SiC MOSFET junction temperature monitoring drive circuit based on high-frequency oscillation suppression and monitoring method

Abstract

The invention discloses a SiC MOSFET junction temperature monitoring circuit and monitoring method based on high-frequency oscillation suppression. The SiC MOSFET junction temperature monitoring circuit comprises a SiC MOSFET to be detected, a PCB mutual inductance coil, a high-frequency oscillation extraction unit, a grid adjustable driving unit and a junction temperature evaluation unit. According to the system, the oscillation time of the transient drain current of the SiC MOSFET switch is used as a temperature-sensitive electrical parameter to represent the junction temperature of the device, and the temperature sensitivity of the oscillation time can be improved by adjusting the grid amplifier to suppress high-frequency oscillation. According to the invention, the rapid detection of the junction temperature of the SiC MOSFET is realized, and the sensitivity of temperature-sensitive electrical parameters and the detection integration level are superior to those of a traditional junction temperature monitoring method.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a SiC MOSFET junction temperature monitoring drive circuit and a monitoring method based on high-frequency oscillation suppression. Background Art

[0002] Online extraction of junction temperature is the basis for reliability assessment and health management of SiC MOSFET. According to industry reports, about 38% of power converter system failures can be traced back to the failure of power devices, and among them, up to 55% of failures are caused by overheating. This phenomenon emphasizes the importance of temperature management in equipment health. Specifically, every time the junction temperature rises by 10°C, the equipment failure rate is likely to double. In order to meet this challenge, the development of junction temperature detection technology provides an effective data support method for power electronic equipment. By real-time monitoring of the junction temperature of SiC modules, engineers can have a good understanding of the thermal behavior of the equipment under different working conditions, so as to take corresponding measures to optimize the performance of the equipment and extend its service life. This monitoring not only helps prevent failures, but also predicts potential failure risks through data analysis, realizes preventive maintenance, reduces maintenance costs, and improves the overall efficiency and reliability of the system.

[0003] The junction temperature monitoring technology of SiC MOSFET is mainly based on two methods: the RC thermal network method and the heat-sensitive electrical parameter method. The RC thermal network method simulates the heat transfer process inside the power module by constructing an equivalent thermal resistance and thermal capacitance network. The core of this method is that the equivalent thermal resistance can reflect the dynamic relationship between the module temperature rise and the power consumption of the heat source, while the thermal capacitance reflects the accumulation and release of heat capacity during the heat transfer process, as well as the buffering effect on temperature rise and heat transfer. The RC thermal network method has certain limitations. The loss and thermal models are usually defined under specific and constant working conditions. They are based on rough estimates. Any changes in working conditions, such as load fluctuations, ambient temperature changes, etc., will lead to inaccuracies in model predictions, thereby affecting reliability assessments throughout the life cycle.

[0004] In order to overcome the limitations of the RC thermal network, the thermistor electrical parameter method is used. This method uses the characteristics of the electrical parameters inside the SiC MOSFET changing with temperature, and indirectly infers the junction temperature by measuring the changes in these parameters. Its core advantage is that it can provide more real-time and accurate temperature information; because it is directly related to the electrical characteristics of the device, rather than relying on external temperature sensing, it reduces the impact of external environmental changes on the measurement results.

[0005] SiC MOSFET performs better in thermal stability, but this also means that the sensitivity of its thermal electrical parameters is relatively lower. The reason for this phenomenon is that SiC MOSFET has a wider bandgap and requires more thermal energy to excite carriers, resulting in lower temperature sensitivity. Therefore, it is still difficult to promote the use of thermal electrical parameters for junction temperature monitoring in SiC MOSFET. Summary of the invention

[0006] The present invention is aimed at the technical problems existing in the prior art and provides a SiC MOSFET junction temperature monitoring drive circuit and a monitoring method based on high-frequency oscillation suppression. The present invention can improve the sensitivity of thermistor electrical parameters, making the application of thermistor electrical parameter method in the junction temperature monitoring of SiC MOSFET feasible.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] The embodiment of the present application provides a SiC MOSFET junction temperature monitoring drive circuit based on high-frequency oscillation suppression, and uses the oscillation time of the transient drain current of the SiC MOSFET switch as a temperature-sensitive electrical parameter to characterize the junction temperature of the device. The junction temperature monitoring circuit includes: a PCB mutual inductance coil, a high-frequency oscillation extraction unit, a junction temperature evaluation unit and a gate adjustable drive unit; wherein,

[0009] The PCB mutual inductance coil is used to provide a state signal of a high-speed change in the drain current of the SiC MOSFET, wherein the state signal is an induced potential of a change rate of the drain current of the SiC MOSFET;

[0010] The high-frequency oscillation extraction unit is used to receive the induced potential of the PCB mutual inductance coil, extract the high-frequency oscillation time, and output the high-frequency oscillation time to the junction temperature evaluation unit and the gate adjustable driving unit;

[0011] The gate adjustable driving unit is used to receive the switching signal and the high-frequency oscillation time signal, change the high-frequency oscillation time of the drain current by adjusting the moment of narrow pulse switching, and output the gate voltage to control the on and off of the SiC MOSFET;

[0012] The junction temperature evaluation unit is used to evaluate and determine the junction temperature of the SiC MOSFET according to the narrow pulse switching moment and the high-frequency oscillation time; the junction temperature evaluation unit stores a data table of the narrow pulse switching moment, the high-frequency oscillation time and the junction temperature under various operating conditions, and obtains the junction temperature of the SiC MOSFET by looking up the table.

[0013] In one embodiment, the gate adjustable driving unit comprises: a narrow pulse gate suspension unit and a gate adjustable amplifier unit; wherein,

[0014] The narrow pulse gate suspension unit is used to receive the switching signal and the high-frequency oscillation time, and output the turn-on transient regulation signal and the turn-off transient regulation signal, as well as the narrow pulse switching time;

[0015] The gate adjustable amplifier unit is composed of a push-pull circuit and is used to output a gate voltage according to the received turn-on transient regulation signal and turn-off transient regulation signal.

[0016] In one implementation, the high-frequency oscillation extraction unit includes: a positive oscillation detection circuit, a negative oscillation detection circuit, and a comparator;

[0017] The positive oscillation detection circuit is used to receive the induced potential of the PCB mutual inductance coil and output a comparison signal V t1 ;

[0018] The negative oscillation detection circuit is used to receive the induced potential of the PCB mutual inductance coil and output a comparison signal V t2 ;

[0019] The comparator is used to compare the signal V t1 As the negative input, the comparison signal V t2 As the positive input, it is compared in comparator CP1 and a comparison voltage is output. The duration of the high level of the comparison voltage is the high-frequency oscillation time.

