3- of the third photovoltaic input module and the ground PE. If there are more photovoltaic input modules, it can be deduced by analogy. PV- is the common negative pole formed by the negative poles of the three photovoltaic input modules. The first end of the auxiliary detection module is connected to the common negative pole PV-, the second end is connected to the ground PE, and the third end is connected to the control module.

[0035] Specifically, the auxiliary detection module includes an auxiliary detection resistor R0 and a detection switch S1. The auxiliary detection resistor R0 is connected in series with the detection switch S1. The control module turns on or off the auxiliary detection module by controlling the detection switch S1. In this embodiment, the detection switch uses a relay, and other types of switches such as a switching tube can also be used. The control end of the detection switch is connected to the control module, and its opening and closing are controlled by the control module. When the detection switch is closed, the auxiliary detection module is turned on; when the detection switch is opened, the auxiliary detection module is turned off. This embodiment adopts a simple auxiliary detection circuit structure, simplifies the control logic and reduces the detection cost.

[0036] Since the leakage current generated by other electronic components (such as Y capacitors and varistors) in the photovoltaic input module will introduce detection errors, selecting a suitable auxiliary detection resistor such that the current flowing through the auxiliary detection resistor during the detection process is much larger than the leakage current can greatly improve the detection accuracy. When the input voltage provided by the positive and negative poles of the photovoltaic input module is in the range of 60V to 550V, the leakage current is between several nanoamperes and more than ten microamperes. The selectable range of the auxiliary detection resistor R0 is between 100kΩ and 1000kΩ. This resistance range ensures that the current flowing through the auxiliary detection resistor is not less than 60 microamperes, which is much larger than the leakage current. The resistance value of the auxiliary detection resistor R0 in this embodiment can be, but is not limited to, 100kΩ, 500kΩ, 900kΩ, or 1000kΩ.

[0037] In one embodiment, the insulation impedance detection system further includes: a plurality of first voltage detection units and a second voltage detection unit. The plurality of first voltage detection units are respectively connected to a photovoltaic input module, and are used to detect the input voltage of the corresponding photovoltaic input module and transmit it to the control module. The second voltage detection unit is connected between the negative poles of all photovoltaic input modules and the ground, and is used to detect the first voltage and the second voltage and transmit them to the control module.

[0038] Among them, the first voltage detection units and the photovoltaic input modules are arranged in one-to-one correspondence, and each first voltage detection unit detects the input voltage of one photovoltaic input module. The second voltage detection unit is used to detect the corresponding first voltage and second voltage of all photovoltaic input modules. The first voltage detection unit and the second voltage detection unit can adopt voltage sensors or other measuring devices.

[0039] As Figure 2 shown, in one embodiment of the insulation impedance detection method for a multi-channel photovoltaic input system of the present invention, the insulation impedance detection method includes the following steps:

[0040] S1. Collect the input voltage between the positive and negative poles of each photovoltaic input module.

[0041] Specifically, before the photovoltaic inverter grid-connected system is grid-connected and controls each photovoltaic input module to be short-circuited, the control module collects the input voltage between the positive and negative poles of the corresponding photovoltaic input module through each first voltage detection unit.

[0042] S2. Respectively collect the first voltage and the second voltage corresponding to each photovoltaic input module; the first voltage and the second voltage are respectively: when the positive and negative poles of all photovoltaic input modules except the photovoltaic input module to be collected are short-circuited, the voltage of the ground to the common negative pole when the auxiliary detection module is in the on or off state.

[0043] In this embodiment, the first voltage is the voltage from the ground to the common negative terminal when the positive and negative terminals of all photovoltaic input modules except the photovoltaic input module to be collected are short-circuited and the auxiliary detection module is in the on state. The second voltage is the voltage from the ground to the common negative terminal when the positive and negative terminals of all photovoltaic input modules except the photovoltaic input module to be collected are short-circuited and the auxiliary detection module is in the off state.

