Method and system for evaluating reliability of dc / dc converter of dc collection system of wind farm considering influence of control strategy

Abstract

This invention relates to a method and system for reliability assessment of DC / DC converters in wind farm DC aggregation systems, comprising the following steps: Step 1, based on the control strategy and operating conditions of the DC / DC converter in the wind farm DC aggregation system, proposing a device-level reliability prediction model for the DC / DC converter; Step 2, based on the BFBIC submodule structure of the DC / DC converter, proposing a submodule-level reliability model for the DC / DC converter; Step 3, based on the hybrid two-level modular structure of the DC / DC converter, proposing a device-level reliability model for the DC / DC converter; Step 4, comparing and analyzing the differences and reasons for the reliability assessment results of the DC / DC converter when considering and not considering the influence of the control strategy. This invention is more applicable to the reliability assessment of DC / DC converters in wind farm DC aggregation systems, improving the reliability assessment results and providing data support for the reliability assessment of wind farm DC aggregation systems.

Description

Technical Field

[0001] This invention belongs to the technical field of DC / DC converter reliability assessment for wind farm DC collection systems, and specifically relates to a method and system for reliability assessment of DC / DC converters in wind farm DC collection systems that takes into account the influence of control strategies. Background Technology

[0002] With the vigorous development of the wind power industry, research on efficient wind power collection is crucial. Currently, wind farms use AC technology to collect electrical energy. While this method is mature and widely used, it suffers from problems such as harmonic resonance and reactive power compensation. To alleviate these issues, DC collection technology for wind farms has attracted widespread attention from scholars both domestically and internationally. A wind farm DC collection system boosts the low-voltage DC output from DC-output wind turbines via a DC / DC converter, then collects and connects it to the grid via a medium-voltage DC line. This technology avoids multiple AC / DC conversions, simplifies the entire process from power generation to grid connection, reduces losses, and lowers system investment, giving it certain development advantages. The DC / DC converter, as a key component in the wind farm DC collection system, is characterized by its small size, light weight, and large transmission capacity, making it a current research hotspot. However, the use of DC / DC converters can also reduce system reliability; therefore, evaluating the reliability of DC / DC converters is of great significance to the research on the reliability of wind farm DC collection systems.

[0003] Currently, high-power, high-ratio DC / DC converters are still in the research and testing phase and have not yet been widely applied in practical engineering. Therefore, research on their reliability is limited. Only scholars have conducted reliability modeling for DAB-type DC / DC converters, considering factors such as operating conditions, submodule redundancy, and correlation. However, DAB-type DC / DC converters have a large number of IGBT modules and high costs, making reliability assessments necessary for DC / DC converters with other topologies. Furthermore, the aforementioned research on DC / DC converter reliability is all based on DC distribution networks, lacking research on the reliability of DC / DC converters in wind farm DC aggregation systems. Additionally, the impact of control strategies has not been considered in the reliability modeling process, and the assessment results need improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a reliability assessment method and system for DC / DC converters in wind farm DC aggregation systems that takes into account the influence of control strategies. This addresses the problem that traditional DC / DC converter reliability assessment methods cannot be fully applied to the reliability assessment of DC / DC converters in wind farm DC aggregation systems, improves the reliability assessment results, and provides data support for the reliability assessment of wind farm DC aggregation systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: Reliability assessment methods for DC / DC converters in wind farm DC collection systems, considering the impact of control strategies, include: Based on the control strategy and operating conditions of the DC / DC converter in the DC collection system of the wind farm, a device-level reliability prediction model for the DC / DC converter is established using an evaluation method based on failure mechanism. Based on the BFBIC submodule topology of the DC / DC converter, a submodule-level reliability model of the DC / DC converter is established using the fault tree method. Based on the hybrid two-stage modular DC / D converter structure, a device-level reliability model for the DC / DC converter is established using the fault tree method. Compare and analyze the differences and reasons for the reliability assessment results of DC / DC converters under the two cases of considering the impact of control strategies and not considering the impact of control strategies.

