Temperature criterion setting method for identifying IGBT aging status

Abstract

An IGBT short-circuit current can serve as a parameter for judging an IGBT aging status, and short-circuit current values are closely related to the IGBT operating junction temperature, so that the key to distinguish whether a short-circuit current value is observed from a normal IGBT at a specified junction temperature, or from a faulty IGBT at a varying junction temperature lies in determining a junction temperature at the moment a short-circuit current occurs. The method provided by the present invention comprises: using a short-circuit excitation circuit for controlling IGBT short-circuit operating conditions, and collecting an IGBT short-circuit current while simultaneously measuring the IGBT junction temperature at the moment, so as to create a data fitted relational graph with respect to the IGBT short-circuit current, variations of temperatures and variations of aging degrees; by means of taking an aging status threshold as a judgment criterion, partitioning a corresponding fixed temperature interval, and executing self-excited short-circuit operations within the temperature interval, so as to generate a self-excited short-circuit current; and measuring the short-circuit current, and comparing the short-circuit current with an aging judgment threshold value so as to perform health degree assessment for the IGBT.

Description

A method for setting temperature criteria to identify IGBT aging conditions Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a method for setting a temperature criterion for identifying the aging state of IGBTs. Background Technology

[0002] As IGBTs age, they inevitably experience aging failures, threatening the reliable operation of power units and the safe production of converter systems. By monitoring certain electrical characteristic parameters of the IGBT and analyzing their changing patterns, the health status of the IGBT can be determined. The internal chips of an IGBT module are electrically connected to the external environment via multiple bonding wires. The aging of the module ultimately manifests as the breakage of these bonding wires; therefore, the health status can be defined as the ratio of the remaining number of bonding wires to the total number of bonding wires.

[0003] Currently, the main electrical characteristic parameters include saturation on-state voltage drop, turn-on delay time, and short-circuit current. Among these, short-circuit current has advantages such as significant numerical changes and ease of online measurement, and is therefore widely used. The condition of artificially inducing an IGBT to enter a short-circuit state to obtain short-circuit current information can be called a self-excited short-circuit state. Self-excited short-circuit monitoring technology actively induces a short circuit in the IGBT, collects the short-circuit current flowing through the IGBT, and compares it with an aging judgment threshold. When the current is less than the judgment threshold, the IGBT is considered to have aged; otherwise, it is in a healthy state.

[0004] Figure 1 shows the transmission characteristic curves of an IGBT module, reflecting the relationship between temperature, gate voltage, and collector current. The collector current increases with increasing gate voltage. At lower gate voltages, the current is positively correlated with temperature, while at higher gate voltages, the current is negatively correlated with temperature. Therefore, the current magnitude is affected not only by the module's health status but also by temperature, making it impossible to accurately determine the module's health status solely based on the current magnitude. As shown at points A, B, and C in the figure, under the same gate voltage and health status, the currents corresponding to these three points show significant differences due to different temperatures. Therefore, during IGBT health status monitoring, it is necessary to set relevant temperature criteria to eliminate the influence of temperature on the monitoring results.

[0005] Existing aging monitoring methods based on short-circuit current at specific junction gate voltages have eliminated the interference of temperature on monitoring results and have been widely used. The principle is shown in Figure 2: According to the transfer characteristic curve of a certain IGBT module, the short-circuit current is affected by both temperature and gate voltage. When the gate drive voltage is the value at the junction of the transfer characteristic curves at different temperatures, the influence of the IGBT module's temperature on the short-circuit current is negligible, and the short-circuit current is only related to its health status. However, the current values ​​corresponding to the junction of the transfer characteristic curves of different IGBT modules vary significantly. For medium- and high-power IGBT modules, the short-circuit current at the junction is often as high as several hundred amperes. If aging condition monitoring is performed under this condition, a large capacitor must be used to generate a short-circuit current of several hundred amperes, and accurate current monitoring is difficult. This method not only greatly increases the size of the entire condition monitoring system but also significantly increases the cost. Furthermore, a large short-circuit current will generate large short-circuit losses, causing the IGBT temperature to rise rapidly in a short time, which will affect the reliability and service life of the IGBT.

