A SiC MOSFET junction temperature monitoring system and method for transient extreme stress

Abstract

The application belongs to the technical field of power semiconductor devices, and particularly relates to a SiC MOSFET junction temperature monitoring system and method for transient extreme stress. doff The application provides a junction temperature monitoring system and method suitable for transient extreme stress (avalanche stress, short-circuit stress and surge stress), the method is suitable for monitoring the junction temperature of a device in a real power conversion system when the device bears transient extreme stress, realizes online monitoring and early warning of the junction temperature of the device in the process of transient extreme stress, and provides guarantee for safe and reliable work of the power conversion system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power semiconductor devices, and particularly relates to a SiC MOSFET junction temperature monitoring system and method for transient extreme stress. BACKGROUND

[0002] Compared with Si-based devices, SiC MOSFETs have advantages in high switching frequency, high power density and high reliability, and have high application potential in the field of power conversion. However, SiC MOSFETs will inevitably be subjected to the impact of transient extreme stress in actual working conditions. The failure mechanism of transient extreme stress is complex, and one of the key criteria for failure is that the junction temperature of the device rises to the melting point of the source metal aluminum, 940K, or the intrinsic temperature of SiC, 1500K (at which temperature the intrinsic carrier concentration of the device reaches the background doping concentration). Therefore, how to accurately obtain the junction temperature of SiC MOSFETs during the transient extreme stress process and provide failure warning for the device is the basis for the safe and reliable operation of SiC MOSFETs in power conversion systems.

[0003] The existing SiC MOSFET junction temperature monitoring is divided into direct monitoring and indirect monitoring, and the direct monitoring is divided into physical contact type and optical non-contact type. The direct monitoring method measures the actual accurate temperature of the device, but this method needs to add additional elements in the system or open the cover of the device, which is invasive and destructive, and is not suitable for junction temperature monitoring during transient extreme stress. Indirect monitoring is divided into thermal resistance network method and thermal sensitive parameter method. The thermal boundary under transient extreme stress is difficult to accurately define in the thermal resistance network method, and the thermal resistance network model parameters are difficult to calibrate, so it is not suitable for junction temperature monitoring during transient extreme stress. The thermal sensitive parameter method obtains the junction temperature of the device by measuring the temperature related electrical parameters, and this method is suitable for junction temperature monitoring of SiC MOSFETs under transient extreme stress due to its non-destructive and non-invasive advantages. SUMMARY

[0004] The application aims to solve the problem that the junction temperature of SiC MOSFETs under transient extreme stress is difficult to monitor. Based on the shutdown delay t doff The application provides a junction temperature monitoring system and method suitable for transient extreme stress (avalanche stress, short circuit stress, surge stress), which is suitable for junction temperature monitoring of devices under transient extreme stress in actual power conversion systems, realizes online monitoring and early warning of the junction temperature of the device during the transient extreme stress process, and provides a guarantee for the safe and reliable operation of the power conversion system.

[0005] The technical scheme of the application is as follows:

[0006] A SiC MOSFET junction temperature monitoring system for transient extreme stress, characterized by comprising a gate drive unit, an inductive load unit, a voltage sampling unit, a load current sampling unit, an off delay time measurement unit and a transient junction temperature calculation unit;

[0007] The gate drive unit is connected with the gate of the SiC MOSFET, and is used for generating a control signal to control the turn-on and turn-off of the SiC MOSFET device, specifically: the gate drive unit comprises a first gate drive unit, a second gate drive unit and a third gate drive unit, wherein the first gate drive unit is used to control the turn-on and turn-off of the SiC MOSFET device in the transient extreme stress mode, and the second gate drive unit and the third gate drive unit are used to control the turn-on and turn-off of the SiC MOSFET device in the steady-state switching mode;

[0008] The voltage sampling unit is used for sampling the drain-source voltage and the gate-source voltage of the SiC MOSFET, specifically, the voltage sampling unit comprises a first voltage sampling unit and a second voltage sampling unit, wherein the first voltage sampling unit is connected with the gate and the source of the SiC MOSFET device, and the second voltage sampling unit is connected with the drain and the source of the SiC MOSFET device, the first voltage sampling unit and the second voltage sampling unit sample the gate-source voltage and the drain-source voltage of the SiC MOSFET respectively, and store the sampling data;

