POWER ELECTRONICS
Reliability Assessment of Power Converters
with Partial Redundancy and Variable Power
Distribution
Challenges
(1) Reliability indicators
· Mean time to failure (MTTF) is not enough
fo r r eliability ass essment when s ystem s
power distribution varies.
Three-step assessment method
Step 1:Compare failure rates of all components
at all states and select necessary ones
· List components in the system
· List the working conditions of components
· Calculate and compare failure rates l (t) of
components at all states
Footstone
(2) Reliability models
2.1 Component-level reliability model
· Should we consider all the failure rates or not?
2.2 System-level reliability model
· Part-count and combinatorial models are simple
but cannot evaluate the r eliability of f aulttolerant system.
· Markov model can evaluate the fault-tolerant
system s reliability but complex.
Step 2:Build Hybrid reliability model
· Distinguish the non-redundant subsystems
and redundant subsystems
· Build part-count model for non-redundant
subsystems
· Build Markov model for redundant subsystms
Core
Step 3: Calculate MTTF and MTTFr
· Calculate MTTF
Proposed
· Calculate MTTFr
Results
metric
Application of the Proposed Reliability
Assessment Method
V'R
Cap1
TRA
0.02
SC
SB
SA
VA
VB
TRB
M
~
VC
TRC
MTTF(10-6 / hour)
S'R
Case I
Case II
0.01
S'Rr
SBb
SAa
V'r
Cap2
SCc
Ldc3
Va
TRa
Ldc2
Vb
TRb
Case III
0
50
40
30
20
Ldc1
o
T A(
Vc
TRc
C)
Sa
Sb
Sc
Vdc1
Vdc3
Vdc2
(Bat) (FC) (U-cap)
4
2
3
1
0
Po(kW)
100
98
94
MTTFr (%)
S'r
90
86
Case I
Case II
82
Case III
78
50
TA ( 40
o 30
C) 20
4
3
2
Po(kW)
1
0
Most Vulnerable Components and Major
Causes of Reliability Issues
 Power semiconductor devices
 High temperature
 Oscillation — High voltage or current stress
 Electrolytic capacitors
 Used to reduce voltage ripples
 Capacitance drops with time
 Electrolyte can dry up
 Electrolyte leaks when temperature increases
 Ripple currents cause temperature to increase
How to Improve the Reliability of Power
Converters?
 Propose compact power converters to reduce the power
semiconductor devices
 Propose impedance-based stabilisation methods to
eliminate the system oscillation and avoid the high
voltage or current stress
 Propose active ripple eliminator to remove Electrolytic
capacitors
Compact Power Electronics
Interface





Six possible power flow modes
Bidirectional with reduced power switch
Higher reliability but lower cost
Flexible control of power/current/voltage
Possible applications in B-UC HEV, FC-B-UC HEV
and hybrid energy storage systems
Compact Power Electronics
Interface
Inverter
+
S4
S6
S8
IAC
M
S3
L2
VDC
I1
+
V2
Battery 1
+
V1
L1
S5
VAC
S7
S2
I2 S
1
DC/DC
Battery 2
The inverter and the DC-DC
converter are integrated
The DC-DC converter can
interface two sources with only
two additional power switches.
More compact with higher
power density, cost effective and
less degradation for components
Stabilisation of Cascaded DC/DC Converters
via Adaptive Series-Virtual-Impedance
Control of the Load Converter
+
Vin
_
vbus iin
+
_
Source
Converter
io
ZSVI +
Load
v¢bus
_
Converter
Z¢iL
ZoS ZiL
Logic of S1 & S2
Out
D
ibus
Input > 0
0
Out
1  Tv ( s)]  Po
+
-
2
bus
Gid ( s )GPWM ( s )V
4 f RC
vbus
HPF
A
|abs|
+
B
PI
E
4 Kr f RC
1/S
1
2
3
-
vˆbus
1  Tv ( s)] Po
vir
GASVI(s)
2
Gid ( s )GPWM ( s )Vbus
+
2
Memory
1
2
3
Relay
S1
fCS
S2
C
vˆor
+
_
Gv(s)
1
ZinOL(s)
iˆo
GiiOL(s)
ZASVI(s)
GvgOL(s)
vˆir
+ +
vˆe
ZoOL(s)
GPWM(s)
+
+
+
iˆbus
Gid(s)
Memory
0
0
Basic idea
Realization
Input £ 0
1
1/S
Δvbus |Δvbus|
_
ZASVI(s)
Logic of Relay
Input2 < 0.5 Input2 ³ 0.5
Input3
Input1
+
Vo
_
d̂
Hs(s)
Gvd(s)
_
+
+
vˆo
Experiment Verification of the ASVI Control
Strategy
Lf
vin1
iL
QL
Cf
LC input filter
+
vin
-
Lf
Cf
Case I 6 mH 150 mF
Case II 6 mH 60 mF
Lf1(400mH)
iL1
DL
PWM
module
Cf1(150mF)
+
vo
-
Io
RLd
(5.76)
vbus, vo and iin
ADC module
Digital control
system
DC/DC converter
Case I
Start ASVI
Case II
iL: [5 A/div]
20.08 ms
Start ASVI
iL: [5 A/div]
8.79 ms
vbus: [20 V/div]
vbus: [20 V/div]
iL1: [5 A/div]
iL1: [5 A/div]
vo: [5 V/div]
vo: [5 V/div]
Active Ripple Eliminators
Adding a ripple eliminator to
the current ripples so that
ripples on the DC bus are
small without using large
capacitors.
compensate
the voltage
maintained
electrolytic
WITH THE
S T R AT E G Y
Outcomes
Journal papers:
1.X. Zh ang , Q.-C. Zho ng an d W.-L. Ming , Stab ilization of Cascad ed DC/DC Converters
via Ad ap tiv e Series -Virtu al -Imp ed an ce Con tro l of th e Lo ad Conv erter , IEEE Trans . o n
Pow er Electro nics , 2016.
