Junction temperature measurement circuit, design method and application of automotive inverter power devices

Abstract

The present application provides a junction temperature measurement circuit of a vehicle inverter power device and its design method and application. The junction temperature measurement circuit includes two measurement circuits and a clamping power supply for measuring two power devices of the upper and lower bridges respectively; each measurement circuit includes an adaptive switch and a clamping module, wherein the adaptive switch is configured to make the potential of the measurement end track the drain or source potential of the measured power device when the measured power device enters the on state, and to maintain the micro-conduction state between the drain or source of the measured power device and the measurement end when the measured power device is in the off state; the clamping module realizes a positive clamping voltage and a negative clamping voltage through a clamping power supply, which are respectively used to clamp the voltage of the measurement end when the measured power device is in the off state. The junction temperature measurement circuit provided by the present application can timely and accurately measure the working junction temperature of the high-speed switching power device.

Description

Technical Field

[0001] The present application belongs to the technical field of power electronic device measurement, and specifically, relates to a junction temperature measurement circuit, design method and application of a vehicle inverter power device. Background Art

[0002] With the electrification of transportation, especially the development of electric vehicles, new third-generation wide-bandgap SiC power inverters with higher voltage resistance, faster switching speed and higher power density are gradually replacing traditional Si-based power inverters. In the automotive field, the power inverter is the weak link of the vehicle's electric drive system. More than 90% of the failures of the electric drive system are caused by the fatigue of the power devices in the inverter. Compared with traditional Si-based IGBT power devices, SiC-based MOSFETs have higher power density and harsh heat dissipation conditions, and reliability issues are particularly prominent: after analyzing the current status of domestic and foreign research, it was found that the fundamental cause of SiC MOSFET fatigue failure is the thermal stress failure under the excitation of junction temperature fluctuations due to the inconsistent thermal expansion coefficients of the interfaces of different packaging materials of the device. Therefore, timely and accurate acquisition of the working junction temperature of the inverter SIC MOSFET is of great significance for protecting and preventing SiC MOSFET thermal failure and improving and optimizing SiC inverter design.

[0003] At present, most of the research on junction temperature measurement of power devices uses the measured parameters such as on-state voltage drop as temperature-sensitive electrical parameters to measure the junction temperature. For example, Chinese invention patent CN115436771A provides a circuit for measuring the junction temperature of a silicon carbide power tube, including a clamping module, a current limiting module, a first power supply and a second power supply. The clamping module in the circuit disconnects the connection between the measurement point and the pulse high voltage during the measurement pulse, and achieves clamping through the second power supply; after the measurement pulse ends, a current is generated in the measured silicon carbide power tube through the first power supply to measure its on-state voltage drop.

[0004] However, since the switching frequency of SiC MOSFET can reach 10 4 The switching time of the on and off states is much shorter than that of conventional silicon-based power tubes. The clamping module in the above measurement circuit uses the method of cutting off and conducting the measurement point and the high-voltage source to perform measurement and clamping state switching, which cannot respond to the high-speed switching of SiC MOSFET in a timely manner, and therefore cannot be applied to the measurement of the on-state voltage drop and operating junction temperature of SiC MOSFET. In addition, the existing junction temperature measurement circuit is not specially designed for the three-phase six-bridge arm power topology of the automotive inverter, and cannot guarantee the efficiency and accuracy of the junction temperature measurement circuit in obtaining temperature-sensitive parameters in real time under the driving conditions of the vehicle. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present application provides a junction temperature measurement circuit for a power device of a vehicle inverter, which can be used to accurately measure the working junction temperature of a first power device under test and a second power device under test of the vehicle inverter, and the power device under test can be either a conventional silicon carbide power tube or a SiC MOSFET with a higher switching frequency. The first power device under test and the second power device under test are connected in series between the positive and negative electrodes of the DC bus power supply of the vehicle inverter, the source of the first power device under test is connected to the drain of the second power device under test and the reference ground, and the two power devices under test are turned on and off in different states when working.

[0006] The junction temperature measurement circuit includes a first measurement circuit, a second measurement circuit and a clamping power supply;

[0007] The first measurement circuit is used to measure the conduction voltage drop of the first power device under test during operation and determine its junction temperature, and includes a first adaptive switch and a first clamping module, wherein the first adaptive switch is configured to make the potential of the first measurement terminal track the drain potential of the first power device under test when the first power device under test enters the conduction state, and to maintain a micro-conduction state between the drain of the first power device under test and the first measurement terminal when the first power device under test is in the off state;

[0008] The second measurement circuit is used to measure the conduction voltage drop of the second power device under test when it is in operation and determine its junction temperature, and includes a second adaptive switch and a second clamping module, wherein the second adaptive switch is configured to make the potential of the second measurement terminal track the drain potential of the second power device under test when the second power device under test enters the conduction state, and to maintain a micro-conduction state between the source of the second power device under test and the second measurement terminal when the second power device under test is in the off state;

[0009] The first clamping module and the second clamping module both realize positive clamping voltage and negative clamping voltage through a clamping power supply, and are respectively used to clamp the first measuring end at the positive clamping voltage when the first power device under test is in the off state, and to clamp the second measuring end at the negative clamping voltage when the second power device under test is in the off state.

[0010] Furthermore, the first adaptive switch includes a first switch tube and a first resistor connected in series, and the second adaptive switch includes a second switch tube and a second resistor connected in series; the first switch tube and the second switch tube are both zero-voltage conduction and negative-voltage cut-off type switch tubes, and their on-off states are switched based on the voltage drop across the first resistor and the second resistor, respectively.

