IEEJ Journal of Industry Applications
Vol.12 No.3 pp.392–400
DOI: 10.1541/ieejjia.22007728

Paper

Estimation of Both Junction Temperature and Load Current of IGBTs
from Output Voltage of Gate Driver
Hiromu Yamasaki∗ Non-member, Katsuhiro Hata∗a)
Makoto Takamiya∗ Member

Member(Manuscript received July 27, 2022, revised Nov. 7, 2022)
J-STAGE Advance published date : Dec. 30, 2022

For the online condition monitoring of IGBTs, a new estimation method of both the junction temperature (T J ) andthe load current (IL ) of IGBTs using a momentary high-Z gate driving (MHZGD) from the output voltage (VOUT ) of thegate driver is proposed, which can be integrated into the gate driver ICs. T J is estimated from VOUT diﬀerence during
and after the MHZGD period, and IL is estimated from VOUT during MHZGD. In the 110 switching measurements at
11 diﬀerent T J ’s from 25◦ C to 125◦ C and 10 diﬀerent IL ’s from 12.5 A to 80 A for each of the three IGBTs, T J andIL estimation errors in a low test cost parameter determination method are +4.9◦ C/−8.4◦ C and +1.1 A/−4.3 A, respectively. In contrast, T J and IL estimation errors in a parameter determination method with small error are +4.9◦ C/−8.1◦ C
and +1.0 A/−1.8 A, respectively.
Keywords: digital gate driver, IGBT, junction temperature, load current, estimation

1.

Introduction

2.

In order to achieve reliable power electronics systems, online condition monitoring for power devices is required to
predict power device failures. The development goals of theonline condition monitoring in this paper include: (a) estimation of both the junction temperature (T J ) and the load current(IL ) without using temperature sensors and current sensors,
because T J and IL are important parameters that determine
the reliability of power devices; and (b) measurement fromthe gate terminal of a power device that can be integrated
into gate driver ICs. Many papers have been published on
the estimation of T J and/or IL (1)–(16) , however, there have beenno papers achieving the two development goals. In Ref. (7),only IL is estimated using a momentary high-Z gate driving(MHZGD) and it is necessary to give T J as a known value forIL estimation. To solve the problems, in this paper, a new estimation method of both T J and IL of IGBTs using MHZGD
from the output voltage (VOUT ) of the gate driver is proposed.
The purpose of this paper is to achieve low cost by eliminating the temperature sensors and current sensors to measure
T J and IL and substituting the sensors with the proposed T J
and IL estimation method using VOUT measurement.

Measurement of ΔV and VOUT,MHZ Using
MHZGD

2.1 Momentary High-Z Gate Driving (MHZGD) to
Estimate TJ and IL
Fig. 1 shows a circuit schematic of agate driver and an IGBT. The target of this work is to estimate
both T J and IL from VOUT , where IC is the collector current,
which matches IL in the steady state when the IGBT is turned
on. Fig. 2 shows waveforms of a conventional gate driving
and MHZGD (7) at turn-oﬀ of IGBT. In the conventional gate
driving shown in Fig. 2(a), VOUT at the Miller plateau is notequal to the internal gate-emitter voltage (VGE,INT ) due to IG(RG,INT + RG,EXT ) drop, where IG is the gate driving current,
RG,INT is the internal gate resistance of IGBT, and RG,EXT isthe external gate resistance. The constant IG flows until thegate capacitance is fully charged as shown in Fig. 2, because
a constant current-source based gate driver instead of a constant voltage-source based gate driver is used in this paper.
In MHZGD (7) shown in Fig. 2(b), the period from the start ofThis paper was presented at IPEC-Himeji 2022, copyrighted by
IEEJ (18) .
a) Correspondence to: Katsuhiro Hata. E-mail: khata@iis.u-tokyo.
ac.jp∗
The University of Tokyo
4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japanc 2023 The Institute of Electrical Engineers of Japan.
Fig. 1. Circuit schematic of gate driver and IGBT
392

Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）Fig. 4. Measured waveforms at T J = 25◦ C and IL =80 A during turn-oﬀ
Fig. 2. Waveforms at turn-oﬀ. (a) Conventional gate
driving. (b) MHZGD (7)Fig. 3. Measurement setup of double pulse test

Fig. 5. Measured VOUT waveforms of T J = 25◦ C and125◦ C at IL = 12.5 A

turn-oﬀ to the end of the Miller plateau is divided into threeparts and defined as t1 , t2 , and t3 . t2 and t3 must be during
the Miller plateau period. In MHZGD, IG is zero during t2 .
In this work, the zero IG is achieved using the digital gate
driver (DGD) (17) . During t2 , VOUT is equal to VGE,INT becauseof zero IG , and this VOUT is defined as VOUT,MHZ . VOUT during t3 is defined as VOUT,CONV , and the diﬀerence between
VOUT,MHZ and VOUT,CONV is defined as ΔV, where ΔV = |IG |(RG,INT + RG,EXT ). Assuming that IG is constant in this paper
because of the constant current-source based DGD (17) , ΔV islinearly dependent on T J , because RG,INT is linearly dependent on T J (1) . Therefore, in this paper, T J is estimated from
ΔV, while IL is estimated from VOUT,MHZ . The principle ofestimating IL from VOUT,MHZ is the same as Ref. (7), while T J
is not estimated and must be known in advance in Ref. (7).
2.2 Measurement Setup
Fig. 3 shows the photo of
the measurement setup of the double pulse test of IGBT module (2MBI100VA-060-50, 600 V, 100 A) at 300 V for the estimation of T J and IL . The DGD IC (17) drives the low side of
the IGBT module. T J is assumed to be equal to the hot plate
temperature. RG,EXT is zero. In this paper, after the switchingmeasurements are performed under 110 diﬀerent conditions
with 11 diﬀerent T J ’s from 25◦ C to 125◦ C in 10◦ C steps and
10 diﬀerent IL ’s from 12.5 A to 80 A in 7.5 A steps for each of
the three IGBTs and VOUT waveform data are saved, the estimations of T J and IL from ΔV and VOUT,MHZ are done. VOUT
waveforms are measured using the diﬀerential probe and ΔV

and VOUT,MHZ are extracted from the VOUT waveforms. In the
future, the measurement of ΔV and VOUT,MHZ can be donewith an A/D converter, which can be integrated on DGD IC.
2.3 Measurement of ΔV and VOUT,MHZ
Fig. 4shows the measured waveforms at T J = 25◦ C and IL = 80 A
during the turn-oﬀ of IGBT. In this paper, t2 is fixed to
2 μs. ΔV and VOUT,MHZ generated by MHZGD are clearlyobserved. In this measurement, t2 is set as long as 2 μs toease the measurement of ΔV and VOUT,MHZ . The long t2 ,however, increases the turn-oﬀ delay and will degrade thecontrol performance of the inverter. In practice, therefore, t2
should be set to the minimum necessary value at which ΔV
and VOUT,MHZ can be measured. Please note that MHZGD has
no eﬀect on the switching loss and VCE overshoot. In this paper, to verify the principle of the proposed estimation method,
ΔV and VOUT,MHZ are measured with a slower turn-oﬀ thanthe data sheet indicated. Specifically, the turn-oﬀ time in thedata sheet of the IGBT is 600 ns, while the measured turnoﬀ time in Fig. 4 is 5.9 μs including 2 μs to achieve the proposed MHZGD. The slow turn-oﬀ is achieved by adjusting
IG of DGD (17) . In practice, the turn-oﬀ should be done following the data sheet, because the slow turn-oﬀ increases theswitching loss. The proposed T J and IL estimation method is
independent of the turn-oﬀ speed. Fig. 5 shows the measured
VOUT waveforms of T J = 25◦ C and 125◦ C at IL = 12.5 A.
With increasing T J , VOUT,MHZ is reduced, because the threshold voltage of IGBT is reduced. Fig. 6 shows the measured
393

