Overview of Actuation Thrust

Fred WangThrust Leader, UTK Professor

ECE 620 CURENT CourseSeptember 13, 2017

Actuation in CURENT

2

Power GridWide Area Control of

Power Grid

Measurement &Monitoring

Communication

Actuation

Communication

WAMS

FDRPMU

PSS

Generator

Storage

HVDC

Wind Farm

FACTS

Solar Farm

Responsive Load

Actuation Technology Linkages

3

Enab

ling

Tec

hnol

ogie

sEn

gine

ered

Sys

tem

sFu

ndam

enta

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owle

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ControlControl Actuation Actuation

Control Architecture

Actuator & Transmission Architecture

System-level Actuation FunctionsCommunication

& Cyber-security

Estimation

Economics & Social Impact

MonitoringMonitoring ModelingModeling

Situational Awareness & Visualization

Wide-area Measurements

Modeling Methodology

Hardware Testbed

Large Scale Testbed

Testbeds

Control Design &

Implementation

Basic Actuation Functions in Power Systems

• Power flow control• Voltage and var support• Stability• Protection

Separation Fault current limiting Overvoltage suppression

• Energy source and load grid interface

4

Power Flow Control

• Power flow is determined by Kirchhoff's Laws, e.g.

2GPG1 G2

1GP

3DP

1DP2V1V

3V

G3

2DP

3GP

2P1P( )21

12

2112 sin δδ −

⋅=

XVVP

5

Non Power Electronics Power Flow Actuators

• Voltage Generators (exciter control - PE) Switched shunt capacitor banks Transformer tap changer

• Impedance Switched lines Series compensation (switched series capacitors)

• Angle Phase-shifting transformers

6

Example of Phase-shifting Transformers

• A direct, symmetrical PST with limited range and voltage magnitude change.

• There are also other types (e.g. indirect PST)

7

Non Power Electronics Voltage & Var Actuators

• Generator (exciter)• Condenser• Switched capacitor banks• Transformer tap changer• Load management

8

Non Power Electronics Actuator for Stability

• Generator Governor Power system stabilizer (excitation)

• Switchgear Line switching Source and load switching

• Switched compensators Reactors Capacitors

9

Protection - Breakers

Live-tank breakers Dead-tank breakers

10

Breaker with Switching Resistors

Switching resistors

Must absorbenergy duringswitching=> shorted afterseveral ms!

11

Overvoltage Protection

12

• Spark Gaps Metallic electrodes providing a gas insulated gap to flash

over Very robust, but large variance in protection level

• Magnetically blown Surge Arresters Same basic principle as spark gaps, adopt SiC varistors

but can handle much higher energy dissipation • Metal Oxide Varistor (MOV)

Ceramic composites based on zinc, bismuth, and cobalt Highly non-linear current-voltage characteristic Very precise and stable protection level Limited overload capability

20>α= αVI

12

Metal Oxide Varistor (MOV)

13

continuousoperating voltage

peak voltage

13

Series Compen-sation (SC)

Static Var Compensation (SVC)

Phase Shifting Transformers

sin )( 2112

21X

VVP δδ −=

V1/δ1 V2/δ2

HVDC and HVDC Light

=~

~=

+ PHVDC

Power flow P

FACTS = Flexible AC Transmission System

Power Electronics Based Power Flow Control

1414

Power Electronics Power Flow Actuator

15

• Voltage SVC (Static Var Compensator) STATCOM (Static Synchronous Compensator)

• Impedance TCSC (Thyristor Controlled Series Compensator) SSSC (Static Series Synchronous Compensator)

• Angle TCPFT (Thyristor Controlled Phase-shifting

Transformers or Angle Regulator)• All

HVDC UPFC (Unified power flow controller)

Thyristor Controlled Series Capacitor (TCSC)

• A capacitive reactance compensator which consists of aseries capacitor bank shunted by a thyristor-controlledreactor in order to provide a smoothly variable seriescapacitive reactance.

• Can be one large unit or several small ones. Limits fault current when reactor is fully on.

16

AC CapacitorLine

Reactor

Thyristor valve

STATCOM and SSSC• A static synchronous generator

operated without an external electric energy source

• Can be shunt or series connected• As a shunt compensator, can

inject reactive power• As a series compensator , its

voltage is in quadrature with, and controllable independently of, the line current for the purpose of increasing or decreasing the overall reactive voltage drop across the line and thereby controlling the transmitted electric power.

17

Transformer

Converter

Interface

Energystorage

Line

Unified Power Flow Controller• The UPFC, by means of angularly unconstrained series

voltage injection, is able to control, concurrently orselectively, the transmission line voltage, impedance,and angle or, alternatively, the real and reactive powerflow in the line.

