A method for improving the operating life of SiC MOSFET devices in inverters

Abstract

This invention discloses a method for improving the operating life of SiC MOSFET devices in an inverter. In a three-phase inverter including main bridge arms A, B, and C, a redundant bridge arm D for time-sharing conduction and a bidirectional thyristor for commutation are provided. T A , T B and T C The controller issues control commands to determine whether time-sharing conduction control is needed based on the phase of the output current of each phase in the three-phase main bridge arms A, B, and C. When it is determined that the current of a certain phase has entered a large range, the controller turns on the bidirectional thyristor connected to that phase and sends the drive signal of that phase bridge arm to the redundant bridge arm, while turning off the SiC MOSFET on that phase bridge arm. This temporarily "rests" that phase bridge arm, thereby reducing the peak junction temperature and junction temperature fluctuation amplitude of that bridge arm, and thus achieving the control of the three-phase main bridge arms A, B, and C, the redundant bridge arm D, and the bidirectional thyristor. T A , T B and T C The time-sharing conduction and commutation are used to improve the operating life of SiC MOSFETs in three-phase inverters.

Description

Technical Field

[0001] This invention relates to the field of power semiconductor device technology, and more specifically to a method for improving the operating life of silicon carbide (SiC) MOSFET devices in inverters. Background Technology

[0002] Since the beginning of the 21st century, countries around the world have attached great importance to the resource shortages and climate change caused by the large-scale development and utilization of fossil fuels. Accelerating the development and utilization of new energy sources has become a common consensus and a unified action among countries worldwide. New energy has entered an era of large-scale development, with its technological and economic efficiency continuously improving. my country's new energy sector will further enter a period of accelerated development, gradually reducing and replacing fossil fuels, and becoming a vital force in promoting the transition of energy towards clean and low-carbon energy.

[0003] Taking solar and wind power as examples, converters play a crucial role in both power generation methods: in wind power, the generator-side converter rectifies AC to DC, while the grid-side converter inverts DC to AC; in solar power, the converter converts DC to AC. In summary, converters are a core component of both wind and solar power systems. According to relevant research, power devices are quite fragile in wind power, solar power, and traction converters. Although power device manufacturers improve reliability through manufacturing processes, and application engineers equip drive circuits with appropriate protection circuits, the fluctuations, intermittency, and uncertainty of power handled by SiC MOSFETs can still cause aging and even failure.

[0004] In existing technologies, the techniques for improving the operating life of SiC MOSFETs in three-phase inverters are limited. Most methods are based on changing the switching frequency or modulation method to reduce switching losses. However, these methods can only reduce the switching losses of SiC MOSFETs in three-phase inverters, but cannot reduce the conduction losses. When the three-phase inverter is in a condition where the conduction loss accounts for a large proportion, changing the switching frequency or modulation method cannot effectively reduce the losses of SiC MOSFETs, and therefore cannot effectively improve the operating life of SiC MOSFET devices. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a method to improve the operating life of SiC MOSFETs in three-phase inverters, and to solve the problem that the high conduction loss of the main bridge arm easily leads to the premature aging or failure of SiC MOSFET devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for improving the operating life of SiC MOSFET devices in an inverter, characterized in that, in a three-phase inverter including main bridge arms A, B, and C, a redundant bridge arm D for time-sharing conduction and a bidirectional thyristor T for commutation are provided. A T B and T C ; wherein, the midpoint of the redundant bridge arm D used for time-division conduction is connected to the three bidirectional thyristors T used for commutation. A T B and T C One end is connected, and the redundant bridge arm is also connected to the bus; three bidirectional thyristors T for commutation A T B and T C The other end is connected to the midpoint of the three-phase bridge arm in the three-phase inverter;

