Power module and method for measuring the temperature of the power module

Abstract

The present invention relates to a power module (1) comprising a semiconductor switch (2) having a gate terminal (2a), and a gate driver (3) for switching the semiconductor switch (2), which is connected to the gate terminal (2), wherein the gate driver (3) is designed to supply an oscillating voltage (V OSC ) in order to thereby set a phase shift between a gate current and a gate voltage to a predefined value, in particular +45° or -45°, wherein the gate driver (3) is designed to detect a deviation of the phase shift from the predefined value, and wherein the gate driver (3) is designed to detect an amplification factor between the gate current and the gate voltage and, based on the amplification factor and the deviation of the phase shift, to set a gate resistance (R Gint ) and an input capacitance (C iss) of an equivalent resonant circuit of the semiconductor switch (2).

Description

State of the art

[0001] The present invention relates to a power module. The power module, in particular, has a temperature measurement feature. Furthermore, the invention relates to a method for adjusting the temperature of the power module.

[0002] To ensure the correct functioning of power semiconductors, the temperature must be monitored during operation. Temperature sensors or parasitic properties of the power semiconductor can be used for this purpose. Using parasitic properties of the power semiconductor, the temperature can typically be measured with a shorter delay than with discrete sensors. Classic temperature-sensitive electrical parameters (TSEPs) of power semiconductors are the diode forward voltage of the body diode of MOSFETs or the collector-emitter voltage of IGBTs. These methods require access to the power path of the power semiconductor and thus a precise measurement with a high dielectric strength of the measurement input.

[0003] On the other hand, it is now possible to determine the temperature using temperature-sensitive elements in the gate circuit. In this case, the temperature dependence of the internal gate resistance of a power semiconductor is used. Until now, this method was used to measure the temperature of IGBTs in the off state, see, for example, M. Denk and M. Bakran, "An IGBT Driver Concept with Integrated Real-Time Junction Temperature Measurement," PCIM Europe 2014; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 2014, pp. 1-8. The gate of the IGBT is excited at the resonant frequency and the current in the gate is measured. The temperature can be determined from the current signal because the current flow decreases with increasing temperature due to the increased series inductance. Disclosure of the invention

[0004] Advantageously, a temperature measurement is performed at the gate of a semiconductor switch, for example, a silicon carbide MOSFET. For this purpose, a recurring signal is applied, and the frequency is selected such that the phase shift between the gate voltage and the gate current is at a predefined value, e.g., 45°. A change in temperature and the resulting change in the internal gate resistance leads to a reduction in the phase shift and thus serves as a TSEP.

[0005] This invention enables current measurement in semiconductor switches, particularly SiC MOSFETs, during active, conducting operation via the gate path, allowing junction temperature measurement under current flow or compensation of the temperature error caused by current flow. This further development of the TSEP measurement via the internal gate resistance using phase shifting allows compensation of the method's current-dependent temperature measurement error.

[0006] This current dependence is caused by the change in the input capacitance of the semiconductor switch, especially MOSFETs, due to the load current through the semiconductor switch. Therefore, the change in the gain factor between gate current and gate voltage is taken into account. From the gain and phase data, the capacitance and resistance of the RLC resonant circuit can now be determined, given a known inductance.

[0007] This compensated measurement can be realized by a phase gain detector, which can be integrated into an ASIC with minimal space requirements. This allows both the current distribution and the temperature distribution of a power module to be determined, thus determining and influencing its symmetry.

[0008] The power module has a semiconductor switch with a gate terminal and a gate driver. The gate driver is connected to the gate terminal to switch the semiconductor switch. The gate driver is also designed to determine the temperature based on measurements in the gate circuit.

[0009] The gate driver is designed to apply an oscillating voltage to the gate terminal. This creates a phase shift between a gate current and a gate voltage, with the frequency of the oscillating voltage being selected such that the phase shift is set to a predefined value.

[0010] The gate driver is further configured to detect a deviation of the phase shift from the predefined value. Additionally, the gate driver is configured to detect a gain factor between the gate current and the gate voltage and, based on the gain factor and the phase shift deviation, to determine a gate resistance and an input capacitance of an equivalent resonant circuit of the semiconductor switch.

[0011] A semiconductor switch, particularly a SiC MOSFET, can alternatively be viewed as an RLC series resonant circuit with an electrical gate resistance, a gate inductance, and an input capacitance. In particular, the gate resistance consists of, among other materials, polysilicon. The gate resistance is intended to be temperature-dependent, which changes the damping of the series resonant circuit with temperature fluctuations. As the temperature increases, the gate resistance and thus the damping increase.

