JST-NSF-DFG-RCN Workshop on Distributed Energy Management Systems
Arlington, Virginia, April 20-22, 2015
Virtual Synchronous Machines for
Supporting Flexible Operation of
Distribution Systems
Jon Are Suul
pos.doc. researcher
Department of Electric Power Engineering
Norwegian University of Science and Technology
Research Scientist
SINTEF Energy Research
Traditional grids vs. "SmartGrids"
Traditional Utility grid
"SmartGrid" Scenario
F. Rahimi, A. Ipakchi, “Demand Response as a Market Resource Under the Smart Grid Paradigm,” in IEEE Transactions on Smart Grid, Vol. 1, No. 1, June 2010, pp. 82‐88
2
Virtual Power Plant (VPP)
• Aggregating energy resources
for dispatchable operation
• Commercial VPP
– For operation in the market
• Technical VPP
– For power system operation and
control
• Demand-Response VPP (load)
• Supply-Side VPP (generation)
• Mixed-Asset VPP (generation
load and storage)
• Requires extensive ability for:
– Data acquisition and
communication
– Remote and local control
3
D. Pudjianto, C. Ramsay, G. Strbac, “Virtual power plant and systems integration of distributed energy resources,” in IET Renewable Power Generation, Vol. 1, No. 1, 2007, pp. 10‐16
Karlsruhe Institute of Technology, http://www.commputation.kit.edu/73.php
http://envirosynthesis.blogspot.com/2010/05/ventyx‐virtual‐power‐plants.html
Virtual Synchronous Machine (VSM)
•
•
Power Electronic converter
controlled to emulate the
behavioral characteristics of
synchronous machines
Concept first introduced about
one decade ago
– Several possible
implementations
•
•
4
Parameters are not limited by
physical design constraints
Emulated characteristics:
– Inertia and damping
– Corresponding powerbalance-based grid
synchronization mechanism
– Active and reactive power
control mechanisms
S. D'Arco, J. A. Suul, "Virtual Synchronous Machines –
Classification of Implementations and Analysis of Equivalence to
Droop Controllers for Microgrids," in Proceedings of IEEE PES
PowerTech 2013, Grenoble, France, 16-20 June 2013, 7 pp.
VSMs in distribution systems
• VSMs can provide ancillary services in local grids:
–
–
–
–
Power-frequency control
Reactive power control
Inertia emulation
MicroGrid operation with temporary islanding
• Most residential sources and loads in distribution systems
have single-phase grid interfaces
– EV chargers
• Load with storage
• Possibility for temporary islanding
– Domestic PV systems
• Down-regulation capability
• Typical configuration:
Grid equivalent
Vg Rg
Lg
Rl
5
Filter
Local Bus
Local Load
Bg
Bl
Io
R2
L2
Vo
R1
Cf
L1
I c Vc
Battery/DC voltage source


VDC
CDC
Single-phase VSM for EV charger
•
•
Assuming bi-directional EV charger for V2G/V2H operation
Single-phase VSMs require particular attention to implementation of
virtual inertia
L2
io
Measurement
vo
Processing
qo
qo*
vˆo*
po
po*
*
Reactive vˆ r*
o
Power
Control
Virtual 
VSM
Inertia
and
VSM
Power
Control
L1 C1
ic
qio'
A

vor*
io
vo
vo
ic
Virtual vo* Resonant ic* Resonant m*
Voltage
Current
Impedance
Controller
Controller
PWM
g PWM
Cdc
vdc

J. A. Suul, S. D'Arco, G, Guidi, "Virtual Synchronous Machine-based Control of a Single-phase Bi-directional Battery Charger for Providing
Vehicle-to-Grid Services," in Proceedings of the 9th International Conference on Power Electronics, ICPE – ECCE Asia, Seoul, Korea, 1-5
June 2015, 8 pp.
6
VSM Power Control Mechanism
•
Based on synchronous machine swing equation
•
•
•
Reduced order approximation of the inertia and damping of a traditional
synchronous machine
Provides a frequency and phase angle reference that can be used to control the
converter
Reactive power controller can provide voltage amplitude reference
p*
*
VSM
Frequency Droop


VSM
p
k
Virtual Synchronous Machine Swing Equation
r*
 p 

1
Ta

pd

VSM
kd
1
s
VSM
b
s
 VSM , f   g

VSM
VSM
1
1  T f ,  s
7
Active and reactive power feedback
•
•
Single-phase power circuit
implies double frequency
oscillations in active and
reactive power
A virtual two-phase system
is established to calculate
active and reactive power
feedback
• Avoids influence of
double frequency
power oscillations on
virtual inertia
'
vo
Voltage processing
SOGI-QSG
'
e
v'
v
Voltage amplitude estimation
qv '
vo' ,
'
o ,
v
x2
vˆo' 2


x
x2
Power calculation

SOGI-QSG
'
io
i
qi '