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Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）Fig. 6. Measured VOUT waveforms of IL = 12.5 A to80 A at T J = 25◦ C
Fig. 8. Overview of proposed T J and IL estimation fromΔV and VOUT,MHZ

Fig. 7. Measured VOUT,CONV and VOUT,MHZ under 60 different conditions with 6 diﬀerent T J ’s and 10 diﬀerent IL ’s

VOUT waveforms of IL = 12.5 A to 80 A at T J = 25◦ C.
VOUT,MHZ increases with increasing IL . Fig. 7 shows the overall view of measured VOUT,CONV and VOUT,MHZ under 60 different conditions with 6 diﬀerent T J ’s ranging from 25◦ C to125◦ C and 10 diﬀerent IL ’s ranging from 12.5 A to 80 A. ΔV
is the diﬀerence between VOUT,MHZ and VOUT,CONV . In thenext chapter, the methods for estimating T J and IL from ΔV
and VOUT,MHZ , respectively, will be explained.
3.

Fig. 9. Two parameter determination methods compared in this paper. (a) Low test cost method. (b) Methodwith small error

TJ and IL Estimations from ΔV and VOUT,MHZ

3.1 Overview of Proposed TJ and IL Estimation

methods, calibration measurements are required for each
IGBT to compensate for variations in characteristics such as
the threshold voltage for each IGBT. Fig. 9(a) shows a low
test cost method, where a five-point calibration is performed
for the first IGBT (IGBT1), and a one-point calibration is
performed for the second and subsequent IGBTs (IGBT2 and
IGBT3). The details of the five-point and the one-point calibrations will be explained later. Fig.9 (b) shows a methodwith small error, where a five-point calibration is performed
for all IGBTs. The two methods have a trade-oﬀ in terms of
the estimation error and the test cost for the calibrations. The
low test cost method has the disadvantage of large estimation
error, while the method with small error has the disadvantage
of high test cost.
Fig. 10(a) shows the steps for the five-point calibration tofind the values of seven parameters shown in Fig. 8. In Step

Fig. 8 shows an overview of the proposed T J and IL estimation from ΔV and VOUT,MHZ . When the measured ΔV and
VOUT,MHZ are given, T J is estimated using Eq. (1) and IL is estimated using Eqs. (2) to (4), where k(T J ) is the T J -dependent
constant, VTH (T J ) is the T J -dependent threshold voltage of
IGBT, T R is the room temperature (25◦ C) whose unit is absolute temperature, k(T R ) is k(T J ) at T J = T R , VTH (T R ) is
VTH (T J ) at T J = T R , and a, b, α, β, and γ are constants. Comparing Ref. (7) with this paper, Eqs. (2) to (4) are identical toRef. (7), and only Eq. (1) is newly added in this paper. The
values of seven parameters (a, b, α, β, γ, k(T R ), and VTH (T R ))are determined by the calibration measurements.
3.2 Parameter Determination Methods for TJ and IL
Estimation
Fig. 9 shows two parameter determination
methods for multiple IGBTs compared in this paper. In both
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Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）

(a)

(b)

Fig. 10. Steps for calibrations. (a) Five-point calibration. (b) One-point calibration

