Device for estimating junction temperature of a power semiconductor and associated method for monitoring such junction temperature

Abstract

Device and method for measuring a junction temperature of a power semiconductor (3) using the resistance Rgint (32) of said semiconductor (3) comprising at least: a current injector circuit (5) injecting current pulses Iinj in the gate path of said power semiconductor (3) through the emitter of said power semiconductor, said current injector circuit (5) being driven by a digital injection control circuit (4, 6) to synchronize said current pulses within a stabilized part of ON states of the power semiconductor driver (1) PWM signal driving said power semiconductor (3), a peak detector circuit (7) to record emitter voltage peaks Ve at the terminals of the current injector circuit and generate a continuous signal Vpks dependent of the junction temperature Tj through integration of said voltage peaks, a signal conditioning circuit (8) to adapt the continuous signal Vpks dependent of the junction temperature into a range of 3V to 5V of a measurement system (9).

Description

DESCRIPTIONTITLE OF INVENTION: DEVICE FOR ESTIMATING JUNCTION TEMPERATURE OF A POWER SEMICONDUCTOR AND ASSOCIATED METHOD FOR MONITORING SUCH JUNCTION TEMPERATURETECHNICAL FIELD

[0001] This disclosure pertains to the field of monitoring of the health of electronic power semiconductors or power semiconductor modules such as solid-state switching modules and concerns a device for estimating junction temperature of a power semiconductor and associated method for monitoring such junction temperature. Priority is claimed on European Patent Application No. EP24306202.3, filed July 17, 2024, the content of which is incorporated herein by reference.BACKGROUND ART

[0002] The on-line estimation of the temperature of the power semi-conductor device such as IGBT or MOSFET is required for over-temperature detection and protection and for monitoring the state of the health of the power module. Different solution exists to detect / measure the junction temperature in the prior art.

[0003] A first prior art method uses a device-embedded sense diode with a reproducible, linear, and high (negative) sensitivity of its threshold voltage with temperature. A relatively simple external circuit is used to detect an under-value or measure the threshold voltage. However, the implementation of the diode on the chip results in a loss of active area of the transistor and increases the number of connections.

[0004] A second prior art method for a MOSFET power semiconductor according to figure 1A uses the internal gate resistor Rgin as a temperature sensitive electric parameter (TSEP). The junction temperature is estimated from the gate temperature. A sense current Ig is injected through the gate during the PWM. The voltage response Vs is temperature sensitive. The injection time is driven by a switch S3 which is OFF to inject the current.

[0005] For over-temperature detection, the voltage response is compared with the voltage response with an emulated gate circuit whose values are defined to correspond to one or several temperature thresholds.

[0006] Since the internal gate resistance value may vary from a power module reference to another, an individual calibration is required which may be complex and costly to implement.

[0007] For temperature measurement, the voltage response is sampled with an analog to digital converter (ADC). The calibration can be software-based.

[0008] In addition, as shown in figure 1 B, during the current injection, the voltage VGS after a starting value dependent of Rgin increases due to the internal capacitor Cgof the MOSFET. Due to such increase, the measurement must be done quickly after opening of the switch S3 and requires a fast analog to digital converter.

[0009] In consequence, this method such as disclosed in European patent application EP24305034.1 filed January 8, 2024, requires a good synchronization between the current injection and the measurement with a complex and costly circuit which can limit it use in industrial application.

[0010] In addition, this requires a high-resolution and fast ADC to precisely monitor samples in a sufficiently short time to not influence the gate voltage and not compromise it normal operation. This can be a limitation for low-cost systems since the resolution and sampling speed of the ADC directly relate to the quality of the temperature estimation.

[0011] As a result, the methods based on the internal gate resistance are precise and accurate. Their main limitation is related to individual calibration and complexity and cost of implementation. Furthermore, it would be easier for the industrial actors to adopt a technique which provides an analog voltage value sensitive to the temperature, such as the one that can be generated with the built-in diodes. This analog value could then be used for either over-temperature detection or temperature estimation, eventually in another circuit board.SUMMARY OF INVENTION

