An Anti-Interference Online Monitoring Method for IGBT Bond Wire Aging

: Due to the constant changes of the environment and load, the insulated-gate bipolar transistor (IGBT) module is subjected to a large amount of junction temperature ( T j ) ﬂuctuations, which often leads to damage to the bond wires. The monitoring parameters of IGBTs are often coupled with T j , which increases the difﬁculty of monitoring IGBTs’ health status online. In this paper, based on the collector current ( I c ) and collector-emitter on-state voltage ( V ce_on ) online monitoring circuit, an online monitoring method of IGBT bond wire aging against interference is proposed. First, the bond wire aging model is established, and the V ce_on is selected as the monitoring parameter. Secondly, taking a three-phase inverter circuit as an example, the V ce_on and I c waveforms of the IGBT module are monitored in real time, and the process of online monitoring is introduced accordingly. Finally, the experimental results indicate that the method proposed in this paper can accurately identify the aging state of IGBT bond wires under different conditions.


Introduction
Compared with other power electronic devices, the insulated-gate bipolar transistor (IGBT) power module has many advantages, such as large input impedance, small driving power, a simple control circuit, small switching loss, and high working frequency, so it has been widely used in power converters [1,2]. In recent years, the application of power converters has been expanding, such as in wind power generation, solar power generation, electric vehicles, and aerospace power systems [3][4][5][6], which have harsh operating conditions and strict requirements for IGBT reliability. According to the reliability survey report of the converter system, the power semiconductor device is the component with the highest failure rate in the converter system, accounting for about 34% of failures [7].
Due to the complex and changeable working conditions of the power converter, the IGBT is subjected to a large number of thermal stress, overvoltage, and overcurrent impacts in the process of operation [8,9]. Bond wire aging and solder layer aging are the two most common fatigue failure types of IGBT modules. On account of the different coefficients of thermal expansion (CTE) of the module materials, the thermal stress of the internal structure is uneven under temperature fluctuations, which eventually leads to damage to the bond wires and the solder layer [10][11][12]. The IGBT module can continue to operate for a period of time before complete failure. Therefore, if potential variations due to aging can be detected before complete failure, catastrophic failure can be avoided. In practical applications, the fatigue failure of IGBT modules is mostly manifested as the bond wires completely lift off [13,14]. IGBT bonding wire aging monitoring is very necessary to improve the reliability of the converter, which is also the focus of this paper. Owing to the hindrance of the package structure of the IGBT module, it is difficult to directly monitor the aging process of bond wires. When the bond wire is broken, the equivalent parameters of the emitter area will change so that the external electrical parameters of the 1.
Current-based parameter: short-circuit current (I s ). In [15], the authors took the I s as the monitoring parameter for bond wire aging. When the number of broken bond wires in the IGBT module gradually increases, the I s will decrease accordingly. However, this method needs to inject current into the IGBT module, which is not suitable for online monitoring application scenarios.

2.
Time-based parameter: turn-on time (t on ) and turn-off time (t off ). The authors in [16,17] calculated t on by measuring the current and voltage waveforms during IGBT turn-on and monitor bond wire failures accordingly. The experimental results show that the t on under the bond wire failure was shorter than that under the healthy state. In [18], the charging time of the gate capacitance was measured by injecting a small current during the IGBT turn-off period to monitor the health status of the bond wires. Since the switching time of the IGBT was in the range of 10-500 ns, the time-based parameters had extremely high requirements for the hardware measurement circuit.

3.
Voltage-based parameter: gate voltage (V g ) and collector-emitter on-state voltage (V ce_on ). In [19], the V ge was used to monitor the multi-chip parallel IGBT modules' health status. The experimental results showed that this method would not be affected by load current changes or noise caused by switching. However, only when all bond wires of a specific IGBT chip were broken did the V ge change significantly. The application of this method was limited to multi-chip parallel IGBT modules, which are not universal. The authors of [20,21] cut the bond wire to simulate IGBT aging and monitor the IGBT health status by measuring V ce_on online. The results indicated that V ce_on could accurately identify the number of broken bond wires.