[0020] In one embodiment, the positive oscillation detection circuit comprises: a resistor R os1 , R os2 , R os3 , R os4 , capacitor C os1 , C os2 , transistor Q osn The capacitor C os1 One end of the resistor R os1 One end of the resistor R os1 The other end of the resistor R os2 One end of the transistor Q osn The base of the resistor R os2 The other end is connected to the negative voltage -V DD , the transistor Q osn The emitter and the capacitor C os2 One end of the transistor Q osn The collector and the capacitor C os2 The other end of the resistor R os4 One end of the resistor R os4 The other end of the resistor R os3 One end of the resistor R is connected to the negative input terminal of the comparator CP1.os3 The other end is connected to the positive voltage V DD connected;

[0021] The negative oscillation detection circuit comprises: a resistor R os5 , R os6 , R os7 , R os8 , capacitor C os3 , C os4 , transistor Q osp The capacitor C os3 One end of the capacitor C os1 The other end, induced potential V i connected; the capacitor C os3 The other end of the resistor R os5 One end of the resistor R os5 The other end of the resistor R os6 One end of transistor Q osp The base of the resistor R os6 The other end is connected to the positive voltage V DD , transistor Q osp The emitter of the transistor Q osp The collector and the resistor R os7 One end of the resistor R os7 The other end of the resistor R os8 One end of the capacitor C os4 One end of the circuit is connected to the positive input terminal of the comparator CP1.

[0022] In one embodiment, a SiC MOSFET junction temperature monitoring circuit based on high frequency oscillation suppression is integrated into a gate driver.

[0023] The embodiment of the present application also provides a monitoring method of the SiC MOSFET junction temperature monitoring circuit based on the above-mentioned high-frequency oscillation suppression, and the monitoring method is:

[0024] During the SiC MOSFET turn-on transient and turn-off transient, the high-frequency oscillation extraction unit transmits the high-frequency oscillation time t in real time. os ; The gate adjustable driving unit is used to adjust and change the narrow pulse switching time so that the high-frequency oscillation time is t osmin and t osmax The junction temperature evaluation unit searches the data table of the junction temperature, high-frequency oscillation time, and narrow pulse switching moment model to evaluate and determine the specific junction temperature.

[0025] In one embodiment, the method for the high-frequency oscillation extraction unit to transmit the high-frequency oscillation time in real time is:

[0026] When the SiC MOSFET is turned on or off, the induced potential of the PCB mutual inductance coil is zero, and the comparison signal V t1 is zero, the comparison signal V t2 is high level, comparator CP1 outputs low level;

[0027] During the turn-on transient, when the drain current I D Entering the high-frequency oscillation process, the induced potential fluctuates positively and negatively, and the comparison signal V t2 Rapidly drops to zero, then the comparison signal V t1 Rapidly rises to a high level, and the comparator outputs a high-frequency oscillation time t os Switch high level until the oscillation process ends, and compare the signal V t1 Slowly decrease, compare signal V t2 Slowly rise until the comparison signal V t1 Greater than the comparison signal V t2 , the high-frequency oscillation time recovers to a low level, and the length of the high-frequency oscillation time high level is the oscillation time of the turn-on transient;

[0028] During the turn-off transient, when the drain current I D Entering the high-frequency oscillation process, the induced potential fluctuates positively and negatively, and the comparison signal V t1 Rapidly rises to a high level, and then compares the signal V t2 The comparator outputs a high-frequency oscillation time and switches to a high level until the oscillation process ends. t1 Slowly decrease, compare signal V t2 Slowly rise until the comparison signal V t1 Greater than the comparison signal V t2 , the high-frequency oscillation time recovers to a low level, and the length of the high-frequency oscillation time high level is the oscillation time of the shutdown transient.

[0029] In one embodiment, the narrow pulse gate suspension unit adjusts the drain current of the SiC MOSFET by controlling the gate adjustable amplifier unit, and the specific process includes:

[0030] When performing narrow pulse gate suspension, the output turn-on transient regulation signal V s_on and the shutdown transient regulation signal V s_of The upper push-pull device and the lower push-pull device are turned off at the same time; in the turn-on transient, the narrow pulse gate suspension occurs at a certain moment in the SiCMOSFET drain current rising process, and in the turn-off transient, the narrow pulse gate suspension occurs at a certain moment in the SiCMOSFET drain current falling process.

[0031] In one implementation, the method for constructing the junction temperature, high-frequency oscillation time, and narrow pulse switching timing model is:

[0032] Set the temperature step to ΔT j , the junction temperature of SiC MOSFET is evenly divided into n temperature segments;

[0033] The narrow pulse switching time t of the xth (x=1,2…,n) temperature range swx (x=1,2…,n) is a fixed value;

[0034] In the xth temperature range, the narrow pulse switching time t swx Ensure the minimum junction temperature T j(x-1) The oscillation time is the minimum value t osmin , the oscillation time at the highest junction temperature is the maximum value t osmax ;

[0035] The operating conditions are set under the condition that the operating voltage, operating current and junction temperature range of SiC MOSFET are not exceeded. For the operating conditions of specific operating voltage and operating current, in the SiC MOSFET switching transient, as the junction temperature T j The gradual increase of high-frequency oscillation time t os , narrow pulse switching time t sw The data of the junction temperature evaluation unit is collected to establish the junction temperature Tj, high-frequency oscillation time t under this operating condition. os And the narrow pulse switching time signal t sw data table.

[0036] In one embodiment, when the junction temperature of the SiC MOSFET is evenly divided into two levels, the lowest junction temperature T j(x-1) The minimum oscillation time t osmin , the maximum oscillation time t at the highest junction temperature osmax The determination process is:

[0037] The first gear is the lowest temperature segment. First, determine the narrow pulse switching moment of the first temperature segment, adjust the temperature to the lowest temperature of the first gear, shield the narrow pulse switching moment during the switching transient process, and when the drain current changes and the comparator CP1 of the high-frequency oscillation extraction unit outputs a high level, it is identified as the latest boundary of the narrow pulse switching moment. Then, the narrow pulse switching moment is continuously advanced from the latest boundary. When the oscillation time t os Reach the minimum value t osmin At this time, the narrow pulse switching time t sw1 That is the narrow pulse switching moment of the first temperature range. The junction temperature of the first temperature range is continuously increased, and the narrow pulse switching moment is kept unchanged. At this time, the oscillation time t osAs the junction temperature increases, when the junction temperature reaches the maximum temperature of the first temperature range, the oscillation time reaches the maximum value t osmax ;

[0038] Entering the second temperature range, the lowest temperature of the second temperature range is also the highest temperature of the first temperature range. First, shield the narrow pulse switching time, confirm the latest boundary of the narrow pulse switching time, and continue to advance the narrow pulse switching time. When the oscillation time t os Reach the minimum value t osmin At this time, the narrow pulse switching time t sw2 This is the narrow pulse switching moment of the second temperature range. The junction temperature of the second temperature range is continuously increased, and the narrow pulse switching moment is kept unchanged. At this time, the oscillation time t os As the junction temperature increases, when the junction temperature reaches the maximum temperature of the second temperature range, the oscillation time reaches the maximum value t osmax .

