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Research on the Reliability of
Uninterruptible Power System
Chen SixiongChief Engineer
Xiamen Kehua Hengsheng Co.,Ltd.
IEEE PEAC 2018 No Reprint Without Authorization
Contents
Background
Topics on concept of reliability
Topics on UPS reliability
Reliability test and verification of Kehua
Brief introduction to Xiamen Kehua
IEEE PEAC 2018 No Reprint Without Authorization
Background
Reliability is very important for power electronics system.
Reliability is basic requirement for system to run in long
time under various complex environment conditions.
Standards MIL-HDBK-217 Reliability Prediction of Electronic Equipment.
GB/T 2900.13-2008/ IEC 60050(191):1990 Electro-technical terminology - Dependability
and quality of service.
GJB 450A-2004 General requirement for materiel reliability program.
GJB 813-1990 Reliability modeling and prediction.
GJB/Z 299C-2006 Reliability prediction handbook for electronic equipment.
IEEE 1413-2010 Standard framework for reliability prediction of hardware.
BS IEC 60605-6-2007 Equipment reliability testing - Part 6: Tests for the validity and
estimation of the constant failure rate and constant failure intensity.
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Background
Most of the opinions in
this presentation are
included in “White Papers
of the UPS Technology for
Data Center”, issued by
the Information System
Power Supply Technical
Committee of CPSS.
The “White Papers of the UPS Technology for Data Center” was drafted by
the Information System Power Supply Technical Committee of CPSS, with the
participation of Chen Sixiong, Zhang Guangming, Xie Shaojun, He Chunhua and
other well-known experts. Professor Xu Dehong, chairman of CPSS, was invited
to make the preface.IEEE PEAC 2018 No Reprint Without Authorization
Basic Terms
Reliability:
Failure rate:
MTBF:
Availability:
0( ) exp( ( ) )
t
R t x dx
0
1 ( ) ( ) ( )( ) lim
( ) ( )t
F t t F t f tt
t R t R t
V
V
V
MTBFA
MTBF MTTR
0 0
1( ) exp( )MTBF R x dx x dx
IEEE PEAC 2018 No Reprint Without Authorization
Topics on concept of reliability
Topic 1: Is reliability a constant?
Topic 2: What is the difference between 99.999% and
99.9999% for reliability?
Topic 3: Reliability or availability?
Topic 4: Maximum N for N+X system
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5 8760h
100,000(5 ) e 64.5%hR years
99.999%R
100 000hMTBF ,
Topic 1: Is reliability a constant?
Reliability is a exponentially decreasing function of time.
The reliability of system, we talking about, is actually the
reliability value in the 1st hour.
Reliability after 5 year
( ) exp( )t
R tMTBF
First Hour99.999%
5 Years64.5%
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Uninterruptible
Power SystemReliability Failure Rate (λ)
Annual Failure
Rate (λ)
A 99.999% 1.0×10-05 h-1 8.76%/year
B 99.9999% 1.0×10-06 h-1 0.876%/year
Topic 2: What is the difference between
99.999% and 99.9999% for reliability?
It's hard for user to distinguish the reliability between
99.999% and 99.9999%.
But, we can easily know the difference between these 2
systems by Annual Failure Rate.
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Topic 3: Reliability or availability?
RELIABILITY(1) The duration or probability of failure-free performance under stated
conditions.
(2) The probability that an item can perform its intended function for a
specified interval under stated conditions.
AVAILABILITYA measure of the degree to which an item is in an operable and
committable state at the start of a mission when the mission is called
for at an unknown (random) time.
Source: MIL-HDBK-338B - MILITARY HANDBOOK, ELECTRONIC RELIABILITY DESIGN HANDBOOK
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Topic 3: Reliability or availability?
Difference
Basic Calculation Equation
Series & Parallel model Equation
Application
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Basic Calculation Equation
Affected by MTBF Affected by MTBF and MTTR
AConstant
Function of Time
( ) exp( )t
R tMTBF
MTBF
AMTBF MTTR
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Series & Parallel Model Equation
Source: Cao Jinhua, Cheng Kan. Introduction to reliability mathematics [M]. Beijing: Higher Education
Press, 2006:182-224.
Series Parallel
RELIABILITY
AVAILABILITY
Unit1 Unit2 UnitnIn Out
Unit1
Unit2In Out
Unitn
…
1
n
i
i
R R
1
1 (1 )n
i
i
R R
1
1
(1 )n
i
i i
MTTRA
MTBF
1
1
11 (1 ( ) )
!
nk
k
MTTRA
k MTBF
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Application
Two different applications
“Reliability” → no failure should be allowed, or as less as
possible
For some case, any system failure will cause huge accident or
economic losses for customer, therefore no failure should be allowed.
Application Example: UPS application for data center
“Availability” → failure is allowed, but failure time should be as
short as possible
In some case, the economic losses is proportional to the time of
system failure, so the occurrence of failure should be avoided and
failure duration should be minimized as possible.
