Overview of Task 1

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Objective: Maximize real power exported to mid-voltage distribution networks from coupled low-voltage microgrids.

Issues:- Voltage-rise problem;

Weak network property;Legacy control’s compatibility.

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Approach:- Reactive power dispatch;

Simulation analysis.-

Benefits:- Minimize impact on existing

voltage regulation policies;Maximize real power exported back to distribution network.

- - Distributed optimal controller;

OLTC

microgrid microgrid microgrid

SVCSTATCOM

Distribution Network with Legacy ControlsFig. 1

Task 1.1 Algorithm Development

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Objective Manage generations coordinatively to export maximum real power and maintain voltage levels within limits.

A hierarchical control architecture includes: Microgrid Consortium Manager (MCM), Microgrid Interface Controller (MIC), and CERTS droop controller. Two levels of optimization problems in MICs: microgrid states are determined locally; set points of microsources are solved in a centralized manner.

Results

OLTC

microgrid microgrid microgrid

MCM

MIC MIC MIC

STATCOMSVC

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-

Hierarchical Control ArchitectureFig. 2

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1.2 Simulation Development

Objective & Approach Performance of the proposed controller is checked in distribution network simulation models. Simulations are built with simpower toolbox in matlab.

A complete simulation model of distribution network is formulated, including the proposed hierarchical control architecture.Legacy control devices are individually integrated into the simulation model to check controller compatibility.

Result -

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V_mcm

cap_mic

trig_ln1

trig_ln2

S_ln1

S_ln2

change_mic

P_opt_mic

Q_opt_mic

V_mag

V_pha

recal_mg1

P_mg

Q_mg

V_mag

V_pha

switch_mg

P_opt1

P_opt2

P_opt3

V_req1

V_req2

V_req3

Microgrid Capacity Estimation

Microgrid Operate PointDetermination

MicrosourceSet Points Determination

Realization of MIC in the Simulation ModelFig. 3

StructuralInformation

State of Neighbors

Microgrid Set Point

Set Points ofMicrosourcesStructural

InformationStructuralInformation

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1.3 Evaluation

Objective Evaluating the compatibility of the controller with existing voltage control mechanisms in distribution networks.

In normal operation, system is optimal with respect to microgrid capacity estimation results.After load or structural changes, stable operation is verified. Control scheme compatible with legacy control devices, including OLTCand SVC.

Result -

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OLTC

STATCOM

Complete Simulink Simpower Model for EvaluationFig. 4

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powergui

Discrete,Ts = 5e-005 s.

mg3_scopemg2_scope

mg1_scope

Vab

cIa

bcP

QR

MS

( V-I)

A B C

a b cVa b

cIa

bcP

QR

MS

( V-I)

A B C

a b cVabcIabcPQ

RMS (V-I)

A

B

C

abc

VabcIabcPQ

RMS (V-I)

A

B

C

abc

Vab

cIa

bcP

QR

MS

( V-I)

A B C

a b c

VabcIabcPQ

RMS (V-I)

A

B

C

abc

VabcIabcPQ

RMS (V-I)

A

B

C

abc

VabcIabcPQ

RMS (V-I)

A

B

C

abc

grid_scope

A*

B*

C** * *

cable_S3_to_S4

ABC

A*B*C*

A*

B*

C*

cable_S2_to_S3

ABC

A*B*C*

cable_S1_to_S4

ABC

A*B*C*

cable_S1_to_S2

ABC

A*B*C*

VabcVabcB2

Three-Phase OLTCRegulating Transformer2

Vm (pu) Tap

A

B

C

a

b

ccom

ABC

abc

comABC

abc

comABC

abc

comABC

abc

Tap1

T4

A B C

a b c n2

T3

A B C

a b c n2

T2

A B C

a b c n2

Substation

A

B

C

S4_scope

S3_scope

S2_scope

S1_scope

Tap1

[S_ln2]

[S_ln1]

[V1_B1]

[S_ln4]

[S_ln3]

Microgrid 1 Microgrid 2 Microgrid 3

TSC194 Mvar

TCR109 Mvar

TSC294 Mvar

TSC394 MVar

P A B CP A B CP A B CP A B C

Secondary

(480 V)

A

B

C

a

b

c

SVC Controller

Vabc_prim

Vabc_sec

TCR

TSC1

TSC2

TSC3

Primary

(13.8 kV)

