SiC MOSFET characteristic evaluation device and method under DC circuit breaker

Abstract

The present application provides a device and method for evaluating the characteristics of SiC MOSFETs under a DC circuit breaker, which belongs to the field of MOSFET characteristic evaluation. The method includes: by changing the preset voltage value of an external adjustable voltage source, performing a single shutdown test on the SiC MOSFET under different fault currents under the DC circuit breaker, obtaining a single maximum shutdown current value and a short-time scale single shutdown characteristic evaluation result; fixing the preset voltage value of the external adjustable voltage source, and performing a long-time scale repeated shutdown test on the SiC MOSFET under the DC circuit breaker at a preset time interval, obtaining a safe operating boundary under a long-time scale and a long-time scale repeated shutdown characteristic evaluation result. The characteristic evaluation device constructed in the present application can fully simulate the operating characteristics of a device such as SiC MOSFET under the task profile of a DC circuit breaker, laying the foundation for its safe and reliable operation in a DC circuit breaker.

Description

Technical Field

[0001] The present application relates to the field of MOSFET characteristic evaluation, and more specifically, to a device and method for evaluating SiC MOSFET characteristics under a DC circuit breaker. Background Art

[0002] In recent years, flexible direct current (DC) transmission and DC grids, primarily powered by renewable energy sources such as wind power and photovoltaics, have experienced rapid development. However, when a system fault occurs, the low impedance of the DC grid causes the fault current in the circuit to rise sharply within a short period of time. In severe cases, this can even lead to the failure of the entire grid. DC circuit breakers (DCCBs) are key components of DC grids, capable of interrupting high short-circuit currents within milliseconds. They offer the ability to reliably and quickly interrupt DC fault currents, making them a crucial component of DC grids. SiC MOSFETs (a metal oxide semiconductor field-effect transistor made of silicon carbide (SiC)) can be used to construct DCCBs. Compared to silicon, SiC MOSFETs offer higher breakdown field strength and a wider bandgap. Furthermore, they offer advantages in thermal conductivity and melting point, making them ideal for high-temperature applications. However, before SiC MOSFETs can be used in DCCBs, experimental evaluation and characterization are required to assess their reliability and characteristics. Currently, the primary method for evaluating the reliability and characteristics of SiC MOSFETs is accelerated power cycling testing. Conventional power cycling tests can determine the aging characteristics and failure mechanisms of SiC MOSFET chips and discuss failure causes related to the SiC MOSFET package. However, this testing method does not account for the specialized mission profile of a DC circuit breaker, which requires shutting off currents several times the rated current in a short period of time. Different mission profiles correspond to specific operating conditions, and a specific operating condition like a DC circuit breaker requires its own specific test setup and measurement methods. Therefore, the application of SiC MOSFETs in DCCB construction requires the construction of a device for evaluating SiC MOSFET characteristics under DC circuit breaker conditions and the development of corresponding test methods to evaluate and test the reliability and characteristics of SiC MOSFETs under DC circuit breaker conditions. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the purpose of this application is to provide a device and method for evaluating the characteristics of SiC MOSFETs under DC circuit breakers, aiming to solve the problem that the reliability and characteristics evaluation of existing SiC MOSFET devices do not take into account the special task profile of DC circuit breakers that require shutting off several times the rated current in a short period of time, resulting in a lack of corresponding testing methods for SiC MOSFETs used in circuit breakers.

[0004] To achieve the above objectives, in a first aspect, the present application provides a device for evaluating the characteristics of a SiC MOSFET under a DC circuit breaker, wherein the SiC MOSFET is used to construct a DC circuit breaker, comprising: an external adjustable voltage source, a switch, an RLC power circuit, an RCD snubber circuit, an MOV clamping circuit, and a drive controller;

[0005] The RLC power circuit, RCD snubber circuit, and MOV clamp circuit are connected in parallel; the drive controller is connected to the SiC MOSFET; the SiC MOSFET is connected in series in the RLC power circuit; and a switch is set in a circuit formed by an external adjustable voltage source and a capacitor in the RLC power circuit.

