11-04-2011, 02:24 PM
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FACTS-based Schemes for Distribution Networks with Dispersed Renewable Wind Energy
Introduction
Wind is a renewable Green Energy source
Introduction
Wind is also a clean Abundant Source
No Emissions, No Pollutions
Wind energy is a promising green energy and becomes increasingly viable &popular.
The cost of wind-generated electric energy has dropped substantially(6-7 per KWH).
By 2005, the worldwide capacity had been increased to 58,982 MW-Cost is $ 2000-2500/KW
World Wind Energy Association expects 120,000 MW to be installed globally by 2010.
Wind Energy Conversion System (WECS) Using Large Squirrel Cage/Slip ring Induction Generators
Stand alone-Village Electricity
Electric Grid Connected WECS
Distributed/Dispersed/Farm Renewable Wind Energy Schemes
Located closer to Load Centers
Low Reliability, Utilization, Security
Motivations
Energy crisis
Shortage of conventional fossil fuel based energy
Escalating/rising cost of fossil fuels
Environmental/Pollution/GHG Issues
Greenhouse gas emission /Carbon Print
Acid Rain/Smog/VOC-Micro-Particulates
Water/Air/Soil Pollution &Health Hazards
Large wind farm utilization is also emerging (50MW-250 MW) Sized Using Super Wind driven Turbines 1.6, 3.6, 5 MW Sizes
Many new interface Regulations/Standards/PQ Requirements regarding full integration of large distributed/dispersed Wind Farms into Utility Grid.
Challenges for Utility Grid–Wind Integration.
Stochastically-Highly Variable wind power injected into the Utility Grid.
Increased Wind MW-Power penetration Level.
Low SCR-Weak Distribution/Sub Transmission/Transmission Networks
- Mostly of a Radial Configuration
- Large R/X ratio distribution Feeder with high Power Losses (4-10 %), Voltage Regulation Problems/Power Quality/Interference Issues.
Required Reactive Power Compensation & Increased Burden brought by the induction generator
Sample Distribution Study System
WECS-Decoupled Interface Scheme
System Description-wind turbine
Wind turbine model based on the steady-state power characteristics of the turbine
S -- the Total BladeArea swept by the rotor blades (m^2)
v -- the wind velocity (m/s)
ρ--air density (kg/v^3)
System Description
System Description – Wind speed
The dynamic wind speed model consists of four basic components:
Mean wind speed-14 m/s
Wind speed ramp with a slope of ±5.6
Wind gust
Ag: the amplitude of the gust
Tsg: the starting time of the gust
Teg: the end time of the gust
Dg = Teg - Tsg
Turbulence components: a random Gaussian series
Wind Speed Dynamic Model
MPFC-FACTS Scheme 1
Complementary PWM pulses to ensure dynamic topology change between switched capacitor and tuned arm power filter
Two IGBT solid state switches control the operation of the MPFC via a six-pulse diode bridge
Tri-loop Error Driven Controller
DVR-FACTS Scheme 2
A combination of series capacitor and shunt capacitor compensation
Flexible structure modulated by a Tri-loop Error Driven Controller
HPFC-FACTS Scheme 3
Use of a 6-pulse VSC based APF to have faster controllability and enhanced dynamic performance
Combination of tuned passive power filter and active power filter to reduce cost
Novel Scheme-3 Multi-loop Error Driven Controller
Novel Decoupled Multi-loop Error Driven Controller
Using decoupled direct and quad. (d , q) voltage components
Using The Phase Locked Loop (PLL) to get the required synchronizing signal- phase angle of the synthesized VSC-Three Phase AC output voltages with Utility-Bus
Using Proportional plus Integral (PI) controller to regulate any tracked errors
Using Pulse Width Modulation-PWM with a variable modulation index -m
Novel Decoupled Multi-loop Error Driven Controller
Outer-Voltage Regulator: Tri-loop Dynamic Error-Driven controller
The voltage stabilization loop
The current dynamic error tracking loop
The dynamic power tracking loop
Inner-Voltage Regulator: Mainly to control the DC-Side capacitor charging and discharging voltage to ensure almost a near constant DC capacitor voltage
Controller Tuning
Control Parameter: Selection/optimization
Using a guided Off-Line Trial-and-Error Method based on successive digital simulations
Minimize the objective function-Jo
Find optimal Gains: kp, ki and individual loop weightings (γ) to yield a near minimum Jo under different set-selections of the controller parameters
Digital Simulation
Digital Study System Validation is done by using Matlab/Simulink/Sim-Power Software Environment under a sequence of excursions:
Load switching/Excusrions
At t = 0.2 second, the induction motor was removed from bus 5 for a duration of 0.1 seconds;
At t = 0.4 second, linear load was removed from bus 4 for a duration of 0.1 seconds;
At t = 0.5 second, the AC distribution system recovered to its initial state.
Wind-Speed Gusting changes modeled by dynamic wind speed-Software model
Digital Simulation
Digital Simulation Environment:
MATLAB /Simulink/Sim-Power
Using the discrete simulation mode with a sample time of 0.1 milliseconds
The digital simulations were carried out without and with the novel FACTS-based devices located at Bus 5 for 0.8 seconds
Comparison of Voltage THD with Different Compensation Scheme
Comparison of Steady-state Bus Voltage with Different Compensation Scheme
Conclusions
Three Novel FACTS-based Converter & Control schemes, namely the MPFC, the DVR, and the HPFC, have been Developed and validated for voltage stabilization, power factor correction and power quality improvement in the distribution network with dispersed wind energy integrated.