Coupling Low Voltage Microgrids into Mid-Voltage ...lemmon/projects/GE-project-2010/pubs/GE-midterm.pdfGE Energy Coupled Microgirid Project - University of Notre Dame - Oct. 21, 2011

Coupling Low Voltage Microgrids into

GE Energy Coupled Microgirid Project - University of Notre Dame - Oct. 21, 2011

Mid-Voltage Distribution Systems


Each bus connected to a microgrid;Representing typical rural distribution network;Usually with severe voltage-rise problem;

Radial system structure with buses connected to primary substation:

Distribution System Control Architecture

VoltageRegulator

microgrid microgrid microgrid

GEMEMwirelesscomm.

GEMEMwirelesscomm.

GEMEMwirelesscomm.

VoltageRegulator switchable

capacitor banks

switchable capacitor banks

Project Objective and Approach


Objective: Maximize real power exported bycoupled low-voltage microgrids.

Issues:- Voltage Rise Problem;

Transient Stability;Legacy Controls.

- -

Approach:- Two-layer Voltage Control Architecture:

Decentralized Voltage Controler

Simulation Studies and Analysis.-

Benefits:- Minimize impact on DSO

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

- Reactive Power Dispatch

VoltageRegulator


wirelesscomm. wirelesscomm.wirelesscomm.

VoltageRegulator switchable

capacitor banks

switchable capacitor banks

MCM

MIC MIC MIC


Talk Outline

Distribution System Model

Voltage Rise Problem

Proposed Controller Architecture

Optimization Problem

Task Status and Schedule


Micro-Source

Bus 1

Bus 2 Bus 3 Bus N. . .

. . .PrimarySubstation 2PP 2Q 3PP 3Q NPP NQ

1PP 1Q

LoadMicro-Source Load

Micro-Source Load

Define voltage magnitude and phase angle of ith bus as:Distribution network is a passive system that only consumes power;

Bus 1 is reference bus with and .

System Model

Ei , δi

2E 2δ E δ3 3 E δN N

Real and reactive power injected through ith bus:Pi , Qi (i = 1,2,· · ·,N)

(i = 2,3,· · ·,N)

E = 1.0 pu1 δ = 0 rad1

Distribution Network

A microgrid can be represented as a microsource and a load;


Schematic diagram of a five-bus example system:

System Model

Primary Substation

B3 B4B1

Load 2

B5

Micro-Source1

Micro-Source2

B2

Load 1

A B C

A B C

A B C

A B C

powergui

Discrete,Ts = 5e-005 s.

ms_4_scope

ms_4_internal_scope

ms_4

E_req

P_req

mabc

ms_3_scope

ms_3_internal_scope

ms_3

E_req

P_req

mabc

Vab

cIa

b cP

QR

MS

(V-I )

A B C

a b c

Vab

cIa

b cP

QR

MS

(V-I )

A B C

a b c

VabcIabcPQ

RMS (V-I)

A

B

C

abc

Vab

cIa

b cP

QR

MS

(V-I )

A B C

a b c

VabcIabcPQ

RMS (V-I)

A

B

C

abc

Vab

cIa

b cP

QR

MS

(V-I )

A B C

a b c

VabcIabcPQ

RMS (V-I)

A

B

C

abc Vabc

IabcPQ

RMS (V-I)

A

B

C

abc

VabcIabcPQ

RMS (V-I)

A

B

C

abc

load_2_scope

load_2

A B C

load_1_scope

load_1

A B C

grid_scope

cable S3-S4ABC

A*B*C*

cable S2-S3ABC

A*B*C*

cable S1-S2ABC

A*B*C*

cable G-S1ABC

A*B*C*

ABC

abcSubstation

A

B

C

S4_scope

S3_scope

S2_scope

S1_scope

P_req40.6P_req3

0.6

E_req4-C-

E_req3-C-

Corresponding SimPower Model:

Z = 0.5+1j Ω Z = 0.5+1j Ω Z = 0.5+1j Ω Z = 0.5+1j Ω480 V

P = 30 kWQ = 10 kvar


P = 0~60 kWQ = -20~20 kvar

P = 0~60 kWQ = -20~20 kvar


Example with farthest bus injecting real power:

Voltage Rise Problem Illustration

Primary Substation

B3 B4B1 B5B2

Bus voltage magnitudes of the distribution network:

P = 0 kWQ = 0 kvar

Z = 0.5+1j ΩZ = 0.5+1j ΩZ = 0.5+1j ΩZ = 0.5+1j Ω

Bus 1 Bus 2 Bus 3 Bus 4 Bus 50.8

0.85

0.9

0.95

1

1.05

1.1

1.15

Bus

Vol

tage

Mag

nitu

de (V

)

