On-line power device aging test circuit facing vehicle working conditions, comprehensive test analysis method and system

Abstract

The invention provides an on-line power device aging test circuit facing vehicle working conditions, a comprehensive test analysis method and a comprehensive test analysis system. The aging test circuit comprises a tested three-phase six-bridge arm circuit composed of a tested power device, a temperature-sensitive electrical parameter measurement circuit, a bridge arm switching circuit and a standby bridge arm circuit. The temperature-sensitive electrical parameter measuring circuit is used for measuring the temperature-sensitive electrical parameter time-varying characteristic of the accessed tested power device; the bridge arm switching circuit is used for connecting the tested power device to the tested three-phase six-bridge arm circuit or the temperature-sensitive electrical parameter measuring circuit; the standby bridge arm circuit is used for replacing any bridge arm circuit where the tested power device connected to the temperature-sensitive electrical parameter measuring circuit is located so as to form a standby three-phase six-bridge arm circuit. The on-line power device aging test circuit provided by the invention can perform on-line detection on the aging condition of the vehicle inverter power device in a power cycle state.

Description

Technical Field

[0001] The present application belongs to the field of new energy vehicle technology, and relates to a performance testing technology for electric drive power devices for vehicles. Specifically, it provides an online power device aging test circuit, a comprehensive test analysis method and a system for vehicle working conditions. Background Art

[0002] As new energy vehicles develop toward higher power density and longer driving range, power devices (such as IGBTs and SiC MOSFETs) have become core components of electric drive systems. Under complex operating conditions (such as frequent starts and stops, and high-current charge and discharge), power devices are subjected to long-term, severe junction temperature fluctuations, which can lead to failures such as bond wire separation and solder fatigue. Accurately assessing device aging has become a key technical challenge in improving vehicle reliability.

[0003] Power cycling tests are widely used to evaluate the aging, reliability, and service life of power devices by simulating the temperature stress of power devices in the on / off states. Although traditional DC power cycling can accelerate the thermal fatigue process, its constant current loading mode makes it difficult to reproduce the actual complex stresses that power devices are subjected to in real automotive operating conditions. In contrast, AC power cycling can more realistically reflect the aging mechanism of devices in scenarios such as motor drives and inverters by applying alternating current loads.

[0004] However, existing AC power cycling tests generally use offline thermal resistance measurement methods, which require interrupting the power cycle and switching the device under test to the thermal resistance test circuit to collect temperature-sensitive parameters. This method is limited in two aspects: First, the long downtime causes interruptions in the cycle and changes in the temperature field. If the device needs to be disassembled for thermal resistance measurement, frequent clamping can also cause fluctuations in the device's heat dissipation conditions, affecting the accuracy of aging tests. Second, frequent starts and stops extend the test cycle. For life assessment experiments requiring thousands of cycles, the impact of offline measurement on the test cycle cannot be ignored. Therefore, current AC power cycling can only use low-frequency thermal resistance monitoring to avoid significantly affecting the power cycle. Summary of the Invention

[0005] The purpose of this application is to solve the problems existing in the existing AC power cycle test scheme. It is aimed at actual vehicle operating conditions, and the temperature-sensitive electrical parameters of the power device under test can be measured online without interrupting the power cycle, and the aging conditions of its various parts can be accurately analyzed.

[0006] A first aspect of the present application provides an online power device aging test circuit for vehicle operating conditions. The detection circuit includes a three-phase six-bridge arm circuit under test composed of the power devices under test; and further includes:

[0007] The temperature-sensitive electrical parameter measurement circuit is used to measure the time-varying characteristics of the temperature-sensitive electrical parameters of the connected power device under test;

[0008] A bridge arm switching circuit, comprising a source switching switch and a drain switching switch corresponding to each power device under test, for connecting the corresponding power device under test to the three-phase six-bridge arm circuit under test, or to the temperature-sensitive electrical parameter measurement circuit;

[0009] The backup bridge arm circuit includes two backup power devices connected in series and a backup coil led out from the connection point of the two backup power devices, which is used to replace any bridge arm circuit where the power device under test is located that is connected to the temperature-sensitive electrical parameter measurement circuit to form a backup three-phase six-bridge arm circuit.

[0010] A second aspect of the present application provides a comprehensive test and analysis method, which uses the aforementioned online power device aging test circuit for automotive operating conditions to analyze the aging of the power device under test without interrupting the power device aging test based on AC power cycling. The method includes the following operations:

[0011] Operation 1: Maintain the three-phase six-bridge-arm circuit under test in a power circulation state corresponding to the working condition of the vehicle under test;

[0012] Operation 2: By switching the state of the bridge arm switching circuit, the power device under test whose aging condition needs to be analyzed is connected to the temperature-sensitive electrical parameter measurement circuit, and the power device in the same bridge arm is turned off at the same time, or the power device in the same bridge arm is connected to another temperature-sensitive electrical parameter measurement circuit;

[0013] Operation three: Use a spare bridge arm circuit to replace the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located, to form a spare three-phase six-bridge arm circuit, and put it into a power cycle state corresponding to the operating conditions of the vehicle under test;

[0014] Operation 4: measuring the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit and analyzing its aging condition;

[0015] Operation five: After completing the measurement of the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test, turn off the standby power device, and by switching the state of the bridge arm switching circuit, use the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located to replace the standby bridge arm circuit, so as to reconstruct the three-phase six-bridge arm circuit under test and put it in the power circulation state corresponding to the vehicle operating conditions under test.

[0016] A third aspect of the present application provides a comprehensive test and analysis system, comprising:

[0017] The aforementioned online power device aging test circuit for automotive conditions;

[0018] A control unit controls the AC power circulation state of the tested three-phase six-bridge-arm circuit or the standby three-phase six-bridge-arm circuit according to a preset vehicle operating condition;

[0019] A switching unit, used to switch the three-phase six-bridge-arm circuit under test to a spare three-phase six-bridge-arm circuit, or to switch the spare three-phase six-bridge-arm circuit to the three-phase six-bridge-arm circuit under test;

[0020] The analysis unit analyzes the aging conditions of various positions of the power device under test according to the measurement results of the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit.