[0009] The load current sampling unit is connected between the drain of the SiC MOSFET and the inductive load unit, and is used for sampling the drain-source current of the SiC MOSFET and storing the sampling data;

[0010] The off delay time measurement unit is connected at the connection point of the load current sampling unit and the inductive load unit, and comprises a prediction unit and an off measurement unit, wherein the prediction unit and the off measurement unit have an operation sequence, the prediction unit first performs function fitting of the relationship between the off delay time and the junction temperature of the SiC MOSFET device in the steady-state switching mode, and then the off delay time measurement unit measures the off delay time after the SiC MOSFET device under test enters the transient extreme stress, the function fitting of the relationship between the off delay time and the junction temperature of the SiC MOSFET device when the SiC MOSFET device does not enter the transient extreme stress is a first-order linear function of the off delay time about the SiC MOSFET junction temperature under different bus voltages and different load currents:

[0011]

[0012] Wherein, t doffFor the turn-off delay, α1, β1, γ1, λ1, α2, β2, γ2, λ2 are fitting constants, obtained by measuring the turn-off delay at different junction temperatures, V ds For the drain-source voltage, obtained by the second voltage sampling unit, I ds For the load current, obtained by the load current sampling unit, T j is the device junction temperature;

[0013] The input of the transient junction temperature calculation unit is connected with the output of the turn-off delay time measurement unit, and the calculation target of the transient junction temperature calculation unit is the turn-off delay of the device after the transient extreme stress obtained by the turn-off delay time measurement unit. The turn-off delay at the end of the extreme stress is obtained by adopting a polynomial fitting, and the device junction temperature T j .

[0014] Further, the transient extreme stress mode includes an avalanche mode, a short circuit mode and a surge mode.

[0015] Further, in the steady-state switching mode, a square wave with a duty cycle of 50% is applied to the gate of the SiC MOSFET device, the high level is 18V, the low level is -3V, and the bus voltage is 800V.

[0016] A monitoring method for a SiC MOSFET junction temperature monitoring system for transient extreme stress, comprising the following steps:

[0017] S1, prediction section:

[0018] The prediction unit in the turn-off delay time measurement unit works, and the relationship function fitting of the turn-off delay and the junction temperature of the SiC MOSFET device to be measured when the SiC MOSFET device to be measured does not enter the transient extreme stress is carried out;

[0019] S2, transient extreme stress section:

[0020] Under the control of the first gate drive unit, the second gate drive unit and the third gate drive unit, the junction temperature monitoring system switches to the transient extreme stress mode, and the SiC MOSFET device to be measured enters the transient extreme stress state;

[0021] S3, steady-state switching section:

[0022] Under the control of the first gate drive unit, the second gate drive unit and the third gate drive unit, the junction temperature monitoring system switches to the steady-state switching mode, and the SiC MOSFET device to be measured enters the steady-state switching state, and the turn-off delay time measurement unit measures the turn-off delay of the SiC MOSFET device to be measured;

[0023] S4, transient junction temperature calculation section:

[0024] After the turn-off delay time measurement unit measures the turn-off delay of the SiC MOSFET device under test, the transient junction temperature calculation unit uses polynomial fitting to back-calculate the turn-off delay at the end of extreme stress, and obtains the device junction temperature T based on a linear function. j .

[0025] The beneficial effects of this invention are as follows: 1) The junction temperature monitoring system proposed in this invention, applicable to transient extreme stress, is compatible with half-bridge switching circuits. The system is simple to build, easy to operate, and has low economic cost. 2) The junction temperature monitoring method proposed in this invention, applicable to transient extreme stress, differs from the traditional method of monitoring junction temperature by measuring turn-off delay. This method is suitable for monitoring device junction temperature under transient extreme stress, enabling online monitoring and early warning of junction temperature during transient extreme stress processes, thus ensuring the safe and reliable operation of power conversion systems. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the junction temperature monitoring system of the present invention;

[0027] Figure 2 This is a schematic diagram of the SiC MOSFET junction temperature monitoring system for avalanche stress according to the present invention.

[0028] Figure 3 This is a schematic diagram of the SiC MOSFET junction temperature monitoring system applicable to short-circuit stress according to the present invention;

[0029] Figure 4 This is a schematic diagram of the SiC MOSFET junction temperature monitoring system applicable to surge stress according to the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments, so that those skilled in the art can better understand the present invention.