1.2

1

P = 200 kW

P = 100 kW

P = 20 kW

P = 0 kWQ = 0 kvar

P = 0 kWQ = 0 kvar

P > 0 kWQ = 0 kvar

2

2

3

3

4

4

5

5

5

5

5

480 V


Example with farthest bus 100 kW real power injection, and keep all bus voltages to be 1.0 pu:

Reactive Power Control Illustration

Primary Substation

B3 B4B1 B5B2

Reactive power support required to maintain 1.0 pu bus voltages:

Z = 0.5+1j ΩZ = 0.5+1j ΩZ = 0.5+1j ΩZ = 0.5+1j Ω

Bus 1 Bus 2 Bus 3 Bus 4 Bus 5

-100

-80

-60

-40

-20

0

20

40

60

80

100

Rea

ctiv

e P

ower

Inje

ctio

n (k

var)

P = 0 kWE = 1.0 pu

P = 0 kWE = 1.0 pu

P = 0 kWE = 1.0 pu

P = 100 kWE = 1.0 pu

2

2

3

3

4

4

5

5

Bus

Vol

tage

Mag

nitu

de (V

)

0.95

1

1.05

1.10

1.15

1.20

0.90

0.85

0.80

Q = 20 kvar

Q = -20 kvar

480 V

GE Energy Coupled Microgrid Project - University of Notre Dame - Oct. 21, 2011

Voltage Rise Problem

Z R jX= +

E

E E

SP jQ= +

I∠φ

V0 ∠ 0° E∠δ

IR

IX

δI∠φ

V0 ∠0°

E∠δ

95%

105%

Distribution line impedance, Z=R+jXSubstation voltage V0∠ 0°Line current, I∠φInjected Power, SE = PE+ jQETerminal voltage, E∠δ

Phasor diagram shows injected power’s impact on current flows result in line voltages that exceed the 5% voltage regulation rule.

Without reactive power support: QE = 0PE > 0


Reactive Control of Voltage Rise Problem

Z R jX= +

E

E E

SP jQ= +

I∠φ

V0 ∠ 0° E∠δ

� Total Injected Power:SE = PE + jQE = EI∠ ( δ － φ )

� We reduce voltage rise by forcing linecurrent to lead terminus voltage

� This strategy implies= EI sin(δ φ) < 0.

� Voltage rise can be reduced by absorbingreactive power at the terminal bus.

� Reactive control mechanisms:static var compensator, voltage regulator, capacitor banks, and Q-E droop controls

I∠φ

V0 ∠ 0°

E∠δ

95%

105%IR

IX

φ δ

－QE


Ancillary Services

Defined by Federal Energy Regulatory Commission (FERC):“... those necessary to support the transmission of electric power from seller to purchaser given the obligations of control areas and transmitting utilities within those control areas to maintain reliable operations of the interconnected transmission system.”

Six Ancillary Services:Scheduling and Dispatch;Load Following;Operating Reserves.

Energy Imbalance;Real-power-loss Replacement;Voltage Control.

Coupled microgrids provide “voltage control” service, and become a player in the market.

Coupled microgrids can provide reactive power support, while exporting real power to the distribution network.


Providing Other Ancillary Services

Microgrid Consortium Manager (MCM):Predicting consortium’s overall capacity;Using the prediction to bid in ancillary service market;Distributing service bid among participating microgrids.

Maintaining set points with both P-freq & Q-E droop control;Rearranging if a microgrid’s capacity or network topology changes.

Microgrid Interface Controller (MIC):

-

- -

- -

�

�

VoltageRegulator



VoltageRegulator capacitor

bankscapacitor banks

MCM

MIC MIC MIC

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController


Objective Function

Maximizing real power exportation by downstream buses;Minimizing real power loss along the distribution line.

Cost function is accordingly defined as:

J(P, E )N�

i=2(Pcap,i � Pload ,i � Pi ) +

N�i=1

Pi =N�

i=2(Pcap,i � Pload ,i ) + P1Σ Σ－－Σ

J(P, E ) = P1 = E1N�

j=1

Ej(GBUS ,1j cos(δ1 δj) + BBUS ,1j sin(δ1 � δj))Σ －－The cost function worked on is actually:

－

Bus 1

Bus 2 Bus 3 Bus N. . .