[0006] Another approach is to assess IGBT health status based on module transconductance, which also considers the impact of temperature on monitoring results. Transconductance (Kin) refers to the slope of the IGBT module's transmission characteristic curve, a characteristic parameter of the IGBT itself. As the IGBT module ages, the slope of its transmission characteristic curve gradually decreases, meaning the module transconductance decreases as the IGBT's health deteriorates. Simultaneously, transconductance exhibits a linear relationship with module temperature, allowing the module transconductance at any given temperature to be normalized to the same temperature. This approach uses a DSP processor to process parameters such as collector current, gate voltage, and temperature measured by the acquisition circuit. After certain processing, a normalized module transconductance value is obtained, which reflects the module's health status by comparing it with a threshold. However, the extraction process of module transconductance is relatively complex, and the calculation requires relatively accurate short-circuit current and temperature values; otherwise, the calculation result error will be large, placing high demands on the accuracy of the detection circuit. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention proposes a temperature criterion setting strategy suitable for predicting the lifespan of self-excited short-circuit IGBTs. Firstly, it proposes a method for setting a temperature criterion to identify the aging state of IGBTs, comprising the following steps:

[0008] Obtain the relevant aging parameters of the actual IGBT module;

[0009] Obtain the relationship between short-circuit current and healthy state at the same temperature, and the relationship between short-circuit current and temperature under the same healthy state;

[0010] Construct a surface plot that fits the relationship between the healthy state, temperature, and short-circuit current;

[0011] Based on the relationship surface diagram, appropriate temperature criteria are set by dividing the temperature range.

[0012] Based on the above scheme, the temperature and short-circuit current are obtained by building an experimental platform;

[0013] The main circuit of the experimental platform consists of a drive module and a test module. The drive module integrates a variable voltage gate output, a constant current source and a short-circuit power supply. The module temperature is increased by heating the platform. The thermocouple module and the host computer monitor the accurate temperature in real time. The collector-emitter voltage and short-circuit current are monitored by a differential probe and a Rogowski coil, respectively.

[0014] Based on the above scheme, the method for establishing the relationship between health status, temperature, and short-circuit current is as follows:

[0015] Establish the short-circuit current equation:

[0016] ;

[0017] Among them, C ox Z represents the oxide layer capacitance, Z represents the channel width, and L represents the channel capacitance. ch μ is the channel length. ni For electron mobility, α PNP V is the common-base gain of the PNP transistor. th V is the gate threshold voltage of the IGBT chip. GE(C) This refers to the gate voltage of the IGBT chip.

[0018] Assume that the parasitic parameters of different chips are all equal;

[0019] Establish the gate loop KVL equations under short-circuit conditions:

[0020] ;

[0021] Where m is the number of chips connected in parallel in the IGBT module, n is the number of bonding wires for each chip, and V Ge V is the gate voltage of the IGBT module. GE(C) This refers to the gate voltage of the IGBT chip, I. g I is the module gate current. SC The module short-circuit current is equal to m times I. SC(chip) ;

[0022] Once the IGBT short-circuit process stabilizes, let I... g =0, dI g / dt=0,dI SC / dt=0;

[0023] Derive the short-circuit current expression for the IGBT module:

[0024] ;

[0025] Based on the above scheme, the relationship surface diagram is specifically as follows: the horizontal axis represents the module temperature, the vertical axis represents the module short-circuit current, and it is composed of two straight lines with equal slopes. The straight line with a larger vertical intercept represents a healthy module, and the straight line with a smaller vertical intercept represents an aging module.

[0026] Based on the above scheme, the method for setting the temperature criterion is as follows: establish a judgment threshold line parallel to the horizontal axis. This line intersects with two fitted curves at two points. By increasing or decreasing the judgment threshold, the temperature range between the two intersection points is made closer to the actual working temperature of the module. The aging judgment threshold is the minimum value under healthy conditions and the maximum value under aging conditions.

[0027] Based on the above scheme, the temperature range between the two intersection points is set as the detection enable range.

