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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3

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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Slow charging layout

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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: waveform measurement

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Volt

age

[V]

Curr

ent

[A]

Time (s)

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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Charging load effects estimation

Vehicles’ charging profiles

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Ch

arg

ing c

urr

ent

RM

S [

A]

EV battery state of charge, %

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 phase angles

• 3rd harmonic

16

Ph

ase

ang

le (

deg

rees

)

Time of day / hr

Harmonic cancellation

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I 1 I 2

I 1 + I 2

φ

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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Thank You!

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