A method for evaluating the stray inductance design of a through-flow circuit of a flexible direct current valve power module

Abstract

The application relates to a method for evaluating the stray inductance design of a through-flow loop of a flexible straight converter valve power module, and belongs to the technical field of power module design. The application judges whether the stray inductance of the designed through-flow loop of the power module meets the stray inductance limit requirement, so as to judge whether the power module structure design is qualified, and meanwhile, the unqualified power module is corrected by optimizing the power module structure, and the corrected power module is re-judged. The application can evaluate whether the power module structure design meets the stray inductance limit requirement in the power module design stage, and effectively improves the strictness of the structure design.

Description

Technical Field

[0001] This invention relates to the field of power module design technology, and in particular to a method for designing and evaluating stray inductance in the current-pass circuit of a flexible DC converter power module. Background Technology

[0002] With the development of fully controllable power electronic devices and the application of power electronics technology in power systems, high-voltage direct current (VDC) transmission technology based on voltage-source converters (VSC-HVDC) is receiving increasing attention. Modular multilevel converters (MMCs) are a type of voltage-source converter used in flexible DC transmission systems, and their significant advantages have led to their widespread application in flexible DC transmission and renewable energy integration systems.

[0003] Each arm of the MMC-HVDC system consists of a certain number of sub-modules and arm reactors connected in series. By controlling the number of sub-modules connected and disconnected in each arm, the output voltage on the AC side is made close to the AC sinusoidal voltage, and the output voltage on the DC side is made close to the DC voltage, thus achieving stable operation of the system.

[0004] An IGBT is a semiconductor power switching device that typically operates in a high-frequency switching state. During the IGBT's turn-off, a voltage spike is applied between the collector and emitter. Because this voltage value far exceeds the IGBT's rated voltage, the switching device is highly likely to be damaged by avalanche breakdown. In power modules, the parasitic inductance and distributed inductance generated by the magnetic flux linkages between current-carrying loops are commonly referred to as stray inductance. Stray inductance includes the parasitic inductance of the device itself and the distributed inductance of the connection structure. Stray inductance is unavoidable; no matter how much the structural design is optimized, it cannot be reduced to zero. The main effects of stray inductance on power modules are: 1) When the stray inductance is large, the voltage spike generated by the IGBT's rapid turn-off may exceed the device's tolerance; 2) It increases the switching losses of the power device, affecting the switching speed.

[0005] Typically, stray inductance is measured after the design and production of MMC power modules, and its impact on the system is verified based on the measured IGBT turn-off voltage spikes. This method fails to assess whether the power module's structural design meets stray inductance limits during the system design phase. To fully consider the impact of stray inductance on power module structural design, this invention provides a method for evaluating the stray inductance design of the current-path of a flexible DC converter valve power module. Summary of the Invention

[0006] The purpose of this invention is to provide a method for evaluating the stray inductance design of the current-pass circuit of a flexible DC converter valve power module, in order to solve the problem of failing to evaluate whether the power module structural design meets the stray inductance limit requirements during the power module design stage.

[0007] To address the aforementioned technical problems, this invention provides a method for designing and evaluating stray inductance in the current-pass circuit of a flexible DC converter valve power module. This method includes the following steps:

[0008] 1) Based on the converter valve system design scheme, the stray inductance limit L was calculated. max ;

[0009] 2) Establish a finite element simulation model of the power module according to the system design scheme, extract its stray inductance simulation value, and then make the power module according to the finite element simulation model of the power module and measure the stray inductance of the current-carrying loop of the power module to obtain the actual value of the stray inductance.

[0010] 3) Compare the simulated value of stray inductance with the actual value of stray inductance. If the deviation is less than or equal to the deviation threshold, the deviation requirement is met; otherwise, the requirement is not met. Iteratively correct the simulation of the finite element model of the power module until the deviation requirement is met.