[0039] In one implementation, the junction temperature evaluation unit searches the data table of the junction temperature, high-frequency oscillation time, and narrow pulse switching time model, and evaluates and determines the specific junction temperature. The specific process is:

[0040] When the SiC MOSFET is not running, the initial narrow pulse switching time is the switching time t of the first temperature range. sw1 During the continuous operation of SiC MOSFET, the high-frequency oscillation extraction unit transmits the high-frequency oscillation time t in real time. os , if the oscillation time t os In t osmin and t osmax If the junction temperature is in the first temperature range, the transmission oscillation time t os When the oscillation time t increases, the junction temperature of SiCMOSFET rises. os Exceeded t osmax , then the temperature range is raised to the next level, and the narrow pulse switching time is changed accordingly until the oscillation time t os In t osmin and t osmax In each temperature range, when the transmission oscillation time t os When the oscillation time t os Lower than t osmin , then the temperature range is reduced by one level, and the narrow pulse switching time is changed accordingly; the narrow pulse switching time t swx Determine the temperature range in which the SiC MOSFET junction temperature is located, and then calculate the high-frequency oscillation time t os Determine the specific junction temperature T j .

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] The present invention can integrate the junction temperature monitoring function into the gate drive, which can extract the drain oscillation current during the switching transient state, and use the high-frequency oscillation time as the temperature-sensitive electrical parameter of the SiC MOSFET junction temperature; the narrow pulse gate suspension method is adopted to improve the temperature sensitivity of the high-frequency oscillation time, thereby making the method of the thermal-sensitive electrical parameter possible; by outputting the narrow pulse switching moment of the junction temperature segment, the oscillation is limited to the range of low oscillation time and high temperature sensitivity, achieving a compromise between high sensitivity of junction temperature monitoring and oscillation suppression. The temperature sensitivity of the present invention exceeds 2ns / ℃, and is more suitable for integration in active gate drive. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work:

[0044] Figure 1 A block diagram of a SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression provided by an embodiment of the present invention;

[0045] Figure 2 A block diagram of a SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression provided by another embodiment of the present invention;

[0046] Figure 3 is a structural block diagram of a high frequency oscillation extraction unit in one embodiment of the present invention;

[0047] Figure 4 is a circuit diagram of a high frequency oscillation extraction unit in one embodiment of the present invention;

[0048] Figure 5 It is a simulation waveform diagram of the node voltage of the high-frequency oscillation extraction circuit in the SiC MOSFET turn-on transient state in one embodiment of the present invention;

[0049] Figure 6 It is a simulation waveform diagram of the node voltage of the high-frequency oscillation extraction circuit in the SiC MOSFET turn-off transient state in one embodiment of the present invention;

[0050] Figure 7 A schematic diagram of the equivalent principle of high-frequency oscillating current induced potential in one embodiment of the present invention;

[0051] Figure 8 This is a schematic diagram of a SiC MOSFET turn-on transient narrow pulse gate suspension in one embodiment of the present invention;

[0052] Fig. 9 The schematic diagram of the SiC MOSFET turn-off transient narrow pulse gate suspension in one embodiment of the present invention;

[0053] Fig.10 This is a schematic diagram of the transient narrow pulse switching timing of turning on SiC MOSFET in one embodiment of the present invention;

[0054] Fig.11 This is a schematic diagram of the transient narrow pulse switching moment of SiC MOSFET turn-off in one embodiment of the present invention;

[0055] Fig.12 is a flow chart for determining the switching time of narrow pulses in each temperature section in one embodiment of the present invention;

[0056] Fig.13 The relationship between the transient high-frequency oscillation time and junction temperature of SiC MOSFET switch under traditional drive;

[0057] Fig.14 A graph showing the relationship between the transient high-frequency oscillation time and junction temperature of a SiC MOSFET switch provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] In order to more clearly understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0059] like Figure 1 As shown, an embodiment of the present invention shows a SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression, the junction temperature monitoring circuit uses the oscillation time of the transient drain current of the SiC MOSFET switch as a temperature-sensitive electrical parameter to characterize the junction temperature of the device, and the junction temperature monitoring circuit includes: a PCB mutual inductance coil, a high-frequency oscillation extraction unit, a junction temperature evaluation unit and a gate adjustable drive unit; wherein,

[0060] The PCB mutual inductance coil is used to provide a state signal of a high-speed change of the drain current of the SiC MOSFET, wherein the state signal is an induced potential of the change rate of the drain current of the SiC MOSFET;

[0061] A high-frequency oscillation extraction unit is used to receive the induced potential of the PCB mutual inductance coil, extract the high-frequency oscillation time, and output the high-frequency oscillation time to the junction temperature evaluation unit and the gate adjustable driving unit;

[0062] The gate adjustable drive unit is used to receive the switching signal and the high-frequency oscillation time, change the high-frequency oscillation time of the drain current by adjusting the moment of narrow pulse switching, and output the gate voltage to control the on and off of the SiC MOSFET;

[0063] The junction temperature evaluation unit is used to evaluate and determine the junction temperature of the SiC MOSFET according to the received adjustment narrow pulse switching moment and high-frequency oscillation time; the junction temperature evaluation unit stores a data table of narrow pulse switching moment, high-frequency oscillation time and junction temperature under various operating conditions, and obtains the junction temperature of the SiC MOSFET by looking up the table.

[0064] Reference Figure 2 As shown, another embodiment of the present invention shows a SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression. In the embodiment of the present application, the gate adjustable driving unit includes a narrow pulse gate suspension unit and a gate adjustable amplifier unit; wherein the narrow pulse gate suspension unit is used to receive a switching signal and a high-frequency oscillation time, and output a turn-on transient adjustment signal and a turn-off transient adjustment signal, as well as a narrow pulse switching moment; the gate adjustable amplifier unit is composed of a push-pull circuit, and is used to output a gate voltage according to the received turn-on transient adjustment signal and the turn-off transient adjustment signal.

