Impact of Electric Vehicles on Power Quality in Central ...

IEEH

Institute of Electrical Power Systems and High Voltage Engineering

Impact of Electric Vehicleson Power Quality in Central Charging Infrastructures

Friedemann Möller, Sascha Müller, Jan Meyer Technische Universität Dresden, Germany

1st E-Mobility Power System Integration SymposiumBerlin, 23rd October 2017

Supported by:


• Introduction

• Measurement Framework

• Effects on

• Unbalance

• Harmonics

• Supraharmonics

• Conclusion

Agenda

Slide 2Berlin, October 23, 2017 Impact of Electric Vehicles on Power Quality in Central Charging Infrastructures


Current political framework result in a significant increase of electrical vehicles (EV)

Increasing of central charging infrastructures (CCI)

Most EVs are equipped with single phase on-board charger

Effects on Power Quality

• Unbalance• Harmonics (Frequency range up to 2 kHz)• Supraharmonics (Frequency between 2 and 150 kHz)

Results

• Higher losses• Malfunction of devices which are connected to the grid

(e.g. interruption / cut-off of EV charging)

Analysis of existing CCIs

Motivation

Berlin, October 23, 2017 Slide 3

Introduction

Impact of Electric Vehicles on Power Quality in Central Charging Infrastructures


Measurements at three different sites (A, B, C)

At site A and B mostly single phase EVs are connected

At site C only three phase EVs are connected

Measurement of Supraharmonics only at site C

Measured Sites / Infrastructures


Measurement Framework

Short circuitpower SSC

Installedpower SA

Maximum utilization SACT

Number and type of charging points

Site A 4.82 MVA 244 kVA 18.4 kVA6 x type 110 x type 2

Site B 1.25 MVA 50 kVA 50 kVA 22 x type 1

Site C 8.89 MVA 177 kVA 133 kVA 8 x type 2

Characteristic of measured sites



All measurement devices are class A devices (IEC 61000-4-30)

Unbalance and Harmonics:

Measuerement of 10-cycle values Analysis of 1 minute values

Supraharmonics: transient recorders with 1MS sampling rate

Infrastructures and measuerement devices


Measurement Framework

Single line diagram of the network



Definition of Voltage Unbalance

𝑘u2 = Τ𝑈2 𝑈1

Dependency of Voltage Unbalance on short circuit power

𝑘u2 ≈ Τ𝑆un2 𝑆SC

Definition of unbalanced power (corresponding with negative sequence current)

𝑆un2 = 𝑆L1 + a2 ∙ 𝑆L2 + a ∙ 𝑆L3 ; 𝑆un2~ 𝐼2

Limit for unbalance emission of customer installation, provided in technical rules “D-A-CH-CZ”

𝑆un2 ≤ 0.007 ∙ 𝑆SC

Unbalance - Basic Information


Effects on Unbalance



New installed infrastructure with a low number of EVs

All single phase EVs use the same phase conductor for charging

Limit: 𝑆un2 ≤ 33.7 kVA is not exceeded

Measuring results Site A



Unbalanced power and voltage unbalance at site A



Site B: Unbalanced power for site A and B is almost equal

High voltage unbalance caused by CCI and other customers

Site C: Maximum unbalanced power lower than 0.5 kVA

Limits: Site B: 𝑆un2 ≤ 8.8 kVA is exceeded

Site C: 𝑆un2 ≤ 62 kVA is not exceeded

Measuring Results Site B + Site C



Unbalanced power and voltage unbalance at site B



Discussion of harmonic emission current by comparison of measured values and limits

Based on measurement accuracy only odd harmonics till the 13th

harmonic order (v) are discussed

Limit for harmonic emission of large installations (e. g. CCI), provided in technical rules “D-A-CH-CZ”

𝐼(𝑣) ≤𝑝v

1000∙

𝑆sc

𝑆A∙ 𝐼A

Currently limits don’t consider the harmonic voltage distortion

Harmonics - Basic Information


Effects on Harmonics

v 3 5 7 11 13

pv 6 15 10 5 4

Proportionality factors pv (phase currents)



Comparison of measured harmonic currents Imeas with the limit Ilim

Use of the 99th percentile of current harmonic magnitude

Measured values higher than the limits for site B and C

Overview measuring results of all sites



Site v 3 5 7 11 13

AImeas (A) 1.8 2.6 1.8 1.1 1.0

Imeas / Ilim (%) 19.2 11.0 11.4 14.0 15.9

BImeas (A) 3.5 1.9 1.0 0.8 0.6

Imeas / Ilim (%) 162.9 34.5 28.8 45.5 39.8

CImeas (A) 0.6 6.8 16.1 13.1 9.6

Imeas / Ilim (%) 5.5 25.1 88.9 144.4 132.3

Assessment of emission limits for different sites



CCI with different types of EVs

Maximum magnitude depends on the type and not on the number of connected EVs

Measuring results site A



Harmonic current for 3rd, 5th and 7th harmonic, depending on the amount of connected EVs at site A



CCI with many EVs of the same type

Magnitude and phase angle of harmonic currents depend on the SOC

Maximum magnitude depends on the number of connected EVs

Measuring results site B



Harmonic current for 3rd, 5th and 7th harmonic, depending on the amount of connected EVs at site B



All EVs from the same type

EVs work as 3-phase loads very low 3rd harmonic

Maximum magnitude depends on the number of connected EVs

Measuring results site C



Harmonic current for 3rd, 5th and 7th harmonic, depending on the amount of connected EVs at site C



Switching frequency of EVs around 10 kHz (red bar in current spectrum)

Frequency at voltage around 13 kHz caused by other devices

Currently no limits for supraharmonic emission

Supraharmonics - Basic Information


Effects on Supraharmonics

Supraharmonic current and voltage (1 EV is charging)



Stepwise connection of EVs

Each Charging Box (CB) has two charging points

Analysis of the first emission band around switching frequency

𝐼B1 = 9.5 kHz

10.5 kHz

𝐼𝐶,𝑓2

With increasing number of EVs

• Emission of the whole CCI (feeder) decrease

• Emission of CBs clearly higher than Emission of whole CCI

Emission at swiching frequency



EV 1 2 3 4 5

CB 1 2 4 3 1

Connection order of EVs to thecharging boxes (CB)

Supraharmonic current emissionof the first emission band

arround switching frequency



Beating effect caused by slightly different switching frequency of EVs

Impedance between CBs (in Combination with EVs) lower than impedance between CCI and transformer busbar

Supraharmonic current between CBs higher than supraharmoniccurrent of the feeder

Beating effect



Supraharmonic current emission of the first emission banod aroundEV switching frequency for one (left) and two (right) connected EVs



To reduce unbalance of CCIs the conductor “L1” of the charging boxes has to distribute equal to the phase conductors of the grid

Reduction of the maximum single phase charging current is recommended

Harmonic currents of CCIs exceed the limits

Limits/Tests for harmonic current emission of devices with regard to the voltage distortion are recommended

Mostly no cancellation effect for harmonic currents

Supraharmonic emission between devices can increase by connection of additional devices to the grid (caused by lower impedance)

Emission limits for supraharmonics are required

Considering of beating effect and a specification if an impedance characteristic for supraharmonics are recommended

Conclusion


Conclusion



Slide 18

Thank you for your attention !

Friedemann MöllerTU Dresden – IEEH

+49 351 463 43209

[email protected]

Berlin, October 23, 2017 Impact of Electric Vehicles on Power Quality in Central Charging Infrastructures

Impact of Electric Vehicles on Power Quality in Central ...

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