. . .PrimarySubstation 2PP 2Q 3PP 3Q NPP NQ

1PP 1Q

2E 2δ E δ3 3 E δN N

Distribution Network

=


Optimization Problem

E 1

N�

j=1

Ej (GBUS,1j cos(δ1－ δj ) + BBUS,1j sin(δ1 � δj ))

w.r.t. Ei , Pi (i = 2, 3, · · · , N)

Pgen,i ≤ Pgen,i ≤ Pgen,iQgen,i ≤ Qgen,i ≤ Qgen,i

(i = 2, 3, · · · , N)

(j = 1, 2, · · · , N －1)

Pi = Ei

N�

j=1

Ej (GBUS,ij cos(δi－ δj ) + BBUS,ij sin(δi－ δj ))

i = 1, 2, · · · , N)

Qi = Ei

N�

j=1

Ej (GBUS,ij sin(δi－ δj � BBUS,ij cos(δi－ δj ))

Σ

Σ

Σ

Minimize

Subject to

－

(

) +

E i ≤ ≤ Ei (i = 2, 3, · · · , N)E i

Pln, j ≤ ≤≤ ≤

Pln, j Pln, j

Qln, j Qln, j Qln, j

Expression of P1

Voltage Magnitude and RealPower Injected at ith Bus;

Voltage Regulation Rule at ith Bus;

Real an Reactive Power Constraints Determined by Generation Capability;

Real and Reactive Power FlowConstraints of jth Distribution Line;

Real and Reactive Power Balance Relationship at ith Bus.


CERTS Microsource Controller

PowerInverterDG

localcontroller

Distributed Dispatch Integrated into Inverter ControlDispatcher generates P and E set points, as inputs to the CERTS inverter controller.

DG source TerminalMeasurement

CERTS DroopController c

3

b2

a1Vpk

w

Va

Vb

Vc

Vabc

IabcA

B

C

a

b

c

v_meas

i_meas

E_req

P_req

Vpk

w

P_req2

E_req1

dispatchagent

Decentralized Inverter Controls (CERTS)-

Provide small-signal stability;Mimic P-freq & Q-E droop control;

- Interface to any DG unit.-

-

Microgrid Simulation Example

simPower Simulation of UWM Microgrid Testbed- validated against UWM testbed- 42.5 kW Generation (storage, micorsource, genset) - 32 kW real load (8 kW can be automatically shed

GE Global Research Telecon - Notre Dame Microgrid Research - October 21, 2011

smartcoupler3

event connected

A

B

C

a

b

c

smartcoupler2

event connected

A

B

C

a

b

c

smartcoupler1

event connected

A

B

C

a

b

c

reset pulses

Out1

powergui

Discrete,

Ts = 2e−05 s.

microsource

E_req

P_req

PQ

V

I

RMS

freq

Pmm

a

b

c

PQ

V

I

RMS

freq

A

B

C

a

b

c

PQ

V

I

RMS

freq

A

B

C

a

b

c

main grid

A

B

C

genset

Ereq

Preq

PQ

V

I

RMS

freq

Pmm

a

b

c

external storage

E_req

P_req

PQ

V

I

RMS

freq

Pmm

a

b

c

dispatch request1

dispatch request

disconnect event2

Out1

disconnect event1

Out1

disconnect event

Out1

Switch

Step1

Step

A B C

a b c

SS

comABC

a

b

c

PC6

PQA B C

A* B * C*

PC5

PQA B C

A * B* C*

PC4

PQA B C

A * B* C*

PC3

PQA B C

A * B* C*

PC2

A

B

C

A*

B*

C*

MainGrid

MS

Line Summary

Level−2 M−fileS−Function1

dispatcher3

L6

A B C

L5

A B C L42

A B C

L4

A B C

L3

A B C

L2

A B C

L1

A B C

[PQgenMS]

[IgenMS]

[VgenMS]

[PmmES]

[PmmMS]

[PmmGS]

[PQcable31]

[PQcable43]

[freqES]

[PQcable42]

[PQcable21]

[loadshed]

[ESconnect]

[MSconnect]

[IslandState]

[RMSeb4]

[Ieb4]

[Veb4]

[PQeb4]

[PQgenES]

[EB4state]

[freqEB4]

[RMSeb3]

[Ieb3]

[RMSeb2]

[Ieb2]

[Veb2]

[PQeb2]

[RMSeb1]

[Ieb1]

[IgenES]

[Veb1]

[PQeb1]

[RMSbus]

[freqmain]

[RMSgenGS]

[RMSgenMS]

[PQgenGS]

[freqMS]

[VgenES]

[Vmain]

[reset]

[RMSgenES]

