iuyoiuyiouy 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 14/06/2004 NORPIE 2004

Overview of lab setup to be built Focus today Overview of lab setup to be built Capacitor Battery Sun Wind : Renewable energy source =/~ 3-phase inverters DC Energy storage Grid Consumers Internal communication system External communication system 14/06/2004 NORPIE 2004

Outline of Presentation iuyoiuyiouy Outline of Presentation Simulation of two 3-phase inverters using a virtual resistor LC filter dampening Load sharing Simulation results 14/06/2004 NORPIE 2004

Problem: LC filter resonance Load Inverter A =/~ Inverter B 1.3mH 0.3mH 1mH 65µF Diode rectifier load Solution: Negative current feedback → Virtual resistor 14/06/2004 NORPIE 2004

Where to place the virtual resistor? IL,αβ VC,αβ 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 14/06/2004 NORPIE 2004

High load problem Series resistor will give voltage drop! Solution: Band-pass filtering 14/06/2004 NORPIE 2004

Band pass filtering of inductor current Still a resistor at 50Hz? 14/06/2004 NORPIE 2004

Load sharing between two voltage sources VE VS L R An inductor L is necessary to decrease the disturbance (load current) frequency A virtual (series) resistor R can be added for improved load sharing 14/06/2004 NORPIE 2004

Phasor diagram – Inductance and resistance contributions to load sharing Vs Is,q R Is IsR Is,pR Is,p VE Is,q Is,p jX IsjX Is,qjX Pure inductance Pure resistance 14/06/2004 NORPIE 2004

Simulations results for traditional (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 14/06/2004 NORPIE 2004

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) 14/06/2004 NORPIE 2004

Thank you for your attention iuyoiuyiouy Thank you for your attention 14/06/2004 NORPIE 2004