[0006] Furthermore, considering the control strategy and operating conditions of the DC / DC converter in the wind farm DC collection system, the steps for establishing a device-level reliability prediction model for the DC / DC converter using a failure mechanism-based evaluation method are as follows: Step 1: Establish the power loss model of the IGBT module based on the control strategy and operating conditions of the DC / DC converter. The specific calculations are as follows: The power loss of an IGBT module mainly includes the on-state loss and switching loss of the IGBT, as well as the on-state loss and turn-off loss of the FWD.

[0007] (1) IGBT on-state loss

[0008] In the formula , V ce For saturation pressure drop, i c It is the on-state current. T j_T The junction temperature is the IGBT temperature. This relationship can be obtained by fitting the IGBT's output characteristic curve. D This refers to the duty cycle of the IGBT control signal.

[0009] The duty cycle in the above formula is usually... D The duty cycle is usually a constant or calculated based on the modulation method. However, in actual operation, the duty cycle... D The duty cycle will also fluctuate due to the control strategy of the DC / DC converter, requiring further calculation using the transfer function of the corresponding control strategy. The duty cycle can be obtained by performing an inverse Laplace transform on the transfer function of the control strategy used by the DC / DC converter. DThe time-domain expression is obtained, and then substituted into the above formula to obtain the on-state loss of the corrected IGBT module.

[0010] (2) IGBT switching losses

[0011] In the formula, f sw For switching frequency, E on and E off These represent the energy losses during IGBT turn-on and turn-off, respectively. U dc and i c For the operating voltage and current of the IGBT module, U N and i N For rated voltage and current, K ET This is the temperature correction factor for switching energy loss.

[0012] (3) IGBT power loss

[0013] (4) FWD on-state loss

[0014] In the formula T j_D This is the FWD junction temperature. Similarly, the duty cycle will be considered in relation to the control strategy. D Substituting the expression into the expression yields the corrected on-state loss of the FWD.

[0015] (5) FWD turn-off loss

[0016] In the formula, E rec For the reverse recovery loss of FWD, K ED The temperature coefficient for shutting off energy loss.

[0017] (6) FWD power loss

[0018] Step 2: Based on the IGBT module structure and power loss model, establish a thermal network model to obtain its junction temperature fluctuation curve, and use the rainflow algorithm to obtain the average junction temperature of the IGBT module. T m Junction temperature fluctuation amplitude ΔTj The specific steps are as follows: (Identification of features, etc.) (1) The junction temperature of the IGBT module is calculated using the Foster thermal network model. The thermal parameters are converted into electrical parameters through thermoelectric analogy theory. Then, the problems in the thermal network are solved through electrical network theory. The conversion relationship between thermal and electrical parameters is shown in Table 1 below.

[0019] Table 1. Values ​​Corresponding to Indicator Evaluation Levels

[0020] In Foster thermal networking, the chip-case thermal network of the IGBT module is equivalent to a fourth-order RC network, while the case-heat sink and heat sink-environment networks are represented by first-order RC networks. This allows us to obtain the thermal impedance of the IGBT and its equivalent thermal network. Furthermore, the junction temperature expressions for the IGBT and FWD can be derived as follows:

[0021]

[0022] In the formula, T a The ambient temperature.

[0023] (2) The measured junction temperature change curve is decomposed into multiple cycle stages by rainflow algorithm, and the junction temperature change amplitude and average value of each cycle are recorded, thereby providing the required parameters for IGBT module life prediction.

[0024] Step 3: Using the Coffin-Manson-Arrheniu lifetime prediction analytical model, which has high reliability assessment accuracy and whose model parameters are relatively easy to obtain, the mean junction temperature and junction temperature fluctuation amplitude obtained in Step 2 are substituted into the selected model to calculate its lifetime. N f :

[0025] In the formula, ΔT j Indicates the junction temperature difference amplitude. T m Indicates the average junction temperature. N f Indicates working condition ΔT j and T m Total number of failure cycles under the following conditions α , β For device-related parameters, E a To activate energy, K B is the Boltzmann constant.