[0006] An external adjustable voltage source is used to provide different preset voltage values ​​to charge the capacitor in the RLC power circuit. The drive controller is used to control the SiC MOSFET to turn off before charging the capacitor and to control the SiC MOSFET to turn on after charging the capacitor is completed. The capacitor in the RLC power circuit is used to increase the short-circuit current in the RLC power circuit by discharging. The drive controller is used to control the SiC MOSFET to turn off when the short-circuit current reaches the maximum value under the current preset voltage value.

[0007] The RCD snubber circuit is used to suppress the transient voltage overshoot of the SiC MOSFET by current transfer after the SiC MOSFET is turned off. The MOV clamping circuit is used to absorb the energy in the RLC power circuit and clamp the voltage across the SiC MOSFET to the clamping value when the voltage across the MOV reaches the operating voltage and the resistance value decreases and the circuit becomes conductive.

[0008] Further preferably, the device for evaluating the characteristics of SiC MOSFET under a DC circuit breaker is used to perform a short-time scale characteristic evaluation test and a long-time scale characteristic evaluation test on the SiC MOSFET under a DC circuit breaker respectively;

[0009] The short-time-scale characteristic evaluation test changes the maximum short-circuit current by changing the preset voltage value of an external adjustable voltage source. The SiC MOSFET is subjected to a single shutdown test under different fault currents to obtain the single maximum shutdown current value. The maximum short-circuit current under the current preset voltage value is taken as the fault current.

[0010] The long time scale characteristic evaluation test is to fix the preset voltage value of the external adjustable voltage source to the preset voltage value of the external adjustable voltage source corresponding to 90% to 95% of the single maximum shutdown current value, and perform a long time scale repeated shutdown test on the SiC MOSFET under a DC circuit breaker at preset time intervals.

[0011] Further preferably, the drive controller is an FPGA development board.

[0012] In a second aspect, based on the above-mentioned SiC MOSFET characteristic evaluation device under a DC circuit breaker, the present application provides a corresponding SiC MOSFET characteristic evaluation method under a DC circuit breaker, which specifically includes the following steps:

[0013] Step 1: By changing the preset voltage value of the external adjustable voltage source to achieve the purpose of changing the maximum short-circuit current, the SiC MOSFET is tested for single shutdown under different fault currents under the DC circuit breaker to obtain the maximum single shutdown current value that the SiC MOSFET can withstand and the short-time scale single shutdown characteristics of the SiC MOSFET under the DC circuit breaker. The maximum short-circuit current under the current preset voltage value is used as the fault current.

[0014] Step 2: Fix the preset voltage value of the external adjustable voltage source to the preset voltage value of the external adjustable voltage source corresponding to the preset proportion of the single maximum switchable current value, and perform long-time scale repeated shutdown tests on the SiC MOSFET under a DC circuit breaker at preset time intervals until the SiC MOSFET fails, thereby obtaining a safe operating boundary under a long-time scale. At the same time, compare and evaluate the characteristics of the SiC MOSFET under different test times to obtain an evaluation result of the long-time scale repeated shutdown characteristics of the SiC MOSFET under a DC circuit breaker; wherein the safe operating boundary under a long-time scale is the number of long-time scale repeated shutdown tests that the SiC MOSFET can withstand.

[0015] Further preferably, a shutdown test is performed on the SiC MOSFET under a DC circuit breaker, specifically comprising the following steps:

[0016] At time 0 to t1, the switch is closed and the capacitor is charged through the external adjustable voltage source, and the charging is completed at time t1;

[0017] Between t1 and t2, the switch is turned off, and the drive controller outputs a drive signal to turn on the SiC MOSFET, thereby turning on the RLC power loop. The capacitor is discharged, causing the short-circuit current in the RLC power loop to increase linearly. At t2, the short-circuit current in the RLC power loop reaches its maximum value, and the drive controller turns off the SiC MOSFET.

[0018] Between t2 and t3, an MOV clamping circuit is used to clamp the overshoot voltage across the SiC MOSFET to the clamping voltage. When the current in the MOV clamping circuit becomes zero at t3, a shutdown test of the SiC MOSFET under the DC circuit breaker is completed.