[0011] 4) Compare the actual value of the stray inductance that meets the deviation requirement with L max A comparison is made to determine whether the power module structural design is qualified: when the actual value of the stray inductance is greater than the stray inductance limit L... max If the power module structure design is deemed unqualified, the design is optimized, the finite element simulation model is revised, and the revised power module is fabricated based on the revised model. The simulated and actual values ​​of stray inductance are then redefined, and the process returns to step 3) for iterative calculation. When the actual value of the stray inductance is less than or equal to L... max The power module structure design was deemed qualified at that time.

[0012] The beneficial effects of the above technical solution are as follows: The stray inductance limit Lmax is calculated based on the design scheme. Simultaneously, a finite element simulation model of the power module is established based on the design scheme. The simulated stray inductance value of the model is extracted and compared with the actual stray inductance value of the power module manufactured according to the model. If the deviation is too large, it is corrected to make the model more reliable. The actual stray inductance value is compared with Lmax to evaluate the design scheme. Furthermore, considering that if the model structure design is unqualified, the finite element simulation model can be modified to change the model structure design, this invention evaluates stray inductance during the model design stage, fully considering the impact of stray inductance on the power module structure design, making the structure design more rigorous.

[0013] Furthermore, in step 1), the stray inductance limit L max Calculation formula:

[0014]

[0015] In the formula L max For stray inductance limits, ΔV ce The maximum allowable peak shutdown voltage is defined as di / dt, where di / dt is the rate of change of current over time.

[0016] The beneficial effect of the above technical solution is that it allows for the calculation of the limit value of stray inductance, which facilitates subsequent comparison.

[0017] Furthermore, optimizing the power module structural design includes changing the stacked busbar structure, reducing the busbar length and the distance between the positive and negative busbars, placing the openings closer to the middle area of ​​the busbar, and avoiding bending in the stacked busbar area, all while meeting the physical connection and mechanical strength requirements.

[0018] The beneficial effects of the above technical solution are: the model is optimized, so that the stray inductance of the optimized model is reduced and meets the requirements of the stray inductance limit.

[0019] Furthermore, in step 3), the deviation threshold is set to 5%.

[0020] The beneficial effects of the above technical solution are: limiting the deviation threshold makes the simulation model closer to the actual power module, which facilitates the subsequent modification and optimization of the model.

[0021] Furthermore, in step 2), the finite element simulation model is established using Ansys Q3D extrator, Ansys Maxwell, or Cosmol software.

[0022] The beneficial effects of the above technical solution are: selecting appropriate software to establish a finite element simulation model can improve the accuracy of the model. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for designing and evaluating stray inductance in the current-pass circuit of a flexible DC converter valve power module according to the present invention;

[0024] Figure 2 This is a topology diagram of the MMC power module in an embodiment of the present invention;

[0025] Figure 3 This is the simulation model for solving the stray inductance of the MMC power module in this embodiment of the invention;

[0026] Figure 4 This is a current density distribution cloud map in the stray inductance solution of the MMC power module in this embodiment of the invention;

[0027] Figure 5 This is the solution result of the inductance matrix in the stray inductance solution of the MMC power module in the embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] An example of a method for evaluating the stray inductance design of a power module current-pass circuit for a flexible DC converter valve:

[0030] This invention addresses the problem in power module design where it fails to assess whether the power module structural design meets stray inductance limits. It proposes an effective design evaluation method, the flowchart of which is shown below. Figure 1 As shown, the specific implementation steps of this method are as follows:

[0031] 1) Based on the converter valve system design scheme, an electrical stress analysis was performed on the power module of the flexible DC converter valve, and the stray inductance limit L was calculated. max Stray inductance limit L max The calculation formula is:

[0032]

[0033] In the formula L max For stray inductance limits, ΔV ce The maximum allowable peak shutdown voltage is defined as di / dt, where di / dt is the rate of change of current over time.

[0034] 2) Based on the system design scheme, establish a finite element simulation model of the power module using Ansys Q3D extrator, Ansys Maxwell, or Cosmol software, and extract its stray inductance simulation value. Then, fabricate the power module according to the finite element simulation model of the power module and measure the stray inductance of the current-carrying loop of the power module to obtain the actual value of the stray inductance.