[0011] Specifically, when there is intermittent leakage current in the first switching tube and the first resistor, the drain of the first power device under test and the first measuring end are in a micro-conduction state; when there is intermittent leakage current in the second switching tube and the second resistor, the source of the second power device under test and the second measuring end are in a micro-conduction state.

[0012] Preferably, the intermittent occurrence frequency of the leakage current is much greater than the switching frequency of the first measured power device and the second measured power device during operation.

[0013] Furthermore, in the process of the first adaptive switch connecting the drain of the first power device under test and the first measuring terminal, the lowest potential of the first measuring terminal is not lower than the negative clamping voltage; in the process of the second adaptive switch connecting the source of the second power device under test and the second measuring terminal, the highest potential of the second measuring terminal is not higher than the positive clamping voltage.

[0014] Preferably, the ratio of the tracking response time of the first adaptive switch to the drain potential of the first power device under test during the conduction process of the first power device under test to the switching period of the first power device under test is less than or equal to 5%;

[0015] The ratio of the tracking response time of the second adaptive switch to the drain potential of the second power device under test during the conduction process of the second power device under test to the switching period of the second power device under test is less than or equal to 5%.

[0016] Preferably, both the first switch tube and the second switch tube are N-channel depletion-type MOSFETs; the drain of the first switch tube is connected to the drain of the first power device under test, the source is connected to the first end of the first resistor, and the second end of the first resistor is respectively connected to the first measuring end and the gate of the first switch tube; the first end of the second resistor is respectively connected to the source of the second power device under test and the gate of the second switch tube, the second end is connected to the source of the second switch tube, and the drain of the second switch tube is connected to the second measuring end.

[0017] Furthermore, the measurement voltage V of the first measurement circuit and the second measurement circuit is out Satisfy the following formula:

[0018] V DS =V DS1 -V GS1 +V out ,

[0019] Among them, V DS is the drain-source voltage of the first power device under test or the second power device under test, V DS1 is the drain-source voltage of the first switch tube or the second switch tube, V GS1 is the gate-source voltage of the first switch tube or the second switch tube.

[0020] Preferably, the first clamping module includes a first Schottky diode and a second Schottky diode, wherein the cathode of the first Schottky diode has a positive clamping voltage, the anode of the second Schottky diode has a negative clamping voltage, and the anode of the first Schottky diode is connected to the cathode of the second Schottky diode and serves as a first measuring end; the second clamping module includes a third Schottky diode and a fourth Schottky diode, wherein the cathode of the third Schottky diode has a positive clamping voltage, the anode of the fourth Schottky diode has a negative clamping voltage, and the anode of the third Schottky diode is connected to the cathode of the fourth Schottky diode and serves as a second measuring end.

[0021] Preferably, the junction temperature measurement circuit further includes a voltage stabilization module connected in parallel with the clamping power supply and used for stabilizing the positive clamping voltage and the negative clamping voltage.

[0022] The present application also provides a design method for designing a junction temperature measurement circuit of the aforementioned automotive inverter power device, the design method comprising the following steps:

[0023] Step 1: Establish a junction temperature measurement model for automotive inverter power devices based on negative pressure cut-off adaptive switch and voltage clamp;

[0024] Step 2, analyzing the time-varying characteristics of the electrical parameters of the junction temperature measurement model when the vehicle inverter power device is working;

[0025] Step three, designing the circuit structure of the junction temperature measurement circuit based on the topological structure of the vehicle inverter, and selecting circuit components based on the time-varying characteristics of the electrical parameters.

[0026] The present application also provides an application of the aforementioned junction temperature measurement circuit of a vehicle inverter power device in a vehicle inverter.

[0027] The present application also provides an application of the aforementioned junction temperature measurement circuit of the automotive inverter power device in a vehicle motor towing test platform.

[0028] An embodiment of the present application provides a junction temperature measurement circuit for a vehicle inverter power device, which utilizes a switch tube with zero-voltage conduction and negative-voltage cutoff characteristics and a resistor between its gate and source to construct an adaptively adjustable switch. The adaptive switch can realize a micro-conduction state between the power device under test and the measuring end when the power device under test is in the off state, and effectively clamp various voltage changes that occur in the power device in the off state and in the process of converting from the off state to the on state through two clamping voltages in opposite directions, thereby realizing timely tracking and response to the drain-source voltage of the power device in the process of converting from the off state to the on state, thereby ensuring the accuracy of the working junction temperature measurement of the power device capable of extremely high-speed switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the circuit principle of a junction temperature measurement circuit of a vehicle inverter power device provided according to an embodiment of the present application;

[0030] Figure 2 A schematic diagram of the architecture of a vehicle motor towing test platform using a junction temperature measurement circuit of a vehicle inverter power device according to an embodiment of the present application;

[0031] Figure 3a The analysis result of the time-varying characteristics of the electrical parameters of the junction temperature measurement model provided according to the embodiment of the present application;

[0032] Figure 3b The analysis result of the output voltage of the junction temperature measurement model provided according to the embodiment of the present application;

[0033] Figure 4a The analysis result of the time-varying characteristics of the electrical parameters of the junction temperature measurement model in the phase I of the turn-on process of the power device under test provided in the embodiment of the present application;

[0034] Figure 4b The analysis result of the time-varying characteristics of the electrical parameters of the junction temperature measurement model in the phase II of the turn-on process of the power device under test provided according to the embodiment of the present application;

[0035] Figure 4c The analysis result of the time-varying characteristics of the electrical parameters of the junction temperature measurement model during the shutdown process of the power device under test provided in the embodiment of the present application;

[0036] Figure 5 A flow chart of a design method for a junction temperature measurement circuit of a vehicle inverter power device provided according to an embodiment of the present application;

[0037] Figure 6 A schematic diagram of a circuit board of a junction temperature measurement circuit of a vehicle inverter power device with a negative pressure cut-off clamping function provided according to an embodiment of the present application;

[0038] Figure 7 The diagram is a schematic diagram of a voltage output result of a junction temperature measurement circuit of a vehicle inverter power device provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0040] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the products of the embodiments of the present application are usually placed when in use, it is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, in the description of the present application, in order to distinguish different units, the words first, second, etc. are used in this specification, but these are not limited by the order of manufacture, nor can they be understood as indicating or implying relative importance, and their names may be different in the detailed description of the present application and the claims. In addition, in order to facilitate understanding, various components on the drawings are enlarged or reduced, but this practice is not intended to limit the scope of protection of the present application.