[0028] In a second aspect, an electronic device is provided, including a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the method described in the first aspect.

[0029] Thirdly, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0030] The beneficial effects of this invention are:

[0031] This invention, using short-circuit current as a characteristic parameter of IGBT aging status, theoretically analyzes short-circuit current, aging degree, and temperature, establishes a practical circuit model capable of implementing the aforementioned aging determination method, and proposes an online aging determination method that eliminates temperature interference based on this circuit. Compared with existing technologies, the judgment logic is simpler, and the aging judgment results are closer to reality. Attached Figure Description

[0032] The present invention includes the following figures:

[0033] Figure 1 shows the transmission characteristic curve of IGBT in the background art of this invention;

[0034] Figure 2 is a schematic diagram of the short-circuit current monitoring method at the gate intersection in the background art of the present invention;

[0035] Figure 3 is the normalized module transconductance variation curve in the background art of this invention;

[0036] Figure 4 is a specific embodiment of the key parameter extraction experimental platform of the present invention;

[0037] Figure 5 is a schematic diagram of the internal structure of an IGBT chip;

[0038] Figure 6 shows the relationship between current and temperature under the same health condition.

[0039] Figure 7 is the IGBT gate circuit diagram under short-circuit conditions;

[0040] Figure 8 shows the relationship between current and health status at the same temperature;

[0041] Figure 9 is a schematic diagram of the temperature range division method in the method of the present invention;

[0042] Figure 10 is a surface diagram showing the relationship between factors affecting short-circuit current and a schematic diagram of temperature range settings. Detailed Implementation

[0043] To make the objectives, advantages and features of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] This invention proposes a temperature criterion setting strategy suitable for estimating the lifespan of self-excited short-circuit IGBTs. First, by building a relevant experimental platform, relevant aging parameters of actual IGBT modules are obtained, and the relationship between short-circuit current and healthy state at the same temperature, as well as the relationship between short-circuit current and temperature under the same healthy state, is acquired. Second, a surface plot fitting the relationship between healthy state, temperature, and short-circuit current is constructed. Finally, based on the relationship surface plot, an appropriate temperature criterion is set by dividing the temperature range to ensure the accuracy of the monitoring results. The factor affecting the accuracy of the monitoring results is the temperature of the IGBT module itself when it is being tested. The purpose of this strategy is to ensure that the short-circuit current is monitored by the drive circuit within a certain set temperature range, thereby eliminating the influence of temperature on the monitoring results.

[0045] Relevant data can be obtained by building the experimental platform shown in Figure 4. Its main circuit uses a short-circuit excitation circuit and consists of a drive module and a module under test. The drive module integrates a variable voltage gate output. It preferably uses a 100mA constant current source and a short-circuit power supply. The module temperature is increased by heating the platform. The thermocouple module and the host computer monitor the accurate temperature in real time. The collector-emitter voltage and short-circuit current under 100mA are monitored by differential probes and Rogowski coils, respectively.

[0046] The internal structure of a common IGBT module chip is shown in Figure 5, where C, G, e, and E represent the module collector, module gate, module auxiliary emitter, module emitter, and C, respectively. C G C E C These represent the chip collector, chip gate, and chip emitter, respectively. R G L is the module gate resistor. G R is the gate lead inductor of the module.g L is the gate parasitic resistance. g R is the gate parasitic inductance. wire For a single bond wire resistance, L wire This is a single-bonded-wire inductor. Each IGBT inside the module consists of three IGBT chips connected in parallel, and each chip is connected to a copper busbar via eight bond wires. Intermittent bonding wire breaks at the chip-to-busbar connections simulate chip aging. When the bond wires remain intact, the module is in a healthy state; when all eight bond wires are cut, the chip has completely failed due to aging.

[0047] Next, a model is constructed to represent the relationship between short-circuit current, temperature, and aging degree. The formula for calculating the short-circuit current is shown in Equation 1.

