Create Presentation
Download Presentation

Download

Download Presentation

Modeling, Simulation, and Analysis of Variable Frequency Transformers

1032 Views
Download Presentation

Download Presentation
## Modeling, Simulation, and Analysis of Variable Frequency Transformers

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Modeling, Simulation, and Analysis of Variable Frequency**Transformers Brian C. Raczkowski Peter W. Sauer**Overview**• Power Flow Control • Langlois Converter Project • Derivation of Model • Small Power System Case • Experimental Case • Future Work**Ways to control power flow**• Prime mover and excitation control of generators • Open and Close Breakers • Reactive Power Compensation**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**Ways to control power flow (cont.)**• Transformers • Tap-Changing-Under-Load (TCUL) Transformers • Ability to change the ratio of transformation while energized • Requires additional circuitry • Phase shifting transformer • Addition of “90° out of phase” voltage • Useful for controlling real power • Most cases there is a fixed range**Drawbacks of These Methods**• Set minimum and maximum constraints • Fixed change • Power transfer frequency requirement • Harmonics**Another Kind of Transformer**• Induction machine • Squirrel cage rotor • Conducting bars laid in slots and shorting rings • Wound rotor • 3Φ windings with mirror images of windings on stator**Another Kind of Transformer (cont.)**• Doubly-Fed Induction Machine (DFIM) • Rotor end not shorted • Wound rotor machine with access to rotor windings • Slip rings provide connection to rotor • Typically used to alter torque-speed curve • Same as Variable Frequency Transformer (VFT)**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**VFT Disadvantages**• Limits on maximum power flow capability • More lossy especially in reactive power losses • Works at low kV range so it needs step up/down transformers**Langlois Converter Project**• GE investigated a new power transmission technology (2002) • Variable Frequency Transformer (VFT) • Controllable, bidirectional transmission device with ability to transfer power between asynchronous networks**World’s First VFT**• Hydro-Quebec’s Langlois substation • Exchange +100MW to -100MW between power grids of Quebec (Canada) and New York (USA) • Closed Loop Control System to increase or decrease power delivery to maintain stability**General VFT**• Core technology is rotary transformer with three phase windings on both rotor and stator • Continuously variable phase shifting transformer • Uses 2 transformers, a switched capacitor bank and a DC motor • Change rotor angle to change the power flow through the machine • Limits of the phase angle can be set as large as needed**Model Derivation**• The machine is assumed to be a two-pole three phase machine with an a:1 turns ratio**Small Power System Case**Glover and Sarma example**Small Power System with 3 VFTs**Line 1 Line 2 Line 3 Just by inserting VFTs, the flows have changed**Experimental System Setup**• GE I689, 7.5 hp, 3Φ, 6-pole induction machine • 2.93:1 turns ratio**Experimental System Notes**• Variac used to match odd turns ratio • Slack Bus was the standard wall outlet • Load is purely resistive 12.8Ω • Source had 10A fuses • 1° mechanical was 3° electrical • Verification in PowerWorld Simulator • Voltage - 1000x • Power – 1e6x**Make Things Better**• System is already inherently lossy • Add a capacitor bank to cut reactive losses • 121.5µF to each phase at Bus 3 • Current reduced from 7.03Arms to 2.45Arms • Needed 61.32V to achieve 7.05Arms • For comparative purposes Vin=20.4Vrms**Interesting Cases**• Results verified in Power World Simulator**VFT Conclusions**• Alternative method to control power flow • Easy model • Use in small power system case • Use in experimental power system case**Future Work**• Larger Test Systems • Higher Voltage • Torque Analysis • Multiple Frequencies • Stability of the System • Economical Impact**Questions**• Questions??