[0041] The vocabulary in this specification is used to illustrate the embodiments of the present application, but is not intended to limit the present application. It should also be noted that, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection, it can be a direct connection, it can be an indirect connection through an intermediate medium, and it can be the internal connection of two components. For those skilled in the art, the specific meanings of the above terms in this application can be specifically understood.

[0042] Figure 1 The schematic diagram of the circuit principle of the junction temperature measurement circuit of the vehicle inverter power device provided according to some embodiments of the present application is as follows: Figure 1 As shown, the junction temperature measurement circuit is arranged in the vehicle inverter to accurately measure the working junction temperature of the power device under test in the vehicle inverter.

[0043] In the embodiments of the present application, the vehicle inverter has a relatively broad meaning. For example, in some embodiments, the vehicle inverter may be an inverter in a vehicle motor controller for outputting power, or may be an inverter in a vehicle motor simulator or other active load for absorbing power. For the above-mentioned vehicle inverter, the junction temperature measurement circuit provided in the present application may be applied to measure the working junction temperature of its power device.

[0044] Furthermore, the vehicle inverter may be an inverter having a three-phase two-level structure, such as Figure 1 As shown, any phase topology includes a DC bus power supply (voltage V DC ) between the positive and negative electrodes of the first power device D UH and the second power device D ULThe topological structure and working mode of the above-mentioned vehicle inverter are known to those skilled in the art. Generally, the first power device D UH and the second power device D UL As the core devices of the upper half bridge and the lower half bridge respectively, among which D UH The drain is connected to the positive pole of the DC bus power supply, and the source is connected to D UL The drain of the device is connected to point U, and the connection point U is used as the power output point. UL The source of the DC bus is connected to the negative pole of the DC bus power supply; during the operation of the inverter, the control system sends a DC UH and D UL The gate sends a control signal T UH 、T UL , and then control the two power devices to alternately switch between on and off states while maintaining different states, thereby converting the DC power of the DC bus power supply into AC power.

[0045] In the embodiment of the present application, the power device D UH and D UL It can be either a conventional silicon carbide power tube or a SiC MOSFET with a higher switching frequency. In order to more clearly explain the creativity of the technical solution of the present application, first of all, Figure 1 The working junction temperature measurement principle of CRRC inverter power devices and the problems of existing solutions are explained.

[0046] It is known to those skilled in the art that the main reason for fatigue failure of power devices during the operation of the inverter is the thermal stress failure caused by the inconsistent thermal expansion coefficients of the interfaces of different packaging materials of the device under the stimulation of junction temperature fluctuations. Therefore, it is necessary to measure the working junction temperature of the power device in real time. The conventional solution for measuring the working junction temperature of the power device is to measure the saturation conduction voltage drop V DS_on The electrical parameters are measured, and then the operating junction temperature is determined based on the pre-established correspondence between the saturation conduction voltage drop and junction temperature of the power device.

[0047] Since the saturation conduction voltage drop is the drain-source voltage when the power device is in the on state, its value is generally less than 1V, and when the power device is in the off state, the voltage difference between its drain and source may exceed several hundred volts. In order to ensure the accurate measurement of the saturation conduction voltage drop, the existing online junction temperature measurement circuit is generally provided with a module for switching on and off the power device and the measurement voltage output terminal and voltage clamping (such as patent CN115436771A, patent CN115060953A, etc.). The above module generally uses a switch tube to switch the on and off state of the line between the power device and the measurement signal output terminal, and clamps the potential of the measurement terminal to a lower value when the power device is disconnected, so as to avoid the potential of the measurement signal output terminal following the rise of the DC bus voltage when the power device is turned off, resulting in a large value range of the measurement terminal and the inability to accurately measure the lower conduction voltage drop.

[0048] However, when the power device in the inverter is SiC MOSFET, the above existing junction temperature measurement methods cannot accurately measure the V DS_on The reason for the measurement is that the switching speed of SiC MOSFET is much faster than that of conventional silicon-based power tubes, reaching 10 switches per second. 4 Therefore, the time from transient to steady state and the time to maintain steady state are extremely short. The existing method of cutting off or conducting the measurement path to the switch tube in the clamping module cannot track the high-speed change of the drain-source voltage of the SiC MOSFET in time due to the limitation of the charging and recovery time of the switch tube, and thus cannot accurately measure the saturation conduction voltage drop of the high-speed switching SiC MOSFET in its shorter steady-state period.

[0049] It can be seen that the existing junction temperature measurement circuit needs to be optimized so that it can not only achieve the isolation and voltage clamping of the measurement output terminal and the DC bus power supply when the SiC MOSFET is turned off, but also track and respond to the changes in the drain-source voltage in a timely manner during the high-speed switching process of the SiC MOSFET.

[0050] To this end, the present application proposes a new junction temperature measurement circuit for automotive inverter power devices. The circuit topology provided by the circuit can not only carry a higher bus voltage, but also respond promptly to the drain-source voltage of various automotive-grade power devices, especially the high-speed switching SiCMOSFET, thereby accurately measuring its operating junction temperature.