[0012] The resonant circuit can now be operated at resonance, meaning the impedance of the inductance and capacitance cancel each other out. As a result, the resistance for the excitation signal corresponds only to the real part and thus to the internal gate resistance. According to the invention, the gate driver is designed not to operate the resonant circuit at resonance, but rather particularly advantageously at a frequency where the real part of the impedance corresponds to the imaginary part. At this operating point, a phase shift of +45° or -45° occurs between the gate voltage and the gate current.

[0013] As the temperature increases, the gate resistance increases, and thus the phase shift decreases. The temperature can be determined by evaluating the phase shift. However, since the input capacitance is also current-dependent, a measurement error occurs when measuring the temperature under current flow due to detuning of the gate resonant circuit. The input capacitance is increased by the Miller effect. The gate-drain capacitance is increased by the gain factor.

[0014] The temperature and current can be determined from the two values ​​of gain and phase shift between the gate voltage and the gate current. For this purpose, the complex resistance of the circuit is particularly advantageously determined from the phase signal and the gain signal.

[0015] The subclaims show preferred developments of the invention.

[0016] The gate driver is preferably configured to determine a temperature of the semiconductor switch from the gate resistance. Alternatively or additionally, the gate driver is configured to determine a load current of the semiconductor switch from the input capacitance. Preferably, a current dependence of the input capacitance and a temperature dependence of the gate resistance are known, so that both temperature and load current values ​​can be determined. The current dependence of the input capacitance due to the Miller effect preferably allows the load current to be determined via the amplification characteristic of the semiconductor switch.

[0017] In an advantageous embodiment, the gate driver is configured to track a frequency of the oscillating voltage if the phase shift deviates from the predefined value. This minimizes said phase shift deviation. The gate driver is further configured to determine the gate resistance and the input capacitance of the equivalent resonant circuit of the semiconductor switch based on the gain factor and the frequency of the oscillating voltage. This creates, in particular, a phase-locked loop with high sensitivity, since the phase angle is set to a value that accurately reflects both the real and imaginary parts of the gate circuit's impedance.

[0018] The gate driver is advantageously an application-specific integrated circuit. The gate driver and semiconductor switch are particularly advantageously integrated. This allows for particularly short gate paths, resulting in a minimal influence of the gate connection on the temperature measurement.

[0019] The semiconductor switch is preferably a MOSFET. Particularly preferably, the semiconductor switch is a silicon carbide MOSFET (SiC MOSFET).

[0020] The invention also relates to a method for measuring the temperature of a power module. The power module comprises a semiconductor switch with a gate terminal and a gate driver. The gate driver is connected to the gate terminal to switch the semiconductor switch. The gate driver is also designed to determine the temperature based on measurements in the gate circuit.

[0021] To implement the process, an oscillating voltage is first applied to the gate terminal. This creates a phase shift between a gate current and a gate voltage, with the frequency of the oscillating voltage being selected such that the phase shift is set to a predefined value.

[0022] Furthermore, a deviation of the phase shift from the predefined value is detected. Additionally, a gain factor between the gate current and the gate voltage is measured, and based on the gain factor and the phase shift deviation, a gate resistance and input capacitance of an equivalent resonant circuit of the semiconductor switch are determined. This results in the same advantages as described above.

[0023] Preferably, a temperature of the semiconductor switch is determined from the gate resistance. Alternatively or additionally, a load current of the semiconductor switch is determined from the input capacitance. Preferably, a current dependence of the input capacitance and a temperature dependence of the gate resistance are known, so that both temperature and load current values ​​can be determined. The current dependence of the input capacitance due to the Miller effect preferably allows the load current to be determined via the amplification characteristic of the semiconductor switch.

[0024] In an advantageous embodiment, if the phase shift deviates from the predefined value, a frequency of the oscillating voltage is also tracked. This minimizes said phase shift deviation. Based on the gain factor and the frequency of the oscillating voltage, the gate resistance and input capacitance of the equivalent resonant circuit of the semiconductor switch are determined. This creates, in particular, a phase-locked loop with high sensitivity, since the phase angle is set to a value that accurately reflects both the real and imaginary parts of the gate circuit's impedance. Short description of the drawings

[0025] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing: Fig. 1 a schematic illustration of a power module according to an embodiment of the invention, Fig. 2 a schematic flow chart of a current determination of a load current of the power module according to the embodiment of the invention, Fig. 3 is a schematic flow chart of a temperature determination of the power module according to the embodiment of the invention, and Fig. 4 a schematic flow chart for determining a gate resistance and an input capacitance of the power module according to the embodiment of the invention by means of a phase-locked loop. Embodiments of the invention

[0026] Preferably, all identical components, elements and / or units in all figures are provided with the same reference numerals.