4.
Temperature-based parameter: junction temperature (T j ) and thermal resistance (R th ). In [22], the case temperature (T c ) and junction temperature (T j ) were observed by thermocouples to calculate the R th . When the R th increased by 20%, the IGBT module failed. However, this method needs to invade the IGBT module package for measurement, which is not conducive to online monitoring. In [23], T j was obtained by measuring the linear relationship between V ce_on and T j , whereas in [24], T j was calculated by the turn-off overshoot voltage. It is worth noting that T j cannot directly reflect the aging state of the IGBT, but it has a close coupling relationship with other parameters, which are called thermosensitive electrical parameters (TSEPs) [25,26]. Almost all the above monitoring parameters for bond wire are TSEPs.
Considering online monitoring capabilities, hardware cost, and measurement accuracy, V ce_on is most suitable for monitoring the aging state of bond wires [27]. Although V ce_on is very suitable as the IGBT monitoring parameter, the voltage between the collector and the emitter can be hundreds of times different when the IGBT is turned on and off at high speed, making it difficult to sample V ce_on online and accurately. In [28], a sampling circuit based on the IGBT, current source, and voltage source is proposed. By modifying the converter's PWM control signal, different currents are injected into the converter during the window period to obtain V ce_on . Although this sampling circuit can realize the online monitoring of the IGBT, it has a significant influence on the converter's working state. In [29], a sampling circuit based on the current source, diode, and MOSFET is proposed which indirectly measures V ce_on by measuring the voltage at the test point. When the IGBT is on, the test point voltage is the sum of the diode conduction voltage drop, the resistance voltage drop, and the V ce_on . When the IGBT is off, the MOSFET is turned on to shield the high voltage between the collector and the emitter. This sampling circuit also needs to inject current into the test circuit and indirectly measure the V ce_on . All in all, the existing V ce_on sampling circuit needs to inject current into the converter or modify the control signal, which will not affect the working state of the converter to varying degrees.
While V ce_on has a strong correlation with bond wire aging, it also has a coupling relationship with T j . During the operation of the photovoltaic, wind power, and new energy vehicles, T j of the IGBT module changes all the time, which will interfere with the judgment of the bond wires' aging state. The existing method eliminates the interference of T j by injecting current into the IGBT module [23,30], which will not be suitable for online monitoring. The authors of [31] calculated the equivalent resistance at the bonding area based on the offline measurement of V ce_on and evaluated the health status of the independent IGBT module accordingly. Although this method considers the influence of T j , it belongs to the field of IGBT offline reliability evaluation and does not provide a solution for online monitoring under actual working conditions. In general, the existing online monitoring methods are difficult for effectively eliminating the interference of T j . Motivated by the analysis described above, based on the voltage and current sampling circuit, this paper proposes an online monitoring method for the IGBT bond wire against T j interference. The method proposed in this paper can non-intrusively monitor IGBT modules online, which can reduce unnecessary downtime for maintenance. The innovation of the sampling circuit is that it can obtain the full-period waveform of V ce_on varying with the collector current (I c ) during the modulation period. The circuit cleverly utilizes the current flowing through the IGBT and the corresponding turn-on voltage drop during the IGBT working process, and it does not need to inject additional current into the circuit or modify the control signal to collect aging parameters. It obtains the intersection collector current (I int ) such that V ce_on is not disturbed by T j via the IGBT bond wire aging model and datasheet. Then, it compares the real-time sampling waveforms of I c and V ce_on to obtain the collector-emitter on-state voltage corresponding to I int (V ce_int ). Finally, the bond wire aging state can be judged based on V ce_int , which is not interfered with by T j . This paper is organized as follows. Section 2 establishes the aging model of the IGBT bond wire and selects the V ce_int value as the aging parameter in combination with the datasheet. Section 3 illustrates the working principle of the sampling circuit and introduces the online monitoring process based on the sampling waveform. Section 4 takes a threephase inverter as an example for experimental verification and uses the method proposed in this paper to monitor the bond wire aging under the interference of DC voltage and T j . Section 5 draws the conclusions.

