1. 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

2. 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

3. 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

4. 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

5. 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

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

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

8. Load sharing between two voltage sourcesVE 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

9. Phasor diagram – Inductance and resistance contributions to load sharingVs
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

10. 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

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)
14/06/2004
NORPIE 2004

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