[0051] In some embodiments, the junction temperature measurement circuit includes two measurement circuits (a first measurement circuit and a second measurement circuit) and a clamping power supply, wherein the first measurement circuit is used to measure the junction temperature of the first power device D under test. UH The conduction voltage drop during operation (V DS_on) is measured, and its junction temperature is determined by a predetermined conduction voltage drop-junction temperature relationship; similarly, the second measurement circuit is used to measure the second power device D under test UL The conduction voltage drop during operation determines its junction temperature.

[0052] The first measurement circuit further includes a first adaptive switch and a first clamping module. In some specific embodiments, Figure 1 As shown, the first adaptive switch includes a first switch tube Q1 and a first resistor R1, and the first clamp module includes a first Schottky diode D1 and a second Schottky diode D2, wherein the drain of the first switch tube Q1 is connected to the first power device D UH The drain of the first switch tube Q1 is connected, the source of the first switch tube Q1 is connected to the first end of the first resistor R1, and the second end of the first resistor R1 is connected to the gate of the first switch tube Q1, that is, the two ends of the first resistor R1 are respectively connected between the source and the gate of the first switch tube Q1.

[0053] In the embodiment of the present application, the first switch tube Q1 is a zero-voltage conduction negative voltage cut-off type switch tube (for example, an N-channel depletion-type MOSFET, or other switch tubes that achieve the same zero-voltage conduction negative voltage cut-off characteristics). When the gate-source voltage of this type of switch tube is 0 or a value greater than 0, the drain and the source are kept turned on, and when the gate-source voltage is negative and reaches the cut-off threshold voltage, the connection between the drain and the source is disconnected. Obviously, when the current flowing through the first resistor R1 increases to a certain extent, the voltage drop V across R1 SG1 (V SG1 =V GS1 ) can make the gate-source voltage of the first switch tube Q1 reach the cut-off threshold, and then use its zero-voltage conduction and negative-voltage cut-off characteristics to make it enter a "micro-conduction state" described later, and the first switch tube Q1 can be kept in the conduction state at other times. Therefore, by using the cooperation of the first switch tube Q1 and the first resistor R1, the first power device D under test can be UH The state of the measurement circuit can be adaptively turned on and off without the need for additional driving circuit.

[0054] Furthermore, in the first clamping module, the first Schottky diode D1 and the second Schottky diode D2 are connected in series, and the cathode of the first Schottky diode D1 is connected to the positive clamping voltage V CC , the anode of the second Schottky diode D2 is connected to the negative clamping voltage -V CC The midpoint between the two is used as the first measuring end and is connected to the second end of the first resistor R1. The first measuring end is relative to the reference ground (in the embodiment of the present application, such as Figure 1 As shown, the first power device D under test UH The second power device D ULThe voltage at the connection point U as the reference ground) is taken as the output voltage (V out_HS ).

[0055] The working condition of the first voltage clamping module is determined by the first measured power device D UH The switch state determines when D UH When the first measurement circuit is turned on, the input voltage V D Small, the first Schottky diode D1 and the second Schottky diode D2 are both in a negative bias state; when D UH When turned off, the first Schottky diode D1 is forward biased, and the voltage output by the first measurement circuit is clamped to the positive clamping voltage V CC .

[0056] The implementation of the second measurement circuit is similar to that of the first measurement circuit. Figure 1 As shown, the second measurement circuit further includes a second adaptive switch and a second clamping module, wherein the second adaptive switch includes a second switch tube Q2 and a second resistor R2, and the second clamping module includes a third Schottky diode D3 and a fourth Schottky diode D4, wherein the first end of the second resistor R2 is respectively connected to the second measured power device T UL The source of the second switch tube Q2 is connected to the gate of the second switch tube Q2, and the second end of the second resistor R2 is connected to the source of the second switch tube Q2, that is, the two ends of the second resistor R2 are respectively connected between the source and the gate of the second switch tube Q2. In the embodiment of the present application, the second switch tube Q2 is also a zero-voltage conduction negative-voltage cut-off switch tube, and its cooperation with R2 and according to the second power device D under test UL The method for realizing adaptive on-off of the second measurement circuit in the state can refer to the first measurement circuit.

[0057] Furthermore, in the second clamping module, the third Schottky diode D3 and the fourth Schottky diode D4 are connected in series, and the cathode of the third Schottky diode D3 is connected to the positive clamping voltage V CC , the anode of the fourth Schottky diode D4 is connected to the negative clamping voltage -V CC The midpoint between the two is used as the second measuring terminal and connected to the drain of the second switch tube Q2. The voltage of the reference ground relative to the second measuring terminal is used as the output voltage of the second measuring circuit (V out_LS ).

[0058] The working condition of the second voltage clamping module is determined by the second measured power device D UL The switch state determines when D UL When the second measurement circuit is turned on, the input voltage V S is smaller, the third Schottky diode D3 and the fourth Schottky diode D4 are both in a negative bias state; when T ULWhen turned off, the fourth Schottky diode D4 is forward biased, and the voltage output by the second measurement circuit is clamped to the negative clamping voltage -V CC .

[0059] Further, in the embodiment of the present application, the clamping power supply can be implemented by a method known to those skilled in the art (for example, composed of a DC-DC converter, a voltage regulator diode and a filter capacitor) to output a positive clamping voltage V to the first clamping module and the second clamping module. CC and negative clamp voltage -V CC .

[0060] In some preferred embodiments, the junction temperature measurement circuit further includes a voltage stabilization module, such as Figure 1 As shown, the voltage stabilizing module includes two Zener diodes D5 and D6 and two filter capacitors C1 and C2, wherein D5 and D6 are connected in series, and C1 and C2 are connected in series and then connected in parallel between the clamping power supplies to stabilize the positive clamping voltage V CC and negative clamp voltage -V CC .