[0044] Further, before collecting the first voltage and the second voltage of the photovoltaic input module to be collected, the method further includes: short-circuiting the positive and negative terminals of all photovoltaic input modules except the photovoltaic input module to be collected by controlling the corresponding voltage conversion module.

[0045] When the voltage conversion module adopts a boost or buck-boost circuit scheme, closing the switch tube in the voltage conversion module can create a short-circuit condition between the positive and negative terminals of the photovoltaic input module, and the characteristics of the photovoltaic panel allow short-circuiting. When collecting a certain photovoltaic input module, the control module controls the switch tube of this photovoltaic input module to turn off, and controls the switch tubes of the remaining photovoltaic input modules to close, so that the positive and negative terminals of this photovoltaic input module are not short-circuited, and the positive and negative terminals of the remaining photovoltaic input modules are short-circuited. The remaining photovoltaic input modules work in a short-circuit state, and a short-circuit current flows through, avoiding affecting the voltage collection of this photovoltaic input module.

[0046] After creating the short-circuit condition, close the detection switch to turn on the auxiliary detection module, collect the voltage from the ground to the common negative terminal as the first voltage through the second voltage detection unit, then open the detection switch to turn off the auxiliary detection module, and collect the voltage from the ground to the common negative terminal as the second voltage through the second voltage detection unit. In other embodiments, the second voltage can also be collected first and then the first voltage.

[0047] Repeat the above steps for each photovoltaic input module in turn to obtain the first voltage and the second voltage corresponding to each photovoltaic input module.

[0048] S3. Calculate the insulation impedance of the positive terminal of each photovoltaic input module to the ground according to the first voltage, the second voltage and the input voltage of each photovoltaic input module.

[0049] In one embodiment, after the control module collects the first voltage and the second voltage of multiple photovoltaic input modules, it calculates the insulation impedance of the positive terminal of each photovoltaic input module to the ground according to the first voltage, the second voltage and the input voltage of each photovoltaic input module. In another alternative embodiment, after the control module collects the first voltage and the second voltage of a photovoltaic input module, it calculates the insulation impedance of the positive terminal of this photovoltaic input module to the ground in combination with the input voltage, and then collects the first voltage and the second voltage of the next photovoltaic input module for calculation.

[0050] S4. Select the first voltage, second voltage, and input voltage of one of the photovoltaic input modules to calculate the nominal negative terminal to ground insulation impedance of the selected photovoltaic input module. The nominal negative terminal to ground insulation impedance of the selected photovoltaic input module is: the parallel equivalent impedance of the common negative terminal to ground insulation impedance and the positive terminal to ground insulation impedance of the remaining photovoltaic input modules.

[0051] In this embodiment, any one of multiple photovoltaic input modules is selected to calculate its nominal negative terminal to ground insulation impedance, which refers to the negative terminal to ground insulation impedance of the photovoltaic input module in the detection state. Taking Figure 1 as an example, the first photovoltaic input module is selected for calculation. Since the first voltage and second voltage of the first photovoltaic input module are collected when the positive and negative terminals of the other two photovoltaic input modules are short-circuited, the nominal negative terminal to ground insulation impedance is actually the parallel equivalent impedance of the common negative terminal to ground insulation impedance and the positive terminal to ground insulation impedance of the second and third photovoltaic input modules, that is, the parallel equivalent impedance of the common negative terminal to ground insulation impedance, R2+, and R3+.

[0052] S5. Calculate the common negative terminal to ground insulation impedance based on the nominal negative terminal to ground insulation impedance of the selected photovoltaic input module and the positive terminal to ground insulation impedance of the remaining photovoltaic input modules.

[0053] According to the calculation relationship of parallel impedance (this calculation relationship can refer to the prior art), substitute R2+, R3+, and the nominal negative terminal to ground insulation impedance into this calculation relationship to obtain the common negative terminal to ground insulation impedance. Among them, the common negative terminal to ground insulation impedance concerned by the safety regulations is the equivalent parallel impedance of R1-, R2-, and R3-, which is obtained by the present invention through the nominal negative terminal to ground insulation impedance.

