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UNIVERSITY OF ZIELONA GORA
INSTITUTE OF ELECTRICAL ENGINEERING
POWER ELECTRONICS ARRANGEMENTS
IN DISTRIBUTED SYSTEMS
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DISTRIBUTED GENERATION: WHAT IS IT?
Distributed Resources (DR) are small (usually under 10 MW),
modular electric generation and storage technologies that
provide electric capacity and/or energy when and where
needed. DR may either be interconnected with the electric grid
or isolated from the grid in "stand-alone" applications, but itslocational value is important to its economics and operation.
Distributed generation = DGDistributed storage = DS
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Today's Central Utility Tomorrow's Distributed Utility?
Central Generation
Customers
CustomerEfficiency
RemoteLoads
Wind
PV
Genset
Fuel Cell
Battery
Central Generation
Microturbine
DISTRIBUTED GENERATION: WHAT IS IT?
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Mass produced
Modular
Small (
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Economic advantages included one or more of the
following:
Load management
Reliability
Power quality Fuel flexibility
Cogeneration
Increased distribution grid reliability/stability
ECONOMIC ADVANTAGE FROM DG SYSTEMS
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IC Engines SmallTurbines
Micro-turbines
Fuel Cell
CommercialAvailability
Wellestablished
Wellestablished
Newindustry
Wellestablished
Size 50 kW-5 MW
1 MW 50 MW
25 kW 75 kW
1 kW 200 kW
InstalledCost ($/kW)
$800 $1500
$700 $900
$500 $1300
$3000
O&M Costs(cents/kWh)
0.7 1.5 0.2 0.8 0.2 1.0 0.3 1.5
Fuel Type Diesel,propane,NG, oil &biogas
Propane,NG,distillate oil& biogas
Propane,NG,distillate &biogas
Hydrogen,biogas &propane
Commercial Status of DG
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Photovoltaicgeneration
Fuel cells
DC-to-ACConversion
Variable-speedwind generator
FrequencyConversion
Smallhydrogenerator
AC Lines(usually isolatedfrom utility lines)
DC AC
Variablefrequency
Fixedfrequency
* kW ~ * MW
POWER ELECTRONICS IN DISTRIBUTED GENERATION
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ENERGY STORAGE
AC/DC
Conversion
Superconductingmagnet energy
storage
LargeCapacitors
AC UtilityLines
DC
AC
* kW ~ * MW
Batteries
DISTRIBUTION: Custom Power
Power electronicsConverters/Controllers
SwitchingEquipments
Automatedprocessing/
manufacturing
customers
Low-qualitypower
High-qualitypower
*0 kW ~ *0 MW
POWER ELECTRONICS IN
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Advanced Solutions
Transmission
Link
Enhanced
Power Transfer
and Stability
Line
Reconfiguration
Fixed
Compensation
FACTS
Energy Storage
BetterProtection
Increased
Inertia
BreakingResistors Load
Shedding
FACTS
Devices
Traditional Solutions
SVC
STATCOM
TCSC, SSSC
UPFC, IPFC,
Steady State
Issues
Voltage Limits
Thermal Limits
Stability Limits
Dynamic
Issues
Transient Stability
Damping Power Swings
Post-Contingency
Voltage Control
Voltage Stability
FACTS - APPLICATIONS AND IMPLEMENTATIONS
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A transmission system can carry power up to its thermal loading limits. But ipractice the system has the following constraints:
-Transmission stability limits
-Voltage limits
Transmission stability limits: limits of transmittable power with which
transmission system can ride through major faults in the system with its powe
transmission capability intact.
Voltage limits: limits of power transmission where the system voltage can b
kept within permitted deviations from nominal. Voltage is governed b
reactive power (Q). Q in its turn depends of the physical length of thtransmission circuit as well as from the flow of active power. The longer th
line and/or the heavier the flow of active power, the stronger will be the flow o
reactive power, as a consequence of which the voltage will drop, until, at som
critical level, the voltage collapses altogether.