[0008] The controller issues control commands to determine whether time-sharing conduction control is needed based on the phase of the output current of each phase in the three-phase main bridge arms A, B, and C. When it is determined that the current of a certain phase enters a large range, the controller turns on the bidirectional thyristor connected to that phase and sends the drive signal of that phase bridge arm to the redundant bridge arm, while turning off the SiC MOSFET on that phase bridge arm. This temporarily "rests" that phase bridge arm, thereby reducing the peak junction temperature and junction temperature fluctuation amplitude of that bridge arm. This, in turn, enables the three-phase main bridge arms A, B, and C, the redundant bridge arm D, and the bidirectional thyristor T... A T B and T C The time-sharing and commutation of the SiC MOSFETs in a three-phase inverter are used to improve their lifespan. Since the output current of a three-phase inverter varies sinusoidally, when the output current of a phase enters a larger range (e.g., phase A), the output current is larger when it reaches 60°-120° and 240°-300°. By turning on the bidirectional thyristor connected to this phase and transferring the phase's drive signal to the drive signal of the redundant bridge arm, and turning off the SiC MOSFET on that phase's bridge arm, the redundant bridge arm can replace the working phase's bridge arm. This reduces the losses of the SiC MOSFET on that phase's bridge arm, thereby reducing the peak junction temperature and junction temperature fluctuation amplitude, and ultimately improving the lifespan of the SiC MOSFETs in the inverter.

[0009] Furthermore, when phase A is turned on in a time-division manner, the SiCMSOFET of phase A bridge arm is first turned off by the controller (software). Then, the modulation wave of phase A bridge arm is sent to the redundant bridge arm D by software control, so that the redundant bridge arm D can replace phase A bridge arm to complete the inverter function. Finally, the bidirectional thyristor T is triggered. A Thus, redundant bridge arm D and bidirectional thyristor T AThey are all turned on at the same time to replace the operation of phase A bridge arm; the control of phases B and C is the same; each bidirectional thyristor realizes the time-division conduction of the corresponding bridge arm.

[0010] When ending the time-sharing conduction of phase A bridge arm, it is necessary to refer to the bidirectional thyristor T... A The direction of the current in the bidirectional thyristor is used to control the drive signal of the redundant bridge arm D; if the current flow of the bidirectional thyristor is outflowing from the redundant bridge arm D, that is, from T... A When the flow from terminal T2 to terminal T1 ends, and the time-sharing conduction of phase A bridge arm is terminated, it is necessary to turn on the lower SiC MOSFET of redundant bridge arm D, thereby turning on the bidirectional thyristor T. A The T2 terminal is connected to the negative bus. Because the bidirectional thyristor T2 is activated when the SiC MOSFET on the upper arm of phase A is turned on... A The T1 terminal is connected to the positive bus, at which point the bidirectional thyristor T... A It withstands a reverse voltage opposite to the direction of current flow during conduction, and does not supply the bidirectional thyristor T. A Provides drive pulse, bidirectional thyristor T A It can then be turned off within the specified time, completing the time-sharing redundancy of phase A bridge arm. If the current direction is flowing into the redundant bridge arm D, then the upper SiC MOSFET of the redundant bridge arm D needs to be turned on. Similarly, when the lower SiC MOSFET of phase A bridge arm is turned on, the bidirectional thyristor T... A It can be successfully turned off when subjected to reverse voltage.

[0011] Furthermore, when the three-phase bridge arms do not need to be time-divisionally turned on, the controller sends a drive signal to the drive circuit of the SiC MOSFET device, so that the A, B, and C bridge arms can complete the inverter function normally, while the D bridge arm does not work, thus realizing the normal driving and time-division switching of the SiC MOSFETs in the three-phase inverter bridge arms.

[0012] Since the distance between each time interval of the A, B and C phase bridge arms is 30°, and the time difference between each time interval is 1.67ms under the condition of output current frequency of 50Hz, there is enough time for time-division switching.