• The UPFC may also provide independently controllableshunt reactive compensation.

18

CouplingXfmr

STATCOM SSSC

DC link

SeriesVSI

ShuntVSI

CouplingXfmr

AC line

Year1954 1970 20001980

Mercury Arc Valve HVDC (Phased out)

Thyristor ValveHVDC Classic

IGBT (Transistor) ValveHVDC Light

Pros: Low lossesCons: Reliability

MaintenanceEnvironment

Pros: ReliableScalable

Cons: Footprint

Pros: Controllability FootprintDC Grids

Cons: Losses

HVDC Technology Development

19

Numberof lines:

Right of way ~300 ~ 120 ~ 90(meter)

800 kV DC for long distance bulk power transmission

Tranmission of 6000 MW over 2000 km. Total evaluated costs in MUSD

0500

100015002000250030003500

765 kV AC 500 kV DC 800 kV DC

MUS

D LossesLine costStation cost

20

Chart3

765 kV AC765 kV AC765 kV AC

500 kV DC500 kV DC500 kV DC

800 kV DC800 kV DC800 kV DC

Station cost

Line cost

Losses

MUSD

Tranmission of 6000 MW over 2000 km. Total evaluated costs in MUSD

673

1482.6666666667

907

880

1027

790

904

664

538

2000

Number of linesStation costLine costLosses

500 kV AC1069746519076255

765 kV AC467322249073804

500 kV DC288010277902697

800 kV DC19046645382106

Number of linesStation costLine costLosses

500 kV AC106973100.66666666679074704.6666666667

765 kV AC46731482.66666666679073062.6666666667

500 kV DC288010277902697

800 kV DC19046645382106

2000

Station cost

Line cost

Losses

MUSD

Transmission cost, 6000 MW, 2000 km

1000

Station cost

Line cost

Losses

Right of way

Station cost

Line cost

Losses

MUSD

Tranmission of 6000 MW over 2000 km. Total evaluated costs in MUSD

Number of linesStation costLine costLosses

500 kV AC54349826552071

765 kV AC24115774871475

500 kV DC28805134541847

800 kV DC19042903701564

Number of linesStation costLine costLosses

500 kV AC10697654.66666666679072258.6666666667

765 kV AC4673384.66666666679071964.6666666667

500 kV DC288010277902697

800 kV DC19046645382106

500 kV AC500 kV AC500 kV AC500 kV AC

765 kV AC765 kV AC765 kV AC765 kV AC

500 kV DC500 kV DC500 kV DC500 kV DC

800 kV DC800 kV DC800 kV DC800 kV DC

Number of lines

Station cost

Line cost

Losses

10

697

3100.6666666667

907

4

673

1482.6666666667

907

2

880

1027

790

1

904

664

538

500 kV AC

800 kV AC75225

500 kV DC4080

600 kV DC4590

800 kV DC6060

Power Electronics Actuator for Stability

21

1st Thyristor-Controlled Series Compensation (TCSC) Project

Power Electronics Actuator for Protection

22

VSC HVDC DC Fault Protection – Solution

23

Main DC breaker

Fast disconnector Auxiliary DC breaker

Disconnect switch

• Fast fault clearance solution (

Summary of Actuation Technologies• Traditional non power electronics based actuators

have limited actuation capability. The system is generally not very flexible

• PE based actuators (FACTS, HVDC) can be very effective for Power flow control Voltage and var control System stability Protection Interface of source and load

• Issues: cost, reliability• Solutions: new PE technology, modular approach,

hybrid approach, different architecture

24

Modular Approach - Distributed FACTS

25

Distributed Series Static Compensator

Modular Converters for Multi-Terminal HVDC Systems

26

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

ABC

P

N

Larm

+ −

Larm

Larm

Larm

Larm

Larm

Csub

Modular multilevel converter (MMC)

Hybrid Approach - Thin AC Converter

27

Actuation Thrust Objectives and Challenges

• Objectives Develop actuation methodology and system architecture that will

enable wide-area control in a transmission grid with high penetration of renewable energy sources

28

• Challenges1) Lack of cost effective wide-area system-level actuators2) Lack of global actuation functions for the existing actuators or

lack of knowledge how to use these actuators for global functions

3) System architecture not best suited for wide-area coordinated actuation and control for network with high penetration of renewable energy sources

4) Lack of design and control methodologies for systems with power electronics converters interfacing a high percentage of sources and loads

Technical Approaches and Research Focus

29

• Multifunctional actuators to exploit full capabilities of existing or future actuators Renewable energy sources supporting system control

FACTS, HVDC

• Flexible and controllable transmission architecture Hybrid AC/DC

Multi-terminal HVDC

Renewable Energy Sources for Grid SupportObjective: • Demonstrate grid

supporting capability of renewable energy sources and energy storage in systems with >50% of renewables

Accomplishments:• Renewable energy

sources and energy storage working modes implemented in simulation & HTB

30

Frequency Support Function Test in HTB

0 2 4 6 8 10

0.650.7

0.750.8

0.850.9

0.95

0 2 4 6 8 1059.2

59.4

59.6

59.8

60

60.2

Wind Turbine Active Power (p.u.)