[0054] Compared with the prior art that simultaneously collects the insulation impedance of multiple photovoltaic input modules, independently detects the positive terminal to ground insulation impedance of each photovoltaic input module, and detects the common negative terminal to ground insulation impedance, it can avoid the errors caused by simultaneous detection of multiple inputs, reduce the error between the detected value and the actual value, improve the detection accuracy, thus ensuring the power consumption safety of the power grid and the utilization efficiency of photovoltaic facilities, and can also avoid the complex calculation process required for simultaneous detection and simplify the calculation process.

[0055] In one embodiment, step S3 includes: calculating the positive terminal to ground insulation impedance based on a first preset formula.

[0056] Step S4 includes: calculating the nominal negative terminal to ground insulation impedance of the selected photovoltaic input module based on a second preset formula.

[0057] Specifically, all the photovoltaic input modules except the one to be collected are short-circuited. In circuit calculation, only the case of the photovoltaic input module to be collected is considered. According to Kirchhoff's Current Law (KCL), the following equations are listed:

[0058] When the auxiliary detection module is cut off:

[0059]

[0060] When the auxiliary detection module is turned on:

[0061]

[0062] Let G1 = 1 / R+, G2 = 1 / R−, G3 = 1 / R0, then the above formula becomes:

[0063] (U PV −U0)G1 = U0G2

[0064] (U PV −U1)G1 = U1(G2 + G3)

[0065] By solving the equations simultaneously:

[0066] The second preset formula is:

[0067]

[0068] The first preset formula is:

[0069]

[0070] Among them, R− is the nominal negative pole to ground insulation impedance, R+ is the positive pole to ground insulation impedance, U PV is the input voltage, U1 is the first voltage, U0 is the second voltage, G3 = 1 / R0, and R0 is the resistance value of the auxiliary detection module.

[0071] According to the above derivation process, it can be seen that the insulation detection calculation method of the present invention is simple. Only the first voltage, the second voltage, and the input voltage need to be collected and substituted into the first preset formula to calculate the positive pole to ground insulation impedance resistance of each photovoltaic input module. Select the data of one of the photovoltaic input modules and substitute it into the second preset formula to calculate the nominal negative pole to ground insulation impedance, and further solve to obtain the common negative pole to ground insulation impedance.

[0072] Furthermore, when the input voltage range of the photovoltaic input module is 60V - 550V, and the resistance value range of the auxiliary detection module is 100kΩ - 1000kΩ. This resistance value range makes the current flowing through the auxiliary detection resistor much larger than the leakage current, greatly improving the detection accuracy.

[0073] In one embodiment, the method further includes: sequentially performing step S2 and step S3 on each photovoltaic input module, and after obtaining the corresponding positive pole-to-ground insulation impedance, determining whether the corresponding positive pole-to-ground insulation impedance exceeds a preset insulation impedance range. If not, perform step S2 and step S3 on the next photovoltaic input module. If so, prohibit the grid connection of the photovoltaic inverter grid-connected system and the multi-path photovoltaic input system, and stop the detection.

[0074] In this embodiment, every time the control module acquires the first voltage and the second voltage of a photovoltaic input module, it calculates the positive pole-to-ground insulation impedance of this photovoltaic input module, and then compares it with the preset insulation impedance range. If it meets the preset insulation impedance range, it indicates that the positive pole-to-ground insulation impedance of this photovoltaic input module meets the requirements, and continue to detect the next photovoltaic input module. After all detections are completed and all meet the requirements, calculate the common negative pole-to-ground insulation resistance, and compare it with the preset insulation impedance range. If it meets this range, allow the photovoltaic inverter grid-connected system to be grid-connected. If any insulation impedance does not meet the preset insulation impedance range, prohibit the grid connection of the photovoltaic inverter grid-connected system, stop the detection, and send out a fault prompt message. Among them, the preset insulation impedance range can be set in combination with safety regulations requirements and detection errors.

