An insulation monitoring system and method for a fuel cell power generation system

Abstract

This invention belongs to the field of insulation monitoring technology and provides an insulation monitoring system and method for a fuel cell power generation system. The system includes an insulation monitor, a protection device, and a grid-connected inverter. The fuel cell module of the fuel cell power generation system is connected to the DC side of the grid-connected inverter, and the AC side of the grid-connected inverter is connected to the low-voltage side of the grid transformer. The insulation monitor is used to detect the insulation impedance of the positive and negative terminals of the DC output of the fuel cell module to ground. The protection device communicates with the insulation monitor and is used to obtain the leakage current of the AC side of the grid-connected inverter. By measuring the insulation impedance or leakage current, it is determined whether a fault has occurred, and corresponding protection is activated and the fault circuit is disconnected when a fault occurs. The grounding terminals of the DC side and AC side of the grid-connected inverter are isolated from each other. This invention realizes the differential detection of insulation impedance and provides comprehensive insulation protection for the fuel cell power generation system.

Description

Technical Field

[0001] This invention belongs to the field of insulation monitoring technology, and specifically relates to an insulation monitoring system and method for a fuel cell power generation system. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Fuel cell power generation is developing rapidly in the field of new energy due to its advantages of high power generation efficiency, adaptability to various fuels and good environmental adaptability. Timely evaluation of the status and performance of fuel cell power generation systems is an important means to ensure power generation quality and safety. Among them, power generation efficiency is a key indicator for evaluating the performance of fuel cell power generation systems, and the use of high-efficiency, non-isolated grid-connected inverters is an important application to ensure high efficiency.

[0004] However, non-isolated grid-connected inverters also bring problems in insulation monitoring. This is because fuel cell power generation systems generally use low-voltage grid connection, while grid-side transformers mostly use neutral-point grounding systems. The DC power supply is coupled to the AC side and grounded through the non-isolated inverter, which makes it extremely difficult to detect the difference in insulation impedance. Summary of the Invention

[0005] To address the crosstalk problem in insulation monitoring of non-isolated grid-connected power generation systems, this invention proposes an insulation monitoring system and method for fuel cell power generation systems. The separation of DC ground and AC ground in this invention reduces leakage current and enables targeted phase-to-shell insulation monitoring of fuel cell modules. At the same time, the application of AC side leakage current transformers provides comprehensive insulation protection for the fuel cell power generation system.

[0006] According to some embodiments, the present invention adopts the following technical solution: In a first aspect, an insulation monitoring system for a fuel cell power generation system is provided, which is applied to the fuel cell power generation system and includes an insulation monitor, a protection device, and a grid-connected inverter, wherein: The fuel cell module of the fuel cell power generation system is connected to the DC side of the grid-connected inverter, and the AC side of the grid-connected inverter is connected to the low-voltage side of the grid transformer to transmit electrical energy to the grid. The insulation monitoring instrument is used to detect the insulation resistance of the positive and negative DC terminals of the fuel cell module to ground. The protection device communicates with the insulation monitoring instrument to obtain the AC side leakage current of the grid-connected inverter. It determines whether a fault has occurred based on the insulation impedance or leakage current, and activates the corresponding protection to disconnect the fault circuit when a fault occurs. The grounding terminals of the DC side and AC side of the grid-connected inverter are isolated from each other.

[0007] In the above scheme, by adopting the measure of separating DC ground and AC ground, i.e. creating a DC virtual ground, the phase-shell targeted detection of the fuel cell module can be realized, and the insulation impedance can be detected differently. In addition, by using DC insulation detection and AC leakage current detection, DC and AC insulation can be monitored simultaneously, so that the fuel cell power generation system can achieve comprehensive insulation protection.

[0008] As an alternative implementation, the grounding terminals of the DC side and AC side of the grid-connected inverter are isolated from each other in the following way: the insulation monitoring instrument, protection device and grid-connected inverter are all installed in the same cabinet as the fuel cell module, and the insulation monitoring instrument uses the outer shell of the fuel cell module as the reference ground; The cabinet is connected to the protective conductor, which is connected to the power grid grounding terminal. The outer casing of the fuel cell module is electrically isolated from the cabinet, thus isolating the reference ground of the insulation monitoring instrument from the power grid grounding terminal.