[0013] The method for selecting the time-sharing interval for phase A bridge arm is as follows: Since the output current of phases A, B, and C bridge arms is a sine wave, taking the SiC MOSFET on the upper part of phase A bridge arm as an example, assuming a power factor of 1, the expression for the output current of phase A bridge arm is: According to the SPWM principle, the losses of the SiC MOSFET on the upper arm of phase A also exhibit a sinusoidal pattern in the 0-180° range, mirroring the trend of the phase A output current. Since the phase A output current is relatively large in the 60°-120° and 240°-300° ranges, the majority of losses are concentrated in these two ranges. Therefore, when the phase A output current enters these ranges, the phase A arm is time-division turned on; otherwise, it is not time-division turned on.

[0014] The final determined time-sharing intervals for phases A, B, and C are as follows: Taking a power factor of 1 as an example, the expression for the output current of phase A of the three-phase inverter is: Where A represents the amplitude of the output current. This refers to the phase of the output current in phase A. When When the angles are between 90° and 120° and between 270° and 300°, according to the sine function expression, the output current of phase A is relatively large in these intervals. Therefore, the losses of the SiC MOSFET in phase A bridge arm are also relatively large. Thus, these intervals are chosen for time-sharing conduction of phase A bridge arm. The expression for the output current of phase B is: The expression for the output current of phase C is: Similarly, from the sine function expression, and ensuring that the service life of phases A, B, and C are consistent, it can be deduced that when... When the angle is between 30° and 60° and between 210° and 240°, the output current of phase B bridge arm is relatively large, so phase B bridge arm is time-division turned on. When the C-phase bridge arm is located between 150° and 180° and between 330° and 360°, the C-phase bridge arm output current is relatively large, so the C-phase bridge arm is turned on in a time-division manner.

[0015] The loss analysis for redundant bridge arm D is as follows: Because it's necessary to ensure consistent operating lifespan for phases A, B, and C, the time-division redundant bridge arm D needs to achieve time-division conduction of phases A, B, and C within one fundamental frequency cycle. Taking the upper SiC MOSFET of bridge arm D as an example, in the three intervals of 90° to 120°, 210° to 240°, and 330° to 360°, the upper SiC MOSFET of bridge arm D replaces the upper SiC MOSFETs of phases A, B, and C for forward conduction. Because the duty cycle is high in these three intervals, i.e., the conduction time is long, the losses are significant. In the three intervals of 30° to 60°, 150° to 180°, and 270° to 300°, the upper SiC MOSFET of bridge arm D shares the reverse freewheeling current of the upper SiC MOSFETs of phases B, C, and A. Because the duty cycle is low in these three intervals, i.e., the conduction time is short, the losses are lower.

[0016] The analysis of TRIAC is as follows: Each bidirectional thyristor needs to achieve time-division multiplexing of its corresponding bridge arm. Taking T... A For example, when the angle is between 90° and 120°, to perform time-division conduction on phase A arm, it is necessary to open T. A To achieve time-sharing redundancy, bridge arm D replaces bridge arm A. As can be seen from the inverter's working principle, at this time, the bidirectional thyristor must complete both the forward conduction of the upper SiC MOSFET of bridge arm A and the reverse freewheeling of the lower SiC MOSFET of bridge arm A. From 210° to 240°, it is necessary to complete both the forward conduction of the lower SiC MOSFET of bridge arm A and the reverse freewheeling of the upper SiC MOSFET of bridge arm A.

[0017] Furthermore, the controller model mentioned in this invention can be selected from the TMS320F28335 digital signal controller from TI, whose EPWM module can complete the driving task of the three-phase four-arm inverter.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The method of the present invention can reduce the conduction loss and switching loss of SiCMOSFET devices in the inverter without changing the modulation mode and switching frequency of the three-phase inverter, effectively reduce the junction temperature peak and junction temperature fluctuation amplitude during the operation of SiC MOSFET, reduce the failure risk of SiC MOSFET application equipment (such as converters) due to overload and other conditions, improve the service life of SiC MOSFET, and improve equipment reliability.