Bond Wire Aging Mechanism
The basic internal structure of the IGBT module is shown in Figure 1a. To meet the rated current requirements and improve the performance, the IGBT module is usually composed of multiple IGBT chips in parallel, in which the emitter and gate of the chip and the corresponding terminals need to be connected via bond wires. Due to the large CTE difference between aluminum and silicon materials, the thermal stress on the chip and the bond wire under the action of the temperature field is inconsistent, causing shear stress at the bonding area of the bond wire and the chip [32], which can be expressed as where α 1 and α 2 are the CTE of the bond wire and the silicon chip, ∆T represents the temperature fluctuation, and L is the length of the bonding area between the bond wire and the silicon chip.
In the actual working process of the IGBT, the continuous thermal stress impact makes the bonding area age, and the specific manifestation is the bond wire's lift-off. As long as one of the bond wires in the IGBT module breaks first, the current passing through the remaining bond wires will increase and bear greater thermal stress impact, which will accelerate the failure of the IGBT device. Therefore, bond wire lift-off is one of the main modes of IGBT failure in practical engineering applications. In the actual working process of the IGBT, the continuous thermal stress impact makes the bonding area age, and the specific manifestation is the bond wire's lift-off. As long as one of the bond wires in the IGBT module breaks first, the current passing through the remaining bond wires will increase and bear greater thermal stress impact, which will accelerate the failure of the IGBT device. Therefore, bond wire lift-off is one of the main modes of IGBT failure in practical engineering applications.

Bond Wire Aging Model
Since the Vce_on of the IGBT module is affected by both aging and Tj, it is necessary to exclude the influence of Tj on the Vce_on to accurately reflect the bond wire aging. In the actual operation of converters, it is difficult to accurately control and measure the internal Tj of the IGBT module, which makes it harder to determine whether the variation in the Vce_on is caused by Tj or aging.
Taking the FF50R12RT4 half-bridge module as an example, the IGBT and diode in the module both contain six bond wires, as shown in Figure 1b. Vce_on is affected by Tj and Ic in a healthy state [28], as shown in Equation (2): where V0 and R0 are the on-state voltage and on-state resistance of the IGBT at the reference junction temperature Tj0, respectively, and k1 and k2 are the temperature coefficients of V0 and R0, respectively. When the IGBT bond wires are broken due to thermal stress impact, R0 will change, which will affect Vce_on. The equation of Vce_on under the bond wire aging is as follows: where ∆R represents the variation in the on-state resistance of the IGBT caused by the broken bond wire and k1·(Tj − Tj0) is inversely proportional to (Tj − Tj0), whereas [R0 + ∆R + k2·(Tj − Tj0)]·Ic is directly proportional to (Tj − Tj0). The contribution of the former is negative, while the contribution of the latter is positive. There is a value Iint, where Vce_on is not affected by the Tj. When Ic = Iint, Vce_on at this time is called Vce_int, as shown in Equation (4), where k1·(Tj − Tj0) and k2·(Tj − Tj0)·Ic cancel each other out and Vce_int is only affected by (R0 + ∆R)·Ic:

Bond Wire Aging Model
Since the V ce_on of the IGBT module is affected by both aging and T j , it is necessary to exclude the influence of T j on the V ce_on to accurately reflect the bond wire aging. In the actual operation of converters, it is difficult to accurately control and measure the internal T j of the IGBT module, which makes it harder to determine whether the variation in the V ce_on is caused by T j or aging.
Taking the FF50R12RT4 half-bridge module as an example, the IGBT and diode in the module both contain six bond wires, as shown in Figure 1b. V ce_on is affected by T j and I c in a healthy state [28], as shown in Equation (2): where V 0 and R 0 are the on-state voltage and on-state resistance of the IGBT at the reference junction temperature T j0 , respectively, and k 1 and k 2 are the temperature coefficients of V 0 and R 0 , respectively. When the IGBT bond wires are broken due to thermal stress impact, R 0 will change, which will affect V ce_on . The equation of V ce_on under the bond wire aging is as follows: where ∆R represents the variation in the on-state resistance of the IGBT caused by the broken bond wire and The contribution of the former is negative, while the contribution of the latter is positive. There is a value I int , where V ce_on is not affected by the T j . When I c = I int , V ce_on at this time is called V ce_int , as shown in Equation (4), where k 1 ·(T j − T j0 ) and k 2 ·(T j − T j0 )·I c cancel each other out and V ce_int is only affected by (R 0 + ∆R)·I c : Therefore, V ce_int can accurately reflect the voltage drop change caused by the bond wire aging and is not affected by T j , which can be regarded as the monitoring parameter of bond wire aging.
Referring to the datasheet of the FF50R12RT4 IGBT module, the typical values of I int and V ce_int can be obtained according to their output characteristic curves, as shown in Figure 2. When T j is 25 • C, 125 • C or 150 • C, the output characteristic curve of the IGBT module will have an intersection where I int = 12 A and V ce_int = 1.05 V. When I c = I int , V ce_int is not affected by T j , which is consistent with the previous discussion.
Referring to the datasheet of the FF50R12RT4 IGBT module, the typical values of Iint and Vce_int can be obtained according to their output characteristic curves, as shown in Figure 2. When Tj is 25 °C, 125 °C or 150 °C, the output characteristic curve of the IGBT module will have an intersection where Iint = 12 A and Vce_int = 1.05 V. When Ic = Iint, Vce_int is not affected by Tj, which is consistent with the previous discussion.

Online Monitoring of IGBT Bond Wire Aging
In this paper, a three-phase inverter is taken as an example to illustrate the working principle of the proposed anti-interference online monitoring method for bond wire aging. It will be explained in two parts: the sampling circuit and online monitoring.

Sampling Circuit
Although Vce_on is very suitable as an IGBT aging parameter, the voltage between the collector and the emitter can be hundreds of times different when the IGBT is turned on and off at a high speed, making it difficult to sample Vce_on online and accurately. The Vce_on sampling circuit utilized in this paper was implemented in three steps: clamping, filtering, and amplifying, as presented in Figure 3. Clamping refers to the high-voltage shielding between the collector and emitter during the turn-off period of the IGBT via the switching of two MOSFETs (M1 and M2). Take the U-phase upper leg IGBT (S1) as an example to explain the working principle. When S1 is turned on, M1 is turned on so that the voltage sampling channel is turned on, thereby sampling Vce_on. When S1 is turned off, M2 is turned on, so the voltage sampling channel is clamped to the ground potential, thereby shielding the high voltage between collector and emitter. The specific control diagram is shown in Table 1.

Online Monitoring of IGBT Bond Wire Aging
In this paper, a three-phase inverter is taken as an example to illustrate the working principle of the proposed anti-interference online monitoring method for bond wire aging. It will be explained in two parts: the sampling circuit and online monitoring.

