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Roland Bründlinger arsenal research, Austria

Behavior of DR-Inverters during Network Disturbances - Experiences from Laboratory Testing and Recommendations. Roland Bründlinger arsenal research, Austria 2nd international conference on integration of Renewable and Distributed Energy Resources, Napa, CA, December 4, 2006. Contents.

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Roland Bründlinger arsenal research, Austria

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  1. Behavior of DR-Inverters during Network Disturbances - Experiences from Laboratory Testing and Recommendations Roland Bründlinger arsenal research, Austria 2nd international conference on integration of Renewable and Distributed Energy Resources, Napa, CA, December 4, 2006

  2. Contents • Introduction – PQ phenomena and DR • arsenal research Inverter R&D activities • Test results – sensitivity to voltage sags • Test results – sensitivity to superposed voltages • Conclusions & Recommendations Renewable Energy Technologies

  3. Power Quality in the network = Grid Feedback + Disturbances Renewable Energy Technologies

  4. Specific PQ aspects in distribution networks with DR • General problem: Discrepancy of stakeholders’ interests • Distribution System OperatorsAs low feedback/influence of DR on the network as possible • DR operatorsOptimal operation and reliability to achieve maximum economy • Result: Disconnection at the first sign of trouble philosophy • Main problem today: Frequent nuisance tripping  complaints  dissatisfaction of DR operators and customers • Potential future risk: Simultaneous loss of large DR capacities Renewable Energy Technologies

  5. Inverters as key component of DR installations • Conversion of DC/non-mains frequency AC to mains f AC • Interface to the network • Often with integrated protection and monitoring functionality •  Behavior of DR inverters during disturbances key issue • Aim of the research work  Characterization of the performance during typical disturbances  Identification of current state of play & potential problems  Recommendations for optimization of device design  Proposals and guidelines for future DR standards Renewable Energy Technologies

  6. Investigated disturbance phenomena • Voltage sags • Decrease to between 0,1 and 0,9 p.u. in RMS voltage at power frequency for durations of ½ cycle to 1 min. • Usually associated with system faults • Switching of heavy loads • Starting of large motors. • Superposed (non-mains frequency) voltages • Harmonics and Interharmonics • Sources: Non-linear loads (rectifiers, switch-mode converters,…)Mains signalling (audio frequency ripple control) Renewable Energy Technologies

  7. Introduction – PQ phenomena and DR • arsenal research Inverter R&D activities • Test results – sensitivity to voltage sags • Test results – sensitivity to superposed voltages • Conclusions & Recommendations Renewable Energy Technologies

  8. Safety Network interface Safety of persons DC injection … Power Quality and EMC Emission and Immunity Performance during network disturbances Compatibilityand Conformity assessment Performance Conversion efficiency MPPT accuracy (PV) Steady State Dynamic Under irregular conditions Thermal behavior Behavior under extreme climatic conditions Highly accelerated lifetime testing Long-term performance … Inverter R&D and testing activities at arsenal research Renewable Energy Technologies

  9. Inverter test facilities @ arsenal research Renewable Energy Technologies

  10. Introduction – PQ phenomena and DR • arsenal research Inverter R&D activities • Test results – sensitivity to voltage sags • Test results – sensitivity to superposed voltages • Conclusions & Recommendations Renewable Energy Technologies

  11. Voltage sags testingTest methodology • Test procedure adapted from • IEC 61000-4-11 “Electromagnetic compatibility Part 4-11 : Testing and measurement techniques – Voltage dips and short interruptions immunity tests.” • EUT • 13 state-of-the-art PV-Inverters • Nominal Power 0,2 – 4,6 kW • ~1500 single tests Renewable Energy Technologies

  12. Two-dimensional representation of a voltage sag by Magnitude (in %) Duration (in ms) Extended parameters Point-on-Wave Phase angle jump Characterization of voltage sags for testing Magnitude Duration Renewable Energy Technologies

  13. Voltage sags – Test resultsVoltage tolerance curves Highly sensitive inverter (No. 4) Prohibited area according to German standard VDE 0126-1-1 Average sensitive inverter (No. 2) “Ride through” inverter (No. 9) Renewable Energy Technologies

  14. Voltage sags – Test resultsObserved behavior patterns (1/3) AC Side Waveforms High sensitivityImmediate trip Trip depending only on sag’s residual voltage. Example Inverter: No. 4 Sag: 85% - 20 ms Immediate trip @ 85% – 20 ms sag Renewable Energy Technologies

