Impact of Electric Vehicles on Power Quality in Central Charging Infrastructures

Transcription

1 Impact of Electric Vehicles on Power Quality in Central Charging Infrastructures Supported by: IEEH Friedemann Möller, Sascha Müller, Jan Meyer Technische Universität Dresden, Germany 1 st E-Mobility Power System Integration Symposium Berlin, 23 rd October 2017

2 Agenda Introduction Measurement Framework Effects on Unbalance Harmonics Supraharmonics Conclusion Berlin, October 23, 2017 Impact of Electric Vehicles on Power Quality Slide 2

3 Introduction Motivation 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 Slide 3

4 Measurement Framework Measured Sites / 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 Short circuit power S SC Characteristic of measured sites Installed power S A Maximum utilization S ACT Site A 4.82 MVA 244 kva 18.4 kva Number and type of charging points 6 x type 1 10 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 Slide 4

5 Measurement Framework Infrastructures and measuerement devices Single line diagram of the network All measurement devices are class A devices (IEC ) Unbalance and Harmonics: Measuerement of 10-cycle values Analysis of 1 minute values Supraharmonics: transient recorders with 1MS sampling rate Slide 5

6 Effects on Unbalance Unbalance - Basic Information Definition of Voltage Unbalance k u2 = Τ U 2 U 1 Dependency of Voltage Unbalance on short circuit power k u2 S un2 ΤS SC Definition of unbalanced power (corresponding with negative sequence current) S un2 = S L1 + a 2 S L2 + a S L3 ; S un2 ~ I 2 Limit for unbalance emission of customer installation, provided in technical rules D-A-CH-CZ S un S SC Slide 6

7 Effects on Unbalance Measuring results Site A New installed infrastructure with a low number of EVs All single phase EVs use the same phase conductor for charging Limit: S un kva is not exceeded Unbalanced power and voltage unbalance at site A Slide 7

8 Effects on Unbalance Measuring Results Site B + Site C 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: S un2 8.8 kva Site C: S un2 62 kva is exceeded is not exceeded Unbalanced power and voltage unbalance at site B Slide 8

9 Effects on Harmonics Harmonics - Basic Information Discussion of harmonic emission current by comparison of measured values and limits Based on measurement accuracy only odd harmonics till the 13 th 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) p v 1000 S sc S A I A Currently limits don t consider the harmonic voltage distortion Proportionality factors p v (phase currents) v p v Slide 9

10 Effects on Harmonics Overview measuring results of all sites Comparison of measured harmonic currents I meas with the limit I lim Use of the 99 th percentile of current harmonic magnitude Measured values higher than the limits for site B and C Assessment of emission limits for different sites Site v A I meas (A) I meas / I lim (%) B I meas (A) I meas / I lim (%) C I meas (A) I meas / I lim (%) Slide 10

11 Effects on Harmonics Measuring results site A CCI with different types of EVs Maximum magnitude depends on the type and not on the number of connected EVs Harmonic current for 3 rd, 5 th and 7 th harmonic, depending on the amount of connected EVs at site A Slide 11

12 Effects on Harmonics Measuring results site B 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 Harmonic current for 3 rd, 5 th and 7 th harmonic, depending on the amount of connected EVs at site B Slide 12

13 Effects on Harmonics Measuring results site C All EVs from the same type EVs work as 3-phase loads very low 3 rd harmonic Maximum magnitude depends on the number of connected EVs Harmonic current for 3 rd, 5 th and 7 th harmonic, depending on the amount of connected EVs at site C Slide 13

14 Effects on Supraharmonics Supraharmonics - Basic Information 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 Supraharmonic current and voltage (1 EV is charging) Slide 14

15 Effects on Supraharmonics Emission at swiching frequency Stepwise connection of EVs Each Charging Box (CB) has two charging points Analysis of the first emission band around switching frequency I B1 = 10.5 khz 2 I C,f 9.5 khz Connection order of EVs to the charging boxes (CB) EV CB Supraharmonic current emission of the first emission band arround switching frequency With increasing number of EVs Emission of the whole CCI (feeder) decrease Emission of CBs clearly higher than Emission of whole CCI Slide 15

16 Effects on Supraharmonics Beating effect 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 supraharmonic current of the feeder Supraharmonic current emission of the first emission banod around EV switching frequency for one (left) and two (right) connected EVs Slide 16

17 Conclusion Conclusion 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 Slide 17

18 Thank you for your attention! Friedemann Möller TU Dresden IEEH Berlin, October 23, 2017 Impact of Electric Vehicles on Power Quality Slide 18