Flicker control using rule based modulated passive

ELEOTRIC

POiER

ELSE VIER

Electric Power Systems Research 33 (1995) 49 52

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Flicker control using rule based modulated passive power filters A.M. Sharaf, H. Huang Department (~/ Electrical Engineering, The University o/ New Brunswick, PO Box 4400, Frederic'ton, N.B., Canada Received 10 October 1994

Abstract

The paper presents a novel modulated passive power filter scheme for nonlinear load bus voltage flicker control using an error-driven, error-scaled rule based controller for online voltage stabilization.

Keywords: Filters; Control strategies; Voltage flicker; Error-driven control

I. Introduction

Power supply quality [1-7] issues and persistent problems are a byproduct of the increasing use of solid state switching devices, nonlinear type loads, including switch-mode power supplies, unbalanced power systems, lighting controls, computer and data processing equipment as well as industrial plant rectifiers and inverters. These electronic type loads cause quasi-static harmonic dynamic voltage distortions and inrush pulse type current phenomena with excessive harmonic content, high distortion, low power factor and low-frequency voltage waveform modulation due to inrush currents, cyclic and acyclic temporal load variations. Power quality problems can cause system equipment malfunction, personnel safety risks, shock hazards, voltage flickering, computer data loss and memory malfunctioning of sensitive loads such as computers, banking machines, PLC controls, protection and relaying equipment as well as erratic operation of electronic controls. This translates into loss of revenue, power interruptions and electric supply utility reliability and security problems, in addition to extra power and energy losses on utility grid systems. The source of electric load nonlinearity can be analog type (saturation, limiter) or nonlinear voltagecurrent characteristics, as in distribution transformers and arc type nonsinusoidal loads, or digital type due to point-on-wave or integral-cycle 'on/off' solid state control with switchings using transistors, IGBT, MOSFET or GTO devices. The use of a capacitor bank alone may be inadequate to compensate for nonsinusoidal loads, owing to the introduction of new definitions of reactive, residual 0378-7796/95/$09.50 ~') 1995 Elsevier Science S.A. All rights reserved SSD1 0378-7796(95)00926-9

and uncommon power terms and currents [8-14]. Disturbance and voltage flicker [14 16] have been major and persistent problems, usually associated with cyclic and acyclic loads with temporal arc type variations, or when starting large (kW) induction motors. Certain types of mechanical loads such as compressors, air conditioning units and reciprocating pumps also introduce this low-frequency (0.5-35 Hz) voltage waveform modulation effect. Most mitigative solutions utilize static var compensators (SVCs), switched passive filters or fixed-type tuned-arm as well as high-pass damped filters [13 15] to ensure enough reactive power compensation, particularly on weaker electrical supply grid systems, hence enhance voltage regulation and compensate for the inductive current voltage drop along the feeder. IEEE defines flicker as the "impression of fluctuations in brightness or color, occurring when the frequency of observed variations lies between a few Hz and the fusion frequency of images". Some electrical equipment manufacturers and power ulilities are utilizing flicker data logging meters and monitoring systems for display, analysis, control and mitigative correction. This paper presents a novel modulated power filter scheme for online flicker control and power quality enhancement using a switched passive (RLC) tuned-arm filter and a rule based error-driven, error-scaled flicker control regulation loop.

2. Modulated filter

The RLC tuned-arm filter shown in Fig. 1 is modulated using a solid state MOSFET/IGBT or GTO

50

33 (I 995)

A,M. Sltarq/i H. Huang Electric Power ,S)'stem,~ Researc/l Vs I

Rs

Ls

'S

Vl

49-52

(a) load current

(b) load voltage

i

i

0.5

t

1,5

2

0

0.5

(c) source current GTO/IGBT/MDSFET SWITCH

1

15

(d) source voltage

A__ NnNLINEAR

LE]AD

time s

Fig. 1. Sample test scheme.

0.5

1

1.5

0

0,5

(el load current

1

15

2

1.5

2

(f) load voltage

IF

0

0.5

1

1.5

2

0

(g) source current

0.5

1

xlO 3

1 Ir add filter

(h) e

~t

add filter

0

0.5

vol'tage V[ too.d bus

Fig. 2. Intelligent error-driven rule based flicker control regulator. 0

0

ev(k) [ev (k)] =

ev(k -

0.5

1

1.5

2

ZI I!I ,mes 0

0.5

0

0.5

0 < ton < T / 2

1) + Ato.(k ) ( T = 16.33 ms)

1.5

2

1.5

2

time sJ

1

1.5

2

0

x 10-3(m) filter duration (pton) 4[ add filter

]

21i pO~lti~e ~ajf c y ~ ] ~

I

:

Jl

00

0.5

1

x 10 3(nl filter duration (nton)

negative half cycle

time s r

0:5

i

time s

1:5

ols

x 10 .3 (o) phase diagram

i

t.s

(p) phase diagram

6x 103

(1) i

(2)

0

e

1

2 X 10.3

00~

2 ptone (r) phase diagram

The PID control action is defined by Eqs. (3) and (4):

to.(k) = to,(k -

1

(I) filter voltage

(q) phase diagram

Z~to.(k ) = koRe(k)[ev(k) + 70v(k)]

1.5

(1) de/dt

x 10 3

tt ..............................