[0012] In view of such prior art, the problem addressed by the invention is to provide an analogue signal linearly dependent of a temperature of a power semi-conductordie, in order to determine the temperature of such power semiconductor die in a simple and low-cost manner with low calibration effort. In this regard, the present disclosure concerns a device for measuring a junction temperature of a power semiconductor using the resistance Rgint of said semiconductor comprising at least:- a current injector circuit injecting current pulses nj in the gate path of said power semiconductor through the emitter of said power semiconductor, said current injector circuit being driven by a digital injection control circuit to synchronize said current pulses within a stabilized part of ON states of the power semiconductor driver PWM signal driving said power semiconductor,- a peak detector circuit to record emitter voltage peaks Veat the terminals of the current injector circuit and generate a continuous signal Vpks dependent of the junction temperature Tj through integration of said voltage peaks,- a signal conditioning circuit to adapt the continuous signal Vpks dependent of the junction temperature into a range of 3V to 5V of a measurement system.In realization modes which may be combined or alternatives:Said current pulses injected in said gate path may have durations calculated to limit contribution of the power semiconductor gate capacitor Cgvalue to the emitter voltage peaks.Said current pulses injected in said gate path have a typical duration of 20 ns to 200 ns.The injection of said current pulses may start between 20% and 50 % of the ON state of the power semiconductor.The current injector circuit may be a current source and wherein the current pulses nj have a typical amplitude of 20 mA to 200 mA.The digital injection control circuit may comprise a switch SW1 shorting said current source when said current pulses are not injected.The device may comprise a gate resistor on the bypass switch 6.Said gate resistor value may be chosen between 1 Ohm and 100 Ohm.The current pulse hnj may be synchronized through the Vge gate signal generated by the gate driver.The current pulse linj may be started between 1 ps and 10ps after a turn-ON order of the power semiconductor from the driver to be injected in a stable on period of the power semiconductor.The present disclosure concerns also a converter comprising at least one power module equipped with at least one power semiconductor and equipped with a device according to the present disclosure.The present disclosure concerns also a method for measuring a junction temperature of a power semiconductor through the measurement of the gate resistance of such power semiconductor comprising injecting current pulses linj in the gate path of said power semiconductor through the emitter of said power semiconductor, said current pulses being synchronized with a stabilized part of ON states of the power semiconductor and detecting emitter voltage peaks Veat terminals of a current generator circuit injecting said current pulses and integrating said peaks Veto generate a continuous signal VPks dependent of the junction temperature Tj,The method may comprise providing said current pulses linj through unshorting a current generator connected between the gate driver ground G and an emitter of said power semiconductor for the duration of said current pulses linj.The continuous signal VPks dependent of the junction temperature may be adapted to correspond to a range of 3V to 5V of a measurement system.Said signal VPks may be converted into a temperature 0j in said measurement system and said temperature 0j is displayed and / or compared to a maximum acceptable temperature 0jmax to provide a warning when said temperature 0j is above said maximum acceptable temperature 0jmax.

[0013] In other aspects, it is proposed a computer software comprising instructions to implement at least a part of a method as defined hereabove when the software is executed by a processor and it is proposed a computer-readable non-transient recording medium on which a software is registered to implement the method as defined hereabove when the software is executed by a processor.BRIEF DESCRIPTION OF DRAWINGS

[0014] Other features, details and advantages will be shown in the following detailed description and on the figures, on which:

[0015] Figure 1A discloses a prior art Rgint measurement device for semiconductor temperature measurement;

[0016] Figure 1 B shows the variation of the VGS voltage during injection;

[0017] Figure 2 discloses a schematic representation of a Rgint measurement circuit of the present disclosure;

[0018] Figure 3 discloses curves showing a temperature measurement based on the measurement circuit of figure 2;

[0019] Figures 4A and 4B show emitter voltage versus time curve depending on a pulse duration;

[0020] Figure 4C shows a representation of Ve versus time and the corresponding ARgint variation versus tnj caused by a semiconductor gate-emitter capacitor;

[0021] Figure 5 shows an example of implementation of a digital injection control circuit as in figure 1 ;

[0022] Figure 6 shows an example of implementation of a peak detector as in figure 1 ;

[0023] Figure 7 shows a schematic representation of the circuit of figure 1 with an additional over-temperature detection circuit;

[0024] Figure 8 shows a simplified flowchart of a method of the present disclosure;

[0025] Figure 9 shows an alternative mode of implementation of a Rgint measurement circuit of the present disclosure.DESCRIPTION OF EMBODIMENTS

[0026] The present disclosure concerns a method and device using the internal gate resistance of a power semiconductor as a temperature sensitive parameter to measure the junction temperature of said semiconductor.