[0021] The embodiment of the present application provides an online power device aging test circuit for automotive working conditions. A three-phase six-bridge arm circuit is constructed by using the power device under test, and a one-phase spare bridge arm circuit is constructed by using a spare power device. The bridge arm switching circuit further realizes the switching of the power device under test between the power circulation circuit and the temperature-sensitive electrical parameter measurement circuit, and the spare bridge arm circuit is used to replace the power device for thermal resistance measurement to maintain the power circulation. Through the above design, the temperature-sensitive electrical parameters of any power device can be measured without interrupting the operation of the power circulation, so that other power devices under test that have not undergone temperature-sensitive electrical parameter measurement are still in the power cycle of the aging test, avoiding the measurement and analysis of the aging state parameters of the power device under test affecting the normal progress of the aging test of other power devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A circuit diagram of the AC power circulation portion of an online power device aging test circuit for vehicle operating conditions provided in accordance with an embodiment of the present application;

[0023] Figure 2 A schematic diagram of a temperature-sensitive electrical parameter measurement circuit in an online power device aging test circuit for vehicle operating conditions provided in accordance with an embodiment of the present application;

[0024] Figure 3 Schematic diagram of a closed-loop control strategy for driving an AC power cycle portion to perform a power device aging test in some embodiments;

[0025] Figure 4 A schematic diagram of phase current simulation for AC power cycling using a bridge arm switching strategy;

[0026] Figure 5 A flow chart of a bridge arm switching strategy provided according to an embodiment of the present application;

[0027] Figure 6 A schematic diagram of phase current simulation for AC power cyclic switching according to the bridge arm switching strategy provided in an embodiment of the present application;

[0028] Figure 7 The actual measured results of the phase current when performing AC power cyclic switching according to the bridge arm switching strategy provided in the embodiment of the present application;

[0029] Figure 8 A flowchart of a comprehensive test and analysis method provided according to an embodiment of the present application;

[0030] Figure 9 A flowchart for measuring the time-varying characteristics of a temperature-sensitive electrical parameter of a power device under test in a specific embodiment;

[0031] Figure 10 This is a physical picture of the junction temperature calibration experimental platform;

[0032] Figure 11 This is a schematic diagram of the junction temperature calibration results;

[0033] Figure 12 FIG1 is a schematic diagram of analysis results of aging conditions of various parts of a tested power device in one embodiment;

[0034] Figure 13 A schematic diagram of the framework structure of a comprehensive test and analysis system provided according to an embodiment of the present application;

[0035] Figure 14 A physical diagram of a comprehensive test and analysis experimental platform provided according to an embodiment of the present application;

[0036] Figure 15 Schematic diagram of the structure function of the device under test before and after aging obtained through online measurement and analysis;

[0037] Figure 16 This is a schematic diagram of the on-state voltage drop of the power device under test during the online measurement of heating before and after aging. DETAILED DESCRIPTION

[0038] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0039] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer" and the like indicate an orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or are the orientation or positional relationship in which the products of the embodiments of the present application are usually placed when in use, they are only for the convenience of describing the present application and simplifying the description, and do 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, words such as first and second 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. Their names may be different in the detailed description and claims of the present application.

[0040] 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, a direct connection, an indirect connection through an intermediate medium, or a communication between the two components. For those skilled in the art, the specific meanings of the above terms in this application can be specifically understood.

[0041] The present application provides an online power device aging test circuit for automotive working conditions through an embodiment. The aging test circuit can perform online temperature-sensitive electrical parameter measurement on the power devices under test whose aging conditions need to be analyzed during the process of continuously performing aging tests based on AC power cycles on multiple power devices under test.

[0042] Specifically, the aging test circuit consists of an AC power cycle part, a thermal resistance measurement part, and a switching part. Figure 1 and Figure 2 Schematic diagrams of the AC power cycle part and the temperature-sensitive electrical parameter measurement circuit of the aging test circuit are shown in some embodiments, and the switching part is also shown in FIG. Figure 1 and Figure 2 .

[0043] <AC Power Cycle Section>

[0044] The AC power cycle part is used to simulate actual vehicle operating conditions, and continuously conducts aging test experiments on at least one power device under test under AC power loading to test its gradual aging under different vehicle operating conditions as the use time continues. Figure 1 ,The AC power cycle part is mainly composed of the three-phase six-bridge arm circuit under test.

[0045] The three-phase six-bridge arm circuit under test is a circuit that performs an aging test on the power device under test based on AC cycle loading. In the embodiments of the present application, the power device under test can be an IGBT (Insulated Gate Bipolar Transistor), a SiC MOSFET (Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistor), or other devices with similar structures that can perform switching actions under the control of a regulating signal to regulate current and voltage. In the field of new energy vehicles, the above-mentioned power devices are widely used in electric drive systems, on-board charging systems and other parts. For example, they are used as core components to constitute inverters to convert the direct current of the battery into alternating current to drive the motor.

[0046] During use, the above-mentioned power devices need to face complex vehicle operating conditions, such as frequent starting and stopping, high-current charging and discharging, etc. The power devices are subjected to severe junction temperature fluctuations for a long time, which will lead to failure problems such as bonding wire shedding and solder layer fatigue. Studies have shown that power devices are the components with the highest failure rate in the power conversion system, accounting for about 34%. For this reason, the three-phase six-bridge arm circuit under test is constructed with the same topology as the three-phase inverter. Through closed-loop modulation control, it can perform AC power circulation in various preset vehicle operating conditions, thereby performing continuous aging tests on each power device under test.

[0047] Specifically, refer to Figure 1 The three-phase six-arm bridge circuit under test adopts a three-phase inverter topology known to those skilled in the art: the A-phase bridge arm circuit is formed by the power device P1 and the power device P4 connected in series, wherein the source of P1 is connected to the drain of P4, and the A-phase line is drawn from the connection point to the A-phase coil; the B-phase bridge arm circuit is formed by the power device P2 and the power device P5 connected in series, wherein the source of P2 is connected to the drain of P5, and the B-phase line is drawn from the connection point to the B-phase coil; the C-phase bridge arm circuit is formed by the power device P3 and the power device P6 connected in series, wherein the source of P3 is connected to the drain of P6, and the C-phase line is drawn from the connection point to the C-phase coil; the drains of P1, P2, and P3 and the positive electrode of the DC power supply are connected to each other; the sources of P4, P5, and P6 and the negative electrode of the DC power supply are connected to each other; the A-phase, B-phase, and C-phase coils are connected in a star connection, and the gates (G A1 , G A2 , G B1 , G B2 , G C1 , G C2) turns on or off its drain and source according to the received gate drive signal, thereby converting the DC power output by the DC power supply into AC power.

