Fuzzy Logic Based Supervision - DSTATCOM

7/28/2019 Fuzzy Logic Based Supervision - DSTATCOM

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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


2/24

OVERVIEW OF THE PRESENTATION

Custom Power

The Distribution Static Compensator Symmetrical Component Theory

Fuzzy Logic

Fuzzy Logic Based Supervision Simulation Results


3/24

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


4/24

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


6/24

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


8/24

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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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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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.

Documents

Fuzzy Logic Based Supervision - DSTATCOM