[0027] The device according to figure 2 comprises a current injector circuit 5 designed to inject current through the gate path of the power semiconductor switch 3. The gate path is the path comprising the junction emitter-gate in case of an IGBT, or gate-source in case of a MOSFET. Such gate path allows to monitor the value of the internal resistance Rgint of the semiconductor switch.

[0028] The device comprises further a digital injection control 4 configured to synchronize the current injection inside the PWM pulse at the output of the driver 1 of the power semiconductor switch 3 in order to inject the current nj during a stable ON state period of the switch and for a precise duration. Such current injection provides at the poles of the current generator a voltage Ve dependent of the value or the resistor Rgmt.

[0029] Figure 5 shows an example of implementation of the digital injection control circuit.

[0030] AOPO is a comparator which translates the Vgevoltage, for a semiconductor switch 3 such as an IGBT, at the output of the gate driver into a logical signal, e.g. a signal comprised between 0V and +5V.

[0031] The components R1 , C1 and AOP1 define the delay t1-tO where tO is the turning ON of the semiconductor switch 3.

[0032] The components C2, R2 and AOP2 define the delay t2-t1 defining the current I inj pulse duration and make such that a pulse is generated only at the rising front of Vge. The reference voltage Vref is typically generated with a simple resistor divider between the +5V and 0V rails.

[0033] Of course, other electronic circuits may be designed to perform such function.

[0034] Advantageously, the injections are made at an instant where the device is in ON-state and sufficiently after the turn ON to avoid any perturbation of the switching and the circuit does not require specific timing information and can be retrofitted to existing gate drivers.

[0035] The device comprises further a peak detector circuit 7 to record every Ve peak and generate through integration of Ve a nearly continuous signal VPks dependent of the junction temperature.

[0036] After the peak detector circuit, the device comprises a signal conditioning circuit 8 to convert the continuous signal VPks in the range of a measurement system 9.

[0037] The current pulses nj injected in the gate path have durations calculated to limit contribution of the power semiconductor gate capacitor 33 value Cgto the emitter voltage peaks. The duration of the current injections within the ON PWMpulses is calculated to have the contribution of the gate capacitor value at least less than 5% of the amplitude of the voltage peak.

[0038] The current injector 5 is typically a constant current source with small sense value. The current nj is typically comprised between 20mA and 200mA in parallel. In idle mode, the switch is ON, and the current source is shorted. During the injection, a semiconductor switch SW1 6 is turned OFF and the current source injects the current hnj through the gate-emitter path of the device. The semiconductor switch 3 is typically a MOSFET whose gate is connected to the digital injection control. A gate resistance 51 between 1 and 100 Ohms between the digital injection control and the gate of the switch SW1 may be used to slow-down its turn-off, reduce the di / dt in the gate loop and the related oscillations in voltage response.

[0039] Advantageously, the voltage response is insensitive to gate loop inductance.

[0040] In figure 4A is shown the voltage Ve for a typical duration of 1 to 2 microseconds. Part 101 of the curve is the voltage rise when the current hnj starts to be injected due to the internal gate resistor Rgint and part 102 of the curve is the voltage rise due to the internal capacitor Cg. Figure 4B shows the curve for a short injection time of 20 to 200 nanoseconds which reduces the capacitive contribution 103. The main contribution to the Ve signal is then the gate resistor.

[0041] Advantageously, the variation of the capacitance with the operation contribution will have a limited impact on the temperature estimation. Moreover, the short time duration of injection will limit the perturbation on the gate voltage provided by the gate driver.

[0042] The error on Rgint, ARgint can be estimated as a function of the time duration t according to the gate capacitance Cgand its variation ACgusing the following equation:[Math. 1]

[0043] For example, for a typical gate capacitance of 50nF with a variation of ±1 %, ARgint as a function of time duration is shown in figure 4C. Thus, the maximum time duration can be estimated according to a specification in term of temperature error. For example, the typical gate resistor variation with temperature is about 0.1 % / °C.Thus, for a gate resistor of 2Q, the variation is about 0.002 Q / °C. For a specification of ±10°C, ARgint = ±20mQ. This will give a maximum time duration of 100ns, as shown in figure 4C.

[0044] The signal during the current injection is recorded by the peak detector 7 of figure 2 which generates a continuous signal dependent of the junction temperature. An example of analog peak detector suited for this function is given in figure 6 where the voltage Ve is input in a voltage follower AOP4 then clamped by a diode D4 and capacitor C4 with a discharge resistor R4.