Application Example: PV Inverter applicationIEEE PEAC 2018 No Reprint Without Authorization
Topic 4: Maximum N for N+X system
Assuming the UPS reliability is 99.99936% (MTBF = 156000h):
For N+1 system, N ≤ 6, RUPS_(N+X) ≥ RUPS
For N+2 system, N ≤ 14, RUPS_(N+X) ≥ RUPS
For N+3 system, N ≤ 23, RUPS_(N+X) ≥ RUPS
The reliability of N+X system
The reliability of N+X system should be greater than one single system
_( )UPS N X UPSR R
_( )
0
= (1 )X
N k N k X k
UPS N X N X
k
R C R R
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Topics on UPS reliability
Topic 5: How does UPS improve the reliability of power
supply for IT equipment?
Topic 6: UPS reliability prediction base on component
counts and FIT-Rates
Topic 7: UPS reliability analysis base on market failure
rates
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Topic 5:How does UPS improve the
reliability of power supply for IT equipment?
Assume:
Then:
R = Rgrid×RUPS = 0.9996455 ≤ Rgrid ?
GridUPS
(RUPS)IT Load
Rgrid R
Rgrid=0.99965 RUPS=0.9999955
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Topic 5:How does UPS improve the
reliability of power supply for IT equipment?
IT
LoadAC/DC
(Rrec)
DC/AC
(Rinv)
Battery
(Rbat)
R'UPS
Bypass
(Rbyp)
Rgrid
RGrid
(Rgrid)
Reliability model for UPS system
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Topic 5:How does UPS improve the
reliability of power supply for IT equipment?
Tab. Typical Reliability Value
' 1 (1 ) (1 )UPS grid rec bat invR R R R R
'1 (1 ) (1 )
99.9998998%
grid UPS bypR R R R
Reliability Value
Rgrid 99.965%
RUPS 99.999%
Rrec , Rinv 99.99955%
Rbyp 99.9999%
Rbat 99.9999287%
R = 99.9998998% > Rgrid = 99.965%, RUPS = 99.999%
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Topic 6: UPS reliability prediction base on
component counts and FIT-Rates
A high power UPS example
Environment
Temperature
Load Rate
20% 60% 100%
25°CFit 1949.899 2902.369 6650.3525
MTBF 512,847 344,546 150,368
40°CFit 2368.47 3694.585 8669.485
MTBF 422,213 270,666 115,347
60°CFit 3394.46 5848.105 14460.59
MTBF 294,598 170,996 69,153
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Topic 7: UPS reliability analysis base on
market failure rates
For MTBF = 100,000h, λ = 8.76% per year, can not satisfy customers'
requirements.
If you want to achieve more than 90% reliability after 5 years, the annual
failure rate should be less than 2%.
According to the current level of UPS technology and product quality, for
high-quality products, the annual failure rate can reach 1%, the MTBF can
reach 876,000 hours.
Annual
Failure RateMTBF R1hour R1year R3years R5years
8.76% 100,000h 99.99900001% 91.61272543% 76.88956611% 64.53257829%
4.38% 200,000h 99.99950000% 95.71453674% 87.68669574% 80.33217182%
2% 438,000h 99.99977169% 98.01986733% 94.17645336% 90.48374180%
1% 876,000h 99.99988584% 99.00498337% 97.04455335% 95.12294245%
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Reliability modeling
Reliability prediction
Reliability test and
verification
Reliabilityimprovement
Reliability test and verification of Kehua
The KEHUA reliability design process
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Reliability test and verification of Kehua
Aging test platform for MW power products Simulates various working condition (high temperature operating life,
full load, unscheduled turn on/off, cycling loading test, AC source etc.)
long-term MTBF test
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Reliability test and verification of Kehua
Environmental reliability test platform temperature test , humidity test
for MW power test
salt spray test, vibration test, etc.
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Reliability test and verification of Kehua
Dust proof Laboratory Test level: IP6X
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Reliability test and verification of Kehua
Water proof Laboratory Test level: IPX1, IPX2, IPX3, IPX4
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Reliability test and verification of Kehua
EMC Laboratory R&S company (German) test system
10m Semi anechoic chamber, for MW power test
RE test, CE test, ESD test, SURGE test, EFT test and DIPS test, etc.
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A brief introduction to
Xiamen KehuaIEEE PEAC 2018 No Reprint Without Authorization
2016 Built IDC in Beijing,
Shanghai and
Guangzhou
1997Started the
international brand
strategy
2014Awarded “National
Enterprise
Technology Center”
2015Firstly developed the
nuclear power plant
UPS in domestic
brand
2017Promoted national
cloud service
business
2010Officially went public
on Shenzhen Stock
Exchange (No.:
002335)
1988The predecessor of
Kehua Technology
was established in
Zhangzhou, China
1996Awarded “National
Key High-tech
Enterprise”
01 02 03 04 05 06 07 08
About us
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Our Business
IDC Service
190km2 IDC
25,000 Racks
Build In Beijing,
Shanghai, Guangzhou
Critical Power
UPS: 0.5kW~1.6MW
Smart Energy
Management
Micro-grid
Renewable Energy
PV Inverter:
1kW~3.125MW
Energy Storage
EV Charging
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Technology Innovation
900+R&D engineers
760+ Patents & Copyrights
60+National and Industrial
Standards
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Thank you
for your attention
Xiamen Kehua Hengsheng Co.,Ltd. www.kehua.com.cnIEEE PEAC 2018 No Reprint Without Authorization
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