[0031] Example 1

[0032] In this embodiment, see Figure 1 A SiC MOSFET junction temperature monitoring system suitable for transient extreme stresses (avalanche stress, short-circuit stress, surge stress) includes a SiC MOSFET device under test 1, a first gate driving unit 2, a second gate driving unit 3, a third gate driving unit 4, an inductive load unit 5, a first voltage sampling unit 6, a second voltage sampling unit 7, a load current sampling unit 8, a turn-off delay time measurement unit 9, and a transient junction temperature calculation unit 10.

[0033] The gate drive unit provides two driving modes: in the transient extreme stress mode (avalanche mode, short circuit mode, surge mode), the first gate drive unit 2 controls the opening and closing of the SiC MOSFET device 1 to be tested; in the steady-state switching mode (a square wave with a 50% duty cycle is applied to the gate of the SiC MOSFET device to be tested, the high level is 18V, the low level is -3V, and the bus voltage is 800V), the second gate drive unit 3 and the third gate drive unit 4 control the opening and closing of the SiC MOSFET device 1 to be tested;

[0034] The first voltage sampling unit 6 and the second voltage sampling unit 7 respectively provide sampling of the gate-source voltage and the drain-source voltage of the SiC MOSFET, and the first voltage sampling unit 6 and the second voltage sampling unit 7 both include a data storage function;

[0035] The load current sampling unit 8 obtains the drain-source current information of the SiC MOSFET through a high-precision wide-band large-current shunt, and the load current sampling unit 8 includes a data storage function;

[0036] The turn-off delay time measurement unit 9 includes a prediction unit and a turn-off measurement unit. The prediction unit performs function fitting of the relationship between the turn-off delay and the junction temperature when the SiC MOSFET device to be tested does not enter the transient extreme stress. The prediction fitting function is a first-order linear function of the turn-off delay about the junction temperature of the SiC MOSFET under different bus voltages and different load currents:

[0037]

[0038] Where, t doff is the turn-off delay, α1, β1, γ1, λ1, α2, β2, γ2, λ2 are fitting constants obtained by measuring the turn-off delay at different junction temperatures. V ds is the drain-source voltage, obtained by the second voltage sampling unit, I ds is the load current, obtained by the load current sampling unit;

[0039] The turn-off measurement unit measures the turn-off delay after the SiC MOSFET device 1 to be tested enters the transient extreme stress;

[0040] The transient junction temperature calculation unit 10 measures the device turn-off delay after the transient extreme stress, uses a polynomial fitting to inversely calculate the turn-off delay at the initial time (the time when the extreme stress ends), and obtains the device junction temperature T j according to the first-order linear function obtained by the prediction unit.

[0041] The junction temperature monitoring system has the following monitoring steps:

[0042] 1) Prediction link:

[0043] The prediction unit in the turn-off delay time measurement unit 9 works to perform function fitting of the relationship between the turn-off delay of the SiC MOSFET device 1 under test and the junction temperature when the SiC MOSFET device 1 under test does not enter the transient extreme stress.

[0044] 2) Transient extreme stress link:

[0045] Under the control of the first gate drive unit 2, the junction temperature monitoring system switches to the transient extreme stress mode, and the SiC MOSFET device 1 under test enters the transient extreme stress state.

[0046] 3) Steady-state switching link:

[0047] Under the control of the second gate drive unit 3 and the third gate drive unit 4, the junction temperature monitoring system switches to the steady-state switching mode, and the SiC MOSFET device 1 under test enters the steady-state switching state, and the turn-off delay time measurement unit 9 measures the turn-off delay of the SiC MOSFET device under test.

[0048] 4) Transient junction temperature calculation link:

[0049] After the turn-off delay time measurement unit 9 measures the turn-off delay of the SiC MOSFET device 1 under test, the transient junction temperature calculation unit 10 uses polynomial fitting to back-propagate the turn-off delay at the initial time (the time when the extreme stress ends), and obtains the device junction temperature T j .

