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TRANSCRIPT
Aggregation of plug-in electric
vehicles in electric power systems
for primary frequency control
Seyedmahdi Izadkhast
Researcher at
Delft University of Technology
• Introduction
• Plug-in electric vehicles
• Power system ancillary services like primary frequency control
• Primary frequency control by plug in electric vehicles
• Case study and simulation scenarios
• Simulation results
• Conclusions
• References
Outline
• Over the past years, new plug-in electric vehicles (PEVs)
registrations have been notably increased in Europe
Introduction - PEVs
3/23
• Currently, 1000 charging points in Amsterdam
• Expected to have 4000 charging points by 2018 in the city
“This largely affects the operation and control of electric power
infrastructure within cities like Amsterdam”
Introduction - PEVs
4/23
• From electrical grid point of view, a single PEV consists of two
main components:
• Battery pack
• Battery charger system
Introduction - PEVs
Batterypack
Batterycharger
Plug-in electric vehicle Grid
system
5/23
PEVs are interesting options for electricity services
1. PEVs store a considerable amount of electrical energy using
battery pack
• PEVs become viable options for energy-based services
2. PEVs using battery charger system control active and
reactive power within a few tens of milliseconds
• PEVs become interesting options for power-based
services
Introduction - PEVs
6/23
• PEVs have a great potential to proivde a wide range of power
system ancillary services from short time scale to long time scale
Introduction – Ancillary Services
Electricity services
provided by PEVs
short time scale
~milliseconds
Transient voltage
stability
Local voltage
management
Primary
frequency
control
Tertiary frequency
control
Black start
Islanded operation
and emergency
backup
Secondary
frequency
control
Congestion and
local operational
constraint
management
Ancillary service time scale
Capacity power based service
Power & energy based service
Energy based service
Short
time scale
~seconds
Medium
time scale
~minutes
Long
time scale
~hours
Very
7/23
• Frequency is an indicator of energy balance in power systems
• If total electricity supply is less than the total demand
Frequency drops
• If total electricity supply is greater than the total demand
Frequency rises
Introduction – Frequency Control
8/23
• Frequency control in power systems • Inertia
• Primary frequency control
Instantaneous balance
• Secondary frequency control
• Tertiary frequency control
Introduction – Frequency Control
9/23
• Over the past decades, PFC has been only procured
by conventional generating units
• In the past years, PFC response has been notably
reduced in power systems due to large-scale
introduction of renewable energy sources
Introduction – Primary Frequency Control
GRID
OPERATOR
10/23
• Nowadays, PFC can be provided by PEVs next to
conventional generating units
• PEVs are much faster compared to conventional
generating units
Introduction – Primary Frequency Control
GRID
OPERATOR
11/23
• PEVs versus conventional generating units
• Battery charger’s time constant (e.g., 30 ms)
• Thermal unit’s time constant (e.g., 4 s)
• Gas unit’s time constant (e.g., 0.4 s)
“Thanks to the fast-controlled battery charger of PEVs,
they are much more promising technologies (ten times
faster) for the PFC compared to the conventional
generating units”
Introduction – Primary Frequency Control
12/23
• Typical Frequency control scheme of power systems
• Frequency deviations due to the mismatch between power
production and consumption
Introduction – Primary Frequency Control
-+
+
Load
Conventional
Power Plants
Wind farms
and solar units
+
fl
PΔ
wPΔ
cpPΔ
pevsPΔ
cLFCP
,Δ
DHs +2
1
LFC
PEV Fleets
pevsLFCP
,Δ
13/23
Research Challenge
• Modelling a large number of plug-in electric vehicles for PFC
can significantly be time-consuming and computationally
complex.
Research Objective
• To reduce computational complexity, an aggregate model of
PEVs are introduced and developed.
