Some European experiences with renewable installations

Transcription

1 Some European experiences with renewable Waveform distortion Ana Maria Blanco, Jan Meyer, Sascha Müller, Anantaram Varatharajan Content 1. Introduction 2. Distributed PV inverters (<10kW) 3. PV plant (1MW) 4. Wind-park (12MW) 5. Conclusions Slide 2 1

2 Terminology Low frequency distortion (below 2 khz) Integer and non-integer multiples of power frequency a. DC component b. Subharmonics c. Harmonics d. Interharmonics Higher frequency distortion (2 khz khz) Independent of power frequency a. Supraharmonics Supra = beyond First mentioned at IEEE PES GM 2013 Slide 3 Scope Distortion of self-commutating technologies vary depending on: Network side Supply voltage distortion Supply voltage magnitude Frequency-dependent network impedance Supply voltage unbalance (3-phase PV-inverters only) Installation side Output power level Implemented control algorithms and their time constants Further parameter settings of inverter (e.g. volt-varcontrol regime) Slide 4 2

3 Content 1. Introduction 2. Distributed PV inverters (<10kW) 3. PV plant (1MW) 4. Wind-park (12MW) 5. Conclusions Slide 5 Voltage in V Harmonic emission Current in A Significant dependency of harmonic currents on voltage distortion Different sensitivity for different types of PVs Current source model is not adequate Slide 6 3

4 Sensitivity to harmonic voltages PV 1 PV 4 PV Inverter PV 1 PV 2 PV 3 PV 4 PV 5 PV 6 Total Auto-Sensitivity 96,1 159,5 150,8 61,4 87,9 158,4 Total Cross-Sensitivity 32,9 43,8 24,1 448,3 33,2 31,8 Testing conditions with the IEC should be revised Slide 7 Input impedance PV 1 PV 3 Capacitive behavior at several frequencies Different resonance frequency PVs can have a high impact on the network stability Slide 8 4

5 Impact of harmonic impedance on stability Current controller swing High oscillations caused by the current controllers produce the trip-off of the PVs Measurements by University of Applied Science Biel, Switzerland within the research project Swinging Grids Slide 9 HF emission of small PV inverters Laboratory measurements of 3 different single-phase PV inverters Current in A Significant differences in magnitude and switching frequency of HF emission We wish to thank the Technical University of Dortmund / Chair of Energy Efficiency for their support of the measurements. Slide 10 5

6 HF propagation Propagation of the 16 khz component in a LV network 0.52 V 0.32 A 0.35 V 0.26 A EV Propagation to the device responsible for the decrease in impedance (the EV in this case) and not towards the grid Supraharmonics usually do not propagate too far in the network Slide 11 Disturbance of communication Day: PV-Inv ON Low level Impact of PV inverters on PLC signal level Night: PV-Inv OFF High signaling level Day: PV-Inv ON Low level f / khz :00 20:00 22:00 00:00 02:00 04:00 06:00 08:00 t / h Significant damping of PLC signal during the day (impedance reduction by PV inverters input impedances) 8/9/2017 European experiences with renewable Slide 12 6

7 Content 1. Introduction 2. Distributed PV inverters (<10kW) 3. PV plant (1MW) 4. Wind-park (12MW) 5. Conclusions Slide 13 Solar campus layout 9 big PVs each of 100 kw (same type, 3-phase) 15 small PVs (total approx. 50 kw, different types, 1-phase) Measurement duration 1 day Normal operation of installation Coordinated switching of inverters Power in kw Active power per phase L1-200 L2 L Time in Mins Slide 14 7

8 5 th harmonic of individual large inverters 5 th current harmonic (L1) during switching OFF interval 5 th voltage harmonic (L1) during switching OFF interval Current in A cosϕ(p)-control OFF / ON 0 Inv 1 Inv 2 Inv 3 Inv 4 Inv 5 Inv 6 Inv 7 Inv 8 Inv 9 Sum Small Inv Voltage in V All ON All OFF Impact of cosϕ(p)-control on magnitude and phase angle Impact of voltage distortion on current harmonic Slide 15 Summation exponent and diversity factor Analysis of the interval when all inverters are switched ON Summation exponent Phase angle diversity factor Summation Exponent I VEC n α α Ii i= 1 = Harmonic Order Diversity Factor k I VEC i= 1 p = = n I ARI n i= 1 i i Harmonic Order I I Virtual arithmetic summation without any considerable cancellation effect Slide 16 8

9 Spannung Voltage in /dbµv HF emission in a larger PV plant Voltage spectrum Frequenz / khz Frequency in khz 80 dbµv 10 mv 100 dbµv 100 mv 120dBµV 1 V 1 V 0,44% at 230 V fund. frequency. The higher the rated power, the lower the switching frequency large inverters of S r =100kW (switching frequencies below 10 khz) small inverters below 10kW (switching frequencies around khz) Narrow-band PLC application for meter communication (35 khz 95 khz, 8 channels) Slide 17 Content 1. Introduction 2. Distributed PV inverters (<10kW) 3. PV plant (1MW) 4. Wind-park (12MW) 5. Conclusions Slide 18 9

10 Wind-park layout Six type 4 turbines (full converter), wind park: 12 MW rated power Measurements: 110kV/20kV substation 23.5 km DE02 DE01 Transient recorder Passive test (1 month): Normal operation Active test (few hours): Test of different operating conditions Harmonics (H), interharmonics (IH) and supraharmonics (SH) PQ analyzer PQ analyzer PQ analyzer PQ analyzer PQ analyzer PQ analyzer Slide Harmonic and interharmonic currents 10 Phase L1 Phase L2 Phase L % I r % I r I (h) in A % I r 0.17% I r Harmonic order Interharmonic order Similar behavior of all turbines Significant variations due to network conditions: harmonic impedance, supply voltage distortion,... wind-park conditions: Type of Q-setting, Output power,... Supraharmonics (2 khz 9 khz) are smaller than 2A in A I i (h) % I r Slide 20 10

11 Comparison with certificates Harmonics Supraharmonics Dots: real measurements Bars: values provided in manufacturer certificate (IEC ) Influence of voltage distortion and harmonic impedance Calculations based on certificate values are uncertain Slide 21 Influence of output power Active test: increasing P mantaining Q=0 P Not consistent behavior for all harmonics Clear secondary cancellation for the 7 th harmonic Consistently increase of current and voltage interharmonics with active output power Level of increase is partly linked to the network impedance Slide 22 11

12 Content 1. Introduction 2. Distributed PV inverters (<10kW) 3. PV plant (1MW) 4. Wind-park (12MW) 5. Conclusions Slide 23 Conclusions Significant dependency of current harmonic emission from voltage distortion and frequency-dependent network impedance Testing with sinusoidal voltage suitable? Virtually no cancellation for harmonics up to 13th order in case of identical units Recommended summation exponents has to be individually adapted to the situation. Significant interaction between inverters and PLC in the frequency range khz Additional stress for other equipment? Impact of high share of PV inverters on mains signaling? Slide 24 12

13 Thank you for your attention! M.Eng. Ana Maria Blanco Technische Universität Dresden Institute of Power Systems and High Voltage Engineering Slide 25 13