FACTS - THE CONCEPT
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FACTS offers ways of attaining an increase of power transmission capacity at
optimum conditions, i.e. at maximum availability, minimum transmission
losses, and minimum environmental impact. Plus, of course, at minimuminvestment cost and time expenditure.
The term FACTS covers several power electronics based systems used for
AC power transmission. Given the nature of power electronics equipment,
FACTS solutions will be particularly justifiable in applications requiring one
or more of the following qualities:
-Rapid dynamic response
-Ability for frequent variations in output
-Smoothly adjustable output.
FACTS - THE CONCEPT
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CONTROLLABLE PARAMETERS
Control of the line impedance X : thyristor-controlled series capacitor
Provides a powerful means of current control
When the angle is not large, substantially provides the control of active power
Control of angle: phase angle regulator
Provides a powerful means of current control Provides active power flow when the angle is not large
Series voltage injection: perpendicular to current
Controls the magnitude of current
Injects reactive power: static synchronous series compensation Provide a powerful means of controlling the active power
Parallel voltage injection: arbitrary phase
Controls the magnitude and the phase of the current.
Provides a powerful means of controlling the active and reactive power flow. Requires injection of both active and reactive power in series.
Line voltage regulation: thyristor-controlled voltage regulator
Very cost-effective means for reactive power flow control
X control (series C) + voltage regulation (shunt C) can also provide a cost-
effective means to control both the active and reactive power flow.
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E1
E2
I
X
E1 - E2
Injected Voltage
Injecting Voltage in series with the line mostly change real power
E1 / 1 E2 / 2I
P&Q
Vin
P1 = E1 . E2 . sin () / (X - Vin / I)
VOLTAGE-SERIES INJECTION
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E2 / 2
P1 = E1 (E2 . sin ())/X
X
I
E1
E2
E1 - E2
Regulating end bus voltage mostly change
reactive power.
E1 / 1I
P&Q
Q / V
VOLTAGE - PARALLEL CONTROL
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X
E1 / 1 E2 / 2I
P&Q
Changes in X will increase or decrease real power flow for a fixed angle or
change angle for a fixed power flow. Alternatively, the reactive power flow
will change with the change of X. Adjustments on the bus voltage have
little impact on the real power flow.
Vs
I
Xeff = X - Xc
Vx
Vr
Vc
Vseff = Vs + Vc
Vx
I
Vxo Vr
Vc
VseffVs
SERIES COMPENSATION
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X
E1 / 1 E2 / 2
I
P&Q
P
E1
E2
I
E1 - E2
Injected Voltage
Integrated voltage series injection and bus voltageregulation (unified) will directly increase or decrease real
and reactive power flow.
SERIES AND PARALLEL COMPENSATION
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SERIES AND PARALLEL COMPENSATION
System bus
C+
Vdc
s
Parallel Compensation
System busV
Transformer leakage
inductance
Transformer
o
X
Converter
SwitchingDC-AC
V
I
Coupling
C+
Vdc
s
Converter
SwitchingDC-AC
Transformer leakage
inductance
TransformerCoupling
Series Compensation
o
XV
I
VV
MULTILEVEL INVERTERS
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MULTILEVEL INVERTERS
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Parallel Connected:
Parallel Active Power Filters (Parallel APF)
Static VAR Compensator (SVC)
Static Synchronous Compensator (STATCOM)Battery Energy Storage System (BESS)
Combined Series and Series-Parallel Connected:
Series Active Power filter (Series APF)Static Synchronous Series Controllers (SSSC)
Thyristor Controlled Series Capacitor (TCSC)
Unified Power Flow Controller (UPFC)
Unified Power Quality Conditioner (UPQC)
Universal Power Line Conditioner (UPLC)
Interline Power Flow Controller (IPFC)
FACTS DEVICES
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Parallel Active Power Filters (Parallel APF)Static Synchronous Compensator (STATCOM)
Parallel-connected static var compensator
Capacitive or inductive output current controlled independently of the acsystem voltage
Static Var Compensator (SVC)
Parallel-connected static var generator or absorber
Output is adjusted to exchange capacitive or inductive current
Maintain or control specific parameters of the electrical power system
(typically bus voltage).