[0048] ;

[0049] Among them, C ox Z represents the oxide layer capacitance, Z represents the channel width, and L represents the channel capacitance. ch The channel length is determined by the chip structure and is not affected by the operating environment. μ ni For electron mobility, α PNP V is the common-base gain of the PNP transistor. th V is the gate threshold voltage of the IGBT chip. GE(C) This represents the gate voltage of the IGBT chip. All of the above parameters are affected by temperature. The short-circuit current has an approximately linear relationship with temperature, and the two are positively correlated. Relevant experimental data are shown in Figure 6; the short-circuit current increases approximately linearly with temperature.

[0050] The internal chip of the module is connected to the outside via multiple bonding wires. Its internal resistance can be equivalent to a parallel structure of parasitic resistances of the bonding wires. The aging of the module ultimately manifests as the breakage of the bonding wires. That is, as the degree of aging increases, the equivalent resistance inside the module increases. Therefore, at the same temperature, the short-circuit current of the IGBT in the aged state is always less than that in the healthy state. When the IGBT is in the short-circuit condition, the gate voltage is the forward turn-on voltage. At this time, the short-circuit current flows through the collector. The equivalent circuit diagram of the IGBT gate circuit in the short-circuit condition is shown in Figure 7.

[0051] The parameters of the individual chips and bond wires connected in parallel within the IGBT module are basically consistent; therefore, it can be assumed that the parasitic parameters of different chips are equal. Under short-circuit conditions, establishing the KVL equations for the gate circuit shown in Figure 7 yields:

[0052] ;

[0053] Where m represents the number of chips connected in parallel in the IGBT module, n represents the number of bonding wires per chip, and V GeV is the gate voltage of the IGBT module. GE(C) This refers to the gate voltage of the IGBT chip, I. g I is the module gate current. SC The module short-circuit current is equal to m times I. SC(chip) .

[0054] Equation 2 is the transient expression for the short-circuit current. After the short-circuit process of the IGBT stabilizes, I... g =0, dI g / dt=0,dI SC When / dt = 0, the expression can be simplified to:

[0055] ;

[0056] Combining Equation 3 with Equation 2, we can obtain the expression for the short-circuit current of the IGBT module:

[0057] ;

[0058] As shown in Equation 4, the short-circuit current of an IGBT module is affected by its own material, structural characteristics, and bonding wires. When an IGBT fails due to aging, the number of bonding wires or the number of parallel chips decreases, i.e., n or m decreases, resulting in a decrease in the short-circuit current I. SC It will also decrease. The relevant experimental data is shown in Figure 8. As the module health level decreases, the short-circuit current generally shows a downward trend. At the same time, when the number of parallel chips decreases, that is, when m decreases, the short-circuit current value decreases significantly. When only the number of bonding wires decreases, that is, when n decreases, the short-circuit current value decreases slowly.

[0059] Based on the above theoretical analysis and experimental data, the temperature range division method is shown in Figure 9. This graph reflects the relationship between short-circuit current, temperature, and health status, where the horizontal axis represents module temperature and the vertical axis represents module short-circuit current. A key feature of this graph is that it consists of two straight lines with equal slopes; the line with the larger vertical intercept represents a healthy module, and the line with the smaller vertical intercept represents an aging module. The data points in the graph represent the short-circuit current at a fixed temperature under healthy or aging conditions; the specific values ​​were obtained through simulated aging experiments.

[0060] Aging determination threshold I old This setting can be manually configured and set to different values ​​according to different performance requirements. In the image, it is represented as a straight line parallel to the horizontal axis. This line intersects the two fitted curves at two points, with horizontal coordinates T and T, respectively. j1 With T j2 To facilitate practical application, the temperature range (T) can be adjusted by increasing or decreasing the judgment threshold. j1 T j2This temperature range is close to the actual operating temperature of the module, and the temperature range set by this method is relatively large, making it easy to implement in practical applications. Within the temperature range T... j1 To T j2 Within this range, the short-circuit current in the healthy state is significantly greater than the short-circuit current in the aging state due to the linear relationship; that is, the aging threshold I is... old It is the minimum value under healthy conditions and the maximum value under aging conditions. This temperature range can then be set as the enable monitoring temperature range, I. old This is the aging assessment threshold. Within this temperature range, if the short-circuit current is less than I... old If the IGBT module is found to be in an aging state, then the IGBT module is considered to have entered an aging state. old This indicates that the IGBT module is still in a healthy state.