[0048] In the embodiment of the present application, the above-mentioned part is referred to as the three-phase six-bridge arm circuit under test, which means that it is necessary to continuously load the AC power to it according to various vehicle operating conditions under test, and measure and analyze the aging condition of at least one power device therein through the temperature-sensitive electrical parameter measurement circuit described later. Accordingly, in the embodiment of the present application, the power device that needs to be measured and analyzed for aging is referred to as the power device under test. For example, in Figure 1 In the embodiment shown, when the aging conditions of power devices P1 to P6 need to be measured and analyzed, these six power devices are referred to as measured power devices; if only the aging condition of power device P1 needs to be measured, then only power device P1 can be referred to as the measured power device.

[0049] The AC power loading of the three-phase six-bridge arm circuit under test can be performed using various closed-loop modulation control strategies known to those skilled in the art. For example, Figure 3 As shown, the target iq, id and electrical angular velocity are determined according to the vehicle working conditions to be tested (such as low-speed heavy-load working conditions, high-speed light-load working conditions, etc.), and the actual three-phase current I is collected by the current sensor. A , I B , I C Clark transformation and Park transformation are performed to transform the current i in the two-phase resolver coordinate system q 、i d . Set the target i q 、i d and actual i q 、i d Make the difference and input it to the proportional integral controller (PI) to calculate the voltage U in the two-phase rotating coordinate system q 、U d , and then through Clark and Park inverse transformation to obtain the three-phase voltage U A 、U B 、U C The three-phase voltage is modulated by the SVPWM algorithm to obtain the gate control signal of the three-phase six-bridge arm under test, and the six power device switches are controlled to realize the output of the sinusoidal three-phase current.

[0050] In some specific embodiments, the device implementing the above-mentioned closed-loop modulation control includes, but is not limited to, a digital signal processor (DSP), a microcontroller unit (MCU), a field-programmable gate array (FPGA), an embedded system based on Linux or RTOS, and the like. It utilizes a high-precision analog-to-digital converter (ADC) to collect three-phase current data from a current sensor in real time. It then utilizes a built-in closed-loop modulation control algorithm or module to generate gate control signals for each power device, converting them into analog signals for output via a digital-to-analog converter (DAC), or directly outputting them as digital signals. Furthermore, an interactive operation interface can be provided for the above-mentioned closed-loop modulation control device to monitor system operating status in real time, adjust control parameters, and perform fault diagnosis.

[0051] <Thermosensitive electrical parameter measurement circuit>

[0052] After the power device under test has been subjected to continuous AC power cycle loading (i.e., continuous aging testing), various parts of the device will age, and the degree of aging of each part will show different trends as the aging test process continues. Therefore, it is necessary to analyze the aging degree of each power device under test at preset time intervals during the aging test.

[0053] Since temperature is the main cause of failure of power devices, the aging degree of the power device under test can be analyzed through temperature stress parameters. Considering that direct temperature measurement requires destroying the packaging structure of the power device, the junction temperature of the power device is generally measured indirectly. That is, the temperature-sensitive electrical parameters related to the junction temperature of the power device are measured, and then the mapping relationship between the temperature-sensitive electrical parameters and the junction temperature obtained in advance is used to obtain the junction temperature change of the power device caused by aging, so as to analyze its aging condition.

[0054] Currently, the commonly used temperature-sensitive electrical parameters include the on-resistance, threshold voltage, and body diode voltage drop of power devices. Among them, the threshold voltage and on-resistance are easily affected by the interface trap charge of the gate oxide layer of the power device, resulting in threshold voltage drift, causing the on-resistance to change, affecting the accuracy of the junction temperature measurement, and the body diode voltage drop is relatively stable during the device aging process and is considered to be the most suitable temperature-sensitive electrical parameter with good linearity and sensitivity. Therefore, in the embodiment of the present application, the temperature-sensitive electrical parameter of the power device under test (preferably, the body diode voltage drop) is selected as the measurement target. By connecting the power device under test to the temperature-sensitive electrical parameter measurement circuit at different stages of the aging test, the time-varying characteristics of its temperature-sensitive electrical parameter can be obtained. In the comprehensive test and analysis method described later, the corresponding relationship between the temperature-sensitive electrical parameter and the junction temperature can be used to further obtain the thermal resistance and thermal capacitance characteristics of each part of the power device under test, thereby accurately analyzing the different aging trends exhibited by each position of the power device under test under actual vehicle operating conditions.

[0055] refer to Figure 2 In an embodiment of the present application, the temperature-sensitive electrical parameter measurement circuit includes a heating module, a measuring current source and a voltage drop measurement module. The heating module, the measuring current source and the voltage drop measurement module are connected in parallel to the drain and source of the power device under test.

[0056] The heating module includes a device for injecting a heating current I H The heating current source and the switch S that controls the heating I When it is necessary to heat the power device under test connected to the measurement circuit, switch S I conduction, while controlling V GS Reaching the conduction voltage, so that a stable conduction current I is formed between the heating current source and the power device under test H (Preferably, I H Greater than 10A), under the action of the conduction current, the power device is continuously heated until its junction temperature is heated to a preset target, wherein the preset target can be that the junction temperature of the power device under test reaches a preset temperature and is stably maintained at the temperature, or the preset target can also be a set heating current I H The set heating time of the power device under test.

[0057] You should know that Figure 2 The heating current source shown is only an optional heating method for the power device under test. Those skilled in the art can also use other optional heating methods to construct a heating module to heat the junction temperature of the power device under test to a preset target.

[0058] After the power device under test is heated to the preset target, the heating process can be ended and V GS Set to the cut-off voltage to completely turn off the power device under test, and then inject a stable measurement current I into its body diode. M (Preferably, I M The size is between 80mA and 120mA), and the change of its body diode voltage drop over time is measured.

[0059] In the embodiment of the present application, a measurement current I is injected into the body diode. M The measurement of the body diode voltage drop is achieved by a measurement current source and a voltage drop measurement module. The two ends of the measurement current source are respectively connected to the source and drain of the power device under test connected to the measurement circuit, and are used to generate a measurement current I flowing through the body diode of the power device under test when the power device under test connected to the measurement circuit is in the off state. MThe two measuring ends of the voltage drop measurement module are respectively connected to the source and drain of the power device under test connected to the measurement circuit, and are used to measure the body diode voltage drop of the power device under test caused by the measurement current when the power device under test connected to the measurement circuit is in the off state.