Thyristor-based Controllers
Lower cost alternative to STATCOM
Battery Energy Storage System (BESS)
PARALLEL FACTS
PARALLEL APF
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PWM CONTROL
V I
L
C
ISi
i*c
ic
Reactive power
compensation Source currents higher
harmonics compensation
DC element voltage contr
MAJOR TASKS:
PARALLEL APF
PARALLEL APF STRUCTURE
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S1 S3
S4 S6
C
Control
L
+
-
ii
i
ca
cb
cc*
*
*
i
C
R
iii
fa
fb
fc
S5
S2
S1 S3
S4 S6
Control
L
iii
fafb
fc
S5
S2
i
i
icacb
cc
*
*
*
CR
iii
ca
cb
cc
VSI
CSI
PARALLEL APF - STRUCTURE
MODULAR ACTIVE POWER FILTER MAPF
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LOADSiL
APF-2
iS=iL-iFA3
iFA
APF-1
APF-K
MODULAR ACTIVE POWER FILTER - MAPF
MAPF EXPERIMENTAL RESULTS
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OFF
SYMMETRIC LOAD
ON
ASYMMETRIC LOAD
MAPF EXPERIMENTAL RESULTS
MAPF EXPERIMENTAL RESULTS
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MAPF EXPERIMENTAL RESULTS
IL
SVC
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SVC
TThyristor
CControlled
RReactor
TThyristor
SSwitched
CCapacitor
SStatic VVar CCompensator
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SERIES CONTROLLERS
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Series Active Power filter (Series APF)Static Synchronous Series Compensator (SSSC)
A static synchronous generator without an external electric energy
source
Output voltages in quadrature with, and controllable independently of,
the line current
Control over the overall reactive voltage drop across the line, and
thereby the transmitted electric power.
May include transiently rated energy storage to enhance the dynamic
behavior of the power system by additional temporary real power
compensation, to increase or decrease momentarily, the overall real(resistive) voltage drop across the line.
Thyristor Controlled Series Capacitor (TCSC)
Smooth control of series capacitive reactance
SERIES CONTROLLERS
SERIES APF
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Voltage harmonics
compensation Stability improvement
Current harmonics blockin
MAJOR TASKS:
Control PW M
L
VC
is
V
V*c
C
VS
iS
V
VV VC
VTV
V c
S
v + vF h
VXL
X LI + IF h
ST
SERIES APF - STRUCTURE
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S1 S3
S4 S6
C1
Control
L
-
V
V
ca
cb
cc**
*
V
C
R
V
VV
fa
fb
fc
S5
S2 C2
C
+
Vca
V a Vsa
i sa
SERIES APF STRUCTURE
SSSC
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X
E1 / 1 E2 / 2I
P&Q
P1 = E1 (E2 . sin ()) / Xeff
Xeff = X - Vinj/I
SSSC
TCSC
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Line Impedance Compensation
Can Control Power Flow Continuously
E1 / 1 E2 / 2P&Q
P1 = E1 (E2 . sin ()) / Xeff
X
Xeff = X- Xc
TCSC
COMBINED CONTROLLERS
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Unified Power Flow Controller (UPFC)
A combination of STATCOM and SSSC coupled via a common dc
link
Bi-directional flow of real power between the SSSC and theSTATCOM
Concurrent real and reactive series line compensation without an
external electric energy source.
The real and reactive power flow control in the line.
Independently controllable shunt reactive compensation.
