Transcript Analytical Power Loss Expressions for Diode Clamped Converters

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
1
Overview
of lab setup
to be built
Renewable
energy
source
Sun
DC
Energy
storage
3-phase
inverters
=/~
Capacitor
Wind
Battery
Consumers
Grid
=/~
:
:
Focus today
Internal communication system
External communication system
14/06/2004
NORPIE 2004
2
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
3
Problem: LC filter resonance
Load
1.3mH
=/~
0.3mH
65µF
1mH
Inverter A
1.3mH
1mH
=/~
65µF
Diode
rectifier load
Inverter B
Solution: Negative current feedback
→ Virtual resistor
14/06/2004
NORPIE 2004
4
Where to place the virtual resistor?
R2
L1
1.3mH
17
VC,αβ
C1
65uF
VE
VS
IL,αβ
R1
 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
5
High load problem
Series
resistor will
give voltage
drop!
14/06/2004
Solution:
Band-pass
filtering
NORPIE 2004
6
Band pass
filtering of
inductor
current
Still a
resistor at
50Hz?
14/06/2004
NORPIE 2004
7
Load sharing between two
voltage sources
VE
L
R
VS
 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
8
Phasor diagram
– Inductance and resistance contributions to load sharing
Is,p
Is
Pure inductance
Is,q
VE
Vs
IsjX
Is,p jX
Is,qjX
Is,pR
Pure resistance
Is,p
Is
Is,q
Vs
IsR
Is,q R
VE
P
X  U1  U 2 sin( ) R  U1  U 2 cos( )

R2  X 2
R2  X 2
14/06/2004
Q
X  U1  U 2 cos( ) R  U1  U 2 sin( ) X  U1  U1

 2
R2  X 2
R2  X 2
R  X2
NORPIE 2004
9
Simulations results for traditional (increased gain by 4x)
and virtual resistor based load sharing vector
12000
10000
10000
Control assuming an
inductive transmission line.
8000
8000
Power [W / VAr]
Power [W / VAr]
6000
6000
4000
2000
P: 4% frequency droop
4000
Q: 24% voltage droop
2000
0
0
+ Good load sharing
-2000
-2000
-4000
-6000
0
0.05
0.1
0.15
0.2
Time [s]
0.25
0.3
-4000
0.35
0.05
0.1
0.15
0.2
Time [s]
0.25
0.3
0.35
7000
5000
6000
4000
5000
3000
4000
Power [W / VAr]
Power [VAr / W]
6000
- Poor dampening
0
2000
1000
0
Control assuming a resistive
transmission line
P: (24%) voltage droop
3000
2000
Q: 4% frequency increase
1000
0
-1000
-2000
-3000
+ Good dampening
-1000
-2000
0
0.05
0.1
0.15
0.2
Time [s]
14/06/2004
0.25
0.3
0.35
-3000
- 20% load sharing difference
0
0.05
0.1
0.15
0.2
Time [s]
NORPIE 2004
0.25
0.3
0.35
10
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
11
Thank you for your attention
14/06/2004
NORPIE 2004
12