FUZZY LOGIC BASED SUPERVISION OF DC LINK PI CONTROL IN A DSTATCOM

Harish Suryanarayana Doctoral Student

Energy Sources and SystemsPurdue University

OVERVIEW OF THE PRESENTATION

Custom Power The Distribution Static Compensator Symmetrical Component Theory Fuzzy Logic Fuzzy Logic Based Supervision Simulation Results

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 to its customers.

Power Electronic Controller – DSTATCOM, DVR Distribution level : 1kV to 38kV High Quality Power: No

sags/swells/harmonics

THE DISTRIBUTION STATIC COMPENSATOR

An SSG or a Static Synchronous Generator is defined by the IEEE as a self-commutated switching power converter supplied from an appropriate electric energy source and operated to produce a set of adjustable multiphase voltages, which may be coupled to an AC power system for the purpose of exchanging independently controllable real and reactive Power.

STATCOM : An SSG with a capacitor as the energy source is known as a STATCOM or a Static Compensator.

DSTATCOM : When a STATCOM is used at the distribution level or the load end, it is known as a DSTATCOM or Distribution Static Compensator.

DSTATCOM

Courtesy : PSERC 2003 Seminar

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.

DSTATCOM SCHEMATIC

scv

d cC

PCC

U n b a la n c e d lo a d

Z c

Z b

Z a

N o n lin ea r lo ad

L s R ssav

sbv

Nn

0i

fi C d ci

dcvn lL nlR

D C L in k

S 2 a

S 3 aS 1 a

S 4 aS 2 c

S 3 cS 1 c

S 4 cS 2 b

S 3 bS 1 b

S 4 b

'n

L f R f i fa i fb i fc

i la

i lb

i lc

isa

isb

isc

A ph a s eH -B ri d ge

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, Negative Sequence and Zero Sequence

c

b

a

a

a

a

iii

aaaa

iii

2

2

2

1

0

11

111

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

pvvvvvvvvvvvv

iii

00

333111 1

( 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

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 sbfc lc sc lc lavg

v v vi i i i P

v v vi i i i P

v v vi 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 vi i i i P P

v v vi i i i P P

2

, ,sj

j a b cv

tan( ) 3

FUZZY LOGIC

Concept introduced in 1965 by Lotfi. A. Zadeh

Crisp set and Fuzzy set. Ex. Set of tall people.

Diagram of a crisp set and a fuzzy set.

FUZZY LOGIC CONTROLLER

The four main components of a Fuzzy Controller. 1) The Fuzzification Interface

2) The Inference Mechanism3) The Rule Base4) The Defuzzification Interface

Fuz z ification InferenceMechanism

R ule B ase

D efuz z ificationIn p u t O u tp u t

FUZZY CONTROLLER Inputs:

Outputs: Calculation of Ploss

refdc dcerr(i) = v - v (i)

derr(i) = err(i) - err(i-1)

p pref pK K K

i iref iK K K

( ) ( )ref refloss p dc dc i dc dcP K v v K v v dt

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 PMNL NM NS

5 10 15-5-10-15 0

1

PLZ PS PMNL NS

derr( t) in Vo lts

NM

INFERENCE MECHANISM The two main functions of the inference mechanism are:

a) Based on the active membership functions in error and the change in error inputs, the rules which apply for the current situation are determined.

b) Once the rules which are on are determined, the certainty of the control action is ascertained from the membership values. This is known as premise quantification. ( Minimum Operation used )

" " is (positive large) " " is (positive medium)

" " is ( Large Kp )" "

IFerror PLchange in error PM

THENKp LKi

is ( Small Ki )SKi

RULE BASECapacitor Voltage Waveform during a load change

t im e (s )Z

N S

N L

P SP MP L

err < 0

Vo lts

N M

derr>0 derr<0derr>0derr<0

e rr > 0

derrerr 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

derrerr 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

FUZZY CONTROLLER Inputs:

Outputs: Calculation of Ploss

refdc dcerr(i) = v - v (i)

derr(i) = err(i) - err(i-1)

p pref pK K K

i iref iK K K

( ) ( )ref refloss p dc dc i dc dcP K v v K v v dt

DSTATCOM SCHEMATIC

scv

d cC

PCC

U n b a la n c e d lo a d

Z c

Z b

Z a

N o n lin ea r lo ad

L s R ssav

sbv

Nn

0i

fi C d ci

dcvn lL nlR

D C L in k

S 2 a

S 3 aS 1 a

S 4 aS 2 c

S 3 cS 1 c

S 4 cS 2 b

S 3 bS 1 b

S 4 b

'n

L f R f i fa i fb i fc

i la

i lb

i lc

isa

isb

isc

A ph a s eH -B ri d ge

SIMULATION VALUESSystem Parameters Values

Supply voltage 220V (phase-rms), 50 Hz

Unbalanced loadRla = 50 , Lla = 20 mHRlb = 35 , Llb = 40 mHRla = 70 , Lla = 20 mH

Non-linear load Three-phase full wave rectifier drawing a dc current of 5 A

DC capacitor 2200 µF

Interface inductor Lf = 20 mH, R f = 5

Reference dc link voltage 500 V

Hysteresis band 0.6 A

Gains tuned using the Energy concept Kp= 110, Ki= 55

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

15Nonlinear Unbalanc ed Load Currents

Time in s ec onds

Cur

rent

in A

mpe

res

p h a s e -a p h a s e -b p h a s e -c

SIMULATION RESULTSFilter 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 s ec onds

Cur

rent

in A

mpe

res

Ref erenc e and A c tual Filter Currents in Phas e A

R e fe re n c e c om p e n s a to r c u rre n t a c tu a l c u rre n t

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

25A c tual Sourc e Current Wavef orms

Time in s econds

Cur

rent

in A

mpe

res

p h a s e -a p h a s e -b p h a s e -c

SIMULATION RESULTSNormally 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

DC L

ink

Volta

ge in

Volts

Normally tuned PI

Fuzzy supervised PI

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 DC Capacitor voltage during load change.