2.X. Zh ang , Q.-C. Zh ong and W.-L. Ming , Stab ilization of a Cascad ed DC Conv erter
Syste m via Adding a Virtual Ad ap tiv e Par allel I mp ed an ce to the Input o f the Load
Converter, IEEE Trans. on Pow er Electronics , 2015.
3.Xin . Zh ang , Xin bo Ru an , Qin g -Ch ang Zhong, “Virtu al -I mp ed an ce -Based Co n tro l
Strateg y of Regu lating th e In pu t I mp ed an ce of Lo ad Converter fo r Imp rov ing th e
Stability of Cascaded Systems ,” IEEE Trans. Industria l Electronics , 2015.
4.Wen -Long Min g, Qin g -Ch ang Zhong , and Xin . Zh ang , “A sing le -ph ase f ou r-switch
rectif ier with signif icantly r edu ced cap acitan ce,” IEEE Trans . Pow er Electronics ,
2015.
5.Xin Cao , Qing -Chang Zhong , Wen -Long Min g, “Ripp le Elimin ato r to S mo oth DC-Bus
Voltag e and Redu ce th e Total Cap acitan ce Requ ired ”, IEEE Trans . Industria l
Electronics , 2015.
6.X. Zh ang , Q.-C. Zhong and W.-L. Min g, A Virtu al RLC Da mp er to Stabilize DC/DC
Converters Having an LC I nput Filter while I mp rov in g th e Filter Perfo r man ce ,
Submit ted , 2016.
Outcomes
Conference papers:
1.Xin . Zh an g, Qing -Ch ang Zhon g, Wen -Lon g Ming , “ Fast Scale Instab ility Proble m and
Phase-Sh if ted -Car rier Solution of Buck Derived Cascaded System ,” IEEE ECCE 2015.
2.Xin . Zh ang , Qing -Ch ang Zho ng, Wen -Long Min g, Xinbo Ruan , “Stab ilization of a
Cascad ed DC Syste m v ia Add ing a Virtual I mp ed an ce in Series with th e Lo ad
Converter,” IEEE PEDG 2015.
3.Xin . Zh ang , Qing -Ch ang Zho ng, Wen -Long Min g, Xinbo Ruan , “Stab ilization of a
Cascad ed DC Syste m v ia Addin g a Virtu al I mp ed an ce in Parallel with th e Lo ad
Converter,” IEEE PEDG 2015.
4.Xin . Zh ang , Qing -Ch ang Zhon g, Wen -Long Min g, “ I mp ed ance -Based Lo cal Stab ility
Criterion for Standalon e PV-battery Hybrid System,” IEEE PEDG 2015.
5.Jun Cai, Qing -Chang Zhong , Dav id Sto ne, “ A n ew po wer converter f o r h y brid en erg y
storage systems,” IEEE IECON 2014.
6.Jun Cai, Qing -Chang Zhong , “An Asy mme trical Ga mma Z -source Hybrid Power
Converter with Space Vector Pulse-wid th Modulation ,” IEEE ECCE 2014.
7.Jun Cai, Qing - Chang Zhong , “ A co mp act b id irectio nal DC-DC co nv erter with two
sources,” IEEE PEDG 2014.
8.Jun Cai, Qing -Ch ang Zh ong , Dav id Ston e, “A ΓZ-sou rce conv erter b ased h yb rid
power converter for battery FCHEVs,” UKACC 2014.
Outcomes
Conference papers:
9.Xin C ao , Qin g-C h ang Zho n g, Wen -Long Min g, “An alysis and Con tro l of R ip p le
Eliminato rs in DC Systems”, IEEE Green Tech 2014.
10.Q.-C. Zhon g, W.-L. Ming , an d M. Krstic, “ Imp rov ing th e p ower qu ality o f tractio n
power syste ms with a sing le-f eed ing wire,” in Pro c. IEEE Green Techno log ies
Conference , 2013.
11.Q.-C. Zho ng , W.-L. Min g, X. C ao , and M. Krstic, “R edu ction o f DC-b us vo ltag e
rip p les and capacito rs fo r single-ph ase PW M-con tro lled rectif iers,” in Pro c. IEEE
IECON 2012.
12.Xin . Zh ang , Qing -Ch ang Zho ng, Wen -Long Ming , “A Virtu al R LC
Da mp er to
Stab ilize a DC /DC Conv erter Hav ing an LC Inpu t Filter wh ile I mp rov ing the Filter
Performan ce ,” Submitted 2016.
13.Xin. Zhang , Qin g -Ch ang Zhong, Wen -Lo ng Ming , “ So urce-sid e Series -v irtu al i mp ed an ce Co ntro l Strateg y to Stab ilize th e C ascad ed Syste m with I mp rov ed
Performan ce ,” Submitted 2016.
14.Xin . Zh ang , Qin g -Ch ang Zhong, Wen -Lo ng Ming , “Stab ilization o f C ascad ed
DC/DC Con ver ters v ia Sh ap in g th e Lo ad Inp ut I mp ed an ce b y Ad ap tiv e Series -Virtual Imp ed an ce Control,” Submitted 2016.
15.Xin. Zh an g, Qing -Ch ang Zhon g, Wen -Lon g Min g, “ Reliab ility Assess men t o f Po wer
Converters with Partial R ed u ndan cy and Variab le Power Distribu tio n,” Sub mitted 2 015 .