[0027] Fig. Figure 1 schematically shows a power module 1 according to an embodiment of the invention. The power module 1 has a semiconductor switch 2 with a gate terminal 2a. The semiconductor switch 2 is a silicon carbide MOSFET and Fig. 1 alternatively by an RLC series resonant circuit with the gate resistance R Gint , the gate inductance L G and the input capacitance C iss The gate resistance R Gint features polysilicon and is temperature dependent. The input capacitance C iss is current dependent.

[0028] The power module 1 also has a gate driver 3 for switching the semiconductor switch 2, wherein the gate driver 3 is connected to the gate terminal 2. The gate driver 3 is an application-specific integrated circuit (ASIC), with the gate driver 3 and the semiconductor switch 2 being integrated. This implementation is particularly advantageous because the gate paths can be kept as short as possible. This results in a minimal influence of the gate connection on the measurement. Furthermore, this combination enables a secure coupling of the parameters of the semiconductor switch 2 with the gate driver 3.

[0029] Gate driver 3 is designed to apply an oscillating voltage VOSC to gate terminal 2a at a frequency such that the real part of the impedance corresponds to the imaginary part. At this operating point, a phase shift of +45° or -45° occurs between the gate voltage and gate current.

[0030] Due to the current dependence of the input capacitance C iss of a load current I through the semiconductor switch 2, a measurement error occurs during temperature measurement under current flow due to a detuning of the gate resonant circuit. The input capacitance C iss is increased by the Miller effect. The gate-drain capacitance C rss increased by the amplification factor, also called gain.

[0031] From the two values ​​of amplification factor or gain and phase shift between the gate voltage and the gate current, both the temperature T and the load current I can be determined. The gate driver 3 is designed to measure the input capacitance C by means of a phase gain detector 4 and a D / A converter 5. iss and the gate resistance R Gint To do this, the complex resistance of the circuit is determined from the phase signal and the gain signal. With a known current dependence of the input capacitance C issand known temperature dependence of the gate resistance R Gint Thus, both values ​​T and I can be determined. The current dependence of the input capacitance due to the Miller effect allows the current dependence via the gain characteristic of the semiconductor switch 2 to be used to determine the load current I. The following formulas are provided for this conversion into the real and imaginary parts: Re{Z}=Z∗cos(α); Im{Z}=Z∗sin(α)

[0032] The amplification factor Gain is composed as follows: Gain=VShuntVGS=IG∗RGVGS

[0033] The current flow is limited by the impedance Z, where X L the reactance of the inductors and X C the reactance of the capacitances of the semiconductor switch 2. Z=(XL+XC)2+(RG(Int)+RG)2)

[0034] Thus, the gain current I G , where V GSthe gate-source voltage of semiconductor switch 2 is: IG=VGSZ

[0035] By inserting the following applies to the gain: Gain=IG∗RGVGS=VGSZ∗RGVGS=RZ

[0036] By rearranging the following results: Z=RextGain

[0037] Since the phase shift φ is also measured, the measured impedance Z can now be decomposed into resistance R and reactance X: cos(φ)=RZ=RGint+RextZ= =>Z=RGint+Rextcos(φ)

[0038] By equating we now get: RextGain=RGint+Rextcos(φ)==>RGint=RextGain∗cos(φ)−Rext

[0039] For the reactance X and the individual reactances of inductances X L and capacities X C of the semiconductor switch 2 applies: sin(φ)=XZ=XL+XCZ==>Z=XL+XCsin(φ)

[0040] Equating this results in: RextGain=XL+XCsin(φ)==>XC=RextGain∗sin(φ)−XL

[0041] The following applies to the previous formula: XL=2π∗Fosc×LG; XC=−12π∗Fosc∗Ciss

[0042] Since the total resistance R Ext by the assembly and the gate inductance L G are constant and known for a design due to the design of the gate path and furthermore the frequency F OSC the oscillating voltage V OSC is known, C iss and R Gint determine.