[0019] Among them, after time t3, the preset voltage value is changed or a fixed preset voltage value is set to recharge the capacitor, and this is repeated several times to obtain the short-time scale single shutdown characteristic evaluation results and long-time scale repeated shutdown characteristic evaluation results of the SiC MOSFET under the DC circuit breaker.

[0020] Further preferably, in step 1, the preset voltage value of the external adjustable voltage source starts from 10V and is gradually increased with an iterative interval of 10V. As the preset voltage value continues to increase, the maximum short-circuit current gradually increases until the maximum short-circuit current exceeds the safety boundary of the SiC MOSFET on a short time scale, and the SiC MOSFET fails to shut down. The safety boundary of the SiC MOSFET on a short time scale is the single maximum shutoff current value that the SiC MOSFET can withstand.

[0021] Further preferably, multiple SiC MOSFETs are selected to repeat step 1 to obtain a short-time scale single turn-off characteristic evaluation result of the SiC MOSFET under a DC circuit breaker.

[0022] Further preferably, the characteristics of the SiC MOSFET in step 2 include a DC circuit breaker turn-off time, a SiC MOSFET drain leakage current, a SiC MOSFET gate threshold voltage, and a SiC MOSFET on-resistance.

[0023] Further preferably, in step 2, the preset voltage value of the external adjustable voltage source is fixed to the preset voltage value of the external adjustable voltage source corresponding to 90% to 95% of the single maximum switchable current value.

[0024] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies:

[0025] Based on the excellent performance of SiC MOSFET, this power semiconductor device is suitable for use in DC circuit breakers. To evaluate the operating characteristics of SiC MOSFET under DC circuit breaker conditions, a complete SiC MOSFET characteristic evaluation device under DC circuit breakers is constructed. The device is based on an RLC charge and discharge circuit and fully considers the RCD snubber circuit and MOV clamping circuit to achieve the purpose of transferring fault current and absorbing residual energy in the system. The constructed characteristic evaluation device can fully simulate the operating characteristics of SiC MOSFET under the DC circuit breaker mission profile, laying the foundation for its safe and reliable operation in DC circuit breakers.

[0026] Based on the SiC MOSFET characteristic evaluation device under a DC circuit breaker provided in this application, it is possible to perform characteristic evaluation tests on SiC MOSFET from two dimensions: a short-time scale test method and a long-time scale test method. The short-time scale test method can determine the safety issues between the stress on the device and the maximum safety margin, and the long-time scale test method can determine the reliability issues of the device due to long-term aging failure. Combining the short-time scale test results and the long-time scale test results can obtain the SiC MOSFET characteristic evaluation test results under a DC circuit breaker. The proposed evaluation test method has good practical application effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a method for evaluating SiC MOSFET characteristics under a DC circuit breaker provided in an embodiment of the present application;

[0028] Figure 2 Schematic diagram of a device for evaluating the characteristics of a SiC MOSFET under a DC circuit breaker provided in an embodiment of the present application;

[0029] Figure 3 : is a test waveform diagram of the SiC MOSFET characteristic evaluation device provided in an embodiment of the present application;

[0030] Figure 4 The embodiment of the present application provides dc =50V short time scale single shutdown test waveform of the device;

[0031] Figure 5 The embodiment of the present application provides dc =120V device long time scale repeated shutdown timing test waveform;

[0032] FIG6( a ) shows the SiC MOSFET gate threshold voltage aging results over a long time scale provided by an embodiment of the present application;

[0033] FIG6( b ) is a SiC MOSFET on-resistance aging result on a long time scale provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0035] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0036] Next, the technical solutions provided in the embodiments of this application are introduced.