Area Frequency (Hz)

Time (s)

Scenario• 80% renewable by onshore

wind & offshore wind through HVDC

• Event triggered by a HVDC converter failure.

• Frequency and voltage support from onshore wind farm and the HVDC converters

• Curtailment and voltage mode control when necessary

• Integration of energy storage to further enable grid support controls

31

Design of Renewable Interface Converters Considering Stability

Objective: Develop stability criterion and design methodology of renewable interfaceconverters to ensure stable operation of multi-bus systems with renewableenergy sources.

Grid-Connected Radial-line Renewable System Stability

+−

Zg

Grid

Vg

*clc1 1G IYoc1

i1 (v1)

Z1

*clc2 2G IYoc2

i2 (v2)

Z2

*clc3 3G IYoc3

i3 (v3)

Z3

PCC

Bus 1 Bus 2 Bus 3

YB2R Yoc3YB1R

YPCCRCheck at Bus 3

Check at Bus 2

Check at Bus 1

Check at PCC

Z3Z2Z1

Zg

ig (vPCC)

Checking sequence

iL3iL2iL1

Inverter 1 Inverter 2 Inverter 3PV Wind turbine

Voltage-feedforward ωff [Hz]

Ph

ase

mar

gin

ϕm [

deg

]

Bus 3, λ1(Tm_B3)Bus 2, λ1(Tm_B2)

Bus 1, λ1(Tm_B1)PCC, λ1(Tm_PCC)

Unstable

Stable

Stable case Unstable case

32

Hybrid AC/DC Transmission

33

AC AC

DC

A

AC Neutral

AC

DC

AC

VDCIDC

2Vg0 t

V(t)

VDC

0 t2Ig

IDC

I(t)

HVAC HVDC HybridAC/DC

Objective: Upgrade existing AC lines to hybrid AC and DC lines, toexpand the power transmission capability

Basic Concept of Hybrid AC/DC System

34

System topology:AC Bus

LCC Station

Idc VdcLCC Station

Transmission Line AC BusCB1

CB3

CBx CByLX

CB2

CB4

IdcCB5 CB6

AC Bus Transmission Line AC BusCB7 CBx CBy CB8

LX

Vdc

●

●

●

●

●

●

●

●

● c1

b1

a1A1B1

C1

a2

b2c2

a

bc

NDC injection link: zigzag transformer

Benefits and Issues

35

Benefits:• A lower cost solution for increased power transfer and improved stability

Issues:• Zigzag transformer may be saturated with unbalanced AC line

resistance, due to the uncanceled DC flux within zigzag windings.• Neutral point of zigzag transformer needs extra insulation to withstand

dc bias voltage

1 2 3 4 5

0.6

0.8

1

1.2

1.4

1.6Cost of H ybr id AC/ DC over H VDC

Power I ncreasing (Base:PH VAC)

Cos

t Rat

io

Balance1% Unbalance2% Unbalance3% Unbalance4% Unbalance

1 2 3 4 5 6 7

0.6

0.8

1

1.2

1.4

1.6Cost of H ybr id AC/ DC over H VDC

Power I ncreasing (Base:PH VAC) Co

st R

atio

Balance1% Unbalance2% Unbalance3% Unbalance4% Unbalance

Power angle limit increase from 30° to 60°

The Same power angle limit

Active Unbalance Mitigation

36

Immunity to unbalance

Method 3: Hybrid line balance control

Low voltage rating, no insulation issue Active impedance with low loss

With extra converter cost, but low compared to main HVDC converters

Hybrid line impedance conditioner:

/

/ 3

AC DC DC

DCAC DC

V VR II∆

∆ = ≈

fLC

aiLC

CbiL

C

CciL

C

Hybrid line

Bidirectional Active Hybrid Line Impedance Conditioners (Two conditioners are active, at the most)

fL

fL

Idc

Same core

Adjust the line resistance by phase.