1, VOUT waveforms under five conditions at (T J , IL ) = (25◦ C,
12.5 A), (25◦ C, 42.5 A), (25◦ C, 80 A), (125◦ C, 12.5 A), and(125◦ C, 80 A) are measured. In Step 2, two ΔV’s are extracted from VOUT waveforms at (T J , IL ) = (25◦ C, 12.5 A)
and (125◦ C, 12.5 A). In Step 3, a and b in Eq. (1) are determined by the curve fitting as shown in Fig. 11(a). In Step 4,
three VOUT,MHZ ’s are extracted from VOUT waveforms at (T J ,IL ) = (25◦ C, 12.5 A), (25◦ C, 42.5 A), and (25◦ C, 80 A). In
Step 5, k(T R ), VTH (T R ), and α in Eqs. (2) to (4) are determined by the curve fitting as shown in Fig. 11(b). In Step 6,
two VOUT,MHZ ’s are extracted from VOUT waveforms at (T J ,IL ) = (125◦ C, 12.5 A) and (125◦ C, 80 A). In Step 7, k(T J =125◦ C) and VTH (T J = 125◦ C) in Eqs. (3) to (4) are determinedby the curve fitting as shown in Fig. 11(c). In Step 8, β andγ are determined by Eqs. (3) and (4) as shown in Figs. 11(d)and (e), respectively, which completes the five-point calibration.
Fig. 10(b) shows the steps for the one-point calibration tofind the values of two parameters (b and VTH (T R )). In the
one-point calibration, five parameters (a, α, β, γ, and k(T R ))of IGBT1 are reused to other IGBTs to reduce the test cost.
The intention of the one-point calibration is to express thevariation of each IGBT in terms of b and VTH (T R ). In Step 1,
a VOUT waveform at (T J , IL ) = (25◦ C, 12.5 A) is measured. In
Step 2, b and VTH (T R ) in Eqs. (1) and (4) are determined by
the curve fitting.
Tables 1(a) and (b) show the measured conditions and thecalibrated parameters obtained by the low test cost method(Fig. 9(a)) and the method with small error (Fig. 9(b)), respectively, for three IGBTs (IGBT1 to IGBT3). In the low
test cost method (Table 1(a)), the five parameters (a, α, β,γ, and k(T R )) of IGBT1 are reused to IGBT2 and IGBT3 toreduce the test cost. As shown in Tables 1(a) and (b), the calibrated parameters of the three IGBTs are obviously diﬀerent,
therefore calibration for each IGBT is mandatory to compensate for the variations in characteristics for each IGBT.
3.3 TJ and IL Estimation Results
As shown in
Fig. 9, Figs. 12 to 16 show T J and IL estimation results in
IGBT1 to IGBT3. Figs. 12 to 14 show T J and IL estimation
results using the low test cost method, while Figs. 12, 15, and16 show T J and IL estimation results using the method withsmall error. Fig. 12 shows the results of IGBT1 using the five-Fig. 11. Example of parameter determination in IGBT1.
(a) Step 3 in Fig. 10(a). (b) Step 5 in Fig. 10(a). (c) Step 7
in Fig. 10(a). (d) and (e) Step 8 in Fig. 10(a)395

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Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）

(a)

(a)

(b)

(b)

(c)

(c)

(d)

(d)

Fig. 12. Results of IGBT1 using five-point calibration,
which is same for both methods. (a) Measured and estimated T J dependence of ΔV at 10 diﬀerent IL ’s. (b) T J
estimation error. (c) Measured and estimated IL dependence of VOUT,MHZ at 11 diﬀerent T J ’s. (d) IL estimation
error

Fig. 13. Results of IGBT2 using one-point calibration
in low test cost method. (a) Measured and estimated T J
dependence of ΔV at 10 diﬀerent IL ’s. (b) T J estimation error. (c) Measured and estimated IL dependence of
VOUT,MHZ at 11 diﬀerent T J ’s. (d) IL estimation error

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Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）

(a)

(a)

(b)

(b)

(c)

(c)

(d)

(d)

Fig. 14. Results of IGBT3 using one-point calibration
in low test cost method. (a) Measured and estimated T J
dependence of ΔV at 10 diﬀerent IL ’s. (b) T J estimation error. (c) Measured and estimated IL dependence of
VOUT,MHZ at 11 diﬀerent T J ’s. (d) IL estimation error