[0065] Specifically, the narrow pulse gate suspension unit is used to adjust the narrow pulse switching time t sw , thereby changing the high-frequency oscillation time of the drain current; the gate adjustable amplifier unit is used to output the gate voltage V gs Control the on and off of SiC MOSFET; the narrow pulse gate suspension unit receives the switching signal V PWM and high frequency oscillation time t os and outputs a turn-on transient adjustment signal V to the gate adjustable amplifier unit s_on and the shutdown transient regulation signal V s_of , outputs narrow pulse switching time t to the junction temperature evaluation unit sw ; The gate adjustable amplifier unit outputs the gate voltage V gs .

[0066] The high-frequency oscillation extraction unit receives the induced potential V of the PCB mutual inductance coil i , output high-frequency oscillation time t to the junction temperature evaluation unit and the narrow pulse gate suspension unit os The narrow pulse gate suspension unit adjusts the drain current of the SiC MOSFET by controlling the gate adjustable amplifier unit.

[0067] Furthermore, the gate adjustable amplifier unit is composed of a push-pull circuit, which turns on the transient adjustment signal V s_on Control the opening and closing of the push-pull device and shut down the transient regulation signal V s_of Control the opening and closing of the push-pull device.

[0068] Figure 3The high-frequency oscillation extraction unit includes: a positive oscillation detection circuit, a negative oscillation detection circuit and a comparator CP1; the positive oscillation detection circuit receives the induced potential V of the PCB mutual inductance coil. i , output comparison signal V t1 ; The negative oscillation detection circuit receives the induced potential V of the PCB mutual inductance coil i , output comparison signal V t2 ; Comparator CP1 compares the signal V t1 As the negative input terminal, the comparison signal V t2 As the positive input terminal for comparison, the output comparison voltage V tos , comparison voltage V tos The duration of the high level is the high frequency oscillation time t os .

[0069] Further, the specific circuit of the high frequency oscillation extraction unit is as follows: Figure 4 As shown. The positive oscillation detection circuit includes: resistor R os1 , R os2 , R os3 , R os4 , capacitor C os1 , C os2 , transistor Q osn ;

[0070] Capacitor C os1 One end of the resistor R os1 One end of the resistor R os1 The other end of the resistor R os2 One end of transistor Q osn The base of the resistor R os2 The other end is connected to the negative voltage -V DD , transistor Q osn The emitter, capacitor C os2 One end of the transistor Q osn The collector and capacitor C os2 The other end of the resistor R os4 One end of the resistor R os4 The other end of the resistor R os3 One end of the comparator CP1 is connected to the negative input terminal, and the resistor R os3 The other end is connected to the positive voltage V DD connected;

[0071] The negative oscillation detection circuit includes: resistor R os5 , R os6 , R os7 , R os8 , capacitor C os3 , C os4 , transistor Qosp ; Capacitor C os3 One end of the capacitor C os1 The other end, induced potential V i Connected, capacitor C os3 The other end of the resistor R os5 One end of the resistor R os5 The other end of the resistor R os6 One end of transistor Q osp The base of the resistor R os6 The other end is connected to the positive voltage V DD , transistor Q osp The emitter of transistor Q osp The collector and resistor R os7 One end of the resistor R os7 The other end of the resistor R os8 One end of the capacitor C os4 One end of the circuit is connected to the positive input terminal of the comparator CP1.

[0072] Furthermore, the SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression is integrated into the gate driver, which is particularly suitable for integration into active gate drivers.

[0073] In one embodiment, a monitoring method of a SiC MOSFET junction temperature monitoring circuit based on the above-mentioned high-frequency oscillation suppression is proposed, and the method includes:

[0074] During the SiC MOSFET turn-on transient and turn-off transient, the high-frequency oscillation extraction unit transmits the high-frequency oscillation time t in real time. os ; The gate adjustable driving unit is used to adjust and change the narrow pulse switching time so that the high-frequency oscillation time is t osmin and t osmax The junction temperature evaluation unit searches the data table of the junction temperature, high-frequency oscillation time, and narrow pulse switching moment model to evaluate and determine the specific junction temperature.

[0075] Combine the following Figure 5 The simulation waveform shown introduces the principle of high-frequency oscillation detection of SiC MOSFET during turn-on transient:

[0076] When the SiC MOSFET is turned on or off, the PCB Rogowski coil induced potential V i is zero, so the capacitance C os1 The voltage is V DD , C os3 The voltage is -V DD ; Transistor Q osp and Q osn Both are in the off state. At this time, the comparison signal V t1 VDD , comparison signal V t2 is zero, comparator CP1 outputs a low level;

[0077] During the turn-on transient, when the drain current I D When it starts to rise, the Rogowski coil induces a positive potential V i ; V i After C os1 Transistor Q osn The base of transistor Q osn is turned on, so the comparison signal V t1 Rapidly decreases. Similarly, transistor Q osp Still in the off state, the comparison signal V t2 By matching the resistor R os3 and R os4 value, ensuring that the comparison signal V t1 Still slightly higher than the comparison signal V t2 , the comparison voltage V output by comparator CP1 tos Keep it at low level until the drain current I D When it starts to decline after reaching the overshoot and enters the high-frequency oscillation process, the PCB mutual inductance coil induces a reverse potential and outputs an induced potential V i is a negative voltage. Transistor Q osn Shutdown, comparison signal V t1 remains unchanged. The induced potential V i Through capacitor C os3 The transistor Q osp Base charge extraction causes transistor Q osp Turn on, compare signal V t2 Rapidly rises to positive voltage V DD , and is higher than the comparison signal V t1 , causing the output of comparator CP1 to switch to a high level, which is represented as the start time of high-frequency oscillation t m0 During the oscillation process, transistor Q osn With Q osp Constantly switching the switch state. Due to the filter capacitor C os3 and C os4 The short-term energy storage capability of the comparison signal V t1 With V t2 remains unchanged, so the comparison voltage V tos Maintain a high level. Due to the energy dissipation caused by the power circuit damping, as the oscillation period increases, the oscillation amplitude decreases. When the induced potential V i Not enough to maintain transistor Q osp or Q osn When the capacitor C os2 and C os4The discharge starts, and this moment is represented as the end time of high-frequency oscillation t m1 Until V t2 Greater than V t1 , the comparison voltage V output by comparator CP1 tos The low level is restored, and this moment is expressed as the discharge crossover moment t m2 Therefore, the high-frequency oscillation time t os_on for:

[0078] t os_on =t m2 -t m0 (1)

[0079] Combination Figure 6 The simulation waveform shown introduces the principle of high-frequency oscillation detection of SiC MOSFET during turn-off transient:

[0080] When the current enters the falling stage, the induced potential V i Through capacitor C os2 Transistor Q osp The base of transistor Q osp Turn on, compare signal V t2 First it rises; then when it enters high frequency oscillation, the reverse rising current will turn transistor Q osn Turn on, compare signal V t1 decreases, causing the comparison voltage V output by comparator CP1 to tos Converted to high level, indicating the start time of high-frequency oscillation t m0 As the oscillation period increases, when the induced potential V i The amplitude is not enough to turn the transistor Q osp and Q osn When turned on, the filter capacitor C os2 and C os4 The discharge starts, and this moment is represented as the end time of high-frequency oscillation t m1 Until the comparison signal V t1 Greater than the comparison signal V t2 , the comparison voltage V output by comparator CP1 tos The low level is restored, and this moment is expressed as the discharge crossover moment t m2 , the oscillation time of the turn-off transient t os_of for:

[0081] t os_of =t m2 -t m0 (2)

[0082] SiC MOSFET oscillation current I os It is expressed as:

[0083]

[0084] Among them A os is the maximum amplitude of the oscillating current, ω0 is the natural frequency, ξ is the damping coefficient, ω d is the damped oscillation frequency.

[0085] The induced potential V of the PCB mutual inductance coil is obtained from the time derivative of the high-frequency oscillation equation (3): i for:

[0086]

[0087] Among them, Mr is the mutual inductance of the PCB mutual inductance coil,

[0088] The equivalent oscillation waveform of the PCB mutual inductance coil is as follows: Figure 7 As shown. It can be seen that as the oscillation period increases, the oscillation peak value decreases. The peak value of the induced potential V i_max for:

[0089]

[0090] Where m is the number of times the high-frequency oscillation generates a peak value.

[0091] When the fitting curve reaches the reference voltage ±V ref_os When the transistor Q osp and Q osn If it cannot be turned on, it is considered that the high-frequency oscillation has ended, so the oscillation end time t m1 Calculated as:

[0092]

[0093] Then the capacitor C os2 and C os4 discharge, the comparison signal V t1 and V t2 They are:

[0094]

[0095] Let R os3 +R os4 =R os8 , C os2 =C os4 , and when high-frequency oscillation occurs, V t1 = 0, then the discharge crossover time t is calculated by (7) and (8) m2 for:

[0096]

[0097] So the oscillation time t os_xfor:

[0098]

[0099] During the turn-on transient, the narrow pulse gate suspension principle is as follows Figure 8 As shown, the optimal narrow pulse generation time is positioned at the end of the current rising process. In the normal turn-on process, first at time t0, the gate-driven upper push-pull device Q1 is turned on and the lower push-pull device Q2 is turned off, and the positive drive voltage V CC Connected to the gate, causing the gate voltage V GS Rise. a0 At this moment, the drain current I D Starts to rise. Positive drive voltage V CC Continue to the gate capacitance C gs charging, causing the gate voltage V GS Rise, V GS It is expressed as:

[0100]

[0101] Among them, τ1 is.

[0102] Drain current rise rate dI D / dt is expressed as:

[0103] dI D / dt=g m dV G / dt(12)

[0104] Among them, g m For transconductance.

[0105] Affected by the parasitic inductance of the SiC MOSFET commutation circuit, the drain voltage V DS A voltage gap appears, causing part of the gate current to discharge to the drain through the Miller platform to form I gd At t sw_on At this moment, when the drain current is about to reach the load current, the gate-driven push-pull device Q1 is turned off with a narrow pulse, t sw_on The moment is the moment of opening the transient narrow pulse switching; the gate of the SiC module is temporarily without external power supply, and the gate capacitance C gs The gate voltage tends to remain unchanged. Since there is no external gate resistor R gon With the internal gate resistor R gin The voltage divider, V GS A voltage gap appears. Affected by the transfer characteristics, the gate voltage V GS The drain current I DSince there is no external gate current injection, the gate voltage cannot rise quickly, and the drain current rise rate tends to zero. However, as the drain current change rate dI D / dt decreases, and the parasitic inductance induced potential decreases, causing the drain voltage to rise in the reverse direction. The positive change rate of the drain voltage dV D / dt will pass through the Miller platform to the gate capacitance C gs The gate voltage rises slowly. D / dt is low, resulting in a decrease in the initial oscillation amplitude, that is, A in formula (3) os After a narrow pulse width, at t a1 At this moment, the upper push-pull device Q1 is turned on again, and the gate resumes the positive drive voltage V CC Normal power supply.

[0106] During the turn-off transient, the narrow pulse gate suspension principle Fig. 9 As shown, the optimal narrow pulse generation time is positioned at the drain current I D At the end of the decline, the gate drive upper push-pull device Q1 is turned off and the lower push-pull device Q2 is turned on. b0 The drain current I D The gate capacitance C gs Continue to drive the voltage V EE Discharge, causing the gate voltage V GS Rapid descent.

[0107]

[0108] Drain current drop rate dI D / dt is expressed by equation (12). Also affected by parasitic inductance, the drain voltage V DS A voltage overshoot occurs, causing part of the Miller current I gd Continue to charge the gate. sw_of At this moment, the drain current I D When the voltage is about to drop to zero, the gate-driven push-pull device Q2 is turned off with a narrow pulse. sw_of The moment is the moment of the turn-off transient narrow pulse switching. The gate has no external power supply path, so the gate capacitance C gs The voltage tends to remain constant. Since there is no external gate resistor R gof With the internal gate resistor R gin The voltage divider, V GS Voltage overshoot occurs. As shown in equation (12), affected by the transfer characteristics, the gate voltage V GS Related to the current drain current. Since there is no external gate current extraction, the gate voltage VGS Unable to drop quickly, the drain current change rate dI D / dt tends to zero. However, as dI D The amplitude of / dt decreases, the parasitic inductance induced potential decreases, and the drain voltage overshoot quickly recovers to the bus voltage. Miller capacitor C gd Discharge to the drain side, causing the gate voltage to slowly decrease. Since the rate of change of the drain current is low when entering oscillation, the initial oscillation amplitude is reduced, and A in formula (3) os After a narrow pulse width, at t b1 At this moment, the push-pull device Q2 is turned on, and the gate recovers the negative drive voltage V EE Normal power supply.