[0075] In another embodiment, the insulation impedance detection method further includes: after obtaining the positive pole-to-ground insulation impedance of all photovoltaic input modules and the common negative pole-to-ground insulation impedance, respectively compare them with the preset insulation impedance range; if the positive pole-to-ground insulation impedance of all photovoltaic input modules and the common negative pole-to-ground insulation impedance are all within the preset insulation impedance range, allow the photovoltaic inverter grid-connected system to be grid-connected with the multi-path photovoltaic input system; if there is an insulation impedance that exceeds the preset insulation impedance range, prohibit the grid connection of the photovoltaic inverter grid-connected system and the multi-path photovoltaic input system.

[0076] Take Figure 1 as an example. In this embodiment, first calculate the positive pole-to-ground insulation impedance of all photovoltaic input modules, including R1+, R2+, R3+, and the common negative pole-to-ground insulation impedance R-, and then compare them with the preset insulation impedance range respectively. If any one does not meet the preset insulation impedance range, prohibit the grid connection of the photovoltaic inverter grid-connected system, stop the detection, and send out a fault prompt message. If all insulation impedances meet the preset insulation impedance range, allow the photovoltaic inverter grid-connected system to be grid-connected.

[0077] The following are the experimental comparison results of the insulation impedance detection methods of the prior art and the present application:

[0078] The prior art simultaneously detects the parallel insulation impedance of two photovoltaic input modules. When the insulation impedance of the negative electrode of the photovoltaic input module to the ground is low (but still meets the grid connection safety regulations requirements) and the insulation impedance of the positive electrode to the ground is normal, there is a large detection error in this scheme. A 20 kΩ resistor is connected in parallel to the insulation impedance of the negative electrode to the ground to simulate the situation where the insulation impedance of the negative electrode to the ground is low. Since the voltage is collected and inversely deduced, the collected voltage value is very small, so even a little error in the voltage value will cause a large error in the inversely deduced insulation impedance value. At different input voltages, the detected insulation impedance value is from 100 kΩ to several hundred kΩ, far exceeding the actual value.

[0079] The insulation impedance detection method of the present invention can greatly reduce the error. Under the same test conditions, the detection error of the actual insulation impedance of 20 kΩ can be controlled below 5 kΩ, greatly avoiding false alarms or missed alarms of insulation impedance problems caused by errors.

[0080] It can be understood that the above embodiments only represent the preferred embodiments of the present invention, and the description is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the invention patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, all equivalent transformations and modifications made to the scope of the claims of the present invention should fall within the scope covered by the claims of the present invention.

Claims

1. An insulation impedance detection method for a multi-channel photovoltaic input system, characterized in that, The multi-channel photovoltaic input system includes multiple photovoltaic input modules. The negative electrodes of all the photovoltaic input modules form a common negative electrode, and the positive electrodes of all the photovoltaic input modules are not common-polar. The auxiliary detection module is connected between the common negative electrode and the ground. The method includes the following steps: S1. Collect the input voltage between the positive and negative electrodes of each photovoltaic input module. S2. Collect the first voltage and the second voltage corresponding to each photovoltaic input module respectively. The first voltage and the second voltage are respectively: when the positive and negative electrodes of all the photovoltaic input modules except the photovoltaic input module to be collected are short-circuited, the voltage of the ground to the common negative electrode when the auxiliary detection module is in the on or off state. S3. Calculate the insulation impedance of the positive electrode of each photovoltaic input module to the ground according to the first voltage, the second voltage and the input voltage of each photovoltaic input module. S4. Select the first voltage, the second voltage and the input voltage of one of the photovoltaic input modules to calculate the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground. The nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground is: the parallel equivalent impedance of the insulation impedance of the common negative electrode to the ground and the insulation impedance of the positive electrodes of the remaining photovoltaic input modules to the ground. S5. Calculate the insulation impedance of the common negative electrode to the ground according to the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground and the insulation impedance of the positive electrodes of the remaining photovoltaic input modules to the ground.

