University of Wisconsin-Madison

CERTS MicrogridMicrogrid Workshop

17 June 2005Bob Lasseter

Representing the research team of:LBNL, SNL

University of WisconsinNorthern Power Systems

TecogenYoutility Inc

American Electric Power

University of Wisconsin-Madison

Generic Microgrid:

Clusters sources with loadsSingle controllable unit to utilitySmoothly move between parallel and islanded modes

University of Wisconsin-Madison

University-of-Wisconsin’s µgrid

75 yd4 wire Cable

9.0 kWY Loads

Utility System

480 V

208 V

480 V

DG 1

DG 2

9.0 kW ∆ Loads

480 V

Static Switch

25 yd4 wire Cable

20 yd4 wire Cable

4.5 kW ∆ Load

University of Wisconsin-Madison

Stability (interactions between grid and other microsources)

Power balance when islanding (load sensors & fast re-dispatch of microsource)

Custom site engineering

Major Microgrid Issues

University of Wisconsin-Madison

Stability: Fixed Power Factor

∆V = f (Z , I)Change in power output changes ∆VResulting in change in µsource currentCan result in change in ∆VOscillation in P and V

DG A DG B

I

ZZZ Z

Increase power output of DG A

Need to control voltage at each inverter

Voltage

University of Wisconsin-Madison

CERT’s Q versus E Droop for stability

E∆

E∆

oE

Q

maxQ

maxQ−

InductiveRegion

CapacitiveRegion

Ereq

maxQ

Qreqo

QEm

QmEE

∆=

−=

DG A DG B

I

∆V = f (Z , I)

Z

Voltage difference between sources is function of impedance and current between them.

University of Wisconsin-Madison

UtilitySystem

4 wire75yd

4 wire25yd

Event:Loss of load

UW’s µgrid traces: Voltage Regulation

P1 P2

Unit P2Unit P1

University of Wisconsin-Madison

Stability (interactions between grid and other microsources)

Power balance when islanding (load sensors & fast re-dispatch of microsource)

Custom site engineering

Major Microgrid Issues

University of Wisconsin-Madison

Power balance Problem: Fast control

Utility System Primary Connection

(13.2 kV)

Utility System Interface Control(Synchronization, fault protection, islanding

detection, etc.)

Campus Owned Distribution (13.2

kV)

Isolating Device (opens during micro-

grid mode)

Heat Distribution

Academic Building A

Dormitory B Administrative Building

Dormitory A

Student Union

Academic Building

B

To Other

Campus Loads

500 kVA 500 kVA 300 kVA

75 kVA

800 kVA300 kVA

Generator Step Up

Transformer

Gen

Gen

Gen

Generator Protection

and Control

Paralleling Bus (4.8 kV)

Voltage Regulator

Heat Distribution

1.75 MVA

1.75 MVA

1.75 MVA

Heat Recovered from ICE Units

Load control

Communication & Control Signal Path

EPRI: Campus Microgrid System: CEC Workshop

University of Wisconsin-Madison

MicroGrid MicroGrid

CERTS MicroGrid

13.8 kV

MicroGrid

480 V

120 kV

480 V

PCC

Peer-to-peer source model (no master element)Plug & Play Model (Avoids extensive site engineering & allows placement near heat load)

Power balancing using local information

University of Wisconsin-Madison

CERTS Microgrid Configuration

Separate load types (sensitive)

Fast islanding switch

Single PCC (1547 LAPS)

No load control required

DR

DR

PCC

Fast switch

Traditional loadsSensitive loads

DR

University of Wisconsin-Madison

DR

DR

PCC

Fast switch

Traditional loadsSensitive loads

Intentional islandingNo communications for load balancingLoad balancing uses local information at each unitAutomatic re-synchronizing of the fast switch

DR

Operational Concept

University of Wisconsin-Madison

Load balancing: P versus Frequency Droop

UtilitySystem P1

F1

P2

F2

L1 L3 L4 L5

4 wire75yd

4 wire25yd

Event:Transfer to Island

Event shows Unit 2 reaching maximum output power after islanding.