[0020] 2. This invention has an ingenious concept and a reasonable design. In terms of hardware, this technology only requires one set of redundant bridge arms and three bidirectional thyristors, which is much cheaper than directly connecting three sets of bridge arms in parallel. It can effectively reduce the peak junction temperature and junction temperature fluctuation amplitude of SiC MOSFETs in the converter. Moreover, if a phase bridge arm device fails, the redundant bridge arm can directly replace the phase bridge arm according to the actual situation, so as not to affect the normal operation of the inverter and avoid economic losses caused by downtime due to device failure.

[0021] 3. In terms of software control, there is no need to change the modulation method of the original three-phase inverter or the switching frequency of the SiC MOSFET devices, thus avoiding impact on the output power quality. It is only necessary to determine which phase arm needs to be turned on in a time-sharing manner based on the output current ranges of phases A, B, and C. The time-sharing process is simple: it only requires turning off a certain phase arm, transferring the corresponding phase arm drive signal to the redundant arm, and driving the corresponding bidirectional thyristor. The method of this invention has a reasonable selection of the time-sharing conduction range. This time-sharing conduction range not only significantly improves the operating life of the main arm SiC MOSFET but also ensures that the operating life of the redundant arm D and the bidirectional thyristor matches the operating life of the main arm SiC MOSFET with minimal difference.

[0022] 4. This method can effectively reduce the peak junction temperature and junction temperature fluctuation amplitude of SiC MOSFETs, thereby reducing the failure risk of SiC MOSFET application equipment (such as converters) due to overload and other operating conditions, improving the service life of SiC MOSFETs, and enhancing the reliability of the equipment. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the three-phase four-arm inverter of the present invention.

[0024] Figure 2 This is a schematic diagram of the time-sharing conduction interval of the three-phase bridge arm of the present invention.

[0025] Figure 3 The waveform diagram shows the loss of the SiC MOSFET in phase A without time division.

[0026] Figure 4 The waveform of the junction temperature of the SiC MOSFET in phase A without time division is shown.

[0027] Figure 5 The waveform diagram of the loss of the upper SiC MOSFET of phase A after time division is shown in the present invention.

[0028] Figure 6 This is a waveform diagram of the junction temperature of the SiC MOSFET in phase A after time division according to the present invention.

[0029] Figure 7 This is a bar chart showing the relative damage level of the SiC MOSFET in phase A before time division in this invention.

[0030] Figure 8 This is a bar chart showing the relative damage level of the SiC MOSFET on phase A after time division in this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] like Figure 1 As shown, this invention provides a method for improving the operating life of SiC MOSFET devices in an inverter. In a three-phase inverter including main bridge arms A, B, and C, a redundant bridge arm D for time-sharing conduction and a bidirectional thyristor T for commutation are provided. A T B and T C ; wherein, one end of the redundant bridge arm D used for time-division conduction is connected to three bidirectional thyristors T for commutation. A T B and T C One end is connected to the busbar, and three bidirectional thyristors T are used for commutation. A T B and T C The other end is connected to the midpoint of the three-phase bridge arm in the three-phase inverter. When the output current of a certain phase in the three-phase inverter enters a specific range, the bidirectional thyristor connected to that phase is turned on, and the drive signal of that phase is transferred to the drive signal of the redundant bridge arm. The SiC MOSFET on that phase bridge arm is turned off, so that the redundant bridge arm can replace the operation of that phase bridge arm, reduce the loss of the SiC MOSFET on that phase bridge arm, thereby reducing the peak junction temperature and junction temperature fluctuation amplitude of that phase bridge arm, and thus improving the operating life of the SiC MOSFET in the inverter.

[0034] This invention employs a controller that issues control commands to determine whether time-division multiplexing (TDM) control is needed based on the phase of the output current of each phase in the three-phase main bridge arms A, B, and C. When it is determined that the current of a certain phase has entered a large range, the controller turns on the bidirectional thyristor connected to that phase, sends the drive signal of that phase bridge arm to the redundant bridge arm, and turns off the SiC MOSFET on that phase bridge arm, thereby temporarily "resting" that phase bridge arm. This reduces the peak junction temperature and junction temperature fluctuation amplitude of that bridge arm, thus achieving the goal of controlling the three-phase main bridge arms A, B, and C, the redundant bridge arm D, and the bidirectional thyristor T. A T B and T C The time-sharing conduction and commutation are used to improve the operating life of SiC MOSFETs in three-phase inverters.