Can be enabled or bypassed

2K3K4K5K

Vdc

0

1000

2000

Ia Ib Ic

980100010201040

Ia_dc Ib_dc Ic_dc

0.5 0.6 0.7 0.8 0.9Time (s)

0100020003000

Ia Vxa

Impedance Conditioner Design and Simulation

37

fLC

aiLC

Idc

System ParametersLine Length 650km

Impedance 0.035Ohm/km+0.9337mH/km

Unbalance 5%

Line voltage (phase)

AC: 115 kV; DC 180 kV

Line current AC: 612A, DC: 1000A

Transmission Power

729 MW (189 AC and 540 DC)

Inverter AC voltage

3.183kV(peak)

DC link voltage

3.617kV

DC linkCapacitance

3300uF

Rectifier AC voltage

3.183 kV(peak)

Zigzag transformerwindings

balance design + conditioner winding (170/138/138/3)

Conditioner enabled at 0.6s. Control reference goes from zero to the desired impedance.

Magnetic Amplifier Controller

38

Magnetic Amplifier Controller

39

Magnetic Amplifier Controller

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0 100 200 300 400 500

AC Winding Reactance (Ω)ac 1500A

ac 1000A

ac 750A

ac 500A

ac 250A

40

Multi-terminal HVDC Modeling & Control

41Wind

Farm IWind

Farm II

DC cable

1G1 5 6

G2

2

3 G31110

G4

4

97 8

L7 L9C7 C9

VSC 3

VSC 2 VSC 1

VSC 4

L12 L13

Area 1 (NYISO) Area 2 (ISO-NE)

Area 3(Load Center)

Area 3(MTDC)

Objective: Build a hardware platform for MT-HVDC system operation/control/protection development and demonstration

Multi-Terminal HVDC Testbed

MTDC Testbed HardwareSystem Structure

• System start-up • Station online re-

commission• Wind farm power variation

• Station outage• Transmission line trip• Station online mode

transition

Offshore IOnshore I Wind emulator I

Wind emulator IIOffshore IIOnshore II

PCC 1

PCC 2

Cable 1

Cable 2

Cab

le 3

Cab

le 4

Testbed Capability on Scenario Emulation:

42

MT-HVDC Testbed Interface

43

44

VSC HVDC DC Fault Protection – A CURENT Proposed Solution

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

P

N

Larm

Larm

Larm

Larm

Larm

Larm

+ −

Csub+ −

Csub

AC grid

Proposed SM

+ −

Csub+ −

Csub

+ −

Csub+ −

Csub

+ −

Csub+ −

Csub

(a)

(b)

(c)

In case of DC short circuit fault

Normal operation

Two half-bridge sub-modules

+ −

Csub+ −

Csub

Smart and Flexible Microgrid

PCC

PCC

PCC

Local protective devices

Local controllers

Microgrid central controller

System control

Normal open smart switchNormal closed smart switch

Electrical networkCommunication and control network

45

Conclusions

• Actuation thrust provides essential technology for wide-area coordinated control, and directly supports the CURENT systems.

• Thrust research focuses on multifunctional actuators and flexible architecture.

46

Overview of Actuation ThrustActuation in CURENTActuation Technology LinkagesBasic Actuation Functions in Power Systems Power Flow ControlNon Power Electronics Power Flow ActuatorsExample of Phase-shifting TransformersNon Power Electronics Voltage & Var ActuatorsNon Power Electronics Actuator for StabilityProtection - BreakersBreaker with Switching ResistorsOvervoltage ProtectionMetal Oxide Varistor (MOV)Power Electronics Based Power Flow ControlPower Electronics Power Flow ActuatorThyristor Controlled Series Capacitor (TCSC)STATCOM and SSSCUnified Power Flow ControllerHVDC Technology Development800 kV DC for long distance bulk power transmissionPower Electronics Actuator for StabilityPower Electronics Actuator for ProtectionVSC HVDC DC Fault Protection – SolutionSummary of Actuation TechnologiesModular Approach - Distributed FACTSModular Converters for Multi-Terminal �HVDC SystemsHybrid Approach - Thin AC ConverterActuation Thrust Objectives and ChallengesTechnical Approaches and Research FocusRenewable Energy Sources for Grid SupportFrequency Support Function Test in HTBDesign of Renewable Interface Converters Considering StabilityHybrid AC/DC TransmissionBasic Concept of Hybrid AC/DC SystemBenefits and IssuesActive Unbalance Mitigation Impedance Conditioner Design and SimulationMagnetic Amplifier ControllerMagnetic Amplifier ControllerMagnetic Amplifier ControllerMulti-terminal HVDC Modeling & ControlMulti-Terminal HVDC TestbedMT-HVDC Testbed InterfaceVSC HVDC DC Fault Protection – A CURENT Proposed SolutionSmart and Flexible MicrogridConclusions