A – Grid B – Island

P1 [pu] 0.08 = 10% 0.4 = 50%

P2 [pu] 0.72 = 90% 0.8 = 100%

Frequency [Hz] 60.00 59.8

Load Level [pu] 1.2 = 150% 1.2 = 150%

Grid Flow [pu] 0.4 = 50% 0.0

Control of P1 and P2

University of Wisconsin-Madison

Unit 1

Unit 2

Wisconsin’s µgrid traces: Islanding

University of Wisconsin-Madison

F1

L

F2

L

Utility System

Series Configuration

Utility System

F1

L

F2

LParallel Configuration

Zone Control: Load Tracking

( )iioFoi FFm −−= ,ωωmaxP

mFω∆

=Fo1ωo

ωo-∆ω

ωo+∆ω

F

ω

Importing from Grid

Exportingto Grid

ωexp

ωparFo2

University of Wisconsin-Madison

A – L3 on B – L3 off

P1 [pu] 0.4 = 50% 0.13 = 16%

P2 [pu] 0.8 = 100% 0.77 = 96%

Frequency [Hz] 59.80 59.968

Load Level [pu] 1.2 = 150% 0.9 = 112%

Grid Flow [pu] 0.0 0.0

Zone Power Control: Parallel Case: F1 = - F2

P1

F1

P2

F2L1

L3 L44 wire75yd

4 wire25yd

L2

UtilitySystem

Event:Load Removal

Event shows Unit 2 backing off from maximum output power after a load is removed.

Parallel Configuration, Control of F1 and F2

University of Wisconsin-Madison

Unit 1

Unit 2

U of W’s µgrid traces: Parallel Case: F1 = - F2

University of Wisconsin-Madison

4 wire25yd

4 wire75 yd.Utility

System1P1

1F

2P

1

2F

1L 3L 4L 5LEvent:

Wrong Set pointF1

P1-max

Import From Grid, Setpoints are 90% and 10% of Unit Rating; Choosing a Wrong Setpoint

University of Wisconsin-Madison

Dynamics of Units; Wrong SetpointUnit 1 Unit 2

University of Wisconsin-Madison

Summary of micro-source controls

Existing DG controls; P at unity pf or constantQHigh penetration levels create interaction problemsCan not smoothly move between grid connected and island operation

CERTS controlsVoltage control with droopPower versus frequency droopAutomatic re-synchronizing to utility grid

University of Wisconsin-Madison

Microgrid Test Bed Layout

Feeder A

Feeder C

Feeder B

B-3

P-2

P-3Zone-1PCC

Zone-2

Zone-3 Zone-4

Zone-5

Zone-6

P-1

B-4

B-513.8 kV

3-Wire 480 V

4-Wire 480 V

4-Wire 480 VEnergy Manager

Sensitive Loads

Traditional Loads

4-Wire 480 V

Micro-source

Power FlowController

Point ofCommonCoupling

Breaker

Grid connected• Load changes• Control of load flow• Voltage control• Protection• P/V dispatch

Isolated operation• Separation• Load pick-up• Voltage and Q control• Protection• Automatic re-syn.

Static Switch

University of Wisconsin-Madison

Microgrid Test Bed Timeline

Test Bed Design & Construction

Design: NPSComponent Construction: NPS

Static Switch : NPS

Microsource Control Modification3-Inverters and System Test: Youtility3- “CERTS” Microsources: Tecogen

Test Bed Performance Testing

Static Switch 1547 tests: AEP

Phase 1 construction & tests: AEP

Field Demo Planning

20062003 20052004

20062003 20052004 May

University of Wisconsin-Madison

Key Tests• Load Flow control

Unit Power, Zone flow & Mixed

• Grid-to-Island-to-GridPower vs. freq power balance Re-closing of the Static Switch using local information

•Protection including Static SwitchInternal, grid side & IEEE 1547events