[0045] The value of the resistor R4, together with the value of C4, define the voltage discharge which is defined based on the cooling time constant of the die and the switching frequency. The minimum voltage ripple Vripple-min can be expressed as: [Math. 2]

[0046] With Tmaxthe maximum temperature decrease in a switching period based on the thermal characteristics of the power module. Note that leakage currents of passive and active components (i.e. operational amplifiers) also contribute to discharging the capacitor C4.

[0047] Alternatively, the circuit can be modified to remove or compensate the temperature drift of the threshold voltage of diode D4. Advantageously, both the rising and decreasing dynamics of the die temperature are reliably captured by the invention. The voltage Vpks thus reflects the voltage Ve interpolated with a small ripple Vrippie and a voltage offset Vak which corresponds to the voltage drop across the diode D4. In the following equation Vrippie is neglected.[Math. 3]

[0048] The curve obtained is shown in figure 3 where is shown a temperature variation curve 110, a PWM curve 120, the current pulses hnj 130 inside the ON pulses of the PWM curve. It can be seen that the resulting train of Vepeaks of every current injection follows the junction temperature of the power semiconductor 3 and where the peak detector 7 provides a continuous signal Vpks 140 resulting of all Vepeaks Vpks which is then dependent of the junction temperature transformed in the signal Vtj in the signal conditioning block 8 of figure 2.

[0049] The signal conditioning circuit converts Vpks into VTJ shown in figure 3 within a range which can be easily compared with a threshold voltage value or measured by a basic measurement system such as an ADC.

[0050] The signal conditioning can typically include a low-pass filter and / or a gain and / or an offset implemented with low-cost operational amplifiers.[Math. 4]VTj« A ■ [(6Rgint■ 7} + i o ■ IinJ- Vak\ + B

[0051] Advantageously, VTj which depends on the junction temperature can be recorded continuously by any kind of measurement system without synchronization and trigger, such as by a low frequency ADC. In addition, the measurement can be performed outside of the device and centralized e.g. in the mother board of the converter.

[0052] The temperature sensitive term of VTJ is relatively robust to the individual power module reference and individual circuit as disclosed in the invention.

[0053] However, the offset term of VTJ may vary for each individual power module reference and individual circuit. A calibration is thus typically performed afterward, at a known temperature, to tune this offset term.

[0054] In a preferred implementation of over-temperature detection, the analogue output is directly compared with a threshold value which can be defined after a calibration at a known temperature.

[0055] In an alternative mode of implementation as shown in figure 7, a threshold value is generated with an analogue circuit which implements a current mirror 5’, at least a resistor emu 11 mimicking the internal gate resistor and a second peak detector PKD2 7’. The resistor circuit can also include a series capacitance and inductance to mimic the gate loop impedance. The resistance can be variable, i.e.a potentiometer, to adjust the over-temperature threshold value (e.g. 125°C or 150°C).

[0056] The rest of the circuit comprises a second signal conditioner SC2 8’ and a comparator 10 receiving the Vtj and Vtj’ signals from the measurement circuit 5, 7, 8 and the threshold value generating circuit 5’, 7’, 8’.

[0057] Figure 8 shows alternative modes of implementation of a Rgint measurement circuit of the present disclosure. In this circuit, the digital injection control 44 includes an enable input “en” and the output of the digital injection control is not only connected to the injection switch SW1 but also connected to a verification circuit CK 45. The verification circuit is configured to output a logical 1 if the injection may be performed, that is during a positive pulse of the PWM and outputs a logical 0 if the injection could not be performed. This may happen when the on-time of the PWM pulse is shorter than the delay set by the digital injection control circuit 44 according to figure 5, which may occur in some applications for some specific operating points where the duty-cycle may be close to 100% or 0%.

[0058] Advantageously, with this implementation mode, the absence of measurement cannot be interpreted as a low temperature.

[0059] Figure 9 describes features of a method for measuring a junction temperature of a power semiconductor 3 through the measurement of the gate resistance 32 of such power semiconductor 3 comprising injecting 200 current pulses linj in the gate path of said power semiconductor 3 through the emitter of said power semiconductor, said current pulses being synchronized 210 with a stabilized part of ON states of the power semiconductor 3 during PWM pulses in the power semiconductor.

[0060] The method comprises detecting 220 emitter voltage peaks Veat terminals of a current generator circuit 5 injecting said current pulses linj and integrating at 230 said peaks Veto generate a continuous signal Vpks dependent of the junction temperature Tj.