Sampling Circuit
Although V ce_on is very suitable as an IGBT aging parameter, the voltage between the collector and the emitter can be hundreds of times different when the IGBT is turned on and off at a high speed, making it difficult to sample V ce_on online and accurately. The V ce_on sampling circuit utilized in this paper was implemented in three steps: clamping, filtering, and amplifying, as presented in Figure 3. Clamping refers to the high-voltage shielding between the collector and emitter during the turn-off period of the IGBT via the switching of two MOSFETs (M 1 and M 2 ). Take the U-phase upper leg IGBT (S1) as an example to explain the working principle. When S1 is turned on, M 1 is turned on so that the voltage sampling channel is turned on, thereby sampling V ce_on . When S1 is turned off, M 2 is turned on, so the voltage sampling channel is clamped to the ground potential, thereby shielding the high voltage between collector and emitter. The specific control diagram is shown in Table 1.  Filtering is related to eliminating the noise contained in the waveform obtained after clamping by a second-order RC circuit, but it also produces a certain degree of attenuation. Amplification refers to the use of an operational amplifier to compensate for the waveform attenuation caused by the filter part, which ensures the accuracy of the sampled waveform. As for the current sampling part, Hall current sensors are used for synchronous sampling. The voltage and current waveforms obtained by the sampling circuit are presented in Figure 3. By comparing the waveforms, Iint and Vint can be further collected to prepare for condition monitoring.

Online Monitoring
Based on the above sampling circuit, this paper proposes an online monitoring method for IGBT bond wire aging, as illustrated in Figure 4. First, the voltage and current sampling circuits are used to collect the Vce_on and Ic waveforms of the three-phase inverter system in real time. Second, considering the impact of fluctuations on the DC side or the load side on Ic, the amplitude of Ic is compared with that of Iint. Only when the amplitude of Ic is greater than Iint is the corresponding Vce_int sampling performed. Then, Vce_int is compared with the aging threshold to judge the aging state of the bond wires. Finally, when the aging state reaches the failure threshold set in advance, a failure warning is triggered to the control system. The measurement of the aging threshold will be described in detail in the next section. Filtering is related to eliminating the noise contained in the waveform obtained after clamping by a second-order RC circuit, but it also produces a certain degree of attenuation. Amplification refers to the use of an operational amplifier to compensate for the waveform attenuation caused by the filter part, which ensures the accuracy of the sampled waveform. As for the current sampling part, Hall current sensors are used for synchronous sampling. The voltage and current waveforms obtained by the sampling circuit are presented in Figure 3. By comparing the waveforms, I int and V int can be further collected to prepare for condition monitoring.

Online Monitoring
Based on the above sampling circuit, this paper proposes an online monitoring method for IGBT bond wire aging, as illustrated in Figure 4. First, the voltage and current sampling circuits are used to collect the V ce_on and I c waveforms of the three-phase inverter system in real time. Second, considering the impact of fluctuations on the DC side or the load side on I c , the amplitude of I c is compared with that of I int . Only when the amplitude of I c is greater than I int is the corresponding V ce_int sampling performed. Then, V ce_int is compared with the aging threshold to judge the aging state of the bond wires. Finally, when the aging state reaches the failure threshold set in advance, a failure warning is triggered to the control system. The measurement of the aging threshold will be described in detail in the next section.

Experiment and Result Analysis
In order to verify the effectiveness of the method proposed in this paper, an experimental platform for aging monitoring was built as presented in Figure 5, which included the DC power supply, three-phase inverter circuit, sampling circuit, thermostat, IR thermal imager, and control unit. The experimental parameter settings are listed in Table 2. It is worth noting that the voltage and current signals collected in this paper were input into RT-LAB for high-precision A/D conversion.

Experiment and Result Analysis
In order to verify the effectiveness of the method proposed in this paper, an experimental platform for aging monitoring was built as presented in Figure 5, which included the DC power supply, three-phase inverter circuit, sampling circuit, thermostat, IR thermal imager, and control unit. The experimental parameter settings are listed in Table 2. It is worth noting that the voltage and current signals collected in this paper were input into RT-LAB for high-precision A/D conversion. In order to verify the effectiveness of the method proposed in this paper, an experimental platform for aging monitoring was built as presented in Figure 5, which included the DC power supply, three-phase inverter circuit, sampling circuit, thermostat, IR thermal imager, and control unit. The experimental parameter settings are listed in Table 2. It is worth noting that the voltage and current signals collected in this paper were input into RT-LAB for high-precision A/D conversion.

