Insulation resistance detection method and system of inverter system based on rectification circuit auxiliary power supply, and storage medium

Abstract

The invention discloses an insulation resistance detection method and system of an inverter system based on rectification circuit auxiliary power supply, and a storage medium. The insulation resistance detection method comprises the following steps: acquiring a resistance value of a first resistor connected in series between a rectifying circuit and a positive direct current bus of an inverter system, and acquiring a resistance value of a second resistor connected in series between the rectifying circuit and a negative direct current bus of the inverter system; obtaining the loss power of the inverter system; sampling the bus voltage of the inverter system; sampling the phase voltage of the power grid; and calculating the ground insulation resistance of the inverter system according to the resistance value of the first resistor, the resistance value of the second resistor, the loss power of the inverter system, the bus voltage and the power grid phase voltage. According to the invention, the problem that the insulation impedance cannot be normally detected when the earth voltage and the main circuit have a potential relationship is solved, and the impedance of the main loop of the inverter system to the ground is calculated by monitoring the bus voltage of the inverter system.

Description

Technical Field

[0001] The present invention belongs to the field of insulation impedance detection of inverter systems, and in particular relates to an insulation impedance detection method, system and computer-readable storage medium of an inverter system based on rectifier circuit auxiliary power supply. Background Art

[0002] According to national or industry standards (such as IEC62109), in order to ensure personal safety, the insulation resistance of the non-isolated grid-connected inverter needs to be tested before it is connected to the grid. If the insulation resistance is less than the standard requirement, the photovoltaic inverter is not allowed to be connected to the grid.

[0003] Existing photovoltaic inverters require that the earth and the main circuit are in a high-resistance or insulated state when performing insulation impedance monitoring. If there is a fixed potential relationship between the earth voltage and the main circuit, the voltage of the insulation impedance detection circuit relay will be clamped before and after the action, resulting in calculation errors and false alarms. In photovoltaic energy storage inverters, there may be only grid access at night or on cloudy days. When the auxiliary power supply circuit is a rectifier circuit, there will be a fixed potential relationship between the main circuit of the inverter and the earth, and normal insulation impedance cannot be monitored at this time.

[0004] The above information disclosed in the Background section is only for enhancement of understanding of the background of the present application and therefore it may contain information that does not constitute the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0005] The present invention proposes an insulation impedance detection method for an inverter system based on rectifier circuit auxiliary power supply, which is used to solve the problem that the insulation impedance cannot be detected normally when there is a potential relationship between the earth and the main circuit, and calculates the impedance of the main circuit of the inverter system to the ground by monitoring the bus voltage of the inverter system. The present invention also provides an insulation impedance detection system for an inverter system based on rectifier circuit auxiliary power supply and a computer-readable storage medium.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for detecting insulation impedance of an inverter system based on rectifier circuit auxiliary power supply comprises the following steps:

[0008] Obtaining a resistance value of a first resistor connected in series between the rectifier circuit and the positive DC bus of the inverter system, and obtaining a resistance value of a second resistor connected in series between the rectifier circuit and the negative DC bus of the inverter system;

[0009] Obtain the power loss of the inverter system;

[0010] Sampling the bus voltage of the inverter system;

[0011] Sampling the grid phase voltage;

[0012] The insulation impedance of the inverter system to ground is calculated according to the resistance value of the first resistor, the resistance value of the second resistor, the power loss of the inverter system, the bus voltage and the grid phase voltage.

[0013] In a preferred embodiment, the system equivalent resistance is obtained according to the bus voltage and the power loss of the inverter system.

[0014] In a more preferred embodiment, the equivalent resistance R of the system loss is obtained according to the following formula: load :

[0015]

[0016] Among them, U bus Indicates bus voltage, P load Represents the power loss of the inverter system, R load Represents the loss equivalent resistance of the inverter system.

[0017] In a preferred embodiment, the insulation resistance R is calculated according to the following formula: iso :

[0018]

[0019] Among them, P load Indicates the inverter system power loss, U bus represents the bus voltage of the inverter system, R1 represents the resistance value of the first resistor, R2 represents the resistance value of the second resistor, and U ac Indicates the grid phase voltage.

[0020] In a preferred embodiment, the rectifier circuit includes multiple rectifier diodes, a first resistor is connected in series between the positive output end of the rectifier circuit and the positive DC bus of the main circuit of the inverter system, and a second resistor is connected in series between the negative output end of the rectifier circuit and the negative DC bus of the main circuit, so as to convert the AC power from the power grid into DC power supplied to the main circuit through the rectifier circuit.

[0021] In a preferred embodiment, the grid phase voltage is a phase voltage of a three-phase grid.

[0022] In a preferred embodiment, the inverter system includes a photovoltaic inverter, an energy storage inverter or a photovoltaic storage inverter.

[0023] Another technical solution adopted by the present invention is as follows:

[0024] An insulation impedance detection system of an inverter system based on rectifier circuit auxiliary power supply comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the insulation impedance detection method when executing the computer program.