[0061] As shown in Figure 10, based on relevant experiments and the temperature range division method, a surface graph of the relationship between current, health status, and temperature can be constructed. This graph can reflect the trend of current change with health status and temperature. A suitable temperature range is set based on the actual operating temperature. The detection function is only enabled within this temperature range. Within this temperature range, the short-circuit current in the healthy state is always greater than the judgment threshold, and the short-circuit current in the aging state is always less than the judgment threshold. The accuracy of the judgment result is not affected by temperature. Therefore, the temperature range divided in this way can eliminate the interference of temperature on the monitoring results and correctly reflect the relationship between short-circuit current and aging status.

[0062] The above embodiments are for illustrative purposes only and are not intended to limit the scope of this invention. Those skilled in the art can make various changes and modifications without departing from the essence and scope of this invention. Therefore, all equivalent technical solutions also fall within the scope of this invention, and the patent protection scope of this invention should be defined by the claims. Content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A method for setting a temperature criterion to identify the aging state of IGBTs, characterized in that, Includes the following steps: Obtain the relevant aging parameters of the actual IGBT module; Obtain the relationship between short-circuit current and healthy state at the same temperature, and the relationship between short-circuit current and temperature under the same healthy state; Construct a surface plot that fits the relationship between the healthy state, temperature, and short-circuit current; Based on the relationship surface diagram, appropriate temperature criteria are set by dividing the temperature range.

2. The setting method as described in claim 1, characterized in that, The temperature and short-circuit current were obtained by building an experimental platform. The main circuit of the experimental platform consists of a drive module and a test module. The drive module integrates a variable voltage gate output, a constant current source and a short-circuit power supply. The module temperature is increased by heating the platform. The thermocouple module and the host computer monitor the accurate temperature in real time. The collector-emitter voltage and short-circuit current are monitored by a differential probe and a Rogowski coil, respectively.

3. The setting method as described in claim 1, characterized in that, The method for establishing the relationship between the health status, temperature, and short-circuit current is as follows: Establish the short-circuit current equation: ； Among them, C ox Z represents the oxide layer capacitance, Z represents the channel width, and L represents the channel capacitance. ch μ is the channel length. ni For electron mobility, α PNP V is the common-base gain of the PNP transistor. th V is the gate threshold voltage of the IGBT chip. GE(C) This refers to the gate voltage of the IGBT chip. Assume that the parasitic parameters of different chips are all equal; Establish the gate loop KVL equations under short-circuit conditions: ； Where m is the number of chips connected in parallel in the IGBT module, n is the number of bonding wires for each chip, and V Ge V is the gate voltage of the IGBT module. GE(C) This refers to the gate voltage of the IGBT chip, I. g I is the module gate current. SC The module short-circuit current is equal to m times I. SC (chip); Once the IGBT's short-circuit process stabilizes, let I... g =0, dI g / dt=0,dI SC / dt=0; Derive the short-circuit current expression for the IGBT module: 。 4. The setting method as described in claim 1, characterized in that, The relationship surface diagram is as follows: the horizontal axis represents the module temperature, and the vertical axis represents the module short-circuit current. It consists of two straight lines with equal slopes. The straight line with a larger vertical intercept represents a healthy module, and the straight line with a smaller vertical intercept represents an aging module.

5. The setting method as described in claim 4, characterized in that, The method for setting the temperature criterion is as follows: establish a judgment threshold line parallel to the horizontal axis. This line intersects with two fitted curves at two points. By increasing or decreasing the judgment threshold, the temperature range between the two intersection points is made closer to the actual operating temperature of the module. The aging judgment threshold is the minimum value under healthy conditions and the maximum value under aging conditions.

6. The setting method as described in claim 5, characterized in that, Set the temperature range between the two intersection points as the detection enable range.

7. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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