po

qo

e
i'
vˆo'
io' ,
io' ,



Current processing
8
*
0
pVSM
-0.2
pVSM
-0.4
-0.6
0
1
2
3
4
5
Time [s]
Speed [pu]
1
*
VSM
0.998
0.996
VSM
0
1
2
3
4
5
Time [s]
Reactive power [pu]
•
Single-phase EV-charger
• 3.3 kVA, 230 VRMS
Response to power step
• Well damped emulation of inertial
behavior
• Reactive power droop control on
voltage amplitude ensures reactive
power compensation when voltage
drops due to increased load
Voltage amplitude [pu]
•
Power [pu]
Examples of results – dynamic response
0.4
*
qVSM
0.2
qVSM
0
0
1
2
3
4
5
Time [s]
1
*
vVSM
0.95
|v|o
r*
0.9
v
0
1
2
3
4
5
Time [s]
Grid equivalent
Vg Rg
Lg
Rl
Local Bus
Bg
Io
Bl
Filter
R2
L2
Vo
R1
Cf
L1
I c Vc
Battery/DC voltage source


VDC
CDC
Local Load
9
Examples of results - islanding
•
Response to sudden islanding
• Power of local load is immediately supplied from the EV battery
• No severe transients
• Local frequency slowly settles to new value according to droop
settings
0.6
1
*
VSM
0.4
VSM
0.995
0.2
0.99
Speed [pu]
Power [pu]
0
-0.2
-0.4
0.985
0.98
-0.6
*
pVSM
-0.8
pVSM
-1
-0.02
po
0
0.02
0.04
0.06
0.08 0.1
Time [s]
0.12
0.14
0.16
0.975
0.97
0
2
4
6
8
Time [s]
10
12
14
10
Summary
•
Virtual Synchronous Machines can provide ancillary services and
support flexible operation of distribution systems
•
•
•
•
•
Load and generation at distribution system level are often based on
single-phase grid interfaces
•
•
•
Inertia emulation, active and reactive power control based on local measurements
References and operational settings provided from higher level system controllers
Can operate as part of Virtual Power Plants or any other system-level control
Can ensure control of local MicroGrids in grid-connected and islanded modes
Three-phase VSM implementations cannot be directly applied for single-phase
systems
Active and reactive power oscillations of single-phase systems can be avoided in
the VSM-based control by utilizing a virtual two-phase system for calculating local
feedback signals
With both three-phase and single-phase implementations VSMs
provide a suitable general framework for local control that can
support flexible operation of distribution systems
11
References
•
•
•
•
•
•
•
•
J. A. Suul, S. D'Arco, G, Guidi, "Virtual Synchronous Machine-based Control of a Single-phase Bi-directional Battery
Charger for Providing Vehicle-to-Grid Services," in Proceedings of the 9th International Conference on Power
Electronics, ICPE – ECCE Asia, Seoul, Korea, 1-5 June 2015, 8 pp.
J. A. Suul, S. D'Arco, G. Guidi, "A Single-Phase Virtual Synchronous Machine for Providing Vehicle-to-Grid Serviced
from Electric Vehicle Battery Chargers," in Proceedings of the International Electric Vehicle Technology Conference
& Automotive Power Electronics, EVTeC & APE Japan, Yokohama, Japan, 22-24 May 2014, 7 pp.
S. D'Arco, J. A. Suul, O. B. Fosso, "Small-signal modelling and parametric sensitivity of a Virtual Synchronous
Machine in islanded operation," accepted for publication in International Journal of Electric Power and Energy
Systems, 2015
S. D'Arco, J. A. Suul, O. B. Fosso, "A Virtual Synchronous Machine Implementation for Distributed Control of Power
Converters in SmartGrids," in Electric Power System Research, Vol. 122, May 2015, pp. 180-197
S. D'Arco, J. A. Suul, O. B. Fosso, "Small-Signal Modeling and Parametric Sensitivity of a Virtual Synchronous
Machine," in Proceedings of the 18th Power Systems Computation Conference, PSCC 2014, Wrocław, Poland, 1822 August 2014, 9 pp.
S. D'Arco, J. A. Suul, "Equivalence of Virtual Synchronous Machines and Frequency-Droops for Converter-Based
MicroGrids," in IEEE Transactions on Smart Grid, Vol. 5, No. 1, January 2014, pp. 394-395
S. D'Arco; J. A. Suul; O. B. Fosso, "Control System Tuning and Stability Analysis of Virtual Synchronous Machines,"
in Proceedings of the 2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013, Denver, Colorado,
USA, 15-19 September 2013, pp. 2664-2671
S. D'Arco, J. A. Suul, "Virtual Synchronous Machines – Classification of Implementations and Analysis of
Equivalence to Droop Controllers for Microgrids," in Proceedings of IEEE PES PowerTech 2013, Grenoble, France,
16-20 June 2013, 7 pp.
12