[RMSmain]

[freqbus]

[Ibus]

[Vbus]

[PQbus]

[Veb3]

[PQeb3]

[EB3state]

[freqEB3]

[Imain]

[PreqGS]

[PreqMS]

[PreqES]

[IgenGS]

[VgenGS]

[freqGS]

[EB2state]

[freqEB2]

[EB1state]

[freqEB1]

[PQmain]

[GSconnect]

Generation Summary

Gain7

−K−

Gain6

−K−

Gain5

−K−

Gain4

−K−

2/15

2/15

2/15

2/15

GS

[freqGS]

[freqES]

[PQgenGS]

[PQgenMS]

[PQgenES]

[PQcable43]

[PQcable42]

[PQcable31]

[RMSmain]

[PQcable21]

[PQcable43]

[PQcable42]

[PQcable31]

[PQcable21]

[PQgenGS]

[PQgenMS]

[PQgenES]

[freqMS]

[PmmGS]

[Vmain]

[PmmMS]

[PmmES]

[GSconnect]

[MSconnect]

[ESconnect]

[IslandState]

[PQgenGS]

[PQgenMS]

[PQgenES]

[PQmain]

[PQmain]

[loadshed]

[loadshed]

[loadshed]

[loadshed]

[loadshed]

[EB1state]

[EB4state]

[EB3state]

[EB2state]

[PQbus]

[Imain]

[Vbus]

[freqES]

[freqEB4]

[Veb4]

[PQeb4]

[Ieb4]

[EB4state]

[RMSeb4]

[freqEB4]

[Veb3]

[reset]

[PQeb3]

[Ieb3]

[EB3state]

[RMSeb3]

[freqEB3]

[Veb2]

[PQeb2]

[Ieb2]

[EB2state]

[RMSeb2]

[reset]

[freqEB2]

[Veb1]

[PQeb1]

[Ieb1]

[EB1state]

[RMSeb1]

[freqEB1]

[RMSbus]

[Vbus]

[PQbus]

[reset]

[Ibus]

[freqbus]

[RMSgenGS]

[VgenGS]

[PreqGS]

[RMSgenES]

[PQgenGS]

[IgenGS]

[freqGS]

[RMSgenMS]

[reset]

[PreqMS]

[PreqES][VgenMS]

[PQgenMS]

[IgenMS]

[freqMS]

[VgenES]

[PQgenES]

[IgenES]

[freqES]

[freqmain]

1

1

1ES

EB4

EB3

EB2

EB1

2

1

1

1

1

1

2

2

.8

.5

−.1

2

Bus SummaryBUS

2 kW e−board4

reset

priority

shed_load

w

state

PQ

V

I

RMS

A

B

C

2 kW e−board3

reset

priority

shed_load

w

state

PQ

V

I

RMS

A

B

C

2 kW e−board2

reset

priority

shed_load

w

state

PQ

V

I

RMS

A

B

C

2 kW e−board1

reset

priority

shed_load

w

state

PQ

V

I

RMS

A

B

C

Measurement Block

Computes amount of shed load

Dispatch Logic

main grid

External Storage (ES)15 kW

Microsource (MS)15 kW

Genset (GS) - 12.5 kW

Load 2 kW Load 6 kW

Load 8 kW

Load 8 kW

eboard 2 kW

eboard 2 kW

eboard 2 kW

eboard 2 kW

smartswitch

smartswitch

smartswitch

cable

cable

cablecable

eboard bus

cable

0 1 2 3 4 5 6 7 8

59

60

61ES and eBoard4 Frequency (Hz)

0 1 2 3 4 5 6 7 8−200

0

200eBoard Bus Voltage (V)

0 1 2 3 4 5 6 7 8−1

0

1

x 104 real/reactive power (W)

0 1 2 3 4 5 6 7 8−0.5

0

0.5

1

1.5Shed Load Power (pu)

dispatcherenabled

islandingevent

loss ofmicrosource

loadshedding

microsourcereconnect

Transient Stability

GE Global Research Telecon - Notre Dame Microgrid Research - October 21, 2011

• System State equations

δ̇i = mP (Pi − P 0i )Ėi = k(E

0i − Ei −mQQi)

Pi = Ei

n∑

j=1

EjYij cos(δi − δj + αij)

Qi = Ei

n∑

j=1

EjYij sin(δi − δj + αij)

• This system interconnects two net-worked systems

– System of coupled nonlinearoscillators (δ)

– Voltage control system (E)

• Stable interconnection occurs whenthe oscillators are synchronized.