[0060] In some specific embodiments, the current source and voltage drop measurement module can be composed of a current source and a voltage meter with appropriate range and accuracy according to the test requirements of the power device under test.

[0061] The specific implementation method of analyzing the aging condition of the power device under test based on the time-varying characteristics of the temperature-sensitive electrical parameters obtained from the measurement results will be described in detail in the section describing the comprehensive test and analysis method later.

[0062] <Switching part and its switching strategy>

[0063] As analyzed above, during the aging test of the three-phase six-bridge arm circuit under test with continuous AC power cycle loading, it is necessary to repeatedly evaluate the changing trend of the aging status of each power device under test at a certain time interval. Each measurement of the time-varying characteristics of the temperature-sensitive parameters includes a heating stage and a cooling stage, both of which generally last about 200 seconds. If an offline measurement method is used, that is, the AC power cycle of the aging test is interrupted and the power device under test is switched to the measurement circuit for the collection of temperature-sensitive electrical parameters, the following problems will arise: First, the shutdown process is long, resulting in interruption of the cycle condition and changes in the temperature field. If the device needs to be disassembled for thermal resistance measurement, frequent clamping will also cause fluctuations in the device's heat dissipation conditions, affecting the accuracy of the aging test; second, frequent starts and stops extend the test cycle. For life assessment experiments that require thousands of cycles, the impact of offline measurement on the test cycle cannot be ignored.

[0064] In order to solve the above problems, in this application, a bridge arm switching circuit and a spare bridge arm circuit are used to form a switching part, and the measurement of the temperature-sensitive electrical parameters of a specific power device under test is realized without interrupting the aging test process of AC power loading, wherein the bridge arm switching circuit includes a source switching switch and a drain switching switch corresponding to each power device under test, which is used to connect the corresponding power device under test to the three-phase six-bridge arm circuit under test, or to connect to the temperature-sensitive electrical parameter measurement circuit; the spare bridge arm circuit includes two spare power devices connected in series, and a spare coil led out from the connection point of the two spare power devices, which is used to replace any bridge arm circuit where the power device under test is located that is connected to the temperature-sensitive electrical parameter measurement circuit, so as to form a spare three-phase six-bridge arm circuit.

[0065] Specifically, in Figure 1 and Figure 2In the embodiment shown, the bridge arm switching circuit includes a total of six source switching switches S S1 、S S2 、S S3 、S S4 、S S5 、S S6 and six drain switches S D1 、S D2 、S D3 、S D4 、S D5 、S D6 .

[0066] S S1 and S D1 Corresponding to the measured power devices P1 and S on the A-phase bridge arm circuit S1 It includes a common input terminal connected to the source of P1, and two switchable output terminals, one of which is connected to the bridge arm circuit where P1 is located (i.e. Figure 1 to the connection point between P1 and P4), and the other is connected to a measurement end of the temperature-sensitive electrical parameter measurement circuit ( Figure 2 Similarly, S D1 It includes a common input terminal connected to the drain of P1, and two switchable output terminals, one of which is connected to the bridge arm circuit where P1 is located (i.e. Figure 1 The other is connected to the other measurement end of the temperature-sensitive electrical parameter measurement circuit ( Figure 2 the lower measuring terminal of the medium voltmeter).

[0067] The power device under test in the A-phase bridge arm circuit with P1 is P4, and its corresponding source switching switch is S S4 , the drain switch is S D4 , S S2 It includes a common input terminal connected to the source of P4, and two switchable output terminals, one of which is connected to the bridge arm circuit where P4 is located (i.e. Figure 1 The other is connected to a measuring terminal of the temperature-sensitive electrical parameter measurement circuit ( Figure 2 Similarly, S D4 It includes a common input terminal connected to the drain of P4, and two switchable output terminals, one of which is connected to the bridge arm circuit where P4 is located (i.e. Figure 1 The other is connected to the other measuring end of the temperature-sensitive electrical parameter measurement circuit ( Figure 2 the lower measuring terminal of the medium voltmeter).

[0068] The above describes the connection method of the source switching switch and the drain switching switch for the A-phase bridge arm circuit where P1 and P4 are located. For the power devices P2 and P5 under test on the B-phase bridge arm circuit, and the power devices P3 and P6 under test on the C-phase bridge arm circuit, their corresponding source switching switches and drain switching switches can adopt the same connection method, which will not be repeated here.

[0069] Each source switching switch and drain switching switch can be switched by a switching signal (such as a high or low level signal) sent by a switching device. Referring to the aforementioned closed-loop modulation control device, the control of the bridge arm switching circuit can also be achieved through a digital signal processor (DSP), a microcontroller unit (MCU), a field programmable gate array (FPGA), an embedded system based on Linux or RTOS, and other devices. Obviously, for any power device under test, the switching actions of its corresponding source switching switch and drain switching switch need to be kept synchronized.

[0070] The source switch and the drain switch can be composed of a circuit switching device with a single-pole double-throw characteristic. For example, a single-pole double-throw (SPDT) electromagnetic relay can be selected. The electromagnetic relay includes a common contact (COM), a normally open contact (NO), and a normally closed contact (NC). When receiving an input signal (such as a high-level signal, or causing current to flow through the electromagnetic coil), an electromagnetic force is generated in the electromagnet core, attracting the armature, thereby connecting the common contact to the normally open contact. When receiving another input signal (such as a low-level signal, or canceling the current through the electromagnetic coil), the electromagnetic force in the magnet core disappears, and the common contact is connected to the normally closed contact. By switching the input signal to the electromagnetic relay, the connection state of the source / drain of each power device and the two measurement terminals of the three-phase six-bridge arm circuit under test or the temperature-sensitive electrical parameter measurement circuit can be switched, thereby selectively connecting the corresponding power device under test to the three-phase six-bridge arm circuit under test or the temperature-sensitive electrical parameter measurement circuit.

[0071] Figure 2 The embodiment shown only includes one temperature-sensitive electrical parameter measurement circuit, so all source switches S S1 ~S S6 One of the switchable output terminals is connected to a measuring terminal of the temperature-sensitive electrical parameter measurement circuit, and all drain switching switches S D1 ~S D6 One of the switchable output terminals is connected to the other measuring terminal of the temperature-sensitive electrical parameter measurement circuit. Obviously, at any time, the temperature-sensitive electrical parameter measurement circuit can only be connected to one power device under test.

