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Erik Hoff, Tore Skjellnes, prof. Lars Norum

Paralleling of 3-phase inverters a part of my PhD study: " Control and monitoring for distributed power supply“ which is a part of the project "Technologies for Reliable Distributed Generation of Electrical Power from Renewable Energy Sources”. Erik Hoff, Tore Skjellnes, prof. Lars Norum.

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Erik Hoff, Tore Skjellnes, prof. Lars Norum

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  1. Paralleling of 3-phase inverters a part of my PhD study:"Control and monitoring for distributed power supply“which is a part of the project "Technologies for Reliable Distributed Generation of Electrical Power from Renewable Energy Sources” Erik Hoff, Tore Skjellnes, prof. Lars Norum NORPIE 2004

  2. Consumers DC Energy storage Renewable energy source 3-phase inverters Grid Capacitor Battery Sun =/~ Focus today Internal communication system Wind =/~ External communication system : : Overview of lab setup to be built NORPIE 2004

  3. Outline of Presentation Simulation of two 3-phase inverters using a virtual resistor • LC filter dampening • Load sharing • Simulation results NORPIE 2004

  4. Load 1.3mH 0.3mH =/~ 1mH 65µF Inverter A 1.3mH 1mH =/~ Diode rectifier load 65µF Inverter B Problem: LC filter resonance Solution: Negative current feedback → Virtual resistor NORPIE 2004

  5. VC,αβ IL,αβ Where to place the virtual resistor? • Two possible locations: • R1 is most common, but expensive • R2 is used here, because the inductor current IL,αβ already is available due to overcurrent protection NORPIE 2004

  6. Solution: Band-pass filtering High load problem Series resistor will give voltage drop! NORPIE 2004

  7. Still a resistor at 50Hz? Band pass filtering of inductor current NORPIE 2004

  8. L R VE VS Load sharing between two voltage sources • An inductor L is necessary to decrease the disturbance (load current) frequency • A virtual (series) resistor R can be added for improved load sharing NORPIE 2004

  9. Pure inductance Pure resistance Is,pR Is,p Is,q R IsR Vs Is Is,q VE Is,p Is,q Is VE IsjX Is,p jX Vs Is,qjX Phasor diagram – Inductance and resistance contributions to load sharing NORPIE 2004

  10. Simulations results fortraditional (increased gain by 4x) and virtual resistor based load sharing vector Control assuming an inductive transmission line. P: 4% frequency droop Q: 24% voltage droop + Good load sharing - Poor dampening Control assuming a resistive transmission line P: (24%) voltage droop Q: 4% frequency increase + Good dampening - 20% load sharing difference NORPIE 2004

  11. Conclusion • A band pass filter makes it possible to use a virtual resistor in series with the load for LC-filter dampening. • Cheaper and simpler than a virtual resistor in series with the filter capacitor. • The use of a virtual resistor requires rotation of the load sharing vector. • Good oscillation dampening, but load sharing may be uneven • The traditional control method assuming inductive transmission line has poor active power dampening. • Some special ”tricks” may be used to decrease response time: Adding a phase angle in addition to the frequency (Patent US6,693,809 by Alfred Engler) NORPIE 2004

  12. Thank you for your attention NORPIE 2004

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