[0025] Another technical solution adopted by the present invention is as follows:

[0026] A computer-readable storage medium stores a computer program, and when the program is executed by a processor, the insulation impedance detection method is implemented.

[0027] The above solution adopted by the present invention has the following advantages:

[0028] The insulation impedance detection method of the inverter system based on the auxiliary power supply of the rectifier circuit of the present invention uses the rectifier circuit as the auxiliary power supply circuit of the inverter system to provide low-voltage power for the control and drive components of the power main circuit of the inverter system when only the power grid is connected at night or on cloudy days. In this case, the insulation impedance detection method of the present invention calculates the insulation impedance of the main circuit of the inverter system to the ground by detecting the bus voltage of the inverter system, and can realize normal detection of the insulation impedance when there is a potential relationship between the earth voltage and the main circuit; in addition, by analyzing the circuit, the insulation impedance is calculated based on the system hardware sampling circuit, and there is no need to add additional hardware circuits to monitor the insulation impedance, which can reduce the hardware cost of the system and improve the economy of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0030] Figure 1 The circuit diagram of an inverter system to which the insulation impedance detection method according to an embodiment of the present invention is applied is shown. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Reference Figure 1 As shown, in the inverter system, when the uncontrolled rectified current 2 is used to power the main circuit 3, since the power grid 1 is connected in TN-S mode, the neutral point of the three-phase winding of the distribution transformer is grounded, and there is a potential relationship between the main circuit 3 and the earth. The midpoint potential of the DC voltage after the three-phase voltage is uncontrolled rectified is equal to the potential of the earth. Figure 1 As shown, the output end of the rectifier circuit 2 is connected in series with resistors R1 and R2 to prevent the BUS bus from being short-circuited and causing damage to the rectifier diodes D1 to D6. The rear stage is connected to the DC bus BUS+ and BUS- of the inverter system. The inverter system is powered by the BUS voltage. The system loss equivalent resistance is R load . R iso It is the insulation impedance of the inverter system to ground.

[0033] The inverter system may include a photovoltaic inverter, an energy storage inverter or a photovoltaic storage inverter. The above-mentioned main circuit includes an inverter circuit, a control circuit, etc.

[0034] When the system impedance to ground is infinite, the bus voltage is determined by R load , R1 and R2 are divided to obtain the voltage. For details, please refer to the following relationship (1).

[0035] Relation (1):

[0036]

[0037] In the inverter system, the PV cables may be damaged. At this time, the impedance of the inverter system to the ground is relatively low. Even at night when there is no voltage on the PV panels, the cables of the strings are still connected to the inverter main circuit, which will reduce the impedance of the system to the ground. iso The voltage across R2 is shown in the following equation (2).

[0038] Relation (2):

[0039]

[0040] In the inverter system, the BUS voltage is measurable and can be obtained by sampling. According to Kirchhoff's law, the following relations (3) to (5) can be obtained.

[0041] Relation (3):

[0042]

[0043] Relation (4):

[0044]

[0045] Relation (5):

[0046]

[0047] In the above formula, U bus is the BUS voltage sampling value of the inverter system, R1 and R2 are fixed resistance resistors, U ac is the grid phase voltage, which can be obtained by sampling the inverter system.load Calculated by the following formula:

[0048]

[0049] The insulation resistance of the inverter system is calculated according to equation (5). It can be seen from the equation that the calculation of ISO resistance requires sampling of the BUS voltage. The resistance values ​​of resistors R1 and R2 are stable. For two-phase (U and V phase) input, this method is still applicable.

[0050] Therefore, the insulation impedance detection method of the inverter system based on the rectifier circuit auxiliary power supply of this embodiment includes the following steps:

[0051] Obtaining the resistance value of a first resistor R1 connected in series between the rectifier circuit and the positive DC bus of the inverter system, and obtaining the resistance value of a second resistor R2 connected in series between the rectifier circuit and the negative DC bus of the inverter system;

[0052] Get the power loss P of the inverter system load ;

[0053] The bus voltage U of the inverter system bus Take samples;

[0054] Phase voltage to grid U ac Take samples;

[0055] According to the resistance value of the first resistor R1, the resistance value of the second resistor R2, the power loss P of the inverter system load , bus voltage U bus And grid phase voltage U ac Calculate the insulation resistance of the inverter system to ground. Calculate according to the following formula:

[0056]

[0057] Example:

[0058] Assume that the grid phase voltage U ac At 230Vac, the inverter standby loss P load For 10W, R1=R2=600Ω.

[0059] When the impedance of the entire inverter system to ground is infinite, according to the above relationship (1), the bus satisfies the following relationship:

[0060]

[0061] U bus =541.2V

[0062] When the inverter system is short-circuited to ground, the midpoint V-PE voltage output by the rectifier circuit is equal to the negative bus voltage:

[0063] U PE-PV- =0

[0064] Therefore, according to the above relationship (1), the bus voltage satisfies the following relationship:

[0065]

[0066] U bus =258.5V

[0067] From the above, we can see that when the impedance of the photovoltaic system to ground is infinite and short-circuited, the corresponding BUS voltage is between the normal bus voltage and 1 / 2 of it.