[0009] As an alternative implementation, the insulation monitoring instrument uses a low-frequency signal injection method for detection, injecting AC power signals into the positive and negative terminals of the DC bus respectively, and determining the circuit insulation impedance by the voltage-current ratio.

[0010] As an alternative implementation, the insulation monitoring instrument calculates the insulation impedance by applying a low-frequency AC voltage and measuring a low-frequency AC current.

[0011] As an alternative implementation, the AC side of the grid-connected inverter is provided with a leakage current transformer, which passes through the three-phase four-wire AC power grid.

[0012] As a further defined embodiment, the protection device is connected to the leakage current transformer to obtain the induced current on the secondary side of the leakage current transformer.

[0013] As a further defined implementation, the protection device is configured to trigger when the induced current on the secondary side of the leakage current transformer exceeds a set threshold, determine the fault type, and execute corresponding protection actions.

[0014] As a further defined implementation, the protection device is also configured to trigger and perform corresponding protection actions when the insulation impedance exceeds a threshold.

[0015] As an alternative implementation, the grid-connected inverter is a non-isolated grid-connected inverter.

[0016] Secondly, an insulation monitoring method for a fuel cell power generation system is provided, which, when applied to the above system, includes the following steps: The grounding terminals of the DC side and AC side of the grid-connected inverter are isolated from each other. The insulation monitoring instrument is used to detect the insulation resistance of the positive and negative DC output terminals of the fuel cell module to ground. The protection device is used to detect the leakage current of the AC side of the grid-connected inverter. Based on the insulation resistance or leakage current, it is determined whether an insulation or grounding fault has occurred, and the corresponding protection is activated and the fault circuit is disconnected when a fault occurs.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention addresses the crosstalk problem in insulation monitoring of non-isolated grid-connected power generation systems. It employs separate DC and AC grounds to reduce leakage current and enables targeted "phase-to-shell" insulation monitoring of fuel cell modules. Simultaneously, the application of AC-side leakage current transformers provides comprehensive insulation protection for the fuel cell power generation system.

[0018] This invention employs a combination of DC insulation monitoring and AC leakage current alarm. The protection device monitors both the DC and AC sides. The DC insulation monitor injects low-frequency AC signals into the positive and negative terminals of the DC bus. When the insulation between the positive and negative terminals and the fuel cell module casing and its connecting metal parts decreases or is damaged, the insulation monitor calculates the insulation impedance or leakage current exceeding the threshold by applying a low-frequency AC voltage and measuring the low-frequency AC current, thereby triggering an alarm and protection action. When insulation decreases or a single-phase ground fault occurs on the AC side, the leakage current transformer detects the core current vector and judges the insulation fault, triggering the protection device to operate.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a structural diagram of an insulation monitoring system according to one embodiment.

[0022] The components include: 1. Generator cabinet; 2. Grid-connected inverter; 3. Protection device; 4. Insulation monitoring instrument; and 5. Fuel cell module. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] Where there is no conflict, the embodiments and features described in this application may be combined with each other.

[0027] Example 1 An insulation monitoring system for a fuel cell power generation system, such as Figure 1 As shown, this is applied to a fuel cell power generation system, including an insulation monitor 4, a protection device 3, and a grid-connected inverter 2, wherein: The fuel cell module 5 of the fuel cell power generation system is connected to the DC side of the grid-connected inverter 2, and the AC side of the grid-connected inverter 2 is connected to the low-voltage side of the grid transformer to transmit electrical energy to the grid. The insulation monitoring instrument 4 is used to detect the insulation resistance of the positive and negative DC terminals of the fuel cell module 5 to ground. The protection device 3 communicates with the insulation monitoring instrument 4 to obtain the AC side leakage current of the grid-connected inverter 2. It determines whether a fault has occurred based on the insulation impedance or leakage current, and activates the corresponding protection to disconnect the fault circuit when a fault occurs. The grounding terminals of the DC side and AC side of the grid-connected inverter 2 are isolated from each other.

[0028] Here, we will also introduce the functions and necessity of each part of the system.