  15. Voltage sags – Test resultsObserved behavior patterns (2/3) No trip even @ deep sag 10% – 140 ms AC Side Waveforms Ride Trough Inverter almostnot affected – no trip Top: No. 9 10% - 140 ms sag Bottom: No. 860% - 80 ms sag Nominal current sine during sag 60% – 80 ms AC Side Waveforms Renewable Energy Technologies

  16. Voltage sags – Test resultsObserved behavior patterns (3/3) Current fluctuationsafter voltage recovery AC Side Waveforms Current control problem Inverter: No. 2, Sag: 60% - 60 ms Followed by trip due to over-current Renewable Energy Technologies

  17. Introduction – PQ phenomena and DR • arsenal research Inverter R&D activities • Test results – sensitivity to voltage sags • Test results – sensitivity to superposed harmonics • Conclusions & Recommendations Renewable Energy Technologies

  18. Superposed harmonic voltagesMethodology • Test method • Based on EMC standard IEC/EN 61000-4-13 “Electromagnetic compatibility (EMC) – Part 4-13: Testing and measurement techniques – Harmonics and Interharmonics including mains signalling at a.c. power port, low frequency immunity tests • Test severity related to EMC Environment Class 2 (IEC 61000-2-4) • Test signals • Combined harmonics (Flat Curve – Overshoot Curve) • Individual Harmonics • Interharmonics (“Meistercurve” – for EUT to be used in networks with Audio Frequency Ripple Control broadly used in Europe) Renewable Energy Technologies

  19. Generally very high sensitivity of EUT Only one inverter passed test without problems (No. 12) Superposed harmonic voltagesTest results Renewable Energy Technologies

  20. Superposed harmonic voltagesAnalysis of key problems • Example: Inappropriate implementation of AC frequency measurement 1 cycle average: Measured deviation up to 1.4 Hz 4 cycles average: Measured deviation less than 0.2 Hz Renewable Energy Technologies

  21. Superposed harmonic voltagesComparison of 2 inverters Frequent trips at disturbances in the range of 100 – 600 Hz No problems over whole frequency range Renewable Energy Technologies

  22. Superposed harmonic voltagesFurther observations • Re-connection after trip • Generally: Automatically after disturbance • One inverter falsely detected an internal fault in the grid- interface (MSD)  Stop until disconnection of DC supply! • Quality of the output current @ non-ideal mains voltage • Large differences between the tested inverters • “Current follows Voltage” behavior • In particular cases problems due to over-currents • Resonance effects at certain frequencies Renewable Energy Technologies

  23. Introduction – PQ phenomena and DR • arsenal research Inverter R&D activities • Test results – sensitivity to voltage sags • Test results – sensitivity to superposed voltages • Conclusions & Recommendations Renewable Energy Technologies

  24. Lab testingConclusions • Generally: High sensitivity of state-of-the-art PV inverters • Network interface & Current Control as critical parts • Complex behavior of the inverters • Determined by implementation of protection (V – f – Z) • Current control & MPPT dynamics (only PV inverters) • Potential negative effects • Generator: Customer satisfaction, lifetime & lost energy • Network operation • Few devices with high immunity show that • Ride through can be realized without additional costs! Renewable Energy Technologies

  25. Reasons for the “non-ideal” behavior & Recommendations • Today: No immunity (ride-through) requirements • Unknown, undetermined behavior and high sensitivity • “Early trip at first sign of trouble” philosophy • Lack of awareness among designers • Current standards only state (often not precisely) when the device must trip BUT do not specify under which situations devices must not trip! • Future interconnection standards: Minimum immunity requirements • Compromise between immunity and safety • Coordinated with network protection • 2-level disconnection characteristic useful • Disconnect at first sign of trouble might not be the best approach. Renewable Energy Technologies

  26. Ride-thru instead of disconnect at first sign of trouble! Source: Christian Sasse, AREVA Renewable Energy Technologies

  27. Acknowledgement & further information • This work was supported by the European commission in the framework of the DISPOWER project • Detailed information can be found on http://www.dispower.org Public DeliverablesDeliverable D2.3 – Identification of general safety problems, definition of test procedures and design-measures for protection (del_2004_0049) Renewable Energy Technologies

  28. Thank you very much! • Contact: Roland Bründlingerarsenal researchRenewable Energy TechnologiesGiefinggasse 2, 1210 Vienna, Austria roland.bruendlinger@arsenal.ac.at • www.arsenal.ac.at/eet Renewable Energy Technologies

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