[0035] See Figure 2 This is a schematic diagram of the time-sharing conduction interval of the three-phase bridge arm of the present invention. Taking a power factor of 1 as an example, the expression for the A-phase output current of the three-phase inverter is: Where A represents the amplitude of the output current. This refers to the phase of the output current in phase A. When When the angle is between 90° and 120° and between 270° and 300°, the output current of phase A is relatively large within this range, resulting in higher losses for the SiC MOSFET in the phase A bridge arm. Therefore, this range is chosen for time-division multiplexing of the phase A bridge arm. The expression for the output current of phase B is: The expression for the output current of phase C is: Similarly, it can be appropriate When the angles are 30° to 60° and 210° to 240°, the B-phase bridge arm is time-division switched on. When the angle is between 150° and 180° and between 330° and 360°, the C-phase bridge arm is switched on in a time-division manner.

[0036] Depend on Figure 2 It can be seen that the time-division redundant bridge arm D needs to achieve time-division conduction of phases A, B, and C within one sinusoidal cycle. Taking the upper SiC MOSFET of bridge arm D as an example, in the three intervals of 90° to 120°, 210° to 240°, and 330° to 360°, the upper SiC MOSFET of bridge arm D replaces the upper SiC MOSFETs of phases A, B, and C for forward conduction, and the losses are relatively large in these three intervals. In the three intervals of 30° to 60°, 150° to 180°, and 270° to 300°, the upper SiC MOSFET of bridge arm D shares the reverse freewheeling current of the upper SiC MOSFETs of phases B, C, and A, and the losses are relatively small in these three intervals.

[0037] When phase A is turned on in a time-division manner, the SiC MSOFET of phase A arm is first turned off by software. Then, the modulation wave of phase A arm is sent to the redundant arm D by software control, so that the redundant arm D can replace phase A arm to complete the inverter function. Finally, the bidirectional thyristor T is triggered. A Thus, redundant bridge arm D and bidirectional thyristor T A They are switched on together to replace the operation of phase A. The control of phases B and C works in the same way.

[0038] The controller issues control commands to achieve normal driving and time-sharing switching of the SiC MOSFETs in the three-phase inverter bridge arms. Because the output current of the A, B, and C phase bridge arms is a sine wave, taking the upper SiC MOSFET of the A phase bridge arm as an example, the loss of the upper SiC MOSFET of the A phase bridge arm is also sinusoidal in the 0-180° range, with most of the loss concentrated between 60° and 120°. Therefore, it is not necessary to time-sharing the upper SiC MOSFET of the A phase bridge arm throughout the entire 0-180° range. Similarly, the lower SiC MOSFET does not need to time-sharing the entire 180°-360° range.

[0039] Each bidirectional thyristor needs to achieve time-division switching of its corresponding bridge arm. (T) A For example, when the A-phase bridge arm is turned on in a time-division manner between 90° and 120°, the bidirectional thyristor must complete both the forward conduction of the upper SiC MOSFET of the A-phase bridge arm and the reverse freewheeling of the lower SiC MOSFET of the A-phase bridge arm. When the A-phase bridge arm is turned on in a time-division manner between 210° and 240°, it must complete both the forward conduction of the lower SiC MOSFET of the A-phase bridge arm and the reverse freewheeling of the upper SiC MOSFET of the A-phase bridge arm.

[0040] Depend on Figure 2 It can be seen that the time-sharing intervals of phases A, B and C do not overlap, and the distance between each time-sharing interval is 30°. Under the condition of output current frequency of 50Hz, the time difference between each time-sharing interval is 1.67ms, which is enough time for time-sharing switching.

