Decentralised Controller for Flicker Mitigation in Converter-Connected DG Networks

1

Decentralised Controller for Flicker Mitigation in Converter-

Connected DG Networks

Piyadanai Pachanapan, Adam Dysko, Olimpo Anaya-Lara, Graeme Burt, Kwok L. Lo

Institute for Energy and EnvironmentUniversity of Strathclyde, Glasgow, UK

21st CIRED, 7th June 2011 RIF Session 2 – Paper ID 1139

Frankfurt (Germany), 6-9 June 2011

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Introduction New Grid Codes require DG to export reactive

power (Q) into MV networks

V/Q support from DG Local Voltage Control

Can Voltage Source Converter (VSC) interfaced DG provide dynamic voltage compensation similar to a STATCOM?

Piyadanai Pachanapan– UK – RIF Session 2 – Paper ID 1139


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Objectives Use converter-connected DG as decentralised

voltage controller to mitigate voltage flicker in MV networks

Reduce the requirements for the deployment of new reactive power compensation devices such as STATCOMs and SVCs.



4

Sub Station

External Grid

Local ZoneController

Communication link

Local Controllable Zone # 1



LCZ # 2

LCZ # 3

P

Pref

Qref

ConverterController

PWMConverter

QVac

PI

Q_min

Q_max

mα

Vac,ref

mβ

-

-

- dq - frame

Decentralised Control Structure of a DG network

P-V control scheme of grid-side interfaced VSC


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Voltage flicker mitigation

~=

DG

HV/MV

ConverterController

P,Q,V# DG

#L1 #R2#R1

#L1– Local Measurement of Converter-connected DG 1 (P,Q,V)

#R1– Remote Measurement, at flicker source bus, for fluctuated DG source (V)

M

# Motor

Flicker Source

#R2– Remote Measurement, at flicker source bus, for fluctuated Load (V)

IEC 61000-3-7

Normalised flickermeter response (Pst = 1.0)


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Test System0

1

1819

20

21

222

23

24

3

4

56

78

910

11

12 13

1415

16 17

32

31

30

29282726

25

~ =DG

Bus 11: 1 MW fixed speed wind turbine Bus 7: 1 MW p.f. ±0.95(ΔQ = ±0.33 Mvar)

Determine controllable area using voltage sensitivity to Q support from bus 07

Q-V curve is plotted to consider the possible value of V/Q support

Bus voltages inside the zone can receive voltage compensation from DG sufficiently

#1

#2


7

Controllable Zone

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

dV (p

.u.)

Bus

V change from Q injection 0.33 MVar at bus 7

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.97 0.98 0.99 1 1.01Q [M

var]

V [p.u.]

V-Q curve of DG buses (bus 07 and 11)

B_07B_11

0

1

1819

20

21

222

23

24

3

4

56

78

910

11

12 13

1415

16 17

32

31

30

29282726

25

~ =DG

Guarantee V compensation 0.5-0.7 %

Bus 11: 1 MW fixed speed wind turbine Bus 7: 1 MW p.f. ±0.95(ΔQ = ±0.33 Mvar)

#1

#2


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Case Study Flicker is assumed as “Sinusoidal” at bus 11 (ΔV ≈ ±1.0 %, 2 Hz)

Case 1: using converter-connected DG to control the flicker at a remote bus (bus 11)

Case 2: using converter-connected DG to control the flicker at a local bus (bus 7)

Case 3: using only a STATCOM (0.3 MVar) at the flicker source bus 11



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0.98

0.982

0.984

0.986

0.988

0.99

0.992

0.994

0.996

-0.1 0.1

0.3

0.4

0.6

0.8

0.9

1.1

1.3

1.4

1.6

1.8

2.0

2.1

2.3

2.5

2.6

2.8

3.0

V (p

.u.)

bus 07

no compensation

1. Remote control

2. Local control

3. STATCOM

0.98

0.982

0.984

0.986

0.988

0.99

0.992

0.994

0.996

0.998

1

1.002

-0.1 0.1

0.3

0.5

0.7

0.9

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.7

2.9

V(p.

u.)

bus 11

no compensation

1. Remote control

2. Local control

3. STATCOM

0.965

0.97

0.975

0.98

0.985

0.99

-0.1 0.1

0.2

0.3

0.5

0.6

0.8

0.9

1.1

1.2

1.3

1.5

1.6

1.8

1.9

2.1

2.2

2.4

2.5

2.6

2.8

2.9

V (p

.u.)

BUS 17 and 24

B_17 no compensation

B_17 1. Remote Control

B_17 2. Local Control

B_17 3. STATCOM

B_24 no compensation

B_24 1. Remote Control

B_24 2. Local Control

B_24 3.STATCOM

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

-0.1 0.9 1.9 2.9Q (M

var)

Q supplying from DG 2 and STATCOM

DG 2 - no compensation

DG 2 - 1.remote control

DG 2 - 2.local control

DG 2 - 3.statcom

STATCOM-3.statcom

2 kHz Sinusoidal flicker ΔV/V < 0.8 % (IEC 61000-3-7)

(Flicker Source) (VSC-DG Bus)


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Calculate Short term Flicker Index (Pst)

IEC 61000-4-15(via MATLAB)

Flicker meterSimulator PstX

AC SinusoidalWaveform

RMS flickerinput10 Minutes

Pst < 1IEC 61000-3-7

Bus

PstNo

compensation case 1 (remote) case 2 (local) case 3 (STATCOM)

6 0.3466 0.1656 0.0709 0.07717 0.6116 0.2594 0.1659 0.170711 1.0325 0.4516 0.5870 0.364017 1.0325 0.4516 0.5870 0.364024 0.0836 0.0372 0.0383 0.038525 0.3156 0.1291 0.1145 0.1159


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Discussion Using STATCOM at flicker source bus provides

the best flicker mitigation.

Using remote measurement (flicker source) gives better mitigation than using only local measurement (PCC bus of DG), but need communication link.

If voltage sensitivity inside the zone is high, using only local bus control of DG may be sufficient.



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Conclusions Converter-connected DG with voltage control

ability can mitigate voltage flicker with similar results as using a STATCOM.

Flicker mitigation using converter-connected DG is very effective without communication system requirements, when it is connected near the flicker source.


Decentralised Controller for Flicker Mitigation in Converter-Connected DG Networks

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