[0037] like Figure 1 As shown, the present application provides a method for evaluating the characteristics of SiC MOSFET under a DC circuit breaker. In order to obtain the characteristic evaluation of SiC MOSFET under the DCCB task profile, the method specifically includes the following steps:

[0038] Step S1: Build a specific characteristic evaluation device for the DC circuit breaker for SiC MOSFET devices:

[0039] like Figure 2 As shown in the figure, a hard switching test is performed on the SiC MOSFET device under test (DUT); the characteristic evaluation device needs to generate a large current far greater than the rated current of the device within a few milliseconds; for this purpose, the test circuit device schematic diagram is shown in the figure. Figure 2 As shown in the figure, the device is essentially an RLC charge-discharge circuit. In each test, the SiC MOSFET device is initially in the off state. First, a preset value is set for the external adjustable voltage source, which charges the capacitor. The charging process ends when the voltage across the capacitor reaches the preset value. After charging is completed, the device under test is controlled to turn on by the drive controller. At this time, the power circuit is turned on and the capacitor is discharged. The short-circuit current in the circuit increases linearly. When the current reaches the maximum value at the preset voltage, the SiC MOSFET is controlled to turn off by the controller, thereby achieving the purpose of the SiC MOSFET device interrupting the high fault current.

[0040] For low-inductance systems like DC grids, DCCBs must be able to interrupt fault currents within milliseconds. The rapid change in current in such a short time can generate overvoltage, which can directly break down the device in severe cases. Furthermore, the energy stored in the inductor must be absorbed. Therefore, effective methods are necessary to suppress overvoltage during shutdown, and additional absorption circuits are required to absorb the remaining energy in the system.

[0041] Therefore, to achieve the above objectives and fully simulate the process of DCCB shutting off the fault current, an RCD snubber circuit and an MOV clamping circuit are connected in parallel at both ends of the device under test to divert the fault current and absorb the remaining energy in the circuit. The RCD snubber circuit can effectively suppress the voltage overshoot of the switching transient and realize the current diversion. The MOV (metal oxide varistor) is essentially a variable resistor. Under normal circumstances, its resistance is large and presents a high-resistance state. When the voltage across it reaches its MOV operating voltage, the resistance value decreases and it appears to be in the on state, thereby consuming most of the circuit energy and clamping the voltage across the SiC MOSFET to the clamping value, thereby protecting the DUT.

[0042] The waveform diagram of the device test is as follows Figure 3 As shown:

[0043] 0~t1: Close the switch S, first pass the external adjustable voltage source V dc Charge capacitor C1 and complete charging at time t1;

[0044] t1~t2: At t1, the switch S is turned off, and the drive controller sends a drive signal to turn on the device under test, the power circuit is turned on, and the capacitor is discharged through the C1-L-DUT-C1 circuit. The short-circuit current I in the power circuit a It rises linearly;

[0045] t2~t3: At t2, I a When the voltage reaches the maximum value, the controller turns off the device under test. At the moment of shutdown, the presence of the MOV clamp circuit will cause the overshoot voltage V ds Clamped to clamp voltage V clamp This is to protect the device under test; after the device is turned off, I a Transfer to RCD circuit and MOV circuit in turn, forming I RCD and I MOV ; MOV absorbs most of the remaining energy in the circuit. MOV When time t3 becomes zero, a test is completed;

[0046] After t3: After one test, the voltage of the capacitor bank will be lower than the preset value and needs to be tested by V dc C1 is charged again for the next test.

[0047] After the test equipment was built, the SiC MOSFET was subjected to short-timescale and long-timescale characteristic evaluation tests under a DC circuit breaker:

[0048] Step S2: For short-time-scale testing, the preset voltage value of the external adjustable voltage source is changed to achieve the purpose of changing the maximum shutdown current of the DUT, thereby performing a single shutdown test on the DUT under different fault currents; the preset voltage value of the external adjustable voltage source starts from 10V and is gradually increased with an iterative interval of 10V. As the preset value continues to increase, the current of the SiCMOSFET shutdown also gradually increases until the shutdown current of the device under test exceeds the safety boundary under the short-time-scale and the device fails to shut down; in order to reduce experimental errors, it is necessary to select multiple identical devices to repeat the above test steps, and finally obtain the short-time-scale single shutdown characteristic evaluation results of the device under test under the DC circuit breaker, and the maximum single shutdown current of the device can be obtained;

