IEEE Power Electronics Magazine - December 2016 - 36

Table 2. Testing samples of metalized
dc film capacitors [31].

Normalized Capacitance

1.05
1.00
0.95

testing samples

testing conditions

0.90
0.85

Group 1 - 1,100 V /40 μF (ten pieces)

85 °C and 85% RH

Group 2 - 1,100 V /40 μF (ten pieces)

85 °C and 70% RH

0.80
0.75

Group 3 - 1,100 V /40 μF (ten pieces)

85 °C and 55% RH

0.70
0.65

Testing Time: 3,850 Hours
Testing Condition: 85 °C and 55% RH

4,000

3,500

3,000

2,500

2,000

1,500

1,000

0

36

IEEE PowEr ElEctronIcs MagazInE

60
70
80
90

50

40

30

20

10

B10 Lifetime (Hours)

Unreliability, F(t ) = 1-R(t)

500

Figure 11 shows a capacitor testing setup. It is composed of a climatic chamber with a temperature range
from -70 to 180 °C and a relative humidity (RH) level from
10 to 95% (within a certain temperature range); three
Time (Hours)
ripple current testers to emulate electrical stresses of
Cap 1 Cap 2 Cap 3 Cap 4 Cap 5
dc-link operation; an inductance, capacitance, and reCap 6 Cap 7 Cap 8 Cap 9 Cap 10
sistance (LCR) meter; and an insulation resistance (IR)
and leakage current meter. The built-up system allows
FIG 12 The normalized capacitances under 55% RH and 85 °C
the testing of a wide range of film capacitors for the dcof ten capacitors (Cap) [31].
link applications in power electronics. Specifically, for
the testing to be presented in this
article, three groups of metalized
Probability-Weibull
film capacitors with the same part
99
Probability
Testing Condition number for dc-link applications
CB at 90% Two Sided
85 °C and 85% RH
are investigated. The specificaData 85% RH
F (t) = 1- e-(t/n)β
tions and testing conditions of the
2P-Weibull
β = 3.6
50 η = 1,686
F = 10/S = 0
capacitors are given in Table 2. The
testing for Group 1, Group 2, and
Data Points
Probability Line
Group 3 lasts for 2,160, 2,700, and
Top CB-I
3,850 hours, respectively. The ten
10
Bottom CB-I
samples in both Group 1 and Group
5
3 testing reach the end of life, with
criteria of 5% of capacitance drop.
As an example, Figures 12 and 13
1
100
1,000 2,000
10,000
show the measured normalized caTime (Hours)
pacitance values (i.e., with respect
to initial capacitance value) and the
FIG 13 A Weibull plot of the testing results under 55% RH and 85 °C with 5% capacicorresponding Weibull plot based
tance drop as the end-of-life criteria of ten capacitors [31].
on the results from Group 3 testing (see Table 2). According to the
testing results, under the three difLifetime Versus RH
ferent RH levels, a humidity-depen100,000
Life
B1 Li
B10
Lifet
fet
etime
time Li
Lin
Line
ne
e
Lifetime
dent B10 lifetime model is obtained
Stress Level RH 55% Points
50% Co
onfi
nf den
dence
ce Lev
ce
evvel
Confidence
Level
as plotted in Figure 14, with an exEta RH 55% Point
Imposed pdf RH 55%
ponent constant of -1.8.
10,000
Stress Level RH 70% Points
Figure 14 shows a typical lifeEta RH 70% Point
time
model for the power electronics
Imposed pdf RH 70%
3,000
Stress Level RH 85% Points
components (film capacitors), which
2,000
Eta RH 85% Point
reveals the relationship between
Imposed pdf RH 85%
1,000
the lifetime of the component (at
L /L 0 ∝ (RH/RH0)-1.8
a certain probability of failure) and
100
the applied stress levels that will
trigger a certain failure mechanism.
RH (%)
Figure 15 shows another example of
the power semiconductor from [25],
FIG 14 The B10 lifetime with 50% confidence level of the specific type of film capaciin which the B10 lifetime (i.e., the
tors versus RH levels under 85 °C and with 5% capacitance drop as the end-of-life
number of cycles or time at which
criteria [31].
0.60

z	December 2016



Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2016

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