[0050] Embodiment 2

[0051] This embodiment is basically the same as Embodiment 1, and the special part is:

[0052] In this embodiment, referring to Figure 2 , a SiC MOSFET junction temperature monitoring system suitable for avalanche stress includes a SiC MOSFET device 1 under test, a first gate drive unit 2, a second gate drive unit 3, a third gate drive unit 4, an inductive load unit 5, a first voltage sampling unit 6, a second voltage sampling unit 7, a load current sampling unit 8, a turn-off delay time measurement unit 9, a transient junction temperature calculation unit 10, and an avalanche energy discharge device 11. The first voltage sampling unit 6, the second voltage sampling unit 7, the load current sampling unit 8, the turn-off delay time measurement unit 9, and the transient junction temperature calculation unit 10 are the same as in Embodiment 1, so they are not labeled in Figure 2 .

[0053] The avalanche energy discharge device 11 is connected in parallel with the SiC MOSFET device 1 to be tested, and the first gate drive unit 2 and the second gate drive unit 3 are used to control the turn-on and turn-off of the avalanche energy discharge device 11 and the SiC MOSFET device 1 to be tested, so as to realize the conversion between the avalanche mode and the steady-state switching mode (the gate of the SiC MOSFET device to be tested is applied with a square wave with a 50% duty cycle, the high level is 18V, the low level is -3V, and the bus voltage is 800V), and realize the accurate control of the avalanche time and the avalanche energy.

[0054] Embodiment 3

[0055] This embodiment is basically the same as embodiment 1, and the difference is that:

[0056] In this embodiment, referring to Figure 3 A SiC MOSFET junction temperature monitoring system suitable for short-circuit stress includes a SiC MOSFET device 1 to be tested, a first gate drive unit 2, a second gate drive unit 3, a third gate drive unit 4, an inductive load unit 5, a first voltage sampling unit 6, a second voltage sampling unit 7, a load current sampling unit 8, a turn-off delay time measurement unit 9, and a transient junction temperature calculation unit 10. The first voltage sampling unit 6, the second voltage sampling unit 7, the load current sampling unit 8, the turn-off delay time measurement unit 9, and the transient junction temperature calculation unit 10 are the same as in embodiment 1, so they are not marked in Figure 3 .

[0057] The second gate drive unit 3 controls the system short-circuit mode, and the turn-on time of the second gate drive unit 3 is the short-circuit time of the system. The third gate drive unit 4 controls the steady-state switching mode (the gate of the SiC MOSFET device to be tested is applied with a square wave with a 50% duty cycle, the high level is 18V, the low level is -3V, and the bus voltage is 800V), thereby realizing the conversion between the system short-circuit mode and the steady-state switching mode.

[0058] Embodiment 4

[0059] This embodiment is basically the same as embodiment 1, and the difference is that:

[0060] In this embodiment, referring to Figure 4A SiC MOSFET junction temperature monitoring system suitable for surge stress, comprising a to-be-measured SiC MOSFET device 1, a first gate drive unit 2, a second gate drive unit 3, a third gate drive unit 4, an inductive load unit 5, a first voltage sampling unit 6, a second voltage sampling unit 7, a load current sampling unit 8, a turn-off delay time measurement unit 9, a transient junction temperature calculation unit 10, a surge current generation unit 11, and a positive and negative power supply unit 12. The first voltage sampling unit 6, the second voltage sampling unit 7, the load current sampling unit 8, the turn-off delay time measurement unit 9, and the transient junction temperature calculation unit 10 are the same as in Embodiment 1, so they are not marked in Figure 4 .

[0061] The surge current generation unit 11 charges the capacitor when the switch is on the right side, and generates a surge current when the switch is on the left side. The to-be-measured SiC MOSFET device 1 enters a surge state.

[0062] The positive and negative power supply unit 12 is in positive power supply mode in steady-state switching mode, and realizes that the to-be-measured SiC MOSFET device 1 operates in steady-state switching mode (the to-be-measured SiC MOSFET device gate applies a 50% duty cycle square wave, the high level is 18V, the low level is -3V, and the bus voltage is 800V); and is in negative power supply mode in surge mode, and realizes that the to-be-measured SiC MOSFET device 1 enters a surge state.