[0061] In the example, said current pulses linj are generated through unshorting 240 the current generator 5 connected between a digital ground G and an emitter e of said power semiconductor 3 for the duration of said current pulses linj.

[0062] The continuous signal VPks dependent of the junction temperature is adapted 250 in a signal conditioning circuit 8 to correspond to a range of 3V to 5V of a measurement system 9.

[0063] The signal VPks is converted 260 into a temperature 6j in said measurement system and said temperature 0j is displayed 270 and / or compared 280 to a maximum acceptable temperature Qjmax to provide a warning 290 when said temperature 0j is above said maximum acceptable temperature 0jmax.INDUSTRIAL APPLICABILITY

[0064] The technical solutions presented here can be used to provide junction temperature measurements to protect semiconductor switches of power converters or electric motor control systems for electric vehicle motors.

[0065] This disclosure is not limited to the example described hereabove and the invention encompasses every alternative comprised in the appended claims.

Claims

CLAIMS

1. A device for measuring a junction temperature Ti of a power semiconductor (3) using a resistance Rgint (32) of said semiconductor (3) comprising at least: a current injector circuit (5) injecting current pulses hnj in a gate path of said power semiconductor (3) through an emitter of said power semiconductor, said current injector circuit (5) being driven by a digital injection control circuit (4, 6) to synchronize said current pulses within a stabilized part of ON states of a power semiconductor driver (1), PWM signal driving said power semiconductor (3), a peak detector circuit (7) to record emitter voltage peaks Veat terminals of the current injector circuit and generate a continuous signal Vpks dependent of the junction temperature Tj through integration of said emitter voltage peaks, a signal conditioning circuit (8) to adapt the continuous signal Vpks dependent of the junction temperature into a range of 3V to 5V of a measurement system (9).

2. The device according to claim 1 , wherein said current pulses injected in said gate path have durations calculated to limit contribution of a power semiconductor gate capacitor Cg(33) value to the emitter voltage peaks.

3. The device according to claim 2, wherein said current pulses injected in said gate path have a typical duration of 20 ns to 200 ns.

4. The device according to claim 1 , 2 or 3 wherein the injection of said current pulses starts between 20% and 50 % of the ON state of the power semiconductor.

5. The device according to any one of the preceding claims, wherein the current injector circuit is a current source and wherein the current pulses nj have a typical amplitude of 20 mA to 200 mA.

6. The device according to any one of the preceding claims, wherein the digital injection control circuit comprises a switch SW1 (6) shorting said current source when said current pulses are not injected.

7. The device according to any one of the preceding claims, comprising a gate resistor (51) on a bypass switch 6.

8. The device according to claim 7, wherein a value of said gate resistor (51) is between 1 Ohm and 100 Ohm.

9. The device according to any one of the preceding claims, wherein the current pulse hnj is synchronized through a Vge gate signal generated by the gate driver (1).

10. The device according to any one of the preceding claims, wherein the current pulse hnj is started between 1 s and 10ps after a turn-ON order of the power semiconductor (3) from the driver (1).

11. A converter comprising at least one power module equipped with at least one power semiconductor equipped with a device according to any one of claims 1 to 10.

12. A method for measuring a junction temperature Ti of a power semiconductor (3) through the measurement of a gate resistance (32) of such power semiconductor (3) comprising injecting (200) current pulses nj in a gate path of said power semiconductor (3) through an emitter of said power semiconductor, said current pulses being synchronized (210) with a stabilized part of ON states of the power semiconductor (3) and detecting (220) emitter voltage peaks Veat terminals of a current generator circuit (5) injecting said current pulses and integrating (230) said peaks Veto generate a continuous signal Vpks dependent of the junction temperature Tj.

13. The method according to claim 12, comprising providing said current pulses hnj through unshorting (240) a current generator (5) connected between a gate driver ground G and an emitter (e) of said power semiconductor (3) for the duration of said current pulses hnj.

14. The method according to claim 12 or 13, wherein the continuous signal Vpks dependent of the junction temperature is adapted (250) to correspond to a range of 3V to 5V of a measurement system (9).

15. The method according to claim 14, wherein said signal Vpks is converted (260) into a temperature 0j in said measurement system and said temperature 0j is displayed (270) and / or compared (280) to a maximum acceptable temperature 0jmax to provide a warning (290) when said temperature 0j is above said maximum acceptable temperature 0jmax.

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