Sampling under DC Voltage Fluctuations
In the actual working process of the inverter, it will be subjected to electrical disturbances on the load or DC voltage side, which will cause I c fluctuations. In order to prove that the sampling circuit could still maintain excellent working performance under this disturbance, this paper carried out relevant sampling under the condition of DC voltage fluctuation, as shown in Figure 6. It could be found that the V ce_on waveform could follow the fluctuation of I c , which indicates that the sampling circuit had good anti-interference performance. The red dotted line marks I int and its corresponding V int , which are the basis for subsequent condition monitoring.
In the case of T j = 25 • C, V ce_int was selected when the IGBT was fully healthy (V ce_int0 ) as the healthy reference value. When 1-4 bond wires were broken (see Figure 7), the corresponding V ce_int was sampled, and Equation (5) was used to calculate the deviation percentage of each aging stage (∆V ce_int ), which was regarded as the aging indicator, as listed in Table 2. For subsequent comparison, this paper also measured the V ce_on amplitude voltage (V ce_f0 ) in the healthy state and calculated the deviation percentage of each aging stage (∆V ce_f ) according to Equation (6), as listed in Table 3. The two dashed lines marked in Figure 7 are the health reference values. After measurement, V ce_int0 and V ce_f0 could be obtained as 1.05 V and 1.32 V, respectively: >4.90% >4.86% V disturbance, this paper carried out relevant sampling under the condition of DC voltage fluctuation, as shown in Figure 6. It could be found that the Vce_on waveform could follow the fluctuation of Ic, which indicates that the sampling circuit had good anti-interference performance. The red dotted line marks Iint and its corresponding Vint, which are the basis for subsequent condition monitoring.  In the case of Tj = 25 °C, Vce_int was selected when the IGBT was fully healthy (Vce_int0) as the healthy reference value. When 1-4 bond wires were broken (see Figure 7), the corresponding Vce_int was sampled, and Equation (5) was used to calculate the deviation percentage of each aging stage (∆Vce_int), which was regarded as the aging indicator, as listed in Table 2. For subsequent comparison, this paper also measured the Vce_on amplitude voltage (Vce_f0) in the healthy state and calculated the deviation percentage of each aging stage (∆Vce_f) according to Equation (6), as listed in Table 3. The two dashed lines marked in Figure 7 are the health reference values. After measurement, Vce_int0 and Vce_f0 could be obtained as 1.05 V and 1.32 V, respectively:

Junction Temperature Interference
Taking three bond wires' lift-off as an example to illustrate the interference of T j , the T j of S1 was stabilized at 25 • C, 50 • C, 75 • C, and 100 • C by adjusting the thermostat to simulate T j fluctuations. In the above four cases, the V ce_on waveform is shown in Figure 8. It can be found that the waveform near V ce_int was not affected by T j . V ce_int did not deviate with the increase in T j and was basically stable at 1.05 V, which could accurately reflect the aging state of the bond wires. In addition, the waveform near V ce_f was most disturbed by T j . V ce_f had a significant deviation as V ce_f increased, and the maximum deviation reached 0.11 V. In summary, selecting V int as the aging indicator could achieve resistance to the interference of T j .

Junction Temperature Interference
Taking three bond wires' lift-off as an example to illustrate the interference of Tj, the Tj of S1 was stabilized at 25 °C, 50 °C, 75 °C, and 100 °C by adjusting the thermostat to simulate Tj fluctuations. In the above four cases, the Vce_on waveform is shown in Figure 8. It can be found that the waveform near Vce_int was not affected by Tj. Vce_int did not deviate with the increase in Tj and was basically stable at 1.05 V, which could accurately reflect the aging state of the bond wires. In addition, the waveform near Vce_f was most disturbed by Tj. Vce_f had a significant deviation as Vce_f increased, and the maximum deviation reached 0.11 V. In summary, selecting Vint as the aging indicator could achieve resistance to the interference of Tj.