[0061] The overall working principle of the junction temperature measurement circuit is introduced as follows.

[0062] For the first power device D under test in the upper half bridge UH , when D UH When it is turned on, due to its on resistance R DS(on) Generally small, at this time, its drain potential V D The bus voltage is reduced from a higher value to a value lower than the positive clamping voltage V in the first measurement circuit. CC and above the negative clamping voltage -V CC Therefore, the two Schottky diodes D1 and D2 are in reverse bias state, and the voltage V output by the first measurement circuit is out_HS D UH The conduction voltage drop. D UH When turned off, it blocks the bus voltage and the drain potential V D When the voltage rises to the bus voltage, the Schottky diode D1 is forward biased, and the midpoint potential V out_HS Clamped at V CC Nearby, while increasing the current I D Under the action of the first resistor R1, the voltage V SG1 (V SG1 =-V GS1 ) further increases, when the gate-source voltage V GS1 Reduced to close to the cut-off threshold voltage V of Q1 GS1(th) When Q1 is in the micro-conduction state described later, due to the zero-voltage conduction and negative-voltage cutoff characteristics of Q1, the larger drain-source voltage V DS1Only intermittent and small leakage current can be generated, which in turn generates a small V GS1 To maintain this micro-conduction state, thereby reaching a steady state, the output voltage V out_HS Positive clamping voltage V CC .

[0063] For the second power device D under test in the lower half bridge UL , U point is the reference point, D UL The source potential V S is a negative value, when D UL When conducting, the current I S will not flow through Q2 because the source voltage V S =-V DS_on >-V CC , the third Schottky diode D3 and the fourth Schottky diode D4 are both in reverse bias state, and the input impedance Z in Very high, at this time, the voltage V output by the second measuring terminal of the second measuring circuit relative to the reference ground out_LS D UL The conduction voltage drop; when D UL When turned off, V S Drop to -V CC Below, the current I S begins to flow and generates a voltage drop across the second resistor R2. S The increase of V applied to Q2 GS2 Gradually decreases until it reaches a micro-conduction state and enters a steady state. At this time, the second measurement circuit outputs V out_LS Negative clamp voltage -V CC .

[0064] In order to further verify the advantage of the micro-conduction state realized by the adaptive switch in the present application in timely responding to the fast switching of SiC MOSFET compared with the direct shut-off switch tube method in the existing voltage clamping scheme, in a specific embodiment, a SiC MOSFET is constructed as follows Figure 2 The motor power pair test platform simulation model is shown, and the junction temperature of each SiC MOSFET during operation is measured using the junction temperature measurement circuit provided in the present application.

[0065] Specifically, the motor power towing test platform is mainly composed of three parts: a test inverter, an active load and a control unit. The three-phase output end of the test inverter composed of six tested SiC MOSFETs (S1 to S6) on the left is connected to the output end of the active load part through a small load inductor. The DC power supply voltage applied to the test inverter side and the active load is the same. The inverter side is based on the set d-axis target current I d,q-axis target current I q And electrical speed ω e , the switching of the tested SiC MOSFET is controlled by the modulation algorithm (SVPWM and dead zone compensation); the active load side first converts the collected three-phase current into dq axis current through Clark transformation and Park transformation, and then adds the electrical angle and obtains the three-phase voltage V based on the voltage equation. A ,V B ,V C , and then control the MOSFET on the load side through SVPWM modulation.

[0066] Further, Figure 1 The simulation models of each measurement circuit in the junction temperature measurement circuit shown are set in the upper and lower bridges of each phase of the inverter to be tested, and the changes in the on-state voltage drops of S1 to S6 under SPWM modulation are monitored to verify the response speed and measurement accuracy of the junction temperature measurement circuit, and at the same time, the changes and mechanisms of the electrical parameters during the operation of the SiC MOSFET are obtained and analyzed.

[0067] Figure 3a The figure shows the voltage and current simulation results of the SiC MOSFET (S1) under test in one upper half bridge during a sinusoidal cycle and the comparison with the output voltage of the measurement circuit. Figure 3b The output voltage of the measurement circuit is magnified and displayed. Figure 3b It can be seen that the SiC MOSFET under test generates a relatively standard sinusoidal current waveform under the action of the PWM modulation signal, and its gate-source voltage V GS The trend is consistent with the PWM signal, which can be used to determine the switching state of the SiC MOSFET under test and the drain-source voltage V DS and the output voltage V of the measuring circuit out By comparing them with a graph, we can see that except for the voltage spike that occurs at the switch instant, when the SiC MOSFET under test is on, the output voltage is almost equal to its on-state voltage drop; when the SiC MOSFET under test is off, V DS The voltage rises to a value close to the bus voltage, and the output voltage of the measuring circuit (for general representation, the output voltage of the measuring circuit of the upper and lower half bridges is expressed as V out ) is clamped at V CC nearby.

[0068] Furthermore, the working mechanism of the tested SiC MOSFET from transient to steady state is further analyzed. Figure 4a , Figure 4b and Figure 4c The changes of various electrical parameters in the measurement circuit during the turn-on and turn-off processes of the SiC MOSFET under test are respectively shown.

[0069] For the conduction process, according to Figure 4a During the t1 period, the drive circuit controlling the SiC MOSFET under test starts to conduct, generating gate current and charging the internal equivalent input capacitance of the SiC MOSFET under test. Before the input capacitance voltage reaches the threshold voltage, the SiC MOSFET under test will remain in the off state. At this time, its drain-source voltage V DS Close to bus voltage.