Claims

1. A SiC MOSFET junction temperature monitoring system for transient extreme stress, characterized in that, It includes a gate drive unit, an inductive load unit, a voltage sampling unit, a load current sampling unit, a turn-off delay time measurement unit, and a transient junction temperature calculation unit; The gate driving unit is connected to the gate of the SiC MOSFET and is used to generate control signals to control the turn-on and turn-off of the SiC MOSFET device. Specifically, the gate driving unit includes a first gate driving unit, a second gate driving unit, and a third gate driving unit. The first gate driving unit is used to control the turn-on and turn-off of the SiC MOSFET device in transient extreme stress mode, and the second and third gate driving units are used to control the turn-on and turn-off of the SiC MOSFET device in steady-state switching mode. The voltage sampling unit is used to sample the drain-source voltage and gate-source voltage of the SiC MOSFET. Specifically, the voltage sampling unit includes a first voltage sampling unit and a second voltage sampling unit. The first voltage sampling unit is connected to the gate and source of the SiC MOSFET device, and the second voltage sampling unit is connected to the drain and source of the SiC MOSFET device. The first voltage sampling unit and the second voltage sampling unit sample the gate-source voltage and drain-source voltage of the SiC MOSFET, respectively, and store the sampled data. The load current sampling unit is connected between the drain of the SiC MOSFET and the inductive load unit. The load current sampling unit is used to sample the drain-source current of the SiC MOSFET and store the sampled data. The turn-off delay time measurement unit is connected at the connection point between the load current sampling unit and the inductive load unit. The turn-off delay time measurement unit includes a prediction unit and a turn-off measurement unit, which operate sequentially. The prediction unit first fits the relationship between the turn-off delay and junction temperature in the steady-state switching mode of the SiC MOSFET device. Then, the turn-off measurement unit measures the turn-off delay after the SiC MOSFET device under test enters transient extreme stress. The prediction unit fits the relationship between the turn-off delay and junction temperature to a linear function of the turn-off delay with respect to the SiC MOSFET junction temperature under different bus voltages and different load currents when the SiC MOSFET device has not entered transient extreme stress. ， Among them, t doff For turn-off delay, α1, β1, γ1, λ1, α2, β2, γ2, and λ2 are fitting constants obtained by measuring turn-off delay at different junction temperatures, V ds The drain-source voltage is obtained from the second voltage sampling unit, I. ds The load current, T, is obtained from the load current sampling unit. j It is the junction temperature of the device; The input of the transient junction temperature calculation unit is connected to the output of the turn-off delay time measurement unit. The calculation objective of the transient junction temperature calculation unit is the device turn-off delay after transient extreme stress obtained by the turn-off delay time measurement unit. Polynomial fitting is used to back-calculate the turn-off delay at the end of the extreme stress, and the device junction temperature T is obtained according to a linear function. j .

2. The SiC MOSFET junction temperature monitoring system for transient extreme stress according to claim 1, characterized in that, The transient extreme stress modes include avalanche mode, short-circuit mode, and surge mode.

3. The SiC MOSFET junction temperature monitoring system for transient extreme stress according to claim 1, characterized in that, In the steady-state switching mode, a square wave with a 50% duty cycle is applied to the gate of the SiC MOSFET device, with a high level of 18V, a low level of -3V, and a bus voltage of 800V.

4. A monitoring method for a SiC MOSFET junction temperature monitoring system for transient extreme stress as described in claim 1, characterized in that, Includes the following steps: S1, Prediction Quantity Stage: The prediction unit in the turn-off delay time measurement unit operates to fit the relationship function between the turn-off delay and the junction temperature when the SiC MOSFET under test has not entered the transient extreme stress. S2, Transient extreme stress element: Under the control of the first gate drive unit, the second gate drive unit, and the third gate drive unit, the junction temperature monitoring system switches to the transient extreme stress mode, and the SiC MOSFET device under test enters the transient extreme stress state. S3, Steady-state switching circuit: Under the control of the first gate drive unit, the second gate drive unit, and the third gate drive unit, the junction temperature monitoring system switches to the steady-state switching mode, the SiC MOSFET device under test enters the steady-state switching state, and the turn-off delay time measurement unit measures the turn-off delay of the SiC MOSFET device under test. S4. Transient junction temperature calculation: After the turn-off delay time measurement unit measures the turn-off delay of the SiC MOSFET device under test, the transient junction temperature calculation unit uses polynomial fitting to back-calculate the turn-off delay at the end of extreme stress, and obtains the device junction temperature T based on a linear function. j .

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