[0072] In some other optional embodiments, the number of temperature-sensitive electrical parameter measurement circuits may also be increased. For example, two temperature-sensitive electrical parameter measurement circuits may be provided, one of which is used to measure the temperature-sensitive electrical parameters of the three power devices P1, P2, and P3 under test in the upper half bridge of each phase bridge arm circuit, and the other is used to measure the temperature-sensitive electrical parameters of the three power devices P4, P5, and P6 under test in the lower half bridge of each phase bridge arm circuit. At the same time, at any time, it is necessary to ensure that the power devices under test connected to each temperature-sensitive electrical parameter measurement circuit are from the same bridge arm circuit. For example, the temperature-sensitive electrical parameters of P1 and P4 may be measured simultaneously by two temperature-sensitive electrical parameter measurement circuits, or the temperature-sensitive electrical parameters of P2 and P5 may be measured simultaneously, or the temperature-sensitive electrical parameters of P3 and P6 may be measured simultaneously, but the temperature-sensitive electrical parameters of P1 and P2, or P1 and P3, or P1 and P5, or P1 and P6 cannot be measured simultaneously, because this measurement method will not be able to maintain the operation of the AC power cycle.

[0073] After a power device under test is connected to the temperature-sensitive electrical parameter measurement circuit through the bridge arm switching circuit, in order to maintain the aging test of other power devices under test, the bridge arm where the power device under test is located needs to be replaced by the spare bridge arm circuit to ensure the continuation of the AC power cycle. Figure 1 As shown, the backup bridge arm circuit includes two backup power devices P7 and P8 connected in series, and a backup coil led out from the connection point of P7 and P8. The models of P7 and P8 are preferably the same as those of each power device under test, and are connected to the three-phase six-bridge arm circuit under test using the same topology as the bridge arm circuit of the three phases A, B, and C. In an embodiment of the present application, this phase bridge arm circuit can be called a D-phase bridge arm circuit, and its backup coil, i.e., the D-phase coil, is connected to the three-phase coils A, B, and C in a star manner.

[0074] The gates of P7 and P8 can also receive gate control signals issued by the aforementioned various closed-loop modulation control devices, and cooperate with the switching action of the bridge arm switching circuit to switch from the three-phase six-bridge arm circuit under test to the spare three-phase six-bridge arm circuit, or from the spare three-phase six-bridge arm circuit to the three-phase six-bridge arm circuit under test.

[0075] For example, when the three-phase six-arm bridge circuit under test is in a normal AC power circulation state, the closed-loop modulation control device controls the standby power devices P7 and P8 to be in the off state. When it is necessary to connect the power device P1 under test on the A-phase bridge arm circuit to the temperature-sensitive electrical parameter measurement circuit, the switching device switches the switch S to the source. S1 and drain switch S D1Send the corresponding switching signal to connect it to the temperature-sensitive electrical parameter measurement circuit, and at the same time the closed-loop modulation control device turns off P4 by controlling the gate of P4, or the switching device switches the switch S to the source. S4 and drain switch S D4 Send the corresponding switching signal to connect P4 to another temperature-sensitive electrical parameter measurement circuit; at the same time, the closed-loop modulation control device sends the gate G of P7 and P8 to the D1 , G D2 The gate control signal originally sent to P1 and P4 is sent to make the D-phase bridge arm circuit replace the A-phase bridge arm circuit, and the three-phase six-bridge arm circuit under test is switched to the standby three-phase six-bridge arm circuit and the AC power circulation state is maintained, thereby ensuring that the aging test of the power devices P3 to P6 under test is continued. When the temperature-sensitive electrical parameter measurement of P1 is completed (or the temperature-sensitive electrical parameter measurement of P1 and P4 is completed), the closed-loop modulation control device controls P7 and P8 to be turned off, and at the same time, the switching device switches the switch S to the source. S1 and drain switch S D1 Send the corresponding switching signal and switch S to the source S4 and drain switch S D4 The corresponding switching signal is sent to reconnect the A-phase bridge arm circuit where P1 and P4 are located to the AC power cycle, and then the closed-loop modulation control device resends the gate control signal to P1 and P4, so that the standby three-phase six-bridge arm circuit is switched back to the three-phase six-bridge arm circuit under test.

[0076] Since each phase coil has inductance characteristics, the current flowing through each coil cannot change suddenly. When switching between the tested bridge arm circuit and the backup bridge arm circuit, if the switching timing is not chosen properly, the energy stored in the inductance will cause fluctuations in the three-phase current. Figure 4 The simulation embodiment shown shows the changes in the currents of each phase under a bridge arm switching strategy. In this embodiment, it is necessary to measure the temperature-sensitive electrical parameters of the power device P3 under test on the C-phase upper bridge, and when the C-phase circuit is at its peak, the C-phase bridge arm circuit is switched to the D-phase bridge arm circuit. Obviously, during the switching process, the D-phase current needs to track the original C-phase current from 0, which makes it unable to transition smoothly, and also causes fluctuations in the A-phase and B-phase currents.

[0077] It can be seen that the selection of the switching timing will affect the smooth operation of the AC power cycle. Therefore, in some preferred embodiments, the following bridge arm switching strategy is adopted to control the switching between the tested three-phase six-bridge arm circuit and the backup three-phase six-bridge arm circuit:

[0078] (1) When the phase current of the bridge arm circuit where the power device under test is located and the temperature-sensitive electrical parameter measurement circuit needs to be connected is zero, the bridge arm circuit where the power device under test is located is replaced by the backup bridge arm circuit, thereby switching the three-phase six-bridge arm circuit under test to the backup three-phase six-bridge arm circuit;

[0079] (2) When the phase current of the standby bridge arm circuit is zero, the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located replaces the standby bridge arm circuit, thereby switching the standby three-phase six-bridge arm circuit to the three-phase six-bridge arm circuit under test.

[0080] Figure 5 The embodiment shown in FIG. 1 shows a specific process of switching the bridge arm circuit using the above strategy, such as Figure 5 As shown, during the aging test process in which the three-phase six-bridge-arm circuit under test maintains an AC power cycle, when it is necessary to measure the temperature-sensitive electrical parameters of the power device under test, the phase current of the bridge arm circuit where the power device under test is located is monitored, and when the phase current is zero, switching is performed. At this time, the temperature-sensitive electrical parameter measurement operation is performed on the power device under test, and the standby three-phase six-bridge-arm circuit maintains an AC power cycle. After the temperature-sensitive electrical parameter measurement is completed, the phase current of the standby bridge arm circuit is monitored, and when the phase current is zero, switching is performed again.