[0029] Fuel cell module 5 is a chemical device that directly converts the chemical energy of fuels such as natural gas or hydrogen into electrical energy.

[0030] In this embodiment, the insulation monitoring instrument 4 refers to a device that monitors the insulation impedance of the positive and negative DC terminals of the fuel cell to ground in real time. The insulation monitoring instrument 4 uses a low-frequency signal injection method for detection, that is, injecting AC power signals into the positive and negative terminals of the DC bus respectively, and determining the circuit insulation impedance by the voltage-current ratio.

[0031] Grid-connected inverter 2 converts the direct current generated by the fuel cell into alternating current for grid-connected power generation. In this embodiment, a non-isolated grid-connected inverter is used to improve the overall system efficiency.

[0032] Protection device 3 communicates with insulation monitoring instrument 4 and collects the secondary current of the AC side leakage current transformer of the inverter to determine whether the system has experienced insulation degradation, insulation failure or other faults, and activates the corresponding protection equipment to disconnect the fault circuit in time when a fault occurs.

[0033] A grid transformer is used to convert 35kV or 10kV high-voltage electricity from the power grid into nominal 380V low-voltage AC electricity. Simultaneously, fuel cell power generation systems transmit electrical energy to the grid via grid transformers.

[0034] In this embodiment, all of the above-mentioned components can be selected from existing equipment or devices, and the specific structure and model are not limited or described in detail here.

[0035] In this embodiment, the grounding terminals of the DC and AC sides of the grid-connected inverter 2 are isolated from each other. This can be achieved by having the insulation monitor 4, protection device 3, and the grid-connected inverter 2 and fuel cell module 5 housed in the same cabinet (in this embodiment, generator cabinet 1). The insulation monitor 4 uses the outer casing of the fuel cell module 5 as its reference ground. One end of the cabinet is connected to the protective conductor (PE), and the other end of the protective conductor is connected to the grounding terminal of the power grid. The outer casing of the fuel cell module 5 is electrically isolated from the cabinet, thus isolating the reference ground of the insulation monitor 4 from the power grid grounding terminal.

[0036] When the signal source Us in the insulation monitor 4 injects a low-frequency AC signal into the DC bus, the signal will not be coupled to the AC side grounding terminal through the non-isolated inverter to form a loop because the grid ground and the reference ground of the insulation monitor 4 are isolated. Therefore, it will not affect the insulation impedance measurement on the DC side.

[0037] A leakage current transformer is installed on the AC side of the grid-connected inverter 2, and the transformer passes through the three-phase four-wire AC circuit. When there is an AC ground fault, the vector sum of the three-phase four-wire currents is greater than zero, generating an induced current on the secondary side of the transformer. When the induced current exceeds the threshold, the protection device 3 is triggered to operate.

[0038] During normal system operation, both the DC and AC sides are monitored. The DC side insulation monitor 4 injects low-frequency AC signals into the positive and negative terminals of the DC bus. When the insulation between the positive and negative terminals and the outer casing and connecting metal parts of the fuel cell module 5 decreases or is damaged, the insulation monitor 4 calculates the insulation resistance or leakage current exceeding the threshold by applying a low-frequency AC voltage and measuring the low-frequency AC current, thereby triggering the protection device 3 to alarm and perform protection actions.

[0039] When insulation degradation or single-phase grounding fault occurs on the AC side, the leakage current transformer detects the core current vector and determines the insulation fault, triggering the protection device 3 to operate.

[0040] In this embodiment, the processes of calculating insulation impedance, setting threshold, and setting threshold can all be determined using existing technology or based on experience, and will not be elaborated here.

[0041] Example 2 An insulation monitoring method for a fuel cell power generation system, using the system provided in Example 1, includes the following steps: The grounding terminals of the DC side and AC side of the grid-connected inverter 2 are isolated from each other. The insulation monitoring instrument 4 is used to detect the insulation resistance of the positive and negative DC terminals of the fuel cell module 5 to ground. The protection device 3 is used to detect the leakage current of the AC side of the grid-connected inverter 2. Based on the insulation resistance or leakage current, it is determined whether an insulation or grounding fault has occurred, and the corresponding protection is activated and the fault circuit is disconnected when a fault occurs.