[0049] Step S3: For long time scale testing, based on the single shutdown characteristic evaluation results obtained under the above short time scale, the preset voltage of the external adjustable voltage source corresponding to 90% to 95% of the single maximum shutdown current value of the device is fixed, and the device under test is subjected to long time scale repeated shutdown test under DC circuit breaker with a time interval of 5 to 10 seconds, and the number of repetitions is repeated until the device fails; using DCCB turn-off time, SiC MOSFET drain leakage current, SiC MOSFET gate threshold voltage and SiC MOSFET on-resistance as reference indicators, the characteristics of the devices under different test times are compared and evaluated, and the safe operation boundary is determined, and finally the long time scale repeated shutdown characteristic evaluation results of the device under test under DC circuit breaker are obtained.

[0050] Example

[0051] Take a 1200V / 66A SiC MOSFET as an example to illustrate:

[0052] For this type of SiC MOSFET, the first step is to select the various components in the device: an adjustable DC voltage source powers the entire circuit, and an FPGA development board provides drive control signals for the device under test. The selected MOV clamping voltage is 405V. In the power circuit, the capacitor bank C1 = 5mF, and the load inductor L = 1mH. In the RCD snubber circuit, R = 100Ω, C2 = 5μF, and the diode D model is 1200V / 128A.

[0053] After the test device is built, a short time scale test is first performed, starting from 10V, and increasing the preset value V of the external DC voltage source by 10V. dc The maximum current in the loop occurs at 3ms, at which point the device under test is controlled to shut off the fault current. Figure 4 V dc =50V as an example, the shutdown waveform of the device under test; Figure 4 It can be seen that before 0ms, the DC voltage source Vdc V ds Charge to the preset value 50V; at 0ms, the DUT is connected and the current in the loop I a It rises approximately linearly and reaches its maximum value at 3ms. The device under test is controlled to shut down at 3ms, and the shutdown current is 48.7A, which is 0.74 times the rated current. After the DUT is shut down, the short-circuit current is transferred through the RCD circuit and the MOV circuit in turn, as shown in Figure 2. Figure 4 As shown on the right; after 205.5μs transfer time, the current in the loop becomes 0, and the single shutdown experiment ends; Figure 4 As can be seen from the left figure, at the moment of shutdown, the MOV clamps the voltage across the device under test to 344.6V to protect the device under test; Table 1 shows the short-time scale single shutdown characteristic evaluation results of the device under test under the DC circuit breaker, which are obtained by taking 5 devices of the same specifications and models and performing 5 repeated single shutdown tests and the average value of the test results; As can be seen from Table 1, V dc The value of I increases from 10V to 130V, a It also increased from 9.31A to 131.4A, and the multiples of the maximum shutdown current of the device under test also gradually increased; the maximum current that the DUT can successfully shut down is approximately 1.99 times the rated current; in addition, the experiment found that under this short time scale test, the cause of SiC MOSFET failure is drain thermal failure.

[0054] Table 1

[0055]

[0056] Based on the short-time scale characteristic evaluation results, a long-time scale test is conducted, and the shutdown current of 122.4A (92% of the maximum shutdown current) is taken to correspond to V dc (120V) is fixed and the test is repeated with a time interval of 5s; Figure 5 The shutdown waveform with timeline; before 0ms, V ds Passed V dc Charge to the preset value 120V; at 0ms, DUT is connected, I a It rises linearly and reaches its maximum value at 3ms. The maximum current passing through the DUT is about 122.4A, which is 1.85 times the rated current. After the DUT is turned off, the current is transferred to the RCD snubber circuit and the MOV clamping circuit. The MOV clamping voltage at the moment of turn-off is 352.8V. Figure 5As shown in Figure 6, the duration of the entire current transfer process after shutdown is 398.4μs. Taking the DCCB turn-off time, drain leakage current, gate threshold voltage and on-resistance as reference indicators, the number of turn-offs of 0.6k times, 1.3k times and 2k times were selected. The changes in the reference indicators under different test times were compared with the initial values, and the long-term characteristic aging results of the device under DC circuit breaker conditions were obtained; the long-term test times exceeded 2000 times, and the device failed to shut down in the 2004th test, indicating that the safety margin of the device in this case is 2004 times; the cause of device failure is a short-circuit fault between the gate and the source; Figure 6(a) and Figure 6(b) show the aging results under long-term scales.