[0026] Step 4: Based on the predicted lifespan, and using the cycle count obtained from rainflow counting under different operating conditions, a linear fatigue damage accumulation model is employed to calculate the failure rate of the IGBT module. The calculation formula is:

[0027] In the formula, N i For specific working conditions i The number of loops.

[0028] Furthermore, based on the BFBIC submodule topology of the DC / DC converter, the steps for establishing a submodule-level reliability model of the DC / DC converter using the fault tree method are as follows: Step 1: Identify the most serious possible fault in the BFBIC submodule of the DC / DC converter, i.e., submodule failure; Step 2: Based on the BFBIC submodule topology, determine the logical relationship between the faults of each component and the faults of the submodule; Step 3: Establish the corresponding BFBIC submodule fault tree based on the logical relationships determined in Step 2; Step 4: Quantitative analysis, calculate the failure rate and repair rate of the BFBIC submodule based on the fault tree.

[0029]

[0030]

[0031] In the formula, The failure rates are for individual bridge arm IGBT modules, capacitors, inductors, FWD, transformers, and clamping IGBT modules within the submodule, respectively. I , J , L , M These represent the number of IGBT modules, capacitors, inductors, and FWDs in the bridge arm of the submodule. T IGBT , T C , T L , T FWD , T T The average repair time is for IGBT modules, capacitors, inductors, transformers, and FWD, respectively.

[0032] Furthermore, considering the hybrid two-stage modular DC / D converter structure, the steps for establishing a device-level reliability model of the DC / DC converter using the fault tree method are as follows: Step 1: Identify the most serious possible failure of the entire DC / DC converter device, i.e., DC / DC converter failure; Step 2: Based on the hybrid two-stage modular DC / DC converter structure, determine the logical relationship between each sub-module fault and the DC / DC converter fault; Step 3: Establish the corresponding DC / DC converter fault tree based on the logical relationships determined in Step 2; Step 4: Quantitative analysis, calculate the failure rate and repair rate of the IPOS module in the DC / DC converter with and without redundancy based on the fault tree.

[0033] The failure rates of the IPOS module with and without redundancy are as follows:

[0034]

[0035] The repair rate for the IPOS module is:

[0036] In the formula, n This represents the number of BFBIC submodules in the IPOS module.

[0037] Step 5: Calculate the failure rate and repair rate of the DC / DC converter based on the fault tree.

[0038]

[0039]

[0040] In the formula, N This represents the number of IPOS modules in the IPOP structure.

[0041] Furthermore, we compare and analyze the differences and reasons for the reliability assessment results of DC / DC converters under the two cases of considering the impact of control strategies and not considering the impact of control strategies.

[0042] Step 1: Based on the calculated failure rate and repair rate of the DC / DC converter, the mean time between failures (MTBF), mean time to repair (MTTR), and reliability function are used as reliability indicators to evaluate its reliability. The specific expressions are as follows: (1) Mean time between failures:

[0043] In the formula, MTTFMean time between failures (MTBF) is the average operating time before failure, and its value is the reciprocal of the failure rate.

[0044] (2) Mean repair time:

[0045] (3) Reliability:

[0046] In the formula, t For runtime, R DC / DC ( t ) represents the reliability of the DC / DC converter, ranging from (0,1).

[0047] Step 2: Based on the DC / DC converter under two cases: considering the impact of control strategy and not considering the impact of control strategy. MBTF and MTTR The values ​​of the reliability function and the changing trends of the reliability function are analyzed to identify the differences and reasons for the reliability assessment results of the DC / DC converter.

[0048] Furthermore, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for reliability assessment of a wind farm DC-DC converter considering the influence of control strategies.

[0049] Furthermore, a computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the reliability assessment method for a wind farm DC-DC converter considering the influence of control strategies.

