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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
tem
sFu
nd
ame
nta
l K
no
wle
dge
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