[0068] When the monitored BUS voltage is 530V,

[0069]

[0070] thereby:

[0071]

[0072] When the monitored BUS voltage is 350V,

[0073]

[0074] thereby:

[0075]

[0076] From the above, it can be seen that the lower the impedance of the inverter system to ground, the closer the BUS voltage is to 1 / 2 of the grid rectifier voltage, which verifies the effectiveness of the insulation impedance detection method of this embodiment.

[0077] This embodiment also provides an insulation impedance detection system for an inverter system based on rectifier circuit auxiliary power supply, including a memory and a processor, wherein the memory stores a computer program, and the processor implements the insulation impedance detection method when executing the computer program.

[0078] This embodiment also provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the program is executed by a processor, the insulation impedance detection method is implemented. The computer-readable storage medium includes but is not limited to a read-only memory, a magnetic disk, or an optical disk.

[0079] In this embodiment, in the case where only the power grid is connected at night or on cloudy days, the rectifier circuit is used as an auxiliary power supply circuit of the inverter system to provide low-voltage power for the control and drive components of the power main circuit of the inverter system. In this case, the insulation impedance detection method of this embodiment calculates the insulation impedance of the main circuit of the inverter system to the ground by detecting the bus voltage of the inverter system. When there is a potential relationship between the earth voltage and the main circuit, the normal detection of the insulation impedance can be achieved. In addition, the insulation impedance is calculated based on the system hardware sampling circuit through analysis of the circuit, and there is no need to add additional hardware circuits to monitor the insulation impedance, which can reduce the hardware cost of the system and improve the economy of the product.

[0080] As shown in this specification and claims, the terms "comprises" and "include" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list, and the method or device may also include other steps or elements. The term "and / or" as used herein includes any combination of one or more of the relevant listed items.

[0081] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. If a definition used herein conflicts or is inconsistent with a definition in other public documents, the definition used herein shall prevail.

[0082] As shown in this specification and claims, the terms "comprises" and "include" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list, and the method or device may also include other steps or elements. The term "and / or" as used herein includes any combination of one or more of the relevant listed items.

[0083] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0084] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0085] In addition, each functional unit in the embodiment may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0086] The above embodiment is only for illustrating the technical concept and features of the present invention, and is a preferred embodiment. Its purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting insulation impedance of an inverter system based on a rectifier circuit auxiliary power supply, characterized in that: The steps include: Obtaining a resistance value of a first resistor connected in series between the rectifier circuit and the positive DC bus of the inverter system, and obtaining a resistance value of a second resistor connected in series between the rectifier circuit and the negative DC bus of the inverter system; Obtain the power loss of the inverter system; Sampling the bus voltage of the inverter system; Sampling the grid phase voltage; The insulation impedance of the inverter system to ground is calculated according to the resistance value of the first resistor, the resistance value of the second resistor, the power loss of the inverter system, the bus voltage and the grid phase voltage.

2. The insulation impedance detection method according to claim 1, characterized in that: The loss equivalent resistance is obtained according to the bus voltage and the loss power of the inverter system.

3. The insulation impedance detection method according to claim 2, characterized in that: Obtain the loss equivalent resistance R according to the following formula load : Among them, U bus Indicates bus voltage, P load Represents the power loss of the inverter system, R lodd Represents the loss equivalent resistance of the inverter system.

4. The insulation impedance detection method according to any one of claims 1 to 3, characterized in that: Calculate the insulation resistance R according to the following formula iso : Among them, P load Indicates the inverter system power loss, U bus represents the bus voltage of the inverter system, R1 represents the resistance value of the first resistor, R2 represents the resistance value of the second resistor, and U ac Indicates the grid phase voltage.

5. The insulation impedance detection method according to claim 1, characterized in that: The rectifier circuit includes multiple rectifier diodes, a first resistor is connected in series between the positive output end of the rectifier circuit and the positive DC bus of the main circuit of the inverter system, and a second resistor is connected in series between the negative output end of the rectifier circuit and the negative DC bus of the main circuit, so as to convert the AC power from the power grid into DC power supplied to the main circuit through the rectifier circuit.

6. The insulation impedance detection method according to claim 1, characterized in that: The grid phase voltage is the phase voltage of the three-phase grid.

7. The insulation impedance detection method according to claim 1, characterized in that: The inverter system includes a photovoltaic inverter, an energy storage inverter or a photovoltaic storage inverter.

8. An insulation impedance detection system for an inverter system based on a rectifier circuit auxiliary power supply, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the insulation impedance detection method according to any one of claims 1 to 7 is implemented.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the program is executed by a processor, the insulation impedance detection method according to any one of claims 1 to 7 is implemented.

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