[0057] In summary, compared with the prior art, this application has the following advantages:

[0058] Based on the excellent performance of SiC MOSFET, this application makes this type of power semiconductor device suitable for building DC circuit breakers. In order to evaluate the operating characteristics of SiC MOSFET under DC circuit breaker conditions, a complete SiC MOSFET characteristic evaluation device under DC circuit breakers is constructed. The device is based on an RLC charge and discharge circuit and fully considers the RCD snubber circuit and MOV clamping circuit to achieve the purpose of transferring fault current and absorbing residual energy in the system. The constructed characteristic evaluation device can fully simulate the operating characteristics of SiC MOSFET devices under the DC circuit breaker mission profile, laying the foundation for their safe and reliable operation in DC circuit breakers.

[0059] Based on the above-mentioned test device, the characteristics of SiC MOSFET can be evaluated and tested from two dimensions: short-time scale test method and long-time scale test method. The short-time scale test method can determine the safety issues between the stress on the device and the maximum safety margin. The long-time scale test method can determine the reliability issues of the device due to long-term aging failure. Combining the short-time scale test results and the long-time scale test results, the characteristics evaluation test results of SiC MOSFET under DC circuit breaker can be obtained. The proposed evaluation test method has good practical application effect.

[0060] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A device for evaluating SiC MOSFET characteristics under a DC circuit breaker, wherein: SiC MOSFET is used to construct a DC circuit breaker, which is characterized by including: an external adjustable voltage source, a switch, an RLC power circuit, an RCD snubber circuit, an MOV clamping circuit and a drive controller; The RLC power circuit, RCD snubber circuit, and MOV clamp circuit are connected in parallel; the drive controller is connected to the SiC MOSFET; the SiC MOSFET is connected in series in the RLC power circuit; and the switch is set in the circuit formed by the external adjustable voltage source and the capacitor in the RLC power circuit. An external adjustable voltage source is used to provide different preset voltage values ​​to charge the capacitor in the RLC power circuit. The drive controller is used to control the SiC MOSFET to turn off before charging the capacitor and to control the SiC MOSFET to turn on after the capacitor is charged. The capacitor in the RLC power circuit is used to increase the short-circuit current in the RLC power circuit by discharging. The drive controller is used to control the SiC MOSFET to turn off when the short-circuit current reaches the maximum value under the current preset voltage value. The RCD snubber circuit is used to suppress the SiC MOSFET's transient voltage overshoot by diverting current after the SiC MOSFET is turned off. The MOV clamp circuit is used to reduce its resistance and become conductive when the voltage across it reaches the operating voltage, absorbing energy in the RLC power circuit and clamping the voltage across the SiC MOSFET to the clamping value. The device for evaluating the characteristics of SiC MOSFET under a DC circuit breaker is used to perform a short-time scale characteristic evaluation test and a long-time scale characteristic evaluation test on SiC MOSFET under a DC circuit breaker; The short-time-scale characteristic evaluation test changes the maximum short-circuit current by changing the preset voltage value of an external adjustable voltage source. The SiC MOSFET is subjected to a single turn-off test under different fault currents to obtain the maximum single turn-off current value that the SiC MOSFET can withstand. The maximum short-circuit current under the current preset voltage value is taken as the fault current. The long time scale characteristic evaluation test is to fix the preset voltage value of the external adjustable voltage source to the preset voltage value of the external adjustable voltage source corresponding to 90%~95% of the single maximum shutdown current value, and perform long time scale repeated shutdown tests on the SiC MOSFET under a DC circuit breaker at preset time intervals.

2. The device for evaluating SiC MOSFET characteristics under a DC circuit breaker according to claim 1, wherein: The drive controller is an FPGA development board.