[0109] Furthermore, the models of junction temperature, high-frequency oscillation time and narrow pulse switching time in the junction temperature evaluation unit are implemented by FPGA, and the model establishment method is as follows:

[0110] Set the temperature step to ΔT j , the junction temperature of SiC MOSFET is evenly divided into n temperature segments;

[0111] The narrow pulse switching time t of the xth (x=1,2…,n) gear swx (x=1,2…,n) is a fixed value; in the xth temperature range, the narrow pulse switching time t swx Ensure the minimum junction temperature T j(x-1) The high frequency oscillation time t os The lowest value t osmin , maximum junction temperature T jx High frequency oscillation time t os is the maximum value t osmax ;

[0112] The operating conditions are set under the condition that the operating voltage, operating current and junction temperature range of SiC MOSFET are not exceeded. For the operating conditions of specific operating voltage and operating current, in the SiC MOSFET switching transient, as the junction temperature T j The gradual increase of high-frequency oscillation time t os , narrow pulse switching time t sw The data of the junction temperature evaluation unit is collected to establish the junction temperature Tj, high-frequency oscillation time t under this operating condition. os And the narrow pulse switching time signal t sw data table.

[0113] The temperature sensitivity of high frequency oscillation is:

[0114]

[0115] For the turn-on transient, the principle of narrow pulse switching time is as follows Fig.10 As shown, the pulse switching time is t swx_on , high frequency oscillation time t os_on The minimum and maximum values ​​of t osmin_on and t osmax_on ; As the junction temperature increases, the optimal narrow pulse switching time is advanced, so when entering the next temperature range, the narrow pulse switching time is shortened. Therefore, in the entire junction temperature range, the narrow pulse time is in a downward step shape. For the turn-off transient, the principle of the narrow pulse switching time is as follows Fig.11 As shown, the pulse switching time is t swx_on , high frequency oscillation time t os_of The minimum and maximum values ​​of t osmin_of and t osmax_of The optimal narrow pulse switching time is delayed, so when entering the next temperature range, the narrow pulse switching time is delayed. Therefore, in the entire junction temperature range, the narrow pulse time is in an upward step shape.

[0116] When the junction temperature of SiC MOSFET is divided into two levels, the lowest junction temperature T j(x-1) The minimum oscillation time t osmin , the maximum oscillation time t at the highest junction temperature osmax The determination process is:

[0117] The first gear is the lowest temperature segment. First, determine the narrow pulse switching moment of the first temperature segment, adjust the temperature to the lowest temperature of the first gear, shield the narrow pulse switching moment during the switching transient process, and when the drain current changes and the comparator CP1 of the high-frequency oscillation extraction unit outputs a high level, it is identified as the latest boundary of the narrow pulse switching moment. Then, the narrow pulse switching moment is continuously advanced from the latest boundary. When the oscillation time t os Reach the minimum value t osmin At this time, the narrow pulse switching time t sw1 That is the narrow pulse switching moment of the first temperature range. The junction temperature of the first temperature range is continuously increased, and the narrow pulse switching moment is kept unchanged. At this time, the oscillation time t os As the junction temperature increases, when the junction temperature reaches the maximum temperature of the first temperature range, the oscillation time reaches the maximum value t osmax ;

[0118] Entering the second temperature range, the lowest temperature of the second temperature range is also the highest temperature of the first temperature range. First, shield the narrow pulse switching time, confirm the latest boundary of the narrow pulse switching time, and continue to advance the narrow pulse switching time. When the oscillation time t os Reach the minimum value t osmin At this time, the narrow pulse switching time t sw2This is the narrow pulse switching moment of the second temperature range. The junction temperature of the second temperature range is continuously increased, and the narrow pulse switching moment is kept unchanged. At this time, the oscillation time t os As the junction temperature increases, when the junction temperature reaches the maximum temperature of the second temperature range, the oscillation time reaches the maximum value t osmax .

[0119] Specifically, the determination process of the narrow pulse switching time in each temperature range is as follows: Fig.12 As shown. j0 = 25℃ as the initial temperature, and find the minimum oscillation time t by adjusting the narrow pulse switching moment. osmin , the narrow pulse switching time is the optimal time t sw1 Keep the narrow pulse switching time unchanged and gradually increase the device temperature. As the junction temperature rises, the optimal switching time of the narrow pulse deviates and the narrow pulse suppression ability weakens, resulting in a high-frequency oscillation time t os When the junction temperature increases by ΔT j , the measured oscillation time is the maximum value t osmax . Start to enter the second temperature range and readjust the narrow pulse switching time. When the oscillation time reaches t osmin , the switching time t sw2 is the optimal switching time for the second temperature segment. When the junction temperature increases by ΔT again j , and enter the next temperature segment. The test process ends when the junction temperature rises to the highest temperature in the nth temperature segment.

[0120] The operating conditions are set under the condition that the operating voltage, operating current and junction temperature range of SiC MOSFET are not exceeded. For the operating conditions of specific operating voltage and operating current, in the SiC MOSFET switching transient, as the junction temperature T j The gradual increase of high-frequency oscillation time t os and narrow pulse switching time t sw The data of the junction temperature evaluation unit is collected to establish the junction temperature Tj, high-frequency oscillation time t under this operating condition. os And the narrow pulse switching time t sw data table.

[0121] Furthermore, the junction temperature evaluation unit searches the data table of the junction temperature, high-frequency oscillation time, and narrow pulse switching time model, and evaluates and determines the specific junction temperature. The specific process is:

[0122] When the SiC MOSFET is not running, the initial narrow pulse switching time is the switching time t of the first temperature range. sw1 During the continuous operation of SiC MOSFET, the high-frequency oscillation extraction unit transmits the high-frequency oscillation time t in real time. os , if the oscillation time tos In t osmin and t osmax If the junction temperature is in the first temperature range, the transmission oscillation time t os When the oscillation time t increases, the junction temperature of SiCMOSFET rises. os Exceeded t osmax , then the temperature range is raised to the next level, and the narrow pulse switching time is changed accordingly until the oscillation time t os In t osmin and t osmax In each temperature range, when the transmission oscillation time t os When the oscillation time t os Lower than t osmin , then the temperature range is reduced by one level, and the narrow pulse switching time is changed accordingly; the narrow pulse switching time t swx Determine the temperature range in which the SiC MOSFET junction temperature is located, and then calculate the high-frequency oscillation time t os Determine the specific junction temperature T j .