Additional external storage: more effective in control of system
dynamics
Unified Power Quality Conditioner (UPQC)
Universal Power Line Conditioner (UPLC)
Interline Power Flow Controller (IPFC)
UPFC
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X
E1 / 1 E2 / 2I
P&Q
Regulating Bus Voltage and Injecting Voltage In
Series With the Line Can Control Power Flow
UUnifiedPPower
FFlow
CController
SStaticSSynchronous
SSeries
CCompensator
SSTTAACC
OOMM
P1 = E1 (E2 . sin ()) / XeffXeff = X - Vinj / I
1 = E1(E2 - E2 . cos ()) / X
UPQC
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L
V
C
Control Control
UPQC
Control
I*CV*C
V
iS
iS
Vf
if
i
iC
Vc
L
MAJOR TASKS:
Source current harmonics
compensationSystem stability improvement
Reactive power compensation
DC element voltage control
Voltage controlVoltage harmonics
compensation
iV Vs
is
Ha rm onicssens ib le load
V s
i c
i
V
i s
V c
U P Q C
UPQC - STRUCTURE
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S1 S3
S4 S6
S5
S2
S7 S9
S10 S12
Vca
V a Vsa
UPQC controlVoltage cntrol Current control
i
i
ca
cb
cc*
*
*
iV
V
ca
cb
cc*
*
*
V
+
+
S11
S8
V fa
V fb
V fc
i fa
Lf
C f
R f
i ca
i co
i so
i sc
i sb
i sa i a
i b
i c
i o
Non-linearload
Linear load
Unbalanced netwith harmonicsi
R sC s
C1
C2
UPLC - STRUCTURE
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LC
Current
cntrol
Voltage
control
UPLC control
V*Ci*C
V
i h
iS
if
i f
L
V
i
ih
VS
is
i c
VC
UPLC =UPFC + UPQC
C
i hVc
L 2
G2
G1
L 1
i c
i s
Vs
V
V
Vsis
VS
V
Vc
i
UPLC VOLTAGE REGULATION
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V
i
G1
G1
L1
VL1
V i
.
.
i (q0)
VL1
VL1
VG1
VG1
V
V
V:
V:
vqi
vqi
)0(
)0(
UPLC POWER FLOW CONTROL
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VG2VsVc
i s
V
L2
Ps G2
VL2
VG2
VL2
Vs
V
(q0)s
VG2
VL2
V
(p>0)VG
.
.
Vs
is
VG2
VL2V
(p
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E1 / 1 E3 / 3
E2 / 2
IPFC PRINCIPLE OF OPERATION
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INVERTER
11Vr
1CVr
1XVr
1Ir 21V
r
1X
12V
r
2CV
r
2X
Vr
2Ir 22V
r
2XDC
LINK
INVERTER
SYSTEM 1
SYSTEM 2
Active power transmitted to the receiving-end bus:
( )444 3444 21444 3444 21
44444 344444 21
11
1
121
1
121
121
1
121
sin
21111121
1
1121
21 cossinsincossincossincos
cpcq V
c
c
V
c
c
X
VV
X
VV
X
VVP
+++=
Reactive power transmitted to the receiving-end bus:
( )444 3444 21444 3444 21
44444 344444 21
11
1
121
1
121
121
1
121
1
2
21
cos
11211121
1
112121 sininscoscossinsincoscos
cqcp V
c
c
V
c
c
X
VV
X
VV
X
V
X
VVQ
+=
IPFC PRINCIPLE OF OPERATION
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11Vr
1CVr
1XV
1Ir 21V
r
1X
12V
r
2CV
r
2XVr
2I
r22V
r
2X
1nVr
INVERTER
DC
LINK
INVERTER
INVERTER
r
SYSTEM 1
SYSTEM 2
SYSTEM n
Parallel inverters power rating:
====
n
1i
max*i2
maximax
i2
mini1n
1i
maxIPFCiParallel Pcos
V
V1PP
IPFC RESULTS OF SIMULATIONS
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2 4 6 8 10
80
70
60
50
40
30
20
case a
Number of Systems
Savin
gsoftheparallelinverterspowerrating
case b
Savings of the parallel inverter's power rating
for given number of Systems.