[0043] Thus, by changing the gate resistance R Gint determine the temperature T. C iss has a temperature dependence and a current dependence: Due to the Miller effect, the Miller capacitance of the semiconductor switch 2 acts, which results from the reaction capacitance C rss and the gate-drain capacitance C GD by C rss / C GDcalculated to increase the gain factor Gain: CMiller=|Gain|∗Crss

[0044] The amplification factor in the ohmic range of the semiconductor switch 2 increases approximately linearly with the current. (ΔV ds = I d ∗ Δr ds ) However, as the temperature T increases, the amplification factor Gain decreases, due, among other things, to the decreasing charge carrier mobility and the smaller proportion of the channel resistance in the total resistance of the semiconductor switch 2 with increasing temperature T. One factor influencing the temperature T on the amplification factor is described in Li, Yaoye: Analysis of basic performance parameters and temperature e_ect of SiC-MOSFET. In: Journal of Physics: Conference Series 2435 (2023), February, No. 1, 012020. http: / / dx.doi.org / 10.1088 / 1742-6596 / 2435 / 1 / 012020. - DOI 10.1088 / 1742-6596 / 2435 / 1 / 012020. - ISSN1742-6588, 1742-6596.

[0045] The single-chip temperature measurement can be carried out for each power module 1 with individually led-out gate connections 2a. In the case of a combined gate, the measurement of an average temperature of the semiconductor switches 2 is possible. In this measurement, an average value of the individual gate resistances R Gint This is in contrast to the temperature measurement via the body diode, where the hottest semiconductor switch 2 determines the voltage drop across the parallel semiconductor switches 2 because it conducts first.

[0046] Fig. Figure 2 schematically shows a flow chart of a current determination of the load current I of the power module 1 according to the embodiment of the invention. The determination of the gate resistance R Gint enables the temperature determination. With a known temperature T and a known temperature dependence of the gain Gain of the semiconductor switch 2, the change in the input capacitance C issThe gain factor Gain is determined by calculating the input capacitance C iss and the gate-source capacitance C GS the Miller capacity C Miller by subtracting 6 and from the Miller capacity C Miller and reaction capacity C rss The amplification factor Gain is determined by a first division 7. Using the amplification factor Gain, a conclusion about the load current I can now be drawn from the temperature dependence of the amplification. For this purpose, a second division 8 of the amplification factor Gain by Δr is carried out. ds , where Δr ds can be determined from the temperature T, as explained in the above-mentioned source. In particular: rds=1μnCOXWL(VGS−VTh) W is the channel width, C OX is the capacitance of the gate oxide layer, µ n is the charge carrier mobility, L is the channel length, V GS is the gate-source voltage, V TH is the threshold voltage.

[0047] Fig. Figure 3 schematically shows a flow chart of a temperature determination of the power module 1 according to the embodiment of the invention. In the case where the load current I is known, the relationship can also be reversed to that previously described with reference to Fig. 2 described variant, starting from the load current I and the input capacitance C iss The temperature T is determined. This improves the accuracy of the temperature measurement and also introduces a compensation factor. This current can be determined, for example, by a current sensor. Another possibility would be to use the setpoint current of the inverter's control system.

[0048] For this purpose, the input capacitance C iss and the gate-source capacitance C GS the Miller capacity C Miller by subtracting 6 and from the Miller capacity C Miller and reaction capacity C rssThe gain factor Gain is determined by a first division 7. Using the gain factor Gain and the load current I, the value for Δr is determined by a third division 10 ds As previously described, Δr ds depends on the temperature T. Thus, for example, using a lookup table 11, the temperature can be determined from Δr ds be determined.

[0049] Fig. 4 shows a schematic flow chart for determining a gate resistance R Gint and an input capacitance C issof the power module 1 according to the exemplary embodiment of the invention using a phase-locked loop. The measurement frequency is continuously adjusted to achieve a constant phase shift φ. To evaluate the temperature T and the load current I, the gain, i.e., a value proportional to the impedance, is recorded in this case. The frequency must also be included in the evaluation. The gain and the phase position allow the resistive and capacitive components of the measurement to be directly determined. The frequency also allows the capacitance to be calculated from the reactance.

[0050] A controlled oscillator 12 generating the oscillating voltage VOSC outputs the oscillating voltage VOSC via a shunt resistor 13 to the gate circuit 14, whereby by means of a phase comparison 15 the frequency F OSCof the controlled oscillator 12. By means of a gain determination 16 and an impedance calculator 17, the gate resistance R Gint and input capacitance C iss .