A

B

C

a

b

c

Vabc_Prim

Vabc_Sec

13.8 kV/480 V

1 MVA

A

B

C

a

b

c

SVCA B C

D-STATCOM+/- 3Mvar

Bstatcom A B C

a b c

ln 1 ln 2 ln 3

ln 4

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1 Simulation Result with OLTC System with structural changes inside and outside of microgrids

Response of Voltage at the PCC of mg 1Fig. 5

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Power Outputs of Microgrid 1Fig. 6

Optimal set points solved by the distributed controller have voltages at 1.0 pu;OLTC tap is kept at 0 throughout the simulation, since the feedback voltage stays within OLTC’s deadband.

line between mg 1 and mg 3 disconnects

line between ms1 and ms3 in mg 1 disconnects

mg1 exports less realpower and consumes more reactive power

real power of mg1 increases but needs more reactive power

1.00625 pu

8 9 10 11 12 13 14 15 16 17 180.99

0.992

0.994

0.996

0.998

1

1.002

1.004

1.006

1.008

1.01

time(s)

Vol

tage

Mag

nitu

de (p

u)

deadbandof OLTC

0.99375 pu

8 9 10 11 12 13 14 15 16 17 18−30

−20

−10

0

10

20

30

40

time(s)P

ower

(kW

/kV

ar)

mg 1 Pmg 1 Q

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1 Simulation Result with SVC System with structural changes inside and outside of microgrids

Response of Voltage at the PCC of mg3Fig. 7

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Power Outputs of Microgrid 3Fig. 9

Voltage feedback of SVC is kept close to 1.0 pu, so there is no switching;The reactive power absorbed by SVC is constant around 2 kVar.

line between mg1 and mg3 disconnects

line between ms7 and ms9 in mg3 disconnects

mg3 exports less realpower and consumes more reactive power

real power of mg3 increases but needs more reactive power

14 16 18 20 22 240.99

0.995

1

1.005

1.01

time(s)

Vol

tage

Mag

nitu

de (p

u)

14 16 18 20 22 24−30

−20

−10

0

10

20

30

40

time(s)P

ower

(kW

/kV

ar)

mg 3 Pmg 3 Q

0 5 10 15 20 250

1

2

number of TSCs

8090100110120130140

alpha TCR (deg)

Operation of SVCFig. 8 time(s)

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1 Conclusion

The hierarchical controller proposed does not interfere with legacyvoltage control devices, such as OLTC and SVC.

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-

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During structural changes inside and outside of microgrids, the operation of legacy control devices is not influenced by microgrids;

Distributed optimal controller reconfigures coupled microgrids to exportmaximum real power and maintain PCC voltages close to 1.0 pu;

Proposed controller is realizable in microgrid controllers from GE, and itwill not interfere with existing distribution network control mechanisms.

If cooperation with DSO is available, voltage control devices beingset according to the connected microgrids, then at least 20% more real power is expected to be provided by coupled microgrids.

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1 Recommendation I

Operate Microgrids Close to the Nominal Voltage Keep voltage of microgrid within deadbands of OLTCs to prevent tap change.Keep microgrid voltages close to the nominal value to reduce reactive power support required from SVC and STATCOM.

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BenefitExisting distribution networks and voltage control mechanisms need no modification. Microgrids operate like good customers, making it easier for DSOs to accept.

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CostCapacities of the coupled microgridsare under-utilized because voltagesof microgrids are fixed. If voltages of microgrids are allowedto change, more real power export is possible, but voltage control deviceswill switch frequently.

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Without the DSO’s coordination, this is the best we can do to integrate microgrids into distribution networks.

GE Energy Coupled Microgrid Project - University of Notre Dame - April 19, 2012

Task 1 Recommendation II

Configure Voltage Control Devices According to Microgrid Set Point Modify the nominal voltage and deadband of OLTCs according to the set points of directly connected microgrids;Keep the nominal voltage of SVCs and STATCOMs close to the set points of microgrids connected.

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BenefitSwitching frequencies of legacy control devices decrease as they are dynamically regulated. Network voltage profile is more flexible, hence the required reactive power support is reduced.

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CostDSOs are required to coordinate withthe microgrid hierarchical controller;Communication structure is necessary to enable information exchange.

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With DSO’s coordination, the coupled microgrids are able to export more real power in a flexible voltage profile without sacrificing legacy control devices. Reactive power dispatch in the network is controlled by the coupled microgrids,hence legacy control devices are saved to respond to emergencies.