[0070] In this measurement circuit, the zero-voltage conduction negative voltage cut-off switch uses a depletion-type MOSFET. During the t1 period, it works in the linear region, and the gate-source voltage V GS1 is a negative value (i.e. the voltage difference across the first resistor R1 is reversed), the output voltage V out Clamped at V CC nearby.

[0071] V DS 、V GS1 、V out and the drain-source voltage V of the depletion-mode MOSFET DS1 Satisfies the following formula (1):

[0072] V DS =V DS1 -V GS1 +V out (1).

[0073] During the t2 period, the gate-source voltage V GS When the voltage exceeds the threshold and reaches the Miller platform, the drain potential decreases. At this time, most of the gate current provided by the driver is used to charge the Miller capacitance to achieve a rapid voltage change on the drain and source. In the measurement circuit, according to formula (1), since V GS1 Keep constant, if V on the left side of the equation DS The right side of the equation only has V out reduce.

[0074] During the t3 period, V out Reduce to -V CC After that, the negative bias Schottky diode acts to make V out It is clamped here and cannot drop further. During this stage, the gate-source capacitance of the depletion-type MOSFET in the measurement circuit begins to charge, and V GS1 According to formula (1), the further turning on of the SiC MOSFET under test causes the drain-source voltage V DS1 Start with V DS At the same time, it decreases rapidly due to the equivalent drain-source capacitance C inside the depletion-mode MOSFET. DS1The existence of D =C DS1 ·(du DS / dt), the drain-source capacitance discharges externally, and at this time a large reverse current I flows through the measurement circuit instantaneously D .

[0075] During the t4 period, the SiC MOSFET under test is fully turned on, and its on-state voltage drop V DS It stabilizes at a lower value. At the same time, in the measurement circuit, since the leakage current and the on-resistance of the depletion-type MOSFET are both small at this time, its on-voltage drop V DS1 The voltage has also stabilized and is approaching zero, and the internal drain-source capacitance of the depletion-type MOSFET stops discharging. GS1 After crossing the Miller platform, it continues to increase. In order to make equation (1) valid, the output voltage V out Start with -V CC rises, and since the first two items remain basically constant, V GS1 The change in V out On, so that V out The value can quickly catch up with V DS changes.

[0076] according to Figure 4b , t5 and t6 periods last longer than the first four turn-on periods, during which the input capacitor of the depletion-type MOSFET continues to charge, V GS1 The higher gate voltage increases exponentially, and the on-state of the depletion-mode MOSFET is fully enhanced. By the end of t5, the input capacitor is fully charged, and V GS1 increases to nearly 0V, while V out According to formula (1), it can be approximately considered that V DS1 and V GS1 is 0V, so V DS =V out , that is, the output voltage of the measurement circuit is equal to the on-state voltage drop of the SiC MOSFET under test.

[0077] Through Figure 4a , Figure 4b From the analysis of the changes of various electrical parameters during the turn-on process of the SiC MOSFET under test, it can be seen that the measurement circuit architecture provided by the present application uses a gate-source resistor to control the gate of the depletion-type MOSFET, which is extremely sensitive to the current changes in the circuit, and can therefore almost synchronously control the V of the SiC MOSFET under test. DS changes; at the same time, during the t3 period, due to the negative clamping voltage -V CC The existence of V out In the V DSThe response process will not drop too much, ensuring that V out During the t4 period, it can quickly reach the same level as V DS That is, during the conduction process of the SiC MOSFET under test, when the drain potential of the SiC MOSFET under test drops to the on state and stabilizes (reference Figure 4a , the drain-source voltage V of the Sic MOSFET under test DS At the end of the t3 period, the voltage drops rapidly from 200V and stabilizes to near 0V, which becomes the on-state voltage drop). The potential at the measuring end can track the drain potential of the SiC MOSFET under test in a very short time (reference Figure 4a , the output V of the measurement end out At the end of the t3 period, V DS The tracking response time is defined as the time from when the SiC MOSFET under test enters a stable on-state to when the potential at the measuring end becomes consistent with the on-state. In an embodiment of the present application, the ratio of the tracking response time to the switching period of the SiC MOSFET under test is less than or equal to 5%. In other preferred embodiments, the ratio of the tracking response time to the switching period of the SiC MOSFET under test is less than or equal to 2%.

[0078] For the shutdown process, according to Figure 4c Before the t7 period, the SiC MOSFET under test is still in the off state. At the beginning of the t8 period, the input capacitance of the MOSFET under test begins to discharge, accompanied by the gate-source voltage V GS The drain potential of the SiC MOSFET under test increases slightly due to the decrease in the drain potential. At the measurement circuit end, the depletion-type MOSFET is still in the on state, and the output voltage V out Continue to follow the drain-source voltage V of the SiC MOSFET under test DS Increases slightly, and then when V out Increase to V CC , is clamped by the forward biased Schottky diode and cannot continue to increase. According to equation (1), the V DS1 starts to increase, and its drain-source capacitance C DS1 The changing voltage generates a positive leakage current I in the measurement circuit. D The leakage current peak is slightly larger than that of the turn-on process because of the conduction voltage drop V DS_on The input impedance is large, and the current in the power circuit will hardly flow through the measurement circuit. D It is mainly generated by the voltage changing across the parasitic capacitor; during the shutdown process, the drain potential of the SiCMOSFET under test gradually increases to the clamping voltage V CCAbove, the measurement circuit is turned on for a short time, plus the contribution of parasitic capacitance, I D Slightly increased. D A voltage drop is generated across the gate-source resistor, causing the V GS1 The output voltage is clamped to V CC .