[0051] For a design of the phase-locked loop for a constant phase shift φ of 45°, the calculation of Ciss and R Gint as follows: F OSC presents itself via: XL(FOSC)+XC(FOSC)=ROSC=RGint For R Gint In this case, the following applies: RGint=RextGain∗cos(45°)−Rext=RextGain∗22−Rext For C iss applies if L is known G in this case: X=XL+XC=−12π∗Fosc∗Ciss+2π∗Fosc∗LG=RextGain∗sin(45°)−Rext=Rext Gain∗22−Rext−12π∗Fosc∗Ciss+2π∗Fosc∗LG=RextGain∗22−Rext−12π∗Fos c∗Ciss=RextGain∗22−Rext−2π∗Fosc∗LG−1=(RextGain∗22−Rext−2π∗Fos c∗LG)∗2π∗Fosc∗Ciss−1(RextGain∗22−Rext−2π∗Fosc∗LG)∗2π∗Fosc=Ciss

[0052] Thus, by means of gain measurement and frequency measurement with a known set phase shift φ between gate current and gate voltage, the input capacitance and the gate resistance can be determined and thus, as with reference to Fig. 2 and Fig. 3 explains how to evaluate current and temperature.

[0053] The advantages of this method are the high sensitivity of the measurement, since the phase angle can be set to a value that accurately reflects both the real and imaginary parts. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] M. Denk and M. Bakran, „An IGBT Driver Concept with Integrated Real-Time Junction Temperature Measurement,“ PCIM Europe 2014; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 2014, pp. 1-8

[0003] Li, Yaoye: Analysis of basic performance parameters and temperature e_ect of SiC-MOSFET. In: Journal of Physics: Conference Series 2435 (2023), Februar, Nr. 1, 012020. http: / / dx.doi.org / 10.1088 / 1742-6596 / 2435 / 1 / 012020. - DOI 10.1088 / 1742-6596 / 2435 / 1 / 012020. - ISSN1742-6588, 1742-6596

[0044]

Claims

[1] Power module (1) comprising, - a semiconductor switch (2) having a gate terminal (2a), and - a gate driver (3) for switching the semiconductor switch (2) which is connected to the gate terminal (2), - wherein the gate driver (3) is designed to supply an oscillating voltage (V OSC ) in order to set a phase shift between a gate current and a gate voltage to a predefined value, in particular +45° or -45°, - wherein the gate driver (3) is designed to detect a deviation of the phase shift from the predefined value, and - wherein the gate driver (3) is designed to detect a gain factor between gate current and gate voltage and, based on the gain factor and the deviation of the phase shift, to determine a gate resistance (R Gint ) and an input capacitance (C iss) of an equivalent resonant circuit of the semiconductor switch (2). [2] Power module (1) according to claim 1, characterized by that the gate driver (3) is designed to consist of the resistor (R Gint ) to determine a temperature (T) of the semiconductor switch (2) and / or from the input capacitance (C iss ) to determine a load current (I) of the semiconductor switch (2). [3] Power module (1) according to one of the preceding claims, characterized by that the gate driver (3) is designed to set a frequency of the oscillating voltage (V OSC ) to minimize the deviation, wherein the gate driver (3) is further designed to adjust the gate resistance (R Gint ) and the input capacitance (C iss ) of the equivalent resonant circuit of the semiconductor switch (2). [4] Power module (1) according to one of the preceding claims, characterized by that the gate driver (3) is an application-specific integrated circuit and the gate driver (3) and semiconductor switch (2) are integrated. [5] Power module (1) according to one of the preceding claims, characterized by that the semiconductor switch (2) is a MOSFET, in particular a SiC MOSFET. [6] Method for measuring the temperature of a power module (1), wherein the power module (1) has a semiconductor switch (2) with a gate terminal (2a) and a gate driver (3) connected to the gate terminal (2) for switching the semiconductor switch (2), the method comprising the steps: - Applying an oscillating voltage (V OSC ) to the gate terminal (2a) to thereby set a phase shift between a gate current and a gate voltage to a predefined value, - detecting a deviation of the phase shift from the predefined value, and - Determining a gain factor between gate current and gate voltage and determining a gate resistance (R Gint ) and an input capacitance (C iss ) of an equivalent resonant circuit of the semiconductor switch (2) based on the gain factor and the deviation of the phase shift. [7] Method according to claim 6, characterized by that from the resistance (R Gint ) a temperature (T) of the semiconductor switch (2) is determined and / or a load current (I) of the semiconductor switch (2) is determined from the input capacitance (Ciss). [8] Power module (1) according to one of the preceding claims, characterized by that if the phase shift deviates from the predefined value, a frequency of the oscillating voltage (V OSC) to minimize the deviation, whereby based on the gain and the frequency of the oscillating voltage, the gate resistance (R Gint ) and the input capacitance (C iss ) of the equivalent resonant circuit of the semiconductor switch (2) is determined.

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