[0123] The experiment was carried out using conventional gate drive, and the oscillation time t os The temperature-sensitive characteristics of the load current are as follows: Fig.13 shown. Fig.13 (a) is the junction temperature T j The turn-on transient high frequency oscillation time t os_on The relationship curve is as follows: when the load current I L =50A, the high-frequency oscillation time t os_on The resolution is 0.42ns / ℃. When the load current I L =300A, the high-frequency oscillation time of the turn-off transient is t os_on The resolution is 1.06ns / ℃. Fig.13 (b) is the junction temperature T j The turn-on transient high frequency oscillation time t os_of When the load current I L =50A, the high-frequency oscillation time t os_on The resolution is 0.22ns / ℃. When the load current I L =300A, the high-frequency oscillation time of the turn-off transient is t os_on The resolution is 0.62ns / ℃. The maximum high-frequency oscillation time reaches 2350ns. Therefore, under normal driving, t os The temperature sensitivity is too low and the oscillation time is too high, which will cause EMI problems.

[0124] The multi-stage narrow pulse suspension gate driving method of the present invention is used for experiments. The junction temperature is divided into a temperature range with a step length of 25°C. Therefore, the temperature range applicable to the SiC module is divided into five sections: j1 (25℃~50℃), T j2 (50℃~75℃), T j3 (75℃~100℃), T j4 (100℃~125℃), T j5 (125℃~135℃). High frequency oscillation time t os With junction temperature T j The change curve of Fig.14 As shown in the figure, the load currents are 100A, 200A and 300A respectively.

[0125] It can be seen that the filter time has a good linear relationship with the junction temperature. Under constant load current, since the maximum and minimum filter times of each temperature segment are basically the same, the temperature sensitivity remains unchanged. If the temperature compensation is further reduced and the number of temperature segments is increased, the oscillation will be further suppressed, and the temperature sensitivity will remain unchanged. Fig.14 In (a), when the load current is 100A, 200A and 300A respectively, the high-frequency oscillation time t os_on The average junction temperature sensitivity is 5.92ns / ℃, 6.48ns / ℃ and 6.82ns / ℃ respectively. Fig.14 In (b), when the load current is 100A, 200A and 300A respectively, the high-frequency oscillation time t os_of The average junction temperature sensitivity is 2.64ns / ℃, 3.32ns / ℃ and 3.58ns / ℃ respectively. Fig.13 According to the detection results, the temperature sensitivity is greatly improved, and the maximum high-frequency oscillation time occurs at a load current of 300A, which is less than 1100ns, ensuring the reliable operation of the SiC MOSFET.

[0126] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression, characterized in that: The oscillation time of the transient drain current of the SiC MOSFET switch is used as a temperature-sensitive electrical parameter to characterize the junction temperature of the device. The junction temperature monitoring circuit includes: a PCB mutual inductance coil, a high-frequency oscillation extraction unit, a junction temperature evaluation unit and a gate adjustable drive unit; wherein, The PCB mutual inductance coil is used to provide a state signal of a high-speed change in the drain current of the SiC MOSFET, wherein the state signal is an induced potential of a change rate of the drain current of the SiC MOSFET; The high-frequency oscillation extraction unit is used to receive the induced potential of the PCB mutual inductance coil, extract the high-frequency oscillation time, and output the high-frequency oscillation time to the junction temperature evaluation unit and the gate adjustable driving unit; The gate adjustable driving unit is used to receive the switching signal and the high-frequency oscillation time signal, change the high-frequency oscillation time of the drain current by adjusting the moment of narrow pulse switching, and output the gate voltage to control the on and off of the SiC MOSFET; The junction temperature evaluation unit is used to evaluate the junction temperature of the SiC MOSFET according to the narrow pulse switching moment and the high-frequency oscillation time; the junction temperature evaluation unit stores a data table of the narrow pulse switching moment, the high-frequency oscillation time and the junction temperature under different load currents, and obtains the junction temperature of the SiC MOSFET by looking up the table.

2. A SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression according to claim 1, characterized in that: The gate adjustable driving unit comprises: a narrow pulse gate suspension unit and a gate adjustable amplifier unit; wherein, The narrow pulse gate suspension unit is used to receive the switching signal and the high-frequency oscillation time, and output the turn-on transient regulation signal and the turn-off transient regulation signal, as well as the narrow pulse switching time; The gate adjustable amplifier unit is composed of a push-pull circuit and is used to output a gate voltage according to the received turn-on transient regulation signal and turn-off transient regulation signal.

3. The SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression according to claim 1, characterized in that: The high-frequency oscillation extraction unit comprises: a positive oscillation detection circuit, a negative oscillation detection circuit and a comparator; The positive oscillation detection circuit is used to receive the induced potential of the PCB mutual inductance coil and output a comparison signal V t1 ; The negative oscillation detection circuit is used to receive the induced potential of the PCB mutual inductance coil and output a comparison signal V t2 ; The comparator is used to compare the signal V t1 As the negative input, the comparison signal V t2 As the positive input, it is compared in comparator CP1 and a comparison voltage is output. The duration of the high level of the comparison voltage is the high-frequency oscillation time.

4. The SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression according to claim 3 is characterized in that: The positive oscillation detection circuit comprises: a resistor R os1 , R os2 , R os3 , R os4 , capacitor C os1 , C os2 , transistor Q osn The capacitor C os1 One end of the resistor R os1 One end of the resistor R os1 The other end of the resistor R os2 One end of the transistor Q osn The base of the resistor R os2 The other end of the transistor Q osn The emitter, the capacitor C os2 One end, negative voltage -V DD connected, the transistor Q osn The collector and the capacitor C os2 The other end of the resistor R os4 One end of the resistor R os4 The other end of the resistor R os3 One end of the resistor R is connected to the negative input terminal of the comparator CP1. os3 The other end is connected to the positive voltage V DD connected; The negative oscillation detection circuit comprises: a resistor R os5 , R os6 , R os7 , R os8 , capacitor C os3 , C os4 , transistor Q osp The capacitor C os3 One end of the capacitor C os1 The other end, induced potential V i connected; the capacitor C os3 The other end of the resistor R os5 One end of the resistor R os5 The other end of the resistor R os6 One end of the transistor Q osp The base of the resistor R os6 The other end is connected to the positive voltage V DD , the transistor Q osp The emitter of the transistor Q osp The collector and the resistor R os7 One end of the resistor R os7 The other end of the resistor R os8 One end of the capacitor C os4 One end of the circuit is connected to the positive input terminal of the comparator CP1.