[0079] By stage t9, the MOSFET under test is almost turned off, and the drain potential is close to the bus voltage value. The drain-source capacitance of the depletion-type MOSFET in the measurement circuit is fully charged, V CC The decrease in V of the depletion-mode MOSFET further reduces the turn-on degree until the system reaches a critical state, that is, the V of the SiC MOSFET under test DS In the measurement circuit, it is manifested as three parts: V blocked by the depletion MOSFET in the amplification region DS1 , the voltage drop across the gate-source resistor, and the clamped output voltage V CC .

[0080] Further analysis shows that when the measurement circuit is in the t8 and t9 stages, the depletion-type MOSFET achieves the bus voltage to V out The depletion-mode MOSFET is isolated from the source, but it is not completely turned off. Instead, it is in a "micro-conduction" state. Specifically, when the gate-source voltage V GS1 Reduced to close to the cut-off threshold voltage V GS1(th) When , the depletion-type MOSFET is in a critical off state, the leakage current flowing through it is reduced to nearly 0, and no leakage current flows through the resistor, so no voltage drop is generated, and thus the depletion-type MOSFET is turned on again, causing the leakage current to reappear and increase, further causing a voltage drop across the resistor again and turning off the depletion-type MOSFET again. The above process is repeated continuously, so that the depletion-type MOSFET is maintained in this micro-on state, thereby reaching a steady state. In this micro-on state, there is an intermittent leakage current in the depletion-type MOSFET and the resistor in the adaptive switch. Obviously, the intermittent frequency of the above leakage current is much greater than the switching frequency of the SiC MOSFET being tested (for example, in some embodiments, the intermittent frequency of the above leakage current reaches or exceeds 10 times the switching frequency of the SiC MOSFET being tested). At the same time, since the leakage current appears intermittently, the amplitude of the above leakage current is small, which can ensure the output voltage V out Clamped at positive clamping voltage V CC .

[0081] At the same time, it should be noted that, because in this micro-conduction state, the depletion-type MOSFET is actually in a state of rapid on-off at a very high frequency, therefore, when the SiC MOSFET under test switches from the off state to the on state again, the measurement circuit can respond to the change of the drain-source voltage of the SiC MOSFET under test in a timely manner, thereby increasing V out The self-clamping voltage switches to the on-state voltage drop.

[0082] The analysis of the electrical parameter changes and junction temperature measurement process of the SiC MOSFET under test in the lower half bridge is similar to that of the upper half bridge and will not be repeated here.

[0083] Obviously, in-depth analysis of the time-varying characteristics of the electrical parameters of the power device under test, and reasonable design of the junction temperature measurement circuit and component selection according to the topological structure of the inverter are the basis for the measurement circuit to achieve timely and accurate working junction temperature measurement. To this end, some embodiments of the present application also provide a design method for designing the junction temperature measurement circuit of the automotive inverter power device, such as Figure 5 As shown, the design method includes the following steps:

[0084] The first step is to establish a junction temperature measurement model for automotive inverter power devices based on negative voltage cutoff adaptive switch and voltage clamp;

[0085] The second step is to analyze the time-varying characteristics of the electrical parameters of the junction temperature measurement model when the automotive inverter power device is working;

[0086] The third step is to design the circuit structure of the junction temperature measurement circuit based on the topological structure of the vehicle inverter, and select circuit components based on the time-varying characteristics of the electrical parameters.

[0087] Specifically, please refer to Figures 3a to 4c , establish a circuit model for measuring the junction temperature of the power device to be tested, and analyze the time-varying characteristics of various electrical parameters during its operation. On this basis, reasonably select circuit components and use Figure 1 or Figure 2 The measurement circuit is designed based on the architecture.

[0088] Figure 6 FIG. 1 shows a physical diagram of a circuit board of a junction temperature measurement circuit designed and manufactured according to the above method in a specific embodiment. The switch tube adopts an N-channel depletion-type MOSFET. Considering the need for a higher drain-source blocking voltage and as low an equivalent parasitic capacitance as possible, the specific model of the selected N-channel depletion-type MOSFET is DMS6014E, and its drain-source voltage V dss =600V, continuous drain current I d =100mA.

[0089] According to the relationship between the drain current and the drain-source voltage of the depletion-type MOSFET at different gate-source voltages, a resistor with a resistance of 2 kΩ is selected as the adapted gate-source resistor.

[0090] For the Schottky diode used for voltage clamping, in order to ensure the measurement accuracy, it is necessary to have the characteristics of low forward conduction voltage drop, short recovery time, and low junction capacitance. The Schottky diode model selected in this embodiment is SS56, and its forward voltage drop v r =700mV.

[0091] In addition, in order to optimize the switching characteristics of N-channel depletion-mode MOSFET (du DS / dt,di D / dt), and added a 680pF gate-source external capacitor.

[0092] The clamp power supply uses an isolated dual-output DC-DC module power supply model A0505S-2W, and two voltage regulator diodes and two 10nF filter capacitors are connected in parallel at both ends of the power module.

[0093] Figure 7 The above junction temperature measurement circuit is used to measure the power-drag system at V dc The bus voltage is 300V, the drive signal frequency is 10kHz, and I d Set to 0A, I q Set to 3A and electric speed ω e The output voltage curve of the measurement circuit obtained experimentally under the condition of 50rad / s.

[0094] It can be seen that when the SiC MOSFET under test is turned on, the output voltage V out It can better reflect the on-state voltage of the MOSFET under test and limit it to a smaller oscillation range after a certain degree of noise processing; when the SiC MOSFET under test is turned off, the upper bridge V out_HS and Lower Bridge V out_LS It is clamped near 7V and -7V and remains basically constant without being affected by the high voltage of the bus.