2. The insulation impedance detection method of the multi-channel photovoltaic input system according to claim 1, wherein step S3 includes: calculating the insulation impedance of the positive electrode to the ground based on a first preset formula; step S4 includes: calculating the nominal insulation impedance of the negative electrode of the selected photovoltaic input module to the ground based on a second preset formula.

3. The insulation impedance detection method of the multi-channel photovoltaic input system according to claim 2, characterized in that The first preset formula is: The second preset formula is: wherein, R― is the nominal negative pole to ground insulation impedance, R+ is the positive pole to ground insulation impedance, U PV is the input voltage, U1 is the first voltage, U0 is the second voltage, G3 = 1 / R0, and R0 is the resistance value of the auxiliary detection module.

4. The insulation impedance detection method of the multi-channel photovoltaic input system according to claim 1, characterized in that, When the input voltage range of the photovoltaic input module is 60V to 550V, the resistance value range of the auxiliary detection module is 100kΩ to 1000kΩ.

5. The insulation impedance detection method for the multi-channel photovoltaic input system according to claim 1, characterized in that, Each photovoltaic input module is connected with a voltage conversion module. Before collecting the first voltage and the second voltage of the photovoltaic input module to be collected, the method further includes: By controlling the corresponding voltage conversion module, short-circuit the positive and negative electrodes of all the photovoltaic input modules except the photovoltaic input module to be collected.

6. The insulation impedance detection method for the multi-channel photovoltaic input system according to claim 1, characterized in that The photovoltaic inverter grid-connected system is connected with the multi-channel photovoltaic input system. The method further includes: Successively execute step S2 and step S3 for each photovoltaic input module, and after obtaining the corresponding insulation impedance of the positive electrode to the ground, judge whether the corresponding insulation impedance of the positive electrode to the ground exceeds the preset insulation impedance range. If not, execute step S2 and step S3 for the next photovoltaic input module. If so, prohibit the photovoltaic inverter grid-connected system from being grid-connected with the multi-channel photovoltaic input system and stop the detection.

7. The insulation impedance detection method of the multi-channel photovoltaic input system according to claim 1, characterized in that The photovoltaic inverter grid-connected system is connected with the multi-channel photovoltaic input system. The method further includes: After obtaining the insulation impedance of the positive electrodes of all the photovoltaic input modules to the ground and the insulation impedance of the common negative electrode to the ground, compare them with the preset insulation impedance range respectively. If the positive pole to ground insulation impedance of all photovoltaic input modules and the common negative pole to ground insulation impedance are within a preset insulation impedance range, the grid connection of the photovoltaic inverter grid connection system and the multi-channel photovoltaic input system is allowed; If there is an insulation impedance that exceeds the preset insulation impedance range, the grid connection of the photovoltaic inverter grid connection system and the multi-channel photovoltaic input system is prohibited.

8. An insulation impedance detection system for a multi-channel photovoltaic input system, characterized in that, The multi-channel photovoltaic input system includes a plurality of photovoltaic input modules. The negative poles of all photovoltaic input modules form a common negative pole, and the positive poles of all photovoltaic input modules are not common. The insulation impedance detection system includes: A control module for executing the insulation impedance detection method of the multi-channel photovoltaic input system according to any one of claims 1-7; An auxiliary detection module, the first end of the auxiliary detection module is connected to the common negative pole, the second end of the auxiliary detection module is connected to the ground, and the third end is connected to the control module.

9. The insulation impedance detection system of the multi-channel photovoltaic input system according to claim 8, characterized in that, The auxiliary detection module includes an auxiliary detection resistor and a detection switch. The auxiliary detection resistor is connected in series with the detection switch, and the control module turns on or off the auxiliary detection module by controlling the detection switch.

10. The insulation impedance detection system of the multi-channel photovoltaic input system according to claim 8, characterized in that, The insulation impedance detection system further includes: A plurality of first voltage detection units, each connected to a photovoltaic input module, for detecting the input voltage of the corresponding photovoltaic input module and transmitting it to the control module; A second voltage detection unit, connected between the negative poles of all photovoltaic input modules and the ground, for detecting a first voltage and a second voltage and transmitting them to the control module.

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