[0081] Figure 6 The simulation example shows the change of each phase current when the above bridge arm switching strategy is used. Figure 7 The actual experimental results are shown. Figure 6 、 Figure 7 It can be seen that the use of the above preferred bridge arm switching strategy can effectively avoid current oscillation caused by inductor freewheeling and ensure the smooth operation of the aging test.

[0082] Some embodiments of the present application also provide a comprehensive test and analysis method, which uses the aforementioned online power device aging test circuit for vehicle working conditions to analyze the aging condition of the power device under test without interrupting the power device aging test based on AC power cycle, such as Figure 8 As shown, the method includes the following operations:

[0083] Operation 1: Maintain the three-phase six-bridge-arm circuit under test in a power circulation state corresponding to the working condition of the vehicle under test;

[0084] Operation 2: By switching the state of the bridge arm switching circuit, the power device under test whose aging condition needs to be analyzed is connected to the temperature-sensitive electrical parameter measurement circuit, and the power device in the same bridge arm is turned off at the same time, or the power device in the same bridge arm is connected to another temperature-sensitive electrical parameter measurement circuit;

[0085] Operation three: Use a spare bridge arm circuit to replace the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located, to form a spare three-phase six-bridge arm circuit, and put it into a power cycle state corresponding to the operating conditions of the vehicle under test;

[0086] Operation 4: measuring the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit and analyzing its aging condition;

[0087] Operation five: After completing the measurement of the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test, turn off the standby power device, and by switching the state of the bridge arm switching circuit, use the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located to replace the standby bridge arm circuit, so as to reconstruct the three-phase six-bridge arm circuit under test and put it in the power circulation state corresponding to the vehicle operating conditions under test.

[0088] Since the duration of the aging test experiment for the power device under test may reach hundreds or even thousands of hours, Figure 8 As shown, for any power device under test whose aging condition needs to be analyzed, the above operations 2 to 5 can be cyclically performed at preset time intervals.

[0089] Furthermore, since the aging degree of power devices may tend to accelerate as the aging test proceeds, and generally more attention needs to be paid to the aging conditions after long-term operation, preferably, the above-mentioned time interval can be continuously shortened as the aging test continues. For example, at the beginning of the aging test, the time-varying characteristics of the temperature-sensitive electrical parameters and the aging analysis are performed on each power device under test at an interval of 30 hours / time. When the aging test continues for 300 hours, the time-varying characteristics of the temperature-sensitive electrical parameters and the aging analysis are performed on each power device under test at an interval of 20 hours / time. When the aging test continues for 500 hours, the time-varying characteristics of the temperature-sensitive electrical parameters and the aging analysis are performed on each power device under test at an interval of 10 hours / time.

[0090] <Analysis of power device aging based on the time-varying characteristics of temperature-sensitive electrical parameters>

[0091] Among the above operations, operation four is used to measure the time-varying characteristics of the temperature-sensitive electrical parameters of the device under test, and analyze the aging conditions of various parts of the power device under test based on the measurement results. In some specific embodiments, this operation includes the following steps:

[0092] The first step is to heat the junction temperature of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit to a preset target, then terminate the heating and measure the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test;

[0093] The second step is to analyze the aging conditions of various positions of the power device under test based on the time-varying characteristics of the temperature-sensitive electrical parameters.

[0094] The specific implementation of the first step has been described in detail in the previous introduction to the temperature-sensitive electrical parameter measurement circuit. The following describes the analysis process of the second step in detail with reference to the accompanying drawings.

[0095] Figure 9 A specific embodiment of analyzing the aging of the power device under test according to the time-varying characteristics of the temperature-sensitive electrical parameters is shown. Figure 9 , the analysis process includes the following steps:

[0096] Step a: Based on the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test, its transient thermal response curve is determined through a pre-calibrated body diode voltage drop-junction temperature relationship model.

[0097] As mentioned above, by continuously collecting the body diode voltage drop of the power device under test during the cooling process through the voltage drop measurement block, the time-varying characteristics of the temperature-sensitive electrical parameter (i.e., the body diode voltage drop) can be obtained. Using the pre-calibrated body diode voltage drop-junction temperature relationship model, a curve showing the junction temperature changing with time can be obtained.

[0098] The calibration method for the relationship between the body diode voltage drop and the junction temperature is well known to those skilled in the art. For example, Figure 10 The junction temperature calibration experimental platform shown in the figure uses a temperature chamber to maintain the power device (DUT) used for calibration at a set junction temperature, and then measures the corresponding body diode voltage drop at various junction temperatures. Figure 11 The calibration results of three power devices of the same model from the same batch are shown. It can be seen that the body diode voltage drop is negatively correlated with the junction temperature. It has high sensitivity and good linearity, making it suitable for monitoring device junction temperature changes. Figure 11 In the embodiment shown, the results of three samples are averaged to obtain the relationship between junction temperature and body diode voltage drop: T j =-356.4V F +999.2, Obviously, for other types of power devices, a similar body diode voltage drop-junction temperature relationship model can be obtained.

[0099] Using the pre-calibrated body diode voltage drop-junction temperature relationship model, the measured body diode time-varying characteristics can be converted into a curve of junction temperature variation over time. The transient thermal impedance a(t) can then be calculated from the junction temperature variation using the following formula:

[0100]

[0101] Among them, T j is the junction temperature that changes with time, T0 is the initial value of the junction temperature, and ΔP is the change in heating power of the device under test during the experiment.

[0102] After obtaining the thermal impedance curve a(t), it can be plotted on a logarithmic time axis to obtain the transient thermal response curve, which is expressed as:

[0103]

[0104] Where z = lnt, ζ = lnτ, a(z) is the thermal impedance, and R(ζ) is the thermal resistance.

[0105] Step b: determining a time constant spectrum based on the transient thermal response curve.

[0106] Specifically, the time constant spectrum can be expressed as follows, which is obtained by differentiating a(z) with respect to z and then performing a deconvolution operation:

[0107]

[0108] in, Denotes a deconvolution operation. In some specific embodiments, the above operation can be implemented using Bayesian deconvolution, Fourier inverse filtering, etc. known to those skilled in the art.

[0109] Step c: discretizing the time constant spectrum to obtain a FOSTER model.