.2 ~z,--

(Tsampling= 0.2 ms)

1

'o['::::r ....................t

1)

Tsampling

(i) Re

(k) filter current

The error-scaled, error-driven control scheme shown in Fig. 2 adjusts the length of the on period (ton) based on the following equations. We define

d

1.5

r add filter

3. Control scheme

(vrref ~ O)

1

x 10 3

switching bridge to ensure correct compensation for flickering frequencies in the range 0.5-35 Hz. The bus voltage signal is fed into a bank of signal filters to extract feedback low-frequency damping signals. Fig. 2 depicts the novel phase portrait error-driven rule based regulator structure. The nonlinear load bus voltage is fed into a bank of low-pass and high-pass signal filters to extract the most dominant flicker frequencies. The power filter current is modulated ('switched') online by varying the 'on' period (to~), depending on the location and magnitude of a flicker voltage excursion vector in the error-error rate, ev-0v, phase portrait.

ev(k) = vfrer- vr

0.5

(3)

#

_ _ . . . _ _ _

o= 0

~-lJ

(4)

x 103

-1

-0.5

O

0.5

1

~

toad voltage 0

0.5

Fig. 3. Dynamic simulation study (time domain).

1

1.5

2

A.M. SharaJ~ Ol Huang / Electric Power Systems Research 33 (1995)49 52 (b) load voltage (no filter)

(a) toad current (no filter)

Olf

Hz

o6

loo

5o

t+o

tion of all low-pass and high-pass filter bank signals). The introduction of the dead-zone Re0 is required to avoid control hunting and instability as well as continuous filter on/off switching.

HZ

50

200

51

200

(d) source voltage (no filter)

(c) source current (no filter)

4. Dynamic simulation

Uo

50

too

tso

00

I 200

50

~°t I o;

so

6o

~50 2o0

o;

Hz

so

60

t~o

~"

n~ ~g

[

200

(h) source voltage (add filter)

1

'200

(it tilter current (add filter)

oo.tl

150

HZ too t5o 2so

go

(g) source current (add filter)

:tl

1O0

(f) load voltage (add filter)

(e) load current (add filter)

~

0.2

t I

'

~°"I °6

so

Hz

loo

t/~o

200

(j) filter voltage (add filter)

t/

Hz

, ,, 500

1000

(I) capacitance voltage of filter

x 107 (k)filter resistor voltage 1.5

3

[

,

,,

500

1000

o6 ,

i

'5'o4 '

'"z't00o

(n) phase diagram

x 104 (m) phase diagram 2

-

•

5. Conclusions

ol,_ /

5 x 104

":~,4

capacitance voltage (o) phase diagram

~fr

-0:2

6 0:2 filter currant (p) phase diagram

0.4

--" i1" ]

-s~

resistanc~fiage

-0',5

6

0'.s

__.

capacJta~ca~ce voI,-~,vo t~

t

Fig. 4. Dynamicsimulationstudy (frequencydomain).

where 7 and ko are optimized and fixed, and the magnitude Re of the excursion vector at any instant is given by

Re(k) =

The sample study grid network used is shown in Fig. 1 and comprises a feeder to a cyclic arc type nonlinear, nonsinusoidal load with temporal arc resistance and arc voltage variations. The full system, filter, and control data are given in the Appendix. The MATLAB software package was used to investigate the voltage and current time and frequency domain spectra of all system, filter, and control signals, to illustrate the phase portrait error plane control action of the novel rule based robust online control regulator. Figs. 3 and 4 depict the voltage flickering conditions without and with the modulated passive power filter scheme. It is apparent that the switched filter had some impact on the flickering low-frequency load bus voltage and current modulation. The control scheme utilized simple first-order low-pass and high-pass signal filters to extract the flicker voltage damping signal. The damping effect and flicker reduction can be enhanced by a high-order tuned band-pass filter to zoom in on dominant offending low frequencies usually ranging between 0.1 and 15 Hz. The proposed scheme enhances power quality by reducing flicker voltage waveform modulation.

( e v 2 q - 6 v 2 ) 1/2 - ~

Re0

(5)

where Reo is a small dead-zone (Reo = 0.0001). The control action level is scaled online based on the dominant flicker voltage aggregate signal level (summa-

This paper presents a simple novel self-compensating modulated 'switched' passive power filter scheme for online control of voltage flickering due to nonlinear, nonsinusoidal type loads. The filtering level is controlled via an on/off switching scheme. The rule based scheme is driven by the flicker voltage signal and its rate of change, and is adjusted by the flicker excursion vector magnitude in the ev-kv error phase portrait. The proposed scheme can be utilized for a multitude of power quality enhancement applications including power factor correction, voltage regulation, reactive compensation, feeder DC bias and harmonic cancellations. Different power filter topologies, control signals and structures can be utilized.

Acknowledgements The authors wish to acknowledge NSERC Canada for financial support.

