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FUZZY LOGIC BASED SUPERVISION
OF DC LINK PI CONTROL IN A DSTATCOM
Harish Suryanarayana
Doctoral Student
Energy Sources and Systems
Purdue University
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OVERVIEW OF THE PRESENTATION
Custom Power
The Distribution Static Compensator Symmetrical Component Theory
Fuzzy Logic
Fuzzy Logic Based Supervision Simulation Results
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CUSTOM POWER
It is a concept based on the use of Power
Electronic controllers in the distribution system to
supply value- added, reliable, high-quality power toits customers.
Power Electronic Controller DSTATCOM, DVR
Distribution level : 1kV to 38kV High Quality Power: No sags/swells/harmonics
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THE DISTRIBUTION STATIC COMPENSATOR
An SSG or a Static Synchronous Generator is defined by theIEEE as a self-commutated switching power converter suppliedfrom an appropriate electric energy source and operated toproduce a set of adjustable multiphase voltages, which may be
coupled to an AC power system for the purpose of exchangingindependently controllable real and reactive Power.
STATCOM : An SSG with a capacitor as the energy source isknown as a STATCOM or a Static Compensator.
DSTATCOM : When a STATCOM is used at the distribution levelor the load end, it is known as a DSTATCOM or Distribution StaticCompensator.
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DSTATCOM
Courtesy : PSERC 2003 Seminar
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DSTATCOM MAIN GOALS
To cancel the effect of harmonics due to load
so that the current drawn from the source is
nearly sinusoidal . To help maintain near unity power factor by
canceling the effect of poor load power factor
To help offset the effect of unbalanced loads,such that the current drawn from the source
is balanced.
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DSTATCOM SCHEMATIC
scv
dcC
PCC
Unbalancedload
Zc
Zb
Za
Nonlinear load
Ls
Rssav
sbv
Nn
0i
fi Cdc
i
dcv
nlL nlR
DC Link
S2a
S3a
S1a
S4a
S2c
S3c
S1c
S4cS2b
S3b
S1b
S4b
'n
Lf
Rf i
faifb
ifc
ila
ilb
ilc
isa
isb
isc
A ph ase
H-Bridge
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SYMMETRICAL COMPONENT THEORY
Any set of n unbalanced polyphase
quantities could be expressed as the sum of
n symmetrical sets of balanced phasors.
Three Phase: Positive Sequence, NegativeSequence and Zero Sequence
c
b
a
a
a
a
i
ii
aa
aa
i
ii
2
2
2
1
0
1
1111
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SYMMETRICAL COMPONENT THEORY
Source Currents are balanced.
Only the average load power is supplied by the source.
Relation between Source Currents and Source Voltages.
All equations in matrix form.
0sa sb sci i i
sa sa sb sb sc sc lavgv i v i v i P
lavgscsbsa
scsbsasbsascsascsb
sc
sb
sa
pvvv
vvvvvvvvv
i
i
i
0
0
333
1111
( 3 ) ( 3 ) ( 3 ) 0sb sc sa sa sc sa sb sb sa sb sc scv v v i v v v i v v v i
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SYMMETRICAL COMPONENT THEORY
Reference Compensator Currents.
Reference Compensator Currents with loss.
*
*
*
sa sb scfa la sa la lavg
sb sc safb lb sb lb lavg
sc sa sb
fc lc sc lc lavg
v v vi i i i P
v v vi i i i P
v v v
i i i i P
*
*
*
sa sb scfa la sa la lavg loss
sb sc safb lb sb lb lavg loss
sc sa sbfc lc sc lc lavg loss
v v vi i i i P P
v v v
i i i i P P
v v vi i i i P P
2
, ,sj
j a b c
v
tan( ) 3
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FUZZY LOGIC
Concept introduced in 1965 by Lotfi. A.
Zadeh
Crisp set and Fuzzy set. Ex. Set of tallpeople.
Diagram of a crisp set and a fuzzy set.
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FUZZY LOGIC CONTROLLER
The four main components of a Fuzzy Controller.
1) The Fuzzification Interface
2) The Inference Mechanism
3) The Rule Base
4) The Defuzzification Interface
Fuzzification InferenceMechanism
Rule Base
DefuzzificationInput Output
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FUZZY CONTROLLER
Inputs:
Outputs:
Calculation of Ploss
ref
dc dcerr(i) = v - v (i)
derr(i) = err(i) - err(i-1)
p pref pK K K
i iref iK K K
( ) ( )ref ref loss p dc dc i dc dcP K v v K v v dt
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FUZZIFICATION
Inputs to the Fuzzy controller: Error and change in
error of the capacitor voltage.