[0041] See Figure 3The image shows the loss waveform of the upper SiC MOSFET in phase A without time-sharing redundancy. Taking a power factor of 1 as an example, the inverter parameters are: DC side voltage 800V, output current RMS value 40A, switching frequency 10kHz, ambient temperature 25℃, and device model IMZA120R030M1H. It can be seen that the loss waveform of the upper SiC MOSFET in phase A of the inverter without time-sharing redundancy is as follows: Since the three-phase inverter power frequency is 50Hz, one cycle is 20ms. Therefore, the starting point is 0.00s and the ending point is 0.02s. From 0.00s to 0.01s, the SiC MOSFET is in forward conduction, hence the higher loss. From 0.01s to 0.02s, the SiC MOSFET is in reverse freewheeling state, hence the lower loss.

[0042] See Figure 4 The figure shows the junction temperature waveform of the SiC MOSFET in phase A without time-division multiplexing. As can be seen from the figure, taking a power factor of 1 as an example, without time-division multiplexing, starting from 0.00s and ending at 0.02s, the SiC MOSFET is in forward conduction from 0.00s to 0.01s, resulting in high losses and a rapid rise in junction temperature. The peak junction temperature in this range is 94.32℃, with a temperature fluctuation of 38.25℃. From 0.01s to 0.02s, because the SiC MOSFET is in reverse freewheeling mode, losses are low, and the junction temperature drops rapidly.

[0043] See Figure 5 The figure shows the loss waveform of the upper SiC MOSFET in phase A after time-sharing redundancy. As can be seen from the figure, taking a power factor of 1 as an example, with time-sharing redundancy added, the loss waveform of the upper SiC MOSFET in phase A of the inverter increases normally from 0.00s to 0.005s. However, from 0.005s to 0.0067s, the upper SiC MOSFET in phase A is in the time-sharing conduction range and does not work, so the loss is zero. After the time-sharing conduction ends, the loss increases again. Similarly, from 0.015s to 0.0167s, the upper SiC MOSFET in phase A is also in the time-sharing conduction range. However, because the body diode of the upper SiC MOSFET in phase A will still conduct when the current is large, the loss of the upper SiC MOSFET in phase A will decrease, but not to zero. After the time-sharing conduction ends, the loss returns to normal.

[0044] refer to Figure 6The image shows the junction temperature waveform of the SiC MOSFET on the upper arm of phase A after time-sharing. Taking a power factor of 1 as an example, it can be seen that when time-sharing is applied, the junction temperature of the SiC MOSFET on the upper arm of phase A in the inverter rises normally from 0.00s to 0.005s. However, from 0.005s to 0.0067s, the SiC MOSFET on the upper arm of phase A is in the time-sharing conduction range, with zero loss, and the junction temperature drops. Subsequently, when the time-sharing conduction ends, the junction temperature continues to rise. Similarly, from 0.015s to 0.0167s, the SiC MOSFET on the upper arm of phase A is also in the time-sharing conduction range. The loss of the SiC MOSFET on the upper arm of phase A decreases, so the junction temperature of the SiC MOSFET on the upper arm of phase A decreases faster in this range. Subsequently, the loss returns to normal, and the junction temperature fluctuates before returning to the normal rate of decrease. With time-sharing enabled, the peak junction temperature of the SiC MOSFET on the upper arm of phase A is 76.14℃, and the junction temperature fluctuation amplitude is 30.75℃. It can be seen that with time-sharing enabled, the peak junction temperature and junction temperature fluctuation amplitude of the SiC MOSFET are greatly reduced, the aging rate of the SiC MOSFET is slowed down and the failure risk is reduced, thus verifying the effectiveness of the time-sharing enabled method.