3. A method for evaluating the characteristics of a SiC MOSFET under a DC circuit breaker based on the device for evaluating the characteristics of a SiC MOSFET under a DC circuit breaker according to claim 1 or 2, characterized in that: The specific steps include: Step 1: By changing the preset voltage value of the external adjustable voltage source to achieve the purpose of changing the maximum short-circuit current, the SiC MOSFET is tested for single shutdown under different fault currents under the DC circuit breaker to obtain the maximum single shutdown current value that the SiC MOSFET can withstand and the short-time scale single shutdown characteristics of the SiC MOSFET under the DC circuit breaker. The maximum short-circuit current under the current preset voltage value is used as the fault current. Step 2: Fix the preset voltage value of the external adjustable voltage source to the preset voltage value of the external adjustable voltage source corresponding to the preset proportion of the single maximum switchable current value, and perform long-time scale repeated shutdown tests on the SiC MOSFET under a DC circuit breaker at preset time intervals until the SiC MOSFET fails, thereby obtaining a safe operating boundary under a long-time scale. At the same time, compare and evaluate the characteristics of the SiC MOSFET under different test times to obtain an evaluation result of the long-time scale repeated shutdown characteristics of the SiC MOSFET under a DC circuit breaker; wherein the safe operating boundary under a long-time scale is the number of long-time scale repeated shutdown tests that the SiC MOSFET can withstand.

4. The method for evaluating SiC MOSFET characteristics under a DC circuit breaker according to claim 3, wherein: The shutdown test of SiC MOSFET under DC circuit breaker includes the following steps: In 0~ At this moment, close the switch and charge the capacitor through an external adjustable voltage source. Complete charging at all times; exist ~ At this moment, the switch is turned off, and the drive controller outputs a drive signal to turn on the SiC MOSFET, thereby turning on the RLC power loop and discharging through the capacitor, causing the short-circuit current in the RLC power loop to rise linearly. At this moment, the short-circuit current in the RLC power loop reaches its maximum value, and the SiC MOSFET is turned off by the driving controller; exist ~ At this moment, the MOV clamp circuit is used to clamp the overshoot voltage at both ends of the SiC MOSFET to the clamping voltage; when the current in the MOV clamp circuit is When the time becomes zero, a shutdown test of the SiC MOSFET under the DC circuit breaker is completed; Among them, After a certain time, the preset voltage value is changed or a fixed preset voltage value is set to recharge the capacitor, and this is repeated several times to obtain the short-time scale single-time shutdown characteristic evaluation results and long-time scale repeated shutdown characteristic evaluation results of the SiC MOSFET under the DC circuit breaker.

5. The method for evaluating SiC MOSFET characteristics under a DC circuit breaker according to claim 3 or 4, wherein: In step 1, the preset voltage value of the external adjustable voltage source starts from 10V and is gradually increased at an iterative interval of 10V. As the preset voltage value continues to increase, the maximum short-circuit current gradually increases until the maximum short-circuit current exceeds the safety boundary of the SiC MOSFET on a short time scale, and the SiC MOSFET fails to shut down. The safety boundary of the SiC MOSFET on a short time scale is the single maximum shutdown current value that the SiC MOSFET can withstand.

6. The method for evaluating SiC MOSFET characteristics under a DC circuit breaker according to claim 5, wherein: Select multiple SiC MOSFETs and repeat step 1 to obtain the short-time scale single-time turn-off characteristic evaluation results of SiC MOSFET under the DC circuit breaker.

7. The method for evaluating SiC MOSFET characteristics under a DC circuit breaker according to claim 3, wherein: The characteristics of the SiC MOSFET in step 2 include the DC circuit breaker turn-off time, the SiC MOSFET drain leakage current, the SiC MOSFET gate threshold voltage, and the SiC MOSFET on-resistance.

8. The method for evaluating SiC MOSFET characteristics under a DC circuit breaker according to claim 3 or 7, wherein: In step 2, the preset voltage value of the external adjustable voltage source is fixed to the preset voltage value of the external adjustable voltage source corresponding to 90% to 95% of the single maximum switchable current value.

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