[0095] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications may be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A junction temperature measurement circuit for a vehicle inverter power device, used to measure the operating junction temperature of a first power device under test and a second power device under test of the vehicle inverter, wherein the first power device under test and the second power device under test are connected in series between the positive and negative electrodes of a DC bus power supply of the vehicle inverter, the source of the first power device under test is connected to the drain of the second power device under test and a reference ground, and the two power devices under test are turned on and off in different states when working, characterized in that: The junction temperature measurement circuit includes a first measurement circuit, a second measurement circuit and a clamp power supply; The first measurement circuit is used to measure the conduction voltage drop of the first power device under test during operation and determine its junction temperature, and includes a first adaptive switch and a first clamping module, wherein the first adaptive switch is configured to make the potential of the first measurement terminal track the drain potential of the first power device under test when the first power device under test enters the conduction state, and to maintain a micro-conduction state between the drain of the first power device under test and the first measurement terminal when the first power device under test is in the off state; The second measurement circuit is used to measure the conduction voltage drop of the second power device under test when it is in operation and determine its junction temperature, and includes a second adaptive switch and a second clamping module, wherein the second adaptive switch is configured to make the potential of the second measurement terminal track the drain potential of the second power device under test when the second power device under test enters the conduction state, and to maintain a micro-conduction state between the source of the second power device under test and the second measurement terminal when the second power device under test is in the off state; The first clamping module and the second clamping module both realize a positive clamping voltage and a negative clamping voltage through a clamping power supply, and are respectively used to clamp the first measuring end at the positive clamping voltage when the first power device under test is in an off state, and to clamp the second measuring end at the negative clamping voltage when the second power device under test is in an off state; The first adaptive switch includes a first switch tube and a first resistor connected in series, and the second adaptive switch includes a second switch tube and a second resistor connected in series; The first switch tube and the second switch tube are both zero-voltage conduction and negative-voltage cutoff switch tubes, and their on and off states are switched based on the voltage drops across the first resistor and the second resistor, respectively; When there is intermittent leakage current in the first switch tube and the first resistor, the drain of the first power device under test and the first measuring end are in a slightly conductive state; When there is intermittent leakage current in the second switch tube and the second resistor, the source electrode of the second power device under test and the second measuring terminal are in a slightly conductive state; The intermittent occurrence frequency of the leakage current is greater than 10 times the switching frequency of the first measured power device and the second measured power device during operation.

2. The junction temperature measurement circuit of a vehicle inverter power device according to claim 1, characterized in that: In the process of the first adaptive switch connecting the drain of the first power device under test and the first measuring terminal, the lowest potential of the first measuring terminal is not lower than the negative clamping voltage; In the process of the second adaptive switch connecting the source of the second power device under test and the second measuring terminal, the highest potential of the second measuring terminal is not higher than the positive clamping voltage.

3. The junction temperature measurement circuit of the vehicle inverter power device according to claim 2, characterized in that: The first power device under test and the second power device under test are both SiC MOSFETs; The ratio of the tracking response time of the first adaptive switch to the drain potential of the first power device under test during the conduction process of the first power device under test to the switching period of the first power device under test is less than or equal to 5%; The ratio of the tracking response time of the second adaptive switch to the drain potential of the second power device under test during the conduction process of the second power device under test to the switching period of the second power device under test is less than or equal to 5%.

4. The junction temperature measurement circuit of a vehicle inverter power device according to claim 1, characterized in that: The first switch tube and the second switch tube are both N-channel depletion-type MOSFETs; The drain of the first switch tube is connected to the drain of the first power device under test, the source is connected to the first end of the first resistor, and the second end of the first resistor is connected to the first measuring end and the gate of the first switch tube respectively; The first end of the second resistor is respectively connected to the source of the second measured power device and the gate of the second switch tube, the second end is connected to the source of the second switch tube, and the drain of the second switch tube is connected to the second measuring end.

5. The junction temperature measurement circuit of the vehicle inverter power device according to claim 4, characterized in that: The measurement voltage output by the first measurement circuit and the second measurement circuit Satisfy the following formula: ， in, is the drain-source voltage of the first power device under test or the second power device under test, is the drain-source voltage of the first switch tube or the second switch tube, is the gate-source voltage of the first switch tube or the second switch tube.

6. The junction temperature measurement circuit of a vehicle inverter power device according to claim 4, characterized in that: The first clamping module includes a first Schottky diode and a second Schottky diode, wherein the cathode of the first Schottky diode has a positive clamping voltage, the anode of the second Schottky diode has a negative clamping voltage, and the anode of the first Schottky diode is connected to the cathode of the second Schottky diode and serves as a first measuring terminal; The second clamping module includes a third Schottky diode and a fourth Schottky diode, wherein the cathode of the third Schottky diode has a positive clamping voltage, the anode of the fourth Schottky diode has a negative clamping voltage, and the anode of the third Schottky diode is connected to the cathode of the fourth Schottky diode and serves as a second measuring end.

7. The junction temperature measurement circuit of a vehicle inverter power device according to claim 6, characterized in that: Also includes: A voltage stabilizing module is connected in parallel with the clamping power supply and is used to stabilize the positive clamping voltage and the negative clamping voltage.

8. A design method for designing a junction temperature measurement circuit for a vehicle inverter power device as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Establish a junction temperature measurement model for automotive inverter power devices based on negative pressure cut-off adaptive switch and voltage clamp; Step 2, analyzing the time-varying characteristics of the electrical parameters of the junction temperature measurement model when the vehicle inverter power device is working; Step three, designing the circuit structure of the junction temperature measurement circuit based on the topological structure of the vehicle inverter, and selecting circuit components based on the time-varying characteristics of the electrical parameters.

9. Application of the junction temperature measurement circuit according to claim 1 in a vehicle inverter.

10. Application of the junction temperature measurement circuit according to claim 1 in a vehicle motor towing test platform.

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