[0050] Compared with the prior art, the present invention has the following technical effects: Based on the BFBIC type DC / DC converter topology, this invention proposes a method for evaluating the reliability of DC / DC converters under the influence of control strategies and operating conditions in wind farm DC collection systems. Attached Figure Description

[0051] Figure 1 This is a graph showing the power loss variation of the IGBT module of the present invention.

[0052] Figure 2 This is a control block diagram of the constant voltage control of the DC / DC converter of the present invention.

[0053] Figure 3 This is the Foster thermal network model of the IGBT module of the present invention.

[0054] Figure 4 This is a curve showing the junction temperature fluctuation of the IGBT module of the present invention.

[0055] Figure 5 This is the fault tree model of the BFBIC submodule of the present invention.

[0056] Figure 6 This is the DC / DC converter fault tree model of the present invention.

[0057] Figure 7 This is a reliability curve of the DC / DC converter considering and not considering the influence of the control strategy according to the present invention. Detailed Implementation

[0058] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0059] Reliability assessment methods for DC / DC converters in wind farm DC collection systems, considering the impact of control strategies, include: Based on the control strategy and operating conditions of the DC / DC converter in the DC collection system of the wind farm, a device-level reliability prediction model for the DC / DC converter is established using an evaluation method based on failure mechanism. Based on the BFBIC submodule topology of the DC / DC converter, a submodule-level reliability model of the DC / DC converter is established using the fault tree method. Based on the hybrid two-stage modular DC / D converter structure, a device-level reliability model for the DC / DC converter is established using the fault tree method. Compare and analyze the differences and reasons for the reliability assessment results of DC / DC converters under the two cases of considering the impact of control strategies and not considering the impact of control strategies.

[0060] Furthermore, considering the control strategy and operating conditions of the DC / DC converter in the wind farm DC collection system, the steps for establishing a device-level reliability prediction model for the DC / DC converter using a failure mechanism-based evaluation method are as follows: Step 1: Establish a power loss model for the IGBT module based on the control strategy and operating conditions of the DC / DC converter. The specific calculations are as follows, and the resulting IGBT module losses are shown in the figure. Figure 1 : The power loss of an IGBT module mainly includes the on-state loss and switching loss of the IGBT, as well as the on-state loss and turn-off loss of the FWD.

[0061] (1) IGBT on-state loss

[0062] In the formula , V ce For saturation pressure drop, i c It is the on-state current. T j_T The junction temperature is the IGBT temperature. This relationship can be obtained by fitting the IGBT's output characteristic curve. D This refers to the duty cycle of the IGBT control signal.

[0063] The duty cycle in the above formula is usually... D The duty cycle is usually a constant or calculated based on the modulation method. However, in actual operation, the duty cycle... D The voltage will also fluctuate continuously due to the control strategy of the DC / DC converter, requiring further calculation using the transfer function of the corresponding control strategy. This example uses a constant voltage control method for the DC / DC converter. The block diagram of the constant voltage control strategy is shown below. Figure 2 As shown, its transfer function and duty cycle after inverse Laplace transform D The time-domain expression is as follows, and then substituting it into the above equation yields the corrected on-state loss of the IGBT module.

[0064] Constant voltage control transfer function:

[0065] In the formula, This is the difference between the input DC voltage and the reference voltage. These are the parameters for the PI controller.

[0066] Duty cycle time-domain expression:

[0067] (2) IGBT switching losses

[0068] In the formula, f sw For switching frequency, E on and E off These represent the energy losses during IGBT turn-on and turn-off, respectively. U dc and i c For the operating voltage and current of the IGBT module, U N and i N For rated voltage and current, KET This is the temperature correction factor for switching energy loss.

[0069] (3) IGBT power loss

[0070] (4) FWD on-state loss

[0071] In the formula T j_D This is the FWD junction temperature. Similarly, the duty cycle will be considered in relation to the control strategy. D Substituting the expression into the expression yields the corrected on-state loss of the FWD.

