Overview of Actuation Thrust

Fred Wang

Thrust Leader, UTK Professor

Prepared for CURENT Course

September 4, 2013

Actuation in CURENT

1-2

Power Grid Wide Area Control of

Power Grid

Measurement

&Monitoring

Communication

Actuation

Communication

WAMS

FDR PMU

PSS

Generator

Storage

HVDC

Wind Farm

FACTS

Solar Farm

Responsive Load

Actuation Technology Linkages

Enab

ling

Te

chn

olo

gie

sEn

gin

ee

red

Sys

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sFu

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ame

nta

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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

1-4

Power Flow Control

• Power flow is determined

by Kirchhoff's Laws, e.g.

2GP

G1 G2

1GP

3DP

1DP

2V1V

3V

G3

2DP

3GP

2P1P

21

12

2112 sin

X

VVP

1-5

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

1-6

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)

1-7

Non Power Electronics Voltage & Var

Actuators

• Generator (exciter)

• Condenser

• Switched capacitor banks

• Transformer tap changer

• Load management

1-8

Non Power Electronics Actuator for Stability

• Generator

Governor

Power system stabilizer (excitation)

• Switchgear

Line switching

Source and load switching

• Switched compensators Reactors

Capacitors

1-9

Protection - Breakers

Live-tank breakers Dead-tank breakers

1-10

Breaker with Switching Resistors

Switching resistors

Must absorb

energy during

switching

=> shorted after

several ms!

1-11

Equivalent Circuit

0 10 20 30 -40

-10

-5

0

5

10

t [ms]

VSrc

US

Fixed Contact Moving Contact RL LL

CL

IS

U1 U2

US

UN

-10 -20 -30

VSw

US

Fault! IS

Fault!

Short-circuit Interruption

rated current

1-12

Equivalent Circuit

0 10 20 30 -40

-10

-5

0

5

10

t [ms]

UN

US

Fixed Contact Moving Contact

rated

current

RL LL

CL

IS

U1 U2

US

UN

-10 -20 -30

Us

US

Fault! IS

Fault!

US

Short-circuit Interruption

1-13

Equivalent Circuit

0 10 20 30 -40

-10

-5

0

5

10

t [ms]

UN

US

Fixed Contact Moving Contact

rated

current

RL LL

CL

IS

U1 U2

US

UN

-10 -20 -30

Us

US

Fault! IS

Fault!

US

Short-circuit Interruption

1-14

Equivalent Circuit

0 10 20 30 -40

-10

-5

0

5

10

t [ms]

UN

US

Fixed Contact Moving Contact

rated

current

RL LL

CL

IS

U1 U2

US

UN

-10 -20 -30

Us

US

Fault! IS

Fault!

US

LLCLf

2

1

Short-circuit Interruption

1-15

Circuit Breaker Modeling

• Mechanical delay time (from command to contact separation): min 10...20 ms “opening time” = contact separation

current interruption: default at zero crossing

• Arcing time: 1...5 cycles depending on CB type and current wave form

include arcing time in “opening time”

• Arc modeling Arc voltage – current relationship highly complex

(parameters: CB design, thermodynamics) generic models mostly insufficient – special modeling necessary

zero arcing voltage for high voltage systems

constant value (10...100 V) for low voltage systems

1-16

Overvoltage Protection

• 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 VI

1-17

ABB arrester

type MWK after overload

test with 20

kA/0.2 s

MOV and Surge Arresters

ABB arrester

with silicon

rubber enclosure

(POLIM

family)

Metal Oxide

Varistor

diam = 38 ... 75 mm

W/V = 3.6 ... 13.3

kJ/kVUc

VI

1-18

Metal Oxide Varistor (MOV)

continuous

operating voltage

peak voltage

1-19

Protection - Arresters

1-20

Series

Compen-

sation (SC)

Static Var

Compensation

(SVC)

Phase Shifting

Transformers

sin ) ( 2 1

12

2 1

X

V V P

V1 /1 V2 /2

HVDC and

HVDC Light

= ~

~ =

+ PHVDC

Powerflow P

FACTS = Flexible AC Transmission System

Power Electronics Based Power Flow Control

1-21

Power Electronics Power Flow Actuator

• 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) 1-22

Thyristor Controlled Series Capacitor (TCSC)

• A capacitive reactance compensator which consists of a

series capacitor bank shunted by a thyristor-controlled

reactor in order to provide a smoothly variable series

capacitive reactance.

• Can be one large unit or several small ones. Limits fault

current when reactor is fully on.

AC Capacitor Line

Reactor

Thyristor valve

1-23

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.

Transformer

Converter

Interface

Energy storage

Line

1-24

Unified Power Flow Controller

• The UPFC, by means of angularly unconstrained series

voltage injection, is able to control, concurrently or

selectively, the transmission line voltage, impedance,

and angle or, alternatively, the real and reactive power

flow in the line.

• The UPFC may also provide independently controllable

shunt reactive compensation.