[0035] 3) Compare the simulated value of stray inductance with the actual value of stray inductance. If the deviation between the two is less than or equal to the deviation threshold of 5%, the requirement is met; otherwise, the requirement is not met. The finite element simulation model of the power module is iteratively corrected until the deviation requirement is met to ensure the accuracy of the simulation model.

[0036] 4) Compare the actual value of the stray inductance that meets the deviation requirement with L max A comparison is made to determine whether the power module structural design is qualified: when the actual value of the stray inductance is greater than the stray inductance limit L... maxIf the power module structure design is deemed unqualified, and while meeting physical connection and mechanical strength requirements, the stacked busbar structure is modified by reducing the busbar length and the distance between the positive and negative busbars, placing necessary openings closer to the middle area of ​​the busbar, and avoiding bending in the stacked busbar area. The finite element simulation model of the power module is then corrected, and the power module design structure is optimized based on the corrected simulation model results. The simulated and actual values ​​of stray inductance are then re-determined, and the process returns to step 3) for repeated iterative calculations. When the actual value of the stray inductance is less than or equal to L... max The power module structure design was deemed qualified at that time.

[0037] The following example, using the design of a half-bridge power module for a flexible DC transmission system in a certain engineering project as an example, further illustrates the specific implementation of this invention. The current-carrying circuit of the power module includes capacitors, busbars, IGBTs, heat sinks, diodes, etc., and the topology of the half-bridge power module is as follows: Figure 2 As shown, the power module structure includes a bypass thyristor T, a bypass switch K, an upper IGBT T1, a lower IGBT T2, a capacitor C, and an equalizing resistor R. The half-bridge power module uses N-type IGBTs with a rated current of 2kA and a rated voltage of 4500V.

[0038] First, based on the system design scheme, an electrical stress analysis is conducted on the power module, including a system-level full-condition electrical stress analysis of the power module, such as rated voltage, maximum operating voltage, and various fault conditions. Finally, based on the power module's hardware and software protection settings and other conditions, the maximum IGBT turn-off current I is comprehensively determined. c 2000A, maximum allowable turn-off voltage spike ΔV ce The limits are 660V and di / dt is 6000A / µs, while L max The calculation formula is: The stray inductance limit L of the power module can be calculated from the above data. max =110nH.

[0039] Secondly, a simulation model of the half-bridge power module, namely the dual-pulse test simulation model, needs to be established. This requires creating a finite element simulation model of the power module based on the IGBT datasheet, establishing an accurate simulation model at the IGBT device level to accurately simulate the IGBT's turn-on and turn-off characteristics. Accurate and detailed material settings are also necessary, ensuring the actual conductive circuit matches real-world operating conditions. Structures affecting stray inductance cannot be omitted or simplified. The finite element simulation model is as follows: Figure 3 As shown, the model includes capacitor C, upper IGBT T1, lower IGBT T2, and load inductance L. The maximum turn-off voltage spike ΔV... ce The voltage is 726V, the di / dt is 6000A / µs, and the equivalent stray inductance L of the entire current-carrying loop of the power module is... max=121nH. The finite element method can extract the stray inductance of each part of the power module, as well as the self-inductance and mutual inductance of the components, thereby determining the contribution of each part of the electrical current-carrying loop of the power module to the overall stray inductance of the power module, and the contribution of self-inductance and mutual inductance to the overall stray inductance of individual components.

[0040] Furthermore, a double-pulse test was conducted on the half-bridge power module used in engineering applications, and the ΔV obtained through the test was... ce Given 744V, calculate the measured stray inductance L. max =124nH. If the deviation between the simulated value and the actual value of stray inductance is higher than 5%, the stray inductance simulation model needs to be iteratively corrected. The comparison shows that the deviation between the two is within 5%, and the accuracy of the stray inductance extraction simulation model has been verified.