[0042] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of one or more computer-usable storage media (including, but not limited to, disk storage, etc.) containing computer-usable program code. CD - ROM It takes the form of a computer program product implemented on (such as optical memory, etc.).

[0043] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0044] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxesFigure 1 The function specified in one or more boxes.

[0045] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art without creative effort within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An insulation monitoring system for a fuel cell power generation system, applied to a fuel cell power generation system, characterized in that, It includes an insulation monitoring device (4), a protection device (3), and a grid-connected inverter (2), wherein: The fuel cell module (5) of the fuel cell power generation system is connected to the DC side of the grid-connected inverter (2), and the AC side of the grid-connected inverter (2) is connected to the low-voltage side of the grid transformer to transmit electrical energy to the grid. The insulation monitoring instrument (4) is used to detect the insulation resistance of the positive and negative DC terminals of the fuel cell module (5) to ground. The protection device (3) communicates with the insulation monitoring instrument (4) to obtain the AC side leakage current of the grid-connected inverter (2), and determines whether a fault has occurred by the insulation impedance or leakage current, and starts the corresponding protection and disconnects the fault circuit when a fault occurs. The grounding terminals of the DC side and AC side of the grid-connected inverter (2) are isolated from each other.

2. The insulation monitoring system for a fuel cell power generation system as described in claim 1, characterized in that, The scheme to isolate the grounding terminals of the DC side and AC side of the grid-connected inverter (2) is as follows: the insulation monitoring instrument (4), the protection device (3) and the grid-connected inverter (2) are all installed in the same cabinet as the fuel cell module (5), and the insulation monitoring instrument (4) takes the outer shell of the fuel cell module (5) as the reference ground. The cabinet is connected to the protective conductor, the protective conductor is connected to the power grid grounding terminal, and the outer shell of the fuel cell module (5) is electrically isolated from the cabinet, so that the reference ground of the insulation monitoring instrument (4) is isolated from the power grid grounding terminal.

3. The insulation monitoring system for a fuel cell power generation system as described in claim 1, characterized in that, The insulation monitoring instrument (4) uses a low-frequency signal injection method for detection, injecting AC power signals into the positive and negative poles of the DC bus respectively, and determining the circuit insulation impedance by the voltage-current ratio.

4. The insulation monitoring system for a fuel cell power generation system as described in claim 1, characterized in that, The insulation monitoring instrument (4) calculates the insulation impedance by applying a low-frequency AC voltage and measuring a low-frequency AC current.

5. The insulation monitoring system for a fuel cell power generation system as described in claim 1, characterized in that, The grid-connected inverter (2) is equipped with a leakage current transformer on the AC side, and the leakage current transformer passes through the AC three-phase four-wire grid.

6. The insulation monitoring system for a fuel cell power generation system as described in claim 5, characterized in that, The protection device (3) is connected to the leakage current transformer to obtain the induced current on the secondary side of the leakage current transformer.

7. The insulation monitoring system for a fuel cell power generation system as described in claim 1, characterized in that, The protection device (3) is configured to be triggered when the induced current on the secondary side of the leakage current transformer exceeds a set threshold, to determine the fault type, and to perform corresponding protection actions.

8. The insulation monitoring system for a fuel cell power generation system as described in claim 4, characterized in that, The protection device (3) is configured to be triggered when the insulation impedance exceeds a threshold, and to perform a corresponding protection action.

9. The insulation monitoring system for a fuel cell power generation system as described in claim 1, characterized in that, The grid-connected inverter (2) is a non-isolated grid-connected inverter.

10. An insulation monitoring method for a fuel cell power generation system, using the system according to any one of claims 1-9, characterized in that, Includes the following steps: The grounding terminals of the DC side and AC side of the grid-connected inverter (2) are isolated from each other. The insulation monitoring instrument (4) is used to detect the insulation resistance of the positive and negative DC terminals of the fuel cell module (5) to ground. The protection device (3) is used to detect the leakage current of the AC side of the grid-connected inverter (2). Based on the insulation resistance or leakage current, it is determined whether an insulation or grounding fault has occurred, and the corresponding protection is activated and the fault circuit is disconnected when a fault occurs.

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