Harmonic Effects in Electrical Distribution Networks due...
Transcript of Harmonic Effects in Electrical Distribution Networks due...
Harmonic Effects in Electrical Distribution Networks due to EV
Charging
Lauri Kütt, Aalto University School of Electrical Engineering (Finland)
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14PESGM2765
Introduction
• EVs and PHEVs: usage would follow present commuting patterns
• Traffic surveys provide the input data:
Finland: Henkilöliikennetutkimus 2010–2011
US: 2009 National Household Travel Survey
UK: National Travel Survey: 2012
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Trip start time
Extended Range Electric Vehicle Driving and Charging Behavior Observed Early in the EV Project. SAE International 2013
Charging modes
Energy likely charged: 3 kWh or higher
Slow charging for households – capability already available; 2 … 3 kW; long charging times (up to 10 ... 12 hours)
Fast chargers for service stations – charging time low but high installation cost
Within this discussion, only the aspects of household slow charging are presented
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Charger converter topology
http://www.ti.com/solution/ev_hev_charger_level_1_2
http://www.ti.com/solution/ev_hev_charger_level_1_2
Standard requirements for chargers
Slow charging is generally using 10 … 16 A
IEC 61000–3–2 : Electromagnetic compatibility (EMC) - Part 3-2: Limits - Limits for harmonic current emissions (equipment input current ≤ 16 A per phase)
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Examples: harmonic levels
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Har-monic order
Har-monic freq-
uency
EV1: THDi = 4.0%
EV2: THDi = 12.2%
EV3: THDi = 3.3%
EV4: THDi = 10.4%
Magni-tude
Phase Magni-
tude Phase
Magni-tude
Phase Magni-
tude Phase
Hz A deg A deg A deg A deg
Main 50 9.69 -6 10.2 -13 12.7 -1 10.2 -6
3 150 0.32 8 1.23 107 0.27 -156 0.90 156
5 250 0.077 -25 0.036 117 0.18 149 0.40 178
7 350 0.077 -77 0.042 -163 0.118 -55 0.32 -109
9 450 0.030 34 0.060 121 0.053 -33 0.119 -100
11 550 0.088 82 0.115 160 0.039 110 0.092 159
IEC61000-3-2 limits:
3rd: 2.30 A; 5th: 1.14 A;
7th: 0.77 A; 9th: 0.40 A; 11th: 0.33 A
Charging load effects estimation
• Charging profiles of vehicles
– Expected levels of harmonics for different state of charge (SOC) levels
• Daily activity profiles of vehicle user
– Start of charge timing
– Daily energy used for commuting
• Present state of networks load harmonics profiles (with added expected future loads)
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Vehicle user activity data
• Derived from traffic surveys, Monte Carlo based stochastic estimations
• Simplification -> user will charge always when connected
• Not-so-smart charging assumed –> no load shifting, charge always when capable
• Weekdays would be the most intense for same-time vehicle charging
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Vehicles charging at the same time
• 40 vehicles in the area
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Nu
mb
er
of
veh
icle
s ch
argi
ng
at t
he
sam
e ti
me
Time of day / hr
90 percentile level
Median load
Minimum load
Harmonic current during charging
• 3rd harmonic
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Cu
rren
t (A
)
Time of day / hr
90 percentile level Median load
Minimum load
Harmonic cancellation patterns #1
• 3rd harmonic
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Lev
el o
f h
arm
onic
can
cell
atio
n
Number of vehicles charging at the same time
Harmonic cancellation patterns #2
• 5th harmonic
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Lev
el o
f h
arm
onic
can
cell
atio
n
Number of vehicles charging at the same time
Harmonics daily patterns
• Measured from existing LV network
• Total load of 115 customers
• No DG, no capacitor banks
• Seasonal variance monitored
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Example from real network
• 3rd harmonic, for 1 day
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I h3_
RM
S, (A
)
I h3_
ph
ase,
deg
Time of day
Example from real network #2
• 5th harmonic, for 1 day
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I h5_
RM
S, (A
)
I h5_
ph
ase,
deg
Time of day
Example: daily harmonics of DN #1
• 3rd harmonic
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Har
mon
ic l
oad
curr
ent
(A)
Time of day / hr
90 percentile level Median load
Minimum load
Example: daily harmonics of DN #2
• 5th harmonic
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Curr
ent
(A)
Time of day / hr
90 percentile level
Median load
Minimum load
Discussion • Role of network impedance and the charger
equivalent impedance.
• DG units’ inverters capabilities to supply the harmonic currents.
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Conclusions
• EV chargers incorporate advanced control and sophisticated circuitry to guarantee AC-network friendliness.
• Commercial (PH)EVs (available & upcoming) most likely have close to sinusoidal current draw = current harmonic levels will be low or very low.
• Multiple EVs charging can provide remarkable cancellation of harmonic currents.
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Conclusions
• The existing networks’ load current harmo-nics will likely be significantly higher than the EV charging load harmonic currents.
• Distribution networks could possibly accom-modate rather high EV penetration, if consi-dering current harmonics.
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