Fig. 15. Results of IGBT2 using five-point calibration
in method with small error. (a) Measured and estimatedT J dependence of ΔV at 10 diﬀerent IL ’s. (b) T J estimation error. (c) Measured and estimated IL dependence of
VOUT,MHZ at 11 diﬀerent T J ’s. (d) IL estimation error

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Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）point calibration, which is the same for both methods. Fig. 13
shows the results of IGBT2 using the one-point calibration in
the low test cost method. Fig. 14 shows the results of IGBT3
using the one-point calibration in the low test cost method.
Fig. 15 shows the results of IGBT2 using the five-point calibration in the method with small error. Fig. 16 shows the results of IGBT3 using the five-point calibration in the methodwith small error.
The details of Figs. 12 to 16 are explained using Fig. 12 asa representative example. Fig. 12(a) shows the measured andestimated T J dependence of ΔV at 10 diﬀerent IL ’s. The estimated curve is calculated using Eq. (1) and Table 1(a). ΔV increases with increasing T J because of increasing RG,INT . ΔV’s
are in the range of 0.96 V to 1.10 V, which is reasonably explained by |IG |RG,INT = 108 mA × 9 Ω = 0.972 V. Fig. 12(b)shows the T J estimation error in Fig. 12(a). Please note thatT J estimation errors at (T J , IL ) = (25◦ C, 12.5 A) and (125◦ C,
12.5 A) are 0◦ C, because the calibration of a and b is doneat (T J , IL ) = (25◦ C, 12.5 A) and (125◦ C, 12.5 A). T J estimation error in the range of 25◦ C to 125◦ C and IL = 12.5 A
to 80 A is within +4.9◦ C/−6.2◦ C. Fig. 12(c) shows the measured and estimated IL dependence of VOUT,MHZ at 11 diﬀerent T J ’s. The estimated curves are calculated using Eqs. (2) to(4) and Table 1(a). Fig. 12(d) shows the IL estimation error in
Fig. 12(c). IL estimation error in the range of 12.5 A to 80 A
and T J = 25◦ C to 125◦ C is within +0.6 A/−0.7 A.
Tables 2(a) and (b) show summaries of T J and IL estimation errors in the low test cost method (Fig. 9(a)) and themethod with small error (Fig. 9(b)), respectively, for IGBT1
to IGBT3. Comparing the estimation errors using the two
methods, the T J and IL estimation errors (+4.9◦ C/−8.4◦ C
and +1.1 A/−4.3 A) of the low test cost method is larger
those (+4.9◦ C/−8.1◦ C and +1.0 A/−1.8 A) of the methodwith small error, as expected. The method with small error, however, requires five measurements at T J = 25◦ C and125◦ C for each IGBT as shown in Step 1 in Fig. 10(a), which
is not practical, because the test cost is too high. Therefore,in conclusion, the low test cost method, which requires only
one measurement at T J = 25◦ C for each IGBT as shown in
Step 1 in Fig. 10(b), is recommended in this paper.
3.4 Comparison with Previous Works
Table 3shows a comparison table of T J and/or IL estimation for thecondition monitoring. This paper is the first work to successfully estimate both T J and IL from the measured values obtained from the gate terminal. Here, improvement methods
for T J estimation errors are discussed. The principle equation for T J estimation in this paper (Eq. (1) in Fig. 8) is basedon Ref. (2). As shown in Table 3, the T J estimation estimation error in Ref. (2) is 7.5◦ C, which is comparable to the T J
estimation error (8.4◦ C and 8.1◦ C) in this paper. Two possible ways to reduce the T J estimation error are as follows.
The first is to refine the principle equation for T J estimation.
Eq. (1) in Fig. 8 is a first-order approximation of the relationship between T J and ΔV, thus a second-order or higher term
should be added. The second is to improve the accuracy of
ΔV measurement. The accuracy of ΔV measurement in thispaper is limited by the noise of the oscilloscope probe, whichshould be improved.