5. The SiC MOSFET junction temperature monitoring circuit based on high-frequency oscillation suppression according to claim 3, characterized in that: A junction temperature monitoring circuit based on high-frequency oscillation suppression is integrated into the SiC MOSFET gate drive.

6. A monitoring method for a SiC MOSFET junction temperature monitoring circuit based on high frequency oscillation suppression according to any one of claims 1 to 5, characterized in that: The monitoring method is: During the SiC MOSFET turn-on transient and turn-off transient, the high-frequency oscillation extraction unit transmits the high-frequency oscillation time t in real time. os ; The gate adjustable driving unit is used to adjust and change the narrow pulse switching time so that the high-frequency oscillation time is t osmin and t osmax The junction temperature evaluation unit searches the data table of the junction temperature, high-frequency oscillation time, and narrow pulse switching moment model to evaluate and determine the specific junction temperature.

7. The monitoring method according to claim 6, characterized in that: The method for the high-frequency oscillation extraction unit to transmit the high-frequency oscillation time in real time is: When the SiC MOSFET is turned on or off, the induced potential of the PCB mutual inductance coil is zero, and the comparison signal V t1 is zero, the comparison signal V t2 is high level, comparator CP1 outputs low level; During the turn-on transient, when the drain current I D Entering the high-frequency oscillation process, the induced potential fluctuates positively and negatively, and the comparison signal V t2 Rapidly drops to zero, then the comparison signal V t1 Rapidly rises to a high level, and the comparator outputs a high-frequency oscillation time t os Switch high level until the oscillation process ends, and compare the signal V t1 Slowly decrease, compare signal V t2 Slowly rise until the comparison signal V t1 Greater than the comparison signal V t2 , the high-frequency oscillation time recovers to a low level, and the length of the high-frequency oscillation time high level is the oscillation time of the turn-on transient; During the turn-off transient, when the drain current I D Entering the high-frequency oscillation process, the induced potential fluctuates positively and negatively, and the comparison signal V t1 Rapidly rises to a high level, and then compares the signal V t2 The comparator outputs a high-frequency oscillation time and switches to a high level until the oscillation process ends. t1 Slowly decrease, compare signal V t2 Slowly rise until the comparison signal V t1 Greater than the comparison signal V t2 , the high-frequency oscillation time recovers to a low level, and the length of the high-frequency oscillation time high level is the oscillation time of the shutdown transient.

8. The monitoring method according to claim 6, characterized in that: The method for constructing the junction temperature, high-frequency oscillation time and narrow pulse switching time model is: Set the temperature step to ΔT j , the junction temperature of SiC MOSFET is evenly divided into n temperature segments; The narrow pulse switching time t of the xth (x=1,2…,n) temperature range swx (x=1,2…,n) is a fixed value; In the xth temperature range, the narrow pulse switching time t swx Ensure the minimum junction temperature T j(x-1) The oscillation time is the minimum value t osmin , the oscillation time at the highest junction temperature is the maximum value t osmax ; The operating conditions are set under the condition that the operating voltage, operating current and junction temperature range of SiC MOSFET are not exceeded. For the operating conditions of specific operating voltage and operating current, in the SiC MOSFET switching transient, as the junction temperature T j The gradual increase of high-frequency oscillation time t os , narrow pulse switching time t sw The data of the junction temperature evaluation unit is collected to establish the junction temperature Tj, high-frequency oscillation time t under this operating condition. os And the narrow pulse switching time signal t sw data table.

9. The monitoring method according to claim 8, characterized in that: When the junction temperature of SiC MOSFET is divided into two levels, the lowest junction temperature T j(x-1) The minimum oscillation time t osmin , the maximum oscillation time t at the highest junction temperature osmax The determination process is: The first gear is the lowest temperature segment. First, determine the narrow pulse switching moment of the first temperature segment, adjust the temperature to the lowest temperature of the first gear, shield the narrow pulse switching moment during the switching transient process, and when the drain current changes and the comparator CP1 of the high-frequency oscillation extraction unit outputs a high level, it is identified as the latest boundary of the narrow pulse switching moment. Then, the narrow pulse switching moment is continuously advanced from the latest boundary. When the oscillation time t os Reach the minimum value t osmin At this time, the narrow pulse switching time t sw1 This is the narrow pulse switching moment of the first temperature range. The junction temperature of the first temperature range is continuously increased, and the narrow pulse switching moment is kept unchanged. At this time, the oscillation time t os As the junction temperature increases, when the junction temperature reaches the maximum temperature of the first temperature range, the oscillation time reaches the maximum value t osmax ; Entering the second temperature range, the lowest temperature of the second temperature range is also the highest temperature of the first temperature range. First, shield the narrow pulse switching time, confirm the latest boundary of the narrow pulse switching time, and continue to advance the narrow pulse switching time. When the oscillation time t os Reach the minimum value t osmin At this time, the narrow pulse switching time t sw2 This is the narrow pulse switching moment of the second temperature range. The junction temperature of the second temperature range is continuously increased, and the narrow pulse switching moment is kept unchanged. At this time, the oscillation time t os As the junction temperature increases, when the junction temperature reaches the maximum temperature of the second temperature range, the oscillation time reaches the maximum value t osmax .

10. The monitoring method according to claim 9, characterized in that: The junction temperature evaluation unit searches the data table of the junction temperature, high-frequency oscillation time and narrow pulse switching time model, and evaluates and determines the specific junction temperature. The specific process is: When the SiC MOSFET is not running, the initial narrow pulse switching time is the switching time t of the first temperature range. sw1 During the continuous operation of SiC MOSFET, the high-frequency oscillation extraction unit transmits the high-frequency oscillation time t in real time. os , if the oscillation time t os In t osmin and t osmax If the junction temperature is in the first temperature range, the transmission oscillation time t os When the oscillation time t increases, the junction temperature of SiCMOSFET rises. os Exceeded t osmax , then the temperature range is raised to the next level, and the narrow pulse switching time is changed accordingly until the oscillation time t os In t osmin and t osmax In each temperature range, when the transmission oscillation time t os When the oscillation time t os Lower than t osmin , then the temperature range is reduced by one level, and the narrow pulse switching time is changed accordingly; the narrow pulse switching time t swx Determine the temperature segment where the SiC MOSFET junction temperature is located, and then calculate the high-frequency oscillation time t os Determine the specific junction temperature T j .

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