[0072] (5) FWD turn-off loss

[0073] In the formula, E rec For the reverse recovery loss of FWD, K ED The temperature coefficient for shutting off energy loss.

[0074] (6) FWD power loss

[0075] Step 2: Based on the IGBT module structure and power loss model, establish a thermal network model to obtain its junction temperature fluctuation curve, and use the rainflow algorithm to obtain the average junction temperature of the IGBT module. T m Junction temperature fluctuation amplitude ΔT j The specific steps are as follows: (Identification of features, etc.) (1) The junction temperature of the IGBT module is calculated using the Foster thermal network model. The thermal parameters are converted into electrical parameters through thermoelectric analogy theory. Then, the problems in the thermal network are solved through electrical network theory. The conversion relationship between thermal and electrical parameters is shown in Table 1 below.

[0076] Table 1. Values ​​Corresponding to Indicator Evaluation Levels

[0077] In Foster thermal networking, the chip-case thermal network of the IGBT module is equivalent to a fourth-order RC network, while the case-heat sink and heat sink-environment networks use first-order RC networks. This allows us to obtain the IGBT's thermal resistance and equivalent thermal network, as shown below. Figure 3 Furthermore, the junction temperature expressions for IGBT and FWD can be obtained as follows:

[0078]

[0079] In the formula, T a The ambient temperature.

[0080] The junction temperature change curve of the IGBT module is obtained based on the above steps, as shown below. Figure 4 .

[0081] (2) The measured junction temperature change curve is decomposed into multiple cycle stages by rainflow algorithm, and the junction temperature change amplitude and average value of each cycle are recorded, thereby providing the required parameters for IGBT module life prediction.

[0082] Step 3: Using the Coffin-Manson-Arrheniu lifetime prediction analytical model, which has high reliability assessment accuracy and whose model parameters are relatively easy to obtain, the mean junction temperature and junction temperature fluctuation amplitude obtained in Step 2 are substituted into the selected model to calculate its lifetime. N f :

[0083] In the formula, ΔT j Indicates the junction temperature difference amplitude. T m Indicates the average junction temperature. N f Indicates working condition ΔT j and T m Total number of failure cycles under the following conditions α , β For device-related parameters, E a To activate energy, K B is the Boltzmann constant.

[0084] Step 4: Based on the predicted lifespan, and according to the cycle count obtained from rainflow counting under different operating conditions, a linear fatigue damage accumulation model is used to calculate the failure rate of the IGBT module. The results are shown in Table 2. The calculation formula is:

[0085] In the formula, N i For specific working conditions i The number of loops.

[0086] Table 2 IGBT module lifespan and failure rate

[0087] Furthermore, based on the BFBIC submodule topology of the DC / DC converter, the steps for establishing a submodule-level reliability model of the DC / DC converter using the fault tree method are as follows: Step 1: Identify the most serious possible fault in the BFBIC submodule of the DC / DC converter, i.e., submodule failure; Step 2: Based on the BFBIC submodule topology, determine the logical relationship between the faults of each component and the faults of the submodule; Step 3: Based on the logical relationships determined in Step 2, establish the corresponding BFBIC submodule fault tree, such as... Figure 5 As shown; Step 4: Quantitative analysis, calculate the failure rate and repair rate of the BFBIC submodule based on the fault tree.

[0088]

[0089]

[0090] In the formula, The failure rates are for individual bridge arm IGBT modules, capacitors, inductors, FWD, transformers, and clamping IGBT modules within the submodule, respectively. I , J , L , M These represent the number of IGBT modules, capacitors, inductors, and FWDs in the bridge arm of the submodule. T IGBT , T C , T L , T FWD , T T The average repair time is for IGBT modules, capacitors, inductors, transformers, and FWD, respectively.

