variable frequency transformer
TRANSCRIPT
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Modeling, Simulation, and Analysisof
Variable Frequency Transformers
Brian C. RaczkowskiPeter W. Sauer
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Ways to control power flow Prime mover and excitation control of
generators
Open and Close Breakers
Reactive Power Compensation
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Ways to control power flow
(cont.) High Voltage DC (HVDC)
Rectifies AC to DC then inverts DC to AC
Economical for long distances
Harmonics
Isolation
Frequency
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Ways to control power flow
(cont.) Transformers
Tap-Changing-Under-Load (TCUL) Transformers
Ability to change the ratio of transformation whileenergized
Requires additional circuitry
Phase shifting transformer
Addition of 90out of phase voltage
Useful for controlling real power
Most cases there is a fixed range
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Another Kind of Transformer
(cont.) Doubly-Fed Induction Machine (DFIM)
Rotor end not shorted
Wound rotor machine with access to rotorwindings
Slip rings provide connection to rotor
Typically used to alter torque-speed curve Same as Variable Frequency Transformer
(VFT)
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VFT Advantages Continuous and no fixed set change points
Response for stability purposes
Simple model for power system use
HVDC alternative
Can transfer power at different frequencies
More control of the real power flow
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VFT Disadvantages Limits on maximum power flow
capability
More lossy especially in reactive powerlosses
Works at low kV range so it needs step
up/down transformers
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Langlois Converter Project GE investigated a new power
transmission technology (2002)
Variable Frequency Transformer (VFT)
Controllable, bidirectional transmissiondevice with ability to transfer power
between asynchronous networks
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Worlds First VFT Hydro-Quebecs Langlois substation
Exchange +100MW to -100MWbetween power grids of Quebec(Canada) and New York (USA)
Closed Loop Control System to increase
or decrease power delivery to maintainstability
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VFT Ideal Use
Drive Motor
Control
System
PowerSystem
Area
#2
PowerSystem
Area
#1
Variable Frequency
Transformer
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Model Derivation The machine is assumed to be a two-
pole three phase machine with an a:1
turns ratio
X
X
X
X
X
X
as
bs
cs
ar
brcr
as
bs
cs
ar
br cr
tm
mrs
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Final Equations
)(2
3)
2
3(
rmsssmslsssss ILjILLjRV
)(23)
23(
smsrrmslrrrrr ILjILLjRV
r
s
mslrrms
msmslss
rr
ss
I
I
LLjRLj
LjLLjR
V
V
)2
3(
2
3 2
3)
2
3(
)(
lsls
LX lrlr
LX msms LX
2
3
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VFT Model (per phase)
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Small Power System Case
Glover and Sarma example
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Small Power System with 3 VFTs
Line 1
Line 2 Line 3
Just by inserting VFTs, the flows have changed
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Power Flows in Small PowerSystem from -21.9to +30
Pin
Pload
Pline2
Ploss
Pline3
Pline1
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Experimental System Setup
GE I689, 7.5 hp, 3, 6-pole inductionmachine
2.93:1 turns ratio
SLACK
1
52 3 VFT
1:93.2 je
6
WALL S R
1:2.93
Line 2
Line 1
Pin
Pline2
Pline1
Pstator Pload
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Experimental System Notes
Variac used to match odd turns ratio
Slack Bus was the standard wall outlet
Load is purely resistive 12.8
Source had 10A fuses
1mechanical was 3
electrical
Verification in PowerWorld Simulator
Voltage - 1000x
Power1e6x
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Test System Results - No Caps
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Make Things Better
System is already inherently lossy
Add a capacitor bank to cut reactive
losses
121.5F to each phase at Bus 3
Current reduced from 7.03Arms
to2.45Arms
Needed 61.32V to achieve 7.05Arms For comparative purposes V
in=20.4V
rms
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Test System Resultswith Caps
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Interesting Cases
Results verified in Power World Simulator
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Circulating Real Power
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VFT Conclusions
Alternative method to control powerflow
Easy model
Use in small power system case
Use in experimental power system case
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Future Work
Larger Test Systems
Higher Voltage
Torque Analysis
Multiple Frequencies
Stability of the System Economical Impact
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Questions
Questions??