Coupling Xfmr

STATCOM SSSC

DC link

Series VSI

Shunt VSI

Coupling Xfmr

AC line

1-25

Year 1954 1970 2000 1980

Mercury Arc Valve

HVDC (Phased out)

Thyristor Valve

HVDC Classic

IGBT (Transistor) Valve

HVDC Light

Pros: Low losses

Cons: Reliability

Maintenance

Environment

Pros: Reliable

Scalable

Cons: Footprint

Pros: Controllability

Footprint

DC Grids

Cons: Losses

HVDC Technology Development

1-26

Number of lines: Right of way ~300 ~ 120 ~ 90 (meter)

Tranmission of 6000 MW over 2000 km. Total

evaluated costs in MUSD

0

500

1000

1500

2000

2500

3000

3500

765 kV AC 500 kV DC 800 kV DC

MU

SD Losses

Line cost

Station cost

800 kV DC for long distance bulk power transmission

1-27

Power Electronics Actuator for Stability

1st Thyristor-Controlled Series

Compensation (TCSC) Project

1-28

PE for Stability: Dynamic Energy Storage

• Energy storage connected on DC-side of

converter (SVC Light)

• Size depends on power level and duration

• Charge energy equal to load energy

• Focus on “dynamic”, manages:

High number charge and discharge cycles

High Power at medium duration

• Chosen high performance battery as energy

storage

1-29

Battery Energy Storage Example

Golden Valley Electric Association BESS Project

40 MW Rating

10 MWH Battery Capacity

1-30

Power Electronics Actuator for Protection

1-31

High Voltage DC Circuit Breaker

Schematic

High-Voltage ETO-based DC circuit breaker with an RC snubber.

Solid-State

Trip Circuit Load

1-32

High-Voltage DC Circuit Breaker

A 3000V high-voltage DC circuit breaker to protect the DC

capacitor bank in industrial power converter applications.

1-33

Anode Voltage

(500 V/div)

Anode Current

(200 A/div)

tf

td

(2 s)

(0.5 s)

Vout (5 V/div)

Shoot-Through

Failure Point

Test Waveform

The high-voltage DC circuit breaker tested at 1kA under 2kV DC bus.

1-34

Fault Current Limiting Circuit Breaker

rectifier DC CB

inductor

Fast acting circuit breaker can function as a fault current limiter

During normal operation, the circuit breaker shorts the high-

impedance inductor, exhibits low impedance. During fault

condition, the circuit breaker is open, the fault current flow

through the high impedance inductor, thus limit the fault current to

a tolerance level.

1-35

Fault Current Limiter Simulation Results

-5000

0

5000

10000

15000

20000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Time (s)

Fa

ult

cu

rre

nt

at

se

co

nd

ery

sid

e (

A)

w/o FCL

w/ FCL

w/ IFCL

Without FCL, the prospective fault current could reach 10x rated

current (red dash line).

Traditional FCL acts at current zero-crossing point, it can’t suppress

the first peak (blue dot line).

Fast acting FCL limits the fault current in all range (pink solid).

1-36

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

1-37

Impedance Based Actuators (1)

1-38

Impedance Based Controllers (2)

1-39

Impedance Based Controllers (3)

All impedance based controllers have common converter functions

– ac bi-directional switch

1-40

Shunt Connected Current Controllers

Controller One-line

Configuration System Functions

Control

Principle

Basic PE

Function

STATCOM

- Static

Synchronous

Compensator

Stability

enhancement

V regulation &

VAR compensation

VAR control

through current

control in shunt

connection

Bi-directional

AC/DC VSI

Mini-HVDC

(Voltage Source)

System Interconnect

Power flow control

Stability

enhancement

Power and Var

control through

back-to-back

converters

Bi-directional

AC/DC VSI

Active Filter

(Shunt

connected)

LO

AD

Harmonic current

filtering

Inject canceling

harmonic current

Bi-directional

AC/DC VSI

UPS

(Line-interactive

type shown)

LOAD

Standby power

Power conditioning

V or I regulation

depending on

operating mode

Bi-directional

AC/DC VSI and bi-

directional AC switch

DER Interconnect

- Mirco-turbine,

fuel cells, wind or

solar generator,

energy storage

systems

LOAD

Interface to AC grid

Power conditioning

V or I regulation

depending on

operating mode

Bi-directional

AC/DC VSI and

DC/DC converter

1-41

Series Connected Voltage Controllers

Controller One-line

Configuration System Functions

Control

Principle

Basic PE

Function

SSSC

- Static Series

Synchronous

compensator

Power flow control

Stability

enhancement

VAR control

through voltage

control

Bi-directional

AC/DC VSI

DVR

- Dynamic

Voltage Restorer

Voltage regulation

and conditioning

Injecting voltage to

compensate for

sags and unbalance

Bi-directional

AC/DC VSI

Active Filter

(Series

connected)

Harmonic voltage

filtering

Inject canceling

harmonic voltage

Bi-directional

AC/DC VSI

All series connected voltage controllers and shunt connected current

controllers have common converter functions

– AC/DC VSI

1-42

Basic PE Building Block Functions

R L

vdc

RdcCv

av

bv

c

ia

ic

ib

ma

mb

mc

R L vdc

m

i

idc

DC-DC

3-ph VSC

3-ph Switch

1-43

Modular Approach - Distributed FACTS

Distributed Series Static

Compensator

1-44

Modular Converters for Multi-Terminal

HVDC Systems

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

A

B

C

P

N

Larm

+

Larm

Larm

Larm

Larm

Larm

Csub

Modular multilevel converter (MMC)

1-45

Hybrid Approach - Thin AC Converter

1-46

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

• Challenges

1) Lack of cost effective wide-area system-level actuators

2) 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

• 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

Hybrid AC/DC Transmission

2

2

2

3 sina

ac dc d d

VP P P V I

X

+ +

2

1

1

3 sinphVP

X

1-49

Multi-terminal HVDC in NPCC System

Wind

Farm I

Wind

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)

MT-HVDC Testbed Interface

Conclusions

• Actuation thrust provides essential technology

for wide-area coordinated control, and directly

supports the CURENT systems.

• Thrust research plan has been established with

focus on multifunctional actuators and flexible

architecture.

1-52