[0091] Furthermore, considering the hybrid two-stage modular DC / D converter structure, the steps for establishing a device-level reliability model of the DC / DC converter using the fault tree method are as follows: Step 1: Identify the most serious possible failure of the entire DC / DC converter device, i.e., DC / DC converter failure; Step 2: Based on the hybrid two-stage modular DC / DC converter structure, determine the logical relationship between each sub-module fault and the DC / DC converter fault; Step 3: Based on the logical relationships determined in Step 2, establish the corresponding DC / DC converter fault tree, such as... Figure 6 ; Step 4: Quantitative analysis, calculate the failure rate and repair rate of the IPOS module in the DC / DC converter with and without redundancy based on the fault tree.

[0092] The failure rates of the IPOS module with and without redundancy are as follows:

[0093]

[0094] The repair rate for the IPOS module is:

[0095] In the formula, n This represents the number of BFBIC submodules in the IPOS module.

[0096] Step 5: Calculate the failure rate and repair rate of the DC / DC converter based on the fault tree.

[0097]

[0098]

[0099] In the formula, N This represents the number of IPOS modules in the IPOP structure.

[0100] Furthermore, we compare and analyze the differences and reasons for the reliability assessment results of DC / DC converters under the two cases of considering the impact of control strategies and not considering the impact of control strategies.

[0101] Step 1: Based on the calculated failure rate and repair rate of the DC / DC converter, the mean time between failures (MTBF), mean time to repair (MTTR), and reliability function are used as reliability indicators to evaluate its reliability. The specific expressions are as follows: (1) Mean time between failures:

[0102] In the formula, MTTF Mean time between failures (MTBF) is the average operating time before failure, and its value is the reciprocal of the failure rate.

[0103] (2) Mean repair time:

[0104] (3) Reliability:

[0105] In the formula,t For runtime, R DC / DC ( t ) represents the reliability of the DC / DC converter, ranging from (0,1).

[0106] The reliability index calculation results are shown in Table 3 and 3 respectively. Figure 7 As shown.

[0107] Table 3 Calculation Results of DC / DC Converter Reliability Indicators

[0108] Step 2: Based on the DC / DC converter under two cases: considering the impact of control strategy and not considering the impact of control strategy. MBTF and MTTR The values ​​of the reliability function and the changing trends of the reliability function are analyzed to identify the differences and reasons for the reliability assessment results of the DC / DC converter.

[0109] Furthermore, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for reliability assessment of a wind farm DC-DC converter considering the influence of control strategies.

[0110] Furthermore, a computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the reliability assessment method for a wind farm DC-DC converter considering the influence of control strategies.

[0111] Compared with the prior art, the present invention has the following technical effects: Based on the BFBIC type DC / DC converter topology, this invention proposes a method for evaluating the reliability of DC / DC converters under the influence of control strategies and operating conditions in wind farm DC collection systems.

[0112] In one embodiment of the present invention, a computer device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions from the computer storage medium to achieve a corresponding method flow or corresponding function. The processor described in this embodiment of the present invention can be used in the operation of a reliability assessment method for DC / DC converters in wind farm DC collection systems that considers the impact of control strategies.

[0113] In one embodiment of the present invention, a storage medium is also provided, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the operating system of the terminal. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the reliability assessment method for the DC / DC converter of a wind farm DC collection system considering the influence of control strategies in the above embodiments.

[0114] 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 a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0115] 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.

[0116] 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 boxes Figure 1 The function specified in one or more boxes.

[0117] 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.