FACTS ATTRIBUTES
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FACTS Controller Control AttributesStatic Synchronous Compensator(STATCOM without storage)
Voltage control, VAR compensation, damping oscillations, voltagestability
Static Synchronous Compensator
(STATCOM with storage,large dc capacitor)
Voltage control, VAR compensation, damping oscillations, transient
and dynamic stability, voltage stability, AGC
Static VAR Compensator (SVC, TCR,TCS, TRS
Voltage control, VAR compensation, damping oscillations, transientand dynamic stability, voltage stability
Thyristor-Controlled Braking Resistor(TCBR)
Damping oscillations, transient and dynamic stability
Static Synchronous Series Compensator(SSSC without storage)
Current control, damping oscillations, transient and dynamic stability,voltage stability, fault current limiting
Static Synchronous Series Compensator(SSSC with storage)
Current control, damping oscillations, transient and dynamic stability,voltage stability
Thrystor-Controlled Series Capacitor(TCSC, TSSC)
Current control, damping oscillations, transient and dynamic stability,voltage stability, fault current limiting
Thyristor-Controlled Series Reactor(TCSR, TSSR)
Current control, damping oscillations, transient and dynamic stability,voltage stability, fault current limiting
Unified Power Flow Controller (UPFC)
Active and reactive power control, voltage control, VAR
compensation, damping oscillations, transient and dynamic stability,voltage stability, fault current limiting
Interline Power Flow Controller (IPFC) Reactive power control, voltage control, damping oscillations,transient and dynamic stability, voltage stability
VOLTAGE POWER QUALITY CONDITIONER
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LOAD
~
Is
IL
VS
VX
VI
C
COMPENSATOR
I
LV S
VX
V I
~I
LI
S2mH
0.1mH
25F
0.25m F
1
VS
VI
VC
PLL
VC
*
BLOCK
A
PI+
_VC
VS
'
}ControlSignals
FILTER
VSd
+
+ +
- VS
~
VS
VSd
'
10ms/d
iv
400V/
div
100A/
div
100A/
div
704
V
696V
VS VI
10ms/d
iv
10ms/d
iv
10ms/d
ivIL
IS
VC
10ms/d
iv
400V/d
iv
100A/
div
100A/d
iv
704
V
696V
VS
VI
10ms/d
iv
10ms/d
iv
10ms/d
ivIL
IS
VC
INTERLINE POWER QUALITY CONDITIONER
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r r
11V
21I
r 21V
XX
11I
r
C1Vr
Ir
C1
12V
22Ir 22V
XX
12Ir
r C2V
Ir
r
11 21
12
C2
22
r
DC LINK
SYSTEM 1
SYSTEM 2
SYSTEM 1
11V
r
1CVr
21Vr11I
r
21Ir
1CI
r
211
11
21
221
2111 >
21XVr
11XVr
12Vr
22Vr
12XVr
22XV
r2CVr
2CIr
22Ir12
Ir
2212
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Series vs. Parallel:
Series is more powerful in controlling the current/power flow anddamp oscillations
Parallel is more effective in voltage control and damping of voltageoscillations
FACTS - POSSIBLE BENEFITS
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Control of power flow. Increase the loading capability of lines to their
thermal capabilities.
Increase the system security through raising the transient stability limit,
damping electromechanical oscillations of power systems and machines.
Provide greater flexibility in siting new generation.
Reduce reactive power flows, thus allowing the lines to carry more active
power.
CONCLUSIONS
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Power supply industry is undergoing dramatic change as a result of
deregulation and political and economical maneuvers. This new marketenvironment puts demands for flexibility and power quality into focus. This
calls for the right solutions as far as power transmission facilities between
countries as well as between regions within countries are concerned.
The choice of FACTS device is simple and needs to be made the subject of
detailed system studies, taking all relevant requirements and prerequisites of
the system into consideration, so as to arrive at the optimum technical andeconomical solution. In fact, the best solution may often be lying in a
combination of devices.
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END