[0045] Figure 7 This is a bar chart showing the relative damage levels of the SiC MOSFET in phase A before time division. Figure 8 This is a bar chart showing the relative damage level of the SiC MOSFET in phase A after time-sharing. Figure 7 and Figure 8 It can be seen that the average junction temperature and the amplitude of junction temperature fluctuation of the SiC MOSFET on the upper arm of phase A before time-sharing are significantly higher than those after time-sharing. Related studies indicate that junction temperature fluctuation is more likely to cause accelerated aging or even failure of SiC MOSFETs than the average junction temperature. Figure 7 and Figure 8 It can also be seen that the higher average junction temperature and junction temperature fluctuation amplitude before time-sharing also caused a more severe degree of relative damage. Therefore, it can be concluded that the time-sharing method can significantly improve the operating life of the SiC MOSFETs in the main bridge arm of the inverter.

[0046] In summary, the control method of this invention does not require interrupting the normal operation of the three-phase inverter, nor does it require changing the modulation method or the switching frequency of the SiC MOSFET. It can reduce the large conduction and switching losses of the SiC MOSFET in the inverter without affecting the current quality. It solves the problem of excessively high conduction losses in the main bridge arm that most lifespan improvement methods cannot solve, effectively improving the operating life of the SiC MOSFET in the inverter and reducing the risk of SiC MOSFET aging too quickly or failing prematurely.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the operating life of SiC MOSFET devices in an inverter, characterized in that, In a three-phase inverter including main bridge arms A, B, and C, there is a redundant bridge arm D for time-sharing conduction and a bidirectional thyristor T for commutation. A T B and T C ; wherein, the midpoint of the redundant bridge arm D used for time-division conduction is connected to the three bidirectional thyristors T used for commutation. A T B and T C One end is connected, and the redundant bridge arm is also connected to the bus; three bidirectional thyristors T for commutation A T B and T C The other end is connected to the midpoint of the three-phase bridge arm in the three-phase inverter; The controller issues control commands to determine whether time-sharing conduction control is needed based on the phase of the output current of each phase in the three-phase main bridge arms A, B, and C. When it is determined that the current of a certain phase has entered a large range, the controller turns on the bidirectional thyristor connected to that phase and sends the drive signal of that phase bridge arm to the redundant bridge arm, while turning off the SiC MOSFET on that phase bridge arm. This temporarily "rests" that phase bridge arm, thereby reducing the peak junction temperature and junction temperature fluctuation amplitude of that bridge arm. This, in turn, enables the three-phase main bridge arms A, B, and C, the redundant bridge arm D, and the bidirectional thyristor T... A T B and T C The time-sharing conduction and commutation are used to improve the operating life of SiC MOSFETs in three-phase inverters; When phase A is turned on in a time-division manner, the SiC MSOFET of phase A arm is first turned off by the controller via software control. Then, the modulation wave of phase A arm is sent to the redundant arm D via software control, so that the redundant arm D can replace phase A arm to complete the inverter function. Finally, the bidirectional thyristor T is triggered. A Thus, redundant bridge arm D and bidirectional thyristor T A They are all turned on at the same time to replace the A-phase bridge arm; the control of the B and C phases is the same; each bidirectional thyristor realizes the time-division conduction of the corresponding bridge arm.

2. The method for improving the operating life of SiC MOSFET devices in an inverter according to claim 1, characterized in that, When the three-phase bridge arms do not need to be turned on in a time-sharing manner, the controller sends a drive signal to the drive circuit of the SiC MOSFET device, so that the A, B, and C bridge arms can complete the inverter function normally, while the D bridge arm does not work, realizing the normal driving and time-sharing switching of the SiC MOSFETs in the three-phase inverter bridge arms.

3. The method for improving the operating life of SiC MOSFET devices in an inverter according to claim 1, characterized in that, The distance between each time-sharing interval of the A, B and C phase bridge arms is 30°. Under the condition of an output current frequency of 50Hz, the time difference between each time-sharing interval is 1.67ms, which provides sufficient time for time-sharing switching.

4. The method for improving the operating life of SiC MOSFET devices in an inverter according to claim 1, characterized in that, The controller is a TI TMS320F28335 digital signal controller, and the EPWM module on the controller can complete the driving task of the three-phase four-arm inverter.

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