(a)

(b)

(c)

(d)

Fig. 16. Results of IGBT3 using five-point calibration
in method with small error. (a) Measured and estimatedT J dependence of ΔV at 10 diﬀerent IL ’s. (b) T J estimation error. (c) Measured and estimated IL dependence of
VOUT,MHZ at 11 diﬀerent T J ’s. (d) IL estimation error

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Estimation of Both Junction Temperature and Load Current of IGBTs from Output Voltage of Gate Driver（Hiromu Yamasaki et al.）Table 1. Measured conditions and calibrated parameters for three IGBTs. (a) Low test cost method. (b) Methodwith small error

(a)

(b)

Table 2. Summaries of T J and IL estimation errors. (a) Low test cost method. (b) Method with small error

(a)

(b)

+4.9◦ C/−8.4◦ C and +1.1 A/−4.3 A, respectively. In contrast,
T J and IL estimation errors in the method with small error are+4.9◦ C/−8.1◦ C and +1.0 A/−1.8 A, respectively. In this paper, the low test cost method is recommended, because thetest cost of the method with small error is too high.

Table 3. Comparison table of T J and/or IL estimation

References
(1)

(2)

4.

(3)

Conclusions

For the online condition monitoring of IGBTs, this paper
is the first work to successfully estimate both T J and IL using MHZGD from VOUT . T J is estimated from ΔV, while IL
is estimated from VOUT,MHZ . In the 110 switching measurements at 11 diﬀerent T J ’s from 25◦ C to 125◦ C and 10 different IL ’s from 12.5 A to 80 A for each of the three IGBTs,
T J and IL estimation errors in the low test cost method are

(4)

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Hiromu Yamasaki (Non-member) received the B.S. degree in mathematical engineering and information physics, and the
M.S. degree in electrical engineering both from the
University of Tokyo, Japan, in 2019 and 2021, respectively. Since 2022, he has been with the Researchand Development Division, Sony Semiconductor Solutions Corporation, Kanagawa, Japan. His current
research interests include analog/mixed- signal IC design.

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Katsuhiro Hata (Member) received the M.S. and Ph.D. degrees fromthe University of Tokyo, Japan in 2015 and 2018,
respectively. He is currently a Research Associatewith the University of Tokyo. His research interests
include hybrid DC-DC converters, digital gate driving, wireless power transfer, and e-mobility for transportation. He is a member of the Institute of Electrical and Electronics Engineers (IEEE), the Instituteof Electronics, Information and Communication Engineers (IEICE), and the Society of Automotive Engineers of Japan (JSAE).

Makoto Takamiya (Member) received the B.S., M.S., and Ph.D. degrees in electronic engineering from the University ofTokyo, Japan, in 1995, 1997, and 2000, respectively.
In 2000, he joined NEC Corporation, Japan, where he
was engaged in the circuit design of high speed digital
LSI’s. He joined University of Tokyo, Japan in 2005,
where he is now a Professor of Institute of Industrial
Science. From 2013 to 2014, he stayed at University of California, Berkeley as a visiting scholar. His
research interests include the digital gate driver andsensor ICs for power electronics and the integrated power management circuits for automotive and industrial applications. He is a member of the technical program committee of IEEE Symposium on VLSI Circuits and IEEE
Asian Solid-State Circuits Conference. He formerly served on the technicalprogram committees of IEEE International Solid-State Circuits Conference(ISSCC) from 2015 to 2020 and IEEE Custom Integrated Circuits Conference from 2006 to 2011. He was a Far East Regional Chair in ISSCC 2020.
He was a Distinguished Lecturer of IEEE Solid-State Circuits Society from2019 to 2020. He received 2009 and 2010 IEEE Paul Rappaport Awards andthe best paper award in 2013 IEEE Wireless Power Transfer Conference.

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IEEJ Journal IA, Vol.12, No.3, 2023