[0110] Step d: converting the FOSTER model into a CAUER model to obtain the thermal resistance-heat capacity structure function of the power device under test.

[0111] Knowing the time constant spectrum R(z) allows us to derive a thermal network model. The theoretical basis of the thermal network model is that when the effective area of the heat source is close to the top surface of the device, the device's thermal model can be considered a one-dimensional heat conduction model. Thermoelectric analogy theory is often used to describe the device's thermal network model using a circuit consisting of thermal resistors and capacitors. Typical examples include the FOSTER model and the CAUER model.

[0112] The time constant spectrum function is an extension of the continuous case of the FOSTER model. The discretization of the time constant spectrum can obtain the expression of the FOSTER model as shown in the following formula:

[0113]

[0114] in, is the local thermal resistance and local heat capacity in the FOSSTER model. The FOSTER model does not have actual physical meaning, so it needs to be converted into a CAUER model that can reflect the device stacking structure, and the local thermal resistance R in the CAUER model is obtained. n and local heat capacity C n .

[0115] By accumulating the local thermal resistance and local heat capacity, we can obtain the cumulative thermal resistance-cumulative heat capacity structure function as shown below:

[0116]

[0117] Alternatively, only the local heat capacity may be accumulated to obtain a local structure function reflecting the relationship between the local thermal resistance and the accumulated heat capacity. In the embodiments of the present application, the above structure functions may all be referred to as thermal resistance-heat capacity structure functions.

[0118] Step e: analyzing the aging conditions of various positions of the power device under test based on the thermal resistance-heat capacity structure function.

[0119] For example, the cumulative thermal resistance R of the power device from junction to case can be ∑ is the horizontal axis, the cumulative heat capacity C ∑ As the vertical coordinate, we can get Figure 12 The cumulative structure function curve shown above can accurately reflect the aging conditions of various parts of the power device under test during the time period when the temperature-sensitive electrical parameters are measured.

[0120] Some embodiments of the present application also provide a comprehensive test and analysis system, such as Figure 13 As shown, the system includes:

[0121] Online power device aging test circuit, control unit, switching unit and analysis unit for automotive working conditions.

[0122] Among them, the online power device aging test circuit for vehicle working conditions is used to perform aging tests on the power devices under test with continuous AC power loading, and in the process, the time-varying characteristics of the temperature-sensitive electrical parameters of each power device under test are measured online; the control unit controls the AC power circulation state of the three-phase six-bridge arm circuit under test or the spare three-phase six-bridge arm circuit according to the preset vehicle working conditions; the switching unit is used to switch the three-phase six-bridge arm circuit under test to the spare three-phase six-bridge arm circuit, or to switch the spare three-phase six-bridge arm circuit to the three-phase six-bridge arm circuit under test; the analysis unit analyzes the aging conditions of each position of the power device under test based on the measurement results of the time-varying characteristics of the temperature-sensitive electrical parameters of the power device connected to the temperature-sensitive electrical parameter measurement circuit.

[0123] The specific implementations of the above-mentioned circuits and units have been described in detail above and will not be repeated here.

[0124] <Specific embodiment 1>

[0125] This embodiment adopts Figure 13 The framework structure shown is a comprehensive test and analysis experimental platform. Figure 14 This is a physical picture of the experimental platform.

[0126] In this experimental platform, the power device under test is a discrete SiC MOSFET model C3M0120065K with a maximum voltage of 650V and a maximum current of 25A, which is close to the voltage and current requirements of automotive inverters. The load inductance is 2mH. The temperature-sensitive electrical parameter measurement circuit is equipped with a 30A / 10V heating power supply, a temperature measurement power supply with an error within 3mA, a differential voltmeter with an error within 1.5mV, and a temperature resolution of 0.02°C. The single-pole double-throw switch is a 380VAC / 20A electromagnetic relay (J107F1CS205VDC.45), and the phase current is acquired using a LEM CAS25-NP current sensor. The experimental platform is monitored and controlled by an ACT200 FPGA board.

[0127] The power cycle aging test process is carried out by alternating the vehicle's high-speed light-load condition and low-speed heavy-load condition: q is 20A, i d The current is 0A, the mechanical speed is 1500Rpm, the device switching frequency is 20kHz, and the high speed and light load condition is i q 4A, i d The current is 0A, the mechanical speed is 7000Rpm, and the device switching frequency is 20kHz.

[0128] The bridge arm circuit switching strategy was verified by online measurement during normal power cycle operation. The results are shown in Figure 7 ,Depend on Figure 7 It can be seen that when the C-phase bridge arm and the D-phase backup bridge arm are switched, the three-phase current does not show obvious fluctuations, proving that the zero-current switching strategy can achieve smooth and reliable switching.

[0129] After 650 hours of AC power cycle test aging, the structure function of the device under test obtained through online measurement and analysis is as follows Figure 15 As shown, it can be seen that the structure function shifts to the left after aging, while the common solder layer aging structure curve should shift to the right. Figure 16 Analysis of the on-state voltage drop during the heating process of the power device under test. After the device is aged, when the device under test is heated with a current of 13A, the on-state voltage drop increases significantly. Therefore, it is speculated that the bonding wire of the power device under test has aged. It can be seen that the use of the comprehensive test and analysis method and system provided in this application can accurately analyze and locate the aging conditions of various parts of the power device under test.

[0130] 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 can 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. An online power device aging test circuit for automotive working conditions, comprising a three-phase six-bridge arm circuit under test composed of power devices under test, characterized in that: Also includes: The temperature-sensitive electrical parameter measurement circuit is used to measure the time-varying characteristics of the temperature-sensitive electrical parameters of the connected power device under test; A bridge arm switching circuit, comprising a source switching switch and a drain switching switch corresponding to each power device under test, for connecting the corresponding power device under test to the three-phase six-bridge arm circuit under test, or to the temperature-sensitive electrical parameter measurement circuit; The backup bridge arm circuit includes two backup power devices connected in series and a backup coil led out from the connection point of the two backup power devices, which is used to replace any bridge arm circuit where the power device under test is located that is connected to the temperature-sensitive electrical parameter measurement circuit to form a backup three-phase six-bridge arm circuit.

2. The on-line power device aging test circuit for vehicle operating conditions according to claim 1 is characterized in that: The backup bridge arm circuit is connected to the three-phase six-bridge arm circuit under test in the same topology as the bridge arm circuit where the power device under test is located, and the backup coil is connected to the three-phase coils of the three-phase six-bridge arm circuit under test in a star connection manner.