[0041] Finally, comparing the simulated stray inductance of the power module's current-carrying loop with the obtained limit value shows that the simulated value is greater than the limit value, indicating that the power module structure needs optimization. Therefore, based on the modified simulation model, stray inductances of each component group in the power module are extracted, the current-carrying loops of the devices are optimized, the design of components such as the busbar is modified, and the trend of stray inductance variation is studied. While meeting the requirements of physical connection and mechanical strength, the structure of the laminated busbar is modified to minimize the busbar length and the distance between the positive and negative busbars, placing necessary openings closer to the middle area of ​​the busbar, and minimizing bending in the laminated portion of the busbar. The final results are as follows. Figure 4 , Figure 5 As shown, the power module simulates the stray inductance L. max =102nH, which is less than the stray inductance limit. Based on simulation results, the power module structure design was optimized, and the stray inductance of the module's current-carrying loop was tested to obtain the measured stray inductance L. max =106nH, the power module structure design is qualified. At the same time, the power module topology of the flexible DC converter valve also includes hybrid flexible DC transmission, and the sub-modules are not limited to half-bridge sub-modules, but also include full-bridge and clamping sub-modules. The power switching devices in the sub-modules are not limited to IGBTs, but also include MOSFET devices.

[0042] Specific implementation methods have been given above, but the present invention is not limited to the described implementation methods. The basic idea of ​​the present invention lies in the above basic scheme. For those skilled in the art, designing various modified models, formulas, and parameters based on the teachings of the present invention does not require creative effort. Changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for designing and evaluating stray inductance in the current-pass circuit of a flexible DC converter valve power module, characterized in that, Includes the following steps: 1) Based on the converter valve system design scheme, the stray inductance limit L was calculated. max ; 2) Establish a finite element simulation model of the power module according to the system design scheme, extract its stray inductance simulation value, and then make the power module according to the finite element simulation model of the power module and measure the stray inductance of the current-carrying loop of the power module to obtain the actual value of the stray inductance. 3) Compare the simulated value of stray inductance with the actual value of stray inductance. If the deviation is less than or equal to the deviation threshold, the deviation requirement is met; otherwise, the requirement is not met. Iteratively correct the simulation of the finite element model of the power module until the deviation requirement is met. 4) Compare the actual value of the stray inductance that meets the deviation requirement with L max A comparison is made to determine whether the power module structural design is qualified: when the actual value of the stray inductance is greater than the stray inductance limit L... max If the power module structure design is deemed unqualified, the power module structure design scheme is then optimized, the finite element simulation model of the power module is corrected, the corrected power module is fabricated according to the corrected simulation model, and the simulated value and actual value of stray inductance are re-determined, and then the process returns to step 3) for repeated iterative calculation. When the actual value of stray inductance is less than or equal to L max The power module structure design was deemed qualified at that time.

2. The method for designing and evaluating stray inductance in the current-pass circuit of a flexible DC converter valve power module according to claim 1, characterized in that, In step 1), the stray inductance limit L max Calculation formula: In the formula L max For stray inductance limits, ΔV ce The maximum allowable peak shutdown voltage is defined as di / dt, where di / dt is the rate of change of current over time.

3. The method for designing and evaluating stray inductance in the current-pass circuit of the power module of the flexible DC converter valve according to claim 1, characterized in that, The optimized power module structural design scheme includes changing the stacked busbar structure, reducing the busbar length and the distance between the positive and negative busbars, placing the opening position closer to the middle area of ​​the busbar, and avoiding bending in the stacked part of the busbar, while meeting the requirements of physical connection and mechanical strength.

4. The method for designing and evaluating stray inductance in the current-pass circuit of the power module of the flexible DC converter valve according to claim 1, characterized in that, In step 3), the deviation threshold is set to 5%.

5. The method for designing and evaluating stray inductance in the current-pass circuit of a flexible DC converter valve power module according to any one of claims 1 to 4, characterized in that, In step 2), the finite element simulation model is established using Ansys Q3D extrator, Ansys Maxwell, or Cosmol software.

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