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52

A.M. Sharq[~ H. Huang ,. Electric Power Systems Research 33 (1995) 49 .52

Appendix All values are in p.u. Cyclic nonlinear arc type load:

[4] [5]

Ez = Eo + Eol sin(ooR ~t) R1 = Ro + Rol sin(ogR 2 t) E2 :

-Et,

[6]

R 2 : R!

Eo = 0.6,

Eol = 0 . 3

Ro = 0.6,

Rol = 0.3

CaR, = 5 rad/s,

[7]

~OR~ = 15 rad/s

Feeder:

Lv =

[8]

RF =

0.005,

0.00025

Passive p o w e r filter L = 0.0005,

(RLC):

C = 0.0005,

[9]

R = 0.001 [10]

Rule based controller: [11]

/Co = 50,

7 = 0.9,

R~o = 0.0001 [12]

R~ = (6~ 2 + 6v2) 11= + Reo Flicker voltage signal low-pass and high-pass filter time constants: LPI:

g=l/9s

fl=9Hz

LP2:

T2=1/15s

f==15Hz

HP:

t3 = 1/500 s f3 = 500 H z

LP3:

t4 = 1/40 s

f4 = 40 H z

[13]

[14]

[15]

[16] [17]

References [1] R.P. Stratford, Harmonic pollution on power s y s t e m s - a change in philosophy, 1EEE Trans. Ind. AppL, IA-16 (1980) 617-623. [2] A. Stalewski, Reactive power compensation and harmonic filters, CIGRE Rep. No. 417, 1960, Appendix III, also in Direct Current, 4 (1959) 130-133. [3] B. Szabados, Measurement of harmonic currents generated in a power transformer, Conj. Digest, IEEE Int. Electrical, Electron-

[18]

[19]

[20]

its Co;TL, Tononto, Canada, 1979, Cat. No. 79-90130. 1EEE, New York, pp. 82 84. A.M. Sharaf, Harmonic interference from distribution systems, IEEE Trans. Power Appar. S3st., PAS-IOI (1982) 2975 2981. R.O.M. Powell, The design of capacitor components of large high voltage a.c. filter networks, ConL High Voltage D.C. Transmission, Manchester, UK, 1966, IEE Conf. Publ. No. 22, Institution of Electrical Engineers, London, pp. 284-286. C.D. Clarke and M.J. Johanson-Brown, The application of self-tuned harmonic filter to H.V.D.C. converters, C~,~/I High Voltage D.C. Transmission, Manchester, UK, 1966. lEE Conf. Puhl. No. 22, Institution of Electrical Engineers, London, pp. 275 276. G.L. Brewer, C.D. Clarke, A. Gavrilovi& Design considerations of a.c. harmonic filters, Cony: High Vohage D.C. Transmission, Manchester, UK, 1966, IEE Conf. Publ. No. 22, Institution of Electrical Engineers, London, pp. 277-279. E.B. Makram, R.B. Haines and A.A. Girgis, Effect of harmonic distortion in reactive power measurement, IEEE Trans. Ind. Appl., IA-28 (1982) 782 787. A.E. Emanuel, Power in nonsinusoidal situations - a review of definitions and physical meanings, IEEE Trans. Power Deliveo,, 5(1990) 1377 1389. S. Fryze, Active and reactive powers in non-sinusoidal systems (in Polish), Przegl. Elektrotech., (7) (1931) 193-202. C.H. Page, Reactive power in nonsinusoidal situations, IEEE Trans. lnstrum. Meas., IM-29 (1980) 420 423. D.D. Shipp, Harmonic analysis and suppression for electrical systems, IEEE Trans. Ind. Appl., IA-15 (1979) 453-458. G.R. Slemon, Equivalent circuits for transformers and machines including nonlinear effects, Proc. Inst. Electr. Eng., Part 4, 101 (1953) 129 143. Disturbances in Supply Systems Caused by Household Applications and Similar Electrieal Equipment, IEC Publ. No. 555, International Electrotechnical Commission, Geneva, 1982. H. Frank and K. Pettersson, Raising the production of arc furnaces by stabilising the voltage with thyristor-switched capacitors, ASEA J., 50 (1) (1977) 9-16. J. Arrillaga, D.A. Bradley and P.S. Bodger, Power System Harmonics, Wiley-lnterscience, New York, 1985. T. Owens, Current harmonics in nonlinear resistance circuits, Trans. AIEE, 54 (1935) 1055- 1057. A. Sharaf, On the need for harmonic limitation - - guidelines for Canadian utilities, Proc. 2nd Int. Con,['. Harmonics in Power Systems, Winnipeg, Man., Canada, 1986, pp. 21-30. D. Hart, Design and analysis of active filters in power systems with HVDC transmission, Ph.D. Thesis, Purdue University, West Lafayette, IN, 1985. S.M.E. Haque, M. Obeid and W. Shepherd, Performance of fixed-filter -thyristor controlled reactor ( F F - T C R ) power factor compensator, J. Eng. Sci. King Saud Univ., Saudi Arabia, 10 (1 2) (1984) 15-26.