[0118] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A reliability assessment method for DC / DC converters in wind farm DC collection systems considering the impact of control strategies, characterized in that, include: Based on the control strategy and operating conditions of the DC / DC converter in the DC collection system of the wind farm, a device-level reliability prediction model for the DC / DC converter is established using an evaluation method based on failure mechanism. Based on the BFBIC submodule topology of the DC / DC converter, a submodule-level reliability model of the DC / DC converter is established using the fault tree method. Based on the hybrid two-stage modular DC / D converter structure, a device-level reliability model for the DC / DC converter is established using the fault tree method. Compare and analyze the differences and reasons for the reliability assessment results of DC / DC converters under the two cases of considering the impact of control strategies and not considering the impact of control strategies; Based on the control strategy and operating conditions of the DC / DC converter in the DC collection system of the wind farm, the steps to establish a device-level reliability prediction model for the DC / DC converter using an evaluation method based on failure mechanisms are as follows: Step 1: Establish the power loss model of the IGBT module based on the control strategy and operating conditions of the DC / DC converter. The specific calculations are as follows: The power loss of an IGBT module mainly includes the on-state loss and switching loss of the IGBT, as well as the on-state loss and turn-off loss of the FWD. (1) IGBT on-state loss In the formula , V ce For saturation pressure drop, i c For the on-state current, T j_T The junction temperature is the IGBT temperature. This relationship can be obtained by fitting the IGBT's output characteristic curve. D The duty cycle of the IGBT control signal; The duty cycle in the above formula is usually... D The duty cycle is usually a constant or calculated based on the modulation method, but in actual operation, it varies. D The duty cycle will also fluctuate due to the control strategy of the DC / DC converter, and needs to be further calculated using the transfer function of the corresponding control strategy. The duty cycle can be obtained by performing an inverse Laplace transform on the transfer function of the control strategy used by the DC / DC converter. D The time-domain expression is obtained, and then substituted into the above formula to obtain the on-state loss of the corrected IGBT module; (2) IGBT switching losses In the formula, f sw For switching frequency, E on and E off These represent the energy losses during IGBT turn-on and turn-off, respectively. U dc and i c For the operating voltage and current of the IGBT module, U N and i N For rated voltage and current, K ET This is the temperature correction factor for switching energy loss. (3) IGBT power loss (4) FWD on-state loss In the formula T j_D For FWD junction temperature; similarly, the duty cycle will be considered in relation to the control strategy. D Substituting the expression into the equation yields the corrected FWD's conduction loss. (5) FWD turn-off loss In the formula, E rec For the reverse recovery loss of FWD, K ED The temperature coefficient for shutting off energy loss; (6) FWD power loss Step 2: Based on the IGBT module structure and power loss model, establish a thermal network model to obtain its junction temperature fluctuation curve, and use the rainflow algorithm to obtain the average junction temperature of the IGBT module. T m Junction temperature fluctuation amplitude ΔT j Feature information, the specific steps are as follows: (1) The junction temperature of the IGBT module is calculated using the Foster thermal network model. The thermal parameters are converted into electrical parameters through thermoelectric analogy theory. Then, the problems in the thermal network are solved through electrical network theory. The conversion relationship between thermal and electrical parameters is shown in Table 1 below. Table 1. Values ​​Corresponding to Indicator Evaluation Levels In Foster thermal networking, the chip-case thermal network of the IGBT module is equivalent to a fourth-order RC network, while the case-heat sink and heat sink-environment networks are represented by first-order RC networks. This allows us to obtain the thermal impedance of the IGBT and its equivalent thermal network. Furthermore, the junction temperature expressions for the IGBT and FWD can be derived as follows: In the formula, T a Ambient temperature; (2) The measured junction temperature change curve is decomposed into multiple cycle stages by rainflow algorithm, and the junction temperature change amplitude and average value of each cycle are recorded, so as to provide the required parameters for IGBT module life prediction. Step 3: Using the Coffin-Manson-Arrheniu lifetime prediction analytical model, which has high reliability assessment accuracy and whose model parameters are relatively easy to obtain, the mean junction temperature and junction temperature fluctuation amplitude obtained in Step 2 are substituted into the selected model to calculate its lifetime. N f : In the formula, ΔT j Indicates the junction temperature difference amplitude. T m Indicates the average junction temperature. N f Indicates working condition ΔT j and T m Total number of failure cycles under the following conditions α , β For device-related parameters, E a To activate energy, K B Boltzmann's constant; Step 4: Based on the predicted lifespan, and according to the number of cycles under different operating conditions obtained from rainflow counting, the failure rate of the IGBT module is calculated using a linear fatigue damage accumulation model. The calculation formula is: In the formula, N i For specific working conditions i The number of loops.