Primary Frequency Control by PEVs
14/23
• Three essential PEV operation modes:
• Disconnected mode
• Idle mode
• Charging mode
• A single PEV technical characteristics:
• Minimum desired state of charge (SOC) of PEV owners
• Battery charger maximum power (unidirectional or
bidirectional)
• Constant current and constant voltage charging modes of
PEVs
PEV Characteristics for PFC
15/23
• To incorporate the PEV characteristics, a participation factor
according to PEV state of charge was introduced and
calculated for a single PEV
An Equivalent Model of A Single PEV
16/23
• An average participation factor of PEVs has been calculated
taking into account the probability distribution functions of SOC
in the fleet
An Aggregate Model of A Single PEV
17/23
• The worst case for PFC analysis has been defined when the
system primary reserve is minimum
• The frequency disturbance of 0.05 pu (1 GW in Spain) is
applied at t=0 s
Case Study Of Spanish Power System
PEV fleet parameters
5.14 kW
55%
0.5%
Number of PEVs 22,800
Battery charger topology Bidirectional
Including PEVs
18/23
To evaluate the performance of the PEV fleet compared to
the conventional units:
– Simulation scenario 1.1
• PEVs do not participate in PFC, and the
conventional units mainly provide the PFC.
– Simulation scenario 1.2
• PEVs along with the conventional units participate in
the PFC.
Scenario 1 For Spanish Power System
19/23
PEV fleet participation improved the minimum system
frequency:
• Scenario 1.1: fmin = 0.33> 0.3 Hz
• Scenario 1.2: fmin = 0.19 Hz.
Simulation Results of Scenario 1
0 1 2 3 4 5 6 7 8 9 10
-6
-5
-4
-3
-2
-1
0x 10
-3
Time (s)
F
(p
u)
Without participation of PEVs in PFC – Scenario 1.1
With participation of PEVs in PFC – Scenario 1.2
20/23
To evaluate the effect of PEV battery charger topology:
– Simulation scenario 2.1
• PEVs participate in PFC with unidirectional battery
chargers.
– Simulation scenario 2.2
• PEVs participate in PFC with bidirectional battery
chargers.
Scenario 2 For Spanish Power System
21/23
PEV fleet participation improved the minimum system
frequency:
• Scenario 2.1: fmin = 0.175 Hz > 0.3 Hz
• Scenario 2.2: fmin = 0.15 Hz > 0.3 Hz
Simulation Results of Scenario 2
0 2 4 6 8 10-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0x 10
-3
Time (s)
F
(p
u)
Scenario 2.1: 0 % bidirectional - 100% unidirectional
Scenario 2.2: 100% bidirectional - 0% unidirectional
22/23
Conclusions
• PEVs can effectively improve the system frequency response
following the disturbance, and furthermore show better
performance than conventional units for PFC.
• PEV constraints such as battery charger’s power limitations,
battery state of charge, and constant current and constant
voltage charging modes of PEVs can remarkably affect PEV
fleet performance for PFC.
• The average participation of PEVs might be significantly
reduced during the day.
23/23
Conclusions
• The unidirectional or bidirectional battery charger topologies
affects the performance of the PEV fleet for PFC, and PEVs
equipped with BBC have better performance than PEVs
equipped with UBC.
• An aggregate model of PEVs, which could flexibly
incorporate the aggregate PEV technical constraints, was
proposed and formulated based on the arithmetic average
technique to notably reduce computational complexity.
24/23
References • P. Kundur, N. J. Balu, and M. G. Lauby, Power system stability and
control, vol. 4. McGraw-hill New York, 1994.
• S. Izadkhast, P. Garcia-Gonzalez, and P. Frías, L. Ramirez-Elizondo,
and P. Bauer, “An aggregate model of plug-in electric vehicles including
distribution network characteristics for primary frequency control,” IEEE
Transactions on Power Systems, vol. 31, no. 4, pp. 2987–2998. Jul
2016.
• S. Izadkhast, P. García-González, and P. Frías, “An aggregate model
of plug-in electric vehicles for primary frequency control,” IEEE
Transactions on Power Systems, vol. 30, no. 3, pp. 1475–1482. May
2015.
• S. Izadkhast, P. García-González, and P. Frías, L. Ramirez Elizondo,
and P. Bauer, “Aggregation of Plug-in Electric Vehicles in Distribution
Networks for Primary Frequency Control,” IEEE International Electric
Vehicle Conference, Florence, Italy, DEC 2014.
Thank you!