Aging Monitoring Results
In order to show that the monitoring method proposed in this paper could eliminate the interference of Tj, in the case of Tj = 75 °C, the sampling circuit was used to measure Vce_on under different bond wire aging stages, as shown in Figure 9. Using Equations (5) and (6), the aging index of each aging stage was calculated. The aging indicators with the previously determined aging threshold (see Table 3) were compared to judge the current aging state, as shown in Table 4.

Aging Monitoring Results
In order to show that the monitoring method proposed in this paper could eliminate the interference of T j , in the case of T j = 75 • C, the sampling circuit was used to measure V ce_on under different bond wire aging stages, as shown in Figure 9. Using Equations (5) and (6), the aging index of each aging stage was calculated. The aging indicators with the previously determined aging threshold (see Table 3) were compared to judge the current aging state, as shown in Table 4.  When Tj rose from 25 °C to 75 °C, Vce_int had a slight deviation compared with Vce_int0, but ∆Vce_int could still accurately reflect the current aging state. On the contrary, Vce_f had a large deviation compared with Vce_f0, and ∆Vce_f was far away from the current aging state. For example, when the IGBT was in aging stage II, ∆Vce_int was 0.86%, which was judged as aging state I according to the aging thresholds. However, ∆Vce_f was 6.21%, which was misjudged as aging stage V.
In order to compare the aging monitoring results more intuitively, different color blocks in Figure 10 are used to indicate the different aging stages. It can be clearly seen that the monitoring results based on ∆Vce_int could accurately distinguish each aging stage, while the monitoring results based on ∆Vce_f deviated far from the actual situation. In general, Vce_int had good resistance to the interference of Tj. For this three-phase inverter system, when the monitoring circuit detected that the aging indicator exceeded 4.90%, the aging state of the IGBT bond wire was judged as stage V. At this time, a shutdown maintenance signal was triggered in the control system.  When T j rose from 25 • C to 75 • C, V ce_int had a slight deviation compared with V ce_int0 , but ∆V ce_int could still accurately reflect the current aging state. On the contrary, V ce_f had a large deviation compared with V ce_f0 , and ∆V ce_f was far away from the current aging state. For example, when the IGBT was in aging stage II, ∆V ce_int was 0.86%, which was judged as aging state I according to the aging thresholds. However, ∆V ce_f was 6.21%, which was misjudged as aging stage V.
In order to compare the aging monitoring results more intuitively, different color blocks in Figure 10 are used to indicate the different aging stages. It can be clearly seen that the monitoring results based on ∆V ce_int could accurately distinguish each aging stage, while the monitoring results based on ∆V ce_f deviated far from the actual situation. In general, V ce_int had good resistance to the interference of T j . For this three-phase inverter system, when the monitoring circuit detected that the aging indicator exceeded 4.90%, the aging state of the IGBT bond wire was judged as stage V. At this time, a shutdown maintenance signal was triggered in the control system. Electronics 2021, 10, x FOR PEER REVIEW 12 of 14 Figure 10. Comparison of aging monitoring results.

Conclusions
The aging parameter Vce_int, which is not affected by Tj, is obtained by combining the IGBT aging model and the datasheet. Moreover, Vce_int t is collected in real time to judge the aging state of the IGBT bond wire by comparing the Ic and Vce_on waveforms. Different from the existing method, this method cleverly utilizes the current flowing through the IGBT and the corresponding turn-on voltage drop during the IGBT working process, and it does not need to inject additional current into the circuit or modify the control signal to collect the aging parameters. In addition, the anti-interference online monitoring method proposed in this paper can reduce downtime for maintenance.
The experimental results prove that the method proposed in this paper can judge the aging state of the IGBT bond wire in the three-phase inverter under the condition of DC voltage disturbance and junction temperature disturbance. It is worth noting that this paper only introduced this method's application in a three-phase inverter system, and it also applies to other power electronic converters.