2. The reliability assessment method for DC / DC converters in wind farm DC collection systems considering the influence of control strategies, as described in claim 1, is characterized in that... Based on the BFBIC submodule topology of a DC / DC converter, the steps for establishing a submodule-level reliability model of the DC / DC converter using the fault tree method are as follows: Step 1: Identify the most serious possible fault in the BFBIC submodule of the DC / DC converter, i.e., submodule failure; Step 2: Based on the BFBIC submodule topology, determine the logical relationship between the faults of each component and the faults of the submodule; Step 3: Establish the corresponding BFBIC submodule fault tree based on the logical relationships determined in Step 2; Step 4: Quantitative analysis, calculate the failure rate and repair rate of the BFBIC submodule based on the fault tree; In the formula, The failure rates are for individual bridge arm IGBT modules, capacitors, inductors, FWD, transformers, and clamping IGBT modules within the submodule, respectively. I , J , L , M These represent the number of IGBT modules, capacitors, inductors, and FWDs in the bridge arm of the submodule. T IGBT , T C , T L , T FWD , T T The average repair time is for IGBT modules, capacitors, inductors, transformers, and FWD, respectively.

3. The reliability assessment method for DC / DC converters in wind farm DC collection systems considering the influence of control strategies, as described in claim 1, is characterized in that... Based on the hybrid two-stage modular DC / D converter structure, a device-level reliability model for the DC / DC converter is established using the fault tree method, including the following steps: Step 1: Identify the most serious possible failure of the entire DC / DC converter device, i.e., DC / DC converter failure; Step 2: Based on the hybrid two-stage modular DC / DC converter structure, determine the logical relationship between each sub-module fault and the DC / DC converter fault; Step 3: Establish the corresponding DC / DC converter fault tree based on the logical relationships determined in Step 2; Step 4: Quantitative analysis, calculate the failure rate and repair rate of the IPOS module in the DC / DC converter with and without redundancy based on the fault tree; The failure rates of the IPOS module with and without redundancy are as follows: The repair rate for the IPOS module is: In the formula, n This represents the number of BFBIC submodules within the IPOS module; Step 5: Calculate the failure rate and repair rate of the DC / DC converter based on the fault tree; In the formula, N This represents the number of IPOS modules in the IPOP structure.

4. The reliability assessment method for DC / DC converters in wind farm DC collection systems considering the influence of control strategies, as described in claim 1, is characterized in that... Compare and analyze the differences and reasons for the reliability assessment results of DC / DC converters under the two cases of considering the impact of control strategies and not considering the impact of control strategies, including the following steps: Step 1: Based on the calculated failure rate and repair rate of the DC / DC converter, the mean time between failures (MTBF), mean time to repair (MTTR), and reliability function are used as reliability indicators to evaluate its reliability. The specific expressions are as follows: Mean Time Between Failures (MTBF): In the formula, MTTF Mean time between failures (MTBF) is the average operating time before failure, and its value is the reciprocal of the failure rate. Mean time to repair: Reliability: In the formula, t For runtime, R DC / DC ( t The reliability of the DC / DC converter is denoted by (0,1]. Step 2: Based on the DC / DC converter under two cases: considering the impact of control strategy and not considering the impact of control strategy. MBTF and MTTR The values ​​of the reliability function and the changing trends of the reliability function are analyzed to identify the differences and reasons for the reliability assessment results of the DC / DC converter.

5. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for assessing the reliability of a DC / DC converter in a wind farm DC collection system, as described in any one of claims 1 to 4, taking into account the influence of control strategies.

6. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for assessing the reliability of a DC / DC converter in a wind farm DC collection system, as described in any one of claims 1 to 4, taking into account the influence of control strategies.

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