Q Calculation Low PassFilter

Q vs E Droop

VoltageControl

P vs FreqDroop

Low PassFilter

Low PassFilter

Magnitude Calculation

P Calculation

Gate PulseGenerator

InverterCurrent

Load Voltage(measured)

Line Current

Q

P

E

RequestedVoltage, Ereq

RequestedPower, Preq

Requestedfrequency, freq

δv

V

E0

δ̇i = mP (Pi(δ, E)− P 0i )

Ėi = k(E0i − Ei −mQQi(δ, E))

P0

E δ

power setpoint

voltage setpoint

coupled oscillators

voltage controllers

CERTS Controller for Fast Inverters


Example of Optimization Problem

P = 60 kW req,1 E = 1.0433 pureq,1 P = 60 kW req,2 E = 1.0426 pureq,2

Set points of microgrid determined by the optimization problem:

Primary Substation

B3 B4B1

Load 2

B5

Micro-Source1

Micro-Source2

B2

Load 1

Z = 0.5+1j Ω Z = 0.5+1j Ω Z = 0.5+1j Ω Z = 0.5+1j Ω480 V



P = 0~60 kWQ = -20~20 kvar

P = 0~60 kWQ = -20~20 kvar

P1 Q1 E2 E3 E4 E543.54 kW -55.35 kvar 0.9570 pu 0.9650 pu 1.0334 pu 1.0502 pu

P = 60 kW req,1 E = 1 pureq,1 P = 60 kW req,2 E = 1 pureq,2

For comparison, we can use set points as:

In this situation, even though more reactive power support is provided, voltages of two load buses exceed the upper and lower limits defined byvoltage regulation rule.


Future Work

Verification of Compatibility with Legacy Equipments:Algorithm must not contradict with current control mechanism;Must consider both automatic controller and DSO controls;Use simpower model to verify the compatibility.

- - -

VoltageRegulator



VoltageRegulator capacitor

bankscapacitor banks

MCM

MIC MIC MIC

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

CERTSController

Task 1 Summary

GE Project Summary - University of Notre Dame - Oct. 21, 2011

Task 1.1 - Algorithm DevelopmentAlgorithm determine “exported real power” and “voltage levels”, microgrid controllers automatically supply reactive power to maintain voltage levels.Zhao Wang currently developing algorithms for optimal power and voltage assignment.Algorithm development to be completed by mid Nov. 2011, technical report by Jan. 2012.

Task 1.2 - Simulation DevelopmentPrototype simPower models of distribution line and microgrid completed in mid-July 2011.Current simulations include UWM controllers, and use capacitor banks for voltage control.Zhao Wang currently integrating microgrid controller and optimization algorithm into MV distribution line simulation.Integration to be completed by mid Nov. 2011, technical report by Jan. 2012.

-

--

---

-

Task 1.3 - EvaluationNot started yet, and expected start date is Jan. 2012.Goal is to integrate capacitor banks and microgrid controls into simulation, and study interaction of microgrid control with automatic capacitor bank controls.Expected completion by end of Apr. 2012, findings to be presented in project final report by May 2012.

--

-

Task 1 Overview - Coupled Microgrid

GE Project Summary - University of Notre Dame - Oct. 21, 2011

- Task 1.1 (algorithm development) about 4 months behind schedule- Task 1.2 (simulation) to be done in parallel with task 1.1- Interim Technical Report on Task 1.1/1.2 to be completed by January 2012- Task 1.3 (evaluation) to start in November 2011 and complete in April 2012- Final Report to be finished by May 2012.

4/1/

2012

Page_1 Cover SlidePage_2 Distribution System Control ArchitecturePage_3 Project Objective and ApproachPage_4 Outline of The TalkPage_5 System ModelPage_6 SimPower Simulation ModelPage_7 Voltage Rise Problem IllustrationPage_8 Reactive Power Control IllustrationPage_9 Voltage Rise ProblemPage_10 Solution to Voltage Rise ProblemPage_11 Ancillary ServicesPage_12 Controller Architecture to Provide Ancillary ServicesPage_13 Objective FunctionPage_14 Optimization Problem DescriptionPage_15 Controller StracturePage_16 Microgrid Simulation ExamplePage_17 Transient StabilityPage_18 Example of Optimization ProblemPage_19 Future WorkPage_20 Task SummaryPage_21 Task Overview

Documents

Coupling Low Voltage Microgrids into Mid-Voltage ...lemmon/projects/GE-project-2010/pubs/GE-midterm.pdfGE Energy Coupled Microgirid Project - University of Notre Dame - Oct. 21, 2011