3. The on-line power device aging test circuit for vehicle working conditions according to claim 1 is characterized in that: Each of the source switching switches is used to switch the connection state between the source of its corresponding power device and the three-phase six-bridge arm circuit under test or a measuring end of the temperature-sensitive electrical parameter measurement circuit; Each of the drain switching switches is used to switch the connection state between the drain of its corresponding power device and the three-phase six-bridge arm circuit under test or the other measuring end of the temperature-sensitive electrical parameter measurement circuit.

4. The on-line power device aging test circuit for vehicle operating conditions according to claim 3 is characterized in that: The source switching switch includes a common input terminal connected to the source of the corresponding power device under test, and two switchable output terminals respectively connected to the bridge arm circuit where the corresponding power device under test is located and a measuring terminal of the temperature-sensitive electrical parameter measurement circuit; The drain switching switch includes a common input terminal connected to the drain of the corresponding power device under test, and two switchable output terminals respectively connected to the bridge arm circuit where the corresponding power device under test is located and the other measuring terminal of the temperature-sensitive electrical parameter measurement circuit.

5. The on-line power device aging test circuit for vehicle working conditions according to claim 1 is characterized in that: For any power device under test, the switching actions of its corresponding source switch and drain switch are kept synchronous.

6. The on-line power device aging test circuit for vehicle working conditions according to claim 1 is characterized in that: The temperature-sensitive electrical parameter is a body diode voltage drop caused by a stable measurement current in the off state of the power device. The temperature-sensitive electrical parameter measurement circuit includes: A heating module, used to heat the junction temperature of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit to a preset target; a measuring current source, the two ends of which are respectively connected to the source and drain of the connected power device under test, and used to generate a measuring current flowing through the body diode of the power device under test when the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is in an off state; A voltage drop measurement module, whose two measuring ends are respectively connected to the source and drain of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit, is used to measure the body diode voltage drop of the power device under test caused by the measurement current when the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is in the off state.

7. The on-line power device aging test circuit for vehicle working conditions according to any one of claims 1 to 6, characterized in that: The number of the temperature-sensitive electrical parameter measurement circuits is greater than or equal to one; At any time, the number of power devices under test connected to any temperature-sensitive electrical parameter measurement circuit does not exceed one, and the number of bridge arm circuits where the power devices under test connected to the temperature-sensitive electrical parameter measurement circuit are located does not exceed one.

8. A comprehensive test and analysis method, using the online power device aging test circuit for automotive working conditions as claimed in claim 1, to analyze the aging condition of the power device under test without interrupting the power device aging test based on AC power cycling, characterized in that: The following operations are included: Operation 1: Maintain the three-phase six-bridge-arm circuit under test in a power circulation state corresponding to the working condition of the vehicle under test; Operation 2: By switching the state of the bridge arm switching circuit, the power device under test whose aging condition needs to be analyzed is connected to the temperature-sensitive electrical parameter measurement circuit, and the power device in the same bridge arm is turned off at the same time, or the power device in the same bridge arm is connected to another temperature-sensitive electrical parameter measurement circuit; Operation three: Use a spare bridge arm circuit to replace the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located, to form a spare three-phase six-bridge arm circuit, and put it into a power cycle state corresponding to the operating conditions of the vehicle under test; Operation 4: measuring the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit and analyzing its aging condition; Operation five: After completing the measurement of the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test, turn off the standby power device, and by switching the state of the bridge arm switching circuit, use the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located to replace the standby bridge arm circuit, so as to reconstruct the three-phase six-bridge arm circuit under test and put it in the power circulation state corresponding to the vehicle operating conditions under test.

9. The comprehensive test and analysis method according to claim 8, characterized in that: For any power device under test whose aging condition needs to be analyzed, operations 2 to 5 are cyclically executed at preset time intervals.

10. The comprehensive test and analysis method according to claim 8, characterized in that: The fourth operation includes the following steps: After heating the junction temperature of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit to a preset target, the heating is terminated and the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test are measured; Based on the time-varying characteristics of the temperature-sensitive electrical parameters, the aging conditions of various positions of the power device under test are analyzed.

11. The comprehensive test and analysis method according to claim 10, characterized in that: The temperature-sensitive electrical parameter is the body diode voltage drop of the power device caused by a stable measurement current in the off state, and the aging conditions of various positions of the measured power device are analyzed by the following steps: Based on the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test, its transient thermal response curve is determined using a pre-calibrated body diode voltage drop-junction temperature relationship model. determining a time constant spectrum based on the transient thermal response curve; Discretizing the time constant spectrum to obtain a FOSTER model; Converting the FOSTER model into a CAUER model to obtain a thermal resistance-heat capacity structure function of the power device under test; The aging conditions of various positions of the power device under test are analyzed based on the thermal resistance-heat capacitance structure function.

12. The comprehensive test and analysis method according to claim 8, characterized in that: The switching between the three-phase six-bridge-arm circuit under test and the backup three-phase six-bridge-arm circuit is controlled based on the following bridge-arm switching strategy: When the phase current of the bridge arm circuit where the power device under test is located and needs to be connected to the temperature-sensitive electrical parameter measurement circuit is zero, the backup bridge arm circuit replaces the bridge arm circuit where the power device under test is located, thereby switching the three-phase six-bridge arm circuit under test to the backup three-phase six-bridge arm circuit; When the phase current of the standby bridge arm circuit is zero, the bridge arm circuit where the power device under test connected to the temperature-sensitive electrical parameter measurement circuit is located replaces the standby bridge arm circuit, thereby switching the standby three-phase six-bridge arm circuit to the three-phase six-bridge arm circuit under test.

13. A comprehensive test and analysis system, characterized in that: include: The online power device aging test circuit for vehicle operating conditions as described in claim 1; A control unit controls the AC power circulation state of the tested three-phase six-bridge-arm circuit or the standby three-phase six-bridge-arm circuit according to a preset vehicle operating condition; A switching unit, used to switch the three-phase six-bridge-arm circuit under test to a spare three-phase six-bridge-arm circuit, or to switch the spare three-phase six-bridge-arm circuit to the three-phase six-bridge-arm circuit under test; The analysis unit analyzes the aging conditions of various positions of the power device under test according to the measurement results of the time-varying characteristics of the temperature-sensitive electrical parameters of the power device under test connected to the temperature-sensitive electrical parameter measurement circuit.

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