5 10 15-5-10-15 0
1
err(t) in Volts
PLZ PS PMNLN
MNS
5 10 15-5-10-15 0
1
PLZ PS PMNL NS
derr(t)in Volts
NM
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INFERENCE MECHANISM
The two main functions of the inference mechanism are:
a) Based on the active membership functions in error and the change in errorinputs, the rules which apply for the current situation are determined.
b) Once the rules which are on are determined, the certainty of the controlaction is ascertained from the membership values. This is known as
premise quantification. ( Minimum Operation used )
" " is (positive large)
" " is (positive medium)
" " is ( Large Kp )
" "
IF
error PL
change in error PM THEN
Kp L
Ki
is ( Small Ki )SKi
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RULE BASE
Capacitor Voltage Waveform during a load change
time(s)Z
NS
NL
PS
PM
PL
err < 0
Volts
NM
derr>0 derr0derr 0
derr
err NL NM NS Z PS PM PL
NL L L L M S S Z
NM L L M S S Z S
NS L M S S Z Z Z
Z M Z Z Z Z Z M
PS Z Z Z S S M L
PM S Z S S M L L
PL Z S S M L L L
derr
err NL NM NS Z PS PM PL
NL SKi SKi SKi Z Z Z Z
NM SKi SKi SKi Z Z Z Z
NS LKi LKi LKi Z Z Z Z
Z LKi LKi LKi Z LKi LKi LKi
PS Z Z Z Z LKi LKi LKi
PM Z Z Z Z SKi SKi SKi
PL Z Z Z Z SKi SKi SKi
Rule base for Kp Rule base for Ki
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FUZZY CONTROLLER
Inputs:
Outputs:
Calculation of Ploss
ref
dc dcerr(i) = v - v (i)
derr(i) = err(i) - err(i-1)
p pref pK K K
i iref iK K K
( ) ( )ref ref loss p dc dc i dc dcP K v v K v v dt
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DSTATCOM SCHEMATIC
scv
dcC
PCC
Unbalancedload
Zc
Zb
Za
Nonlinear load
Ls
Rssav
sbv
Nn
0i
fi Cdc
i
dcv
nlL nlR
DC Link
S2a
S3a
S1a
S4a
S2c
S3c
S1c
S4cS2b
S3b
S1b
S4b
'n
Lf
Rf i
faifb
ifc
ila
ilb
ilc
isa
isb
isc
A ph ase
H-Bridge
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SIMULATION VALUES
System Parameters Values
Supply voltage 220V (phase-rms), 50 Hz
Unbalanced load
Rla= 50 ,L
la= 20 mH
Rlb= 35 ,L
lb= 40 mH
Rla= 70 ,L
la= 20 mH
Non-linear load Three-phase full wave rectifier drawing a dc current of 5 A
DC capacitor 2200 F
Interface inductor Lf= 20 mH, Rf = 5
Reference dc link voltage 500 V
Hysteresis band 0.6 A
Gains tuned using the Energy concept Kp= 110, Ki= 55
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SIMULATION RESULTS
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-15
-10
-5
0
5
10
15
Nonlinear Unbalanced Load Currents
Time in seconds
CurrentinAmperes
phase-a phase-b phase-c
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SIMULATION RESULTS
Filter Current - Reference and Actual
0.1 0.102 0.104 0.106 0.108 0.11 0.112 0.114 0.116 0.118 0.12
-4
-3
-2
-1
0
1
2
3
4
5
Time in seconds
Cu
rrentinAmperes
Reference and Actual Filter Currents in Phase A
Reference compensator current actual current
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SIMULATION RESULTS
Source Currents Balanced and Sinusoidal
0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05-25
-20
-15
-10
-5
0
5
10
15
20
25
Actual Source Current Waveforms
Time in seconds
Cu
rrentinAmperes
phase-a phase-b phase-c
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SIMULATION RESULTS
Normally tuned PI and Fuzzy Supervised waveforms
0 0.1 0.2 0.3 0.4 0.5 0.6460
470
480
490
500
510
520
530
540DC link Voltages - Normally tuned and Fuzzy tuned
Time inseconds
D
CL
inkVoltagein
Volts
Normally tuned PI
Fuzzy supervised PI
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SUMMARY TAKE HOME POINTS
The DSTATCOM can be used to ensure
balanced and sinusoidal source currents
even if the load is unbalanced and non-
linear.
Fuzzy supervision of the DC link PI controller
can be used to reduce the error in DCCapacitor voltage during load change.